Stabilized lead dioxide anodes and methods of use thereof

Abstract

Aspects disclosed herein include a method of stabilizing a lead anode, the method comprising: operating an electrochemical cell including electrochemical reduction at a first cathode and electrochemical oxidation at a first anode; wherein: the electrochemical cell comprises a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; the first anode is a lead electrode; the first anolyte and the first catholyte respectively and independently comprise water-based iron cations and water-based anions; and the first anolyte includes the aqueous iron cations at a concentration selected from a range of 0.01 M to 0.5 M.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the priority benefit of U.S. Provisional Patent Application No. 63 / 410,092, filed on September 26, 2022, the entire content of which is incorporated herein by reference for all purposes to the extent not inconsistent with this application. Background Art

[0003] In a variety of electrochemical systems, lead electrodes can be used as oxygen evolution anodes for the oxygen evolution reaction (OER). However, persistent problems complicate the use of lead electrodes in many such processes. Two main problems are: (1) mechanical stripping of lead oxide and lead sulfate materials from the electrode, resulting in dimensional instability, loss of catalyst material, and loss of electrode conductivity, ultimately limiting the electrode service life; and (2) manganese oxide deposits accumulate on and around the electrode, requiring regular cleaning to prevent clogging of PbO2 catalyst sites and uneven current distribution. For example, manganese metal is typically included in the zinc electrowinning anolyte to minimize lead dissolution and lead incorporation into the galvanized coating. The presence of manganese may also be due to its being an impurity in the raw process materials (such as ores).

[0004] When OER is required at the anode, to avoid the above challenges, the typical solution in the art is to use more expensive OER anodes, such as iridium-based anode materials, instead of the inexpensive lead anodes. In addition to being expensive, iridium-based anode materials also have their own set of challenges, such as limited global supply.

[0005] To utilize the inexpensive lead anode for OER, the above challenges and other challenges are addressed by the methods, systems, and related aspects disclosed herein. Summary of the Invention

[0006] Aspects disclosed herein include a method for stabilizing a lead anode, the method comprising: operating an electrochemical cell, including electrochemical reduction at a first cathode and electrochemical oxidation at a first anode; wherein: the electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; the first anode is a lead electrode; the first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; and the first anolyte includes the aqueous iron cations at a concentration of at least 0.01 M.

[0007] Aspects disclosed herein include a method of stabilizing a lead anode, the method comprising: operating an electrochemical cell, including electrochemical reduction at a first cathode and electrochemical oxidation at a first anode; and recycling a second electrolyte from a metal plating cell into a first anolyte, the second electrolyte having aqueous iron cations; wherein: the electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; the first anode is a lead electrode; the first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; and the first anolyte includes the aqueous iron cations at a concentration of at least 0.01 M, but not exceeding 0.5 M, optionally not exceeding 0.45 M, optionally not exceeding 0.445 M, optionally not exceeding 0.44 M, optionally not exceeding 0.4 M. Optionally, in aspects of the present invention, the first anolyte includes the aqueous iron cations at a concentration of at least 0.01 M, but not exceeding 0.4 M (in some aspects, not exceeding 0.44 M; in some aspects, not exceeding 0.445 M). Optionally, in aspects of the present invention, the first anolyte includes the aqueous iron cations at a concentration of at least 0.02 M, but not exceeding 0.4 M. Optionally, in aspects of the present invention, the first anolyte includes the aqueous iron cations at a concentration of at least 0.03 M, but not exceeding 0.4 M. Optionally, in aspects of the present invention, the first anolyte includes the aqueous iron cations at a concentration of at least 0.04 M, but not exceeding 0.4 M. Optionally, in aspects of the present invention, the first anolyte includes the aqueous iron cations at a concentration of at least 0.05 M, but not exceeding 0.4 M. Optionally, in aspects of the present invention, the first anolyte includes the aqueous iron cations at a concentration of at least 0.1 M, but not exceeding 0.4 M.

[0008] Aspects disclosed herein include a method of stabilizing a lead anode, the method comprising: operating an electrochemical cell, including electrochemical reduction at a first cathode and an oxygen evolution reaction (OER) at a first anode; wherein: the electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; the first anode is a lead electrode; the first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; and the first anolyte includes the aqueous sulfate at a concentration of at least 0.01 M.

[0009] Anion exchange membranes (AEMs) can "leak" cations that move towards the negative electrode under the action of diffusion and the electric field. Therefore, to maintain the iron sulfate concentration within a target range (also referred to herein as the stable concentration range of iron cations), it is necessary to add aqueous iron cations to replenish the aqueous iron lost due to the above-mentioned leakage. Optionally, for example, in some aspects, replenishing or maintaining the stable or target concentration range of iron cations in the anolyte can be achieved by flowing the anolyte or a portion thereof through a solid iron salt, such as ferrous sulfate and / or ferric sulfate, iron oxide and / or ferrous oxide, metallic iron, one or more ores such as magnetite, or any combination thereof. Optionally, for example, in some aspects, replenishing or maintaining the stable or target concentration range of iron cations in the anolyte can be achieved by adding or dosing an aqueous solution having aqueous iron cations (also referred to herein as an aqueous dosing solution or liquid iron source) to the anolyte. Optionally, for example, in some aspects, metallic iron can be provided to the catholyte or the catholyte can be exposed to metallic iron to consume protons (acids) that leak through the AEM from the anolyte.

[0010] Aspects disclosed herein include a method that includes: operating an electrochemical cell, including electrochemical reduction at a first cathode and electrochemical oxidation at a first anode; wherein: the electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; the first anode is a lead electrode; and the first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; wherein the method further includes: dissolving solid manganese oxide in the first anolyte in the presence of aqueous ferrous ions.

[0011] Aspects disclosed herein include a method that includes: operating an electrochemical cell, including electrochemical reduction at a first cathode and electrochemical oxidation at a first anode; wherein: the electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; the first anode is a lead electrode; and the first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; wherein the method further includes: reverse-biasing the first anode for a time, including electrochemically reducing aqueous ferric ions to aqueous ferrous ions at the first anode in the presence of the first catholyte.

[0012] Aspects disclosed herein include a method that includes: operating an electrochemical cell that includes electrochemical reduction at a first cathode and electrochemical oxidation at a first anode; wherein: the electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; the first anode and the first cathode are each independently a lead electrode; and the first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions.

[0013] Without being bound by any particular theory, ideas or understandings of fundamental principles related to the devices and methods disclosed herein may be discussed herein. It should be recognized that embodiments of the present invention may still be effective and useful regardless of the ultimate correctness of any mechanical explanations or assumptions. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic cross-sectional view showing a three-dimensional porous substrate having a lead layer on one or two surfaces.

[0015] Figure 2 is a schematic cross-sectional view showing a bipolar electrode structure.

[0016] Figure 3 is a schematic cross-sectional view showing a bipolar stack including a series of bipolar electrodes between end plates.

[0017] Figure 4 is a schematic cross-sectional view showing a bipolar electrode structure, showing some reaction examples that may optionally be catalyzed by corresponding electrodes according to some aspects.

[0018] Figure 5 is a schematic view showing an acid-producing ferric iron reduction cell that optionally includes a lead-containing oxygen evolution anode.

[0019] Figure 6 is a schematic view showing an iron electroplating cell that optionally includes a lead-containing oxygen evolution anode.

[0020] Figure 7 is a schematic view showing a two-step iron conversion system having multiple subsystems according to aspects herein, the system including an oxygen evolution reaction at a first anode.

[0021] Figure 8 is a schematic view showing a two-step iron conversion system having multiple subsystems, the system including an oxygen evolution reaction at an acid regeneration subsystem anode (first anode) and an oxygen evolution reaction at an electroplating cell anode (second anode).

[0022] Figure 9 It is a schematic diagram showing a two-step iron conversion system with multiple subsystems, which includes an oxygen evolution reaction at the anode (first anode) of the acid regeneration subsystem, and further illustrates the possible fluid flow between the subsystems.

[0023] Figure 10 It is a schematic diagram showing a two-step iron conversion system with multiple subsystems, which includes an oxygen evolution reaction at the anode (first anode) of the acid regeneration subsystem and an oxygen evolution reaction at the anode (second anode) of the electroplating cell, and further illustrates the possible fluid flow between the subsystems.

[0024] Figure 11 It is a schematic diagram showing an ore dissolution subsystem including an acid regeneration cell.

[0025] Figures 12A - 12C It is a scanning electron microscope (SEM) image of the electrode surface before electrochemical cycling in acid ( Figure 12A ), a scanning electron microscope (SEM) image of the equivalent electrode surface after electrochemical cycling in sulfuric acid without dissolved iron ( Figure 12B ), and a scanning electron microscope (SEM) image of the equivalent electrode surface after electrochemical cycling in an aqueous solution of iron sulfate or sulfuric acid containing dissolved iron ions ( Figure 12C ). The surface of the lead electrode exposed to acid without aqueous iron cations has large PbSO4 crystals, which will damage the dimensional stability of the lead electrode. The lead electrode exposed to acid containing aqueous iron cations has much smaller PbSO4 crystals, corresponding to a lead electrode with higher dimensional stability.

[0026] Figure 13 It is a series of schematic diagrams showing the potential mechanisms according to some aspects when the lead electrode is exposed to sulfuric acid without aqueous cations (left figure) and when the lead electrode is exposed to sulfuric acid containing aqueous iron cations or iron sulfate and / or ferrous sulfate (right figure). Generally, in the absence of iron sulfate, a large amount of surface-destabilizing PbSO4 crystals will form; when oxygen bubbles precipitate on the surface, the destabilizing effect will be exacerbated. In contrast, generally, according to some aspects, the presence of iron sulfate can prevent or significantly hinder or slow down the formation of large PbSO4 crystals, thereby stabilizing and strengthening the surface, including when oxygen bubbles precipitate from the surface. In some aspects, the presence of iron sulfate can lead to the formation of a protective layer on the surface of the lead electrode, which optionally includes an Fe-Pb-S-O composition (e.g., Fe x Pb y SO4).

[0027] Figure 14A series of SEM images of the surfaces of Pb and PbO2 that were air-dried (without liquid rinsing) after being soaked in H2SO4, PbSO4, or Pb2(SO4)3 (as indicated) for 12 hours. It is evident that, compared to the other surfaces shown, the surface of PbO2, particularly that of PbO2 exposed to sulfuric acid without iron sulfate, is significantly rougher and has large PbSO4 crystals.

[0028] Figure 15 A series of SEM images of the surface of Pb that was exposed to 1 M iron sulfate (upper figure) or 0.1 M sulfuric acid (lower figure) at approximately 30 mA / cm 2 or approximately 50 mA / cm 2 and cycled at a 50% duty cycle for one day.

[0029] Declaration Regarding Compounds and Terms

[0030] In general, the terms and phrases used herein have meanings that are generally recognized in the art, and these meanings can be found by reference to standard texts, journal references, and the context known to those skilled in the art. The following definitions are intended to clarify their specific use in this disclosure.

[0031] As used herein, the term "electrolyte" refers to an aqueous solution containing one or more dissolved ionic species. The pH of the electrolyte can be acidic, basic, or neutral, although the examples herein are described with reference to acidic electrolytes.

[0032] As used herein, the term "anolyte" refers to the electrolyte in contact with the "anode" electrode. Similarly, the term "catholyte" refers to the electrolyte in contact with the "cathode" electrode. In some examples and aspects, the anolyte and catholyte can be maintained as separate, non-mixing solutions, typically separated from each other within an electrochemical cell by a diaphragm and outside the cell by separate fluid conduits. However, in some cases, the terms "anolyte" and "catholyte" can refer to a single electrolyte, such as in an undivided electrochemical cell.

[0033] In electrochemical cell technology, for example, in the case of electrolytic cells, the anode refers to the electrode where electrochemical oxidation occurs, while the cathode refers to the electrode where electrochemical reduction occurs. As used herein, a reverse-biased anode refers to applying a voltage such that electrochemical reduction occurs at the anode. In this document, in the case of a reverse-biased anode, although reduction occurs at the anode during reverse biasing, the anode is not renamed but is described as being reverse-biased to maintain electrode identification consistency. Optionally, but not necessarily, the anode can be reverse-biased by applying a negative potential to the anode or a negative potential that is smaller or larger than the potential on the corresponding counter electrode (such as the cathode), such that electrons can flow from the circuit into the reverse-biased anode, thereby promoting electrochemical reduction of the reverse-biased anode in the presence of an electrolyte. Optionally, but not necessarily, a reverse-biased anode particularly refers to a potential on the anode such that ferric ions are reduced to ferrous ions on the anode.

[0034] The term "lead electrode" refers to an electrode that exposes lead and / or lead oxide to an electrolyte (such as anolyte). The lead electrode optionally includes massive lead or is optionally substantially formed of massive lead. Optionally, the lead electrode can include one or more layers of lead and / or lead oxide located on a different material that serves as a mechanical and electrical support and / or substrate, such that the lead and / or lead oxide is exposed to the electrolyte. As the oxygen evolution reaction (OER) proceeds, the lead metal surface of the lead electrode oxidizes to lead oxide (PbO x ), or in some aspects, in the presence of sulfate ions, first oxidizes to lead sulfate (PbSO4), and then oxidizes to lead oxide (PbO x ). Therefore, the lead electrode can also include some PbSO4. The lead electrode can include intentional dopants and / or alloying species to modify its electrochemical or other properties. As used herein, the formula PbO x represents lead oxide, including lead dioxide (PbO2), and also includes non-stoichiometric oxygen-deficient (di)lead oxide variants, such as where x is greater than or equal to 1 and less than or equal to 2. As used herein, the formula PbO2 is an abbreviation for lead dioxide and is intended to include its non-stoichiometric oxygen-deficient variants. Thus, the compounds represented by the formula PbO2 include the compounds represented by PbO x .

[0035] As used herein (including in the claims), the terms "aqueous iron cations" and "aqueous iron ions" mean all aqueous iron cations in any oxidation state, such as at least aqueous ferrous (Fe 2+ (aq) ) ions and aqueous ferric (Fe 3+ (aq) ) ions.

[0036] The term "solid manganese oxide" refers to any solid manganese oxide or undissolved manganese oxide precipitate. The terms "solid MnO 2-δ ", "solid MnO x ", "solid MnO2" are used interchangeably and also refer to any solid or undissolved MnO x precipitate, where x is greater than or equal to 1 and less than or equal to 2. The term "manganese oxide" refers to manganese dioxide (MnO2) and also includes oxygen-deficient or non-stoichiometric manganese dioxide, such as represented in the art by the formula MnO 2-δ and / or the formula MnO x where δ is greater than or equal to 0 and less than or equal to 1, and where x is greater than or equal to 1 and less than or equal to 2. Optionally, the term "manganese oxide" also includes any other manganese oxide species, such as but not limited to manganese(II) oxide (MnO), manganese(II,III) oxide (Mn3O4), manganese(III) oxide (Mn2O3), manganese(VI) oxide (MnO3), manganese(VII) oxide (Mn2O7), Mn5O8, Mn7O 12 and Mn7O 13 and any oxygen-deficient or non-coordinated variants thereof. As used herein, the formula MnO2 is an abbreviation for manganese dioxide and is intended to further include its non-stoichiometric oxygen-deficient variants, so the compounds represented by the formula MnO2 include the compounds represented by MnO x where x is greater than or equal to 1 and less than or equal to 2.

[0037] The term "manganese sulfate" refers to MnSO4. Optionally, the term "manganese sulfate" refers to MnSO4 and other manganese sulfate species.

[0038] The term "spent" electrolyte is intended to be consistent with the term used in the applicant's PCT patent application #PCT / US2022 / 021732 entitled "Two-Step Iron Conversion System", which was published as a PCT patent on September 29, 2022, with publication number WO2022204394, hereinafter referred to as "PCT '732", which is incorporated herein by reference and is also included as Appendix A in U.S. Provisional Patent Application No. 63 / 410,092 filed on September 26, 2022, hereinafter referred to as "Provis '092", the priority interest of which is claimed herein, and the entire content of which is incorporated herein by reference. Generally, spent electrolyte (which can be spent catholyte and / or spent anolyte) is electrolyte that has been used in an electrochemical cell for electrochemical reduction and / or electrochemical oxidation and then removed from its corresponding electrochemical cell. For example, spent catholyte (or spent anolyte) refers to electrolyte that has participated in an electrochemical reduction (or oxidation) reaction in an electrochemical cell and has then been removed from the electrochemical cell. During the corresponding electrochemical reaction (reduction or oxidation) process in the presence of the electrolyte (catholyte or anolyte), one or more reactants (such as iron ions) in the electrolyte may be consumed, and / or one or more products may accumulate. Thus, spent electrolyte can optionally be characterized as an electrolyte in which one or more reactants are consumed and / or one or more products accumulate during the corresponding electrochemical reaction process to an amount that is technically and / or commercially undesirable or disadvantageous for the same corresponding electrochemical reaction, whereupon the spent electrolyte is thus removed from the corresponding electrochemical cell. For example, the catholyte in an iron plating cell, such as the second catholyte of the second electrochemical cell according to the aspects in PCT '732 and Provis '092, may consume ferrous ions during the process of plating iron to an extent that it is optimal to remove the (spent) catholyte from the plating cell. The removed (spent) catholyte, although containing ferrous ions, has too low a concentration to be used for plating and can optionally be recycled directly or indirectly into the first anolyte of the electrochemical cell according to the aspects disclosed herein. The removal and recycling of the spent electrolyte can be carried out as part of a batch process or a continuous process.

[0039] As used herein, the terms "pure iron" and "high-purity iron" are used in a relative sense to refer to metallic iron materials that are purer than the iron source material and contain an acceptable low amount of one or more impurities.

[0040] As used herein, the terms "iron source material" and "iron feedstock" are used synonymously to refer to iron-containing materials that can be used as inputs to the various systems and methods described herein. "Iron source material" and "iron feedstock" can include any form of iron in its naturally occurring state or in a beneficiated or purified state through reduction processing, such as iron oxides, hydroxides, oxyhydroxides, carbonates, or other iron-containing compounds, ores, rocks, or minerals, including any mixtures thereof. The term "iron ore" or simply "ore" can include materials of one or more iron ores, rocks, natural rocks, sediments, natural sediments, minerals, and / or natural minerals recognized, known, or mentioned in the art, whether in their naturally occurring state or in a state that has been beneficiated through reduction processing or otherwise purified or modified. Some embodiments of the processes and systems described herein may be particularly applicable to iron ores, including hematite, goethite, magnetite, limonite, siderite, ankerite, turgite, bauxite, or any combination thereof.

[0041] Optionally, the iron source material or iron feedstock can include iron metal materials such as, but not limited to, iron dust (e.g., fine particles generated as a byproduct of ironmaking or steelmaking processes in blast furnaces, oxygen furnaces, electric arc furnaces, etc.), iron powder, scrap steel, and / or scrap cast iron. "Iron source material" and "iron feedstock" can also contain various other non-iron materials that are commonly referred to as "impurities".

[0042] As used herein, the term "impurity" refers to an element or compound other than the desired final product material (e.g., iron). In various aspects, a given element or compound can be considered an "impurity" or not, depending on the intended final use of the product material. In some cases, one or more elements or compounds that may be impurities in a process or subprocess can be separated or purified, collected, and sold as secondary product materials.

[0043] In various aspects herein, various compositions, compounds, or solutions can be substantially "separated" or "purified" to an extent sufficient to achieve the purposes described herein. In various aspects, the chemical purity of a substantially purified composition, compound, or formulation (e.g., an iron solution of ferrous iron, an iron solution of ferric iron, or plated metallic iron) can be 90% (e.g., measured as molar concentration of ionic concentration or by weight), optionally 95% for some applications, optionally 99% for some applications, optionally 99.9% for some applications, optionally 99.99% for some applications, and optionally 99.999% for some applications.

[0044] As used herein, the term "tank" is intended to include any container suitable for holding a liquid (such as a highly acidic or corrosive aqueous solution, if desired). In some aspects, such a container may include additional features or components to assist or improve the mixing of the solid and / or liquid contents of the container. For example, a dissolution tank may include passive or actively operated structures or features for agitating a solution or a solid / liquid mixture. A dissolution tank or other tank useful in the systems and methods herein may also include features that allow a gas to be injected into or passed through the solid and / or liquid contents of the tank to increase the contact of the gas with the solid and / or liquid materials within the tank. A variety of tanks may also include baskets, sieves, pans, filters, or other structures to collect and separate solids from a liquid. In some aspects, the tank may be configured to direct a liquid or gas through the tank (e.g., via flow-directing structures, pumps, impellers, baffles, agitators, stirring blades, vibrators, swirl channels, etc.) in such a way as to agitate the mixture therein.

[0045] In some aspects described herein, a system for converting iron ore into iron metal (i.e., an "iron conversion system") may include two or more subsystems. Some aspects include a "dissolution subsystem" in which components of an iron-containing feedstock are dissolved in an aqueous solution. Some aspects also include a "ferroplating subsystem" in which the dissolved iron is electrochemically reduced to iron metal during an "electroplating (or simply 'plating') process". The iron metal may then be removed from the ferroplating subsystem.

[0046] The term "electroplating iron" (or "ferroplating", which is used synonymously herein) refers to the process of electrochemically reducing dissolved iron to metallic iron on a cathode surface. The equivalent terms "electrodeposition", "electroforming", and "electrolytic deposition" are also used synonymously with "electroplating iron" herein. By any definition of the term, the shape or dimensional specification of the electroplated iron need not be a "plate". For example, the electroplated iron may take any shape or form and may be deposited on any suitable cathode surface, as described in various aspects herein.

[0047] The term "dissolution step" includes the processes that occur in the dissolution subsystem, including but not limited to the dissolution of iron oxide materials and the electrochemical processes that occur in or through an "acid regeneration cell", including but not limited to the claimed step of electrochemically reducing Fe 3+ ions to Fe 2+ ions in the acid regeneration cell. The dissolution step process may also include the oxidation of water or hydrogen in a first electrochemical cell, for example, to generate protons, which may allow for the regeneration of an acid (in the form of protons) that is used to facilitate the dissolution of the iron-containing feedstock.

[0048] The terms "acid regenerator" and "acid regeneration cell" refer to an electrochemical cell according to the embodiments and aspects herein, such as an electrochemical cell according to any one of aspects 1-56 below. Optionally, the "acid regenerator" and "acid regeneration cell" may correspond to and / or further include any embodiment or aspect disclosed in PCT'732 and Provis'092, which are incorporated herein by reference as part of this disclosure.

[0049] The term "iron plating step" includes processes occurring in an iron plating subsystem, including but not limited to electrochemical processes occurring in or through a claimed "plating cell", including but not limited to the step of electrochemically reducing Fe 2+ ions to Fe metal in a "plating cell", also referred to herein as a "plating cell". The iron plating process may further include oxidizing a second portion of Fe 2+ ions to form Fe 3+ ions. In some aspects, such Fe 2+ ions may be provided by a first electrochemical cell or another part of the system.

[0050] As used herein, unless otherwise specified, the term "ferrous iron solution" or "ferrous solution" may refer to an aqueous solution containing dissolved iron, where the dissolved iron is at least predominantly (i.e., 50% to 100%) in the Fe 2+ (i.e., "ferrous") ionic state, and the remaining dissolved iron is in the "ferric" Fe 3+ state. Similarly, the term "ferrous ion" refers to one or more ions in the ferrous (Fe 2+ ) state.

[0051] As used herein, unless otherwise specified, the term "ferric iron solution" or "ferric solution" may refer to an aqueous solution containing dissolved iron, where the dissolved iron is at least predominantly (i.e., 50% to 100%) in the Fe 3+ (i.e., "ferric") ionic state, and the remaining dissolved iron is in the "ferrous" Fe 2+ state. Similarly, the term "ferric ion" refers to one or more ions in the ferric (Fe 3+ ) state. A "ferric solution" or "ferrous solution" may also contain other dissolved ions or colloidal or particulate materials, including impurities.

[0052] As used herein, any reference to a "PEM" or "proton exchange membrane" may be interpreted to also include a "CEM" or "cation exchange membrane", and these two terms may include any available membrane material that selectively allows positively charged cations and / or protons to pass through. The abbreviation "AEM" is used to refer to an anion exchange membrane that is selective for negatively charged aqueous ions and includes any available anion-selective membrane.

[0053] As used herein, aqueous protons and electrochemically generated protons are intended to include aqueous protons and aqueous hydronium ions.

[0054] As used herein, the term "raw ore" refers to an iron-containing ore that has not been thermally reduced or air-roasted according to aspects disclosed herein. Optionally, the raw ore is an iron-bearing feedstock ore.

[0055] As used herein, electrochemically generated ions, such as electrochemically generated protons and electrochemically generated iron ions (e.g., Fe 2+ 、Fe 3+ ), refer to ions generated or produced in an electrochemical reaction. For example, the electrochemical oxidation of water at the anode can electrochemically generate protons and electrochemically generate oxygen.

[0056] As used herein, the term "air roasting" refers to a heat treatment conducted at an elevated temperature in the presence of air. The air roasting of an ore, such as an iron-containing ore, can decompose or reduce the average particle size of the ore. Optionally, the air roasting is conducted at a temperature selected from the range of 300 °C to 500 °C. Additional descriptions and aspects that may be useful for air roasting can be found in the following reference, which is incorporated herein by reference in its entirety: "Study of the calcination process of two limonitic iron ores between 250 °C and 950 °C", Revista de la Facultad de Ingenieria, p. 33 (2017).

[0057] As used herein, the term "redox pair" refers to two chemical species, such as ions and / or molecules, corresponding to a reducing substance and an oxidizing substance for an electrochemical reaction or a half-cell reaction. For example, in the electrochemical reduction of Fe 3+ ions to Fe 2+ ions, the corresponding redox pair is Fe 3+ / Fe 2+ , where Fe 3+ is the oxidizing substance and Fe 2+ is the reducing substance. As used herein, the order of the described redox pairs (e.g., Fe 3+ / Fe 2+ vs. Fe 2+ / Fe 3+)It is not intended to indicate which substance is the reducing substance and which is the oxidizing substance. Additional descriptions and potentially useful aspects of redox pairs can be found in the following reference, which is incorporated herein by reference in its entirety: "Redox–Principles and Advanced Applications": Book by Mohammed Khalid, Chapter 5: Redox Flow Battery Fundamental and Applications.

[0058] As used herein, the terms "steady state" and "steady - state" generally refer to the condition or set of conditions that characterize a process, a method step, one or more reactions, a solution, a (sub)system, etc., and during the operation or implementation of such process, method step, one or more reactions, solution, (sub)system, etc., the condition is true for a longer time than it is false. For example, the dissolution of an ore or feedstock can be characterized by steady - state conditions, where the steady - state conditions are true for at least 50%, optionally at least 60%, optionally at least 70%, optionally at least 80%, optionally at least 90%, optionally at least 95% of the time during which the dissolution occurs. For example, the steady - state conditions may not include the conditions that characterize the transient start - up and shut - down phases of a process such as the dissolution of a feedstock.

[0059] The term "cathode chamber" refers to a region, compartment, container, etc. that includes a cathode or at least a part or surface of the cathode, and the catholyte. The term "anode chamber" refers to a region, compartment, container, etc. that includes an anode or at least a part or surface of the anode, and the anolyte.

[0060] As used herein, the term "iron - rich solution" may also be referred to as "iron - iron - rich solution" or "ferrous product solution", corresponding to the iron - rich ion solution formed in the ore dissolution subsystem.

[0061] As used herein, the term "precipitation pH" refers to the pH at which one or more of the recited ions or salts are thermodynamically favored or expected to precipitate from the bulk aqueous solution. Generally, the solubility of ions and salts dissolved in an aqueous solution depends on the pH of the aqueous solution. As the pH increases in the acidic region, many metal ions form metal hydroxides, which tend to precipitate from the bulk solution due to decreased solubility. The precipitation pH is defined herein as the pH corresponding to the point at which the solubility of a given ion or salt is less than a concentration threshold. The precipitation pH can be an upper limit above which the solubility of a given ion or salt is less than 1 mM, optionally less than 0.1 mM.

[0062] As used herein, the term "metallic iron" refers to a material that contains metallic iron, such as but not limited to scrap iron, electroplated iron, iron powder, etc.

[0063] As used herein, the terms "supporting salt" and "supporting ion" refer, respectively, to a salt and an ion that corresponds to or serves as a supporting electrolyte, or that at least partially forms a supporting electrolyte when dissolved to increase the conductivity of the bulk solution. In some aspects, for example, the electrolytes and solutions in the dissolution subsystem and the plating subsystem can include dissolved iron species, acids, and additional inert salts that serve as supporting electrolytes to enhance the conductivity of the electrolyte, which can be particularly beneficial at low ferrous concentrations, where the inert salts that serve as supporting electrolytes to enhance conductivity can be referred to as supporting salts. Supporting salts can include any electrochemically inert salt, such as sodium chloride, potassium chloride, ammonium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, sodium chloride, potassium chloride, ammonium chloride, or other salts, or combinations of salts. If used, the concentration of the supporting salt in the solution can be in the range of, for example, about 0.1 to about 1 M.

[0064] As used herein, the terms "dissolved iron", "dissolved iron ion", "aqueous iron", and "aqueous iron ion" are used interchangeably and refer to aqueous or dissolved iron ions present in a solution, including ferrous ions, ferric ions, and combinations thereof.

[0065] As used herein, the term "weight % (wt.%)" or "weight % (wt%)" refers to weight percentage, or mass fraction expressed as a percentage by mass. The term "atomic % (at.%)" or "atomic % (at%)" refers to atomic percentage, or atomic ratio expressed as the percentage of one type of atom relative to the total atoms in a given substance such as a molecule, compound, material, nanoparticle, polymer, dispersion. The term "mole % (mol.%)" refers to mole percentage or percentage by mole. The term "volume % (vol.%)" refers to volume percentage.

[0066] The terms "substantially" and "approximately" are used interchangeably and mean within 20%, within 10%, within 5%, within 1%, optionally within 0.1%, or an equivalent property, condition, or value of a reference property, condition, or value. The terms "substantially equal", "substantially equivalent", "substantially unchanged", when used with a reference value describing a property or condition, mean within 20%, within 10%, optionally within 5%, optionally within 1%, optionally within 0.1%, or optionally an equivalent value of the provided reference value. For example, if the value of a diameter is within 20%, optionally within 10%, optionally within 5%, optionally within 1%, optionally within 0.1%, or optionally equal to 20% of 100 nm, then the diameter is approximately substantially equal to or approximately equal to 100 nm (or, "substantially 100 nm" or "approximately 100 nm"). The term "substantially greater than", when used with a reference value describing a property or condition, means a value that is at least 1%, optionally at least 5%, optionally at least 10%, or optionally at least 20% greater than the provided reference value. The term "substantially less than", when used with a reference value describing a property or condition, means a value that is at least 1%, optionally at least 5%, optionally at least 10%, or optionally at least 20% less than the provided reference value. As used herein, the term "about" means a numerical range that includes the specified value and that a person of ordinary skill in the art would consider to be reasonably similar to the specified value. In some aspects, about means a range of standard deviations of measurements commonly accepted in the art. In some aspects, about means a range extending to + / - 10% of the specified value. In some aspects, about means the specified value. In some aspects, the terms "about", "approximately", and "substantially" are interchangeable and have the same meaning. For example, a particle having a size of about 1 μm can have a size within 20%, optionally within 10%, optionally within 5%, optionally within 1%, optionally within 0.1%, or optionally equal to 20% of 1 μm.

[0067] As used herein, in the specification and claims, the term "and / or" is used herein to refer to only a single element, or any combination of elements, in a list in which the term "and / or" appears. For example, a list of two or more elements having the term "and / or" is intended to cover embodiments having only any single element, or aspects having any combination of the listed elements. For example, the phrase "element A and / or element B" is intended to cover aspects having only element A, aspects having only element B, or aspects having elements A and B in combination. For example, the phrase "element A, element B, and / or element C" is intended to cover aspects having only element A, aspects having only element B, aspects having only element C, aspects having elements A and B in combination, aspects having elements A and C in combination, aspects having elements B and C in combination, or aspects having elements A, B, and C in combination.

[0068] As used herein, the term "±" refers to an inclusive range of values such that "X ± Y" refers to an inclusive range of values selected from the range of X - Y to X + Y, where both X and Y are independent numerical values. In the case of "X ± Y" where Y is a percentage (e.g., 1.0 ± 20%), the inclusive range of values is selected from the range of X - Z to X + Z, where Z is equal to X·(Y / 100). For example, 1.0 ± 20% refers to an inclusive range of values selected from the range of 0.8 to 1.2. Detailed Description

[0069] In the following description, numerous specific details of the devices, device components, and methods are set forth in order to provide a thorough explanation of the exact nature of the various inventions described herein. However, it will be apparent to those skilled in the art that the various inventions may be practiced without these specific details.

[0070] In some aspects, the present disclosure provides processes, systems, and methods for stabilizing lead anodes against shedding, dissolution, and / or other degradation processes, such as in the case where lead anodes are used for the oxygen evolution reaction (OER). In various aspects, the present disclosure provides processes, systems, and methods for reducing or eliminating solid manganese oxide sludge or contamination that may detrimentally accumulate in the anode chamber or the anolyte, or may poison or coat the anode, such as by dissolving manganese oxides in the anolyte. In various aspects, the present disclosure further includes processes, systems, and methods for achieving an efficient, low-temperature aqueous hydrometallurgical process for producing pure iron from a variety of iron source materials, including iron feedstock materials of relatively low purity.

[0071] Numerous other useful aspects, aspects, and definitions of the present systems and methods are further elaborated and illustrated in PCT'732 and Provis'092.

[0072] For many years, electrodes containing lead and / or lead oxides (commonly lead dioxide) have been used as oxygen evolution anodes in a variety of electrochemical systems. However, long-standing problems have complicated the use of lead electrodes in many processes. Two major problems include shedding and sludge formation.

[0073] The "shedding" or mechanical peeling of lead oxide materials (in some aspects lead sulfate) from the electrode causes dimensional instability, loss of catalyst material, and loss of electrode conductivity, ultimately limiting the electrode life. As a prelude to lead shedding, large PbSO4 crystals typically form (e.g., see the SEM image labeled "PbO2 in H2SO4" in the upper right of Figure 14 ), and promote mechanical peeling, especially during (re)start of the OER.

[0074] Manganese oxide deposits or "sludge" accumulate on and around the electrodes and need to be cleaned regularly to prevent (a) PbO2 blockage, (b) permanganate formation, and (c) uneven current distribution that can impede battery operation. For example, zinc electrowinning anolyte typically includes manganese ions to minimize lead dissolution and lead incorporation into the galvanized coating. The presence of manganese may also be due to its being an impurity in the original process feedstock (such as iron ore).

[0075] Unexpected findings disclosed and anticipated herein include that the operation of lead dioxide anodes is beneficial for using lead as a viable electrode material in iron electrodeposition systems and / or other electrodeposition systems in the presence of limited concentrations of dissolved iron. Additionally, several system configurations, electrode structures, and operating methods are anticipated that can effectively utilize the discovered operation.

[0076] First, for example, it has been found that the performance of the lead dioxide electrode surface is significantly different in the presence of iron sulfate compared to the electrode in an acid without iron sulfate. In the presence of a large concentration of iron sulfate, when the lead electrode is cycled between OER and open-circuit rest, the electrode surface remains relatively dense and does not exhibit the highly crystalline, cracked, and fragmented surface seen on electrodes cycled in sulfuric acid without trivalent iron ions. In the absence of iron ions (such as trivalent iron ions), when sulfate ions are present in the anolyte, under transient or non-operating conditions (such as when the lead anode is at open-circuit voltage (OCV), the potential is too low to perform OER, and / or if / when the anode potential drops too quickly), the lead electrode surface self-discharges to form PbSO4. Without wishing to be bound by a particular theory, when iron ions (such as trivalent iron ions) and sulfate ions are present in the anolyte, it is expected that an iron-lead compound (such as Fe x Pb y SO4) can form, which can protect the lead electrode surface from forming large lead sulfate (PbSO4) crystals that can easily cause the common shedding phenomenon of lead electrodes. It has been found that lead / dioxide electrodes operating OER in an iron sulfate-containing electrolyte have better mechanical stability and less shedding than similar electrodes operating in an iron sulfate-free electrolyte. The iron-lead compound can also be smooth, which may further promote the stability of the lead electrode surface.

[0077] For example, Figure 14 A series of SEM images of Pb and PbO2 surfaces after being air-dried (without liquid rinsing) after being soaked in H2SO4, PbSO4, or Pb2(SO4)3 (as labeled) for 12 hours are shown. It is evident that in the absence of iron sulfate, even without current-voltage cycling, the PbO2 exposed to sulfuric acid has a significantly rougher surface and large PbSO4 crystals compared to the other surfaces shown. Figures 12B - 12CSimilar results were shown for the surface of lead oxide after electrochemical cycling, where electrochemical cycling was carried out in the presence of sulfuric acid without dissolved iron ions ( Figure 12A ) led to the formation of large PbSO4 crystals, while the presence of dissolved iron ions and sulfuric acid ( Figure 12B ) inhibited the formation of PbSO4, so any PbSO4 crystals present were much smaller and less unstable. Figure 15 Images of the surface of a lead electrode exposed to iron sulfate or sulfuric acid were also shown, indicating that the surface of the lead electrode exposed to sulfuric acid without iron sulfate became rougher and, correspondingly, less dimensionally stable compared to the lead electrode in the presence of iron sulfate. Figure 13 It is shown that, without being bound by any particular theory in some aspects, the presence of iron sulfate protects the surface of the PbO2 electrode from forming large unstable PbSO4 crystals, or at least can slow down the formation of said PbSO4 crystals. When oxygen bubbles evolve from the PbO2 electrode, the bubbles can severely damage the components weakly attached to the surface and the surface roughness features, resulting in the detachment of Pb from the PbO2 electrode exposed to sulfuric acid. By adding iron sulfate to the electrolyte, the formation of PbSO4 crystals can be reduced, slowed down or prevented, thus stabilizing the PbO2 electrode.

[0078] Accordingly, it is expected that lead can be advantageously used as an oxygen evolution anode in contact with an electrolyte (e.g., acidic, basic or neutral pH) containing at least 0.01 M total dissolved iron (optionally at least 0.05 M) in a variety of electrochemical cells, including electrolytic deposition cells (e.g., iron electrolytic deposition cells with an OER anode), acid regeneration cells (e.g., cells with an OER anode and a ferric iron reduction cathode), and water electrolysis cells (e.g., PEM electrolyzers for hydrogen production). It is further expected that lead can be used as an anode and / or cathode in a decoupled iron plating cell, which is defined as an iron electroplating cell, such as the "iron plating subsystem" or "second electrochemical cell" described in PCT'732 and Provis'092, where ferrous iron is oxidized at the anode. It is further expected that in a two-step (or "decoupled") iron electrolytic deposition system, such as the "iron plating subsystem" described in PCT'732 and Provis'092, at least a portion of the "waste" anolyte or catholyte from the plating anode can be introduced as anolyte to the oxygen evolution anode of an acid regeneration cell (such as the "dissolution subsystem" or "first electrochemical cell" described in PCT'732 and Provis'092).

[0079] The use of a lead anode in an iron electrodeposition cell can result in a certain amount of lead incorporation into the electroplated iron. It has been found that electroplated iron containing from 0.014% to 0.022% by weight of lead can be produced in a ferrous sulfate electroplating electrolyte saturated with lead ions (optionally having from about 30 to 40 micromoles or from about 5 to 10 ppm of lead ions). Thus, electroplated iron containing a measurable amount of lead (e.g., greater than about 3 ppm) can indicate an iron electrodeposition process using a lead anode.

[0080] Another challenge commonly encountered when using a lead dioxide electrode as an OER anode in a standard electrodeposition process is that if dissolved manganese is present in the electrolyte, manganese dioxide (MnO2) will form in the anolyte during the oxygen evolution process. This MnO2 does not tend to adhere to the lead dioxide anode but instead precipitates as a solid sludge in the electrolyte and on the electrode surface. While Zn electrodeposition processes often utilize Mn impurities in the ore to "protect" the PbO2 from the above-mentioned sloughing challenges, these processes require very frequent cleaning schedules to remove the excess MnO2 sludge in the anolyte. Cu electrodeposition processes tend to strive to minimize the Mn concentration in the electrolyte to avoid using expensive or destructive MnO2 removal methods. In aspects of the present disclosure, if, for example, a salt solution resulting from ore dissolution (e.g., the salt solution in the "dissolution subsystem" described in PCT'732 and Provis'092) is used as described above to provide dissolved iron to the anolyte ("first anolyte"), the electrolyte may contain a certain concentration of dissolved Mn, which may concentrate over time.

[0081] It has been found that ferrous sulfate can be used in situ in an electrochemical cell to reduce or eliminate solid MnO2 without degrading cell performance since ferrous sulfate can very rapidly react with any solid MnO2 and dissolve it to form aqueous MnSO4 as a product. For example, it is contemplated that if / when MnO2 forms in the OER anolyte, a maintenance procedure can be performed by introducing or generating an amount of ferrous sulfate sufficient to dissolve the MnO2.

[0082] For example, the (first) anolyte or (first) anode chamber can be rinsed or washed with a solution containing an aqueous ferrous salt (such as aqueous ferrous sulfate) to dissolve any solid manganese oxides. Another example is that a certain amount of a solution containing an aqueous ferrous salt (such as aqueous ferrous sulfate) can be added to the (first) anolyte. For example, ferrous sulfate can be introduced into the anolyte (first anolyte) by introducing a certain amount of a ferrous-containing solution from a decoupled electrowinning system (such as the "iron plating subsystem" described in PCT'732 and Provis'092) into the anode chamber (first anode chamber) of an electrochemical cell or acid regenerator according to the aspects disclosed herein. For example, the ferrous-containing solution can include the acid regenerator catholyte and the "waste" plating cell anolyte or catholyte, such as the electrolyte from the "iron plating subsystem" described in PCT'732 and Provis'092, optionally, the waste electrolyte. For example, a ferrous sulfate solution stored in a separate tank specifically for removing manganese sludges in the anode chamber can be introduced into the (first) anode chamber periodically or occasionally. In this method, the manganese compounds are not returned to the main electrolyte circuit, thus achieving the natural separation of manganese impurities from the main circuit.

[0083] As an alternative or supplement, ferric iron in the anolyte can be reduced to ferrous iron by briefly allowing the cell to self-discharge or applying a reverse-polarity current to the cell or stack, thereby producing ferrous sulfate in-situ in the acid regenerator anode chamber (first anode chamber). This production can be carried out with or without the anolyte and / or catholyte flowing through the acid regeneration cell / stack.

[0084] Lead electrodes can be fabricated and constructed in a variety of ways. In some aspects, the lead electrode can include a substantially solid or porous bulk lead structure. Since operating lead electrodes in a ferrous sulfate (and / or ferric sulfate) electrolyte results in reduced shedding, lead anode structures that cannot be used in other systems can be employed. For example, in some aspects, the lead electrode can include a non-lead substrate that supports one or more layers of lead (including thin layers and porous layers). The lead can provide a protective layer for the substrate material, which might otherwise be chemically eroded by the liquid electrolyte.

[0085] Reference Figure 1, the lead electrode 100 may include a porous substrate 102 coated with a single layer of lead on a single side 104, coated with a lead coating on both sides 104 and 106, or a coating covering the inner surface of a three-dimensional substrate. Such a lead coating can be applied to the substrate surface by the following processes: electroplating, spray pyrolysis (e.g., spraying the substrate with a liquid containing dissolved lead, heating the substrate to evaporate and / or burn the liquid and / or binder material, and causing the lead to adhere to the substrate surface), dipping the substrate into molten lead and cooling, spraying or painting molten lead on one or both sides of the substrate, or other processes. As an alternative or supplement, lead can be applied to the solid substrate in a selected manner to impart a microstructured and / or nanostructured surface. For example, lead can be applied by chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), sol-gel deposition, or any other method. In some cases, the method of applying the lead coating can be selected according to the thickness of the layer to be applied. For example, techniques such as electroplating, spray pyrolysis, PVD, CVD, and ALD may be suitable for applying relatively thin layers, while techniques involving dipping the substrate into molten lead, brushing, or spraying molten lead onto the substrate may be suitable for thicker layers. In other aspects, thin layer techniques can be used to apply multiple layers to form a thicker total lead coating.

[0086] The porous substrate 102 can be made of a conductive material, such as titanium, graphite, carbon, stainless steel, nickel, or other conductive materials suitable for the selected electrolyte (e.g., acidic, alkaline, or neutral). In various aspects, the porous substrate can include a foam, woven mesh, non-woven mesh, expanded metal (such as "EXMET"), felt, porous plate, or other two-dimensional or three-dimensional structure made of metal, carbon, graphite, or other materials or combinations of these materials. In some aspects, the substrate can advantageously have sufficient mechanical strength to resist bending, warping, compression, etc. For example, the substrate material can have a compressive yield strength of about 10 to about 200 MPa and / or a Young's modulus of about 600 to about 1,500 MPa.

[0087] The thickness of the lead layer can be from about 50 microns to up to about 5 mm. In some specific aspects, the average or minimum thickness of the lead layer on the porous or three-dimensional substrate can be about 50 microns, about 100 microns, about 500 microns, about 1 mm, about 1.5 mm, about 2 mm, about 2.5 mm, about 3 mm, about 3.5 mm, about 4 mm, about 4.5 mm, or about 5 mm.

[0088] Reference Figure 2, the bipolar lead electrode 200 can be manufactured by coating lead layers 204, 206 on each face of a solid (non-porous and electrolyte-impermeable) substrate. Using lead protective layers can allow the use of low-cost materials that are more vulnerable to electrolyte chemical erosion. Optionally, the edge surfaces of the substrate can also be coated with lead, thereby completely encapsulating the substrate in lead. Preferably, the lead layers 204, 206 have sufficient thickness and density to prevent the liquid electrolyte and dissolved ions from reaching the substrate 202.

[0089] The bipolar electrode 200 may further include a carbon cathode layer 208 on one face and a lead anode layer 210 on the opposite face.

[0090] In some aspects, each face of the porous or non-porous substrate 102 or 202 can be coated with lead layers of equal or different thicknesses. For example, one face 204 can have a thinner or thicker lead layer than the opposite face 206. In some aspects, the thickness of the lead layers 204, 206 can be from about 0.1 mm to about 2 mm.

[0091] In some aspects, the protective layer 204 under the carbon cathode 208 can include a material other than lead that has sufficient thickness and density to protect the substrate 202 while providing through-plane and in-plane conductivity, such as graphite, conductive polymers, conductive graphitized polymers, polymers impregnated with carbon nanotubes, carbon paste, carbon adhesives, or other carbon-based materials.

[0092] The carbon cathode layer 208 can include a high-surface-area structure of carbon, graphite, graphene, or other conductive carbon materials. The cathode layer can be provided in the form of felt, foam, paper, machined or cast graphite sheets, or other structures with a high specific surface area.

[0093] The carbon cathode layer 208 can be conductively adhered to the protective layer 204 (whether lead or other material) by any suitable method, thereby maintaining conductivity between the cathode layer 208, the protective layer 204, and the substrate 202. Such techniques can include conductive adhesives, welding, brazing, mechanical compression, or a combination of these techniques or other techniques.

[0094] In some aspects, the lead anode layer 210 can be part of the lead layer 206 or an additional layer on top of the lead layer 206. For example, in order to form a dense protective layer, the lead layer 206 can have a very low surface area. Such a dense low-surface-area layer may not provide sufficient electrochemically active surface area to catalyze an effective electrochemical oxidation reaction (such as oxygen evolution). Thus, the lead anode layer 210 can be made to have a higher surface area than the underlying protective lead layer 206. In various aspects, the high-surface-area lead anode layer can be fabricated by creating porous lead or "spongy" lead on top of the protective layer 206. In some aspects, such porous lead or spongy lead can be made directly on the protective layer 206 or formed separately and adhered to the protective lead layer 206 by welding, adhesives, brazing, mechanical compression, or a combination of these techniques or other techniques. U.S. Patent No. 778,894 (issued in 1905) describes a method for making spongy lead that can be used to form the high-surface-area lead anode layer 210.

[0095] In other aspects, the high-surface-area lead anode layer 210 can be made by laminating Figure 1 the lead electrode 100 of the type described onto the protective lead layer 206. Such lamination can be achieved by heating the protective lead layer sufficiently to soften it and then mechanically pressing the lead electrode 100 into the protective lead layer. Alternatively, the lead electrode 100 can be connected to the protective lead layer using a conductive adhesive, welding, or other techniques while maintaining electrical conductivity between the lead layer 206 and the lead electrode 100.

[0096] The solid substrate 202 can include a solid monolithic piece, plate, or laminated structure configured to provide electrical conductivity and mechanical support to the lead layers 204, 206 while also providing mechanical strength when the bipolar electrode is compressed in a battery stack. Alternatively, in some aspects, the solid substrate can include a solid lead sheet or plate. As used herein, the term "solid" refers to a non-porous material, or a material that is impermeable to solutions, anions, or both.

[0097] In various aspects, the material composition and properties of the substrate 202, the lead deposition techniques, and the lead layer thickness can include those described above for a porous substrate. The solid substrate 202 can be made of a conductive material such as titanium, graphite, carbon, stainless steel, nickel, or other conductive materials suitable for use in the selected electrolyte (such as acidic, alkaline, or neutral). In some aspects, the substrate can advantageously have sufficient mechanical strength to resist bending, warping, compression, etc. For example, the substrate material can have a compressive yield strength of about 10 to about 200 MPa and / or a Young's modulus of about 600 to about 1,500 MPa.

[0098] Reference Figure 3, in some aspects, a series of bipolar electrodes 200 can be combined in an electrically series-connected manner in a bipolar cell stack 300. As shown, when stacked in a bipolar cell, an impermeable, non-porous conductive substrate (such as Figure 2 202 therein) can form a bipolar plate 302. The bipolar plate 302 is so named because it carries charges of different or opposite polarities on its opposite faces, for example, a positive charge on its anode-adjacent face and a negative charge on its cathode-adjacent face.

[0099] In Figure 3 , each bipolar plate 302 can be a substrate 202 of the type referred to Figure 2 above. Similarly, each bipolar plate 302 can be coated with a cathode-side protective layer 304 and an anode-side protective layer 306. In addition, each cathode-side protective layer 304 can be covered by a cathode layer 308, and each anode-side protective layer can be covered by an anode layer 310.

[0100] Each anode layer 310 is separated from an adjacent cathode layer 308 by a separator 316 (which can be a PEM, AEM, or microporous spacer). In the bipolar stack 300, end plates 320 and 321 can be provided to apply mechanical compression and conductivity. The anode-side end plate 320 can be covered (coated or simply mechanically covered) with a protective layer 326 (such as lead), and this protective layer can be covered by an end anode 326. The cathode-side end plate 321 can be covered with a protective layer 324 (such as lead or other materials mentioned above), and this protective layer can be covered by an end cathode layer 308 (coated or simply mechanically covered).

[0101] In some aspects, the bipolar stack 300 can also include conductive spacer layers or flow field layers ( Figure 3 not shown in ), through which fluids can flow. Such fluids can include liquid electrolytes, gaseous reactants, gaseous electrolysis products, etc. Alternatively, a flow field, spacers, or other fluid flow channels can be provided as features of the anode layer 310 and the cathode layer 308 themselves. The anolyte and the catholyte (as well as any other reactants) can flow through each electrode chamber in a common direction or in opposite (or orthogonal) directions as needed.

[0102] In some aspects, the bipolar stack 300 as Figure 3 shown can be configured as an acid regeneration battery as described in PCT'732 and Provis'092. In this case, an iron sulfate anolyte solution can flow through the anode chamber. The anolyte can mainly contain ferric sulfate because any ferrous ions present in the anolyte tend to be oxidized to the ferric state. As described in PCT'732 and Provis'092, the catholyte can contain a mixture of ferric sulfate and ferrous sulfate, depending on the dissolution and reduction stages.

[0103] Figure 4 is a schematic cross-sectional view showing an exemplary bipolar electrode structure incorporating a lead structure in accordance with some aspects of the present disclosure. As Figure 4 shown, the substrate (e.g., 202) can be formed of stainless steel. Protective lead sheets (e.g., examples of layers 204 and 206) can be used on each side of the substrate facing the anode side and the cathode side. The cathode (such as a carbon electrode) can be deposited on the lead sheet on the cathode-facing side of the substrate. The lead anode can be deposited on the lead sheet on the anode-facing side of the substrate. When used as an “acid regenerator” battery, the reduction reaction of ferric to ferrous can occur at the carbon cathode, while the water oxidation reaction can occur at the lead anode. In other aspects, different reactions can occur at the anode and / or cathode.

[0104] In various aspects, the lead coating, lead layer, or lead mass structure described in the above examples can also include additives or dopants or alloying elements such as silver, tin, calcium, cobalt, cadmium, antimony, copper, strontium, barium, titanium, or other metallic or non-metallic elements or compounds.

[0105] In some aspects, the lead anode in contact with the iron sulfate-containing anolyte solution can be configured as a monopolar cell stack.

[0106] In various aspects, the lead anode in contact with the iron sulfate-containing anolyte solution can be used in iron electroplating cells such as those described in PCT'732 and Provis'092, Figure 1 A, Figure 1 B, Figure 3 , Figure 4 and other parts thereof.

[0107] In various aspects, the first anode (lead anode) is a high-surface-area lead anode. The high-surface-area lead anode can be microstructured and / or nanostructured. The high-surface-area lead anode or its lead microstructures and / or nanostructures can be electroplated. For example, electroplated high-surface-area lead anodes can include high-current density (e.g., in some aspects greater than about 50 mA / cm 2 ) lead electroplating on a lead protective layer or other substrate, and the removal or reduction of any leveling additives present in the electroplating electrolyte used to electroplate the high-surface-area lead anode. The microstructures and / or nanostructures can be introduced onto the lead surface (such as on a lead protective layer or on an additional lead anode layer) through surface roughening (such as electrochemical cycling) and / or mechanical techniques (such as grooving, sandblasting, laser etching, chemical etching, etc.). In some aspects, the lead anode can be a catalyst-coated membrane (CCM) or include a catalyst-coated membrane (CCM) that includes a lead catalyst layer coated on the membrane surface.

[0108] In several aspects, bipolar stacks can include zero-gap bipolar stacks. For example, in at least some electrochemical cells, a first anode and a first cathode can be in direct contact with a separator having a thickness less than 2 mm, less than 1 mm, less than 0.5 mm, less than 0.3 mm, or less than 0.2 mm.

[0109] In other aspects, contacting a lead anode with an anolyte solution containing iron sulfate can be used in copper electrowinning cells, where oxygen is evolved at the anode and metallic copper is plated at the cathode. Some copper electrowinning cells use a single electrolyte and there is no separator between the anode and the cathode. Thus, in such cases, "anolyte" and "catholyte" are the same solution.

[0110] Aspects that are explicitly contemplated include an electrochemical cell having a lead oxide electrode in contact with an electrolyte having an iron (ferric, ferrous, or total iron) salt at a concentration of at least 0.01 mol / l or at least 0.05 mol / l, such as iron sulfate or iron chloride, and the lead electrode operating as follows:

[0111] (1) As an anode for performing OER;

[0112] (2) As an anode for performing Fe 2+ oxidation to Fe 3+ (e.g., in an acid regenerator); and / or

[0113] (3) As a cathode for performing Fe 3+ reduction to Fe 2+ (e.g., in an acid regenerator).

[0114] Aspects that are explicitly contemplated include operating an electrochemical cell in which an oxygen evolution lead (or lead dioxide) anode is in contact with an anolyte solution containing at least 0.01 mol / l of total dissolved iron, then reversing the polarity of the cell before shutdown, and converting at least a portion of Fe 3+ to Fe 2+ before turning off the power of the cell.

[0115] Aspects that are explicitly contemplated include, in a two-step iron conversion system (such as the systems described in PCT'732 and Provis'092), introducing spent electrolyte (such as spent anolyte and / or spent catholyte) from a metal electroplating cell into the anolyte chamber (first anolyte chamber) of an acid regenerator and operating the acid regenerator (an electrochemical cell according to the embodiments and aspects herein) to generate O2 at the anode.

[0116] Aspects that are clearly contemplated include periodically introducing a solution containing at least 0.01 mol / l of ferrous into the OER anode chamber (first anode chamber) containing solid MnO2 sludge to dissolve the MnO2. For example, preferably, for some applications, the molar ratio of aqueous ferrous ions in the anolyte (first anolyte) to the MnO2 in the anode chamber or the MnO2 exposed to the anolyte (first anolyte) is 1:1 or higher. For example, preferably, for some applications, the molar ratio of aqueous ferrous ions in the anolyte (first anolyte) to the MnO2 in the anode chamber or the MnO2 exposed to the anolyte (first anolyte) is 2:1 or higher. For example, preferably, for some applications, the molar ratio of aqueous ferrous ions in the anolyte (first anolyte) to the MnO2 in the anode chamber or the MnO2 exposed to the anolyte (first anolyte) is 3:1 or higher.

[0117] Aspects that are clearly contemplated include producing ferrous in the OER anode chamber (first anode chamber) containing a certain amount of solid MnO2 sludge by electrochemically reducing a certain amount of dissolved ferric iron.

[0118] Stable lead anode in acid regeneration

[0119] Figure 5 is a schematic diagram showing an exemplary system 500 having an electrochemical cell 580 in accordance with aspects herein. The cell 580 can be substantially similar to the "acid regeneration" cell described in PCT'732 and further detailed hereinbelow. The cathode of the cell 580 electrochemically reduces Fe 3+ ions to Fe 2+ ions in the catholyte. The anode of the cell 580 electrochemically oxidizes water to oxygen, also known as the oxygen evolution reaction (OER). According to some aspects, a proton exchange membrane (PEM) separates the catholyte compartment and the anolyte compartment.

[0120] The catholyte is shown fluidly connected to the catholyte recycle tank 570 and can contain an acidic aqueous solution containing a mixture of dissolved ferric (Fe 3+ ) and ferrous (Fe 2+ ) ions. In various embodiments and aspects, the ferric and ferrous ions can be provided to the catholyte as an aqueous solution or as a soluble solid that contacts the catholyte to dissolve the iron-containing material into the solution, as described in multiple examples in PCT'732 and herein.

[0121] The anolyte (anode electrolyte) is shown fluidly connected to the anolyte recycle tank 560. In some aspects, the anolyte can be an acidic aqueous solution having an iron cation concentration within the ranges described herein.

[0122] In multiple aspects, the electrolyte can be recycled between the respective half-cells and storage tanks. In some aspects, reactants (such as dissolved or soluble iron and water) can be added to the electrolyte stream through the tank or directly into the respective half-cell compartments.

[0123] In some cases, iron cations (ferric or ferrous) from the anolyte can pass through or remain in the diaphragm separating the anolyte from the catholyte, reducing the availability of the iron cations for the lead anode stabilizing function as described herein. Thus, the iron concentration in the anolyte may drop too low to provide the stabilizing function described herein. In multiple embodiments and aspects, additional iron can be "injected" into the anolyte periodically or continuously by one or more mechanisms to replenish the iron cations lost from the anolyte.

[0124] Optionally, iron cations can be injected into the anolyte to supplement, maintain, or establish a target concentration or a PbO2 - electrode stabilizing concentration of iron cations, or in terms of iron (ferric and / or ferrous) sulfate. Inputs 501, 502, and 503 and the solid iron source 505 represent optional sources or methods for injecting iron cations into the catholyte. For example, optionally, in some aspects, an aqueous injection solution and / or one or more solid iron-containing materials can be provided through input 503. For example, optionally, in some aspects, the anolyte from an iron electroplating cell can be provided through input 501 to inject into the anolyte. For example, optionally, in some aspects, the catholyte from an iron electroplating cell can be provided through input 502 to inject into the anolyte. For example, optionally, in some aspects, the anolyte can be injected by providing the solid iron source 505, which can dissolve into the anolyte quickly or slowly depending on the application.

[0125] System 500 optionally includes a tap 510 for providing liquid and / or solid to the anolyte and / or for extracting the anolyte. Optionally, for example, inputs 501, 502, and 503 can be provided to / through the tap 510 instead of directly into the tank 560. System 5 includes an "iron extraction" mechanism. Optionally, the iron extraction mechanism can include extracting a ferrous-containing solution and providing the ferrous-containing solution to an iron electroplating cell to extract metallic iron. Optionally, the iron extraction mechanism can include extracting a ferrous-containing solution and precipitating an iron-containing material, such as an iron salt, from the extracted solution, thereby extracting iron from system 500.

[0126] In some embodiments and aspects, iron can be extracted as a solid from the catholyte. In some aspects, iron can be extracted from the catholyte by precipitating or crystallizing iron salts, iron oxides, or iron hydroxides from the solution. Alternatively, iron in the ferrous-rich catholyte can be introduced into an electroplating cell where iron can be electroplated out of the solution.

[0127] Single-step iron conversion using a lead anode

[0128] Figure 6 is a schematic diagram showing an exemplary system 600 for electroplating metallic iron from an aqueous solution containing dissolved iron. According to aspects herein, system 600 includes an electrochemical cell 680. The cathode 634 of cell 680 undergoes an iron electroplating reaction, or electrochemically reduces aqueous Fe 2+ ions and / or Fe 3+ to metallic iron (Fe 0 ). The cathode 634 can be made of any conductive material suitable for use as a substrate or support onto which metallic iron is electroplated.

[0129] In some aspects, any Fe 3+ “ferric” ions present in the catholyte solution can be advantageously reduced to Fe 2+ “ferrous” oxidation state prior to electroplating. In some aspects, an acid regeneration cell (such as the acid regeneration cell described above with reference to Figure 5 ) can be used to reduce ferric ions to ferrous ions. In other aspects or aspects, aqueous ferric ions can be reduced to aqueous ferrous ions by contacting the solution with a reducing gas such as hydrogen sulfide or sulfur dioxide. In other aspects, ferric ions can be reduced to ferrous ions by contacting the solution with metallic iron.

[0130] The anode 636 of cell 680 undergoes electrochemical oxidation of water to produce oxygen and acid in the anolyte (anode electrolyte). The anode 363 can be a lead dioxide anode for catalyzing the oxygen evolution reaction (OER). The anolyte can be an acidic aqueous solution containing dissolved iron cations, the concentration of which is as described herein and is suitable for stabilizing the lead dioxide electrode. The anolyte is shown as being connected in series to the anolyte tank 660, and the catholyte is shown as being connected in series to the catholyte tank 670.

[0131] In multiple aspects, the acid generated in the anolyte can be removed or consumed, such as in a dissolution reaction for converting an iron-containing feed material into an aqueous solution containing iron.

[0132] According to some aspects, an anion exchange membrane (AEM) can separate the catholyte and the anolyte. Some anion exchange membranes may tend to "leak" cations (such as aqueous iron cations) from the anolyte into the catholyte, resulting in a decrease in the iron concentration in the anolyte over time. Thus, the iron concentration in the anolyte may drop too low to provide the stable functionality described herein. In various embodiments and aspects, additional iron can be "injected" into the anolyte periodically or continuously by one or more mechanisms to replenish the iron ions lost from the anolyte.

[0133] Optionally, iron cations can be injected into the anolyte to supplement, maintain, or establish a target concentration or a PbO2 - electrode stable concentration of iron cations, or in terms of iron (ferric and / or ferrous) sulfate. Input 604 and solid iron source 605 represent optional sources or methods for injecting iron cations into the catholyte. For example, optionally, in some aspects, an aqueous injection solution and / or one or more solid iron-containing materials can be provided through input 604. For example, optionally, in some aspects, the anolyte can be injected by providing solid iron source 605, which can dissolve into the anolyte quickly or slowly depending on the application. System 500 optionally includes a stopcock 610 for providing liquid and / or solid to the anolyte and / or for extracting the anolyte. Optionally, for example, input 604 can be provided to / through stopcock 610 rather than directly into tank 660. Stopcock 612 is optional and can similarly be used for providing liquid and / or solid to the catholyte and / or for extracting the catholyte.

[0134] Two - step iron conversion using a lead anode

[0135] Reference Figures 7 - 11 , in some aspects, the iron conversion systems 700, 800, 900, 1000, or 1100 can be divided into two main subsystems: a dissolution subsystem 102 and a plating subsystem 130. The dissolution subsystem 102 can generally be configured to efficiently and relatively quickly dissolve the iron feed material 152 at a low temperature to form a dissolved iron solution 122. The dissolution subsystem 102 can be further configured to convert ferric ions (Fe 3+ ) in the dissolved iron solution 122 into ferrous ions (Fe 2+)。The plating subsystem 130 can generally be configured to electroplate dissolved ferrous iron into a solid form, which can be removed at 148 and sold as relatively pure iron while preparing the plating subsystem 130 for further plating. Once the plating cell 132 has sufficiently consumed the ferrous iron in the dissolved iron solution 122, it can be returned to the dissolution subsystem 102 for subsequent dissolution in combination with the acid regeneration cell 104.

[0136] As shown, the acid regeneration cell 104 can be configured to reduce ferric iron ions (generated during the dissolution of the feedstock 120) to ferrous iron ions in the cathode chamber 106 (first cathode chamber), while oxidizing a consumable reactant provided by the reactant source 116 at the anode 112 (first anode). In some aspects, the anode reactant can be water, and the anode 112 (first anode) can evolve oxygen 111 from the anode chamber 110 (first anode chamber). In some aspects, water 154 is added to the anode chamber 110 to replenish the water consumed by the OER.

[0137] In various aspects, one or more processing steps 124, 126, 128, 127 can be performed to condition the dissolved iron solution 122 to remove substances or increase or decrease the concentration of one or more components in the solution. For example, the processing step 124 can include withdrawing the dissolved iron solution 122 from the dissolution tank 118 through a processing vessel configured to remove solid particles and / or colloidal dispersions of materials released during dissolution. In some cases, silica in the iron feedstock may enter the dissolved iron solution 122 as a gel-like mass of colloidal dispersion, which may interfere with the operation within the acid regeneration cell 104. The processing step 124 can include contacting the solution with a flocculant (such as polyethylene glycol, polyethylene oxide, or other known flocculants effective in removing colloidal silica from the solution). The processing step 124 can also include, as needed, any other solid-liquid separation techniques, devices, or additives to remove substances that may be detrimental to the operation within the acid regeneration cell 104.

[0138] The plating subsystem 130 can include a plating cell 132 having a cathode electrode 136 (second cathode) located in a cathode chamber 134 (second cathode chamber), which is fluidly coupled to a cathode electrolyte tank 142 (second cathode electrolyte tank); and an anode electrode 140 (second anode) located in an anode chamber 138 (second anode chamber), which is fluidly coupled to an anode electrolyte tank 144 (second anode electrolyte tank). Ferrous iron ions can be reduced to plated metallic iron in the cathode chamber 134 (second cathode chamber) of the plating cell 132. An oxidation reaction, such as OER or the conversion of ferrous iron ions to ferric iron ions, occurs in the anode chamber 138 (second anode chamber) of the plating cell 132.

[0139] In some aspects, the plating reaction is for Fe 2+ to Fe 3+The oxidation reaction proceeds, for example, as Figure 7 and Figure 9 systems 700 and 900 shown respectively. In these aspects, for example, in system 700 or 900, the dissolved iron solution 122 can be divided into a plating anolyte and a plating catholyte. The plating anolyte can be recycled between the plating anolyte tank 144 and the anode chamber 138 of the plating cell 132, where substances in the plating anolyte will be oxidized at the anode electrode 140. The plating catholyte can be recycled between the plating catholyte tank 142 and the cathode chamber 134 of the plating cell 132, where iron will be electroplated onto the cathode electrode 108. Iron can be removed from the plating cell 132 at 148 by a variety of methods, examples of which are described below. In some cases, hydrogen gas can be evolved 146 from the plating cell cathode chamber 134. This hydrogen gas can be captured and stored for use in other sub-processes described herein.

[0140] In some aspects, the plating reaction is carried out for the oxygen evolution reaction (OER), for example, as Figure 8 and Figure 10 systems 800 and 1000 shown respectively.

[0141] In some aspects, the anolyte (first anolyte) of the acid regeneration cell of the dissolution subsystem includes a certain concentration of aqueous iron cations. In some aspects, the electrochemical oxidation reaction carried out in the anolyte (second anolyte) of the plating cell of the plating subsystem is the oxygen evolution reaction, as Figure 8 (system 800) and Figure 10(System 1000), wherein the second anolyte includes a certain concentration of aqueous iron cations. In some aspects, the aqueous iron cations can be consumed from the first anolyte over time by one or more processes, including but not limited to: the aqueous iron cations leaking through the membrane into the corresponding catholyte; the aqueous iron cations being retained in or at the components of the battery by chemical and / or physical mechanisms, such as in the membrane or in the pores of the porous lead electrode, so that optionally when the porous electrode or the anode chamber is rinsed or washed, the aqueous iron cations are lost; side reactions or parasitic reactions; or others. Thus, in some aspects, the concentration of aqueous iron cations in the first anolyte, the second anolyte (e.g., in systems 800 and 1000, for example), or both the first anolyte and the second anolyte (e.g., in systems 800 and 1000, for example) can be maintained within a stable concentration range during one or more transient operations of the acid regeneration battery, where operation means the battery is operating at a working voltage such that the expected electrochemical reduction occurs at the cathode and the expected electrochemical oxidation occurs at the anode, such as OER. Generally, in some aspects of this disclosure, a battery at open circuit voltage is not in an operating state. In some aspects, the concentration of aqueous iron cations in the first anolyte, the second anolyte (e.g., in systems 800 and 1000, for example), or both the first anolyte and the second anolyte (e.g., in systems 800 and 1000, for example) can be maintained within a stable concentration range throughout or at least most of the operation of the acid regeneration battery.

[0142] Establishing and / or maintaining the concentration of aqueous iron cations in the first anolyte and / or the second anolyte within a stable concentration range can include injecting a liquid iron source and / or a solid iron source into the first anolyte and / or the second anolyte. The injection can be carried out continuously and / or by one or more discrete events. The injection can be carried out directly, for example, by directly providing a liquid iron source and / or a solid iron source to the anode chamber or its anolyte; and / or indirectly, for example, by providing a liquid iron source and / or a solid iron source to a circulation tank that is fluidly connected to the anode chamber or its anolyte. In some aspects, the liquid iron source is an aqueous solution including aqueous iron cations (also referred to herein as the injection solution). As described throughout this disclosure, the injection solution can include waste or used electrolyte from different batteries and / or leachate from metal and / or ore processing systems, an aqueous solution formed by dissolving one or more iron-containing materials therein, such as by dissolving an iron salt or an iron oxide in the solution and / or flowing the solution through an iron-containing substrate, or any combination thereof.

[0143] Optionally, the first anolyte can be directly and / or indirectly injected into the aqueous injection solution and / or the solid iron source through inputs 703, 803, 903, 1003, or 1103. Optionally, for aspects of performing OER in the second anolyte, the second anolyte can be directly and / or indirectly injected into the aqueous injection solution and / or the solid iron source through input 804 or 1004. For example, optionally, a solid iron-containing material such as an iron salt or an iron oxide can be provided through inputs 703, 803, 903, 1003, 804, or 1004. For example, optionally, an aqueous injection solution can be provided through inputs 703, 803, 903, 1003, 804, or 1004. In some aspects, direct injection is equivalent to directly providing a liquid iron source and / or a solid iron source into the anode chamber or its anolyte. In some aspects, indirect injection is equivalent to providing a liquid and / or solid iron source into a circulation tank that is fluidly connected to the anode chamber or its anolyte.

[0144] Optionally, the first anolyte can be injected by including a solid iron source 705, 805, 905, or 1005 in contact with the first anolyte. Optionally, the conditions of the first anolyte (such as but not limited to temperature) and the conditions of the solid iron source 705, 805, 905, 1005, or 1105 (such as but not limited to its composition) are selected or controlled such that the solid iron source dissolves slowly or at a selected rate during battery operation to maintain a stable concentration of aqueous iron cations. The solid iron source 705, 805, 905, or 1005 can be disposed in the first anode chamber, or in a circulation tank that is fluidly connected to the first anode chamber or its first anolyte, or both.

[0145] Optionally, for the case where OER is performed in the second anolyte, the second anolyte can be injected by including a solid iron source 805 or 1005 in contact with the second anolyte. Optionally, the conditions of the second anolyte (such as but not limited to temperature) and the conditions of the solid iron source 805 or 1005 (such as but not limited to its composition) are selected or controlled such that the solid iron source dissolves slowly or at a selected rate during battery operation to maintain a stable concentration of aqueous iron cations. The solid iron source 805 or 1005 can be disposed in the second anode chamber, or in a circulation tank 810 or 1010 that is fluidly connected to the second anode chamber or its first anolyte, or both.

[0146] Optionally, in the case where the iron reduction / iron plating reaction is carried out for the iron cation oxidation (Fe 2+ to Fe 3+ ) reaction, an aqueous injection solution containing the used or waste anolyte (second anolyte) of the plating cell can be injected into the first anolyte, such as Figure 7 and Figure 9as shown, for example, by input 701 or 901.

[0147] Optionally, an aqueous solution containing an anion solution (second anion solution) that has been used or is used in the electroplating cell (second anion solution) can be injected into the first anolyte, such as Figures 7 - 10 as shown, for example, by input 702, 802, 902, 1002, or 1102.

[0148] Optionally, in some aspects, metallic iron can be provided to the first catholyte or the first catholyte can be exposed to metallic iron to consume protons (acids) leaking from the first anolyte through the AEM. Optionally, in some aspects, metallic iron can be provided to the second catholyte or the second catholyte can be exposed to metallic iron to consume protons (acids) leaking from the second anolyte through the separator.

[0149] Multiple other aspects:

[0150] Multiple aspects are contemplated herein, several of which are set forth in the following paragraphs. It is expressly contemplated that any aspect or portion thereof can be combined to form an aspect. Additionally, it is expressly contemplated that any reference to aspect 1 includes a reference to aspects 1a, 1b, and / or 1c, any reference to aspect 5 includes a reference to aspects 5a and 5b, and so on (i.e., any reference to an aspect includes a reference to the lettered versions of that aspect). Further, the terms "any of the foregoing aspects" and "any one of the foregoing aspects" mean any aspect that appears before the aspect containing the phrase (in other words, the sentence "Aspect 32: A method or system of any of the foregoing aspects..." means a reference to any aspect before aspect 32, including aspects 1a through 31). For example, it is contemplated that, optionally, any system or method of any of the following aspects can be used or combined with any other aspect provided below. Additionally, for example, it is contemplated that any of the foregoing aspects can optionally be combined with any of the aspects listed below.

[0151] Aspect 1a: A method of stabilizing a lead anode, the method comprising:

[0152] operating an electrochemical cell, including performing electrochemical reduction at a first cathode and electrochemical oxidation at a first anode;

[0153] wherein:

[0154] the electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode,

[0155] and a first separator separating the first anolyte from the first catholyte; the first anode is a lead electrode;

[0156] The first anolyte and the first catholyte each independently comprise an aqueous iron cation and an aqueous anion; and

[0157] The first anolyte comprises the aqueous iron cation at a concentration of at least about 0.01 M or in a range selected from: about 0.01 M (optionally about 0.02 M, optionally about 0.03 M, optionally about 0.04 M, optionally about 0.05 M, optionally about 0.06 M, optionally about 0.07 M, optionally about 0.08 M, optionally about 0.09 M, optionally about 0.095 M, optionally about 0.099 M, optionally about 0.1 M) to 0.5 M (optionally about 0.49 M, optionally about 0.48 M, optionally about 0.47 M, optionally about 0.46 M, optionally about 0.45 M, optionally about 0.44 M, optionally about 0.43 M, optionally about 0.42 M, optionally about 0.41 M, optionally about 0.40 M, optionally about 0.39 M, optionally about 0.38 M), e.g., a concentration optionally selected from the range of about 0.01 M to about 0.45 M, optionally a concentration selected from the range of about 0.01 M to about 0.4 M, optionally a concentration selected from the range of about 0.01 M to about 0.44 M, optionally a concentration selected from the range of about 0.01 M to about 0.445 M, optionally a concentration selected from the range of about 0.01 M to about 0.440 M, optionally a concentration selected from the range of about 0.02 M to about 0.08 M.

[0158] Aspect 1b: A system for stabilizing a lead anode, the system comprising:

[0159] An electrochemical cell, comprising:

[0160] A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte;

[0161] Wherein:

[0162] The first anode is a lead electrode;

[0163] The first anolyte and the first catholyte each independently comprise an aqueous iron cation and an aqueous anion; and

[0164] The first anolyte includes the aqueous iron cations at a concentration of at least about 0.01 M or in a range selected from: about 0.01 M (optionally about 0.02 M, optionally about 0.03 M, optionally about 0.04 M, optionally about 0.05 M, optionally about 0.06 M, optionally about 0.07 M, optionally about 0.08 M, optionally about 0.09 M, optionally about 0.095 M, optionally about 0.099 M, optionally about 0.1 M) to about 0.5 M (optionally about 0.49 M, optionally about 0.48 M, optionally about 0.47 M, optionally about 0.46 M, optionally about 0.45 M, optionally about 0.44 M, optionally about 0.43 M, optionally about 0.42 M, optionally about 0.41 M, optionally about 0.40 M, optionally about 0.39 M, optionally about 0.38 M), e.g., a concentration optionally selected from the range of about 0.01 M to about 0.45 M, optionally a concentration selected from the range of about 0.01 M to about 0.4 M, optionally a concentration selected from the range of about 0.01 M to about 0.44 M, optionally a concentration selected from the range of about 0.01 M to about 0.445 M, optionally a concentration selected from the range of about 0.01 M to about 0.440 M, optionally a concentration selected from the range of about 0.02 M to about 0.08 M.

[0165] Aspect 1c: A method of stabilizing a lead anode, the method comprising:

[0166] Operating an electrochemical cell, including performing electrochemical reduction at a first cathode and electrochemical oxidation at a first anode; and

[0167] Recycling a second electrolyte from a metal electroplating cell into the first anolyte, the second electrolyte having aqueous iron cations;

[0168] Wherein:

[0169] The electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte;

[0170] The first anode is a lead electrode;

[0171] The first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; and

[0172] The first anolyte comprises the aqueous iron cations at a concentration of at least about 0.01 M or in a range selected from: about 0.01 M (optionally about 0.02 M, optionally about 0.03 M, optionally about 0.04 M, optionally about 0.05 M, optionally about 0.06 M, optionally about 0.07 M, optionally about 0.08 M, optionally about 0.09 M, optionally about 0.095 M, optionally about 0.099 M, optionally about 0.1 M) to about 0.5 M (optionally about 0.49 M, optionally about 0.48 M, optionally about 0.47 M, optionally about 0.46 M, optionally about 0.45 M, optionally about 0.44 M, optionally about 0.43 M, optionally about 0.42 M, optionally about 0.41 M, optionally about 0.40 M, optionally about 0.39 M, optionally about 0.38 M), e.g., a concentration optionally selected from the range of about 0.01 M to about 0.45 M, optionally a concentration selected from the range of about 0.01 M to about 0.4 M, optionally a concentration selected from the range of about 0.01 M to about 0.44 M, optionally a concentration selected from the range of about 0.01 M to about 0.445 M, optionally a concentration selected from the range of about 0.01 M to about 0.440 M, optionally a concentration selected from the range of about 0.02 M to about 0.08 M.

[0173] Aspect 1d: A system for stabilizing a lead anode, the system comprising:

[0174] An electrochemical cell, comprising:

[0175] A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte; and

[0176] A metal electroplating cell; and

[0177] An electrolyte recirculation subsystem for recirculating the electrolyte in the metal electroplating cell into the first anolyte;

[0178] Wherein:

[0179] The first anode is a lead electrode;

[0180] The first anolyte and the first catholyte each independently comprise aqueous iron cations and aqueous anions; and

[0181] The first anolyte comprises the aqueous iron cations at a concentration of at least about 0.01 M or in a range selected from: about 0.01 M (optionally about 0.02 M, optionally about 0.03 M, optionally about 0.02 M, optionally about 0.03 M, optionally about 0.04 M, optionally about 0.05 M, optionally about 0.06 M, optionally about 0.07 M, optionally about 0.08 M, optionally about 0.09

[0182] M, optionally about 0.095 M, optionally about 0.099 M, optionally about 0.1 M) to about 0.5

[0183] M (optionally about 0.49 M, optionally about 0.48 M, optionally about 0.47 M, optionally about 0.46 M, optionally about 0.45 M, optionally about 0.44 M, optionally about 0.43 M, optionally about 0.42 M, optionally about 0.41 M, optionally about 0.40 M, optionally about 0.39 M, optionally about 0.38 M), e.g., a concentration optionally selected from the range of about 0.01 M to about 0.45 M, optionally a concentration selected from the range of about 0.01 M to about 0.4 M, optionally a concentration selected from the range of about 0.01 M to about 0.44 M, optionally a concentration selected from the range of about 0.01 M to about 0.445 M, optionally a concentration selected from the range of about 0.01 M to about 0.440 M, optionally a concentration selected from the range of about 0.02 M to about 0.08 M.

[0184] Aspect 1e: The method or system according to aspect 1, such as the method or system according to any one of aspects 1a - 1d, wherein the concentration of the aqueous iron cations in the first anolyte is selected from the range of about 0.01 M to about 0.1 M, and any value and range therebetween are expressly contemplated and disclosed herein, e.g., optionally about 0.02 M to about 0.09 M, or optionally about 0.03 M to about 0.08 M, or optionally about 0.04 M to about 0.07 M, or optionally about 0.03 M to about 0.08 M, or optionally about 0.05 M.

[0185] Aspect 2a: The method or system according to aspect 1, wherein the second electrolyte comprises a catholyte and / or anolyte from an iron electroplating cell, and wherein the second electrolyte comprises aqueous iron ions. Aspect 2b: The method or system according to aspect 1 or 2a, wherein the second electrolyte comprises spent catholyte and / or spent anolyte from an iron electroplating cell.

[0186] Aspect 3: The method or system according to any one of the preceding aspects, wherein performing the electrochemical oxidation comprises an oxygen evolution reaction (OER) at the first anode.

[0187] Aspect 4: The method or system according to any one of the preceding aspects, wherein the first anolyte comprises aqueous sulfate anions.

[0188] Aspect 5a: A method of stabilizing a lead anode, the method comprising:

[0189] Operating an electrochemical cell, including performing electrochemical reduction at a first cathode and an oxygen evolution reaction (OER) at a first anode;

[0190] Wherein:

[0191] The electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte;

[0192] The first anode is a lead electrode;

[0193] The first anolyte and the first catholyte each independently comprise aqueous iron cations and aqueous anions; and

[0194] The first anolyte comprises aqueous iron sulfate at a concentration of at least about 0.01 M or in a range selected from: about 0.01 M (optionally about 0.02 M, optionally about 0.03 M, optionally about 0.04 M, optionally about 0.05 M, optionally about 0.06 M, optionally about 0.07 M, optionally about 0.08 M, optionally about 0.09 M, optionally about 0.095 M, optionally about 0.099

[0195] M, optionally about 0.1 M) to about 0.5 M (optionally about 0.49 M, optionally about 0.48 M, optionally about 0.47 M, optionally about 0.46 M, optionally about 0.45 M, optionally about 0.44

[0196] M, optionally about 0.43 M, optionally about 0.42 M, optionally about 0.41 M, optionally about 0.40 M, optionally about 0.39 M, optionally about 0.38 M), e.g., optionally selected from a concentration in the range of about

[0197] 0.01 M to about 0.45 M, optionally selected from a concentration in the range of about 0.01 M to about 0.4 M, optionally selected from a concentration in the range of about 0.01 M to about 0.44 M, optionally selected from a concentration in the range of about 0.01 M to about 0.445 M, optionally selected from a concentration in the range of about 0.01 M to about 0.440 M, optionally selected from a concentration in the range of about 0.02 M to about 0.08 M.

[0198] Aspect 5b: A system for stabilizing a lead anode, the system comprising:

[0199] An electrochemical cell comprising:

[0200] A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte;

[0201] Wherein:

[0202] An oxygen evolution reaction (OER) occurs at the first anode;

[0203] The first anode is a lead electrode;

[0204] The first anolyte and the first catholyte each independently comprise aqueous iron cations and aqueous anions; and

[0205] The first anolyte comprises aqueous iron sulfate at a concentration of at least about 0.01 M or in a range selected from: about 0.01 M (optionally about 0.02 M, optionally about 0.03 M, optionally about 0.04 M, optionally about 0.05 M, optionally about 0.06 M, optionally about 0.07 M, optionally about 0.08 M, optionally about 0.09 M, optionally about 0.095 M, optionally about 0.099

[0206] M, optionally about 0.1 M) to about 0.5 M (optionally about 0.49 M, optionally about 0.48 M, optionally about 0.47 M, optionally about 0.46 M, optionally about 0.45 M, optionally about 0.44

[0207] M, optionally about 0.43 M, optionally about 0.42 M, optionally about 0.41 M, optionally about 0.40 M, optionally about 0.39 M, optionally about 0.38 M), for example, optionally selected from a concentration in the range of about

[0208] 0.01 M to about 0.45 M, optionally selected from a concentration in the range of about 0.01 M to about 0.4 M, optionally selected from a concentration in the range of about 0.01 M to about 0.44 M, optionally selected from a concentration in the range of about 0.01 M to about 0.445 M, optionally selected from a concentration in the range of about 0.01 M to about 0.440 M, optionally selected from a concentration in the range of about 0.02 M to about 0.08 M.

[0209] Aspect 6a: The method or system according to any one of the preceding aspects, wherein the concentration of aqueous iron cations in the first positive electrolyte is at least about 0.05 M or in a range selected from about 0.05 M to about 0.5 M.

[0210] Aspect 7a: The method or system according to any one of the foregoing aspects, wherein the concentration of aqueous iron cations in the first anolyte is less than the concentration of aqueous iron cations in the first catholyte. Aspect 7b: The method or system according to any one of the foregoing aspects, wherein the concentration of aqueous iron cations in the first anolyte is equal to, greater than, or less than the concentration of aqueous iron cations in the first catholyte. Aspect 7c: The method or system according to any one of the foregoing aspects, wherein the concentration of aqueous iron cations in the first anolyte is greater than the concentration of aqueous iron cations in the first catholyte. Aspect 7d: The method or system according to any one of the foregoing aspects, wherein the concentration of aqueous iron cations in the first anolyte is equal to the concentration of aqueous iron cations in the first catholyte.

[0211] Aspect 8a: The method or system according to any one of the foregoing aspects, wherein the steady-state concentration of aqueous iron cations in the first anolyte is at least about 0.01 M or is a concentration selected from the range of about 0.01 M (optionally about 0.02 M, optionally about 0.03 M, optionally about 0.04 M, optionally about 0.05 M, optionally about 0.06 M, optionally about 0.07 M, optionally about 0.08 M, optionally about 0.09 M, optionally about 0.095 M, optionally about 0.099 M, optionally about 0.1 M) to about 0.5 M (optionally about 0.49 M, optionally about 0.48 M, optionally about 0.47 M, optionally about 0.46 M, optionally about 0.45 M, optionally about 0.44 M, optionally about 0.43 M, optionally about 0.42 M, optionally about 0.41 M, optionally about 0.40 M, optionally about 0.39 M, optionally about 0.38 M), for example, optionally a concentration selected from the range of about 0.01 M to about 0.45 M, optionally a concentration selected from the range of about 0.01 M to about 0.4 M, optionally a concentration selected from the range of about 0.01 M to about 0.44 M, optionally a concentration selected from the range of about 0.01 M to about 0.445 M, optionally a concentration selected from the range of about 0.01 M to about 0.440 M, optionally a concentration selected from the range of about 0.02 M to about 0.08 M.Aspect b8: The method or system according to any one of the foregoing aspects, wherein the steady-state concentration of aqueous iron cations in the first anolyte is at least about 0.01 M [or a concentration selected from the range: about 0.01 M (optionally about 0.02 M, optionally about 0.03 M, optionally about 0.04 M, optionally about 0.05 M, optionally about 0.06 M, optionally about 0.07 M, optionally about 0.08 M, optionally about 0.09 M, optionally about 0.095 M, optionally about 0.099 M, optionally about 0.1 M) to about 0.5 M (optionally about 0.49 M, optionally about 0.48 M, optionally about 0.47 M, optionally about 0.46 M, optionally about 0.45 M, optionally about 0.44 M, optionally about 0.43 M, optionally about 0.42 M, optionally about 0.41 M, optionally about 0.40 M, optionally about 0.39 M, optionally about 0.38 M), e.g., optionally a concentration selected from the range of about 0.01 M to about 0.5 M, or optionally a concentration selected from the range of about 0.01 M to about 0.45 M, or optionally a concentration selected from the range of about 0.01 M to about 0.4 M], and the steady-state concentration of aqueous sulfate anions in the first anolyte is at least about 0.01 M [or a concentration in the following range: about 0.01 M (optionally about 0.02 M, optionally about 0.03 M, optionally about 0.04 M, optionally about 0.05 M, optionally about 0.06 M, optionally about 0.07 M, optionally about 0.08 M, optionally about 0.09 M, optionally about 0.095 M, optionally about 0.099 M, optionally about 0.1 M) to 0.5 M (optionally about 0.49 M, optionally about 0.48 M, optionally about 0.47 M, optionally about 0.46 M, optionally about 0.45 M, optionally about 0.44 M, optionally about 0.43 M, optionally about 0.42 M, optionally about 0.41 M, optionally about 0.40 M, optionally about 0.39 M, optionally about 0.38 M), e.g., optionally a concentration selected from the range of about 0.01 M to about 0.5 M, or optionally a concentration selected from the range of about 0.01 M to about 0.45 M, or optionally a concentration selected from the range of about 0.01 M to about 0.445 M, or optionally a concentration selected from the range of about 0.01 M to about 0.44 M, or optionally a concentration selected from the range of about 0.01 M to about 0.4 M].

[0212] Aspect 9a: The method or system according to any one of the preceding aspects, wherein the steady-state concentration of aqueous iron cations in the first anolyte is at least about 0.05 M or selected from the range of about 0.05 M to 0.5 M. Aspect 9b: The method or system according to any one of the preceding aspects, wherein the steady-state concentration of aqueous iron cations in the first anolyte is at least about 0.05 M or selected from the range of about 0.05 M to 0.5 M, and the steady-state concentration of aqueous sulfate anions in the first anolyte is at least about 0.05 M or selected from the range of about 0.05 M to 0.5 M.

[0213] Aspect 10a: The method or system according to any one of the preceding aspects, wherein the steady-state concentration of aqueous iron cations in the first anolyte is less than the steady-state concentration of aqueous iron cations in the first catholyte. Aspect 10b: The method or system according to any one of the preceding aspects, wherein the steady-state concentration of aqueous iron cations in the first anolyte is greater than, equal to, or lower than the steady-state concentration of aqueous iron cations in the first catholyte. Aspect 10c: The method or system according to any one of the preceding aspects, wherein the steady-state concentration of aqueous iron cations in the first anolyte is greater than the steady-state concentration of aqueous iron cations in the first catholyte. Aspect 10d: The method or system according to any one of the preceding aspects, wherein the steady-state concentration of aqueous iron cations in the first anolyte is equal to the steady-state concentration of aqueous iron cations in the first catholyte.

[0214] Aspect 11: The method or system according to any one of the preceding aspects, wherein the aqueous iron cations in the first anolyte include aqueous ferric ions.

[0215] Aspect 12a: A method comprising:

[0216] Operating an electrochemical cell, including performing electrochemical reduction at a first cathode and electrochemical oxidation at a first anode;

[0217] Wherein:

[0218] The electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte;

[0219] The first anode is a lead electrode; and

[0220] The first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; and

[0221] Wherein the method further comprises:

[0222] In the presence of aqueous ferrous ions, the solid manganese oxide is dissolved in the first positive electrolyte solution.

[0223] Aspect 12b: A system comprising:

[0224] An electrochemical cell, comprising:

[0225] A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte;

[0226] Wherein:

[0227] The first anode is a lead electrode;

[0228] The first anolyte and the first catholyte each independently comprise aqueous iron cations and aqueous anions; and

[0229] The first anolyte comprises aqueous ferrous ions that promote the dissolution of the solid manganese oxide present in the first anode chamber in the first anolyte.

[0230] Aspect 13: The method or system according to aspect 12, wherein the dissolving step comprises converting the solid manganese oxide into one or more aqueous manganese salts in the presence of aqueous ferrous ions.

[0231] Aspect 14: The method or system according to aspect 13, wherein the converting step comprises (i) reacting the solid manganese oxide with the aqueous ferrous ions, and / or (ii) electrochemically reducing the solid manganese oxide to one or more aqueous manganese salts in the presence of the aqueous ferrous ions.

[0232] Aspect 15: The method or system according to aspect 13 or 14, wherein during at least a portion of the dissolving step (optionally at the start of the dissolving step, optionally throughout the dissolving step), the ratio of the number of moles of aqueous ferrous ions in the first anolyte to the number of moles of solid manganese oxide in the first anode chamber is at least 0.9 (optionally at least 0.95, optionally at least 0.99, optionally at least 1, optionally at least 1.2, optionally at least 1.5, optionally at least 1.7, optionally at least 2, optionally at least 2.2, optionally at least 2.5, optionally at least 2.7, optionally at least 3).

[0233] Aspect 16: The method or system according to aspect 15, wherein during at least a portion of the dissolving step, the ratio of the number of moles of ferrous ions in the first anolyte to the number of moles of solid manganese oxide in the first anode chamber is at least 2.

[0234] Aspect 17a: The method according to any one of claims 12 - 16, wherein during at least a part of the dissolution step (optionally at the start of the dissolution step, optionally during the entire dissolution step), the first anolyte comprises at least 5 mM of aqueous ferrous ions. Aspect 17b: The method according to any one of claims 12 - 16, wherein during at least a part of the dissolution step (optionally at the start of the dissolution step, optionally during the entire dissolution step), the first anolyte comprises at least 5 mM of aqueous iron cations. Aspect 17c: The method according to any one of claims 12 - 16, wherein during at least a part of the dissolution step (optionally at the start of the dissolution step, optionally during the entire dissolution step), the first anolyte comprises at least 10 mM of aqueous ferrous ions. Aspect 17d: The method according to any one of claims 12 - 16, wherein during at least a part of the dissolution step (optionally at the start of the dissolution step, optionally during the entire dissolution step), the first anolyte comprises at least 10 mM of aqueous iron cations.

[0235] Aspect 18: The method or system according to aspects 12 - 17, comprising the step of providing aqueous ferrous ions to the first anolyte before and / or during the dissolution step.

[0236] Aspect 19a: The method or system according to aspect 18, wherein the providing step comprises flushing the first anolyte chamber with a solution comprising aqueous ferrous ions. Aspect 19b: The method or system according to aspect 18, wherein the providing step comprises adding a solution comprising aqueous ferrous ions to the first anolyte chamber.

[0237] Aspect 20: The method or system according to aspect 18 or 19, wherein the providing step comprises directly or indirectly recycling a ferrous-containing electrolyte from an electroplating cell to the first anolyte.

[0238] Aspect 21: The method or system according to aspects 18 - 20, wherein the providing step comprises electrochemically generating aqueous ferrous ions in the first anolyte.

[0239] Aspect 22: The method or system according to aspects 12 - 21, wherein the first anolyte comprises aqueous Mn ions.

[0240] Aspect 23a: A method, comprising:

[0241] Operating an electrochemical cell, comprising electrochemical reduction at a first cathode and electrochemical oxidation at a first anode;

[0242] Wherein:

[0243] The electrochemical cell includes a first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte;

[0244] The first anode is a lead electrode; and

[0245] The first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; and

[0246] Wherein the method further includes:

[0247] Reverse biasing the first anode for a time, including electrochemically reducing aqueous ferric ions to aqueous ferrous ions at the first anode in the presence of the first catholyte.

[0248] Aspect 23b: A system, comprising:

[0249] An electrochemical cell, which includes:

[0250] A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte;

[0251] Wherein:

[0252] The first anode is a lead electrode;

[0253] The first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; and

[0254] The electrochemical cell is configured to reverse bias the first anode for a time to electrochemically reduce aqueous ferric ions to aqueous ferrous ions at the first anode in the presence of the first anolyte.

[0255] Aspect 24a: A method, comprising:

[0256] Operating an electrochemical cell, including performing electrochemical reduction at a first cathode and electrochemical oxidation at a first anode;

[0257] Wherein:

[0258] The electrochemical cell includes a first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte;

[0259] Each of the first anode and the first cathode includes lead, and

[0260] The first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions.

[0261] In embodiments and aspects herein, an electrode including lead may include a lead layer as a bottom layer or a support layer. For example, a cathode including lead may include a lead layer as a bottom layer or a support layer, but the surface or electrocatalyst material exposed to the catholyte does not necessarily include lead, such that a cathode including lead does not necessarily have lead in contact with the catholyte, since lead is optionally only part of the cathode as a support layer or a bottom layer. For example, a cathode including lead may be a carbon electrode on a lead support layer or a lead bottom layer.

[0262] Aspect 25a: The method or system according to any one of the preceding aspects, including operating two or more electrochemical cells; wherein adjacent electrochemical cells share a bipolar plate therebetween; and wherein each bipolar plate includes a first lead electrode as the first anode of the electrochemical cell and a second electrode including lead as the first cathode of the adjacent electrochemical cell. In embodiments and aspects herein, an electrode including lead may include a lead layer as a bottom layer or a support layer. For example, a cathode including lead may include a lead layer as a bottom layer or a support layer, but the surface or electrocatalyst material exposed to the catholyte does not necessarily include lead, such that a cathode including lead does not necessarily have lead in contact with the catholyte, since lead is optionally only part of the cathode as a support layer or a bottom layer. For example, a cathode including lead may be a carbon electrode on a lead support layer or a lead bottom layer. Aspect 25b: The method or system according to any one of the preceding aspects, including operating two or more electrochemical cells; wherein adjacent electrochemical cells share a bipolar plate therebetween; and wherein each bipolar plate includes a first electrode as the first anode of the electrochemical cell and a second electrode as the first cathode of the adjacent electrochemical cell.

[0263] Aspect 26: The method or system according to any one of the preceding aspects, including operating a bipolar stack of electrochemical cells, wherein the electrochemical cells in the stack are each independently the electrochemical cell according to any one of the preceding claims.

[0264] Aspect 27a: The method or system according to aspect 26, wherein:

[0265] The bipolar stack includes one or more bipolar plates;

[0266] Adjacent electrochemical cells share a bipolar plate therebetween; and

[0267] Each bipolar plate includes a first lead electrode as the first anode of an electrochemical cell and a second electrode containing lead as the first cathode of an adjacent electrochemical cell. In embodiments and aspects herein, the electrode containing lead may include a lead layer as a bottom layer or support layer. For example, the cathode containing lead may include a lead layer as a bottom layer or support layer, but the surface or electrocatalyst material exposed to the cathode electrolyte does not necessarily include lead, such that the cathode containing lead does not necessarily have lead in contact with the cathode electrolyte, as lead optionally only forms part of the cathode as a support layer or bottom layer. For example, the cathode containing lead may be a carbon electrode on a lead support layer or lead bottom layer.

[0268] Aspect 27b: The method or system of aspect 26, wherein:

[0269] The bipolar stack includes one or more bipolar plates;

[0270] Adjacent electrochemical cells share a bipolar plate therebetween; and

[0271] Each bipolar plate includes a first anode as the first electrode of an electrochemical cell and a second electrode as the first cathode of an adjacent electrochemical cell.

[0272] Aspect 28a: A method, comprising:

[0273] Operating two or more electrochemical cells, including performing electrochemical reduction at a first cathode and electrochemical oxidation at a first anode;

[0274] Wherein:

[0275] Each electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode,

[0276] and a first separator separating the first anolyte from the first catholyte; the first anode is a lead electrode;

[0277] The first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions;

[0278] Adjacent electrochemical cells share a bipolar plate therebetween; and

[0279] Each bipolar plate includes a first lead electrode as the first anode of an electrochemical cell and a second electrode containing lead as the first cathode of an adjacent electrochemical cell. In embodiments and aspects herein, the electrode containing lead may include a lead layer as an underlying or support layer. For example, the cathode containing lead may include a lead layer as an underlying or support layer, but the surface or electrocatalyst material exposed to the cathode electrolyte does not necessarily include lead, such that the cathode containing lead does not necessarily have lead in contact with the cathode electrolyte, as lead is optionally only part of the cathode as a support layer or underlying layer. For example, the cathode containing lead can be a carbon electrode on a lead support layer or lead underlying layer.

[0280] Aspect 28b: A method comprising

[0281] operating two or more electrochemical cells, including performing electrochemical reduction at a first cathode and electrochemical oxidation at a first anode;

[0282] wherein:

[0283] each electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte;

[0284] the first anode is a lead electrode;

[0285] the first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions;

[0286] adjacent electrochemical cells share a bipolar plate therebetween; and

[0287] each bipolar plate includes a first lead electrode as the first anode of an electrochemical cell and a second electrode as the first cathode of an adjacent electrochemical cell.

[0288] Aspect 28c: A method comprising:

[0289] operating a bipolar stack of electrochemical cells, each of the stacked electrochemical cells independently having a first cathode at which electrochemical reduction occurs and a first anode at which electrochemical oxidation occurs;

[0290] wherein:

[0291] each electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte;

[0292] the first anode is a lead electrode;

[0293] The first anolyte and the first catholyte each independently comprise an aqueous iron cation and an aqueous anion;

[0294] The bipolar stack comprises one or more bipolar plates;

[0295] Adjacent electrochemical cells share the bipolar plate therebetween; and

[0296] Each bipolar plate comprises a first lead electrode as the first anode of an electrochemical cell and a second electrode comprising lead as the first cathode of an adjacent electrochemical cell. In embodiments and aspects herein, the electrode comprising lead may comprise a lead layer as an underlying or support layer. For example, the cathode comprising lead may comprise a lead layer as an underlying or support layer, but the surface or electrocatalyst material exposed to the catholyte does not necessarily comprise lead, such that the cathode comprising lead does not necessarily have lead in contact with the catholyte, as lead is optionally only part of the cathode as a support layer or underlying layer. For example, the cathode comprising lead may be a carbon electrode on a lead support layer or lead underlying layer.

[0297] Aspect 28d: A method comprising:

[0298] Operating a bipolar stack of electrochemical cells, each of the electrochemical cells in the stack independently having a first cathode for electrochemical reduction and a first anode for electrochemical oxidation;

[0299] Wherein:

[0300] Each electrochemical cell comprises a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte;

[0301] The first anode is a lead electrode;

[0302] The first anolyte and the first catholyte each independently comprise an aqueous iron cation and an aqueous anion;

[0303] The bipolar stack comprises one or more bipolar plates;

[0304] Adjacent electrochemical cells share the bipolar plate therebetween; and

[0305] Each bipolar plate comprises a first lead electrode as the first anode of an electrochemical cell and a second electrode as the first cathode of an adjacent electrochemical cell.

[0306] Aspect 28e: A system comprising:

[0307] Two or more electrochemical cells, each cell comprising:

[0308] A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte; and

[0309] A bipolar plate between two adjacent electrochemical cells such that the adjacent electrochemical cells share the bipolar plate therebetween;

[0310] Wherein:

[0311] The first anode is a lead electrode;

[0312] The first anolyte and the first catholyte each independently comprise aqueous iron cations and aqueous anions; and

[0313] Each bipolar plate includes a first lead electrode as the first anode of an electrochemical cell and a second electrode containing lead as the first cathode of an adjacent electrochemical cell. In embodiments and aspects herein, an electrode containing lead may include a lead layer as an underlying or support layer. For example, a cathode containing lead may include a lead layer as an underlying or support layer, but the surface or electrocatalyst material exposed to the catholyte does not necessarily include lead, such that a cathode containing lead does not necessarily have lead in contact with the catholyte, as lead is optionally only part of the cathode as a support layer or underlying layer. For example, a cathode containing lead can be a carbon electrode on a lead support layer or lead underlying layer.

[0314] Aspect 28f: A system comprising:

[0315] Two or more electrochemical cells, each cell comprising:

[0316] A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte; and

[0317] A bipolar plate between two adjacent electrochemical cells such that the adjacent electrochemical cells share the bipolar plate therebetween;

[0318] Wherein:

[0319] The first anode is a lead electrode;

[0320] The first anolyte and the first catholyte each independently comprise aqueous iron cations and aqueous anions; and

[0321] Each bipolar plate includes a first lead electrode as the first anode of an electrochemical cell and a second electrode as the first cathode of an adjacent electrochemical cell.

[0322] Aspect 28g: A system comprising:

[0323] A bipolar stack of two or more electrochemical cells, each cell comprising:

[0324] A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte;

[0325] Wherein:

[0326] The first anode is a lead electrode;

[0327] The first anolyte and the first catholyte each independently comprise aqueous iron cations and aqueous anions;

[0328] The bipolar stack comprises one or more bipolar plates;

[0329] Adjacent electrochemical cells share the bipolar plate therebetween; and

[0330] Each bipolar plate comprises a first lead electrode as the first anode of an electrochemical cell and a second electrode comprising lead as the first cathode of an adjacent electrochemical cell. In embodiments and aspects herein, an electrode comprising lead may comprise a lead layer as a bottom layer or support layer. For example, a cathode comprising lead may comprise a lead layer as a bottom layer or support layer, but the surface or electrocatalyst material exposed to the catholyte does not necessarily comprise lead, such that a cathode comprising lead does not necessarily have lead in contact with the catholyte, as lead is optionally only part of the cathode as a support layer or bottom layer. For example, a cathode comprising lead may be a carbon electrode on a lead support layer or lead bottom layer.

[0331] Aspect 25h: A system comprising:

[0332] A bipolar stack of two or more electrochemical cells, each cell comprising:

[0333] A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte;

[0334] Wherein:

[0335] The first anode is a lead electrode;

[0336] The first anolyte and the first catholyte each independently comprise aqueous iron cations and aqueous anions;

[0337] The bipolar stack comprises one or more bipolar plates;

[0338] Adjacent electrochemical cells share a bipolar plate therebetween; and

[0339] Each bipolar plate includes a first lead electrode as the first anode of an electrochemical cell and a second electrode as the first cathode of an adjacent electrochemical cell.

[0340] Aspect 29: The method or system according to any one of aspects 25 - 28, wherein each bipolar plate includes a conductive substrate, an anode-facing side, and a cathode-facing side.

[0341] Aspect 30: The method or system according to aspect 29, wherein the conductive substrate is porous or permeable to the electrolyte and dissolved ions.

[0342] Aspect 31: The method or system according to aspect 30, wherein each bipolar plate includes a lead coating on at least a portion of the inner surface or pore surface of the porous substrate.

[0343] Aspect 32: The method or system according to aspect 31, wherein the coating has a thickness selected from the range of 50 μm to 5 mm.

[0344] Aspect 33: The method or system according to aspect 29, wherein the conductive substrate is non-porous or impermeable to the electrolyte and dissolved ions.

[0345] Aspect 34: The method or system according to any one of aspects 29 - 33, wherein each bipolar plate includes a first lead layer on the anode-facing side, a second lead layer on the cathode-facing side, or independent lead layers on the anode-facing side and the cathode-facing side respectively.

[0346] Aspect 35: The method or system according to aspect 34, wherein each lead layer is a layer on the substrate.

[0347] Aspect 36: The method or system according to aspect 34 or 35, wherein each lead layer is non-porous or impermeable to the electrolyte and dissolved ions.

[0348] Aspect 37: The method or system according to any one of aspects 34 - 36, wherein each lead layer protects the substrate from exposure to the nearest electrolyte.

[0349] Aspect 38: The method or system according to any one of aspects 34 - 37, wherein each lead layer independently has a thickness selected from the range of 50 μm to 5 mm.

[0350] Aspect 39: The method or system according to any one of aspects 29 - 38, wherein the conductive substrate is characterized by a compressive yield strength selected from the range of 10 MPa to 200 MPa, and / or a Young's modulus selected from the range of 600 MPa to 1500 MPa.

[0351] Aspect 40: The method or system according to any one of Aspects 25 - 39, wherein the first cathode of each bipolar plate is a carbon cathode or a carbon-containing cathode.

[0352] Aspect 41: The method or system according to any one of Aspects 34 - 40, wherein each bipolar plate includes a first lead layer on the anode-facing side; and wherein the first lead layer is the first anode of the corresponding bipolar plate.

[0353] Aspect 42: The method or system according to any one of Aspects 34 - 40, wherein each bipolar plate includes a lead layer on the anode-facing side; and wherein each bipolar plate further includes a first anode located on, adhered to, coated on, or otherwise adjacent to the first lead layer.

[0354] Aspect 43: The method or system according to any one of Aspects 28 - 42, wherein the bipolar stack includes a conductive spacer layer or a flow field layer through which fluid can flow.

[0355] Aspect 44a: The method or system according to any one of the preceding aspects, wherein the first anode is a lead electrode comprising a microstructured lead-containing surface and / or a nanostructured lead-containing surface in contact with an anolyte. Aspect 44b: The method or system according to any one of the preceding aspects, wherein the lead electrode is porous and at least partially permeable to the first anolyte. Aspect 44c: The method or system according to any one of the preceding aspects, wherein the lead electrode is a lead-containing and / or lead-coated wool or foam.

[0356] Aspect 45: The method or system according to any one of the preceding aspects, wherein the first anode has no lead shedding, or is characterized by a lead shedding rate less than that of an equivalent electrochemical cell with an anolyte free of aqueous iron cations under the same conditions.

[0357] Aspect 46: The method or system according to any one of the preceding aspects, wherein the aqueous anions include aqueous sulfur-containing anions, aqueous chlorine anions, or both.

[0358] Aspect 47a: The method or system according to aspect 46, wherein the aqueous sulfur-containing anion comprises aqueous sulfate ions. Aspect 47b: The method or system according to aspect 46, wherein the aqueous sulfur-containing anion is aqueous sulfate ions. Aspect 47c: The method or system according to aspect 46, wherein the aqueous sulfur-containing anion is aqueous sulfate ions, and the concentration thereof is stoichiometrically related to the concentration of aqueous iron cations in the respective electrolyte. Aspect 47d: The method or system according to aspect 46, wherein the aqueous sulfur-containing anion comprises aqueous sulfate ions, and the first anolyte does not contain aqueous chloride anions.

[0359] Aspect 48a: The method or system according to any one of the preceding aspects, wherein the first anolyte comprises aqueous lead ions at a concentration of at least 10 ppm. Aspect 48b: The method or system according to any one of the preceding aspects, wherein the first anolyte comprises aqueous lead ions at a concentration of at least 10 ppm or selected from the range of 10 ppm to 0.5 M.

[0360] Aspect 49: The method or system according to any one of the preceding aspects, wherein the first anolyte comprises aqueous lead ions, and the concentration of the aqueous lead ions is greater than 10 ppm and equal to or less than the saturation concentration of lead ions in the first anolyte at its temperature (e.g., the saturation concentration of lead ions in H2SO4 and / or HCl at about 50 °C to 80 °C).

[0361] Aspect 50: The method or system according to any one of the preceding aspects, wherein the electrochemical cell further comprises a secondary lead ion source or a sacrificial lead ion source (other than the first anode itself) in contact with the first anolyte to slow down or prevent the dissolution of Pb from the first anode into the first anolyte.

[0362] Aspect 51: The method or system according to any one of the preceding aspects, wherein the step of operating the electrochemical cell comprises:

[0363] Electrochemically reducing the first Fe 3+ ions at the first cathode to form Fe 2+ ions in the first catholyte.

[0364] Aspect 52: The method or system according to any one of the preceding aspects, wherein the step of operating the electrochemical cell further comprises:

[0365] Electrochemically oxidizing water at the first anode to produce O2 and aqueous protons in the first anolyte.

[0366] Aspect 53a: The method or system according to any one of the preceding aspects, wherein: the operating step includes that the first anode is characterized in that the steady-state anode potential is selected from the range of 1.2 to 3.0 V vs. NHE; and / or the operating step includes that each electrochemical cell is characterized in that the current density is selected from the range of 5 to 200 mA / cm 2 (optionally about 30 to 100 mA / cm 2 ); and / or the operating step includes that each electrochemical cell is characterized in that the bias current density is 5 to 50 mA / cm 2 . Aspect 53b: The method or system according to any one of the preceding aspects, wherein the operating step includes that the first anode is characterized in that the steady-state anode potential is at least 1 V vs. NHE (optionally at least 1.1 V, optionally at least 1.2 V, optionally at least 1.3 V, optionally at least 1.4 V, optionally at least 1.5 V, optionally at least 1.6 V vs. NHE), and optionally less than or equal to 2.5 V vs. NHE (optionally 2.7 V, optionally 2.9 V, optionally 3.0 V, optionally 3.2 V, optionally 3.5 V vs. NHE). Aspect 53c: The method or system according to any one of the preceding aspects, wherein: the operating step includes that each electrochemical cell is characterized in that the current density is selected from the range of 5 to 200 mA / cm 2 (optionally about 30 to 100 mA / cm 2 ); and / or the operating step includes that each electrochemical cell is characterized in that the bias current density is 5 to 50 mA / cm 2 .

[0367] Aspect 54a: The method or system according to any one of the preceding aspects, wherein the electrochemical cell is characterized in that the steady-state current density is selected from the range of 1 to 500 mA / cm 2 . Aspect 54b: The method or system according to any one of the preceding aspects, wherein the electrochemical cell is characterized in that the steady-state current density is at least 1 mA / cm 2 (optionally at least 5 mA / cm 2 , at least 10 mA / cm 2 , optionally at least 20 mA / cm 2 , optionally at least 50 mA / cm 2 , optionally at least 75 mA / cm 2 , optionally at least 100 mA / cm 2 ), and optionally less than or equal to 2 A / cm 2 (optionally 1.5 A / cm 2 , optionally 1 A / cm 2 , optionally 900 mA / cm 2 , optionally 800 mA / cm 2, optionally 700 mA / cm 2 , optionally 600 mA / cm 2 , optionally 500 mA / cm 2 , optionally 400 mA / cm 2 ).

[0368] Aspect 55a: The method or system according to any one of the preceding aspects, including adding an injection solution having aqueous iron cations to the first anode chamber and / or the first anolyte. Aspect 55b: The method or system according to any one of the preceding aspects, including washing or rinsing the anode chamber with a solution having aqueous iron cations.

[0369] Aspect 56a: The method or system according to aspect 55, wherein the injection solution comprises aqueous ferrous. Aspect 56b: The method or system according to aspect 55, wherein the aqueous iron cations in the solution are mostly or substantially aqueous ferrous ions.

[0370] Aspect 57: The method or system according to aspect 55 or 56, wherein the injection solution is an electrolyte from a different electrochemical cell or system.

[0371] Aspect 58: The method or system according to any one of aspects 55-57, wherein the injection solution comprises an electrolyte from a metal electroplating cell or system.

[0372] Aspect 59: The method or system according to any one of aspects 55-58, wherein the injection solution is provided by a separate solution storage tank.

[0373] Aspect 60: The method or system according to any one of the preceding aspects, including recycling a second electrolyte having aqueous iron cations from a metal electroplating cell into the first anolyte.

[0374] Aspect 61a: The method or system according to aspect 60, wherein the second electrolyte comprises an aqueous iron cation at a concentration of at least about 0.01 M or in a range selected from: about 0.01 M (optionally about 0.02 M, optionally about 0.03 M, optionally about 0.04 M, optionally about 0.05 M, optionally about 0.06 M, optionally about 0.07 M, optionally about 0.08 M, optionally about 0.09 M, optionally about 0.095 M, optionally about 0.099 M, optionally about 0.1 M) to 0.5 M (optionally about 0.49 M, optionally about 0.48 M, optionally about 0.47 M, optionally about 0.46 M, optionally about 0.45 M, optionally about 0.44 M, optionally about 0.43 M, optionally about 0.42 M, optionally about 0.41 M, optionally about 0.40 M, optionally about 0.39 M, optionally about 0.38 M), e.g., optionally a concentration in a range selected from about 0.01 M to about 0.5 M, or optionally a concentration in a range selected from about 0.01 M to about 0.45 M, or optionally a concentration in a range selected from about 0.01 M to about 0.445 M, or optionally a concentration in a range selected from about 0.01 M to about 0.44 M, or optionally a concentration in a range selected from about 0.01 M to about 0.4 M, or optionally a concentration in a range selected from about 0.05 M to about 0.5 M. Aspect 61b: The method or system according to aspect 60, wherein the second electrolyte comprises aqueous ferrous or ferric ions at a concentration of at least about 0.01 M or in a range selected from about 0.01 M to about 0.5 M, optionally in a range selected from about 0.05 M to about 0.5 M.

[0375] Aspect 62: The method or system according to aspect 60 or 61, wherein the second comprises catholyte and / or anolyte from an iron electroplating cell.

[0376] Aspect 63: The method or system according to aspect 62, wherein the catholyte and / or anolyte from the iron electroplating cell are waste catholyte and / or waste anolyte, respectively.

[0377] Aspect 64: The method or system according to any one of the preceding aspects, further comprising:

[0378] dissolving iron ore in an acid to form an acidic iron salt solution; and

[0379] providing the acidic iron salt solution to the cathode chamber of the electrochemical cell.

[0380] Aspect 65: The method or system according to any one of the preceding aspects, further comprising:

[0381] electrochemically reducing Fe ions to Fe metal at a second cathode in the presence of a second catholyte; 2+ at the second cathode.

[0382] Among them, the iron electroplating cell includes the second cathode and the second cathode electrolyte solution.

[0383] Aspect 66: The method or system according to any one of the foregoing aspects, including the step of switching the first electrochemical cell to a first temporary intermediate state; wherein, the first temporary intermediate state includes the first anode contacting the first anode electrolyte solution and is characterized by an open-circuit voltage.

[0384] Aspect 67: The method or system according to aspect 66, wherein during the electrochemical oxidation step and / or during the switching step, the surface of the first anode is free of lead sulfate.

[0385] Aspect 68: The method or system according to aspect 67, wherein when the first anode contacts the first anode electrolyte solution and has an open-circuit voltage, the surface of the first anode is free of lead sulfate.

[0386] Aspect 69: The method or system according to any one of aspects 66-68, wherein the first temporary intermediate state further includes that the surface of the first anode has a lead-iron alloy including Pb, Fe, S, and O.

[0387] Aspect 70: The method or system according to aspect 69, wherein the lead-iron alloy is characterized by formula FX1: Fe x Pb 2- x SO4, where x is greater than 0 and less than 2.

[0388] Aspect 71: The method or system according to aspect 69 or 70, wherein during the steady-state operation of the electrochemical oxidation step, the surface of the first anode is free of the lead-iron alloy.

[0389] Aspect 72: The method or system according to any one of aspects 69-71, including the step of forming the lead-iron alloy during the switching step or when the surface of the first anode contacts the first anode electrolyte solution and has an open-circuit voltage.

[0390] Aspect 73: The method or system according to aspect 72, wherein the lead-iron alloy is formed in the presence of aqueous iron sulfate in the first anode electrolyte solution.

[0391] Aspect 74: The method or system according to any one of the foregoing aspects, wherein the electrochemical cell is a cell according to any embodiment or aspect of the "first electrochemical cell" disclosed in PCT'732 and Provis'092, and / or further includes any embodiment or aspect of the "first electrochemical cell" disclosed in PCT'732 and Provis'092, and the entire contents of these two applications are incorporated herein by reference.

[0392] Aspect 75: The method or system according to any one of the foregoing aspects, wherein the metal electroplating cell or iron electroplating cell is any embodiment or aspect of the "second electrochemical cell" disclosed in PCT'732 and Provis'092.

[0393] Aspect 76: The method or system according to any one of the foregoing aspects, further comprising any feature, step, embodiment or aspect disclosed in PCT'732 and Provis'092.

[0394] Aspect 77: The method or system according to any one of the foregoing aspects, wherein the first separator is the first separator according to any embodiment or aspect described in PCT'732 and Provis'092.

[0395] Aspect 78: The method or system according to any one of the foregoing aspects, wherein the first cathode comprises lead as an underlying or support layer.

[0396] Aspect 79: The method or system according to any one of the foregoing aspects, wherein the first cathode does not include lead in contact with the first cathode electrolyte.

[0397] Aspect 80: The method or system according to any one of the foregoing aspects, wherein the first cathode comprises a carbon electrode in contact with the first cathode electrolyte.

[0398] Aspect 81: A method of manufacturing one or more electrochemical cells according to any of the foregoing aspects and / or any embodiment disclosed herein (such as those described in paragraphs

[0064] to

[0093] and in Figures 1 - 4 any embodiment, feature, aspect, process, technique and step shown).

[0399] Aspect 82: A method of manufacturing a bipolar stack according to any of the foregoing aspects and / or any embodiment disclosed herein (such as those described and Figures 1 - 4 shown in any embodiment, feature, aspect, process, technique and step in paragraphs

[0064] to

[0093] ).

[0400] Aspect 83a: The method or system according to any one of the preceding aspects, wherein the operating step includes one or more steps of establishing the concentration of aqueous iron cations in the first anolyte within a stable concentration range, and / or the operating step includes maintaining the concentration of aqueous iron cations in the first anolyte within a stable concentration range; wherein the stable concentration range is selected from the range of about 0.01 M (optionally about 0.02 M, optionally about 0.03 M, optionally about 0.04 M, optionally about 0.05 M, optionally about 0.06 M, optionally about 0.07 M, optionally about 0.08 M, optionally about 0.09 M, optionally about 0.095 M, optionally about 0.099 M, optionally about 0.1 M) to about 0.5 M (optionally about 0.49 M, optionally about 0.48 M, optionally about 0.47 M, optionally about 0.46 M, optionally about 0.45 M, optionally about 0.44 M, optionally about 0.43 M, optionally about 0.42 M, optionally about 0.41 M, optionally about 0.40 M, optionally about 0.39 M, optionally about 0.38 M). Optionally, in any aspect herein, the stable concentration range is selected from the range of about 0.01 M to about 0.1 M, wherein any value and range therebetween are explicitly contemplated and disclosed herein, for example, optionally about 0.02 M to about 0.09 M, or optionally about 0.03 M to about 0.08 M, or optionally about 0.04 M to about 0.07 M, or optionally about 0.03 M to about 0.08 M, or optionally about 0.05 M. Aspect 83b: The method or system according to any one of the preceding aspects, wherein the operating step includes the one or more establishing steps. Aspect 83c: The method or system according to any one of the preceding aspects, wherein the operating step includes a maintaining step.

[0401] Aspect 84: The method or system according to Aspect 83, wherein each establishing step temporarily provides the stable concentration range.

[0402] Aspect 85: The method or system according to aspect 83 or 84, wherein the establishing step is carried out before starting up and / or shutting down the electrochemical cell. Optionally, starting up the cell includes the cell voltage, e.g., the voltage between the first anode and the first cathode, transitioning from the open circuit voltage (OCV) to the operating voltage, where the operating voltage corresponds to a voltage corresponding to the performance of the electrochemical reduction at the first cathode and the electrochemical oxidation at the first anode such as an oxygen evolution reaction. Optionally, shutting down the cell includes the cell voltage, e.g., the voltage between the first anode and the first cathode, transitioning from the operating voltage to the open circuit voltage (OCV), where the operating voltage corresponds to a voltage corresponding to the performance of the electrochemical reduction at the first cathode and the electrochemical oxidation at the first anode such as an oxygen evolution reaction. When the cell is at OCV, the electrochemical reduction at the first cathode and the electrochemical oxidation reaction at the first anode do not occur or cannot occur.

[0403] Aspect 86a: The method or system according to any one of aspects 83 - 85, wherein each of the establishing step and the maintaining step (if present) includes injecting the aqueous iron cations into the first anode electrolyte. Aspect 86b: The method or system according to any one of aspects 83 - 85, wherein each establishing step includes injecting the aqueous iron cations into the first anode electrolyte. Aspect 86c: The method or system according to any one of aspects 83 - 85, wherein the maintaining step includes injecting the aqueous iron cations into the first anode electrolyte. Aspect 86d: The method or system according to any one of aspects 83 - 85, wherein each of the establishing step and the maintaining step includes injecting the aqueous iron cations into the first anode electrolyte.

[0404] Aspect 87: The method or system according to aspect 86, wherein the injecting step is carried out as one or more discrete events during the step of operating the cell.

[0405] Aspect 88: The method or system according to aspect 86, wherein the injecting step is carried out continuously during the step of operating the cell.

[0406] Aspect 89: The method or system according to any one of aspects 86 - 88, wherein the injecting step includes providing a liquid iron source; the liquid iron source is an aqueous solution comprising aqueous iron cations at an injection concentration.

[0407] Aspect 90: The method or system according to aspect 89, wherein the liquid iron source includes spent anode electrolyte or used anode electrolyte from a metal electroplating cell or system.

[0408] Aspect 91: The method or system according to aspect 89 or 90, wherein the liquid iron source comprises spent cathode electrolyte or used cathode electrolyte from a metal electroplating cell or system.

[0409] Aspect 92: The method or system according to any one of aspects 89 - 91, wherein the liquid iron source is directly provided to the first anolyte or the first anode chamber having the first anolyte.

[0410] Aspect 93: The method or system according to any one of aspects 89 - 92, wherein the liquid iron source is indirectly provided to the first anolyte or the first anode chamber having the first anolyte.

[0411] Aspect 94: The method or system according to any one of aspects 89 - 93, wherein the liquid iron source is provided to a first anolyte circulation tank in fluid communication with the first anode chamber having the first anolyte, a fluid line entering the first anode chamber, and / or a fluid line leaving the first anode chamber.

[0412] Aspect 95: The method or system according to any one of aspects 89 - 94, wherein the liquid iron source comprises aqueous ferrous ions.

[0413] Aspect 96: The method or system according to any one of aspects 89 - 95, wherein the liquid iron source is iron-containing slag and / or iron-containing leachate from a metal and / or ore processing system.

[0414] Aspect 97: The method or system according to any one of aspects 89 - 96, wherein the injection concentration of aqueous iron cations in the liquid iron source is greater than 0 M and less than 0.5 M.

[0415] Aspect 98: The method or system according to any one of aspects 83 - 97, wherein the injection step comprises providing a solid iron source in the presence of the first anolyte; wherein the solid iron source can be at least partially dissolved by the first anolyte.

[0416] Aspect 99: The method or system according to aspect 98, wherein the solid iron source is raw ore and / or processed ore.

[0417] Aspect 100: The method or system according to aspect 98 or 99, wherein the solid iron source is heat-treated ore.

[0418] Aspect 101: The method or system according to any one of aspects 98 - 100, wherein the solid iron source comprises solid ferrous ions.

[0419] Aspect 102: The method or system according to any one of aspects 86 - 101, wherein each injection is made in response to a trigger event; wherein the trigger event includes:

[0420] the concentration of aqueous iron cations in the first anolyte drops below the stable concentration range, and / or

[0421] the current density of the electrochemical cell drops below the normal operable current density.

[0422] Aspect 103: The method or system according to any one of the preceding aspects, wherein the electrochemical reduction at the first cathode is an iron electroplating reaction; and wherein the electrochemical oxidation reaction is an oxygen evolution reaction (OER) at the first anode.

[0423] Aspect 104: The method or system according to aspect 103, wherein the separator is an anion exchange membrane.

[0424] Aspect 105: The method or system according to any one of the preceding aspects, wherein the first anode does not contain a mixed metal oxide (MMO) material.

[0425] Aspect 106: The method or system according to any one of the preceding aspects, wherein the first anode does not contain Ir, Ru, and Pt.

[0426] Aspect 107: The method or system according to any one of the preceding aspects, wherein the first anode is an undoped lead electrode or a non - alloyed lead electrode.

[0427] Statement regarding incorporation by reference and variations

[0428] All references throughout this application, such as patent documents, including issued or granted patents or equivalents; patent application publications; and non - patent literature documents or other source materials; to the extent that each reference is at least partially not in conflict with the disclosure in this application, its entire content is incorporated herein by reference as if incorporated herein individually (e.g., incorporating a partially conflicting reference by reference except for the parts that are conflicting in the reference).

[0429] The terms and expressions used herein are used only as descriptive terms and not as limiting terms, and in using these terms and expressions, there is no intention to exclude any equivalents of the features shown and described or parts thereof, but it should be recognized that various modifications can be made within the scope of any particular claimed invention. Accordingly, it should be understood that although the present invention has been specifically disclosed by way of preferred embodiments, exemplary embodiments and optional features, those skilled in the art can make modifications and variations to the concepts disclosed herein, and such modifications and variations are considered to be within the scope of the present invention as defined by the appended claims. The specific embodiments provided herein are examples of useful embodiments of the present invention, and it will be apparent to those skilled in the art that the present invention can be practiced using a large number of variations of the devices, device components, and method steps described in this specification. It will be apparent to those skilled in the art that the methods and the devices that can be used in the methods can include a large number of optional components, processing elements, and steps.

[0430] As used herein and in the appended claims, the indefinite articles in the singular form ("a", "an") and the definite article ("the") include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a cell" includes a plurality of such cells known to those skilled in the art and their equivalents. Similarly, the terms indefinite article in the singular form ("a" (or "an")), "one or more", and "at least one" can be used interchangeably herein. It should also be noted that the terms "comprising", "including", and "having" can be used interchangeably. The expression "any one of claims XX-YY" (where XX and YY refer to claim numbers) is intended to provide multiple dependent claims in an alternative form and can be interchanged with the expression "as claimed in any one of claims XX-YY" in some embodiments.

[0431] When a group of substituents is disclosed herein, it is to be understood that all individual members and all subgroups of the group, including the iron oxide materials of ores or the polymorphs of the structure and composition of the members of the group, are disclosed individually. When a Markush group or other grouping is used herein, all individual members of the group and all possible combinations and subcombinations of the group are intended to be included individually in the present disclosure. When a compound is described herein without specifying a particular isomer, enantiomer or diastereomer of the compound, e.g., in a chemical formula or chemical name, the description is intended to include each isomer and enantiomer of the described compound individually or any combination thereof. In addition, unless otherwise stated, the present disclosure is intended to cover all isotopic variants of the compounds disclosed herein. For example, it is to be understood that any one or more hydrogens in the disclosed molecule may be replaced with deuterium or tritium. Isotopic variants of a molecule are generally useful as standards in the determination of the molecule and in chemical and biological studies related to the molecule or its use. Methods for preparing such isotopic variants are known in the art. The specific names of the compounds are intended to be exemplary, as it is known that one of ordinary skill in the art may name the same compound in different ways.

[0432] Regarding the salts of the compounds of the present invention, one of ordinary skill in the art can select those from a variety of available counterions that are suitable for preparing the salts of the present invention for a given application. In a specific application, the selection of a given anion or cation for preparing a salt may result in an increase or decrease in the solubility of the salt.

[0433] Unless otherwise stated, each apparatus, system, subsystem, method, process, component, and / or combination of components described or exemplified herein can be used to implement any claimed invention.

[0434] Whenever a range is given in the specification, e.g., a temperature range, a time range, a composition range or a concentration range, all intermediate ranges and subranges, as well as all individual values included in the given range, are included in the present disclosure. It is to be understood that any subrange or individual value within a range or subrange included in the specification herein may be excluded from the claims herein.

[0435] All patents and publications mentioned in this specification indicate the level of skill of those skilled in the art to which the disclosed apparatus, systems, methods and processes pertain. The references cited herein are hereby incorporated by reference in their entirety to show the prior art as of their publication or filing date, and if needed, this information may be used herein to exclude specific embodiments of the prior art. For example, when claiming the composition of a substance, it is to be understood that compounds known and available in the art prior to the applicant's invention, including those disclosed in the authorized publications cited herein, are not intended to be included in the composition of the substance claims herein.

[0436] As used herein, "comprising" is synonymous with "including", "containing", or "characterized by", and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, "consisting of" excludes any element, step, or component not specified in the claim element. As used herein, "consisting essentially of" does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. In each case herein, any of the terms "comprising", "consisting essentially of", and "consisting of" may be replaced by any of the other two terms. The claimed inventions described herein by way of example can be practiced without any element or elements, limitation or limitations not specifically disclosed herein.

[0437] Those of ordinary skill in the art will recognize that starting materials, reagents, synthetic methods, purification methods, analytical methods, and assay methods other than those specifically recited can be used in the practice of the claimed inventions without undue experimentation. All known functional equivalents of any such materials and methods are intended to be included in these inventions.

Claims

1. A method for stabilizing a lead anode, the method comprising: Operating an electrochemical cell, including electrochemical reduction at a first cathode and electrochemical oxidation at a first anode; Wherein: The electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; The first anode is a lead electrode; The first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; and The first anolyte includes the aqueous iron cations at a concentration selected from the range of 0.01 M to 0.5 M.

2. A method for stabilizing a lead anode, the method comprising: Operating an electrochemical cell, including electrochemical reduction at a first cathode and electrochemical oxidation at a first anode; And Recycling a second electrolyte from a metal electroplating cell into the first anolyte, the second electrolyte having aqueous iron cations; Wherein: The electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; The first anode is a lead electrode; The first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; and The first anolyte includes the aqueous iron cations at a concentration selected from the range of 0.01 M to 0.5 M.

3. The method of claim 2, wherein the second electrolyte includes spent catholyte and / or spent anolyte from an iron electroplating cell.

4. The method according to any one of the preceding claims, wherein the electrochemical oxidation includes an oxygen evolution reaction (OER) at the first anode.

5. The method according to any one of the preceding claims, wherein the first anolyte includes aqueous sulfate anions.

6. A method for stabilizing a lead anode, the method comprising: Operating an electrochemical cell, including electrochemical reduction at a first cathode and an oxygen evolution reaction (OER) at a first anode; Wherein: The electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; The first anode is a lead electrode; The first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; and The first anolyte includes aqueous iron sulfate at a concentration selected from the range of 0.01 M to 0.5 M.

7. The method according to any one of the preceding claims, wherein the concentration of the aqueous iron cations in the first anolyte is selected from the range of 0.05 M to 0.5 M.

8. The method according to any one of the preceding claims, wherein the concentration of aqueous iron cations in the first anolyte is less than the concentration of aqueous iron cations in the first catholyte.

9. The method according to any one of the preceding claims, wherein the steady-state concentration of aqueous iron cations in the first anolyte ranges from 0.01 M to 0.5 M.

10. The method according to any one of the preceding claims, wherein the steady-state concentration of aqueous iron cations in the first anolyte ranges from 0.05 M to 0.5 M.

11. The method according to any one of the preceding claims, wherein the steady-state concentration of iron cations in the first anolyte is less than the steady-state concentration of aqueous iron cations in the first catholyte.

12. The method according to any one of the preceding claims, wherein the aqueous iron cations in the first anolyte include aqueous ferric ions.

13. A method comprising: operating an electrochemical cell, including performing electrochemical reduction at a first cathode and electrochemical oxidation at a first anode; wherein: the electrochemical cell includes a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; the first anode is a lead electrode; and the first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; and wherein the method further comprises: dissolving solid manganese oxide in the first anolyte in the presence of aqueous ferrous ions.

14. The method of claim 13, wherein the dissolving step comprises converting the solid manganese oxide into one or more aqueous manganese salts in the presence of the aqueous ferrous ions.

15. The method according to claim 14, wherein the conversion step comprises: (i) reacting the solid manganese oxide with the aqueous ferrous ions, and / or (ii) electrochemically reducing the solid manganese oxide to one or more aqueous manganese salts in the presence of the aqueous ferrous ions.

16. The method according to any one of claims 13-15, wherein during at least a portion of the dissolving step, the molar ratio of aqueous ferrous ions in the first anolyte to the molar amount of solid manganese oxide in the first anode chamber is at least 0.

9.

17. The method of claim 16, wherein during at least a portion of the dissolving step, the molar ratio of aqueous ferrous ions in the first anolyte to the molar amount of solid manganese oxide in the first anode chamber is at least 2.

18. The method according to any one of claims 13-17, wherein during at least a portion of the dissolving step, the first anolyte includes at least 5 mM of aqueous ferrous ions.

19. The method according to any one of claims 13-18, including the step of providing aqueous ferrous ions to the first anolyte before and / or during the dissolving step.

20. The method according to claim 19, wherein the providing step comprises rinsing the first anode chamber with a solution comprising aqueous ferrous ions.

21. The method according to claim 19 or 20, wherein the providing step comprises directly or indirectly recycling the ferrous-containing electrolyte from the electroplating cell into the first anolyte.

22. The method according to any one of claims 19-21, wherein the providing step comprises electrochemically generating aqueous ferrous ions in the first electrolyte.

23. The method according to any one of claims 13-22, wherein the first anolyte comprises aqueous Mn ions.

24. A method comprising: operating an electrochemical cell, comprising electrochemically reducing at a first cathode and electrochemically oxidizing at a first anode; wherein: the electrochemical cell comprises a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; the first anode is a lead electrode; and the first anolyte and the first catholyte each independently comprise aqueous iron cations and aqueous anions; and wherein the method further comprises: reverse biasing the first anode for a time, comprising electrochemically reducing aqueous ferric ions to aqueous ferrous ions at the first anode in the presence of the first catholyte.

25. The method according to any one of the preceding claims, comprising operating a bipolar stack of electrochemical cells, each electrochemical cell in the stack independently being an electrochemical cell according to any one of the preceding claims.

26. The method according to claim 25, wherein: the bipolar stack comprises one or more bipolar plates; adjacent electrochemical cells share the bipolar plate therebetween; each bipolar plate comprises a first lead electrode as the first anode of the electrochemical cell and a second lead-containing electrode as the first cathode of the adjacent electrochemical cell.

27. A method comprising: operating two or more electrochemical cells, comprising electrochemically reducing at a first cathode and electrochemically oxidizing at a first anode; wherein: each electrochemical cell comprises a first anode chamber having a first anolyte in contact with the first anode, a first cathode chamber having a first catholyte in contact with the first cathode, and a first separator separating the first anolyte from the first catholyte; the first anode is a lead electrode; the first anolyte and the first catholyte each independently comprise aqueous iron cations and aqueous anions; adjacent electrochemical cells share the bipolar plate therebetween; and each bipolar plate comprises a first lead electrode as the first anode of the electrochemical cell and a second lead-containing electrode as the first cathode of the adjacent electrochemical cell.

28. A method comprising: operating a bipolar stack of electrochemical cells, the electrochemical cells of the stack each independently having a first cathode for electrochemically reducing and a first anode for electrochemically oxidizing; wherein: Each electrochemical cell includes a first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte; The first anode is a lead electrode; The first anolyte and the first catholyte each independently include aqueous iron cations and aqueous anions; The bipolar stack includes one or more bipolar plates; Adjacent electrochemical cells share the bipolar plate therebetween; and Each bipolar plate includes a first lead electrode as the first anode of an electrochemical cell and a second lead-containing electrode as the first cathode of an adjacent electrochemical cell.

29. The method according to any one of claims 25-28, wherein each bipolar plate includes a conductive substrate, an anode-facing side, and a cathode-facing side.

30. The method according to claim 29, wherein the conductive substrate is porous or permeable to electrolytes and dissolved ions.

31. The method according to claim 30, wherein each bipolar plate includes a lead coating on at least a portion of the inner surface or pore surface of the porous substrate.

32. The method according to claim 31, wherein the coating has a thickness selected from the range of 50 μm to 5 mm.

33. The method according to claim 29, wherein the conductive substrate is non-porous or impermeable to electrolytes and dissolved ions.

34. The method according to any one of claims 29-33, wherein each bipolar plate includes a first lead layer on the anode-facing side, a second lead layer on the cathode-facing side, or independent lead layers on the anode-facing side and the cathode-facing side.

35. The method according to claim 34, wherein each lead layer is a layer on the substrate.

36. The method according to claim 34 or 35, wherein each lead layer is non-porous or impermeable to electrolytes and dissolved ions.

37. The method according to any one of claims 34-36, wherein each lead layer protects the substrate from exposure to the nearest electrolyte.

38. The method according to any one of claims 34-37, wherein each lead layer independently has a thickness selected from the range of 50 μm to 5 mm.

39. The method according to any one of claims 29-38, wherein the conductive substrate is characterized by a compressive yield strength selected from the range of 10 MPa to 200 MPa and / or a Young's modulus selected from the range of 600 MPa to 1500 MPa.

40. The method according to any one of claims 25-39, wherein the first cathode of each bipolar plate is a carbon cathode or a carbon-containing cathode.

41. The method according to any one of claims 34-40, wherein each bipolar plate includes a first lead layer on the anode-facing side; and wherein the first lead layer is the first anode of the corresponding bipolar plate.

42. The method according to any one of claims 34 - 40, wherein each bipolar plate comprises a lead layer on the anode - facing side; and wherein each bipolar plate further comprises a first anode located on, adhered to, coated on, or otherwise adjacent to the first lead layer.

43. The method according to any one of claims 28 - 42, wherein the bipolar stack comprises a conductive spacer layer or a flow - field layer through which fluid can flow.

44. The method according to any one of the preceding claims, wherein the first anode is a lead electrode, and the lead electrode comprises a microstructured lead - containing surface and / or a nanostructured lead - containing surface in contact with the anolyte.

45. The method according to any one of the preceding claims, wherein the lead electrode is porous and at least partially permeable to the first anolyte.

46. The method according to any one of the preceding claims, wherein the lead electrode is a lead - containing and / or lead - coated felt or foam.

47. The method according to any one of the preceding claims, wherein the first anode has no lead shedding, or is characterized by a lead - shedding rate less than the lead - shedding rate in an equivalent electrochemical cell with the first anolyte without aqueous iron cations under the same conditions.

48. The method according to any one of the preceding claims, wherein the aqueous anions comprise aqueous sulfur - containing anions, aqueous chlorine anions, or both.

49. The method according to claim 48, wherein the aqueous sulfur - containing anions comprise aqueous sulfate ions.

50. The method according to any one of the preceding claims, wherein the first anolyte comprises aqueous lead ions at a concentration of at least 10 ppm.

51. The method according to any one of the preceding claims, wherein the first anolyte comprises aqueous lead ions, and the concentration of the aqueous lead ions is greater than or equal to 10 ppm and less than or equal to the saturation concentration of lead ions in the first anolyte.

52. The method according to any one of the preceding claims, wherein the electrochemical cell further comprises a secondary lead - ion source or a sacrificial lead - ion source in contact with the first anolyte to slow down or prevent the dissolution of Pb from the first anode.

53. The method according to any one of the preceding claims, wherein the step of operating the electrochemical cell comprises: Electrochemically reduce the first Fe at the first cathode 3+ ions to form Fe 2+ ions in the first cathode electrolyte.

54. The method according to any one of the preceding claims, wherein the step of operating the electrochemical cell further comprises: electrochemically oxidizing water at the first anode to produce O2 and hydrated protons in the first anolyte.

55. The method according to any one of the preceding claims, wherein: the operating step comprises that the first anode is characterized by a steady - state anodic potential selected from the range of 1.2 to 3.0 V, The operating steps include that each electrochemical cell is characterized by a current density selected from the range of 5 to 200 mA / cm 2 , and / or The operating steps include that each electrochemical cell is characterized by a bias current density of 5 to 50 mA / cm 2 .

56. The method according to any one of the preceding claims, wherein the electrochemical cell is characterized in that the steady-state current density is selected from the range of 1 to 500 mA / cm 2 .

57. The method according to any one of the preceding claims, comprising adding an injection solution having aqueous iron cations to the first anode chamber and / or the first anolyte.

58. The method according to claim 57, wherein the injection solution comprises aqueous ferrous ions.

59. The method according to claim 57 or 58, wherein the injection solution is an electrolyte from different electrochemical cells or systems.

60. The method according to any one of claims 57-59, wherein the injection solution comprises an electrolyte from a metal electroplating cell or system.

61. The method according to any one of claims 57-60, wherein the injection solution is provided by a separate solution storage tank.

62. The method according to any one of the preceding claims, comprising recycling a second electrolyte from a metal electroplating cell into the first anolyte, the second electrolyte having aqueous iron cations.

63. The method according to claim 62, wherein the second electrolyte comprises aqueous iron cations at a concentration of 0.01 M to 0.5 M.

64. The method according to claim 62 or 63, wherein the second electrolyte comprises a catholyte and / or anolyte from an iron electroplating cell.

65. The method according to claim 64, wherein the catholyte and / or anolyte from the iron electroplating cell are waste catholyte and / or waste anolyte, respectively.

66. The method according to any one of the preceding claims, further comprising: dissolving iron ore in an acid to form an acidic iron salt solution; and providing the acidic iron salt solution to the cathode chamber of the electrochemical cell.

67. The method according to any one of the preceding claims, further comprising: In the presence of a second catholyte, Fe is 2+ ion is electrochemically reduced a second time to Fe metal; wherein the iron electroplating cell comprises the second cathode and the second catholyte.

68. The method according to any one of the preceding claims, wherein the operating step comprises one or more steps of establishing the concentration of aqueous iron cations in the first anolyte within a stable concentration range, and / or the operating step comprises maintaining the concentration of aqueous iron cations in the first anolyte within a stable concentration range; wherein the stable concentration range is selected from the range of 0.01 M to 0.5 M.

69. The method according to claim 68, wherein each establishing step temporarily provides the stable concentration range.

70. The method according to claim 68 or 69, wherein the establishing step is performed at startup of the electrochemical cell and / or before shutdown of the electrochemical cell.

71. The method according to any one of claims 68-70, wherein each of the establishing step and the maintaining step (if present) comprises injecting the aqueous iron cations into the first anolyte.

72. The method according to claim 71, wherein the injecting step is performed as one or more discrete events during the step of operating the cell.

73. The method according to claim 71, wherein the injecting step is performed continuously during the step of operating the cell.

74. The method according to any one of claims 71-74, wherein the injecting step comprises providing a liquid iron source; the liquid iron source is an aqueous solution comprising aqueous iron cations at an injection concentration.

75. The method according to claim 74, wherein the liquid iron source comprises waste anolyte or spent anolyte from a metal electroplating cell or system.

76. The method according to claim 74 or 75, wherein the liquid iron source comprises spent cathode electrolyte or used cathode electrolyte from a metal electroplating cell or system.

77. The method according to any one of claims 74 - 76, wherein the liquid iron source is directly provided to the first anolyte or the first anode chamber having the first anolyte.

78. The method according to any one of claims 74 - 77, wherein the liquid iron source is indirectly provided to the first anolyte or the first anode chamber having the first anolyte.

79. The method according to any one of claims 74 - 78, wherein the liquid iron source is provided to a first anolyte circulation tank in fluid communication with the first anode chamber having the first anolyte, a fluid line entering the first anode chamber, and / or a fluid line leaving the first anode chamber.

80. The method according to any one of claims 74 - 79, wherein the liquid iron source comprises aqueous ferrous ions.

81. The method according to any one of claims 74 - 80, wherein the liquid iron source is iron - containing slag and / or iron - containing leachate from a metal and / or ore processing system.

82. The method according to any one of claims 74 - 81, wherein the injection concentration of aqueous iron cations in the liquid iron source is greater than 0 M and less than 0.5 M.

83. The method according to any one of claims 71 - 82, wherein the injection step comprises providing a solid iron source in the presence of the first anolyte; wherein the solid iron source is at least partially soluble in the first anolyte.

84. The method according to claim 83, wherein the solid iron source is raw ore and / or processed ore.

85. The method according to claim 83 or 84, wherein the solid iron source is heat - treated ore.

86. The method according to any one of claims 84 - 85, wherein the solid iron source comprises solid ferrous ions.

87. The method according to any one of claims 71 - 86, wherein each injection is performed in response to a trigger event; wherein the trigger event comprises: the concentration of aqueous iron cations in the first anolyte drops below the stable concentration range, and / or the current density of the electrochemical cell drops below the normal operable current density.

88. The method according to any one of the preceding claims, wherein the electrochemical reduction at the first cathode is an iron electroplating reaction; and wherein the electrochemical oxidation reaction is an oxygen evolution reaction (OER) at the first anode.

89. The method according to claim 88, wherein the separator is an anion - exchange membrane.

90. The method according to any one of the preceding claims, wherein the first anode does not contain a mixed metal oxide (MMO) material.

91. The method according to any one of the preceding claims, wherein the first anode does not contain Ir, Ru, and Pt.

92. The method according to any one of the preceding claims, wherein the first anode is an undoped lead electrode or a non - alloyed lead electrode.

93. A system for stabilizing a lead anode, the system comprising: an electrochemical cell, which comprises: A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte; Wherein: The first anode is a lead electrode; The first anolyte and the first catholyte each independently comprise an aqueous iron cation and an aqueous anion; and The first anolyte comprises the aqueous iron cation at a concentration selected from the range of 0.01 M to 0.5 M.

94. A system for stabilizing a lead anode, the system comprising: An electrochemical cell, which comprises: A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte; and A metal electroplating cell; and An electrolyte recirculation subsystem for recirculating the electrolyte in the metal electroplating cell into the first anolyte; Wherein: The first anode is a lead electrode; The first anolyte and the first catholyte each independently comprise an aqueous iron cation and an aqueous anion; and The first anolyte comprises the aqueous iron cation at a concentration selected from the range of 0.01 M to 0.5 M.

95. A system for stabilizing a lead anode, the system comprising: An electrochemical cell, which comprises: A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte; Wherein: An oxygen evolution reaction (OER) occurs at the first anode; The first anode is a lead electrode; The first anolyte and the first catholyte each independently comprise an aqueous iron cation and an aqueous anion; and The first anolyte comprises the aqueous iron sulfate at a concentration selected from the range of 0.01 M to 0.5 M.

96. A system, comprising: An electrochemical cell, which comprises: A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte; Wherein: The first anode is a lead electrode; The first anolyte and the first catholyte each independently comprise an aqueous iron cation and an aqueous anion; and The first anolyte comprises aqueous ferrous ions, and the aqueous ferrous ions promote the dissolution of solid manganese oxide present in the first anode chamber in the first anolyte.

97. A system, comprising: An electrochemical cell, which comprises A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte; Wherein: The first anode is a lead electrode; The first anolyte and the first catholyte each independently comprise an aqueous iron cation and an aqueous anion; and The electrochemical cell is configured to reverse bias the first anode for a time to electrochemically reduce aqueous ferric ions to aqueous ferrous ions on the first anode in the presence of the first anolyte.

98. A system comprising: Two or more electrochemical cells, each cell comprising: A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte; and A bipolar plate between two adjacent electrochemical cells such that the adjacent electrochemical cells share the bipolar plate therebetween; Wherein: The first anode is a lead electrode; The first anolyte and the first catholyte each independently comprise an aqueous iron cation and an aqueous anion; and Each bipolar plate comprises a first lead electrode as the first anode of the electrochemical cell and a second electrode containing lead as the first cathode of the adjacent electrochemical cell.

99. A system comprising: A bipolar stack of two or more electrochemical cells, each cell comprising: A first anode chamber having a first anolyte in contact with a first anode, a first cathode chamber having a first catholyte in contact with a first cathode, and a first separator separating the first anolyte from the first catholyte; Wherein: The first anode is a lead electrode; The first anolyte and the first catholyte each independently comprise an aqueous iron cation and an aqueous anion; The bipolar stack comprises one or more bipolar plates; Adjacent electrochemical cells share the bipolar plate therebetween; and Each bipolar plate comprises a first lead electrode as the first anode of the electrochemical cell and a second electrode containing lead as the first cathode of the adjacent electrochemical cell.

100. The system according to claim 98 or 99, wherein the first cathode comprises lead as an underlying or support layer.

101. The system according to claim 100, wherein the first cathode does not include lead in contact with the first catholyte.

102. The system according to claim 100 or 101, wherein the first cathode comprises a carbon electrode in contact with the first catholyte.

103. The method according to claim 1, wherein the first anolyte comprises the aqueous iron cation at a concentration selected from the range of at least 0.01 M to 0.44 M.

104. The method according to claim 2, wherein the first anolyte comprises the aqueous iron cation at a concentration selected from the range of at least 0.01 M to 0.44 M.

105. The method according to claim 3, wherein the first anolyte comprises the aqueous iron cation at a concentration selected from the range of at least 0.01 M to 0.44 M.

106. The system according to claim 93, wherein the first anolyte comprises the aqueous iron cation at a concentration selected from the range of at least 0.01 M to 0.44 M.

107. The system according to claim 94, wherein the first anolyte comprises the aqueous iron cations at a concentration selected from the range of at least 0.01 M to 0.44 M.

108. The system according to claim 95, wherein the first anolyte comprises the aqueous iron cations at a concentration selected from the range of at least 0.01 M to 0.44 M.

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