Electrochemical production of Ca(OH)2 and / or Mg(OH)2 from industrial wastes and Ca / Mg-bearing rocks

Abstract

A method for preparing metal hydroxides from industrial waste or alkaline rocks is provided, the method comprising subjecting a mixture comprising a solvent and a solid substrate to stimulation to leach metal cations from the solid substrate into the solvent, thereby forming a solution comprising the metal cations in the solvent, and contacting the solution comprising the metal cations with a cathode, thereby electrolytically precipitating the metal hydroxides from the solution. The stimulation can be chemical, mechanical, or both.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Application No. 63 / 271,059, filed October 22, 2021, the contents of which are incorporated herein by reference in their entirety.

[0002] Statement regarding government support This invention was made with Government support under Grant No. DE-FE0031705 awarded by the Department of Energy. The Government has certain rights in this invention. [Background technology]

[0003] Ca(OH)2 (portlandite) can be used as a raw material in the carbonation process of concrete as well as a "CO2-free" raw material in conventional silicate cement production. However, the production of portlandite is achieved on an industrial scale by pyrolysis and hydration of limestone, resulting in the production of more than 0.75 tonnes of CO2 per tonne of Ca(OH)2. 1 Similarly, traditional production of brucite (Mg(OH)2) requires the decomposition of MgCO3 into MgO and CO2. Thus, the production of both portlandite and brucite requires large amounts of energy and contributes to large amounts of CO2 emissions. Therefore, there is a need for more energy-efficient processes to produce metal hydroxides such as Ca(OH)2 and Mg(OH)2. Summary of the Invention [Means for solving the problem]

[0004] The present disclosure relates to a method for producing hydroxide solids from solid substrates such as industrial waste or rocks. In some embodiments, the present disclosure provides a method for preparing metal hydroxides, the method comprising: subjecting a mixture comprising the solvent and the solid substrate to a stimulus to leach metal cations from the solid substrate into the solvent, thereby forming a solution comprising the metal cations in the solvent; contacting a solution containing metal cations with a cathode, thereby electrolytically precipitating metal hydroxides from the solution; The stimulus may be a chemical stimulus, a mechanical stimulus, or both.

[0005] In some embodiments, the chemical stimulus is an acid. For example, the acid can be HNO3, HCl, or HClO4, or a combination thereof. In some embodiments, the solvent has a pH of less than 6. In preferred embodiments, the solvent has a pH of about 0 to about 3. In some embodiments, the acid is regenerated by electrolytic precipitation of a metal hydroxide.

[0006] In some embodiments, the mechanical stimulus is sonication. In more specific embodiments, the sonication is applied by a sonic horn, a sonic probe, or a sonic plate. The frequency of the sonication can range from about 2 Hz to about 2 MHz.

[0007] In a preferred embodiment, the solvent is water.

[0008] In some embodiments, the solvent comprises a salt, such as NO3, NaCl, NaClO4, or any combination thereof.

[0009] In some embodiments, the metal cation is a divalent metal cation such as Ba(II), Ca(II), Cd(II), Co(II), Cu(II), Fe(II), Mg(II), Mn(II), Mo(II), Ni(II), Sr(II), Zn(II), Zr(II), or any combination thereof. In more preferred embodiments, the divalent metal cation is Ca(II), Mg(II), or a combination thereof. Preferably, the divalent metal cation is Ca(II).

[0010] In some embodiments, the method further comprises concentrating the solution containing the metal cations, thereby increasing the concentration of the metal cations, hi some embodiments, concentrating the solution is accomplished using reverse osmosis (RO), nanofiltration (NF), electroseparation, or a combination thereof.

[0011] In certain embodiments, the method is carried out at a temperature of about 100° C. or less.

[0012] In some embodiments, the solid substrate comprises industrial waste, alkaline rock, or a combination thereof. In certain embodiments, the industrial waste comprises slag, fly ash, or a combination thereof.

[0013] In some embodiments, the surface comprises a metallic composition, a non-metallic composition, or a hybrid of metallic and non-metallic compositions. More specifically, the electroactive surface comprises stainless steel, titanium oxide, carbon nanotubes, one or more polymers, graphite, or a combination thereof. In a preferred embodiment, the mesh cathode comprises stainless steel.

[0014] In some embodiments, the electroactive surface comprises a mesh that includes pores having diameters ranging from about 0.11 nm to about 10,000 μm.

[0015] In certain embodiments, the cathode is a rotating disk cathode.

[0016] In some embodiments, the method further comprises removing one or more hydroxide solids from the surface of the cathode. In more particular embodiments, removing one or more hydroxide solids from the surface of the cathode comprises scraping the surface of the cathode. In even more particular embodiments, removing one or more hydroxide solids from the surface of the cathode comprises rotating a rotating disk cathode over a scraper. [Brief description of the drawings]

[0017] [Figure 1]Schematic diagram of electrolytic Ca(OH)2 or Mg(OH)2 production from industrial waste and Ca-bearing rocks. Sonic stimulation is used to directly influence and control Ca / Mg extraction with or without acid treatment, and precipitation of Ca(OH)2 and / or Mg(OH)2 can be achieved by reverse osmosis (RO) and / or nanofiltration (NF) and electrolytic processes. [Diagram 2] Figure 1 shows a graph of cathode surface pH versus hydrogen evolution overpotential, demonstrating that preferential surface precipitation of Ca(OH)2 and / or Mg(OH)2 can be achieved. The inset shows Ca(OH)2 crystals precipitated on the cathode (stainless steel mesh) surface upon electrolysis of 100 mM NaNO3 + 100 mM Ca(NO3)2 solution. [Diagram 3] FIG. 2 is a schematic diagram of a multi-chamber electrolysis reactor for producing metal hydroxides (e.g., Ca(OH)2 or Mg(OH)2) according to the proposed scheme in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present disclosure provides methods for producing metal hydroxides, such as calcium hydroxide and magnesium hydroxide, from industrial waste sources and alkaline rocks.

[0019] Industrial alkaline wastes and abundant mineral species are precursors containing large amounts of valuable metallic elements such as alkaline earth metals (e.g., beryllium, magnesium, calcium) and / or transition metals (e.g., cobalt, cadmium, nickel, copper, platinum, gold, silver). However, these precursors rarely contain only one element. For example, steel slag and fly ash may contain significant amounts of calcium, iron, and magnesium. Aqueous solutions leached from these precursors (e.g., steel slag and / or fly ash) may contain several metal and metalloid species in solution. Each species may contain one or more metals that are useful for various applications, and it is desirable to sequentially remove each species in high purity. The present disclosure provides a system and process that combines sonic stimulation, acid dissolution, and optionally membrane filtration to leach metals from precursor solids, followed by an electrolytic precipitation step to obtain metal hydroxides. In some embodiments, the metal hydroxide is a hydroxide such as Ba(II), Ca(II), Cd(II), Co(II), Cu(II), Fe(II), Mg(II), Mn(II), Mo(II), Ni(II), Sr(II), Zn(II), Zr(II), or any combination thereof. In more specific embodiments, the metal hydroxide is a hydroxide of Ca(II), Mg(II), or both. Preferably, the metal hydroxide is calcium hydroxide. The methods disclosed herein advantageously use sonic stimulation in conjunction with acid stimulation of a mixture comprising a solid substrate and a solvent to extract divalent metal cations into solution, followed by electrolysis to precipitate the metal hydroxide from the solution.

[0020] FIG. 1 is a schematic diagram illustrating a process according to a particular embodiment of the invention. An inlet 101 allows the introduction of solvent and solid precursors for stimulated leaching into a leaching tank 102. Sonication can be applied to the leaching tank via a sonication device 105 (sonication probe, plate, horn, etc.). The stimulated leaching tank can be a batch, semi-batch, continuous stirred tank reactor, or plug flow reactor. Leachate from the tank is introduced into a concentration reactor 103, the resulting retentate is fed to an electrolysis tank 104, and the permeate is returned to the leaching tank. Regenerated acid can flow back from the electrolysis tank to the leaching tank 102.

[0021] Then, by alkalizing the Ca and / or Mg-rich solution (e.g., retentate from the RO / NF process), an electrolytic Ca(OH)2 and / or Mg(OH)2 precipitation and production process can be realized. The feasibility of Ca(OH)2 and / or Mg(OH)2 precipitation is demonstrated by simulation of the pH at the cathode surface (shown in Figure 2A). Preliminary electrolysis experiments combined with geochemical simulations indicate that preferential precipitation of Ca(OH)2 and / or Mg(OH)2 is obtained in the high pH region at the surface (i.e., pH > 12.5, Figure 2A and inset). 2

[0022] As shown in FIG. 3, a schematic diagram 300 of an electrolysis reactor is illustrated to conceptualize the formation of Ca(OH)2 and / or Mg(OH)2 in the electrolysis process. The reactor includes an electrolysis reactor tank 301 having a rotating disk / drum-type cathode 307 (e.g., stainless steel surface or mesh) and coupled anode 309 (e.g., Pt-coated titanium, mixed metal oxide) to produce alkali and acid. The rotating disk-type cathode 307 rotates about a shaft 303. The reactor further includes a porous (or semi-porous) partition 308 used to separate the anolyte from the catholyte. The porous partition can include asbestos, cellulose, polyvinyl chloride, organic rubber, polyamide, polyolefin, polyethylene, polypropylene, ion exchange membrane, filtration membrane, and other suitable materials, or combinations thereof. The porous partition separates the catholyte and anolyte to: (1) minimize neutralization reactions between the anolyte and catholyte, resulting in a stable catholyte pH required for Ca(OH)2 precipitation; (2) increase the energy efficiency of the reactor; and (3) facilitate recovery of the gas streams (H2 and O2). H2 outlet 314 and O2 outlet 313 are also shown. The reactor contains catholyte and anolyte, which produce alkalinity and hydrogen, acid and oxygen (and possibly other gases), respectively. The catholyte can be an electrolyte with a negative electrode configured to flow around or through the cathode. The anolyte can be an electrolyte with a positive electrode configured to flow around or through the anode. The cathode may be rotated past or through a scraper 310 (e.g., metal brush, blade, or high-pressure nozzle) to remove Ca(OH)2 / Mg(OH)2, thereby regenerating the cathode for subsequent hydroxide production as the wheel rotates back into the tank. In other embodiments, hydroxide solids may be removed from the catholyte by filtration. The anolyte is then circulated to the leach tank 312 via the anolyte loop 315, and the acid produced is consumed to dissolve the Ca / Mg-containing alkaline precursors and keep the pH neutral. The reactor 300 also includes a thickener 304. The catholyte is circulated to the leachate and thickener via the catholyte loop 305.The leachate from the leach tank is introduced into the thickener via leachate outlet 317, where the permeate returns to the leach tank via permeate outlet 311, while the retentate returns to the reaction tank 305 via retentate outlet 316. The leach tank 312 may further include a sonication device 318 (sonic probe, sonic plate, sonic horn, etc.).

[0023] The energy consumption of the electrolysis process can be estimated based on a state-of-the-art commercial electrolyzer operating at 79% efficiency (i.e., 50 kWh of electricity to produce 1 kg of H, assuming a thermodynamic demand for the stoichiometric hydrogen evolution reaction (HER) of 39.4 kWh / kg). 3 The energy demand of the electrolysis step can vary from a thermodynamic minimum of 1.35 MWh / ton to about 10 MWh / ton, depending on factors such as the concentration of divalent cation(s) in the inflow to the electrolyzer, the applied potential, the pH difference between the anode and cathode, and the faradaic efficiency. Thus, the electrolysis step is the most energy-intensive step of the process. The lowest energy intensity values ​​above produce less CO2 per ton of Ca(OH)2 or Mg(OH)2 than conventional Ca(OH)2 / Mg(OH)2 production from any power source (e.g., coal, natural gas), while the highest energy intensity values ​​produce less CO2 per ton of Ca(OH)2 / Mg(OH)2 than conventional Ca(OH)2 / Mg(OH)2 production from renewable power sources (e.g., wind, solar). Additionally, the process produces 20-40 kg of H2 per tonne of Ca(OH)2 / Mg(OH)2 produced, providing 0.6-1.3 MWh of stored energy.

[0024] The method of the present invention can be advantageously carried out at a relatively low temperature, for example, the temperature can be 100° C. or less, for example, about 20 to about 100° C., about 25 to 100° C., about 30 to 100° C., about 40 to 100° C., about 50 to 100° C., about 60 to 100° C., about 70 to 100° C., about 80 to 100° C., about 90 to 100° C., or any range therebetween.

[0025] In embodiments including a rotating disk cathode, inducing precipitation of hydroxide solids includes rotating a cylinder of electroactive mesh in the solution while applying suction to draw the solution onto the exterior surface of the mesh.

[0026] In various embodiments, the stimulated dissolution reactor applies sonic energy to the mixture, thereby increasing dissolution. Sonic stimulation provides a rapid, low energy, additive-free method compared to traditional grinding and leaching. In various embodiments, the stimulated dissolution reactor performs ultrasonic stimulation. Ultrasonic stimulation is also referred to herein as sonication, sonic stimulation, or ultrasonic perturbation. In various embodiments, the stimulated dissolution reactor performs megasonic stimulation. In various embodiments, calcium and / or other metals are extracted from solid substrates via sonic stimulation at ultrasonic (20-500 kHz) or megasonic (>500 kHz) frequencies in acidic media.

[0027] In a preferred embodiment, the solvent is water. In some embodiments, the chemical stimulus is an acid, such as a mineral acid or an organic acid. In some embodiments, the acid is hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, boric acid, phosphoric acid, nitric acid, perchloric acid, sulfuric acid, acetic acid, acetylsalicylic acid, carbonic acid, citric acid, and combinations thereof. Preferably, the acid is HNO3, HCl, or HClO4, or combinations thereof. In some embodiments, the concentration of the acid in the solvent is up to about 1 mole / L. In some embodiments, the solvent has a pH of less than 6. In a preferred embodiment, the solvent has a pH of about 0 to about 3. In some embodiments, the acid is regenerated by electrolytic precipitation of metal hydroxides.

[0028] In some embodiments, the solvent comprises a salt such as a nitrate, chloride, perchlorate, sulfate, phosphate, bromide, fluoride, borate, acetate, salicylate, carbonate, citrate, or any combination thereof. Preferably, the salt is a nitrate, chloride, perchlorate, or any combination thereof. In a preferred embodiment, the salt is a sodium salt or a potassium salt. More preferably, the salt is a potassium salt.

[0029] In some embodiments, the concentration of the acid in the solvent is up to about 1 mole / L. In various embodiments, the pH of the mixture is less than 7, less than 6, less than 5, or less than 4. In more specific embodiments, the pH is from about 0 to about 3.

[0030] In various embodiments, an ultrasonic stimulus is applied to the stimulus dissolution tank. In some embodiments, the frequency range of the acoustic stimulus is about 10 kHz to about 2 MHz. In various embodiments, the ultrasonic frequency is about 18 kHz to about 2000 kHz. In various embodiments, the ultrasonic stimulus frequency is about 20 kHz to about 40 kHz. In various embodiments, the ultrasonic stimulus frequency is about 800 kHz to about 1200 kHz. In various embodiments, the ultrasonic stimulus frequency is about 18 kHz or more. In various embodiments, the ultrasonic stimulus frequency is about 2000 kHz or less, in various embodiments, the ultrasonic stimulus frequency is about 20 kHz. In various embodiments, the ultrasonic stimulus frequency is about 30 kHz. In various embodiments, the ultrasonic stimulus frequency is about 40 kHz. In various embodiments, the ultrasonic stimulus frequency is about 50 kHz. In various embodiments, the ultrasonic stimulus frequency is about 60 kHz. In various embodiments, the ultrasonic stimulus frequency is about 70 kHz. In various embodiments, the ultrasonic stimulus frequency is about 80 kHz. In various embodiments, the ultrasonic stimulation frequency is about 90 kHz. In various embodiments, the ultrasonic stimulation frequency is about 100 kHz. In various embodiments, the ultrasonic stimulation frequency is about 200 kHz. In various embodiments, the ultrasonic stimulation frequency is about 300 kHz. In various embodiments, the ultrasonic stimulation frequency is about 400 kHz. In various embodiments, the ultrasonic stimulation frequency is about 500 kHz. In various embodiments, the ultrasonic stimulation frequency is about 600 kHz. In various embodiments, the ultrasonic stimulation frequency is about 700 kHz. In various embodiments, the ultrasonic stimulation frequency is about 800 kHz. In various embodiments, the ultrasonic stimulation frequency is about 900 kHz. In various embodiments, the ultrasonic stimulation frequency is about 1000 kHz (1 MHz). In various embodiments, the ultrasonic stimulation frequency is about 1100 kHz (1.1 MHz). In various embodiments, the ultrasonic stimulation frequency is about 1200 kHz (1.2 MHz). In various embodiments, the ultrasonic stimulation frequency is about 1300 kHz (1.3 MHz). In various embodiments, the ultrasonic stimulation frequency is about 1400 kHz (1.4 MHz).In various embodiments, the ultrasonic stimulation frequency is about 1500 kHz (1.5 MHz). In various embodiments, the ultrasonic stimulation frequency is about 1600 kHz (1.6 MHz). In various embodiments, the ultrasonic stimulation frequency is about 1700 kHz (1.7 MHz). In various embodiments, the ultrasonic stimulation frequency is about 1800 kHz (1.8 MHz). In various embodiments, the ultrasonic stimulation frequency is about 1900 kHz (1.9 MHz). In various embodiments, the ultrasonic stimulation frequency is about 2000 kHz (2 MHz).

[0031] In various embodiments, the ultrasonic stimulation is provided by a sonic probe at least partially immersed in the solvent-substrate mixture. In various embodiments, the ultrasonic stimulation is provided by one or more ultrasonic plates in contact with the leaching tank. In yet another embodiment, the ultrasonic stimulation is provided by both a sonic (e.g., ultrasonic) probe and a sonic (e.g., ultrasonic) plate. In various embodiments, the sonic probe causes agitation of the solvent by rapid movement of the probe. In various embodiments, the solvent-substrate mixture may be stirred, mixed, or blended in the leaching tank to ensure complete mixing of the solvent. In various embodiments, the solid substrate to be leached contains other elements (e.g., non-target substances) that are less soluble, so that a portion of the solid substrate remains undissolved and may be removed as spent solids.

[0032] In some embodiments, the solid substrate is an industrial waste or by-product obtained from metal processing and fuel combustion (e.g., coal fly ash), among other sources that are typically enriched in Ca and Mg. In some embodiments, Ca is extracted from slag, fly ash, or other alkaline solids by dissolving or exposing them to water or other aqueous leach solutions at ambient or moderately elevated temperatures and ambient pressure, with or without certain leaching aids. 2+ and Mg 2+is extracted. Slag, a by-product from metal production, includes slags from iron production (e.g., air-cooled blast furnace (BF) slag) and steel production (electric arc furnace (EAF) slag and basic oxygen furnace (BOF) slag), and is typically composed of Ca and Mg oxides, silicates, and silicon dioxide. Vitreous slags are used as a substitute for ordinary Portland cement (OPC), while crystalline slags are currently used in limited applications as low-value aggregates. Such crystalline slags are abundant and contain high amounts of Ca and Mg. Fly ash is a coal combustion by-product that also contains high concentrations of Ca, including that sourced from historical reservoirs (e.g., landfills and ash ponds). To increase the rate of leaching, one or more metal leaching agents (e.g., acetates, ethylenediaminetetraacetic acid (EDTA), etc.) and / or one or more acids (e.g., acetic acid, hydrochloric acid, etc.) can be added to the leaching solution. The slag may also be crushed or pulverized to finer particle sizes to increase the extraction rate of the light metals.

[0033] The solid in some embodiments is fly ash. Fly ash (also called flue ash, coal ash, or pulverized fuel ash) is a coal combustion product that includes particulate matter (fine particles of burned fuel) that is exhausted with flue gas from a coal-fired boiler. The ash that falls to the bottom of the boiler's combustion chamber (commonly called the firebox) is called bottom ash. In modern coal-fired power plants, the fly ash is usually captured by an electrostatic precipitator or other particulate filtering device before the flue gas reaches the chimney. Together with the bottom ash that is removed from the bottom of the boiler, it is known as coal ash.

[0034] Although the composition of fly ash varies significantly depending on the source and composition of the coal being burned, all fly ashes contain significant amounts of silicon dioxide (SiO2) (both amorphous and crystalline), aluminum oxide (Al2O3), and calcium oxide (CaO), which are the major mineral compounds in coal-bearing rock formations.

[0035] In another embodiment, the solid is an alkaline rock. Alkaline rocks are generally considered to contain more alkali than can be accommodated by feldspar alone. The excess alkali thus appears as feldspars, sodium pyroxene / amphibole, or other alkali-rich phases. Alkaline rocks are deficient in SiO2 to the extent that they are highly undersaturated with SiO2, nepheline, or acmite (Na clinopyroxene) relative to NaO, KO, and CaO.

[0036] In various embodiments, larger solid substrates may be comminuted by first grinding, crushing, or pulverizing the substrate to a particle size of about 10 mm or less, 5 mm or less, 1 mm or less, 0.5 mm or less, or 0.1 mm or less prior to leaching. In various embodiments, the particles may be about 100 μm or greater. In various embodiments, the particles may have an average diameter of about 500 nm to 5 mm, about 100 μm to about 5 mm, about 500 μm to about 5 mm, or about 500 μm to about 3 mm.

[0037] In various embodiments, the dissolution tank may be operated as a continuous flow reactor. In various embodiments, the dissolution tank may be operated as a batch reactor.

[0038] In some embodiments, the solution containing metal cations is concentrated prior to the electrolysis step. In various embodiments, the concentrator performs nanofiltration and / or reverse osmosis. In various embodiments, the membrane concentrator performs filtration. In various embodiments, the membrane concentrator may perform filtration to filter particles larger than a certain size (e.g., diameter). In various embodiments, the membrane concentrator selectively filters multivalent ions and passes monovalent ions. In other embodiments, the nanofiltration is based on ionic charge. In yet other embodiments, the nanofiltration is based on both ionic size and ionic charge. In various embodiments, the membrane concentrator outputs a concentrated retentate stream of ionic species (e.g., a concentrated divalent cation stream).

[0039] In various embodiments, the anolyte from the electrolysis process is returned to the leach tank.

[0040] In an electrolysis system, reduction occurs at the cathode and oxidation occurs at the anode. The anodic reaction (2H2O → 4H++O2) has the advantage of generating sufficient acidity in the dissolution tank for elemental extraction. At the cathode, reduction of water (2H2O → H2 + 2OH-) occurs, releasing alkali and raising the pH. In various implementations, metal hydroxides precipitate when the pH exceeds a certain value. In various embodiments, CaOH2 is preferentially produced when the pH at the cathode surface exceeds about 12 (see Figure 2).

[0041] The terms "approximately," "about," "substantially," and similar terms will be understood by those of ordinary skill in the art and will vary to some extent based on the context in which they are used. If there is a use of a term that is not clear to a person of ordinary skill in the art, the term will be plus or minus 10% of the disclosed value, taking into account the context in which the term is used. When "approximately," "about," "substantially," and similar terms are applied to structural features (e.g., to describe their shape, size, orientation, direction, etc.), these terms are meant to include slight variations in the structure that may result, for example, from the manufacturing or assembly process, and are intended to have a broad meaning consistent with common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. Thus, these terms should be interpreted as indicating that slight or insignificant modifications or variations of the described and claimed subject matter are considered to be within the scope of the disclosure as set forth in the appended claims.

[0042] The use of the terms "a" and "an" and "the" and similar referents in the context of describing elements (particularly in the context of the claims below) should be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The recitation of ranges of values ​​herein is intended merely to serve as a shorthand method of individually referring to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated herein as if it were individually recited herein. All methods described herein may be performed in any suitable order, unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples or illustrative language (e.g., "such as") presented herein is intended merely to facilitate a better understanding of the embodiments and does not limit the scope of the claims, unless otherwise indicated. No language in this specification should be construed as indicating any non-claimed element as essential.

[0043] As used herein, the term "comprising" is intended to mean that the compounds, compositions, and methods include the indicated elements, but do not exclude other elements. "Consisting essentially of," when used to define compounds, compositions, and methods, means excluding other elements that are of essential importance to the combination. Thus, a composition consisting essentially of the elements defined herein does not exclude trace contaminants from, for example, isolation and purification methods, as well as pharma- ceutically acceptable carriers, preservatives, and the like. "Consisting of" means excluding trace elements or more of the other components. Embodiments defined by each of these transitional terms are within the scope of the present technology.

[0044] The embodiments illustratively described herein may be suitably implemented in the absence of any element(s), limitation(s) not specifically disclosed herein. Thus, for example, terms such as "comprising", "including", "containing" and the like are intended to be interpreted broadly without limitation. Furthermore, the terms and expressions employed herein are used as terms of description rather than limitation, and the use of such terms and expressions is not intended to exclude the features shown and described or equivalents of portions thereof, but is recognized to be capable of various modifications within the scope of the claimed technology. Furthermore, the term "consisting essentially of" is understood to include the specifically described elements and additional elements that do not materially affect the basic and novel characteristics of the claimed technology. The term "consisting of" is intended to exclude any elements not specified. EXAMPLES

[0045] Example 1: Scheme (Figure 1) describes a process without or with additives (i.e., acids and bases) where acoustic stimulation is used to directly influence and control the precursor leaching process. Acoustic stimulation can be applied by ultrasonic horn or ultrasonic plate with stimulation frequencies between 10 kHz and 2 MHz. The acoustic stimulation device can be operated in semi-batch, continuously stirred tank (CSTR), or plug flow (PFR) reactors, where acoustic stimulation is applied in situ by a submerged sonotrode or through the reactor wall(s) by external sonotrode(s). The estimated energy requirement (i.e., W in Figure 1) of such a stimulated leaching process is L ) is about 10 kWh per tonne of Ca(OH)2 and / or Mg(OH)2 produced. To increase the electrical conductivity of the leachate, salts such as NaNO3, NaCl, NaClO4 can be added during the leaching process. The leachate is then 2+ / Mg 2+To increase the concentration, it is sent to a thickening reactor utilizing, but not limited to, reverse osmosis (RO) and / or nanofiltration (NF). Experimental data has demonstrated that the energy consumption of the thickening reactor is approximately 40-80 kWh per ton of Ca(OH)2 / Mg(OH)2 produced.

[0046] While particular embodiments have been illustrated and described, it is to be understood that changes and modifications may be made in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims.

[0047] The present disclosure is not limited to the specific embodiments described in this application. Many modifications and variations can be made without departing from the spirit and scope thereof, as will be apparent to those skilled in the art. Functionally equivalent methods and compositions falling within the scope of the present disclosure, as well as those enumerated herein, will be apparent to those skilled in the art from the above description. Such modifications and variations are intended to be included within the scope of the appended claims. Accordingly, the present disclosure is limited only by the appended claims, in addition to the full scope of equivalents to which the appended claims are entitled. It is to be understood that the present disclosure is not limited to specific methods, reagents, compounds, compositions, or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0048] It will be understood by those skilled in the art that for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges. Any range described fully represents and can be readily recognized as being capable of dividing the same range into at least one half, one third, one quarter, one fifth, one tenth, etc. As a non-limiting example, each range described herein can be readily categorized into a lower third, a middle third, an upper third, etc. As will be understood by those skilled in the art, all words such as "up to," "at least," "greater than," "less than," etc. refer to ranges that include the recited numbers and can then be subdivided into subranges as described above. Finally, it will be understood by those skilled in the art that a range includes each individual member. References [1]Environmental Protection Agency.Technical Support Document for the Lime Manufacturing Sector;2015. [2]Parkhurst,DL;Appelo,CAJDescription of Input and Examples for PHREEQC Version3--AComputer Program for Speciation,Batch-Reaction,One-Dimensional Transport,and Inverse Geochemical Calculations,2013. [3] Ivy, J. Summary of Electrolytic Hydrogen Production: Milestone Completion Report; National Renewable Energy Lab., Golden, CO(US), 2004. [4]Portland Cement Association Labor-Energy Input Survey.https: / / www.cement.org / docs / default-source / market-economics-pdfs / more-reports / labor-energy-sample-2.pdf(accessed2021-09-03).

[0049] Other embodiments are set forth in the following claims.

[0050] Incorporation by Reference All publications and patents mentioned herein are herein incorporated by reference in their entirety as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. In case of conflict, the present application, including definitions herein, will control.

Claims

1. 1. A method for preparing a metal hydroxide, said method comprising: subjecting a mixture comprising a solvent and a solid substrate to a stimulus to leach at least one target metal cation from the solid substrate into the solvent, thereby forming a solution comprising the metal cation in the solvent; concentrating the solution containing the target metal cations by contacting the solution with a reverse osmosis or nanofiltration membrane; contacting the solution containing the target metal cations with cathode-produced alkalinity, thereby electrolytically precipitating the metal hydroxides from the solution; The method, wherein the stimulus is a chemical stimulus, a mechanical stimulus, or both.

2. The method of claim 1 , wherein the chemical stimulus is an acid.

3. 3. The method of claim 2, wherein the acid comprises hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, boric acid, phosphoric acid, nitric acid, perchloric acid, sulfuric acid, acetic acid, acetylsalicylic acid, carbonic acid, citric acid, and combinations thereof, preferably hydrochloric acid, nitric acid, perchloric acid, or any combination thereof.

4. 4. The method of claim 2 or 3, wherein the solvent has a pH of less than 6.

5. The method of claim 4, wherein the solvent has a pH of from 0 to about 3.

6. 4. The method of claim 2, wherein the acid is regenerated by electrolytic precipitation of the metal hydroxide.

7. The method according to any one of claims 1 to 3, wherein the mechanical stimulus is sonication.

8. 8. The method of claim 7, wherein the frequency range of the sonication ranges from about 2 Hz to about 2 MHz.

9. The method according to any one of claims 1 to 3, wherein the solvent is water.

10. The method of any one of claims 1 to 3, wherein the solvent comprises a salt.

11. 11. The method of claim 10, wherein the salt comprises a nitrate, chloride, perchlorate, sulfate, phosphate, bromide, fluoride, borate, acetate, salicylate, carbonate, citrate, or any combination thereof.

12. 4. The method of claim 1, wherein the precipitated metal hydroxide is a divalent metal hydroxide.

13. 13. The method of claim 12, wherein the divalent metal cation is Ba(II), Ca(II), Cd(II), Co(II), Cu(II), Fe(II), Mg(II), Mn(II), Mo(II), Ni(II), Sr(II), Zn(II), Zr(II), or any combination thereof.

14. The method of any one of claims 1 to 3, further comprising concentrating the solution containing the metal cations, thereby increasing the concentration of the metal cations in the solution.

15. 15. The method of claim 14, wherein concentrating the solution is accomplished by using reverse osmosis (RO), nanofiltration (NF), or electroseparation.

16. The method of any one of claims 1 to 3, wherein the method is carried out at a temperature of about 100°C or less.

17. The method of any one of claims 1 to 3, wherein the solid substrate comprises industrial waste, alkaline rock, or a combination thereof.

18. The method of any one of claims 1 to 3, wherein the cathode comprises an electroactive surface.

19. 20. The method of claim 18, wherein the electroactive surface comprises stainless steel, titanium oxide, carbon nanotubes, one or more polymers, graphite, or a combination thereof.

20. 20. The method of claim 18, wherein the electroactive surface comprises an electroactive mesh comprising pores having diameters ranging from about 0.1 nm to about 10,000 μm.

21. The method according to any one of claims 1 to 3, wherein the cathode is a rotating disk cathode.

22. The method of any one of claims 1 to 3, further comprising removing one or more hydroxide solids from the surface of the cathode.

23. 23. The method of claim 22, wherein removing the one or more hydroxide solids from the surface of the cathode comprises scraping the surface of the cathode or rotating the spinning disk cathode over a scraper.

24. A system for preparing a metal hydroxide, comprising: a leaching tank including a stimulus, the leaching tank configured to leach at least one metal cation from a solid substrate; a thickener coupled to an outlet of the leaching tank, the thickener configured to concentrate the solution; and an electrolytic reactor tank coupled to the outlet of the leaching tank, the electrolytic reactor tank comprises an anode and a cathode; an electrolytic reactor tank, the electrolytic reactor tank configured to electrolytically precipitate at least one metal hydroxide.

25. The system of claim 24, wherein the stimulus is sonication and / or acid.

26. The system of claim 24, wherein the concentrator comprises a nanofiltration membrane or a reverse osmosis membrane.

27. ​​A system described in any one of claims 24 to 26, wherein the solid substrate comprises industrial waste, alkaline rock, or a combination thereof.

28. The system described in claim 27, wherein the industrial waste includes slag, fly ash, or a combination thereof.

29. A system described in any one of claims 24 to 26, wherein the cathode has an electroactive surface comprising stainless steel, titanium oxide, carbon nanotubes, one or more polymers, graphite, or a combination thereof.

30. The system described in claim 29, wherein the electroactive surface comprises an electroactive mesh containing pores having diameters in the range of about 0.1 nm to about 10,000 μm.

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