Anodic Dissolution System for Nickel and Cobalt Metals
Patent Information
- Authority / Receiving Office
- MX · MX
- Patent Type
- Patents
- Current Assignee / Owner
- AQUA METALS INC
- Filing Date
- 2025-07-14
- Publication Date
- 2026-06-12
Abstract
Description
ANODIC DISSOLUTION SYSTEM FOR NICKEL AND COBALT METALS
[0001] This application claims priority to our US Provisional Patent Application with the serial number 63 / 438,699, which was filed 1 / 12 / 2023, and which is incorporated by reference herein in its entirety.Field of the Invention
[0002] The field of the invention is the electrochemical anodic dissolution of valuable metals, and especially as it relates to anodic dissolution of recycled nickel and cobalt metals in sulfuric and other acids in producing their corresponding metal salts for use as battery grade materials in the manufacture of lithium ion and other types of batteries.Background of the Invention
[0003] The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0004] All publications and patent applications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0005] Nickel and cobalt metals are now being recovered and recycled from lithium ion and other battery types. These metals are valuable and are typically recovered by electroplating or electrowinning and come in the form of metallic plates, metal pieces, or as powders. These metals can then be converted into the corresponding battery grade metal salts, which may then be precipitated or suitably processed in the proper atomic ratios and compositions to form the cathode materials suitable for re-use in manufacturing new lithium ion and other types of batteries.
[0006] Nickel and cobalt metals are highly soluble in nitric acid as well as hydrochloric acid under the proper acid concentrations and temperature conditions and will readily form thecorresponding nitrate and chloride salts. The use of nickel and cobalt sulfate salts in the preparation of the cathode materials in lithium ion batteries have some advantages over the nitrate and chloride salts in the subsequent recycling and recovery of the byproduct sulfate salts. Unfortunately, both nickel and cobalt metals have a very slow chemical dissolution rate in sulfuric acid, even at high concentrations of sulfuric acid and at high temperatures. Such slow dissolution is attributed to the poor dissolution properties of a surface passivation (oxide) layer that is formed on these metals. The rate of the dissolution can be accelerated to at least some degree by addition of an oxidation agent (e.g., hydrogen peroxide) or other additives to the sulfuric acid, but this renders such process significantly less attractive economically. In addition, some of these additives, such as chlorides, thiosulfates, or organics also can leave trace chemical components or contaminants in the metal salt solutions which may be detrimental to the performance in the end applications for these salts such as in the manufacture of new lithium ion batteries.
[0007] Alternative methods have also been investigated, including electrochemical methods in the anodic dissolution of these metals to the corresponding acid salts. However, all or almost all of the known electrochemical dissolution methods have various drawbacks and are in need of improvement. For example, Venkateswaran etal. (Bulletin of Electrochemistry 8(10), 1992, pp 504-506) reported the electrochemical anodic dissolution of nickel in sulfuric acid using a 1 liter beaker with a centrally located nickel anode and two stainless steel cathodes in a sulfuric acid solution with no membrane or separator divider between the nickel anode and stainless steel cathodes. In that approach it was found that the current efficiency (CE) of the anodic dissolution of nickel in 0.1 M sulfuric acid solution decreased from 100% at a current density (CD) of 25 A / m2to about 20% in a current range of 200 A / m2to 400 A / m2. It was also found that at an operating current density of 400 A / m2, the anodic dissolution current efficiency increased with increasing sulfuric acid concentration, from about 20% CE at 0.6 M H2SO4 to about 70% CE in 1.0 M H2SO4. In addition, it was found that increasing the solution temperature to 60 °C to 80 °C increased the CE to about 90-95% in a 0.1 M H2SO4 concentration solution, and that a small addition of sodium chloride, 0.1-0.2 g / L in a 0.1 M H2SO4 solution at a CD of 400 A / m2had a CE of about 100%. They did not report any details on the electrolytic plating of nickel onto the stainless steel cathode during the tests.
[0008] In another approach, Deo et al. (Journal of Applied Electrochemistry Vol.6, pp 37-43 (1976)) investigated the effect of alternating or square wave current on the current efficiencyof electrochemical nickel dissolution in sulfuric acid. Using an alternating current (AC) sine wave of 50 cycles per sec (cps), they found that the dissolution efficiency increased with an increase in the concentration of sulfuric acid. For an applied square wave current, the current efficiency decreased with an increase of current density, but the efficiency increased with the applied square wave frequency. For the applied sine wave results, the sulfuric acid concentration was varied from 1-12 N, the current efficiency increased from 85 to 94% with increasing sulfuric acid concentration. The experiments were carried out in a Perspex (acrylic plastic) cell using electrolytic nickel plates having an electrode spacing of 1.5 cm with no separator between the electrodes.
[0009] In still another approach, Li et al. (Ultrasonics - Sonochemistry 40 (2018) 1021-1030) investigated how ultrasound could augment the leaching of nickel blocks into nickel sulfate in sulfuric acid and hydrogen peroxide. In their testing, conventional nickel leaching would have a leaching rate of 46.29% in 5 hours. Using ultrasound, the authors achieved a leaching rate of 40% in about half the time. In an optimized set-up using ultrasound, the nickel leaching rate reached 60.41% using a sulfuric acid concentration of 30%, a hydrogen peroxide concentration of 10%, a leaching temperature of333 K (59.9 °C), an ultrasonic power of200 W, and leaching time of 4 hours.
[0010] In yet a further approach, as described in US Patent 8,177,956, Micyus et al., nickel was electrolytically dissolved into an electroless nickel plating solution to replenish the nickel in the bath. Here, the concentration of nickel ions in a working electroless nickel bath was maintained by means of electrolytic dissolution of nickel from a nickel anode immersed in the bath, with current being supplied to the anode via a counter electrode that consisted of a lead, platinized titanium or iridium / tantalum oxide coated cathode, where the cathode was separated from the working bath using a (perfluorinated) cation ion exchange membrane, and where the catholyte consisted of sulphuric, phosphoric, phosphorous or hypophosphorous acids or salts. As the nickel was dissolved in the bath, the pH of the plating solution increased, requiring the addition of acid. The nickel anode comprised of nickel S-rounds in a titanium basket and the system preferably operates at about a current density of 30-40 A / ft2.
[0011] Chinese Patent Application CN 107675199 A, Guo et al., disclosed an electrolysis technique that yielded nickel sulfate. A metal nickel plate was used as the anode material and a nickel plate, graphite plate, or titanium plate as the cathode. The pH was 0.5-5.0 and the nickel sulfate anolyte solution was 50 to 120 g / L, and the catholyte was 0.5-5 moles / L sulfuricacid. The tests were performed at a current density of 150-300 A / m2, and at temperatures of 20-100 °C while a diaphragm bag separated the anolyte from the catholyte. Guo et al. discussed that their technique was simple, compared to a chemical method, and that their electrolyzing rate may be up to 30% (presumably current efficiency), with a nickel power consumption as low as 600 kWh / ton [= 0.6 kWh / kg Ni],
[0012] Canadian Patent CA 1193827 A, Devuyst et al., teach a process where cobalt salts were produced by dissolving cobalt metal in hydrochloric acid containing a small amount of thiosulfate ions. Here, the inventors described a process that could be operated to obtain a high strength and purity cobalt chloride solution and that would be suitable for the production in a manner known per se of pure cobalt salts, which may be obtained with a sulfur content of less than 0.05% by weight.
[0013] European Patent Application EP 3967661, Lantto et al. described a chemical process for preparing battery grade metal sulphate solutions employing a leaching solution comprising at least one acid leaching agent and a liquid oxidizing agent in a continuous process at elevated temperatures in a leaching column or reaction vessel. Examples of acid leaching solution included sulfuric acid and oxidizing agents selected from a list including hydrogen peroxide, halogen compounds, citric acid, and oxalic acid.
[0014] US Patent 1,936,829, Corson described a process of making nickel sulphate using sulfuric acid at elevated temperatures and in the presence of oxygen.
[0015] Bilczuk et al. (The Canadian J. of Chemical Engineering, Vol. 9999, pp. 1-8 92016)) did a kinetic study of the chemical dissolution of metallic nickel particles in sulfuric acid solutions investigating temperature, sulfuric acid concentration, and the effect of different types of oxidants on the dissolution rate. They measured the reaction rate with the addition of dissolved oxygen, ferric sulphate, and hydrogen peroxide as oxidants.
[0016] While most of these known processes can provide metal salt solutions and metals salts, various disadvantages nevertheless remain. Among other drawbacks, the currently known processes will include contaminants that require their removal, require relatively expensive equipment, have low current efficiency, and / or have limited utility when scaled up for production of industrially meaningful quantities of metal salts, especially where such salts and salt solutions must have a high purity such as 99.0 wt% purity.Summary of The Invention
[0017] The inventive subject matter is directed to various improved systems and methods of dissolution of nickel and cobalt metal which are, for example, recovered from disused or spent lithium ion and other battery types, into the corresponding metal salts, such as metal sulfates when using sulfuric acid or metal acetates when using acetic acid. The processes presented herein produce high purity metal salts and do not add any potential contaminants to the dissolution end product, making them suitable in making battery grade materials. Most typically, the metal salts produced by the methods presented herein will have a purity of at least 99.0 wt%, or at least at least 99.5 wt%, or at least at least 99.8 wt% purity. These salts or their solutions, such as Ni or Co metal sulfates, can then be advantageously used in producing the metal oxide materials used in the fabrication of the various types of lithium-ion batteries.
[0018] In preferred embodiments, the process utilizes a two compartment design using an anion exchange membrane as a separator. The use of a membrane separator helps to safely separate the hydrogen produced in the cathode compartment from any oxygen produced in the anode compartment. The anion exchange membrane also blocks 85% to 99% (or even higher) the transport of the cation metal ions into the cathode compartment. Trace metal impurities in fact are collected on the cathode during the anodic dissolution operation. Moreover, the process according to the inventive subject matter is energy efficient in the amount of electrical energy, kWh, used in the dissolution of the metals, and requires only electricity and no other chemical additives that could potentially contaminate the metal salt end products. Surprisingly, the current efficiencies of the anode dissolution process were found to be 100% for cobalt in sulfuric acid and acetic acid at current densities of up to 800 A / m2in acetic acid and up to 4,000 A / m2in sulfuric acid. For nickel, the current efficiencies were near 100% at current densities up to about 1,500 A / cm2. Advantageously, the incorporation of a membrane distillation unit in contemplated systems will help concentrate the metal salt solution in addition to providing high purity recycle water back into the anode dissolution process.
[0019] In this context, it should be appreciated that chemical dissolution of nickel in sulfuric acid is very slow, and that the chemical reaction produces hydrogen as a byproduct as follows:
[0021] Moreover, the inventors contemplate that when hydrogen peroxide is used as an oxidant to increase the dissolution of nickel in sulfuric acid, the reaction is thought to occur intwo steps. The first step is the surface oxidation of the nickel to nickel oxide by hydrogen peroxide as follows:
[0023] The reaction is then followed by the dissolution of the NiO to nickel sulfate as follows:
[0025] The overall combined reaction is as follows:
[0027] However, it should be recognized that peroxymonosulfuric acid, H2SO5, or peroxydisulfuric acid, H2S2O8, may be formed as the intermediate active oxidizer(s) from the reaction of hydrogen peroxide and sulfuric acid that actively dissolves the nickel in the sulfuric acid solution.
[0028] Moreover, it should be appreciated that the amount of hydrogen peroxide used in the nickel dissolving solution needs to be in excess of the 1 : 1 molar ratio in reaction (2) because of the limited chemical stability of hydrogen peroxide in the system, especially if the reaction is conducted at temperatures greater than 50 °C. In typical embodiments, the molar ratio of hydrogen peroxide to nickel will be at least a 2: 1 molar ratio. Advantageously, the only byproduct of a hydrogen peroxide decomposition reaction is oxygen as follows:
[0030] In one aspect of the inventive subject matter, it should be recognized that the use of DC electrical power in the dissolution of nickel and cobalt as presented herein can result in a significant process cost savings as compared to the use of hydrogen peroxide in sulfuric acid. As an example, if a 2: 1 molar ratio of hydrogen peroxide to nickel is required to dissolve 1 kg of nickel in sulfuric acid, then the required amount of hydrogen peroxide needed would be about 1.160 kg (100% H2O2 basis). The calculated cost of the hydrogen peroxide, at a delivered price of about $5.8 / kg in the United States in 2022, would cost about $6.73 of ftCh / kg of dissolved nickel. In comparison, at an electrical cost of $0.05 / kWh, and using a power consumption number of 4 kWh / kg nickel, as shown in more detail below (see e.g., FIG. 6), the power cost for the dissolution would be only about $0.20 / kg of nickel dissolved, resulting in a cost more than 33.65 times less than the peroxide route.
[0031] In still another embodiment, magnets may be employed to magnetically hold or align the nickel and cobalt metal strips in place in the anodic dissolution system, and even hold them to the electrical connections to the DC power supply. Alternatively, magnets may be used to capture or hold small undissolved particles in the anode solution, so they can be further collected, dissolved, or removed from the acid solutions. The magnets would be encased in plastic material or film for protection from the acid solutions. These can be placed inside the anode compartment in various positions or locations as needed. In another embodiment, the hydrogen generated in the cathode compartment of the can be captured and used for another application.
[0032] In yet another embodiment, it is contemplated that the temperature of the anode side compartment may be higher than that of the cathode side compartment, which advantageously will allow for less heat energy required for the anodic dissolution process. For example, the anode compartment may be operated at 60 °C, and the cathode compartment may be operated with no heat addition, such as at room temperature (e.g., 18-25 °C).
[0033] In an additional embodiment, the applied current during anodic dissolution may be varied as needed, especially near the exhaustion point of the residual free acid so that the applied voltage potential can be lowered as the solution conductivity is decreasing.
[0034] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components. In addition, discussions using examples using nickel can also be applicable to cobalt.Brief Description of The Drawings
[0035] FIG. 1 is an exemplary schematic of a two compartment anodic dissolution system used in evaluating the electrolytic dissolution of nickel and / or cobalt into their corresponding salts in sulfuric acid and acetic acid.
[0036] FIG. 2 is an exemplary and simplified schematic of a two compartment anodic dissolution system utilizing an anode basket to help in the dissolution of smaller pieces of nickel or cobalt metal in sulfuric acid and acetic acid.
[0037] FIG. 3 is an exemplary schematic for a two compartment anodic dissolution system showing an example of a system with multiple anodic dissolution cells.
[0038] FIG. 4 is a table showing exemplary experimental data in the anodic dissolution of nickel in sulfuric acid at various temperatures.
[0039] FIG. 5 is a graph showing exemplary current efficiency in the anodic dissolution of nickel in sulfuric acid versus current density and temperature.
[0040] FIG. 6 is a graph showing exemplary power consumption of nickel dissolution in sulfuric acid as kWh / kg nickel versus current density and temperature.
[0041] FIG. 7 is a table showing exemplary tabulated experimental results in the anodic dissolution of cobalt in sulfuric acid.
[0042] FIG. 8 is a graph showing exemplary current efficiency in the anodic dissolution of cobalt in sulfuric acid as a function of current density and temperature.
[0043] FIG. 9 is a graph showing exemplary power consumption in anodic dissolution of cobalt as kWh / kg cobalt in sulfuric acid as a function of current density and temperature.
[0044] FIG. 10 is a table showing exemplary tabulated experimental results in the anodic dissolution of cobalt in acetic acid.
[0045] FIG. 11 is a graph showing exemplary current efficiency of the anodic dissolution of cobalt in acetic acid as a function of current density and temperature.
[0046] FIG. 12 is a graph showing exemplary power consumption of nickel dissolution as kWh / kg cobalt in acetic acid versus current density and temperature.
[0047] FIG. 13 is an exemplary schematic diagram of a membrane distillation system for removing water from a cobalt sulfate solution.
[0048] FIG. 14 is a table showing exemplary tabulated results from membrane distillation to concentrate a cobalt sulfate solution.
[0049] FIG. 15 is an exemplary schematic diagram incorporating membrane distillation in an anodic dissolution of cobalt or nickel system.Detailed Description
[0050] Disclosed herein is an improved and efficient method for the electrochemical anodic dissolution of valuable metals, such as nickel and cobalt, into their corresponding metal salts in acid solutions to produce battery grade materials. Nickel and cobalt are among the most expensive metals used in the construction of lithium ion and other similar types of batteries. These materials can be obtained from used, defective, or non-functioning batteries and are being recycled, processed, and recovered as metal compounds in many conventional processes. Typically, the so recovered metals are converted into salts, such as sulfates, allowing them to be converted into mixed metal oxide components, containing lithium, nickel, cobalt, and manganese that are commonly used as the cathode materials in the construction of new lithium ion based batteries.
[0051] Unfortunately, nickel and cobalt metals are particularly difficult to dissolve in nonoxidizing acids, such as sulfuric acid, without the addition of chemical oxidizers such as hydrogen peroxide or oxygen, due to their protective oxide film surfaces. The slow dissolution reaction of nickel in sulfuric acid is as follows:
[0053] For cobalt, the slow dissolution in sulfuric acid reaction is as follows:
[0055] In contrast, the electrochemical anodic dissolution system presented herein allows for the rapid and efficient recycling and direct conversion of these recovered battery metals into nickel and cobalt salts of the acid they are being dissolved into with little or no byproduct hydrogen formation. Oxygen formation may occur as an anodic electrochemical dissolution byproduct depending on the electrochemical properties of the metal, the acid concentration, and the applied voltage potential and current density.
[0056] In one embodiment, the anodic electrochemical dissolution system presented herein comprises a two compartment unit system employing an anion exchange membrane separator, a nickel or cobalt metal as the anode in the anode compartment, and a non-consumable cathode, such as a 316 type stainless steel, nickel, or cobalt, in the cathode compartment. As an example, sulfuric acid in a 0.1-10 M concentration range can be used as the acid solution in both the anolyte and catholyte compartments. The anolyte and catholyte solutions are heated to an operating temperature in the range of 10 °C to 100 °C, or more preferably in a range of 20 °C to 95 °C. The temperature range limit may be limited to the specific temperature limitation ofthe anion exchange membrane employed. An applied DC voltage is applied to a current density in the range of 50-10,000 A / m2or higher based on the anode area to electrochemically dissolve the anode material, being nickel or cobalt, which electrochemically dissolves in the acid solution. If sulfuric acid is used, the corresponding metal sulfate salt of the metal is produced in the anode compartment. The metal sulfate solution in the anode compartment becomes more concentrated as more of the metal is anodically dissolved in the acid. The free sulfuric acid concentration in the anode compartment gets depleted with time. The residual free acid concentration is preferably in a range of 0.2 wt% to 10 wt%, and more preferably in a range of 0.5 wt% to 5 wt%. Where desired, the anode compartment acidic metal sulfate solution can be passed through a membrane distillation system to further concentrate the metal sulfate solution during the dissolution or after final dissolution by removing water from the solution. The recovered permeate water from the membrane distillation system can then be recycled back into the anodic dissolution system as needed. The nickel or cobalt sulfate product solution from the anodic dissolution can then be further concentrated to the desired metal salt concentrations suitable for direct use in producing the various composition cathode materials used in the construction of lithium ion and other battery types. As will be readily appreciated, the anodic dissolution process presented herein can be conducted in a batch or continuous type process. Moreover, the metal sulfate anodic dissolution solution product can also be further concentrated sufficiently to precipitate the metal salts as solids, which can be separated from the solution and dried and which can also be potentially used in new lithium ion and other battery type manufacturing.
[0057] FIG. 1 shows an exemplary anodic dissolution system 100 that was used for evaluating and developing the anodic dissolution system for dissolving nickel and cobalt metals in acid. System 100 comprises two compartments, cathode compartment 102 and anode compartment 124 that are separated by anion exchange membrane 113 in membrane holding assembly 112. Compartments 102 and 124 were made of a clear polycarbonate plastic that were solvent welded together. Anode clamp 114a and cathode clamp 114b are used to respectively hold anode 128 and cathode 110 which were positioned in the respective anode and cathode compartments and were electrically connected to DC power supply 118 with the positive connection to clamp 114a to anode 128 and cathode clamp 114b to cathode 110. Acidic solutions 104 and 130 are used to fill the two compartments, such as 1 M sulfuric acid. Polytetrafluoroethylene (PTFE) coated magnetic stirring bars 134 and 106 are used to providing solution mixing in the respective compartments using magnetic stirrers 136 and 108.Immersion heater 126 having a fluorinated ethylene propylene (FEP) coating is used in anode compartment 124 and connected to heat controller 122 with digital temperature display and having a temperature control sensor 132 located in anode compartment 129. An immersion heater and temperature controller was not used in cathode compartment 102 in these tests but could also be installed. Anode gas 120 generated from the dissolution of the anode may be a combination of mostly oxygen and potentially a small amount of hydrogen. Cathode gas 116 generated during dissolution would be typically hydrogen. Anion exchange membrane 113 was a Membranes International AMI-7000 strong base anion exchange membrane with a membrane window having 4” x 4” (10.2 cm x 10.2 cm) size. The dimensions of anode compartment 102 and cathode compartment 124 were approximately 6” (15.25 cm) wide x 6” length x 6” tall and having a volume of about 3 liters each. The area dimensions of anode 128 that was exposed to the solution during the tests was measured and used in the calculation to determine the applied current density for the applied amperage during the run. Cathode 110 was a 2” (5.1 cm) wide by 8” (20.3 cm) long perforated metal made of 316 stainless steel.
[0058] During test operation, the anolyte temperature was set to the desired controlled temperature, such as 55 °C or 60 °C. An applied voltage potential was then applied between the anode and cathode and the current set at a constant amperage. The voltage potential and applied current were recorded.
[0059] FIG. 2 shows alternate anodic dissolution system 200 that employs anode basket 228 that can hold and be used to anodically dissolve smaller pieces of nickel or cobalt metal. Anode basket 228 is typically an expanded titanium metal material having an iridium oxide coating, which will not dissolve anodically. Contact of the nickel and cobalt metal with the electrically conductive basket 228 surface provides the electrical contact for anodically dissolving the metals in the acidic solution. System 200 has anode compartment 234 and cathode compartment 252 with cathode 248 in cathode compartment 252 and anode basket 228 in anode compartment 234. Circulation pump 204 and circulation pump 254 recirculate the anolyte and catholyte solutions respectively. Heater 208 heats anolyte 202 solution flow using temperature controller 210 and UV-VIS sensor 216 monitors the concentration of the dissolved anolyte metal salt and sensor 218 monitors the anolyte acid concentration / solution density. Control valve 214 controls anolyte product solution 212 discharge from anode compartment using signal inputs from level controller 232 and UV-VIS sensor 216. Anode compartment 234 has acid addition 224 and deionized water addition 226 inputs controlled by level controller 232 and anolyte acid concentration / density sensor 218. Anode gas 222 exits anode compartment234. DC power supply 236 applies the voltage potential between anode basket 228 holding metal 230 and cathode 248. Cathode compartment has recirculation pump 254 which flows catholyte 254 through heat exchanger 258 using temperature controller 260. Deionized water 242 is added using liquid controller 250 to replace consumed water in the cathode compartment. Cathode compartment 252 has cathode gas 240 exit the compartment. Anion exchange membrane 244 in anion exchange membrane assembly 246 separates anode compartment 234 from cathode compartment 252 and electrode holders 238 retain the anode basket 228 and the cathode 248 in the respective electrolytes.
[0060] FIG. 3 shows exemplary anodic dissolution system 300 comprising multiple cell compartments. The first anode and cathode compartment set is numbered and corresponds to the multiple other compartment sets in the dissolution system 300. In the first set, anolyte compartment 302 has anode basket 304 filled with nickel or metal flakes or cut metal sheet fragments 306. Anode basket 304 is mechanically connected to electrical bus 312 to the positive connection to a DC power supply (not shown). Membrane holder separator assembly 308 holds anion ion exchange membrane separator 310, which fluidically separates anode compartment 302 from cathode compartment 318. Membrane holder assembly has two cut windows 311 that expose anion exchange membrane 310 to the solution in anode compartment 302 and the solution in cathode compartment 318. Anode compartment 302 has an outlet in each of the cell anode / cathode compartment pairs which are all connected to a common outlet manifold line 326 which is connected to the inlet of centrifugal pump 322. The output solution stream from centrifugal pump 322 is distributed back into each of the anode compartment(s) 302 using manifold 323. This provides the common circulation flow into and out of all of the anode compartment(s) 302. Each cathode compartment(s) 318 are connected to common manifold 324 which carry the catholyte solution streams to the inlet of centrifugal pump 320, which is then pumped through manifold 326 to each of the cathode compartment(s) 318, providing circulation through all of the common cathode compartment(s) 318. Cathode 314 is connected to electrical bus 316 which is connected to the negative side of DC power supply (not shown). All of the solution heaters and other sensors and controllers in anodic dissolution system 300 are not shown for clarity.
[0061] In some embodiments, the anion ion exchange membranes used in contemplated processes are typically hydrocarbon based, manufactured from powdered ion exchange resins and bonded to a reinforcement fabric or screen. For example, suitable anion ion exchangemembranes include strong-base anion ion exchange membranes or cast using polyethylene, styrene-divinylbenzene or other backbone structures with quaternary ammonia ion exchange or other anion exchange functional groups. Examples of these types of anion ion exchange membranes are the those manufactured by Membranes International (Ringwood, NJ) AMI- 7001 or AXM-100, Rising Sun Membranes (Beijing, China) anion ion exchange types AE1, AE2, and AE3, Lanxess / Sybron brand (business now sold to Suez Group) lonac MA-3475, lonac MA-7500, Snowpure, LLC (San Clemente, CA) Excellion anion exchange 1-200, and the various Fumatech (Bietigheim-Bissingen, Germany) reinforced anion exchange membranes including Fumasep FAA-3-PK120. There are also anion ion exchange membranes available from Dioxide Materials (Boca Raton, FL) and lonomr Innovations (Vancouver, Canada) that may be used. In general, it is contemplated that the anion ion exchange membranes need to be mechanically and chemically stable at the operating temperature for the anodic dissolution cell and the operating pH and / or acid concentrations.
[0062] Moreover, suitable membranes also need to effectively block the passage of the metal cations, nickel and cobalt, from entering the cathode compartment. Typically, the cation metal rejection efficiency should be 90% or greater, or 92% or greater, or 94% or greater, or 97% or greater, for example between 95 and 99%, or even greater. In this context, it should be appreciated that the use of an anion membrane only allows anions (such as sulfate) to pass through while preventing nickel cations from reaching the cathode, thus lowering to near zero the concentration of nickel in the catholyte. Consequently, with no nickel in the catholyte, one will not be plating nickel out on the cathode. Thus, use of an anion membrane will provide at least three significant benefits: (1) Higher overall current efficiency since one is not re-plating the nickel that was already dissolved. (2) The anolyte can operate at a lower free acid concentration, thus lowering downstream processing costs since the nickel sulfate is subsequently converted to nickel hydroxide by addition of a base (e.g., sodium hydroxide). Accordingly, a reduction in free acid means less demand for addition of the base. (3) One can use a lower concentration of sulfuric acid in a starting solution, since the anion membrane pulls sulfate over to the anolyte. As such the sulfate concentration will increase within the product solution.
[0063] Consequently, it should therefore be appreciated that the use of cation exchange membranes in the anodic dissolution process is not preferred, as disclosed in Micyus et al. in US Patent 8,177,956 as well as the diaphragm used in Chinese Patent ApplicationCN107675199A, because this allows for the loss of the metal cations through the membrane to the cathode, resulting in the loss of the valuable nickel and cobalt metals. Similarly, this would occur if there was no separator used, as shown in the processes of Venkateswaran et al. and Deo et al. in these systems, the metals would plate directly onto the cathode. To verify such disadvantage, an experiment was conducted with cobalt and acetic acid using a cobalt anode and a 316SS stainless steel cathode and using a thin open mesh plastic screen (instead of an anion ion exchange membrane) to separate them. The application of current dissolved the cobalt and produced cobalt acetate in the solution, but on inspection, significant quantities of cobalt had also plated onto the 316SS stainless steel cathode. As such, operation of this specific configuration without an anion ion exchange membrane was not considered practical.
[0064] The aqueous acid solutions used in the anodic dissolution of nickel and cobalt are typically inorganic non-oxidizing types of acids such as sulfuric acid, phosphoric acid, hydrochloric acid as well as organic type acids, which include acetic acid, citric, oxalic, and formic acid as examples. Oxidative acids can also be used, such as nitric acid, perchloric acid, hydrobromic acid, but anion membranes may not be stable in these acids. Thus, where anion membranes are used that are oxidation resistant to these oxidizing acids, then these acids can be used in the anodic dissolution system presented herein. The concentrations of the acids in the anode and cathode compartments may range from 0.1 M to 12 M depending on the selected acid solution solubility and the concentration needed in producing the desired metal salt concentration. It should further be recognized that the acid concentration in the cathode compartment does not have to be the same acid concentration as the solution in the anode compartment. It may be a lesser or greater concentration than the anode compartment. Also, the operating temperature of the solution in the cathode compartment does not need to be the same temperature as the anode compartment. The cathode compartment solution temperature may be lower or higher than the anode compartment solution temperature. In addition, if desired, different acids can be employed in the anode and cathode compartments. Alternatively, more than one acid type can be used in the anode and cathode compartments, such as a mixture of sulfuric and acetic acid as an example. The addition of some sulfuric acid to acetic acid can supply some ionic conductivity to the solution, helping reduce the anodic dissolution system overall cell voltage.
[0065] The metal salt concentration of the anode solution products depends on the acid concentration and the amount of metal dissolved in the acid during the anodic dissolution. Thesolutions can be further concentrated by evaporation as well as by membrane distillation to the solubility limit of the metal salt at the temperatures employed. For example, nickel sulfate has a solubility of 44.4 g / 100 mL of water at 20 °C and cobalt sulfate has a solubility of 36.1 g / 100 mL of water. So as not to be limited, suitable concentrations of the metal salts with residual amounts of acids can be prepared as needed for use in manufacturing the cathode materials for the subject lithium ion and other battery types.
[0066] The preferred metals for anodic dissolution are nickel and cobalt because of their high economic value. However, it should be noted that numerous other metals can also be similarly anodically dissolved in selected acids such as vanadium and chromium, as well as precious metals such as gold, silver, palladium, platinum, rhodium, iridium, ruthenium, rhenium, osmium, and the like.
[0067] The operating temperature of the anodic dissolution system may range from 10 °C to 100 °C or higher depending on the boiling point of the acid solution. The maximum temperature will also depend on the temperature limits of the anion ion exchange membrane employed. The selected operating temperature will also depend on the operating current efficiency at those temperatures and the selected current density to get the best overall operating cost of the system.
[0068] Surprisingly and unexpectedly, cobalt has anodic dissolution current efficiencies in the systems presented herein of greater than 100% at extremely high current densities as shown graphically in FIG. 8, where at 50-60 °C, at operating current densities of 1,000 to 4,000 A / m2, and the anodic dissolution current efficiency was still greater than 100%. It is theorized that cobalt has a high overpotential for the generation of the side reaction producing oxygen from the oxidation of water.
[0069] The preferred metals for the anodic dissolution basket if used, are titanium metal mesh with an iridium oxide-based coating, which is resistant to many of the selected acids that could be used in the system and is resistant to anodic oxidation reaction where oxygen is evolved. Platinum coatings on titanium may also be used. Other oxide coatings on titanium may be used such as lead dioxide and the like if they are corrosion resistant in the solution. If the metals used for the anodes are available as sheets, these are the more preferred form since they would not need the anode dissolution basket.
[0070] Additives to the anode solution may be used that may enhance the metal dissolution if desired. Preferably the additive does not add any foreign or unwanted anions in the solution. Hydrogen peroxide is the most preferred, and the amount employed adds to the cost of the anodic metal dissolution process. The hydrogen peroxide may be added in small amounts at the end of the dissolution process to aid in dissolving any small residual metal fines or small particles in the solution.EXAMPLES
[0071] Example 1 - Nickel Dissolution in 1.0 M Sulfuric Acid
[0072] FIG. 4 shows exemplary tabulated anodic dissolution data for nickel in 1.0 M sulfuric acid in the laboratory test system as shown in FIG. 1. A metal strip of nickel 200 alloy metal was used as the anode which was subjected to anodic dissolution for various time periods at various applied current densities in 1.0 M sulfuric acid at different temperatures. The nickel strip was removed after each run, rinsed, dried, and weighed for mass loss, and then placed back into the same anode position in the solution. The data is graphed in FIG. 5. The anodic current efficiency (CE) is calculated from the actual amount of nickel metal dissolved divided by the theoretical amount of nickel metal that should have been dissolved by the amount of electrical Faradays that were passed through the metal as follows:
[0073] (Actual Ni amount dissolved / theoretical) x 100 = % CE (6)
[0074] The Faraday calculation for the theoretical amount of metal that should be dissolved was based on the applied amperage, operating time in minutes, the molecular weight (MW) of the metal, and divided by the Faraday constant and the number of equivalents for the metal (= 2 for nickel) as follows:
[0075] (amps) x (min x 60) x (MW) / ((96,450) x (2)) = g metal (7)
[0076] At room temperature, 20.5 °C to 22 °C, the nickel dissolution % CE was very low, decreasing from 13.5% at a current density (CD) of 558 A / m2to much lower 4.3% at a CD of 2,192 A / m2. This indicated that low temperatures were not efficient in the anodic dissolution of nickel. At temperatures of 47 °C to 49 °C, it was found that the anodic dissolution CE improved dramatically, slightly decreasing from 104.7% at a CD of 398 A / m2to a CE of 94.1% at 1,592 A / m2. At a temperature of 55 °C, the dissolution CE decreased from 109.5% at 548 A / m2to 71.1% at 3288 A / m2. During the anodic dissolution, when there was a sufficientamount of nickel sulfate in the solution, it was noted that the color of the nickel sulfate solution leaving the anode surface was not a clear greenish color, but a darker color that was not transparent. The nickel sulfate solution, minutes or hours later, turned into a transparent darker greenish color. It is theorized that the nickel was being oxidized producing a either a higher valence oxide (Ni3+) instead of the Ni2+or forming micron sized undissolved nickel oxide (NiO) particles that were evolving from the nickel surface that were slowly being dissolved in the bulk solution. The higher than theoretical CE results are theorized to be the additional action of sulfuric acid dissolution on the anodically exposed nickel metal surfaces, adding to the electrochemical dissolution efficiency. Run 15 was conducted to determine the nickel metal dissolution rate without any electrochemical current and indicated a 1.42% nickel chemical dissolution rate at those acid and temperature conditions. The cathode solution remained water clear during the runs, indicating that nickel metal was not being significantly transferred into the cathode compartment. Inductively coupled plasma (ICP) analysis showed that only ppm trace quantities of nickel were present in the solution. The cathode showed a thin grayish layer film, which was determined by ICP analysis to contain nickel and other metals. So during anodic dissolution, the cathode was capturing some nickel and other trace metal impurities that had passed through the membrane, since the anion exchange membrane is not 100% efficient in blocking the metal cations in the anode compartment during the dissolution process.
[0077] FIG. 6 shows exemplary nickel anodic dissolution power consumption in kWh / kg Ni dissolved as a function of current density and temperature from the tabulated data in FIG. 4. The data shows that a lower power consumption for anodic nickel dissolution is obtained using higher sulfuric acid solution temperatures. Higher applied current densities can be used to process larger amounts of nickel metal.
[0078] Example 2 - Cobalt Dissolution in 0.5 M and 1.0 M Sulfuric Acid Solutions
[0079] FIG. 7 show exemplary tabulated data in the anodic dissolution of cobalt in 0.5 M and 1.0 M sulfuric acid at various current densities and two solution temperatures. FIG. 8 is a compilation of the data graphically, showing the cobalt dissolution efficiency as a function of the current density and temperature. Cobalt turned out to have unexpected properties in electrochemical dissolution. Surprisingly, it was found that cobalt generated little or no gas evolution during electrochemical dissolution, and demonstrated unexpected current efficiencies of greater of 100% at temperatures of 50 °C and 60 °C at the applied current densities between 1,200 to 4000 A / m2in sulfuric acid concentrations of 0.5 and 1.0 M.
[0080] FIG. 9 shows exemplary cobalt anodic dissolution power consumption in kWh / g Co as a function of the applied current density, where the anodic dissolution at a sulfuric acid strength of 1.0 M at 50 °C operated at a much lower cobalt power consumption than cobalt dissolution at 60 °C in a lower 0.5 M sulfuric acid concentration.
[0081] Example 3 - Cobalt Dissolution in 1.75 M Acetic Acid
[0082] FIG. 10 shows exemplary experimental tabulated data for cobalt anodic dissolution in acetic acid, producing cobalt acetate. The data is plotted graphically in FIG. 11. Acetic acid is not a very conductive acid, which has a peak conductivity between 16 - 20 wt.% acetic acid. The anodic dissolution voltage potential was significantly higher than that in sulfuric acid. The anodic dissolution current efficiency was found to be in the 102-104% range at applied current densities of 200-800 A / m2. FIG. 12 shows exemplary cobalt anodic dissolution power consumption in kWh / g Co in producing cobalt acetate as a function of the applied current density.
[0083] FIG. 13 shows an exemplary laboratory membrane distillation (MD) test apparatus used to evaluate the performance of membrane distillation in removing water from a cobalt sulfate containing sulfuric acid and the water removal flux rate. FIG. 13 shows membrane distillation system 400 having solution feed tank 402 containing cobalt sulfate solution 408 produced from the laboratory test system 100 as shown in FIG. 1 using the product produced using 0.5 M sulfuric acid in Example 2. With further reference to FIG. 13, immersion heater 404 was controlled using heat controller 410 having a temperature sensor 406. Heated cobalt sulfate solution 408 was pumped through line 414 to peristaltic pump 412 into the inlet solution side compartment 418 of membrane distillation cell 416 which then exits as stream 420 back into solution feed tank 402. Membrane distillation cell 416 has a PTFE membrane separator 422 which separates membrane distillation cell 416 into the solution compartment 418 and a gas compartment 424. PTFE membrane separator was a hydrophobic membrane with a 0.22 micron pore PTFE layer bonded to a polypropylene non-woven reinforcement backing. The membrane was obtained from Tisch Scientific (Cleveland, OH). Water vapor from solution compartment 418 passes through the PTFE membrane separator 422 into gas / permeate compartment 424. Aquarium air pump 428 was used to pump incoming air 426 which exits air pump 428 as air stream 430 into the inlet of air compartment 424, picking up the water vapor that has passed through PTFE membrane separator 422 into air compartment 424 and exits the outlet port of gas / permeate compartment 424 as exit stream 432 as a mixed water vapor in airgas stream. Gas stream 432 then passes into cooled glass condenser bottle 442, condensing water vapor as water 440 from the gas stream in condenser bottle 442. The water depleted air gas stream 444 exits condenser bottle 442. Condenser bottle 442 is immersed in cold water 438 in glass bath 434. Immersion pump 436 pumps water through a solid state thermoelectric chiller unit 446 to cool the water in glass bath to a temperature of 2 °C-5 °C to cool and condense the water vapor from gas stream 432.
[0084] In the experiments, sulfate solution 408 was heated to 60 °C, and the air flow through membrane distillation cell 416 air compartment 424 was set at 1.5 L / min. Condensed water 440 was collected at specified times to determine the water flux rate through membrane 422. The concentration of the cobalt sulfate and sulfuric acid in solution feed tank 402 was analyzed to determine the change in concentrations. Since the solution tank did not have a cover on the solution feed tank, there was also evaporation of water from the heated solution during the run and did not have to fully rely on the membrane distillation unit for removal of all the water from the cobalt solution.
[0085] FIG. 14 shows exemplary tabulated results for the two membrane distillation runs conducted. Run 1 showed that the cobalt sulfate concentration increased from 49.02 g / L to 68.96 g / 1 and the sulfuric acid increased from 0.506 M to 0.692 M. The collected permeate water volume, which is the collected water vapor that had passed through the membrane, was 30 mL, so the calculated water flux rate was 0.75 kg ELO / h-m2. This is the calculated flux rate of water vapor through the specific area membrane and time period. In consecutive Run 2, the cobalt sulfate solution concentration further increased to 96.90 g / L and the sulfuric acid to 1.0095 M. The collected permeate water was 23 mL, having a calculated water flux rate of 0.66 kg ELO / h-m2. The PTFE membrane separator did an excellent job of preventing the passage of any bulk cobalt sulfate into the gas / permeate compartment. ICP (inductively coupled plasma) analysis of the water permeates showed 0 ppm Co and 0 ppm sulfate ion in the Run 1 permeate and a trace 10 ppm of cobalt and 23 ppm sulfate ion in Run 2 water permeate. There may have been a small imperfection in the PTFE membrane separator, but the permeate water would be suitable for recycling water back into the anodic dissolution system. This experiment demonstrates that membrane distillation is a suitable technology to concentrate metal salt solutions and to recover water for re-use in the remainder of the process.
[0086] FIG. 15 shows an integrated system 500 that incorporates an anodic dissolution system with a membrane distillation unit. Anodic dissolution system 504 has an anode compartment515, a cathode compartment 509 with cathode 506, anode 512, anion exchange membrane 510, power supply 502, and acid solution 508 in the cathode compartment and acid solution 514 in the anode compartment. During anodic dissolution, anode solution 514 is pumped or transferred as stream 516 into the inlet of solution compartment 524 in membrane distillation unit 518. Solution exit stream 525 from the outlet of solution compartment 524 is recycled back to anode compartment 515 of anodic dissolution unit 504. Air stream 522 is passed into the inlet of gas / permeate compartment 520 of membrane distillation unit and sweeps out water vapor 526 that passes through PTFE membrane 528 into gas / permeate compartment 520. Air and water vapor exits air / permeate compartment 520 outlet as stream 530, and then passes through chiller 532 to condense water product stream 533 and exits as depleted water vapor air stream 534. Stream 534 can be optionally recycled as an input to air stream 522. The membrane distillation unit can optionally be operated with a vacuum pump (not shown) after the chiller to remove the water vapor from exit stream 530 from gas / permeate compartment 520.
[0087] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. As also used herein, and unless the context dictates otherwise, the term "coupled to" is intended to include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms "coupled to" and "coupled with" are used synonymously.
[0088] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the scope of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification or claims refer to at least one of something selected from the group consisting of A, B, C . . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.
Claims
CLAIMSWhat is claimed is:
1. A method of converting a metal into a corresponding metal salt, comprising: providing an anodic dissolution cell that includes an anode compartment having an anode with an anode metal to be dissolved and a cathode compartment containing a non-dissolvable cathode; wherein an anion ion exchange membrane separator is disposed between and fluidly separates the anode compartment from the cathode compartment; loading an acidic electrolyte into the anode and cathode compartments, and optionally heating the acidic electrolyte in the anode and / or cathode compartments; and applying an electrical DC potential and current between the anode and cathode to dissolve the anode metal in the anode compartment and thereby form in the anode compartment a solution comprising the corresponding metal salt of the acid.
2. The method of claim 1, wherein the anode metal is nickel, cobalt, rhenium, ruthenium, or osmium.
3. The method of claim 2, wherein the nickel or cobalt is obtained from a used or spent lithium ion battery.
4. The method of claim 1, wherein the acidic electrolyte is an inorganic acid or an organic acid solution.
5. The method of claim 4, wherein the acidic electrolyte comprises sulfuric acid, phosphoric acid, acetic acid, formic acid, oxalic acid, lactic acid, citric acid, malic acid, uric acid, or hydrochloric acid.
6. The method of claim 4, wherein the acidic electrolyte comprises hydrobromic acid, nitric acid, perchloric acid, or chloric acid, and wherein the anion exchange membrane is resistant to oxidation by the acid solution.
7. The method of claim 1, wherein the acidic electrolyte in the anode and cathode compartments has independently an acid concentration of between 0.1 M and 12 M.
8. The method of claim 1, wherein the anion ion exchange membrane separator comprises a material that has a 90% or higher metal cation rejection efficiency.
9. The method of claim 1, wherein an operating temperature of the anode and cathode compartments is from about 10 °C to 100 °C, and optionally wherein the anode and cathode compartments operate at different temperatures.
10. The method of claim 1, wherein the anode is operated at a current density of 1 to 10,000 A / m2.
11. The method of claim 1, wherein anodic dissolution current efficiency is 20% to 100% or greater.
12. The method of claim 1, further comprising adding an oxidizer to the acidic electrolyte in the anode compartment.
13. The method of claim 1, wherein anodic dissolution is operated in a batch mode or a continuous mode, and optionally wherein the corresponding metal salt of the acid is removed from the anode compartment.
14. The method of claim 1, wherein the anode comprises a conductive container that contains the anode metal.
15. The method of claim 1, wherein the anode is formed at least in part by the anode metal.
16. The method of any one of the preceding claims, further comprising removing from the anode compartment the solution comprising the corresponding metal salt and passing the solution through a membrane distillation system to produce a concentrated metal salt solution and permeate water.
17. The method of claim 16, wherein the permeate water is recycled to the anodic dissolution cell.
18. An anodic dissolution cell, comprising: an anode compartment having an anode and configured to retain anode metal to be dissolved and a cathode compartment containing a non-dissolvable cathode; an anion ion exchange membrane separator is disposed between and fluidly separating the anode compartment from the cathode compartment;an acidic electrolyte disposed in the anode and cathode compartments; and optionally a membrane distillation unit fluidly coupled to the anode compartment and configured to generate a concentrated anolyte and recovered water.
19. The anodic dissolution cell of claim 18, wherein the anode metal is nickel, cobalt, rhenium, ruthenium, or osmium.
20. The anodic dissolution cell of claim 18, wherein the acidic electrolyte comprises sulfuric acid, phosphoric acid, acetic acid, formic acid, oxalic acid, lactic acid, citric acid, malic acid, uric acid, or hydrochloric acid.