Method of recovering a metal from a metal-containing electrical or electronic material

Abstract

This invention provides for a method of recovering a metal from a metal-containing electrical or electronic material comprising the steps of: a) culturing at least one microorganism to produce at least one acid; b) adding the at least one acid and a reducing agent to the metal-containing electrical or electronic material and indirectly bioleaching the metal-containing electrical or electronic material; and c) recovering the metal.

Description

[0001]METHOD OF RECOVERING A METAL FROM A METAL-CONTAINING ELECTRICAL OR ELECTRONIC MATERIAL Technical Field of the Invention The present invention relates to a method of recovering a metal from a metal- containing electrical or electronic material. Background to the Invention Bioleaching is a sustainable and environmentally friendly method of extracting valuable metals from metal containing materials. Bioleaching reduces the need for traditional, energy-intensive methods by using microorganisms to extract metals from metal containing materials. Bioleaching is not only cost-effective but also capable of extracting metals from low-grade ores and complex matrices where conventional methods fail. Indirect bioleaching is a bioleaching method in which microorganisms are not in direct contact with the metal containing materials during the process and instead microorganisms produce leaching agents to leach the metal containing materials. A known weakness of methods of recovering a metal from metal-containing electrical or electronic materials is that the percentage of metal recovered may be low such that the process needs to be repeated, or a substantial amount of the metal is not able to be recovered. A further known weakness of methods of recovering a metal from metal- containing electrical or electronic materials is that the method may not be able to recover a substantial amount of metal from large amounts of material. This results in the method needing to be repeated for smaller amounts of material which may require and increased amount of energy, time and bioleaching reagents. It would therefore be advantageous to provide a method of recovering a metal from metal-containing electrical or electronic materials which is capable of recovering a relatively high percentage of the metal in the metal-containing electrical or electronic materials. It would be advantageous to provide a method of recovering a metal from metal- containing electrical or electronic materials which is capable of recovering a relatively high percentage of the metal in the metal-containing electrical or electronic materials without significant work-up steps or without repeating the process multiple times. It would also be advantageous to provide a method of recovering a metal from metal-containing electrical or electronic materials which is capable of recovering a relatively high percentage of metal from a large amount of metal-containing electrical or electronic materials. It would therefore be advantageous to provide a method of recovering a metal from metal-containing electrical or electronic materials which is capable of recovering a high percentage of the metal in the metal-containing electrical or electronic materials in one step. It is an aim of embodiments of the invention to overcome one or more problems of the prior art, whether expressly disclosed herein or not. Summary of the Invention According to a first aspect of the invention there is provided a method of recovering a metal from a material, preferably a metal-containing electrical or electronic material, comprising the steps of: a) culturing at least one microorganism to produce at least one acid; b) combining the at least one acid and a reducing agent with the metal- containing electrical or electronic material and indirectly bioleaching the metal-containing electrical or electronic material; and c) recovering the metal. The acid may be considered a “bio acid”, i.e. it is an acid produced by the microorganism. Bio acids can also be known as biogenic acids. The method of the invention may be advantageous because the presence of the reducing agent in step b) may result in a high percentage of recovered metal from the metal-containing electrical or electronic material. The method of the invention may be advantageous because the reducing agent reduces the metal during step b), thereby increasing the solubility of the metal during indirect bioleaching and therefore increasing the amount of metal recovered in step c). The method of the invention may be advantageous because it results in a high amount of metal recovered in step c) mitigating or reducing the need to repeat the indirect bioleaching multiple times. The metal-containing electrical or electronic material may comprise a battery, a printed circuit board (PCB) or a hard drive. The metal-containing electrical or electronic material may comprise a carbon, silicon or polymer substrate on which the metal to be recovered is connected, mixed, melded or otherwise integrated. The metal-containing electrical or electronic material may be a solid material. The metal-containing electrical or electronic material may be a battery material or a waste battery material. The metal-containing electrical or electronic material may be a lithium-battery material or waste lithium-battery material. The lithium-battery material or waste lithium-battery material may comprise at least one component of a battery selected from the group consisting of: a lithium nickel manganese cobalt battery (NMC), a lithium nickel cobalt aluminium oxide battery (NCA), lithium nickel cobalt manganese aluminium oxide battery (NCMA), a lithium-ion manganese oxide battery (LMO), a lithium iron phosphate battery (LFP) and a lithium-ion cobalt oxide battery (LCO), lithium titanate oxide (LTO), or any combination thereof. The metal-containing electrical or electronic material may comprise black mass. “Black mass” comprises spent battery material which has been shredded and separated from a base metal to provide a material rich in valuable metals. Valuable metals may comprise metals which make up battery anodes and cathodes. The metal may be selected from the group consisting of: lithium, nickel, cobalt, manganese, titanium, iron and copper, and any combination thereof. The metal-containing electrical or electronic material may be a lithium nickel manganese cobalt battery waste, and the metal may be selected from the group consisting of: lithium, nickel, cobalt, manganese and any combination thereof. The metal-containing electrical or electronic material may be a lithium nickel manganese cobalt battery waste, and the metal may be lithium, nickel, cobalt and manganese. The reducing agent may be ascorbic acid or ferrous sulfate. These embodiments may be advantageous because the reducing agents may be substantially environmentally benign. These embodiments may be advantageous because the reducing agents may significantly increase the amount of metal recovered by the method of the invention. Ascorbic acid is also known as vitamin C. Ascorbic acid comprises the following formula. Ferrous sulfate comprises the chemical formula FeSO4. Step a) may comprise culturing at least 2, 3 or 4 microorganisms. At least one microorganism may comprise a bacteria. At least one microorganism may comprise an iron-oxidising bacteria. At least one microorganism may comprise a sulfur-oxidising bacteria. The sulfur-oxidising bacteria may comprise a mesophilic sulfur-oxidising bacteria. The sulfur-oxidising bacteria may comprise thermophilic sulfur-oxidising bacteria. Step a) may comprise culturing a mesophilic and a thermophilic sulfur-oxidising bacteria. These embodiments may be advantageous because sulfur-oxidising bacteria may provide a higher concentration of protons and therefore a lower pH value in the absence of iron ions during step a). At least one microorganism may be selected from the group consisting of: an Acidothiobacillus sp. such as Acidothiobacillus ferrooxidans, Acidothiobacillus ferrodurans, Acidothiobacillus ferriphilus, Acidothiobacillus caldus, Acidothiobacillus thiooxidans, or Acidothiobacillus ambivalens; an Alicyclobacillaceae such as Alicyclobacillus sp.; a Lentosprillum sp. such as Leptosprillum ferriphilum or Leptosprillum ferrooxidans; a Sulfobacillus sp. such as Sulfobacillus acidophilus or Sulfobacillus thermosulfidooxidans; and a Ferroplasma sp, or any combination thereof. In preferred embodiments at least one microorganism may be selected from Alicyclobacillus sp. and at least one microorganism may be Acidothiobacillus thiooxidans. Step a) may comprise culturing a mixture comprising Alicyclobacillus sp. and Acidothiobacillus thiooxidans. Step a) may comprise culturing the at least one microorganism in or on a culture medium. The culture medium may be a liquid, a semi-solid or a solid. The culture medium may comprise 9k medium. The culture medium may comprise 4.5 k medium. The culture medium may comprise a heterotrophic basal salt (HBS), acidophilic basal salt (ABS) and / or a trace element medium. The culture medium may comprise MgSO4. The culture medium may comprise (NH4)2SO4. The culture medium may comprise K2HPO4. The culture medium may comprise KCl. The culture medium may comprise Ca(NO3). The culture medium may comprise: MgSO4,(NH4)2SO4, Na2SO4, K2HPO4, KCl, and Ca(NO3)2. The culture medium may comprise: MgSO4,(NH4)2SO4, Na2SO4, K2HPO4, KCl, and Ca(NO3)2and distilled water. Step a) may comprise culturing at least one microorganism in a culture medium until the pH of the culture medium comprising the at least one microorganism is less than 3 is achieved. Step a) may comprise culturing at least one microorganism in a culture medium until the pH of the culture medium comprising the at least one microorganism is less than 2.5, 1.5, 2, 1 or less than 0.5 is achieved. These embodiments may be advantageous because reduced pH indicates a high concentration of acid has been produced and increased amounts of acid may result in a higher metal recovery rate in step b). Step a) may comprise culturing the at least one microorganism in the presence of sulfur (S0). Step a) may comprise culturing the at least one microorganism in the presence of sulfur powder. The concentration of sulfur may be at least 5 g / L of culture medium. The concentration of sulfur may be at least 6, 7, 8, 9 or at least 10 g / L of culture medium. The concentration of sulfur may be no more than 20 g / L of culture medium. The concentration of sulfur may no more than 18, 16, 14, 12, or no more than 11 g / L of culture medium. The concentration of sulfur may be between 5 and 20 g / L of culture medium. The concentration of sulfur may be between 6 and 18 g / L, 7 and 16 g / L of culture medium, 8 and 14 g / L of culture medium, 8 and 12 g / L of culture medium, 9 and 12 g / L of culture medium or between 10 and 12 g / L of culture medium. In preferred embodiments the concentration of sulfur is approximately 10 g / L of culture medium. These embodiments may be advantageous because it enables a high concentration of acid to be produced in step a). Step a) may comprise culturing at least one microorganism for at least 6 days. Step a) may comprise culturing at least one microorganism for at least 7, 8, 9, 10, 11 or at least 12 days. The acid may comprise sulfuric acid (H2SO4). The method may comprise separating the acid and the microorganism(s) in a step between step a) and step b). The method may comprise extracting the acid from the microorganism(s) in a step between step a) and step b). The method may comprise filtering the acid in a step between step a) and step b). The method may comprise filtering the acid in a step between step a) and step b) to remove at least a portion of the or each microorganism from the acid. The method may comprise filtering the acid in a step between step a) and step b) to remove substantially all of the or each microorganism from the acid. These embodiments may be advantageous because it may prevent the adsorption of metal ions onto the cell surfaces thereby increasing the amount of recovered metal. The acid of step b) may comprise less than 10 wt.% microorganism(s). The acid of step b) may comprise less than 9, 8, 7, 6, 5, 4, 3, 2, 1 or less than 0.5 wt.% microorganism(s). The acid of step b) may be substantially free of the microorganism(s). These embodiments may be advantageous because it may prevent the adsorption of metal ions onto the cell surfaces thereby increasing the amount of recovered metal. The method may comprise filtering the acid in a step between step a) and step b) using a syringe filter. The method may comprise filtering the acid in a step between step a) and step b) using a syringe filter comprising a pore size of no more than 0.5 µm. The method may comprise filtering the acid in a step between step a) and step b) using a syringe filter comprising a pore size of no more than 0.4, 0.3 or 0.2 µm. These embodiments may be advantageous because it may remove at least part of or substantially all of the microorganisms from the acid before step b). These embodiments may be advantageous because it may remove at least part of or substantially all of the microorganisms from the acid before step b). Step b) may comprise combining the acid, the reducing agent and the metal- containing electrical or electronic material at substantially the same time. Step b) may comprise combining the reducing agent and the metal-containing electrical or electronic material and then adding the acid. Step b) may comprise combining the acid and the metal-containing electrical or electronic material and then adding the reducing agent. The acid, the metal-containing electrical or electronic material and the reducing agent mixture of step b) forms a reaction mixture. The reaction mixture may comprise a culture medium. The reaction mixture may comprise a solvent. The reaction mixture may comprise an aqueous solvent. The reaction mixture may comprise at least 5 wt.% of the metal-containing electrical or electronic material as a wt.% of the total weight of the reaction mixture. The reaction mixture may comprise at least 6, 7, 8, 9, or at least 10 wt.% of the metal-containing electrical or electronic material as a wt.% of the total weight of the reaction mixture. The reaction mixture may comprise at least 5 wt.% solid metal-containing electrical or electronic material as a wt.% of the total weight of the reaction mixture. The reaction mixture may comprise at least 6, 7, 8, 9, or at least 10 wt.% solid metal-containing electrical or electronic material as a wt.% of the total weight of the reaction mixture. Step b) may be carried out at a temperature of between 20 and 90 °C. Step b) may be carried out at a temperature of between 30 and 90 °C, 40 and 90 °C, 50 and 90 °C, 60 and 90 °C, 70 and 90 °C or between 75 and 85 °C. Step b) may be carried out at a temperature of approximately 80 °C. These embodiments may be advantageous because the increased temperature may supply the required energy for the reducing agent to reduce the metal thereby resulting in an increase in the amount of recovered metal. Step b) may be carried out for a duration of at least 30 minutes. Step b) may be carried out for a duration of at least 1 hour, 2 hours or at least 2.5 hours. Step b) may be carried out for a duration of no more than 12 hours. Step b) may be carried out for a duration of no more than 10, 8, 6, 5, 4 or no more than 3 hours. Step b) may be carried out for a duration of between 30 minutes and 10 hours. Step b) may be carried out for a duration of between 1 and 8 hours, 2 and 6 hours, 2 and 5 hours, 2 and 4 hours, 2.5 and 4 hours or between 2.5 and 3 hours. Step c) may comprise filtering the bioleached metal-containing electrical or electronic material of step b). Step c) may comprise drying the bioleached metal- containing electrical or electronic material of step b). Step c) may comprise drying the bioleached metal-containing electrical or electronic material of step b) at at least 80 °C. Step c) may comprise drying the bioleached metal-containing electrical or electronic material of step b) at at least 90 °C, 95 °C or at least 100 °C. Step c) may comprise filtering and drying the bioleached metal-containing electrical or electronic material of step b). The method of recovering a metal from a metal-containing electrical or electronic material may comprise the steps of: a) culturing at least one microorganism to produce at least one acid; b) filtering the at least one acid to provide at least one filtered acid wherein at least part or substantially all of the microorganisms are removed from the acid; c) combining the at least one filtered acid and a reducing agent with the metal- containing electrical or electronic material and indirectly bioleaching the metal-containing electrical or electronic material; and d) recovering the metal. The method of recovering a metal from a metal-containing electrical or electronic material may comprise the steps of: a) culturing at least one microorganism to produce at least one acid; b) filtering the at least one acid to provide at least one filtered acid wherein at least part or substantially all of the at least one microorganism is removed from the acid; c) combining the at least one filtered acid and ascorbic acid with the metal- containing electrical or electronic material and indirectly bioleaching the metal-containing electrical or electronic material; and d) recovering the metal. The method of recovering a metal from a metal-containing electrical or electronic material may comprise the steps of: a) culturing at least one microorganism to produce at least one acid; b) filtering the at least one acid to provide at least one filtered acid wherein at least part or substantially all of the at least one microorganism is removed from the acid; c) combining the at least one filtered acid and ferrous sulfate with the metal- containing electrical or electronic material and indirectly bioleaching the metal-containing electrical or electronic material; and d) recovering the metal. The method of recovering a metal from a lithium-battery waste may comprise the steps of: a) culturing at least one microorganism to produce at least one acid; b) combining the at least one acid and a reducing agent with the metal- containing electrical or electronic material and indirectly bioleaching the metal-containing electrical or electronic material; and c) recovering the metal, wherein the metal is at least one metal selected from the group consisting of: lithium, cobalt, nickel, magnesium and any combination thereof. The method of recovering a metal from a lithium-battery waste may comprise the steps of: a) culturing at least one microorganism to produce at least one acid; b) filtering the at least one acid to provide at least one filtered acid wherein at least part or substantially all of the at least one microorganism is removed from the acid; c) combining the at least one filtered acid and a reducing agent with the metal- containing electrical or electronic material and indirectly bioleaching the metal-containing electrical or electronic material; and d) recovering the metal, wherein the metal is at least one metal selected from the group consisting of: lithium, cobalt, nickel, magnesium and combinations thereof. Detailed Description of the Invention In order that the invention may be more clearly understood an embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1A is a graph showing the change in pH of cultures 1 to 9 as defined in table 2 over a period of 15 days in the culture conditions of 30 °C whilst being stirred at 140 rpm. Figure 1B is a graph showing the change in oxidation reduction potential (ORP) of cultures 1 to 9 as defined in table 2 over a period of 15 days in the culture conditions of 30 °C whilst being stirred at 140 rpm. Figure 1C is a graph showing the change in cell concentration of cultures 1 to 9 as defined in table 2 over a period of 15 days in the culture conditions of 30 °C whilst being stirred at 140 rpm. Figure 1D is a graph showing the change in sulfate concentration of cultures 1 to 9 as defined in table 2 over a period of 15 days in the culture conditions of 30 °C whilst being stirred at 140 rpm. Figure 1B is a graph showing the change in ferric concentration of cultures 1, 2, 4 and 5 as defined in table 2 over a period of 15 days in the culture conditions of 30 °C whilst being stirred at 140 rpm. Figure 2A is a graph showing the pH of a culture comprising Alicyclobacillus sp. and Acidothiobacillus thiooxidans in a culture medium comprising 0.5 g / L MgSO4·7H2O, 0.45 g / L (NH4)2SO4, 0.15 g / L Na2SO4·10H2O, 0.05 g / L KH2PO4, 0.05 g / L KCl and 0.014 g / L Ca(NO3)2·4H2O as with 10 grams sulfur per litre of culture medium, wherein the bacteria are cultured over a period of 12 days in the culture conditions of 30 °C whilst being stirred at 140 rpm. Figure 2B is a graph showing the cell concentration of the culture of figure 2A, wherein the bacteria are cultured over a period of 12 days in the culture conditions of 30 °C whilst being stirred at 140 rpm. Figure 2C is a graph showing the sulfate concentration of the culture of figure 2A and 2B, wherein the bacteria are cultured over a period of 12 days in the culture conditions of 30 °C whilst being stirred at 140 rpm. Example methods Example methods of recovering a metal from a waste lithium-battery material were carried out as follows. The method comprised the steps of: a) culturing at least one microorganism to produce at least one acid; b) combining the at least one acid and a reducing agent with the waste lithium- battery material and indirectly bioleaching the waste lithium-battery material; and c) recovering the metal. The waste lithium-battery material comprised Lithium-Nickel Manganese- Cobalt-Oxide (NMC) black mass obtained from the production scrap of a battery manufacturing company. Step a) comprised producing sulfuric acid by culturing Acidothiobacillus thiooxidans and Alicyclobacillus sp. for 12 days at 30 °C in a culture medium comprising 0.5 g / L MgSO4·7H2O, 0.45 g / L (NH4)2SO4, 0.15 g / L Na2SO4·10H2O, 0.05 g / L KH2PO4, 0.05 g / L KCl and 0.014 g / L Ca(NO3)2·4H2O at pH of 1.8, plus 1 mL of a concentrated trace elements solution. Sulfur was added to the culture medium at a concentration of 10 g / L of culture medium. After the culture medium reached a pH of 0.5, sulfur residue was removed from the culture medium by filtration. The bioleaching experiments were performed in 100 mL Erlenmeyer flask containing 30 mL of acid (sulfuric acid with pH 0.5) and 3.33 g black mass (10% of the reaction mixture). The acid and black mass mixture was agitated by a hot-plate magnetic stirrer at 20 or 80 °C for 3 hours. Inventive experiments 1 to 8 in table 1 comprise adding the reducing agent to the acid and black mass mixture. Table 1 summarises the conditions of the experiments. Table 1 Control experiments 1 to 4 did not comprise adding a reducing agent. Inventive experiments 1 to 4 comprised adding the reducing agent ferrous sulfate. Inventive experiments 5 to 8 comprised adding the reducing agent ascorbic acid. Control experiments 2 and 4 and inventive experiments 2, 4, 6 and 8 comprised filtering the acid using a 0.2 µm syringe filter at the end of step a) such that the bacterial cells were removed. The acid was not filtered in the remaining experiments such that control experiments 1 and 3 and inventive experiments 1, 3, 5, and 7 comprised bacterial cells in the reaction material during step b). After the indirect bioleaching step, the leached material was filtered, and the solid residue was dried in an oven at 100 °C and weighed by a four-decimal-place balance. All the experiments were carried out in duplicate, and the metal concentrations of the obtained solutions were measured by inductively coupled plasma (ICP-OES), Perkin Elmer, USA calculated according to the following equation: ^× ^R (%) =^ × ^ × 100Wherein R is metal recovery, C is the metal concentration (mg / L) in the leachate, V is the volume (L) of the leachate, G is the metal assay (mg / g) of the solid (black mass), and M is the mass (g) of the solid. In conclusion, it was observed that the addition of ferrous sulfate to the acid and waste material mixture increased metal recovery to around 50 % and the addition of ascorbic to the acid and waste material mixture improves it to about 80% whereas the control experiments which did not comprise adding a reducing agent comprised the lowest metal recovery. It is understood that the improved performance when a reducing agent is added may be because the reducing agent reduces the metal thereby increasing the solubility of the metal in the reaction mixture. The absence of a reducing agent results in a higher amount of precipitated material or metal which slows the rate of reaction and requires removal for the method to be continued. A further 15 % increase in metal recovery was discernible after increasing the bioleaching temperature from 20 to 80 °C. It is understood that this may be because the temperature increase supplies the required energy for the reducing agent to reduce the metal. When a reducing agent was present, the filtering of the bacterial cells from acid (filtered acid) further increased the metal concentration by approximately 10 %. It is understood that the presence of bacterial cells (unfiltered acid) may be disadvantageous due to the adsorption of dissolved metal ions on the cell surfaces and therefore by removing the bacterial cells, the metal recovery was increased. Selecting the bacteria The ability of Acidothiobacillus Ferrooxidans (A. ferroxidans), Acidothiobacillus ferrodurans (A. ferrodurans), Acidothiobacillus caldus (A. caldus), Acidothiobacillus thiooxidans (A. thiooxidans), Alicyclobacillus sp. or mixtures thereof to biologically synthesize sulfuric acid according to step a) was investigated.9 cultures were prepared comprising a culture medium comprising 0.5 g / L MgSO4·7H2O, 0.45 g / L (NH4)2SO4, 0.15 g / L Na2SO4·10H2O, 0.05 g / L KH2PO4, 0.05 g / L KCl and 0.014 g / L Ca(NO3)2·4H2O at pH of 1.8, plus 1 mL of a concentrated trace elements solution, and microorganisms as listed in table 2. Table 2 10 grams of sulfur (S0) per litre of culture medium was added to each culture to produce biogenic sulfuric acid. Additionally, 44.22 g / L of culture medium of ferrous sulfate was added to the cultures comprising iron oxidizing bacteria. A cell concentration of 107cell / mL was achieved and then the cultures were cultured at 30 °C whilst being stirred at 140 rpm for 15 days. The pH, oxidation-reduction potential (ORP), cell concentration, sulfate ion concentrations and ferric ion concentrations of each culture medium was measured and the data is shown in figures 1A, 1B, 1C, 1D and 1E respectively. The pH and oxidation / reduction potential (ORP) of the cultures were measured by a Thermo-Scientific ph-Eh meter equipped with an Ag / AgCl electrode. The cell number of the cultures was counted using a counting chamber under an optical microscope. Ferric ion and sulfate concentrations of the culture media were measured by a BIOCHROM WPA Biowave II UV / Visible spectrophotometer using sulfosalicylic acid and barium chloride as the main chemical reagents at the wavelengths of 500 and 420 nm. The pH of all culture media continuously decreased over time indicating the effective oxidation of sulfur during the test; however, the pH of the sulfur oxidizing cultures was significantly lower than the cultures comprising both iron and sulfur oxidizing microorganisms. Without being bound by theory, this is thought to indicate inferior proton (H+) concentration and lower acid production by the cultures comprising both iron and sulfur oxidizing microorganisms. It was expected that a higher concentration of H+ would be accompanied by higher SO42-concentrations, but figure 1D shows that sulfate concentration in iron and sulfur oxidizing cultures is much higher than sole sulfur oxidizing microorganisms. Figure 1B shows that the ORP of the iron and sulfur oxidizing cultures increases from 550 mV at the beginning of the experiment to more than 800 mV on the third day. However, the ORP value of the sulfur oxidizing microorganisms and A. ferrooxidans without FeSO4 does not significantly vary during the experiment due to the absence of ferric ions in the solutions. The higher ORP value of the culture comprising A. ferrooxidans without FeSO4 (culture 8) is because of the presence of ferric ions in the culture. An increase in the cell concentration of all the bacterial cultures depicted in Figure 1C is an indication of the appropriate growth conditions. Culture 3 comprising A. thiooxidans reached the highest cell concentration (3.6×109cell / mL) at the end of the test. The cultures comprising iron and sulfur oxidizing microorganisms showed better growth than the cultures comprising only sulfur oxidizing microbes. Without being bound by theory, it is understood that the initial increase in sulfate and ferric ion concentrations as shown in Figure 1D and Figure 1E, is due to the oxidation of sulfur and ferrous ions, respectively and then after the 11thand 13thday, the sulfate and ferric ion concentration falls suddenly due to the formation of jarosite precipitates. As shown in figure 1A, culture 6 comprising Alicyclobacillus sp. resulted in the lowest pH after 15 days of culturing the culture. As shown in Figure 1C, culture 3 comprising Acidothiobacillus thiooxidans resulted in the highest cell concentration after 15 days of culturing the culture. Alicyclobacillus sp. and Acidothiobacillus thiooxidans were therefore selected as the best bacteria for the biosynthesis of sulfuric acid and the indirect bioleaching of black mass. Figure 2A shows that the combination of Alicyclobacillus sp. and Acidothiobacillus thiooxidans successfully reduced the pH of the culture medium to less than 0.5. Figure 2B shows that the combination of Alicyclobacillus sp. and Acidothiobacillus thiooxidans successfully increased sulfate concentration to near 7 g / L (Figure 2B). Moreover, figure 2C shows that the combination of Alicyclobacillus sp. and Acidothiobacillus thiooxidans achieves a cell concentration of over 3×109cell / mL at the end of the growth duration. The combination of Alicyclobacillus sp. and Acidothiobacillus thiooxidans is therefore advantageous because it efficiently produces the acid. The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.

Claims

1. CLAIMS 1. A method of recovering a metal from a metal-containing electrical or electronic material comprising the steps of: a) culturing at least one microorganism to produce at least one acid; b) adding the at least one acid and a reducing agent to the metal-containing electrical or electronic material and indirectly bioleaching the metal- containing electrical or electronic material; and c) recovering the metal.

2. A method according to claim 1 wherein the metal-containing electrical or electronic material is a battery material, preferably a waste battery material.

3. A method according to claim 1 or claim 2 wherein the metal-containing electrical or electronic material is a waste lithium-battery material.

4. A method according to any preceding claim wherein the reducing agent is ascorbic acid or ferrous sulfate.

5. A method according to any preceding claim wherein the acid, the metal- containing electrical or electronic material and the reducing agent mixture of step b) forms a reaction mixture and the reaction mixture may comprise at least 5 wt.% of the metal-containing electrical or electronic material as a wt.% of the total weight of the reaction mixture.

6. A method according to any preceding claim wherein at least one of said microorganism comprises a sulfur-oxidising bacteria.

7. A method according to any preceding claim wherein at least one of said microorganism comprises Alicyclobacillus sp. and at least one of said microorganism comprises Acidothiobacillus thiooxidans.

8. A method according to any preceding claim wherein the acid comprises sulfuric acid.

9. A method according to any preceding claim wherein step b) comprises combining the acid, the reducing agent and the metal-containing electrical or electronic material at substantially the same time.

10. A method according to any of claims 1 to 8 wherein step b) comprises combining the reducing agent and the metal-containing electrical or electronic material and then adding the acid.

11. A method according to any of claims 1 to 8 wherein step b) comprises combining the acid and the metal-containing electrical or electronic material and then adding the reducing agent.

12. A method according to any preceding claim wherein the metal is selected from the group consisting of: lithium, nickel, cobalt and manganese, or any combination thereof.

13. A method according to any preceding claim wherein step a) comprises culturing the at least one microorganism for at least 12 days.

14. A method according to any preceding claim wherein step a) comprises culturing the at least one microorganism in a culture medium in the presence of sulfur (S0).

15. A method according to claim 14 wherein the concentration of sulfur in step a) is about 10 g / L of culture medium.

16. A method according to any preceding claim comprising separating the acid and the microorganism(s) in a step between step a) and step b).

17. A method according to any preceding claim comprising filtering the acid in a step between step a) and step b).

18. A method according to any preceding claim wherein step b) is carried out at a temperature of between 20 and 90 °C, preferably between 70 and 90 °C.

19. A method according to any preceding claim wherein step c) comprises a filtration step and a drying step.

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