Recycled graphite material purification process

Abstract

The present invention relates to a process for the recovery of purified graphite materials from a recycled graphite concentrate, the process comprising: treating the recycled graphite concentrate in a caustic leach step, the caustic leach step comprising the contact of the recycled graphite concentrate with a sodium hydroxide solution at a temperature of at least 200°C and elevated pressure, and recovering a solid caustic leach product; and treating the solid caustic leach product in an acid leach step, the acid leach step comprising the contact of the solid caustic leach product with an acidic solution, and recovering a solid acid leach product, wherein the solid acid leach product comprises a purified graphite material.

Description

“Recycled Graphite Material Purification Process”Field of the Invention

[0001] The present invention relates to a process for the recovery of purified graphite materials from a recycled graphite concentrate. In particular, the graphite material purification process of the present invention recovers a purified graphite material that is of a purity suitable for use in the production of lithium-ion batteries (LiBs).

[0002] The present invention further relates to the use of the purified graphite material in the production of anode materials.Background Art

[0003] Graphite that is to be utilised in the production of lithium-ion batteries (LiBs) is typically required to be highly pure, for example greater than 99.90% (more specifically >99.95%) Loss on Ignition (LOI).

[0004] Graphite can be sourced from naturally occurring graphite ores. These materials are mined and concentrated to produce a graphite concentrate. The graphite concentrate typically has a relatively low graphite content, for example 60 to 70% Cg, and in which there are relatively high levels of gangue that may include silicate, sulphide, titanium and base metal minerals, depending on the graphite source. The graphite concentrate is then treated to an extensive purification process to produce a purified graphite material.

[0005] The volume of LiB being manufactured and used worldwide has been growing rapidly in recent years and is set for further expansion with the emerging markets of electric vehicles and mass electric power storage. As the volume of LiBs increases, so does the volume of associated waste materials, such as scrap materials from the LIB production process and spent LiBs that have reached their end of life. The increasing volume of these waste materials has warranted significant investigations into the recycling of these waste materials to improve the overall sustainability of LiBs.

[0006] Graphite is a large component of LiB waste materials and so the treatment of these waste materials to recover graphite is an attractive option, both economically andenvironmentally. However, the graphite containing waste materials contain high levels of impurities that must be removed before the graphite can be used. The impurities present in recycled graphite materials are typically different to those that are present in naturally occurring graphite ores. As such, purification processes developed for graphite ores are not suitable for removing all the impurities from recycled graphite materials. Purification processes specifically suited to the treatment of recycled graphite materials are therefore required.

[0007] The graphite material purification process and product of the present invention have as one object thereof to overcome substantially one or more of the abovementioned problems associated with prior art processes, or to at least provide a useful alternative thereto.

[0008] The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. This discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0009] Throughout the specification and claims, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0010] It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, a range from about 1 micrometer (pm) to about 2 pm should be interpreted to include not only the explicitly recited limits of from between from about 1 pm to about 2 pm, but also to include individual values, such as about 1.2 pm, about 1.5 pm, about 1.8 pm, etc., and sub-ranges, such as from about 1.1 pm to about 1.9 pm, from about 1.25 pm to about 1.75 pm, etc. Furthermore, when “about” and / or “substantially” are / is utilised to describe a value, they are meant to encompass minor variations (up to + / - 10%) from the stated value. Still further, when reference is made to a “trace amount” of something it is a reference to a concentration of less than about 100 micrograms per gram, this corresponds to less than 100 ppm in analytical terms.

[0011] It is to be further understood that references to the % recovery or % removal of an element or mineral, or similar, are, unless the context demands otherwise, a reference to the % of that component recovered or removed relative to the original content of the feed to the described process. Other references to % are, again as long as the context does not require otherwise, to be taken as references to weight or wt % (rather than volume or v %).Disclosure of the Invention

[0012] In accordance with a first aspect of the present invention there is provided a process for the recovery of purified graphite materials from a recycled graphite concentrate, the process comprising: treating the recycled graphite concentrate in a caustic leach step, the caustic leach step comprising the contact of the recycled graphite concentrate with a sodium hydroxide solution at a temperature of at least 200°C and elevated pressure, and recovering a solid caustic leach product; and treating the solid caustic leach product in an acid leach step, the acid leach step comprising the contact of the solid caustic leach product with an acidic solution, and recovering a solid acid leach product, wherein the solid acid leach product comprises a purified graphite material.

[0013] In one form of the present invention, at least a portion of the recycled graphite concentrate is recovered from waste battery materials. In one form of the present invention, at least a portion of the recycled graphite concentrate is recovered from waste lithium-ion battery materials. Preferably, the waste battery materials are subjected to one or more graphite concentration steps. In one form of the present invention, the graphite concentration steps comprise the separation of anode materials comprising a recycled graphite concentrate from the waste battery materials. In one form of the present invention, the graphite concentration steps comprise the hydro metallurgical treatment of the waste battery materials. Suitable hydrometallurgical treatment options include the acid leaching of the waste battery materials and the recovery of a leach residue comprising a recycled graphite concentrate. Additionally or alternatively, the graphite concentration steps comprise the pyrometallurgical treatment of the waste battery materials.

[0014] In one form of the present invention, at least a portion of the recycled graphite concentrate is recovered from scrap anode materials. The graphite contained in the scrap anode material may be a synthetic graphite or a natural graphite, or a combination there-of. Preferably, the scrap anode materials are subjected to one or more graphite concentration steps. In one form of the present invention, the graphite concentration steps comprise the separation of anode materials comprising a recycled graphite concentrate from waste electrode foils. Preferably, the graphite concentration steps comprise communition of the scrap anode materials and classification of the comminuted material. In one form of the present invention, the graphite concentration steps comprise a heat treatment step. Preferably, the heat treatment step will remove carbon additives and / or binders from the scrap anode materials.

[0015] In one form of the present invention, the solid acid leach product is subjected to a washing step to recover the purified graphite material. Preferably, the washing step will remove soluble impurities from the purified graphite material.

[0016] In one form of the present invention, the recycled graphite concentrate is subjected to one or more pre-treatment steps prior to the caustic leach step. The one or more pre-treatment steps may be selected from size reduction, size classification, physical separation, chemical separation, drying, heat treatment or combinations thereof. Suitable physical separation steps include gravity separation, flotation, and magnetic separation. Suitable chemical separation steps include froth flotation and chemical leaching. In one form of the present invention, the one or more pre-treatment steps does not include a caustic bake step. In this context, a caustic bake step refers to the baking of the recycled graphite concentrate under caustic conditions, for example, by mixing the recycled graphite concentrate with caustic soda and baking the mixture. The inventors have found that the high temperature caustic leach of the present invention may avoid the need for a caustic bake step when treating certain recycled graphite feedstocks. In an alternative form of the present invention, the one or more pre-treatment steps includes a caustic bake step. The inventors have found that the inclusion of a caustic bake step prior to the caustic leach step can increase the overall amount of impurities removed from the recycled graphite concentrate. Preferably, the caustic bake step is included when treating recycled graphite concentrates that contain refractory aluminium oxide. Without wishing to be bound by theory, it is understood that the combination of the caustic bake step and the high temperaturecaustic leach step will render the refractory aluminium oxide phases more amenable to leaching in the downstream acid leach step. This increases the amount of aluminium removed from the recycled graphite concentrate when compared to the caustic bake step or the high temperature caustic leach step in isolation. Furthermore, it has been found that that inclusion of the caustic bake step will reduce the valence of certain metals in the recycled graphite concentrate, such as cobalt and manganese, assisting in their subsequent leaching in the downstream acid leach steps. The inclusion of a caustic bake step has also been found to assist in the removal of fluorine components found in the binders and plastics of waste battery materials. It should be understood that the inclusion of the caustic bake step is not essential to the purification of the recycled graphite concentrate, but may improve the purity of the graphite recovered from certain recycled graphite feeds.

[0017] In one form of the present invention, the sodium hydroxide solution is a concentrated sodium hydroxide solution. Preferably, the concentration of the sodium hydroxide solution is at least 400 g / L. More preferably, the concentration of the sodium hydroxide solution is at least 500 g / L. Still preferably, the concentration of the sodium hydroxide solution is at least 600 g / L.

[0018] Preferably, the caustic leach step is conducted at a temperature of at least 220°C. Alternatively, the caustic leach step is conducted at a temperature between 200°C and 220°C.

[0019] In one form of the present invention, the starting slurry density of the caustic leach step is 150 to 250 g / L solids.

[0020] In one form of the present invention, the residence time of the caustic leach step is 2 to 16 hours.

[0021] In one form of the present invention, the caustic leach step is conducted at a pressure of at least 2 bar.

[0022] In one form of the present invention, the caustic leach step comprises a two-stage leach. Preferably, at least one stage is operated at a temperature of at least 200°C and elevated pressure. In one embodiment, both stages are operated at a temperature of atleast 200°C and elevated pressure. In an alternative embodiment, the first stage is conducted at a temperature of at least 200°C and elevated pressure and the second stage is conducted at temperature between 50° and 100°C, for example 80°C, and atmospheric pressure. Still preferably, the two-stage leach operates in a counter-current manner.

[0023] In one form of the present invention, the caustic leach step comprises the contact of the recycled graphite concentrate with a sodium hydroxide solution at a temperature of at least 200°C and elevated pressure, to form a caustic leach slurry and recovering a solid caustic leach product from the caustic leach slurry. Preferably, the caustic leach slurry is subjected to a solid liquid separation step to recover a solid caustic leach product and a caustic leachate solution. In one form of the present invention, the solid caustic leach product is treated in one or more re-pulp stages and / or washing stages. Preferably, the solid caustic leach product is re-pulped with a sodium hydroxide solution. In one form of the present invention, the solid caustic leach product is subjected to a drying step.

[0024] In one form of the present invention, the solid caustic leach product from the caustic leach step is subjected to a secondary caustic leach step prior to the acid leach step. Preferably, the secondary caustic leach step is operated at the same conditions as the caustic leach step.

[0025] In one form of the present invention, the acid leach step comprises one or more separate acid leach stages. Preferably, each acid leach stage comprises the contact of the solid caustic leach product with an acidic solution, thereby forming an acidic leach slurry and recovering a solid acid leach product from the acidic leach slurry. It is envisaged that different acidic solutions may be used at different acid leach stages to target different impurities remaining in the solid caustic leach product. Preferably, the solid leach product from each acid leach stage is washed before advancing to downstream acid leach stages or further processing steps. It is understood that washing may minimise soluble impurity carry over and help reduce reagent consumption.

[0026] In one form of the present invention, the acid leach step comprises the contact of the solid caustic leach material with a hydrofluoric acid solution. Preferably, the acid leach step comprises two or more acid leach stages, where at least one of the acid leach stages comprises the contact of the solid caustic leach material with a hydrofluoric acid solution.

[0027] In embodiments where the acid leach step comprises the contact of the solid caustic leach material with a hydrofluoric acid solution, the acid leach step preferably comprises: treating the solid caustic material in a first sulphuric acid leach stage comprising the contact of the solid caustic leach product with a sulphuric acid solution and separating undissolved leach solids; treating the leach solids of the first sulphuric acid leach stage in a hydrofluoric acid leach stage comprising the contact of the leach solids with a hydrofluoric acid solution and separating undissolved leach solids; treating the leach solids of the hydrofluoric acid leach stage in a second sulphuric acid leach stage comprising the contact of the leach solids with a sulphuric acid solution and separating undissolved leach solids; and treating the leach solids of the second sulphuric acid leach stage to one or more washing stages, and recovering a solid acid leach product comprising a purified graphite material.

[0028] Preferably, the undissolved leach solids from the first sulphuric acid leach stage are washed prior to advancing to the hydrofluoric acid leach stage. Preferably, the undissolved leach solids from the hydrofluoric acid leach stage are washed prior to advancing to the second sulphuric acid leach stage.

[0029] The first sulphuric acid leach stage is preferably undertaken at between about 5 to 60°C, for example about 40°C ±5°C. Still preferably, the first sulphuric acid leach stage has a retention time of between about 30 to 240 minutes, for example about 120 minutes.

[0030] Preferably, concentrated sulphuric acid is added in the first sulphuric acid leach stage. Still preferably, the residual free acid at the end of the first sulphuric leach stage is in the range of about 5-75 g / L H2SO4, for example about 50 g / L ±5 g / L H2SO4. The first sulphuric acid leach stage preferably operates with between about 5 to 25% solids, for example about 10% solids.

[0031] The hydrofluoric acid leach stage is preferably undertaken at between about 5 to 60°C, for example about 40°C ±5°C. Preferably, the residual free acid at the end of the hydrofluoric acid leach stage is in the range of about 15-75 g / L HF, for example about 60 g / L ±5 g / L HF. The hydrofluoric acid leach stage operates with between about 5 to 25% solids, for example about 10% solids.

[0032] Preferably, the hydrofluoric acid added to the hydrofluoric acid leach stage is in the range of about 20 to 70% concentration. The hydrofluoric acid concentration in the hydrofluoric acid leach stage is preferably in the range of about 15-50 g / L.

[0033] Still preferably, the leach solids from the hydrofluoric acid leach stage have no remaining silicon therein, or only trace amounts thereof.

[0034] The second sulphuric acid leach stage is preferably undertaken at between about 5 to 60°C, for example about 40°C ±5°C. The second sulphuric acid leach stage preferably operates with between about 5 to 25% solids, for example about 10% solids.

[0035] Preferably, the second sulphuric acid leach stage has a retention time of between about 30 to 240 minutes, for example about 120 minutes.

[0036] Preferably, concentrated sulphuric acid is added in the second sulphuric acid leach stage. Still preferably, the residual free acid at the end of the second sulphuric leach stage is in the range of about 5-75 g / L H2SO4, for example about 50 g / L ±5 g / L H2SO4. Acid solutions from the second sulphuric acid leach stage are preferably recovered and recycled to the first sulphuric acid leach stage.

[0037] The washing stages preferably comprise a single repulp-filtration stage using deionised water, multiple counter-current repulp-filtration stages, or, for example, five multiple counter-current repulp-filtration stages, using deionised water. Preferably, the washing stages operate with between about 5 to 25% solids, for example about 10% solids using three stages of counter-current repulp-filtration stages.

[0038] Preferably, liquid, residual salts, and / or acidity from the residual solids of the second sulphuric acid leach stage are recovered in the washing stages and returned to one or both of the first sulphuric acid leach stage and the second sulphuric acid leach stage.

[0039] In accordance with an alternative embodiment of the present invention, the acid leach step does not comprise the contact of the solid caustic leach material with a hydrofluoric acid solution. In this embodiment, the acidic solution used in the acid leach step is selected from only a hydrochloric acid solution and a sulphuric acid solution. More preferably, the only acidic solution used in the acid leach step is a hydrochloric acid solution.

[0040] In embodiments where the acid leach step comprises a hydrochloric acid leach solution, the hydrochloric acid concentration is between about 30 to 60 g / L. Hydrochloric acid is preferably added to the acid leach step at a rate of between about 150 to 500 kg / t feed, preferably 150 to 350 kg / t feed, to acidify residual alkalinity. The rate of addition of hydrochloric acid is preferably undertaken with consideration of background acid requirements.

[0041] In one form of the present invention, the acid leach step is operated at a temperature of between about 60 to 100°C.

[0042] In one form of the present invention, the acid leach step is operated with a slurry density of between about 10 to 35% w / w. In one form of the present invention, the acid leach step is operated with a slurry density of between about 15 to 35% w / w. In one form of the present invention, the acid leach step is operated with a slurry density of about 20% w / w.

[0043] In one form of the present invention, the acid leach step is operated with a total residence time of between about 2 to 6 hours.

[0044] In a preferred form of the present invention, the acid leach step is conducted at a temperature of about 80°C and with a total residence time of between about 2 to 6 hours.

[0045] In embodiments where the acid leach step does not comprise the contact of the solid caustic leach product with a hydrofluoric acid solution, the process preferably comprises treating the recycled graphite concentrate in an oxidative leach step. Morepreferably, the recycled graphite concentrate is treated in an oxidative leach step prior to the caustic leach step.

[0046] In one form of the present invention, the oxidative leach step comprises a first oxidative leach stage comprising the contact of the recycled graphite concentrate with an oxidant solution to form a first oxidative leach slurry. At least one of sodium hypochlorite, sodium chlorite, hydrogen peroxide, sodium meta bisulphite or sodium chlorate is utilised as the oxidant in the first oxidative leach stage. Preferably, the concentration of the oxidant in the first oxidative leach stage is based on the concentration of impurities in the recycled graphite concentrate. Those skilled in the art would understand the amount of oxidant required to ensure an appropriate EH (ORP). In one form of the present invention, the first oxidative leach step operates with a target redox potential of > about 425 mV (versus Ag / AgCI), preferably > about 550 mV (versus Ag / AgCI).

[0047] In one form of the present invention, the first oxidative leach step operates with a pH of > 10. Preferably, adjustment of the pH occurs first in the first oxidative leach stage. NaOH is added to adjust the pH, in the range of about 10 to 50 kg / t feed, for example in the range of about 20 to 25 kg / t feed, dependent upon the specific process requirements related to impurity load.

[0048] In one form of the present invention, the first oxidative leach step operates with a slurry density of between about 10 to 35% w / w. In one form of the present invention, the first oxidative leach step operates with a slurry density of between about 15 to 35% w / w. In one form of the present invention, the first oxidative leach step operates with a slurry density of about 20% w / w

[0049] In one form of the present invention, the first oxidative leach step operates at a temperature of between about 30 to 60°C.

[0050] In one form of the present invention, the first oxidative leach step operates with a residence time of between about 30 to 60 minutes.

[0051] In one form of the present invention, the target redox potential of the first oxidative leach step is in the range of about 800 to 1200 mV (versus Ag / AgCI). More preferably, thetarget redox potential of the first oxidative leach step is in the range of about 950 to 1000 mV (versus Ag / AgCI).

[0052] In one form of the present invention, the target redox potential of the first oxidative leach step is in the range of about 750 to 1500 mV (versus Ag / AgCI). More preferably, the target redox potential of the first oxidative leach step is in the range of about 850 to 1150 mV (versus Ag / AgCI).

[0053] In one form of the present invention, the oxidative leach step further comprises a second oxidative leach stage. Preferably, second oxidative leach stage comprises the contact of the first oxidative leach slurry with a hydrochloric acid solution. Preferably, the second oxidative leach stage targets a background HCI acidity of between about 30 to 60 g / L. More preferably, the second oxidative leach stage targets a background HCI acidity of at least 60 g / L.

[0054] In one form of the present invention, the second oxidative leach stage operates at a temperature of about 40 to 100oC.

[0055] In one form of the present invention, the second oxidative leach stage operates with a slurry density of between about 15 to 35% w / w, for example about 20% w / w.

[0056] In one form of the present invention, the second oxidative leach stage operates with a residence time in the range of about 2 to 6 hours.

[0057] In one form of the present invention, the second oxidative leach stage operates with an HCI addition rate of between about 150 to 500 kg / t feed. In one form of the present invention, the second oxidative leach stage operates with an HCI addition rate of between about 150 to 350 kg / t feed.

[0058] In one form of the present invention, the second oxidative leach stage may be conducted in multiple leach vessels arranged in counter current operation.

[0059] In a preferred embodiment, the second oxidative leach stage operates with a residence time of between about 2 to 4 hours and with an HCI addition rate of about 300 kg / t feed.

[0060] Aluminium and / or calcium minerals are at least partially leached in the second oxidative leach stage.

[0061] Following the completion of the second oxidative leach stage, the leach slurry in subjected to a solid liquid separation step to recover an oxidative leach residue. In this embodiment, the oxidative leach residue is subjected to the caustic leach step as discussed above.

[0062] In this embodiment of the present invention, the solid caustic material recovered from the caustic leach step is preferably subjected to a secondary caustic leach step, prior to the acid leach step.

[0063] Preferably, the process further comprises a drying step in which the purified graphite material is dried, providing a dried purified graphite material. The dried purified graphite material preferably contains between 0 to 2.5% moisture, for example less than about 1 % and further preferably 0.1 % moisture. In one form of the invention, the purified graphite material will preferably contain about 40% moisture prior to the drying step.

[0064] Preferably, the purified graphite material has a pH of 7 ± 2.5.

[0065] In one form of the present invention, the purified graphite material is classified in or after the drying step. The purified graphite material is preferably classified in the drying step into multiple products having different particle size and surface area properties, for example into at least two fractions. In one form the classification utilises a dry powder classification method, for example cyclone classification.

[0066] Preferably, the carbon recovery of the graphite material purification process is greater than about 93%, for example between about 90% and 98%.

[0067] Preferably, the Loss on Ignition (LOI) for the purified graphite material product of the process is greater than or equal to about 99.90%, for example about 99.90 to 99.98%, or 99.96 to 99.97%. The final purity is related to the impurities in the incoming recycled graphite feed stock.

[0068] Preferably, the carbon as graphite content of the purified graphite material product of the process is greater than 99.5% w / w.

[0069] Preferably, surface area (BET) of the purified graphite material product of the process is in the range of about 1 to 10 m2 / g, preferably about 3.0 m2 / g ±1 .0 m2 / g. The final purified product surface area is related to the properties of the incoming recycled graphite feedstock.

[0070] In accordance with the present invention there is further provided a purified graphite material product produced in accordance with the graphite material recovery process described hereinabove.

[0071] In one form of the present invention, the process further comprises the step of processing the purified graphite material to prepare an anode material.

[0072] In one form of the present invention, the purified graphite material is coated with a carbon based material and subjected to a pyrolysis, thereby producing an anode material.

[0073] Preferably, the carbon based material is one or more of pitch, polyethylene oxide and polyvinyl alcohol. Still preferably, the amount of carbon based material used in coating the purified graphite material is in the range of 2 to 12 wt% relative to graphite.

[0074] Preferably, the temperature of pyrolysis is between about 880°C to 1100°C. Still preferably, the time for pyrolysis is in the range of about 12 to 40 hours.

[0075] Preferably, the anode material has a Dso of between about 3 to 20 microns. Still preferably, the anode material has a Dso of between about 10 to 20 microns.

[0076] Preferably, the anode material has a surface area of about 1 to 9 m2 / g. More preferably, the anode material has a surface area of about 1 to 6 m2 / g.

[0077] In one form of the present invention, the purified graphite material is subjected to a shaping step prior to coating with the carbon based material. Alternatively, the coated purified graphite material is subjected to a shaping step.

[0078] In one form of the present invention, the purified graphite material is subjected to a classification step prior to coating with a carbon based material. In one form of the present invention, the particle size of the classified graphite material has a D50 of less than about 15 microns. In one form of the present invention, the particle size of the classified graphite material has a D50 of less than about 10 microns. In one form of the present invention, the particle size of the classified graphite material has a D50 in the range of about 4 to 6 microns.

[0079] Preferably, the surface area of the classified graphite material is about 1 to 9 m2 / g, for example 7 to 9 m2 / g.

[0080] Preferably, the anode material has a D50 of between about 3 to 20 microns. Still preferably, the anode material has a D50 of between about 10 to 20 microns.

[0081] Preferably, the anode material has a surface area of about 1 to 9 m2 / g. Preferably, the anode material has a surface area of about 1 to 6 m2 / g.

[0082] In an alternative form of the present invention, the purified graphite material is subjected to a mechanical exfoliation process to prepare high surface area (HSA) graphite material. Preferably, the mechanical exfoliation process is carried out in a grinding apparatus. More preferably, the grinding apparatus imparts a shearing force on the purified graphite material.

[0083] In one form of the present invention, the mechanical exfoliation process is conducted in the presence of a liquid medium.

[0084] In accordance with a second aspect of the present invention there is provided a process for the recovery of purified graphite materials from a recycled graphite concentrate, the process comprising: treating the recycled graphite concentrate in a caustic leach step, the caustic leach step comprising the contact of the recycled graphite concentrate with a sodium hydroxide solution at a temperature of at least 200°C and elevated pressure, and recovering a solid caustic leach product; andtreating the solid caustic leach product in an acid leach step, the acid leach step comprising the contact of the solid caustic leach product with a hydrofluoric acid solution, and recovering a solid acid leach product, wherein the solid acid leach product comprises a purified graphite material.

[0085] Preferably, the acid leach step comprises: treating the solid caustic leach product in a first sulphuric acid leach stage comprising the contact of the solid caustic leach product with a sulphuric acid solution and separating undissolved leach solids; treating the leach solids in a hydrofluoric acid leach stage comprising the contact of the leach solids with a hydrofluoric acid solution and separating undissolved leach solids; treating the leach solids in a second sulphuric acid leach stage comprising the contact of the leach solids with a sulphuric acid solution and separating undissolved leach solids; and treating the leach solids to one or more washing stages wherein at least a portion of any remaining soluble impurities are separated, and recovering a solid acid leach product, wherein the solid acid product comprises a purified graphite material.

[0086] In accordance with a third aspect of the present invention there is provided a process for the recovery of purified graphite materials from a recycled graphite concentrate, the process comprising: treating the recycled graphite concentrate in an oxidative leach step and recovering an oxidative leach residue; treating the oxidative leach residue in a caustic leach step, the caustic leach step comprising the contact of the recycled graphite concentrate with a sodium hydroxide solution at a temperature of at least 200°C and elevated pressure, and recovering a solid caustic leach product; and treating the solid caustic leach product in an acid leach step, the acid leach step comprising the contact of the solid caustic leach product with an acidic solutionselected from only hydrochloric acid and sulphuric acid, and recovering a solid acid leach product, wherein the solid acid leach product comprises a purified graphite material.

[0087] Preferably, the acid leach step does not comprise the contact of the solid caustic leach material with a hydrofluoric acid solution.

[0088] Preferably, the oxidative leach step comprises a first oxidative leach stage comprising the contact of the recycled graphite concentrate with an oxidant solution to form a first oxidative leach slurry and recovering an oxidative leach residue from the first oxidative leach slurry.

[0089] Preferably, the oxidative leach step further comprises a second oxidative leach stage, comprising the contact of the first oxidative leach slurry with a hydrochloric acid solution.

[0090] In accordance with a fourth aspect of the present invention there is provided a process for the preparation of anode materials from a recycled graphite concentrate, the process comprising: treating the recycled graphite concentrate in a caustic leach step, the caustic leach step comprising the contact of the recycled graphite concentrate with a sodium hydroxide solution at a temperature of at least 200°C and elevated pressure, and recovering a solid caustic leach product; treating the solid caustic product in an acid leach step, the acid leach step comprising the contact of the solid caustic leach product with an acidic solution, and recovering a solid acid leach product from the acidic leach slurry, wherein the solid acid leach product comprises a purified graphite material; and processing the solid acid leach product to prepare anode materials.

[0091] In accordance with a fifth aspect of the present invention there is provided a process for the preparation of HSA graphite materials from a recycled graphite concentrate, the process comprising:treating the recycled graphite concentrate in a caustic leach step, the caustic leach step comprising the contact of the recycled graphite concentrate with a sodium hydroxide solution at a temperature of at least 200°C and elevated pressure, and recovering a solid caustic leach product; treating the solid caustic product in an acid leach step, the acid leach step comprising the contact of the solid caustic leach product with an acidic solution, and recovering a solid acid leach product, wherein the solid acid leach product comprises a purified graphite material; and processing the solid acid leach product to prepare HSA graphite materials.Brief Description of the Drawings

[0092] The present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawing, in which:-Figure 1 is a schematic representation of a flow chart depicting a graphitic material purification process in accordance with a first embodiment of the present invention;Figure 2 is a schematic representation of a flow chart depicting a graphitic material purification process in accordance with a second embodiment of the present invention;Figure 3 is a table showing the results of a trial conducted to purify an end of life recycled graphite concentrate; andFigure 4 is a table showing the results of a trial conducted to purify an end of life recycled graphite concentrate treated under a range of caustic leaching conditions post baking.Best Mode(s) for Carrying Out the Invention

[0093] The process of the present invention is used to treat recycled graphite concentrates to remove impurities, thereby recovering purified graphite materials. Throughout the specification and claims, unless the context requires otherwise, recycled graphite concentrates, will be understood to refer to graphite-containing materials recoveredfrom recycled, scrap, spent or discarded source materials. The recycled graphite concentrate may be obtained directly from the source material or the source material may be treated in one or more concentration steps to recover the recycled graphite concentrate.

[0094] In one embodiment, the recycled graphite concentrate is recovered from waste battery materials. In one embodiment, the recycled graphite concentrate is recovered from waste lithium-ion battery materials. Batteries, including lithium-ion batteries contain anode materials that have a high graphite content, together with cathode material, electrolyte and separator material. The graphite contained in the waste battery materials may be a synthetic graphite or a natural graphite. The batteries may be subjected to a physical separation method to separate the anode materials from the other components. The physical separation method may include dismantling, crushing, screening, and other mechanical processes. The recovered anode material is suitable for use as the recycled graphite concentrate of the present invention. Alternatively, the recycled graphite concentrate may be recovered from battery black mass. Black mass refers to a concentrated mixture of valuable metals that is recovered from waste batteries. Black mass is typically prepared by shredding waste batteries, followed by the beneficiation of the shredded material to remove unwanted components such as casings, electrolyte materials and plastic wrappers. The black mass contains a mixture of anode and cathode materials. The black mass may first be treated in a hydrometallurgical process to recover valuable metals such as lithium, manganese, cobalt and nickel. Such hydrometallurgical processes typically involve the leaching of the majority of the valuable metals in an aqueous solution. The leach residues typically have a high concentration of graphite, together with residual impurities, and may be used as the recycled graphite concentrate of the present invention.

[0095] In an alternative embodiment, the recycled graphite concentrate is recovered from scrap anode materials. In this context, scrap anode materials refer to scraps or waste materials generated during the manufacture of battery components, including lithium-ion battery components. Such anode scraps comprise the graphite anode film adhered to a current collector foil with a polyvinylidene fluoride binder. The anode scraps have a high concentration of graphite and may be used as the recycled graphite concentrate of the present invention. The graphite contained in the scrap anode material may be a synthetic graphite or a natural graphite. Preferably, the scrap anode materials are subjected to one or more graphite concentration steps. In one form of the present invention, the graphiteconcentration steps comprise the separation of anode materials comprising a recycled graphite concentrate from waste electrode foils. Preferably, the graphite concentration steps comprise communition of the scrap anode materials and classification of the comminuted material. In one form of the present invention, the graphite concentration steps comprise a heat treatment step. Preferably, the heat treatment step will remove carbon additives and / or binders from the scrap anode materials.

[0096] Recycled graphite materials contain a certain amount of organic and inorganic impurities, mainly including organic binders, solid electrolyte interphase films and current collectors. Recycled graphite materials recovered from waste batteries also contain residual electrolytes, intercalated ions and metals from other battery components. The process of the present invention is intended to remove a substantial amount of these impurities to allow for the recovery of a purified graphite material. The purified graphite material may, in some embodiments of the present invention, be suitable as feed material in the preparation of new anode materials or HSA graphite materials.

[0097] The present invention provides a process for the recovery of purified graphite materials from a recycled graphite concentrate, the process comprising: treating the recycled graphite concentrate in a caustic leach step, the caustic leach step comprising the contact of the recycled graphite concentrate with a sodium hydroxide solution at a temperature of at least 200°C and elevated pressure, and recovering a solid caustic leach product; and treating the solid caustic leach product in an acid leach step, the acid leach step comprising the contact of the solid caustic leach product with an acidic solution, and recovering a solid acid leach product, wherein the solid acid leach product comprises a purified graphite material.

[0098] The caustic leach step of the present invention is used to remove silica and other impurities from the recycled graphite concentrate. The inventors have identified that a common impurity present in recycled graphite concentrates is crystalline aluminium oxide (AI2O3). It has been found that low temperature caustic leaches used to solubilise amorphous AI2O3 do not solubilise crystalline AI2O3, meaning that such solutions do notremove all aluminium impurities. The inventors have found that the majority of crystalline AI2O3 may be solubilised in a caustic leach step operated at a temperature of at least 200°C and elevated temperature. Following the completion of the caustic leach step, the acid leach step is used to remove the remaining impurities from the recycled graphite concentrate.

[0099] In Figures 1 and 2 there are shown processes for the recovery of purified graphite materials from a recycled graphite concentrate in accordance with separate embodiments of the present invention. The inventors have found that different acidic solutions may be employed in the acid leach step and that the choice of acidic solution may impact the overall process employed. In the embodiment shown in Figure 1 , the acid leach step includes the use of a hydrofluoric acid solution. In the embodiment shown in Figure 2, the acid leach step does not include the use of a hydrofluoric acid solution.HF Circuit

[0100] In Figure 1 , there is shown a process 10 for the recovery of purified graphite materials from a recycled graphite concentrate 12 in accordance with the present invention. If required, the recycled graphite concentrate 12 may be passed to a pre-treatment circuit (not shown) in which the recycled graphite concentrate 12 is subjected to one or more pretreatment steps. The pre-treatment steps required will depend on the nature of the recycled graphite concentrate to be treated. The one or more pre-treatment steps may include size reduction, size classification, physical separation, chemical separation, drying, heat treatment or combinations thereof. Suitable physical separation steps include gravity separation, flotation and magnetic separation. Suitable chemical separation steps include froth flotation and chemical leaching. The particle size of the recycled graphite concentrate should be less than 50 microns and preferably less than 30 microns. It should be noted that the pre-treatment circuit may not be required for all incoming feeds, in which case the recycled graphite concentrate 12 may be processed directly.

[0101] In one embodiment, the recycled graphite concentrate 12 is subjected to a caustic bake step (not shown) prior to the caustic leach step. The caustic bake step subjects a mixture of the recycled graphite concentrate 12 and sodium hydroxide and baked (roasted) at elevated temperature. The inventors have found that the caustic bake step can assist with the solubilisation of metals in the subsequent caustic leach step. The caustic bakestep is undertaken at between about 150 and 350°C, typically 250°C. The caustic bake step has a residence time in the range of about 60 to 240 minutes, for example about 120 minutes. The amount of caustic soda added to the graphite material to be purified is calculated using the ratio of NaOH / (AI-Ca-Fe-Mg-Si) > 7.0. The caustic bake step is undertaken, for example, in a rotating kiln.

[0102] The recycled graphite concentrate 12 is subjected to a caustic leach step 16. The caustic leach step 16 comprises the contact of the recycled graphite concentrate 12 with a sodium hydroxide solution 18 to form a caustic leach slurry. The caustic leach step 16 is conducted at a temperature of at least 200°C and elevated pressure. As detailed above, the caustic leach step will solubilise silica, amorphous AI2O3 and crystalline AI2O3 present in the recycled graphite concentrate 12.

[0103] In one embodiment, the concentration of the sodium hydroxide solution is at least 400 g / L. In one embodiment, the concentration of the sodium hydroxide solution is at least500 g / L. In one embodiment, the concentration of the sodium hydroxide solution is at least600 g / L. In one embodiment, the concentration of the sodium hydroxide solution is at least700 g / L. In one embodiment, concentrated sodium hydroxide is dosed into the caustic leach step throughout the caustic leach step. In an alternative embodiment, the concentration of sodium hydroxide is not controlled throughout the caustic leach step.

[0104] In one embodiment, the caustic leach step is conducted at a temperature of at least 220°C. In one embodiment, the caustic leach step is conducted at a temperature between 200°C and 240°C. In one embodiment, the caustic leach step is conducted at a temperature between 200°C and 220°C

[0105] In one embodiment, the caustic leach step is conducted at a pressure of at least 2 bar.

[0106] In one embodiment, the starting slurry density of the caustic leach step is 150 to 250 g / L solids.

[0107] In one embodiment, the residence time of the caustic leach step is 2 to 16 hours.

[0108] The caustic leach step is conducted in a suitable pressurised leach reactor constructed from a material that exhibits sufficient resistance to the caustic leach step. The caustic leach step may comprise a single leach stage conducted in a single leach reactor or may comprise two or more leach stages conducted across multiple leach reactors. It is preferred that the leach reactors are operated in a countercurrent manner (not shown). In embodiments where the caustic leach step is operated over multiple stages, at least one of the stages is operated at a temperature of at least 200°C and elevated pressure. However, it is preferable to operate all stages at a temperature of at least 200°C and elevated pressure.

[0109] The caustic leach slurry is subjected to a solid liquid separation step (not shown) to recover a solid caustic leach product 20 and a caustic leachate solution 21. In one embodiment, the solid material recovered in the solid liquid separation step is subjected to one or repulp steps to remove residual or entrained soluble species. In one embodiment, the solid material is repulped in a sodium hydroxide solution and the slurry is subjected to a further solid liquid separation step to recover a solid material. For example, the solid material may be repulped into a 200 g / l NaOH solution at 80°C for 30 minutes. In one embodiment, the solid material is repulped in water and the slurry is subjected to a further solid liquid separation step to recover a solid material. For example, the solid material may be repulped into water at 80°C for 30 minutes. The solid caustic leach product 20 is preferably dried at elevated temperature, for example 105°C, prior to further processing.

[0110] Caustic containing leachate 21 from the caustic leach step 16 is treated in a caustic regeneration step 22 to which lime and / or hydrated / slaked lime is fed, and from which regenerated caustic 23 is recovered, optionally concentrated, and recycled to the caustic leach step 16.[0011 1 ] The solid caustic leach product 20 is then passed to acid leach step 24. In embodiments where the acid leach step comprises the contact of the solid caustic leach product with a hydrofluoric acid solution, the acid leach step preferably comprises several acid leach stages. In the embodiment shown in Figure 1 , the acid leach step 24 comprises a first sulphuric acid leach stage 26, a hydrofluoric acid leach stage 28, a second sulphuric acid leach stage 30 and a washing stage 32.

[0112] The first sulphuric acid leach stage 26 comprises the contact of the solid caustic leach product 20 with a sulphuric acid solution 34 to form a leach slurry and the separation of an acidic leachate 36 from undissolved leach solids 38.

[0113] The first sulphuric acid leach stage is preferably undertaken at between about 5 to 60°C, for example about 40°C ±5°C. Still preferably, the first sulphuric acid leach stage has a retention time of between about 30 to 240 minutes, for example about 120 minutes. The residual free acid at the end of the first sulphuric leach stage is in the range of about 5- 75 g / L H2SO4, for example about 50 g / L ±5 g / L H2SO4. Concentrated sulphuric acid is added to the slurry to maintain target residual free acid. The first sulphuric acid leach stage preferably operates with between about 5 to 25% solids, for example about 10% solids. The first sulphuric acid leach step may be conducted in a single leach vessel or may be conducted across multiple leach vessels arranged in series.

[0114] The leach slurry is directed to a solid liquid separation step, for example a filter, to recover acidic leachate 36. Acidic leachate 36 is recycled to the process or diverted to effluent treatment (discussed below3) as required based on water balance and impurity build-up. Filter cake is washed and repulped with water at 40°C during 30 minutes at a solid / liquid ratio of about 165 g / l and the repulp slurry is directed to a solid liquid separation step, for example a filter, to recover a wash solution and undissolved leach solids 38.

[0115] The hydrofluoric acid leach stage 28 comprising the contact of the undissolved leach solids 38 with a hydrofluoric acid solution 42 to form a leach slurry and the separation of an acidic leachate 44 from undissolved leach solids 46.

[0116] The hydrofluoric acid leach stage is preferably undertaken at between about 5 to 60°C, for example about 40°C ±5°C. Preferably, the residual free acid at the end of the hydrofluoric acid leach stage is in the range of about 15-75 g / L HF, and preferably about 60 g / L ±5 g / L HF. The hydrofluoric acid leach stage operates with between about 5 to 25% solids, for example about 10% solids. Hydrofluoric acid added to the hydrofluoric acid leach stage is in the range of about 20 to 70% concentration. The hydrofluoric acid concentration in the hydrofluoric acid leach stage is preferably in the range of about 15-50 g / L. The hydrofluoric acid leach stage may be conducted in a single leach vessel or may be conducted across multiple leach vessels arranged in series.

[0117] The leach slurry is directed to a solid liquid separation step, for example a filter, to recover acidic leachate 44. Acidic leachate 44 is recycled to the process or diverted to effluent treatment (discussed below) as required based on water balance and impurity buildup. Filter cake is washed and repulped with water at 40°C during 30 minutes at a solid / liquid ratio of about 165 g / l and the repulp slurry is directed to a solid liquid separation step, for example a filter, to recover a wash solution and undissolved leach solids 46.

[0118] The second sulphuric acid leach stage 30 comprising the contact of the undissolved leach solids 46 with a sulphuric acid solution 48 to form a leach slurry and the separation of an acidic leachate 50 from undissolved leach solids 52.

[0119] The second sulphuric acid leach stage is preferably undertaken at between about 5 to 60°C, for example about 40°C ±5°C. The second sulphuric acid leach stage preferably operates with between about 5 to 25% solids, for example about 10% solids. Preferably, the second sulphuric acid leach stage has a retention time of between about 30 to 240 minutes, for example about 120 minutes. Concentrated sulphuric acid is added in the second sulphuric acid leach stage. Still preferably, the residual free acid at the end of the second sulphuric leach stage is in the range of about 5-75 g / L H2SO4, for example about 50 g / L ±5 g / L H2SO4. Acid solutions from the second sulphuric acid leach stage are preferably recovered and recycled to the first sulphuric acid leach stage and the second sulphuric acid leach stage. The leach slurry is directed to a solid liquid separation step, for example a filter, to recover acidic leachate 50. Acidic leachate 50 is recycled to the process or diverted to effluent treatment (discussed below) as required based on water balance and impurity buildup. Filter cake is washed and repulped with water at 40°C during 30 minutes at a solid / liquid ratio of about 165 g / l and the repulp slurry is directed to a solid liquid separation step, for example a filter, to recover a wash solution and undissolved leach solids 52.

[0120] The washing stage 32 comprises the contact of the undissolved leach solids 52 with a wash solution 54 and the separation of a purified graphite material 56. The washing stage 32 comprises a single repulp-filtration stage using deionised water, multiple countercurrent repulp-filtration stages, or, for example, five multiple counter-current repulp-filtration stages, using deionised water. Preferably, the washing stages operate with between about 5 to 25% solids, for example about 10% solids using three stages of counter-current repulpfiltration stages. Water, residual salts, and / or acidity from the residual solids of the secondsulphuric acid leach stage are recovered in the washing stages and returned to one or both of the first sulphuric acid leach stage and the second sulphuric acid leach stage. It is envisaged that carbonation may be incorporated during the washing stages 32, through the addition of sodium bicarbonate or the bubbling of carbon dioxide with caustic soda for pH control. This will help to neutralise carry-over acid from the second sulphuric acid leach stage and reduce the number of counter current washing steps required.

[0121] The purified graphite material 56 may be further treated in a drying step (not shown) to remove residual liquids.

[0122] A first effluent treatment plant 58 receives leachate streams 36 and 50 from the two sulphuric acid leach steps 26 and 30, respectively. The first effluent treatment plant 58 contacts the leachates with lime and iron sulphate, for example ferric sulphate, producing a neutralised solution 60 and a gypsum product 62. The volume of gypsum precipitation, or residue, may be minimised through use of caustic soda rather than lime in this step.

[0123] A second effluent treatment plant 64 receives leachate 44 from the hydrofluoric leach step 28. The second effluent treatment plant 64 also receives lime and iron sulphate, for example ferric sulphate, producing a neutralised solution 66 and a calcium fluoride product 68. Alternatively, the second effluent treatment plant receives aluminium hydroxide, thereby producing an aluminium fluoride product. It is envisaged that first effluent treatment plant 58 and second effluent treatment plant 64 can be combined in certain embodiments.Non-HF Circuit

[0124] In the embodiment shown in Figure 1 , hydrofluoric acid is used to solubilise certain impurities present in the recycled graphite concentrate. As would be appreciated by a person skilled in the art, the use of hydrofluoric acid brings with it significant environmental and occupational health and safety concerns. This makes the use of hydrofluoric acid unviable in certain settings. In accordance with a second aspect of the present invention, there is provided a process for the recovery of purified graphite materials from a recycled graphite concentrate in which the acid leach step does not include the use of hydrofluoric acid solutions.

[0125] In Figure 2, there is shown a process 100 for the recovery of purified graphite materials from a recycled graphite concentrate 12 in accordance with an embodiment of the present invention. As with the embodiment shown in Figure 1 , process 100 comprises a caustic leach step 16 and acid leach step 24. However, in this embodiment, the acid leach step only comprises the contact of the solid caustic leach product with an acidic solution selected from a hydrochloric acid solution and a sulphuric acid solution.

[0126] The recycled graphite concentrate 12 may be optionally passed to a pretreatment circuit as described above. The recycled graphite concentrate 12 is directed to an oxidative leach step 102 prior to the caustic leach step 16.

[0127] The oxidative leach step 102 comprises a first oxidative leach stage comprising the contact of the recycled graphite concentrate 12 with an oxidant solution 103 to form a first oxidative leach slurry. The recycled graphite concentrate 12 is repulped, for example using recycled process water, adjusted to a pH in the range of 10-11 with caustic soda. The first oxidative leach stage operates with a target redox potential of > about 425 mV (versus Ag / AgCI), with a pH of > 10, with a slurry density of between about 15 to 35% w / w solids, for example about 20% w / w, at a temperature of between about 30 to 60°C, and with a residence time of between about 30 to 60 minutes. The target redox potential is in the range of about 800 to 1200 mV (versus Ag / AgCI), for example in the range of about 950 to 1 000 mV (versus Ag / AgCI).

[0128] At least one of sodium hypochlorite, sodium chlorite, hydrogen peroxide, sodium meta bisulphite or sodium chlorate, which is to be understood to the option of a mixture thereof, is utilised as the oxidant in the first oxidative leach stage 102. It should be understood that the oxidant will oxidise certain impurity metals in the recycled graphite concentrate, while also acting to reduce other impurity metals in the recycled graphite concentrate. The oxidation / reduction of these impurity metals allows the efficient dissolution of these metals in the acid leach step. Added sodium hypochlorite is based on operating in the desired EH redox potential window defined by the impurity type and load in the feedstock.

[0129] The oxidative leach step 102 further comprises a second oxidative leach stage that comprises the contact of the first oxidative leach slurry with a hydrochloric acid solution. The second oxidative leach stages operates at a temperature of about 40 to 100°C, overmultiple leach stages, with a slurry density of between about 15 to 35% w / w, for example about 20% w / w, with a residence time in the range of about 2 to 6 hours, with an HCI addition rate of between about 150 to 350 kg / t feed, and with a background HCI acidity of between about 30 to 60 g / L. For example, the second oxidative leach portion operates with a residence time of between about 2 to 4 hours, and with an HCI addition rate of about 320 kg / t feed.

[0130] The slurry product of the oxidative leach step 102 is passed to a solid liquid separation step (not shown) to recover an oxidative leach residue 104 and a liquid product 106. Liquid product 106 is recycled or diverted to effluent treatment (discussed below) as required based on water balance and impurity build-up.

[0131] The oxidative leach residue 104 is directed to a caustic leach step 16 as described above to produce a solid caustic leach product 108. In the embodiment shown in Figure 2, the solid caustic leach product 108 is directed to a secondary caustic leach step 1 10 to produce a solid caustic leach product 1 1 1. The secondary caustic leach step 1 10 is conducted under the same or similar conditions as the caustic leach step 16. Caustic containing leachate 21 from the caustic leach step 16 and secondary caustic leach step 1 10 is treated in a caustic regeneration step 22 to which lime and / or hydrated / slaked lime is fed, and from which regenerated caustic 23 is recovered, optionally concentrated, and recycled to the caustic leach step 16 and / or secondary caustic leach step 1 10.

[0132] The solid caustic leach product 1 11 is directed to an acid leach step 24. In the embodiment shown in Figure 2, the acid leach step comprises a single acid leach stage 1 12. Acid leach stage 1 12 comprises the contact of the solid caustic leach product with an acidic solution 1 13 selected from hydrochloric acid and sulphuric acid.

[0133] Acid leach stage 1 12 Is conducted at a temperature of between about 60 to 100°C, with a slurry density of between about 15 to 35% w / w, for example about 20% w / w, with a total residence time of between about 2 to 6 hours. In embodiments where a hydraulic acid solution is used, the background HCI acidity is between about 30 to 60 g / L. The hydrochloric acid solution is added to acid leach stage 112 at a rate of between about 150 to 500 kg / t feed, for example about 320 kg / t feed. The rate of addition of hydrochloric acidto the acid leach stage 1 12 is undertaken with consideration of background acid requirements.

[0134] Acid leach stage 112 may be conducted in a single reactor or multiple reactors arranged in series.

[0135] The leach slurry is directed to a solid liquid separation step, for example a filter, to recover acidic leachate 1 14. Acidic leachate 114 is either recycled to the process or bled to effluent treatment (discussed below) based on water balance and impurity build-up requirements. Filter cake 1 16 is directed to a water repulping step 1 18 in which it is repulped with water 1 19 at 40°C during 30 minutes at a solid / liquid ratio of about 165 g / l. The repulp slurry is directed to a solid liquid separation step, for example a filter, to recover a wash solution and the separation of a purified graphite material 120.

[0136] The purified graphite material 120 may be further treated in a drying step (not shown) to remove residual liquids.

[0137] The process further comprises an effluent treatment stage 122 in which liquid products from the oxidative leach step 102, the caustic leach step 16, the secondary caustic leach step 1 10 and the acid leach step 1 12 are combined and treated. The treatment may comprise neutralisation by addition of an alkali and / or calcium precipitation by addition of sodium sulphate or other reagents to facilitate impurity removal by precipitation for example or ion exchange. The liquid product 124 is directed to a reagent recovery step 126 to recover sodium hydroxide, hydrochloric acid or sodium hypochlorite reagents to be recycled or reused within the process. Reagent recovery step 126, may include, for example, the recovery of a concentrated sodium chloride solution and a chlor-alkali electrolysis step to generate chlorine gas.

[0138] Additionally or alternatively, the caustic containing leachate from the caustic leach step 16 and / or the secondary caustic leach step 110 are treated in a caustic regeneration step 22 to which lime and / or hydrated / slaked lime is fed, and from which regenerated caustic 23 is recovered and recycled to the caustic leach step 16 and / or the secondary caustic leach step 1 10.Anode Preparation

[0139] The recovered purified graphite material may be used as a feed material for the preparation of new anode materials.

[0140] In one embodiment, the process further comprises the step of processing the purified graphite material to prepare an anode material. There are many different anode production processes known in the art. Those skilled in the art would be able to readily recognise the suitability of the purified graphite material for use in those processes. The Applicant’s International Patent Applications W02020 / 261194 and W02021 / 059171 , the entire content of which are incorporated herein by reference, describe suitable methods for preparing anode materials from the purified graphite material.Anode Preparation - Pyrolysis Option

[0141] In one embodiment, the purified graphite material is coated with a carbon based material and subjected to a pyrolysis, thereby producing an anode material. In one embodiment, the anode material has a Dso of between about 3 to 20 microns. In one embodiment, the anode material has a Dso of between about 10 to 20 microns.

[0142] In one embodiment, the anode material has a surface area of about 1 to 9 m2 / g. In one embodiment, the anode material has a surface area of about 1 to 6 m2 / g.

[0143] In one embodiment, the carbon based material is one or more of pitch, polyethylene oxide and polyvinyl alcohol. In one embodiment, the amount of carbon based material used in coating the purified graphite material is in the range of 2 to 12 wt% relative to graphite.

[0144] In one embodiment, the temperature of pyrolysis is between about 880°C to 1100°C. In one embodiment, the time for pyrolysis is in the range of about 12 to 40 hours.

[0145] In one embodiment, the purified graphite material is subjected to a size reduction step to produce a ground graphite material prior to coating with a carbon based material. In one embodiment, the particle size of the ground graphite material has a Dso of less than about 15 microns. In one embodiment, the particle size of the ground graphite material hasa D50 of less than about 10 microns. In one embodiment, the particle size of the ground graphite material has a D50 in the range of about 4 to 6 microns.

[0146] In one embodiment, the surface area of the ground graphite material is about 1 to 9 m2 / g, for example 7 to 9 m2 / g.Anode Preparation - Agglomeration Option

[0147] In one embodiment, the purified graphite material is processed by way of an agglomeration and / or surface modification step so as to produce the anode material.

[0148] In one embodiment, the agglomeration and / or surface modification step comprises a spray drying process. The spray drying process may preferably be achieved utilising a fluidised bed.

[0149] In one embodiment, the anode material has a D50 of between about 3 to 20 microns. In one embodiment, the anode material has a D50 of between about 10 to 20 microns.

[0150] In one embodiment, the anode material has a surface area of about 1 to 9 m2 / g. In one embodiment, the anode material has a surface area of about 1 to 6 m2 / g.HSA Graphite Preparation

[0151] The recovered purified graphite material may be used as a feed material for the preparation of HSA graphite material. In one embodiment, the process further comprises the step of processing the purified graphite material to prepare HSA graphite particles. In one embodiment, the purified graphite material is subjected a mechanical exfoliation process to produce HSA graphite particles.

[0152] In one embodiment, the mechanical exfoliation step is conducted in the presence of a liquid medium. Alternatively, the mechanical exfoliation step is a dry mechanical exfoliation step, for example jet milling.

[0153] In one form of the present invention, the specific milling energy of the mechanical exfoliation step is in the range 50 - 500 kWh / t, but preferably greater than 200 kWh / t.

[0154] In one form of the present invention, the process further comprises the step of processing the HSA graphite material to prepare an electrode material. Preferably, the HSA graphite material is used as an additive in an electrode material. Those skilled in the art would be aware of electrode production processes that incorporate HSA graphite materials. For example, the Applicant’s International Patent Application PCT / IB2020 / 056050 (WO 2020 / 261194), the entire content of which is incorporated herein by reference, describes a silicon and graphite containing composite material comprising a plurality of silicon nanoparticles coated with graphite particles, few-layer graphene particles, graphite nanoparticles, a carbon matrix, and an amorphous carbon external shell, wherein each of the graphite particle coated silicon nanoparticles, the few-layer graphene particles, and the graphite nanoparticles are held within the carbon matrix.Example 1

[0155] Four samples of recycled graphite concentrates were obtained from various sources. Details of the samples are provided in Table 1Table 1 : Sample Analysis

[0156] A chemical analysis of each sample was conducted using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The results are shown in Table 2.Ta&te 2: Sample AssayExample 2 - Comparative HF Purification Route:

[0157] Several samples were treated in a purification process that comprised a caustic baking step followed by a hydrofluoric acid leach to determine whether such a process would be suitable to purify recycled graphite concentrates. The purification process comprised the following steps:(i). The recycled graphite concentrate samples were mixed batchwise with sodium hydroxide and water was added until pellets of a size between 2 and 4 mm were obtained. The quantity of NaOH added was calculated based on the LOI measurement of the graphite. The graphite / NaOH mixture was baked in an oven at 250°C during 4 hours.(ii). The baked material was leached in water at 40°C during 2 hours targeting L / S(liquid / solid) ratio = 6.(iii). The water leached cake was leached in diluted sulphuric acid at 40°C during 4 hours targeting a L / S ratio = 6.(iv). The sulphuric acid leached cake was repulped in water at 40°C during 30 minutes targeting a L / S ratio = 6.(v). The water repulped cake was leached in diluted hydrofluoric acid at 40°C during 4 hours targeting a L / S ratio = 6.(vi). The hydrofluoric acid leached cake was repulped in water at 40°C during 30 minutes targeting a L / S ratio = 6.(vii). The water repulped cake was leached a second time in diluted sulphuric acid at 40°C during 4 hours targeting a L / S ratio = 6.(viii). The sulphuric acid leached cake was repulped five times consecutively in water at 40°C during 30 minutes targeting a L / S ratio = 6: After the completion of the fifth water repulping, the cake was dried at 105°C in an oven.

[0158] The results of the tests are shown in Table 3:Table 3: HP Purification Results

[0159] The results of the tests show that aluminium remains as a major impurity in the samples. This indicates that purification processes that include a caustic bake step followed by a HF leach step are not sufficient to solubilise all aluminium values in the sample.Example 3 - Comparative Non-HF Purification Route

[0160] One sample was treated in a purification process that comprised a caustic leach step operated at a temperature of about 140°C under pressure to determine whether such a process would be suitable to purify recycled graphite concentrates. The purification process comprised the following steps:(i). The sample was treated in an oxidation leach step, in which the sample was pulped with de-ionized water having pH of about 10. 14.7% NaCIO solution was added to the slurry to target 200% of the stoichiometric quantity required for oxidizing the sulphur contained in the graphite sample. After 60 minutes of leaching, the temperature was raised to 80°C and a 37% HCI solution was added. The amount of HCI added was calculated so as to obtain an initial concentration of about 60 g / L of HCI in the slurry. After 6 hours of leaching, the slurry was filtered and the cakes were then washed with water at 80°C. Finally, the cakes were dried at 105°C.(ii). The oxidative leach cakes were then treated in a first caustic pressure leach stage, in which the dry oxidative acid leaching cakes were added into a 400 g / l NaOHsolution in a pressure vessel. The vessel was heated to 140°C and the sample was leached during 4 hours. The slurry was then filtered on a pressure filter and the cake was repulped into 1 000 ml of a 200 g / l NaOH solution at 80°C during 30 min. The slurry was filtered on a pressure filter and the cake was repulped into de-ionized water at 80°C during 30 min, followed by filtration and cake washing. The cake was finally dried at 105°C.(iii). The caustic pressure leach cakes were treated in a second caustic pressure leach stage, conducted in the same manner as first caustic pressure leach stage to recover dried caustic pressure leach cakes.(iv). The caustic pressure leach cakes were treated in a hydrochloric acid leach stage, in which 100 g samples were added into 1000 ml of a 50 g / l HCI solution at 80°C for 4 hours under agitation. The slurry was then filtered on Buchner and the cake was repulped into 1000 ml of de-ionized water at 80°C, followed by filtration and further washing. The cake was finally dried at 105°C and the solutions and the solid were analysed.

[0161] The results of the tests are shown in Table 4:Tafefe 4: Caustic Leach Purification Results

[0162] The results of the tests show that a purification process that includes a caustic leach conducted at a temperature of around 140°C resulted in a lower amount of aluminium in the purified product than the combined caustic bake / hydrofluoric acid leach process of Example 2. However, the results also show that a caustic leach conducted at a temperature of around 140°C is not sufficient to solubilise all aluminium values in the sample.

[0163] X-ray diffraction (XRD) analysis on the samples of indicated that the recycled graphite concentrates all contained AI2O3 in its crystalline form. Without wishing to be bound by theory, it is understood by the inventors that crystalline-AhOa exhibits increased chemical stability due to the highly ordered crystalline structure and this results in limited dissolution of crystalline-AhOa in sodium hydroxide at 140°C. The inventors understand that the operation of the caustic leach step at a temperature of at least 200°C will improve the reaction mechanics and allow for more complete dissolution of crystalline-AhOa in sodium hydroxide.Example 4 - High Temperature Caustic Leach

[0164] A series of tests were conducted on a recycled graphite feed containing 1 .84% aluminium to determine whether the process of the present invention was suitable to reduce impurities.

[0165] A first test was conducted using a purification route that did not include the use of hydrofluoric acid. In this test, the recycled graphite feed was subjected to the following treatment:(i). The recycled graphite feed is subjected to an oxidative leach in which the feed is repulped at a solid / liquid ratio = 250 g / l in diluted NaCIO solution at 30°C during 30 minutes after having raised the pH above 10 with NaOH solution. After 30 minutes, the temperature is raised to 80°C and concentrated HCI solution is added to reach 60 g / l HCI in the slurry. 6 hours later, the slurry is filtered on Buchner and the cake is washed with water at 80°. The cake is dried at 105°C;(ii). The oxidative hydrochloric acid leached graphite is leached at a solid / liquid ratio =150 g / l in concentrated NaOH solution (400 g / l) at 220°C during 4 hours. The slurry is filtered under pressure. The cake is repulped into a 200 g / l NaOH solution at 80°C during 30 minutes and the slurry is filtered on Buchner. The cake is repulped into water at 80°C during 30 minutes and the slurry is filtered on Buchner. The cake is dried at 105°C;(iii). The NaOH leached graphite is leached a second time at a solid / liquid ratio = 150 g / l in concentrated NaOH solution (400 g / l) at 220°C during 4 hours. The slurry is filtered under pressure. The cake is repulped into a 200 g / l NaOH solution at 80°C during 30 minutes and the slurry is filtered on Buchner. The cake is repulped into water at 80°C during 30 minutes and the slurry is filtered on Buchner. The cake is dried at 105°C;(iv). The NaOH leached graphite is leached at a solid-liquid ratio = 100 g / l in diluted HCI solution (50 g / l) at 80°C during 4 hours. The slurry is filtered on Buchner. The cake is repulped into water at 80°C during 30 minutes and the slurry is filtered on Buchner. The cake is dried at 105°C.

[0166] A second test was conducted using a purification route that included the use of hydrofluoric acid. In this test, the recycled graphite feed was subjected to the following treatment:(i). The concentrate graphite is mixed with NaOH and water and mixed in Eirich mixer.The graphite / NaOH mixture is baked at 250°C during 4 hours;(ii). The baked mixture is leached at a solid / liquid ratio = 150 g / l in concentrated NaOH solution (400 g / l) at 220°C during 4 hours. The slurry is filtered under pressure. The cake is repulped into a 200 g / l NaOH solution at 80°C during 30 minutes and the slurry is filtered on Buchner. The cake is repulped into water at 80°C during 30 minutes and the slurry is filtered on Buchner and the cake is dried at 105°C;(iii). The NaOH leached cake is leached in diluted sulfuric acid (50 g / l) at 40°C during 4 hours at a solid / liquid ratio ~ 165 g / l. The sulfuric acid leached cake is repulped in water at 40°C during 30 minutes at a solid / liquid ratio ~ 165 g / l;(iv). The water repulped cake is leached in diluted hydrofluoric acid (60 g / l) at 40°C during4 hours at a solid / liquid ratio ~ 165 g / l. The hydrofluoric acid leached cake is repulped in water at 40°C during 30 minutes at a solid / liquid ratio ~ 165 g / l;(v). The water repulped cake is leached a second time in diluted sulfuric acid (50 g / l) at40°C during 4 hours at a solid / liquid ratio ~ 165 g / l;(vi). The sulfuric acid leached cake is repulped five times consecutively in water at 40°C during 30 minutes at a solid / liquid ratio ~ 165 g / l and the cake is dried at 105°C.

[0167] A third test was conducted that mirrors the second test, but with the acid bake (step (i)) omitted. In this test, the concentrate graphite was leached directly in concentrated NaOH solution (400 g / l) at 220°C during 4 hours. The remaining treatment step were the same as the second test.

[0168] A fourth test was completed for comparative purposes. The fourth test mirrored the second test, but with the omission of the high temperature caustic acid leach. Instead, the baked material was leached three times consecutively in water at 40°C at a solid / liquid ratio ~ 165 g / l. The duration of the respective water leaches was 2 hours, 1 hour and 30. The water leached cake was then subjected to a first sulphuric acid leach, a hydrofluoric acid leach and a second sulphuric acid leach per the second test.

[0169] The results of the tests are shown in the table of Figure 3. The results showed that by subjecting the recycled graphite material to a purification process that includes a high temperature caustic leach step followed by an acid leach step, that aluminium and otherimpurities could be removed. The results also show that the absence of the high temperature caustic leach step in the fourth test resulted in poorer aluminium removal.Example 5 - Comparative Caustic Leach Studies

[0170] A series of tests were conducted to determine the effect that the temperature of the caustic leach step had on the purification of a recycled graphite material containing 1.84% aluminium. In each test the recycled graphite material was carried out on pellets produced by baking a mixture of the recycled graphite material and 250 kg / t NaOH (ratio NaOH / (AI-Ca-Fe-Mg-Si) = 7.0) at 250°C for 4 hours. The pellets were subjected to a caustic leach step in accordance with the conditions set out in Table 5.Table 5: Cawsf c Leac / i i est Conditions

[0171] Following the caustic leach step, each sample was subjected to an acid leaching circuit that comprises a first sulphuric acid leach at 50°C for 4 hours, a hydrofluoric acid leach at 50°C for 4 hours followed by water repulping / washing and a second sulphuric acid leach at 50°C for 4 hours followed by four stages of water repulping / washing.

[0172] The results of the tests are shown in the table of Figure 4. The results showed that the purification processes with caustic leach steps operated below 200°C did not sufficiently remove aluminium from the recycled graphite material.Example 6 - Performance Testing

[0173] A test was conducted on the recovered purified graphite material to investigate its suitability for use an anode material. Anode material was prepared using the recovered purified graphite material. The purified graphite was coated using pitch (4wt.%) in a dry mixing process. The coated material was pyrolyzed under inert atmosphere to form graphite anode material. Both uncalendared and calendered anodes were produced from the graphite anode material. The prepared anodes were subjected to electrochemical performance testing using the testing program of Table 6 and the following cell conditions:Slurry formula: Graphite blend: CMC: SBR is 96.5%: 1 .5%:2%CMC: Nippon Paper Mac350HC20980169 / 1 .50 wt%Solid content in the slurry: 44-46%Separator: Fiber glass Whatman GF / BElectrode information:• Calendaring density is 1 .6 g cm’3• Loading: 2.7-2.8 mAh cm’2Area: 1 .767 cm2Table 6: Testing program (time controlled CCCV method):

[0174] The results of the tests are shown in Table 7:Tci&fe 7: Anode Performance Test Results

[0175] The results show that the recovered purified graphite material was suitable for use as an anode material. The capacity of the material was -347 mAh / g capacity, which is similar to the typical capacities of synthetic graphite anodes, which range from 340-350 mAh / g of synthetic graphite. The results also show the high first cycle efficiency, which is understood to result from the high purity of the graphite and the quality of the carbon coating.

Claims

Claims1 . A process for the recovery of purified graphite materials from a recycled graphite concentrate, the process comprising: treating the recycled graphite concentrate in a caustic leach step, the caustic leach step comprising the contact of the recycled graphite concentrate with a sodium hydroxide solution at a temperature of at least 200°C and elevated pressure, and recovering a solid caustic leach product; and treating the solid caustic leach product in an acid leach step, the acid leach step comprising the contact of the solid caustic leach product with an acidic solution, and recovering a solid acid leach product, wherein the solid acid leach product comprises a purified graphite material.

2. A process according to claim 1 , wherein the recycled graphite concentrate is subjected to one or more pre-treatment steps prior to the caustic leach step.

3. A process according to claim 2, wherein the one or more pre-treatment steps includes a caustic bake step.

4. A process according to claim 2, wherein the one or more pre-treatment steps do not include a caustic bake step.

5. A process according to any of preceding claims, wherein the sodium hydroxide solution is a concentrated sodium hydroxide solution.

6. A process according to any of preceding claims, wherein the acid leach step comprises one or more separate acid leach stages.

7. A process according to any of preceding claims, wherein the acid leach step comprises the contact of the solid caustic leach material with a hydrofluoric acid solution.

8. A process according to claim 7, the acid leach step comprises two or more acid leach stages, where at least one of the acid leach stages comprises the contact of the solid caustic leach material with a hydrofluoric acid solution.

9. A process according to claim 8, wherein the acid leach step preferably comprises: treating the solid caustic material in a first sulphuric acid leach stage comprising the contact of the solid caustic leach product with a sulphuric acid solution and separating undissolved leach solids; treating the leach solids of the first sulphuric acid leach stage in a hydrofluoric acid leach stage comprising the contact of the leach solids with a hydrofluoric acid solution and separating undissolved leach solids; treating the leach solids of the hydrofluoric acid leach stage in a second sulphuric acid leach stage comprising the contact of the leach solids with a sulphuric acid solution and separating undissolved leach solids; and treating the leach solids of the second sulphuric acid leach stage to one or more washing stages, and recovering a solid acid leach product comprising a purified graphite material.

10. A process according to any of claims 1 to 6, wherein the acid leach step comprises contact of the solid caustic leach product with an acidic solution selected from only a hydrochloric acid solution and a sulphuric acid solution.1 1. A process according to claim 10, wherein the acid leach step comprises contact of the solid caustic leach product with only a hydrochloric acid solution.

12. A process according to claim 10 or 11 , wherein the acid leach step does not comprise the contact of the solid caustic leach material with a hydrofluoric acid solution.

13. A process according to any of claims 10 to 12, wherein the process comprises treating the recycled graphite concentrate in an oxidative leach step prior to the caustic leach step.

14. A process according to claim 13, wherein the oxidative leach step comprises a first oxidative leach stage comprising the contact of the recycled graphite concentrate with an oxidant solution to form a first oxidative leach slurry.

15. A process according to claim 13, wherein the oxidative leach step further comprises a second oxidative leach stage comprising the contact of the first oxidative leach slurry with a hydrochloric acid solution.

16. A process according to any of preceding claims, wherein the carbon recovery of the graphite material purification process is greater than about 87%.

17. A process according to any of preceding claims, wherein the process further comprises the step of processing the purified graphite material to prepare an anode material.

18. A process for the recovery of purified graphite materials from a recycled graphite concentrate, the process comprising: treating the recycled graphite concentrate in a caustic leach step, the caustic leach step comprising the contact of the recycled graphite concentrate with a sodium hydroxide solution at a temperature of at least 200°C and elevated pressure, and recovering a solid caustic leach product; and treating the solid caustic leach product in an acid leach step, the acid leach step comprising the contact of the solid caustic leach product with a hydrofluoric acid solution, and recovering a solid acid leach product, wherein the solid acid leach product comprises a purified graphite material.

19. A process according to claim 18, wherein the acid leach step comprises: treating the solid caustic leach product in a first sulphuric acid leach stage comprising the contact of the solid caustic leach product with a sulphuric acid solution and separating undissolved leach solids; treating the leach solids in a hydrofluoric acid leach stage comprising the contact of the leach solids with a hydrofluoric acid solution and separating undissolved leach solids; treating the leach solids in a second sulphuric acid leach stage comprising the contact of the leach solids with a sulphuric acid solution and separating undissolved leach solids; andtreating the leach solids to one or more washing stages wherein at least a portion of any remaining soluble impurities are separated, and recovering a solid acid leach product, wherein the solid acid product comprises a purified graphite material.

20. A process for the recovery of purified graphite materials from a recycled graphite concentrate, the process comprising: treating the recycled graphite concentrate in an oxidative leach step and recovering an oxidative leach residue; treating the oxidative leach residue in a caustic leach step, the caustic leach step comprising the contact of the recycled graphite concentrate with a sodium hydroxide solution at a temperature of at least 200°C and elevated pressure, and recovering a solid caustic leach product; and treating the solid caustic leach product in an acid leach step, the acid leach step comprising the contact of the solid caustic leach product with an acidic solution selected from only hydrochloric acid and sulphuric acid, and recovering a solid acid leach product, wherein the solid acid leach product comprises a purified graphite material.21 . A process for the production of an anode material from a recycled graphite concentrate, the process comprising: subjecting the recycled graphite concentrate to the process of any of claims 1 to 20 to recover a purified graphite material; and processing the purified graphite material to prepare an anode material.

22. A process according to claim 21 , wherein the purified graphite material is coated with a carbon based material and subjected to a pyrolysis, thereby producing an anode material.

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