Graphite material purification process

Abstract

A graphite material purification process (10), the process comprising: a pelletization step (14); an alkaline baking step (16) providing a sintered product; a water leaching step (18), whereby the impurity minerals are dissolved, effluent treatment is carried out and separation is carried out; a first sulfuric acid leaching step (20) in which the remaining impurity minerals are dissolved, an effluent treatment is carried out and the leached solids are separated; a hydrofluoric acid leaching step (22) in which the partially leached impurity minerals are dissolved, subjected to an effluent treatment and separated from the leached solids; a second sulfuric acid leaching step (24) in which the impurity minerals not leached in the previous step and the components precipitated in the hydrofluoric acid leaching step (22) are dissolved, an effluent treatment is carried out and separated from the leached solids; and a washing step in which residual soluble impurities are separated and a purified graphite material (32) is provided.

Description

Technical Field

[0001] The present invention relates to a process for purifying graphite materials.

[0002] More specifically, the graphite material purification process of the present invention is designed to be applicable to the purification of materials with low graphite content.

[0003] In particular, the graphite material purification process of the present invention is designed for the production of graphite materials having a purity suitable for use in the production of lithium-ion batteries (LiBs). Background Art

[0004] Graphite utilized in the production of lithium-ion batteries (LiBs) typically requires high purity, e.g., greater than 99.90% loss on ignition (LOI). However, it should be noted that LiB purity requirements do also depend on LiB blend and formulation specifics. The purity requirements pose challenges for producing suitable graphite products from materials having a relatively low graphite content, e.g., 60% to 70% Cg, and in which there are relatively high levels of silicate, sulfide, titanium, and base metal minerals. These challenges are exacerbated if the contaminant minerals are highly dispersed throughout the graphite ore and carbon loss is desired to be reduced or minimized.

[0005] Currently employed methods for purifying graphite for use in LiB production utilize particularly aggressive acid leaching steps, typically leaching steps that require high concentrations and volumes of hydrofluoric acid. This results in significant environmental and occupational health and safety concerns. These methods also have low levels of carbon recovery, e.g., below about 85%. Further, these methods generally also start with graphite materials having a carbon content of greater than or equal to 90%.

[0006] Providing an improved graphite material purification process that reduces carbon loss and / or reduces dependence on large amounts of highly concentrated acids would have significant advantages and benefits.

[0007] The graphite material purification process and product of the present invention have as one of its objects: substantially overcoming one or more of the above-mentioned problems associated with the prior art processes, or at least providing a useful alternative thereto.

[0008] The foregoing discussion of the background art is only intended to facilitate an understanding of the present invention. The discussion does not admit or recognize that any of the materials mentioned were or were part of common general knowledge at the priority date of the present 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 the stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0010] It is understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, a range of from about 1 micrometer (μm) to about 2 μm should be interpreted to include not only the explicitly listed limits between about 1 μm and about 2 μm, but also individual values such as about 1.2 μm, about 1.5 μm, about 1.8 μm, etc., and sub-ranges such as from about 1.1 μm to about 1.9 μm, from about 1.25 μm to about 1.75 μm, etc. Further, when using "about" and / or "substantially" to describe a value, it is intended to cover minor variations (up to + / - 10%) from the stated value. Still further, when referring to a "trace" of something, it means a concentration of less than about 100 micrograms per gram.

[0011] It is further understood that, unless the context requires otherwise, the % recovery or % removal of an element or mineral or the like mentioned refers to the % of that component recovered or removed relative to the original content of the feed to the described process. Other mentions of %, still as long as the context does not otherwise require, are understood to refer to weight % or wt% (rather than volume % or v%). Summary of the Invention

[0012] According to the present invention, there is provided a process for purifying graphite material, the process comprising the following steps:

[0013] (i) Feeding a graphite material to be purified at a certain concentration to a granulation step to provide a granulated material;

[0014] (ii) Baking the granulated material of step (i) under alkaline conditions to provide a sintered product and thereby rendering one or more impurity minerals soluble;

[0015] (iii) Feeding the sintered product of step (ii) to a water leaching step, thereby dissolving at least a part of the impurity minerals from step (ii), treating the effluent, and separating it from the leach solid;

[0016] (iv) Feeding the leach solid of step (iii) to a first sulfuric acid leaching step, wherein the impurity minerals partially leached in step (iii) are dissolved, treating the effluent, and separating it from the leach solid;

[0017] (v) Feed the leached solids from step (iv) to a hydrofluoric acid leaching step, where partially leached impurity minerals are dissolved, effluent treatment is carried out, and separation from the leached solids is effected;

[0018] (vi) Feed the leached solids from step (v) to a second sulfuric acid leaching step, where impurity minerals or components that were not leached in the previous steps and precipitated during step (v) are dissolved, effluent treatment is carried out, and separation from the leached solids is effected; and

[0019] (vii) Feed the leached solids from step (vi) to one or more washing stages, where at least a portion of any remaining soluble impurities is separated, and thereby produce a purified graphite material.

[0020] Preferably, the process further includes a drying step, where the purified graphite material from step (vii) is dried, thereby providing a dried purified graphite material. The dried purified graphite material preferably contains between 0 and 2.5% moisture, such as less than about 1% and further preferably 0.1% moisture. In one form of the invention, the purified graphite material from step (vii) will preferably contain about 40% moisture prior to the drying step.

[0021] Preferably, the purified graphite material from step (vii) has a pH of 7 ± 2.5.

[0022] More preferably, the purified graphite material from step (vii) is sized during or after the drying step. The purified graphite material from step (vii) is preferably sized during the drying step into a plurality of products having different particle size and surface area properties, such as sized into at least two fractions. In one form, sizing utilizes a dry powder sizing method, such as cyclone sizing.

[0023] The granulation step (i) preferably includes adding caustic soda and water to the graphite material to be purified in a stepwise manner. The granules produced in the granulation step (i) are preferably fine granules having a diameter of about 2 - 0 mm, such as 5 mm ± 2 mm.

[0024] In one form of the invention, dry fine powder of the purified graphite material is added during the granulation step (i). Dry fine powder is preferably added in an amount of about 50 kg / t ± 25 kg / t order. The granules produced in the granulation step (i) preferably have a moisture content of about 10 to 25% w / w, such as about 20% w / w.

[0025] More preferably, the graphite material to be purified has a moisture content of up to about 25% w / w ± 5% w / w before the granulation step (i). However, the graphite material can be dried to a moisture content of about 0.1 - 2.5% w / w before granulation to facilitate the process.

[0026] The alkaline baking step (ii) is preferably carried out at between about 150 and 300 °C and causes the caustic soda to react with impurity minerals, especially silicate impurities, and renders them soluble in water and mild acid conditions.

[0027] Preferably, the alkaline baking step has a residence time in the range of about 60 to 240 minutes, preferably about 120 minutes.

[0028] More preferably, the amount of caustic soda added to the graphite material to be purified is calculated using the following ratio: at least 1 mole of caustic: 1 mole of silicon, for example between 2.5 and 5.5 moles of caustic: 1 mole of silicon, especially 3.2 moles of caustic: 1 mole of silicon.

[0029] In one form of the invention, the alkaline baking step (ii) is carried out in a rotary kiln.

[0030] The water leaching step (iii) is preferably carried out at between about 5 - 60 °C, for example about 35 °C ± 5 °C. Preferably, the water leaching step (iii) is carried out in a single stage. In some cases, the water leaching step (iii) can be carried out in multiple, for example three, countercurrent leaching stages. Even more preferably, the water leaching step (iii) has a retention time between about 30 and 240 minutes.

[0031] The first sulfuric acid leaching step (iv) is preferably carried out at between about 5 and 60 °C, for example about 40 °C ± 5 °C. More preferably, the first sulfuric acid leaching step (iv) has a retention time between about 30 and 240 minutes, for example about 120 minutes.

[0032] Preferably, the impurities leached in the first sulfuric acid leaching step (iv) include sodium silicate, sodium alum, iron oxides, and iron hydroxide mineral phases formed during the alkaline baking step, as well as any residual alkali.

[0033] Preferably, concentrated sulfuric acid is added in the first sulfuric acid leaching step (iv). The impurities leached in the sulfuric acid leaching step (iv) preferably include the remaining amounts of sodium silicate, sodium alum, iron oxides, and iron hydroxides not removed in step (iii), as well as titanium mineral phases. More preferably, the residual free acid at the end of the first sulfuric acid leaching step (iv) is in the range of about 5 - 75 g / L H 2 SO 4 , for example about 50 g / L ± 5 g / L H2 SO 4 The first sulfuric acid leaching step (iv) is preferably carried out under the following conditions: solids between about 5% and 25%, such as about 10% solids.

[0034] The hydrofluoric acid leaching step (v) is preferably carried out between about 5 - 60 °C, such as about 40 °C ± 5 °C. Preferably, the impurities leached in the hydrofluoric acid leaching step (v) include, but are not limited to, quartz, titanium mineral phases, and residual amounts of albite, biotite, and pyrophyllite. More preferably, the residual free acid at the end of the hydrofluoric acid leaching step (v) is in the range of about 5 - 75 g / L HF, such as about 25 g / L ± 5 g / L HF. The hydrofluoric acid leaching step (v) is carried out under the following conditions: solids between about 5% and 25%, such as about 10% solids.

[0035] Preferably, the hydrofluoric acid added to the acid leaching step (v) is in the range of about 20 - 70% concentration. The hydrofluoric acid concentration in the acid leaching step (v) is preferably in the range of about 15 - 50 g / L.

[0036] More preferably, the leached solids from the hydrofluoric acid leaching step (v) do not have residual silicon, or only have trace amounts of silicon.

[0037] The second sulfuric acid leaching step (vi) is preferably carried out between about 5 - 60 °C, such as about 40 °C ± 5 °C. Preferably, the impurities leached in the second sulfuric acid leaching step (vi) include precipitated fluoride phases, such as calcium fluoride and residual base metals. The second sulfuric acid leaching step (vi) is preferably carried out under the following conditions: solids between about 5% and 25%, such as about 10% solids.

[0038] Preferably, the second sulfuric acid leaching step (iv) has a retention time between about 30 and 240 minutes, such as about 120 minutes.

[0039] Preferably, concentrated sulfuric acid is added in the second sulfuric acid leaching step (vi). More preferably, the residual free acid at the end of the second sulfuric acid leaching step (iv) is in the range of about 5 - 75 g / L H 2 SO 4 in the range of, such as about 50 g / L ± 5 g / LH 2 SO 4 Preferably, the acid solution from the second sulfuric acid leaching step (vi) is collected and recycled to the first sulfuric acid leaching step (iv) and the second sulfuric acid leaching step (vi).

[0040] The washing step of step (vii) preferably comprises a single repulping - filtration stage using deionized water, multiple counter - current repulping - filtration stages, or, for example, five multiple counter - current repulping - filtration steps using deionized water. Preferably, the washing step of step (vii) operates with a three - stage counter - current repulping - filtration stage at solids between about 5 to 25%, for example about 10% solids.

[0041] Preferably, in the washing step of step (vii), the acidity (acid) of the liquid, residual salts, and / or residual solids from the second sulfuric acid leaching step (vi) is collected and sent back to one or both of the sulfuric acid leaching steps (iv) and (vi).

[0042] Preferably, the first effluent treatment device receives the effluents from the water leaching step (iii) and the two sulfuric acid leaching steps (iv) and (vi). The first effluent treatment device preferably also receives lime or caustic soda, and iron sulfate as an iron salt or ferrous salt. The first effluent treatment device preferably produces a first effluent, and in the case of adding lime, produces a mixed silicate - hydroxide - gypsum product.

[0043] The first effluent treatment device preferably receives the effluent bled from the leaching step at a rate determined by the silicon level in the first sulfuric acid leaching step (iv). Preferably, the level in the first sulfuric acid leaching step (iv) is about 5 g / L of silicon.

[0044] Preferably, the second effluent treatment device receives the effluent discharged from the hydrofluoric acid leaching step (v). The second effluent treatment device preferably also receives lime and ferrous or iron sulfate, thereby producing a second effluent and a calcium fluoride product.

[0045] In one form of the invention, the second effluent treatment device receives aluminum hydroxide, thereby producing a second effluent and an aluminum fluoride product.

[0046] The second effluent treatment device preferably receives the effluent discharged from the leaching step at a rate determined by the silicon level in the hydrofluoric acid leaching step (v).

[0047] Preferably, the first effluent and the second effluent are combined to provide a combined effluent product.

[0048] Preferably, silica gel formation in the leaching steps (iii), (iv), and (vi) is avoided by discharging the leachate to the effluent treatment step. The silicon content in the leaching steps (iii), (iv), and (vi) is maintained in the range of 2.5 to 7.5 g / L, for example below about 5 g / L, by such discharge of the leachate.

[0049] Preferably, dehydration is provided between the leaching stages.

[0050] Preferably, the carbon recovery rate of the graphite material purification process is greater than about 87%, for example between about 87.3% and 96.0%.

[0051] Preferably, the loss on ignition (LOI) of the purified graphite material product of the process is greater than or equal to about 99.90%, for example about 99.90 to 99.97%, or 99.96 to 99.97%.

[0052] Preferably, the content of carbon as graphite in the purified graphite material product of the process is greater than 99.5% w / w.

[0053] Preferably, the surface area (BET) of the purified graphite material product of the process is in the range of about 5 to 10 m2 / g, preferably about 7.0 m2 / g ± 2.0 m2 / g.

[0054] Preferably, the d50 of the purified graphite material product of the process is in the range of about 5 to 10 μm, preferably about 7.0 μm ± 2.0 μm.

[0055] According to the present invention, there is further provided a purified graphite material product produced according to the graphite material purification process described above. Description of the Drawings

[0056] By way of example only, the present invention will now be described with reference to one of its embodiments and the drawings, in which: -

[0057] Figure 1 is a schematic diagram depicting a flow chart of the graphite material purification process according to the present invention; and

[0058] Figure 2 shows the results from the pelletization test work and a summary of the test conditions according to Table 10, as discussed in the examples. Detailed Description

[0059] The present invention provides a graphite material purification process, the process comprising the following steps:

[0060] (i) feeding a graphite material to be purified at a certain concentration to a pelletization step to provide a pelletized material;

[0061] (ii) baking the pelletized material of step (i) under alkaline conditions to provide a sintered product and thereby enabling one or more impurity minerals to dissolve;

[0062] (iii) The sintered product of step (ii) is sent to a water leaching step, whereby at least a part of the impurity minerals from step (ii) is dissolved, the effluent is treated, and separated from the leached solids;

[0063] (iv) The leached solids of step (iii) are sent to a first sulfuric acid leaching step, wherein the impurity minerals partially leached in step (iii) are dissolved, the effluent is treated, and separated from the leached solids;

[0064] (v) The leached solids of step (iv) are sent to a hydrofluoric acid leaching step, wherein the partially leached impurity minerals are dissolved, the effluent is treated, and separated from the leached solids;

[0065] (vi) The leached solids of step (v) are sent to a second sulfuric acid leaching step, wherein the impurity minerals or components not leached in the previous steps and precipitated during step (v) are dissolved, the effluent is treated, and separated from the leached solids; and

[0066] (vii) The leached solids of step (vi) are sent to one or more washing stages, wherein at least a part of any remaining soluble impurities is separated, and thereby a purified graphite material is produced.

[0067] The process further includes a drying step, wherein the purified graphite material of step (vii) is dried to provide a dried purified graphite material. The dried purified graphite material contains moisture between 0 and 2.5%, such as less than about 1% and further preferably 0.1% moisture. In one form of the invention, the purified graphite material of step (vii) will contain about 40% moisture before the drying step, although this moisture content is related to the dehydration and drying equipment employed by the operator. The purified graphite material of step (vii) has a pH of 7 ± 2.5, whereby if desired, the purified graphite material is directly suitable for calendering of electrodes without the need to pyrolyze the purified graphite material before calendering.

[0068] The purified graphite material of step (vii) is sized during or after the drying step. The purified graphite material of step (vii) is sized during or after the drying step into a variety of products having different particle size and surface area properties, such as sized into at least two fractions. In one form, sizing utilizes a dry powder sizing method, such as cyclone sizing.

[0069] The granulation step (i) includes adding caustic soda and water to the graphite material to be purified in a stepwise manner. The granules produced in the granulation step (i) are fine granules having a diameter of about 2 - 10 mm, such as 5 mm ± 2 mm.

[0070] In one form of the invention, in cases where the properties of the material to be pelletized need to be improved, a dry fine powder of purified graphite material is added during the pelletization step (i). A dry fine powder of the order of about 50 kg / t ± 25 kg / t is added. The pellets produced in pelletization step (i) have a moisture content of about 10 to 25% w / w, for example about 20% w / w, depending on the amount of caustic soda added. Before pelletization step (i), the graphite material to be purified has a moisture content of up to about 25% w / w ± 5% w / w. However, the graphite material can be dried to a moisture content between about 0.1 and 2.5% w / w before pelletization to facilitate the process.

[0071] The alkaline baking step (ii) is carried out at between about 150 and 300 °C and causes the caustic soda to react with, in particular, silicate impurity minerals and renders them soluble in water and mild acid conditions. The alkaline baking 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 following ratio: at least 1 mole of base: 1 mole of silicon, for example between 2.5 and 5.5 moles of base: 1 mole of silicon, particularly 3.2 moles of base: 1 mole of silicon. The alkaline baking step (ii) is carried out, for example, in a rotary kiln.

[0072] The water leaching step (iii) is carried out at between about 5 - 60 °C, for example about 35 °C ± 5 °C. The water leaching step (iii) is carried out in a single leaching step, although in some cases it can be carried out in multiple, for example three, countercurrent leaching stages. The water leaching step (iii) has a retention time between about 30 and 240 minutes.

[0073] The first sulfuric acid leaching step (iv) is carried out at between about 5 and 60 °C, for example about 40 °C ± 5 °C, where the retention time is between about 30 and 240 minutes, for example about 120 minutes. Concentrated sulfuric acid is added in the first sulfuric acid leaching step (iv). The impurities leached in the sulfuric acid leaching step (iv) preferably include residual amounts of sodium silicate, sodium alum, iron oxides and iron hydroxides, and titanium mineral phases that were not removed in step (iii). More preferably, the residual free acid at the end of the first sulfuric acid leaching step (iv) is in the range of 5 - 75 g / L H 2 SO 4 for example about 50 g / L ± 5 g / L H 2 SO 4 . The first sulfuric acid leaching step (iv) is preferably operated at between 5 and 25% solids, for example 10% solids.

[0074] The impurities leached in the first sulfuric acid leaching step (iv) include sodium silicate, sodium alum, iron oxides and iron hydroxide mineral phases formed during the alkaline roasting step, as well as any remaining alkali.

[0075] It is contemplated that all or part of the product of the first sulfuric acid leaching step (iv) can be recycled to step (i) to expose it to the second roasting step (ii). It is understood that this can be advantageous in terms of solving the titanium level, as the roasting step (ii) is the stage of the process of the present invention in which titanium minerals are "cracked" (e.g., ilmenite and rutile).

[0076] The hydrofluoric acid leaching step (v) is carried out at a temperature between about 5 - 60 °C, for example about 40 °C ± 5 °C. The impurities leached in the hydrofluoric acid leaching step (v) include, but are not limited to, quartz, titanium mineral phases, and residual amounts of albite, biotite, and pyrophyllite. The residual free acid at the end of the hydrofluoric acid leaching step (v) is in the range of about 5 - 75 g / L HF, for example about 25 g / L ± 5 g / L HF. The hydrofluoric acid leaching step (v) is operated at: between 5 to 25% solids, for example 10% solids.

[0077] The hydrofluoric acid added to the acid leaching step (v) is in the range of about 20 - 70% concentration. The hydrofluoric acid concentration in the acid leaching step (v) is preferably in the range of 15 to 50 g / L, depending on the grade and mineralogical composition of the starting graphite material. The leached solids from the hydrofluoric acid leaching step (v) are substantially free of silicon or have only trace amounts of silicon remaining therein.

[0078] The second sulfuric acid leaching step (vi) is carried out at a temperature between about 5 - 60 °C, for example about 40 °C ± 5 °C. The impurities leached in the second sulfuric acid leaching step (vi) include precipitated fluoride phases, such as calcium fluoride and residual base metals. The second sulfuric acid leaching step (vi) is operated at: between 5 to 25% solids, for example 10% solids. The second sulfuric acid leaching step (iv) has a retention time between about 30 to 240 minutes, for example about 120 minutes.

[0079] Concentrated sulfuric acid is added in the second sulfuric acid leaching step (vi). The residual free acid at the end of the second sulfuric acid leaching step (iv) is in the range of 5 - 75 g / L H 2 SO 4 for example about 50 g / L ± 5 g / L H 2 SO 4 . The acid solution from the second sulfuric acid leaching step (vi) is collected and recycled to the first sulfuric acid leaching step (iv) and the second sulfuric acid leaching step (vi).

[0080] The washing stage of step (vii) includes a plurality of countercurrent repulping - filtration steps, such as five or more countercurrent repulping - filtration stages using deionized water. The washing stage of step (vii) operates using a three - stage countercurrent repulping - filtration stage at solids between 5% and 25%, such as about 10% solids. In the washing stage of step (vii), the acidity of the liquid, residual salts, and / or residual solids from the second sulfuric acid leaching step (vi) is collected and sent back to one or both of the sulfuric acid leaching steps (iv) and (vi). It is contemplated that the acidity of the liquid, residual salts, and / or residual solids from the second sulfuric acid leaching step (vi) may further be sent back to the water leaching step (iii).

[0081] The first effluent treatment device receives the effluents from the water leaching step (iii) and the two sulfuric acid leaching steps (iv) and (vi). The first effluent treatment device also receives lime or caustic soda, and iron sulfate as an iron salt or ferrous salt. The first effluent treatment device produces a first effluent, and in the case of adding lime, produces a mixed silicate - hydroxide - gypsum product.

[0082] The first effluent treatment device receives the effluent discharged from the leaching step at a rate determined by the silicon level in the first sulfuric acid leaching step (iv). The level in the first sulfuric acid leaching step (iv) is about 5 g / L of silicon.

[0083] The second effluent treatment device receives the effluent discharged from the hydrofluoric acid leaching step (v). The second effluent treatment device also receives lime and ferrous or iron sulfate, thereby producing a second effluent and a calcium fluoride product.

[0084] In one form of the present invention, the second effluent treatment device receives aluminum hydroxide, thereby producing a second effluent and an aluminum fluoride product.

[0085] The second effluent treatment device receives the effluent discharged from the leaching step at a rate determined by the silicon level in the hydrofluoric acid leaching step (v).

[0086] The first effluent and the second effluent are combined to provide a combined effluent product.

[0087] Silica gel formation in the leaching steps (iii), (iv), and (vi) is avoided by discharging the leachate to the effluent treatment step. The silicon content in the leaching steps (iii), (iv), and (vi) is maintained in the range of 2.5 to 7.5 g / L, such as below about 5 g / L, by such discharge of the leachate.

[0088] Filters and / or centrifugal decanters are utilized between the leaching steps to provide dehydration.

[0089] The carbon recovery rate of the graphite material purification process is greater than about 87%, for example, between about 87.3% and 96.0%. The loss on ignition (LOI) of the purified graphite material product of the process is greater than or equal to about 99.90%, for example, about 99.90 to 99.97%, or 99.96 to 99.97%.

[0090] The content of carbon as graphite in the purified graphite material product of the process is greater than 99.5% w / w.

[0091] The surface area (BET) of the purified graphite material product of the process is in the range of about 5 to 10 m 2 / g, for example, about 7.0 m 2 / g ± 2.0 m 2 / g, although it should be understood that the surface area (BET) will depend to some extent on the initial starting graphite material concentrate. The d 50 of the purified graphite material product of the process is in the range of about 5 to 10 μm, for example, about 7.0 μm ± 2.0 μm, although it should be understood that the d 50 will depend to some extent on the initial starting graphite material concentrate.

[0092] If desired, the graphite material concentrate can be ground before the granulation step (i), so that a purified graphite material with a surface area (BET) greater than or equal to about 25 m 2 / g can be obtained.

[0093] The present invention further provides a purified graphite material product produced according to the graphite material purification process described herein, and it has a purity suitable for use in the production of LiBs.

[0094] In Figure 1 , the graphite material purification process 10 according to the present invention is shown, and the process 10 includes the following steps:

[0095] (i) Feeding the concentrate 12 of the graphite material to be purified to the granulation step 14 to provide a granulated concentrate;

[0096] (ii) In the alkaline baking step 16, baking the granulated concentrate of step (i) under alkaline conditions to provide a sintered product, and thereby enabling one or more impurity minerals to dissolve;

[0097] (iii) Feeding the sintered product of step (ii) to the water leaching step 18, so that at least a part of the impurity minerals from step (ii) dissolve, performing effluent treatment, and separating from the leached solids;

[0098] (iv) Feed the leached solids from step (iii) to a first sulfuric acid leaching step 20, where the impurity minerals partially leached in step (iii) are dissolved, effluent treatment is carried out, and separation from the leached solids is effected;

[0099] (v) Feed the leached solids from step (iv) to a hydrofluoric acid leaching step 22, where the partially leached impurity minerals are dissolved, effluent treatment is carried out, and separation from the leached solids is effected;

[0100] (vi) Feed the leached solids from step (v) to a second sulfuric acid leaching step 24, where the impurity minerals or components that precipitated during step (v) and were not leached in previous steps are dissolved, effluent treatment is carried out, and separation from the leached solids is effected; and

[0101] (vii) Feed the leached solids from step (vi) to one or more washing stages 26, where at least a portion of any remaining soluble impurities is separated, and thereby produce a purified graphite material 28.

[0102] The process further includes a drying step 30, where the purified graphite material 28 from step (vii) is dried, thereby providing a dried purified graphite material 32 (also referred to herein as Talphite-C™). It is expected that, although the purified graphite material 28 from step (vii) will contain approximately 40% moisture prior to the drying step, the dried purified graphite material contains between 0 and 2.5% moisture, for example less than approximately 0.1% moisture. When repulped in water, the purified graphite material 28 from step (vii) has a pH of 7 ± 2.5, whereby the purified graphite material is directly suitable for use in the calendaring of electrodes (not shown).

[0103] The purified graphite material 28 from step (vii) is classified into at least two fractions in the drying step 30, for example using a cyclone separator. These two fractions will typically include a fine fraction and a coarse fraction.

[0104] The graphite material concentrate 12 has a moisture content of up to approximately 26 to 28% w / w. This concentrate 12 is first fed to a concentrate drying step 34, such as a flash drying stage or a drum dryer. Although a portion of the material 12 exits as flue gas, it is collected and reintroduced into the dried concentrate, which is fed to a granulation step 14.

[0105] The granulation step 14 includes the stepwise addition of caustic soda in the form of alkaline prills and water to the graphite material to be purified. The granules produced in the granulation step 14 are fine granules with a diameter of approximately 2 - 10 mm, for example 5 mm ± 2 mm.

[0106] Dry fine powder of the purified graphite material is added during the granulation step 14, for example, dry fine powder of the order of about 50 kg / t is added. The dry fine powder of the purified graphite material is derived from the drying step 30. The granules produced in the granulation step 14 have a moisture content of about 13 to 24% w / w, for example, about 20% w / w.

[0107] The alkaline baking step 16 is carried out at between about 150 - 300 °C and causes the caustic soda to react with especially silicate impurity minerals and render them water-soluble. The alkaline baking step 16 has a residence time of greater than about 60 minutes, for example, about 120 minutes. The amount of caustic soda added to the graphite material to be purified is calculated using the following ratio: at least 1 mole of base: 1 mole of silicon, for example, 3.2 moles of base: 1 mole of silicon. The alkaline baking step 16 is carried out, for example, in a rotary kiln.

[0108] The water leaching step 18 is carried out at between about 5 - 60 °C, for example, about 35 °C. The water leaching step 18 is carried out in a single stage or in multiple stages, for example, up to three countercurrent leaching stages, and has a retention time between about 30 and 240 minutes.

[0109] The first sulfuric acid leaching step 20 is carried out at between about 25 - 50 °C, for example, about 40 °C, and has a retention time between about 30 and 240 minutes, for example, 120 minutes. Concentrated sulfuric acid is added in the first sulfuric acid leaching step 20, and the free acid remaining at the end of the first sulfuric acid leaching step (iv) is about 50 g / L H 2 SO 4 . The first sulfuric acid leaching step (iv) is operated at: solids between 5 and 25%, for example, about 10% solids.

[0110] The impurities leached in the first sulfuric acid leaching step 20 include sodium silicate, sodium alum, iron oxide and iron hydroxide mineral phases, and any remaining alkali.

[0111] The hydrofluoric acid leaching step 22 is carried out at between about 30 - 45 °C. The impurities leached in the hydrofluoric acid leaching step 22 include quartz, titanium mineral phases, and residual amounts of albite, biotite and pyrophyllite. The free acid remaining at the end of the hydrofluoric acid leaching step 22 is about 25 g / L HF. The hydrofluoric acid leaching step (v) is operated at: solids between 5 and 25%, for example, about 10% solids.

[0112] The hydrofluoric acid added to the leaching step 22 is in the range of about 20% to 70% concentration, and the hydrofluoric acid concentration in the acid leaching step 22 is in the range of 15 - 50 g / L. The leached solids from the hydrofluoric acid leaching step 22 substantially do not have silicon or only have trace amounts of silicon remaining therein.

[0113] The second sulfuric acid leaching step 24 is carried out at a temperature between about 25 - 50 °C, for example about 40 °C. The impurities leached in the second sulfuric acid leaching step 24 include but are not limited to precipitated fluoride phases such as calcium fluoride and residual base metals. The second sulfuric acid leaching step 24 has a retention time between about 30 to 240 minutes, for example about 120 minutes.

[0114] Concentrated sulfuric acid is added in the second sulfuric acid leaching step 24 and the free acid remaining at the end of the second sulfuric acid leaching step 24 is about 50 g / L. The second sulfuric acid leaching step (vi) is operated at between 5 to 25% solids, for example 10% solids.

[0115] The washing stage of step 26 includes a plurality of countercurrent repulping - filtration stages, for example three or more countercurrent repulping - filtration stages using deionized water. The washing stage of step 26 is operated at between 5 to 25% solids, for example 10% solids. The acidity of the liquid, residual salts and / or residual solids from the second sulfuric acid leaching step 24 is collected in the washing stage of step 26 and returned to one or both of the sulfuric acid leaching steps 20 and 24. It is contemplated that the acidity of the liquid, residual salts and / or residual solids from the second sulfuric acid leaching step (vi) may further be returned to the water leaching step (iii).

[0116] It is contemplated that carbonation may be introduced during the washing stage of step 26 as follows: by addition of sodium bicarbonate, or by bubbling of carbon dioxide, with pH control using caustic soda. This will help to neutralize the carry - over acid from the second sulfuric acid leaching step 24 and reduce the number of countercurrent washing steps required.

[0117] The first effluent treatment device 36 receives the effluents from the water leaching step 18 and the two sulfuric acid leaching steps 20 and 24. The first effluent treatment device 36 also receives lime and iron sulfate, such as ferric sulphate, thereby producing a first effluent 38 and a gypsum product 40. By using caustic soda instead of lime in this step, the volume of gypsum precipitate or residue can be minimized.

[0118] The second effluent treatment device 42 receives the effluent discharged from the hydrofluoric acid leaching step 22. The second effluent treatment device 42 also receives lime and iron sulfate, such as ferric sulfate, thereby producing a second effluent 44 and a calcium fluoride product 46.

[0119] In one form of the present invention, the second effluent treatment device receives aluminum hydroxide, thereby producing a second effluent and an aluminum fluoride product.

[0120] The second effluent treatment device 42 receives the effluent discharged from the leaching step 22 at a rate determined by the silicon level in the hydrofluoric acid leaching step 22.

[0121] Subsequently, the first effluent 38 and the second effluent 44 can be combined to provide a combined effluent product 48.

[0122] Silica gel formation in the leaching steps 18, 20, and 24 is avoided by discharging the leaching liquid to the effluent treatment step. The silicon content in the leaching steps 18, 20, and 24 is maintained below about 5 g / L by the discharge of the leaching liquid in this manner.

[0123] As needed, dehydration is provided using a filter and / or a centrifugal decanter between the leaching steps.

[0124] The carbon recovery rate of the graphite material purification process 10 of the present invention is greater than about 87%, for example, between about 87.3% and 96.0%. The loss on ignition (LOI) of the purified graphite material product of the process is greater than or equal to about 99.90%, for example, about 99.90 to 99.97%, or 99.96 to 99.97%.

[0125] The carbon content of the purified graphite material product of the process 10 of the present invention as graphite is greater than 99.5% w / w.

[0126] The surface area (BET) of the purified graphite material product of the process 10 of the present invention is in the range of about 5 to 10 m 2 / g, for example, about 7.0 m 2 / g ± 2.0 m 2 / g. The d 50 of the purified graphite material product of the process 10 of the present invention is in the range of about 5 to 10 μm, for example, about 7.0 μm ± 2.0 μm, although it should be understood that d 50 will depend to some extent on the initial starting graphite material concentrate.

[0127] The process of the present invention can be better understood with reference to the following non-limiting examples.

[0128] Example

[0129] The natural graphite precursor or ore used in this study was extracted from the Vittangi graphite mine in Norrbotten County in northern Sweden. This natural graphite source is characterized by hard particles with a very narrow distribution and microcrystalline flakes. The mineral phases can be roughly divided into two main categories:

[0130] (i) Dispersed minerals within the graphite matrix parent rock; and

[0131] (ii) discrete and / or veined minerals present at grain boundaries as released minerals or compounds.

[0132] The approximate values of the mineral phases present in these two categories and their relative abundances are summarized in Table 1 below.

[0133]

[0134] The applicant has prepared a concentrate from the above ore and used it as the basis for a computer model (utilizing METSIM™ software) of the process of the present invention. The assumed mineralogy of the purified plant feed used in METSIM modeling is summarized in Table 2 below, showing all the carbon present in the form of graphite carbon (C g ).

[0135]

[0136] The graphite concentrate undergoes alkaline roasting in an alkaline roasting step to convert gangue minerals into sodium salts, followed by multiple stages as follows: water and acid leaching, and repulping / washing to dissolve the gangue species and remove them from the solid graphite phase. The more dilute process water generated in the later stages of the washing step is recycled to the upstream repulping and cake washing tasks, flowing countercurrently to the graphite material or concentrate in the process to maximize the washing efficiency of the raw water input to the process.

[0137] The expected functions of each stage of the process of the present invention are described below. The solution and slurry flow information described is presented for illustrative purposes only.

[0138] Concentrate drying step

[0139] This stage receives the wet concentrate cake in bulk bags and produces loose solids dried to a moisture content of 0.5% w / w, which are transferred to the alkaline roasting step by a screw feeder.

[0140] The flash dryer feed bin equipped with a bag breaker receives the bags of wet concentrate cake from a suitable delivery lay-down pad via a hoist. The loose cake is transferred from the bottom of the feed bin to the flash dryer by a screw feeder running at a constant rate.

[0141] The concentrate is flash dried and transported by a screw feeder to the dry concentrate bin, from where it is pushed by a screw feeder into the alkaline roasting step / calcination. It is estimated that 12.5% of the concentrate leaves the dryer (after the cyclone) as flue gas and is reported to the bag filter. It is estimated that 99.5% of the solids reported to the bag filter are captured and directed to the dry concentrate bin.

[0142] It is contemplated that the final moisture could be controlled to a higher value (closer to but below the pellet moisture) to avoid inefficiencies such as evaporating moisture and then having to re-add moisture.

[0143] Alkaline roasting step and pelletizing step

[0144] The alkaline roasting / calcination step combines the dried concentrate with sodium hydroxide to form pellets with an average diameter of about 5 mm, which are then fed to a kiln. The high temperature causes the conversion of silicates and other gangue minerals to sodium salts.

[0145] The dried concentrate, alkaline (sodium hydroxide) pellets, and water are fed to a pelletizing package to produce pellets with a target moisture of 15% w / w suitable for feeding to the calcination kiln. Also, dried graphite product fines from the product drying bag filter bins are added to the formed pellets to reduce their tendency to agglomerate (cake) in a step that can be referred to as "curing". The graphite fines are added at a rate of 5% w / w of the uncured pellets.

[0146] The cured graphite pellets are transferred to a direct fired rotary kiln where their temperature is raised to 200 °C and held for 2 hours. The applicant's test work has shown that approximately 95% of the gangue minerals are converted to sodium salts and about 13.7% of the graphite is lost in reaction with the alkali during this process. It is assumed that 5% of the solids are reported as dust to the flue gas.

[0147] The flue gas is directed to a bag filter where it is assumed that 99.5% of the solids are captured. The bag filter solids are combined with the kiln discharge solids ("clinker") in a clinker bin and a screw feeder transfers the clinker from the clinker bin to the next processing area.

[0148] Water leaching step

[0149] The water leaching step dissolves the sodium salts and separates them from the remaining solids in three stages of leaching, filtration, washing, and repulping.

[0150] The sintered material is transferred to a stage 1 working repulper via a screw feeder where it is mixed with stage 2 filtrate. Another stage 1 repulper operates in a continuous feed mode where a working feed pump discharges the graphite slurry to the first of two baffled agitated stage 1 leaching tanks connected in series by gravity overflow. The precipitated salts dissolve and the slurry overflows from the final leaching tank to the stage 1 filter feed tank.

[0151] The Stage 1 batch filter press is fed from the filter feed tank by a centrifugal slurry pump. The filter cake is washed with Stage 2 filtrate fed by a dedicated pump. The Stage 1 primary filtrate and wash filtrate are collected in a single tank before being transferred by pump to the effluent treatment unit 1.

[0152] The Stage 1 filter cake is transferred to the Stage 2 working repulper tank by a screw feeder, where it is mixed with Stage 3 filtrate. Another Stage 2 repulper tank operates in continuous feed mode, where the working feed pump discharges the graphite slurry into the first of two baffled agitated leaching tanks connected in series by gravity overflow. The precipitated salts dissolve and the slurry overflows from the final leaching tank to the Stage 2 filter feed tank.

[0153] The Stage 2 batch filter press is fed from the Stage 2 filter feed tank by a centrifugal slurry pump. The filter cake is washed with Stage 3 filtrate fed by a dedicated pump. As required, the Stage 2 primary filtrate and wash filtrate are collected in the Stage 2 filtrate tank before being transferred by dedicated pump to the Stage 1 repulping and filter cake washing operations.

[0154] The Stage 2 filter cake is transferred to the Stage 3 working repulper tank by a screw feeder, where it is mixed with raw water. Another Stage 3 repulper tank operates in continuous feed mode, where the working feed pump discharges the graphite slurry into the first of two baffled agitated leaching tanks connected in series by gravity overflow. The precipitated salts dissolve and the slurry overflows from the final leaching tank to the Stage 3 filter feed tank.

[0155] The Stage 3 batch filter press is fed from the Stage 3 filter feed tank by a centrifugal slurry pump. The filter cake is washed with raw water. As required, the Stage 3 primary filtrate and wash filtrate are collected in the Stage 3 filtrate tank before being transferred by dedicated pump to the Stage 2 repulping and filter cake washing operations.

[0156] The Stage 3 filter cake is transferred to the next processing area by a screw feeder.

[0157] First sulfuric acid leaching step

[0158] The first sulfuric acid leaching step area partially dissolves the gangue minerals and separates them from the remaining solids.

[0159] The water-leached Stage 3 filter cake is transferred to the working acid leaching repulper tank by a screw feeder, where it is mixed with leach filtrate and raw water to a pulp density of 12% w / w solids. Another repulper tank operates in continuous feed mode, where the working feed pump discharges the acidic graphite slurry into the first of three baffled agitated acid leaching tanks connected in series by gravity overflow. 70% sulfuric acid is added to the leaching tanks to maintain a background or residual acid concentration of 50 g / L. The gangue minerals dissolve and the slurry overflows from the final leaching tank to the filter feed tank.

[0160] The acid leaching batch filter press is fed from the filter feed tank by a centrifugal slurry pump. The filter cake is washed with water leaching filtrate fed by a dedicated pump. The acid leaching primary filtrate and the wash filtrate are collected in a single tank, and the solution is partially recycled from the single tank to the acid leaching repulping tank by a dedicated pump, and the remaining part is transferred by a pump to a first effluent treatment device activated by a level controller in the transfer tank.

[0161] The acid leaching filter cake is transferred to the water leaching working repulping tank by a screw feeder, where it is combined with a mixture of raw water and the final water repulping filtrate. Another water leaching repulping tank operates in a continuous feed mode, where the working feed pump discharges the graphite slurry into the first of two baffled agitated leaching tanks connected in series by gravity overflow. The precipitated salts dissolve and the slurry overflows from the final leaching tank to the water leaching filter feed tank.

[0162] The water leaching batch filter press is fed from the water leaching filter feed tank by a centrifugal slurry pump. The filter cake is washed with raw water. As needed, the primary filtrate and the wash filtrate are collected in the water leaching filtrate tank before being transferred by a dedicated pump to wash the acid leaching filter cake, where the excess water is pumped to the first effluent treatment device.

[0163] The final washed filter cake is transferred to the next processing area by a screw feeder.

[0164] Hydrofluoric acid leaching step

[0165] The hydrofluoric acid leaching step further dissolves the silicate gangue minerals and separates them from the remaining solids.

[0166] The first sulfuric acid leaching filter cake is transferred to the working acid leaching repulping tank by a screw feeder, where it is mixed with the leaching filtrate and raw water to a pulp density of 11% w / w solids. Another repulping tank is in continuous feed mode, where the working feed pump discharges the acidic graphite slurry into the first of three baffled agitated leaching tanks connected in series by gravity overflow. 70% hydrofluoric acid is added to the leaching tank to maintain a background acid concentration of 25 g / L. The gangue minerals dissolve and the slurry overflows from the final leaching tank to the filter feed tank.

[0167] The acid leaching batch filter press is fed from the filter feed tank by a centrifugal slurry pump. The filter cake is washed with water leaching filtrate fed by a dedicated pump. The acid leaching primary filtrate and the wash filtrate are collected in a single tank, and the solution is partially recycled from the single tank to the acid leaching repulping tank by a dedicated pump, and the remaining part is transferred by a pump to a second effluent treatment device activated by a level controller in the transfer tank.

[0168] The acid leach cake is transferred to the water leach repulping tank by a screw feeder, where it is combined with raw water. Another water leach repulping tank is operated in a continuous feed mode, where the working feed pump discharges the graphite slurry into the first of two baffled agitated leaching tanks connected in series by gravity overflow. The precipitated salts dissolve and the slurry overflows from the final leaching tank to the water leach filter feed tank.

[0169] The water leach batch filter press is fed from the water leach filter feed tank by a centrifugal slurry pump. The filter cake is washed with raw water. As required, the primary filtrate and wash filtrate are collected in the water leach filtrate tank before being transferred by a dedicated pump to the acid leach cake wash, where the excess water is pumped to the second effluent treatment unit.

[0170] The final washed filter cake is transferred to the next processing area by a screw feeder.

[0171] Second sulfuric acid leaching step

[0172] The second sulfuric acid leaching step mainly dissolves the calcium fluoride precipitate formed in the previous area. An important consideration in this area is to ensure that the calcium sulfate solubility is not exceeded, as exceeding it will result in the formation of gypsum precipitate and cause dilution of the graphite. This is achieved through careful control of the water balance and pulp density parameters.

[0173] The washed hydrofluoric acid leach cake is transferred to the working second sulfuric acid leaching step repulping tank by a screw feeder, where it is mixed with leach filtrate and process water to a pulp density of 12% w / w solids. Another repulping tank is operated in a continuous feed mode, where the working feed pump discharges the acidic graphite slurry into the first of three baffled agitated leaching tanks connected in series by gravity overflow. 70% sulfuric acid is added to the leaching tanks to maintain a background / residual acid concentration of 25 g / L. The fluoride precipitate dissolves and the slurry overflows from the final leaching tank to the filter feed tank.

[0174] The batch filter press is fed from the filter feed tank by a centrifugal slurry pump. The filter cake is washed with process water fed by a dedicated pump. The acid leach primary filtrate and wash filtrate are collected in a single tank, and the solution is partially recycled from the single tank to the acid leach repulping tank, partially recycled to the first sulfuric acid leaching working repulping tank, and the remaining portion is transferred by pump to the first effluent treatment step.

[0175] The filter cake is transferred to the next processing area by a screw feeder.

[0176] Water repulping and washing step

[0177] The final water repulping step consists of three stages of repulping, continuous mixing, and filtration. This provides a final opportunity to remove dissolved gangue elements from the liquid contained in the interstitial voids of the graphite filter cake and from the liquid film surrounding each graphite particle. Any dissolved species remaining after this stage will become part of the solid phase due to the evaporation of water in the product drying step.

[0178] The acid leached filter cake is transferred to the Stage 1 working repulping tank by a screw feeder, where it is mixed with the Stage 2 filtrate. Another Stage 1 repulping tank is in continuous feed mode, where the working feed pump discharges the graphite slurry into the first of two baffled agitated Stage 1 mixing tanks connected in series by gravity overflow. Dissolved solids transfer to the bulk solution by diffusion and the slurry overflows from the final mixing tank to the Stage 1 filter feed tank.

[0179] The Stage 1 batch filter press is fed from the filter feed tank by a centrifugal slurry pump. The filter cake is washed with demineralized water fed by a dedicated pump. The Stage 1 primary filtrate and wash filtrate are collected in a single process water tank before being transferred upstream to repulping and washing operations by dedicated pumps.

[0180] The Stage 1 filter cake is transferred to the Stage 2 working repulping tank by a screw feeder, where it is mixed with the Stage 3 filtrate. Another Stage 2 repulping tank is operated in continuous feed mode, where the working feed pump discharges the graphite slurry into the first of two baffled agitated mixing tanks connected in series by gravity overflow. Dissolved solids transfer to the bulk solution by diffusion and the slurry overflows from the final mixing tank to the Stage 2 filter feed tank.

[0181] The Stage 2 batch filter press is fed from the Stage 2 filter feed tank by a centrifugal slurry pump. The filter cake is washed with demineralized water fed by a dedicated pump. The Stage 2 primary filtrate and wash filtrate are collected in the Stage 2 filtrate tank before being partially recycled to Stage 1 repulping by a dedicated pump, with the remaining portion being advanced to the process water tank.

[0182] The Stage 2 filter cake is transferred to the Stage 3 working repulping tank by a screw feeder, where it is mixed with demineralized water. Another Stage 3 repulping tank is in continuous feed mode, where the working feed pump discharges the graphite slurry into the first of two baffled agitated mixing tanks connected in series by gravity overflow. Dissolved solids transfer to the bulk solution by diffusion and the slurry overflows from the final mixing tank to the Stage 3 filter feed tank.

[0183] The Stage 3 batch filter press is fed from the Stage 3 filter feed tank by a centrifugal slurry pump. The filter cake is washed with demineralized water. The Stage 3 primary filtrate and wash filtrate are collected in the Stage 3 filtrate tank before being partially recycled via a dedicated pump to the Stage 2 repulping, with the remaining portion being advanced to the process water tank.

[0184] The Stage 3 filter cake is transferred to the next processing area by a screw feeder.

[0185] Product drying step

[0186] The drying step dries the refined graphite filter cake in a flash dryer to 0.5% w / w moisture, resulting in loose, dry, refined graphite suitable for feeding to subsequent equipment for the manufacture of anodes.

[0187] The flash dryer receives the wet refined graphite filter cake via a screw feeder. The concentrate is flash dried and transported via a screw feeder to the dry product bin. It is estimated that 12.5% of the concentrate leaves the dryer (after the cyclone) as flue gas and is reported to the bag filter. It is estimated that 99.5% of the solids reported to the bag filter are captured and mainly directed to the dry product bin, with a small amount recycled to the granulation step for granule solidification.

[0188] First effluent treatment device

[0189] The first effluent treatment unit treats the sulfate waste solution to produce a liquid effluent containing mainly sodium and calcium sulfates, and a solid wet filter cake containing mainly gypsum and metal hydroxides for waste disposal.

[0190] The waste solution is directed to a baffled and agitated neutralization tank where the pH is balanced to ~pH 6, if necessary, by adding sulfuric acid to maintain the desired pH set point.

[0191] The pH-stabilized solution overflows from the neutralization tank to the iron addition tank. Also baffled and agitated, ferric sulfate solution is dosed into this tank to achieve 1 g / L of iron in the slurry. Depending on the natural pH after neutralization, iron may precipitate in this tank or in subsequent stages.

[0192] The slurry with added iron overflows from the iron addition tank into the first of three baffled and agitated settling tanks. As needed, lime slurry is added to each tank to maintain a target pH of 12.0. Dissolved salts other than sodium sulfate are almost completely hydrolyzed and precipitate as hydroxides. Calcium sulfate is formed by the reaction of lime with sulfuric acid, and gypsum precipitates at the calcium sulfate solubility limit. The slurry overflows from the last settling reactor to a thickener. When the slurry enters the feed port, a dilute flocculant is added to the slurry and mixed with it so that rapidly settling flocs are formed. The mixed gypsum and metal hydroxide precipitates settle, while the clarified solution overflows from the thickener to an overflow tank.

[0193] The first effluent treatment plant precipitation train will operate as a high-density sludge unit to support the formation of rapidly settling solids. The rate of solids generation is low, and a high rate of thickener underflow recycle is required to maintain the target 10% w / w solids in the thickener feed slurry. Therefore, it is envisaged that the working underflow pump will operate in a fully recycled mode for approximately 85% of the plant operating time and discharge to the filter feed tank for the remaining time to reduce the thickener bed level.

[0194] The batch filter press is fed periodically from the filter feed tank by a centrifugal slurry pump, and the filtrate is pushed to the thickener underflow tank for discharge.

[0195] Second effluent treatment device

[0196] The second effluent treatment plant treats the fluoride waste solution to produce a liquid effluent containing mainly calcium sulfate, and a filter cake containing mainly calcium fluoride, gypsum, and metal hydroxides for disposal.

[0197] The waste solution is directed to a baffled and agitated iron addition tank, and a ferric sulfate solution is added to it to achieve 1 g / L iron in the slurry. Due to the expected low pH in this tank, ferric iron will remain soluble.

[0198] The slurry with added iron overflows from the iron addition tank into the first of three baffled agitated settling tanks. Lime slurry is dosed into each tank as required to maintain a target pH of 12.0 in the final tank. Dissolved salts other than sodium sulfate are almost completely hydrolyzed and precipitate as hydroxides. Insoluble calcium fluoride is formed by the reaction of lime with hydrofluoric acid, and calcium sulfate is formed by the reaction of lime with sulfuric acid, where gypsum precipitates at the calcium sulfate solubility limit. The slurry overflows from the final precipitation reactor to a thickener. When the slurry enters the feed port, a diluted flocculant is dosed into the slurry and mixed with it such that rapidly settling flocs are formed. The mixed calcium fluoride, gypsum, and metal hydroxide precipitates settle while the clarified solution overflows from the thickener to an overflow tank.

[0199] The second effluent treatment plant precipitation train will operate as a high-density sludge plant to support the formation of rapidly settling solids. The rate of solids generation is low and a high rate of thickener underflow recycle is required to maintain a target of 10% w / w solids in the thickener feed slurry. It is thus envisaged that the working underflow pump will operate in a fully recycled mode for approximately 85% of the plant operating time and discharge to the filter feed tank for the remaining time to reduce the thickener bed level.

[0200] The batch filter press is fed periodically from the filter feed tank by a centrifugal slurry pump and the filtrate is advanced to the thickener underflow tank for discharge.

[0201] Further tests have been carried out on aspects of the process of the present invention.

[0202] Production data for Talphite C™ material (where a final purity of ≥99.9% LOI was achieved) are summarized in Table 3 below. The data also show a reduction in surface area (BET) after purification, which the applicant believes is most likely the result of the removal of impurity fines by the purification process.

[0203]

[0204] Bench purification of selected GTK concentrate samples

[0205] In the laboratory, three graphite material concentrate samples were purified according to the following conditions:

[0206] (i) Alkaline roasting - at 250 °C for 4 hours with a NaOH:Si molar ratio of 5.2.

[0207] (ii) Water leaching - three consecutive water leaching steps were carried out at 15 °C for 2 hours, 1 hour, and 30 minutes respectively.

[0208] (iii) Sulfuric acid leaching (Stage 1) - Add 250 kg / t acid and operate at 15 °C for 4 hours.

[0209] (iv) Hydrofluoric acid leaching - Add 300 kg / t acid and operate at 15 °C for 4 hours.

[0210] (v) Sulfuric acid leaching (Stage 2) - Add 250 kg / t acid and operate at 15 °C for 4 hours.

[0211] (vi) Water repulping - 7 stages, each operating at 15 °C for 30 minutes.

[0212] Key metallurgical data are summarized in Table 4 below.

[0213]

[0214] Scaling up the production scale (~150 kg scale) improved the carbon recovery rate of Sample 1 from 87.4% obtained in the laboratory to 95.7%. Compared with laboratory tests, the carbon loss in larger-scale production runs was lower. The final purified product had a surface area of 6.4 m 2 / g.

[0215] Optimization of the acid leaching stage

[0216] Optimization of the acid leaching conditions showed that the residence time for these steps could be significantly reduced while still maintaining high purity. The results of the test work are summarized in Table 5 below. The roasting, water leaching, and repulping washing steps were kept the same as the baseline conditions described above, while the acid leaching step was run at 15 °C.

[0217]

[0218] Reducing the acid addition to 50% and the residence time to 25% resulted in lower purity, below the acceptable level.

[0219] Further optimization of the acid leaching stage

[0220] For a concentrate sample, the baseline purification conditions failed to achieve the minimum LOI purity target, triggering optimization test work on this sample, which focused on the temperature of the leaching step. This test work also coincided with the time period during the production run for processing the concentrate material, where the temperature conditions inside the building were 5 - 10 °C due to winter conditions. Under these conditions, two batches returned LOI values of 99.88% and 99.89%. However, when the solution was heated to approximately 20 °C and the batches were reprocessed, the purity target was restored. This observation highlighted the sensitivity of the purification process to temperature changes. The results are summarized in Table 6 below.

[0221]

[0222] By applying elevated temperature leaching conditions (25 - 35 °C) during the larger scale production purification of this material, a final LOI purity of 99.9% was achieved, with an overall carbon recovery rate of 91.3%.

[0223] HF acid leaching using recycled solution

[0224] A series of tests have been completed to simulate recycling HF leaching liquids with different compositions to evaluate the impact on purification efficiency.

[0225] These tests confirmed that even with elevated levels of silicon, potassium, titanium, aluminum, and iron in the starting leaching solution, a LOI purity target of >99.90% can be achieved. When recycling the leaching liquid, a recycled liquid with a fluoride ion concentration of ≥55 g / l F ions and / or an HF concentration of ≥60 g / l will be required to achieve the purity target. The key test results are summarized in Table 7 below.

[0226]

[0227] Characterization of purified graphite samples

[0228] The detailed analysis and characterization information for the Talphite C™ product generated by the applicant in laboratory tests has been collated and summarized in Table 8 below.

[0229]

[0230] Larger scale purification tests

[0231] The applicant has successfully purified graphite material concentrate samples on a larger scale (~150 kg batches of wet filter cake), confirming the results from laboratory-scale tests and the scale-up process. Compared to laboratory tests, the carbon recovery rate has improved to 90% to 96%, while still achieving the LOI purity target of ≥99.90%.

[0232] Table 9 below summarizes the production data.

[0233]

[0234] Pelletizing and rotary kiln roasting pilot tests

[0235] The applicant has conducted pelletization and rotary kiln baking tests.

[0236] Pelletization tests were carried out using a 5 L Eirich Intensive Mixer (Model R01) to establish operating conditions to prevent the formation of lumps, reduce the stickiness of the pellets, and keep the target pellets in the range of 2 - 10 mm.

[0237] The test work showed that adding dry fines during the operating pelletization step improved the properties of the final pellet mixture by coating the surface of the pellets and thus reducing their stickiness. Adding 50 kg / t of dry concentrate fines resulted in pellets with good flowability and a final moisture of 13% w / w.

[0238] Further test work exploring the effect of moisture in the feed and water addition showed that suitable pellets could be formed when feeding wet filter cake to the Eirich mixer. The maximum feed moisture content appeared to be in the range of 26 - 28% w / w; above this, large agglomerates and / or pastes were formed even with the addition of large amounts of dry fines.

[0239] Scale-up tests using a 75 L Eirich Mixer (Model R08W) confirmed that pellets with excellent size and flow properties and a final moisture of approximately 24% could be produced by adding 50 kg / t of fines. The pelletized material from these tests was advanced to the rotary kiln pilot test.

[0240] The results of the pelletization test work and the test conditions are summarized in Figure 2 Table 10. The results indicate that prior to pelletization, the concentrate drying can be eliminated or at least reduced.

[0241] The pellets produced in the 75 L Eirich unit had a bulk density of 1.10 t / m 3 and an angle of repose measured at 40°.

[0242] Alkaline calcination pilot test

[0243] Fresh (“green”) pellets were loaded and stored in a hopper equipped with a variable speed belt conveyor and fed to a rotary kiln with the following specifications:

[0244] (i) Kiln length - 2.5 m

[0245] (ii) Kiln diameter - 300 mm

[0246] (iii) Kiln inclination - 2.3°

[0247] (iv) Kiln rotation - 0.5 rpm

[0248] (v) Measured residence time - 50 minutes (tracer)

[0249] (vi) Inner wall electric heating - At the point of the sintered product bed, the outer wall temperature sensor differs from the inner wall by 30 °C

[0250] (vii) Countercurrent heated air flow

[0251] The kiln residence time was measured to be 50 minutes, and each campaign was run twice to provide a longer baking time and study the effect of residence time. Two campaigns were completed, and the operating conditions and key metallurgical data are summarized in Table 11 below.

[0252]

[0253] Purification of samples from Pass 1 and 2 of the two campaigns (using ambient temperature leaching, i.e., ~15 °C) returned an LOI purity value of 99.88%, regardless of the baking conditions. Material handling data was measured only for the Campaign 1 product.

[0254] Further leaching tests on the Campaign 2 Pass 1 material at 45 °C did not improve the final purity, returning an LOI value of 99.88%.

[0255] For further study, the Campaign 2 granulated feed material was baked in a static oven for 4 hours and leached in the laboratory at 15 °C, 30 °C, and 45 °C. The LOI values for these tests were 99.89%, 99.81%, and 99.92% respectively, and indicate that the leaching temperature is important. However, more importantly, comparing the 45 °C leaching results with the pilot baked product, the bake time residence time is also important. A pilot kiln residence time of 100 minutes (2 x 50 minutes) does not seem sufficient to allow the reaction between sodium hydroxide and silicate minerals to complete, which is required to achieve the final purity requirements.

[0256] Concentrate dryer pilot test

[0257] DryTech (equipment supplier) flash dryers have been used to complete the concentrate drying test work, confirming that the wet filter cake can be easily processed using the process of the present invention to obtain a final dry product with <0.2% w / w moisture.

[0258] Filter cake samples with moisture levels ranging from 39% to 55% were tested. The use of the recycle mixer and disintegration stage used by DryTech for other commercially available graphite drying applications demonstrated the successful handling and feeding of concentrate materials with these high levels of moisture. Recycling the dried material in the recycle mixer yielded a product with ≤43% w / w moisture. This material was found to be suitable for feeding into the flash dryer unit.

[0259] The properties of the final dried concentrate measured are summarized as follows:

[0260] (i) Final moisture: < 0.2% w / w

[0261] (ii) Angle of repose: 36°

[0262] (iii) Flow properties: Free flowing

[0263] Talphite C™ dryer & classifier pilot test

[0264] The Talphite C™ drying and product classification test work has been completed using a DryTech flash dryer, which has confirmed that the dried Talphite C™ material can be separated into three product streams with different PSD and surface area properties. The flash dryer exhaust gas is classified using a two-stage cyclone separator and a bag filter to capture the fines leaving the overflow stream of the paired secondary cyclone separators.

[0265] As can be seen from the above description, the graphite material purification process of the present invention provides an improved graphite material purification process which, when compared with the prior art processes, reduces carbon loss and / or reduces the dependence on large amounts of highly concentrated acids in at least some forms.

[0266] Modifications and variations such as will be apparent to those skilled in the art are regarded as falling within the scope of the present invention.

Claims

1. A process for purifying graphite material, the process comprising the following steps: (i) Feeding the graphite material to be purified at a certain concentration to a granulation step to provide granulated material; (ii) Baking the granulated material of step (i) under alkaline conditions to provide a sintered product and thereby render one or more impurity minerals soluble; (iii) Feeding the sintered product of step (ii) to a water leaching step, thereby dissolving at least a part of the impurity minerals from step (ii), treating the effluent, and separating it from the leached solids; (iv) Feeding the leached solids of step (iii) to a first sulfuric acid leaching step, wherein the partially leached impurity minerals in step (iii) are dissolved, the effluent is treated, and it is separated from the leached solids; (v) Feeding the leached solids of step (iv) to a hydrofluoric acid leaching step, wherein the partially leached impurity minerals are dissolved, the effluent is treated, and it is separated from the leached solids; (vi) Feeding the leached solids of step (v) to a second sulfuric acid leaching step, wherein the impurity minerals or components that were not leached in the previous steps and precipitated during step (v) are dissolved, the effluent is treated, and it is separated from the leached solids; and (vii) Feeding the leached solids of step (vi) to one or more washing stages, wherein at least a part of any remaining soluble impurities is separated and thereby producing purified graphite material.

2. The process according to claim 1, wherein the process further comprises a drying step in which the purified graphite material of step (vii) is dried to provide dried purified graphite material.

3. The process according to claim 2, wherein the dried purified graphite material contains: (i) Moisture between 0 and 2.5%; (ii) Less than about 1% moisture; or (iii) 0.1% moisture.

4. The process according to claim 2 or 3, wherein the purified graphite material of step (vii) contains about 40% moisture before the drying step.

5. The process according to any one of claims 1 to 4, wherein the purified graphite material of step (vii) has a pH of 7 ± 2.

5.

6. The process according to any one of the preceding claims, wherein the purified graphite material of step (vii) is classified as follows: (i) During or after the drying step; (ii) Classified into multiple products having different particle size and surface area properties during the drying step; (iii) Classified into at least two fractions; (iv) By a dry powder classification method; or (v) By a cyclone separator classification.

7. The process according to any one of the preceding claims, wherein the granulation step (i): (i) Comprises adding caustic soda and water to the graphite material to be purified in a stepwise manner; (ii) Produces granules of fine granules having a diameter of about 2 - 10 mm; and / or (iii) Produces granules of fine granules of 5 mm ± 2 mm.

8. The process according to any one of the preceding claims, wherein: (i) adding the dry fine powder of the purified graphite material during pelletization step (i); or (ii) adding the dry fine powder of the purified graphite material at an amount of about 50 kg / t ± 25 kg / t during pelletization step (i).

9. The process according to any one of the preceding claims, wherein the pellets produced in pelletization step (i) have a moisture content of: (i) about 10 to 25% w / w; or (ii) about 20% w / w.

10. The process according to any one of the preceding claims, wherein the graphite material to be purified has a moisture content of up to about 25% w / w ± 5% w / w before pelletization step (i).

11. The process according to any one of the preceding claims, wherein the alkaline baking step (ii) is carried out between about 150 and 300 °C and causes the reaction of caustic soda and silicate impurity minerals and being soluble in water and mild acid conditions.

12. The process according to any one of the preceding claims, wherein the alkaline baking step (ii) has a residence time in the following range: (i) about 60 to 240 minutes; or (ii) about 120 minutes.

13. The process according to any one of the preceding claims, wherein the amount of caustic soda added to the graphite material to be purified in the alkaline baking step (ii) is calculated using the following ratio: (i) at least 1 mole of base: 1 mole of silicon; (ii) between 2.5 and 5.5 moles of base: silicon; or (iii) 3.2 moles of base: 1 mole of silicon.

14. The process according to any one of the preceding claims, wherein the water leaching step (iii) is carried out as follows: (i) between about 5 - 60 °C; (ii) at about 35 °C ± 5 °C; (iii) in a single leaching stage; (iv) in multiple countercurrent leaching stages; (v) in three countercurrent leaching stages; and / or (vi) the water leaching step (iii) has a retention time between about 30 and 240 minutes.

15. The process according to any one of the preceding claims, wherein the first sulfuric acid leaching step (iv) is carried out as follows: (i) between about 5 and 60 °C; (ii) at about 40 °C ± 5 °C; (iii) having a retention time between about 30 and 240 minutes; and / or (iv) having a retention time of about 120 minutes.

16. The process according to any one of the preceding claims, wherein the impurities leached in the first sulfuric acid leaching step (iv) include sodium silicate, sodium alum, iron oxide and iron hydroxide mineral phases formed during the alkaline baking step (ii), and any residual base.

17. The process according to any one of the preceding claims, wherein concentrated sulfuric acid is added in the first sulfuric acid leaching step (iv).

18. The process according to any one of the preceding claims, wherein the free acid remaining at the end of the first sulfuric acid leaching step (iv) is: (i) in the range of about 5 - 75 g / L H 2 SO 4 ; or (ii) Approximately 50 g / L ± 5 g / L H 2 SO 4 。 19. The process according to any one of the preceding claims, wherein the first sulfuric acid leaching step (iv) is operated under the following conditions: (i) Solids between about 5% and 25%; or (ii) About 10% solids.

20. The process according to any one of the preceding claims, wherein the hydrofluoric acid leaching step (v) is carried out at: (i) Between about 5 - 60 °C; or (ii) About 40 °C ± 5 °C.

21. The process according to any one of the preceding claims, wherein the impurities leached in the hydrofluoric acid leaching step (v) include quartz, titanium mineral phases, and residual amounts of albite, biotite, and pyrophyllite.

22. The process according to any one of the preceding claims, wherein the free acid remaining at the end of the hydrofluoric acid leaching step (v): (i) Is in the range of about 5 - 75 g / L HF; (ii) Is about 25 g / L ± 5 g / L HF.

23. The process according to any one of the preceding claims, wherein the hydrofluoric acid leaching step (v) is operated at: (i) Solids between about 5% and 25%; or (ii) About 10% solids.

24. The process according to any one of the preceding claims, wherein the hydrofluoric acid added to the acid leaching step (v) is at a concentration of about 20 - 70%.

25. The process according to any one of the preceding claims, wherein the hydrofluoric acid concentration in the acid leaching step (v) is in the range of about 15 - 50 g / L HF.

26. The process according to any one of the preceding claims, wherein the leached solids from the hydrofluoric acid leaching step (v) are substantially free of silicon or have only trace amounts of silicon remaining therein.

27. The process according to any one of the preceding claims, wherein the second sulfuric acid leaching step (vi) is carried out as follows: (i) At between about 5 - 60 °C; or (ii) About 40 °C ± 5 °C.

28. The process according to any one of the preceding claims, wherein the impurities leached in the second sulfuric acid leaching step (vi) include: (i) Precipitated fluoride phases; or (ii) Calcium fluoride and residual alkali metals.

29. The process according to any one of the preceding claims, wherein the second sulfuric acid leaching step (vi) is operated at: (i) Solids between about 5% and 25%; (ii) About 10% solids.

30. The process according to any one of the preceding claims, wherein the second sulfuric acid leaching step (iv) has the following retention time: (i) Between about 30 and 240 minutes; or (ii) About 120 minutes.

31. The process according to any one of the preceding claims, wherein concentrated sulfuric acid is added in the second sulfuric acid leaching step (vi).

32. The process according to any one of the preceding claims, wherein the free acid remaining at the end of the second sulfuric acid leaching step (iv) is in the following range: (i) About 5 - 75 g / L H2SO4; or (ii) Approximately 50 g / L ± 5 g / L H 2 SO 4 .

33. The process according to any one of the preceding claims, wherein the acid solution from the second sulfuric acid leaching step (vi) is collected and recycled to the first sulfuric acid leaching step (vi) and the second sulfuric acid leaching step (vi).

34. The process according to any one of the preceding claims, wherein the washing stage of step (vii) comprises: (i) a single repulping - filtration stage using deionized water; (ii) a plurality of counter - current repulping - filtration stages using deionized water; or (iii) five or more counter - current repulping - filtration stages using deionized water.

35. The process according to any one of the preceding claims, wherein the washing stage of step (vii) operates using a three - stage counter - current repulping - filtration stage under the following conditions: (i) between about 5% and 25% solids; or (ii) about 10% solids.

36. The process according to any one of the preceding claims, wherein in the washing stage of step (vii), the acidity of the liquid, residual salts, and / or residual solids from the second sulfuric acid leaching step (vi) is collected and returned to one or both of the sulfuric acid leaching steps (iv) and (vi).

37. The process according to any one of the preceding claims, wherein the first effluent treatment device receives the effluents from the water leaching step (iii) and the two sulfuric acid leaching steps (iv) and (vi).

38. The process according to claim 37, wherein the first effluent treatment device also receives lime or caustic soda, and iron sulfate as an iron salt or ferrous salt.

39. The process according to claim 38, wherein the first effluent treatment device produces a first effluent, and in the case of adding lime, produces a mixed silicate - hydroxide - gypsum product.

40. The process according to any one of claims 37 to 39, wherein the first effluent treatment device receives the effluent discharged from the leaching step at a rate determined by the silicon level in the first sulfuric acid leaching step (iv).

41. The process according to claim 40, wherein the silicon level in the first sulfuric acid leaching step (iv) is about 5 g / L of silicon.

42. The process according to any one of the preceding claims, wherein the second effluent treatment device receives the effluent discharged from the hydrofluoric acid leaching step (v).

43. The process according to claim 42, wherein the second effluent treatment device also receives lime and ferrous or iron sulfate, thereby producing a second effluent and a calcium fluoride product.

44. The process according to claim 42 or 43, wherein the second effluent treatment device receives aluminum hydroxide, thereby producing a second effluent and an aluminum fluoride product.

45. The process according to any one of claims 42 to 44, wherein the second effluent treatment device receives the effluent discharged from the leaching step at a rate determined by the silicon level in the hydrofluoric acid leaching step (v).

46. The process according to any one of claims 39 to 45, wherein the first effluent and the second effluent are combined to provide a combined effluent product.

47. The process according to any one of claims 39 to 46, wherein the formation of silica gel in the leaching steps (iii), (iv), and (vi) is avoided by discharging the leaching liquid to the effluent treatment step.

48. The process according to any one of claims 39 to 47, wherein the silicon content in leaching steps (iii), (iv) and (vi) is maintained within a selected range by discharging the leachate, the range being: (i) from about 2.5 to 7.5 g / L; or (ii) below about 5 g / L.

49. The process according to any one of the preceding claims, wherein dehydration is provided between the leaching stages.

50. The process according to any one of the preceding claims, wherein the carbon recovery rate of the graphite material purification process is: (i) greater than about 87%; or (ii) between about 87.3% and 96.0%.

51. The process according to any one of the preceding claims, wherein the loss on ignition (LOI) of the purified graphite material product of the process is: (i) greater than or equal to about 99.90%; (ii) from about 99.90 to 99.97%; or (iii) 99.96 to 99.97%.

52. The process according to any one of the preceding claims, wherein the carbon content as graphite of the purified graphite material product of the process is greater than 99.5% w / w.

53. The process according to any one of the preceding claims, wherein the surface area (BET) of the purified graphite material product of the process is: (i) in the range of about 5 to 10 m 2 / g; or (ii) Approximately 7.0 m 2 / g ± 2.0 m 2 / g。 54. The process according to any one of the preceding claims, wherein the d of the purified graphite material product of the process 50 is: (i) in the range of about 5 to 10 μm; or (ii) about 7.0 µm ± 2.0 µm.

55. A purified graphite material product produced by the graphite material purification process according to any one of claims 1 to 54.

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