Purification process of graphite material

Abstract

The purification process of the graphite material includes a pelletizing step (14), a caustic firing step (16) to provide a sintered product, a water leaching step (18) to solubilize impurity minerals, send them to waste liquid treatment, and separate them, a first sulfuric acid leaching step (20) to solubilize remaining impurity minerals, send them to waste liquid treatment, and separate them from the leached solids, a hydrofluoric acid leaching step (22) to solubilize partially leached impurity minerals, send them to waste liquid treatment, and separate them from the leached solids, a second sulfuric acid leaching step (24) to solubilize impurity minerals not leached in the previous step and components precipitated in the hydrofluoric acid leaching step (22), send them to waste liquid treatment, and separate them from the leached solids, and a washing stage to separate remaining soluble impurities and provide a purified graphite material (32).

Description

Technical Field

[0001] Technical Field of the Invention The present invention relates to a purification process for graphite materials.

[0002] More specifically, the purification process of the graphite material of the present invention is intended to be applied to the purification of low-graphite-containing materials.

[0003] In particular, the purification process of the graphite material of the present invention is intended to produce a graphite material of suitable purity for use in the manufacture of Lithium-Ion Batteries (LiBs).

Background Art

[0004] Graphite used in the manufacture of Lithium-Ion Batteries (LiBs) is typically required to be of high purity, such as a Loss On Ignition (LOI) of 99.90% or more, for example. However, it should be noted that the purity requirements of LiBs also depend on the specifications of the mixing and compounding of LiBs. The purity requirements are an issue when producing a suitable graphite product from raw materials with a relatively low graphite content, such as 60 - 70% Cg, and a relatively high content of silicates, sulfides, titanium, and base metal minerals. These problems increase when contaminant minerals are highly dispersed throughout the graphite ore and it is desired to reduce or minimize carbon loss.

[0005] The currently adopted purification methods for graphite used in the manufacture of LiBs particularly employ an aggressive acid leaching step, typically an acid leaching step that requires high-concentration and high-volume hydrofluoric acid. As a result, significant concerns arise regarding the environment and occupational safety and health. These methods also have a low carbon recovery rate, for example, 85% or less. Furthermore, these methods generally start with a graphite material having a carbon content of 90% or more.

[0006] There are significant advantages and benefits in providing an improved purification process for graphite materials that reduces carbon loss and / or reduces dependence on large amounts of high-concentration acids.

[0007] One objective of the purification process and product of the graphite material of the present invention is to substantially overcome one or more of the above-mentioned problems associated with prior art processes or, at least, to provide a useful alternative thereto.

[0008] The foregoing discussion of the background art is intended only to facilitate understanding of the present invention. This discussion does not admit that any of the materials mentioned is, or was part of, common general knowledge at the priority date of the present application.

[0009] Throughout this specification and the 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 should 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 of from about 1 μm (micrometer) to about 2 μm includes not only the explicitly stated limits of 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 about 1.1 μm to about 1.9 μm, about 1.25 μm to about 1.75 μm, etc. Further, when "about" and / or "substantially" are used to describe a value, they are meant to encompass minor variations (up to ±10%) from the stated value. Further, any reference to "trace amounts" means a reference to a concentration of less than about 100 micrograms per gram.

[0011] Furthermore, references to the recovery or removal rate of an element or mineral, or the like, are to be understood as references to the % of that component recovered or removed relative to the original content of the feed to the described process, unless the context requires otherwise. Other references to % are to be construed as references to weight or wt% (not volume or v%) unless the context indicates otherwise. Summary of the Invention Means for Solving the Problems

[0012] Disclosure of the Invention According to the present invention, there is provided a process for purifying a graphite material, the process comprising: (i) passing a concentrate of the graphite material to be purified to a pelletizing step that provides a pelletized material; (ii) firing the pelletized material of step (i) under caustic conditions to provide a sintered product, thereby rendering one or more impurity minerals soluble; (iii) passing the sintered product of step (ii) to a water leaching step, whereby at least a portion of the impurity minerals from step (ii) are solubilized, sent to waste liquid treatment, and separated from the leached solids; (iv) passing the leached solids of step (iii) to a first sulfuric acid leaching step, whereby the impurity minerals that were partially leached in step (iii) are solubilized, sent to waste liquid treatment, and separated from the leached solids; (v) passing the leached solids of step (iv) to a hydrofluoric acid leaching step, whereby the impurity minerals that were partially leached are solubilized, sent to waste liquid treatment, and separated from the leached solids; (vi) passing the leached solids of step (v) to a second sulfuric acid leaching step, whereby the impurity minerals or components that precipitated during step (v) and were not leached in the previous step are solubilized, sent to waste liquid treatment, and separated from the leached solids; (vii) passing the leached solids of step (vi) through one or more washing steps to separate at least a portion of the remaining soluble impurities, thereby producing a purified graphite material;

[0013] Preferably, the process further includes a drying step of drying the purified graphite material of step (vii) to provide a dried purified graphite material. The dried purified graphite material preferably contains 0 to 2.5% moisture, for example less than about 1%, more preferably 0.1% moisture. In one aspect of the invention, the purified graphite material of step (vii) preferably contains about 40% moisture prior to the drying step.

[0014] Preferably, the purified graphite material of step (vii) has a pH of 7 ± 2.5.

[0015] More preferably, the purified graphite material of step (vii) is classified during or after the drying step. The purified graphite material of step (vii) is preferably classified into a plurality of products having different particle size and surface area characteristics, for example at least two fractions, during the drying step. In one aspect, a dry powder classification method, such as a cyclone classification method, is utilized for the classification.

[0016] The pelletizing step (i) preferably includes a stepwise addition of caustic soda and water to the graphite material to be purified. The pellets produced in the pelletizing step (i) are preferably micropellets having a diameter of about 2 to 0 mm, for example 5 mm ± 2 mm.

[0017] In one aspect of the invention, during the pelletizing step (i), dry fine powder of the purified graphite material is added. Preferably, dry fine powder on the order of about 50 kg / t ± 25 kg / t is added. The pellets produced in the pelletizing step (i) preferably have a moisture content of about 10 to 25% w / w, for example about 20% w / w.

[0018] More preferably, the graphite material to be purified has a moisture content of up to about 25% w / w ± 5% w / w before the pelletization step (i). However, the graphite material can be dried to a moisture content of about 0.1 - 2.5% w / w before pelletization to facilitate the steps.

[0019] The caustic firing step (ii) is preferably carried out at about 150 - 300 °C to react caustic soda and especially silicate impurity minerals and solubilize them under water and weak acid conditions.

[0020] Preferably, the caustic firing step has a residence time in the range of about 60 - 240 minutes, preferably about 120 minutes.

[0021] More preferably, the amount of caustic soda added to the graphite material to be purified is calculated using a ratio of at least 1 mol of caustic soda to 1 mol of silicon, for example, a ratio of 2.5 - 5.5 mol of caustic substance to silicon, especially a ratio of 3.2 mol of caustic substance: 1 mol of silicon.

[0022] In one aspect of the present invention, the caustic firing step (ii) is carried out in a rotary kiln.

[0023] The water leaching step (iii) is preferably carried out at 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 certain situations, the water leaching step (iii) may be carried out in multiple, for example, three countercurrent leaching stages. More preferably, the water leaching step (iii) has a holding time of about 30 minutes - 240 minutes.

[0024] The first sulfuric acid leaching step (iv) is preferably carried out at about 5 - 60 °C, for example, about 40 °C ± 5 °C. More preferably, the first sulfuric acid leaching step (iv) has a holding time of about 30 - 240 minutes, for example, about 120 minutes.

[0025] Preferably, 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 caustic calcination step, together with residual caustic substances.

[0026] 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 residual amounts of sodium silicate, sodium alum, iron oxide and iron hydroxide, and titanium mineral phases not removed in step (iii). More preferably, the residual free acid at the end of the first sulfuric acid leaching step (iv) is H2SO4 in the range of about 5 - 75 g / L, for example, about 50 g / L ± 5 g / L of H2SO4. The first sulfuric acid leaching step (iv) is preferably carried out at about 5 - 25% solids, for example, about 10% solids.

[0027] The hydrofluoric acid leaching step (v) is preferably carried out at about 5 - 60 °C, for example, 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 anorthite, 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 of HF, for example, about 25 g / L ± 5 g / L of HF. The hydrofluoric acid leaching step (v) is carried out at about 5 - 25% solids, for example, about 10% solids.

[0028] Preferably, the hydrofluoric acid added to the acid leaching step (v) is at a concentration in the range of about 20 - 70%. The concentration of hydrofluoric acid in the acid leaching step (v) is preferably in the range of about 15 - 50 g / L.

[0029] More preferably, the leached solids from the hydrofluoric acid leaching step (v) have no silicon remaining therein or only trace amounts.

[0030] The second sulfuric acid leaching step (vi) is preferably carried out at about 5 to 60 °C, for example about 40 °C ± 5 °C. Preferably, the impurities leached in the second sulfuric acid leaching step (vi) include the precipitated fluoride phase, such as calcium fluoride and the remaining base metals. The second sulfuric acid leaching step (vi) is preferably carried out at about 5 to 25% solids, for example about 10% solids.

[0031] Preferably, the second sulfuric acid leaching step (iv) has a holding time of about 30 minutes to 240 minutes, for example about 120 minutes.

[0032] 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 to 75 g / L of H2SO4, for example about 50 g / L ± 5 g / L of H2SO4. The acid solution from the second sulfuric acid leaching step (vi) is preferably recovered and recycled to the first sulfuric acid leaching step (iv) and the second sulfuric acid leaching step (vi).

[0033] The washing stage of step (vii) preferably includes a single repulping filtration stage using deionized water, a plurality of countercurrent repulping filtration stages using deionized water, or for example a plurality of 5 countercurrent repulping filtration stages. Preferably, the washing stage of step (vii) is carried out at about 5 to 25% solids, for example about 10% solids, using a three-stage countercurrent repulping filtration stage.

[0034] Preferably, the liquid, residual salts, and / or acidity from the residual solids of the second sulfuric acid leaching step (vi) are recovered in the washing stage of step (vii) and returned to one or both of the sulfuric acid leaching steps (iv) and (vi).

[0035] Preferably, the first waste liquid treatment plant receives waste liquids from the water leaching step (iii) and the two sulfuric acid leaching steps (iv) and (vi). The first waste liquid treatment plant preferably also receives lime or caustic soda, and iron sulfate as the ferric salt or ferrous salt. The first waste liquid treatment plant preferably produces a mixed product of silicate - hydroxide - limestone with the first waste liquid when lime is added.

[0036] Preferably, the first waste liquid treatment plant receives the waste liquid discharged from the first sulfuric acid leaching step (iv) at a rate determined by the silicon level in that leaching step. Preferably, this level is about 5 g / L of silicon in the first sulfuric acid leaching step (iv).

[0037] Preferably, the second waste liquid treatment plant receives the waste liquid discharged from the hydrofluoric acid leaching step (v). Preferably, the second waste liquid treatment plant also receives lime and ferrous sulfate or ferric sulfate and produces the second waste liquid and a calcium fluoride product.

[0038] In one aspect of the present invention, the second waste liquid treatment plant receives aluminum hydroxide and thereby produces the second waste liquid and an aluminum fluoride product.

[0039] Preferably, the second waste liquid treatment plant receives the waste liquid discharged from the hydrofluoric acid leaching step (v) at a rate determined by the silicon level in that leaching step.

[0040] The first effluent and the second effluent are preferably combined to provide a combined waste liquid product.

[0041] Preferably, the formation of silica gel in the leaching steps (iii), (iv) and (vi) is avoided by discharging the leachate into the waste liquid treatment step of the leachate. The silicon content in the leaching steps (iii), (iv) and (vi) is preferably maintained in the range of 2.5 to 7.5 g / L, for example, about 5 g / L or less, by discharging the leachate by this method.

[0042] Preferably, dehydration is carried out between multiple leaching stages.

[0043] Preferably, the carbon recovery rate of the purification process of the graphite material is greater than about 87%, for example, about 87.3% to 96.0%.

[0044] Preferably, the loss on ignition (LOI) of the purified graphite material product of the process is about 99.90% or more, for example, about 99.90 to 99.97%, or 99.96 to 99.97%.

[0045] Preferably, the carbon content of the product of the purified graphite material of the process as graphite is 99.5% w / w or more.

[0046] Preferably, the surface area (BET) of the product of the purified graphite material of the process is about 5 to 10 m 2 / g, preferably about 7.0 m 2 / g ± 2.0 m 2 / g.

[0047] Preferably, the d 50 of the product of the purified graphite material of the process is in the range of about 5 to 10 μm, preferably about 7.0 μm ± 2.0 μm.

[0048] According to the present invention, a purified graphite material product produced according to the purification process of the graphite material described herein is further provided.

Brief Description of the Drawings

[0049] Next, the present invention will be described by way of example only with reference to one embodiment thereof and the accompanying drawings.

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0050] (Best Mode for Carrying Out the Invention) The present invention provides a purification process for a graphite material, the process comprising: (i) passing a concentrate of the graphite material to be purified to a pelletization step that provides a pelletized material; (ii) firing the pelletized material of step (i) under caustic conditions to provide a sintered product, thereby solubilizing one or more impurity minerals; (iii) passing the sintered product of step (ii) to a water leaching step, whereby at least a portion of the impurity minerals from step (ii) are solubilized, sent to waste liquid treatment, and separated from the leached solids; (iv) passing the leached solids of step (iii) to a first sulfuric acid leaching step, whereby the impurity minerals that were partially leached in step (iii) are solubilized, sent to waste liquid treatment, and separated from the leached solids; (v) passing the leached solids of step (iv) to a hydrofluoric acid leaching step, whereby the partially leached impurity minerals are solubilized, sent to waste liquid treatment, and separated from the leached solids; (vi) passing the leached solids of step (v) to a second sulfuric acid leaching step, whereby the impurity minerals or components that precipitated during step (v) and were not leached in the previous step are solubilized, sent to waste liquid treatment, and separated from the leached solids; (vii) passing the leached solids of step (vi) through one or more washing stages to separate at least a portion of the remaining soluble impurities, thereby producing a purified graphite material;

[0051] The process further includes a drying step of drying the purified graphite material of step (vii) to provide a dried purified graphite material. The dried purified graphite material contains 0 to 2.5% moisture, for example less than about 1%, more preferably 0.1% moisture. In one aspect of the invention, the purified graphite material of step (vii) contains about 40% moisture prior to the drying step, but this moisture content is associated with the dehydration and drying equipment employed by the operator. The purified graphite material of step (vii) has a pH of 7 ± 2.5, whereby the purified graphite material is suitable for direct use in the calendaring of electrodes, if desired, without the need to pyrolyze the purified graphite material prior to calendaring.

[0052] The purified graphite material of step (vii) is classified during or after the drying step. The purified graphite material of step (vii) is classified into a plurality of products having different particle size and surface area characteristics, for example at least two fractions, during or after the drying step. In one aspect, the classification utilizes a dry powder classification method, such as a cyclone classification method.

[0053] The pelleting step (i) includes the stepwise addition of caustic soda and water to the graphite material to be purified. The pellets produced in the pelleting step (i) are micropellets having a diameter of about 2 to 10 mm, for example 5 mm ± 2 mm.

[0054] In one aspect of the present invention, if necessary to improve the properties of the pelletized material, during pelletization step (i), a dry fine powder of the purified graphite material is added. A dry fine powder on 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 - 25% w / w, for example about 20% w / w, depending also on the amount of caustic soda added. The graphite material to be purified has a moisture content of up to about 25% w / w ± 5% w / w prior to pelletization step (i). However, the graphite material can be dried to about 0.1 - 2.5% w / w moisture prior to pelletization to facilitate the steps.

[0055] The caustic firing step (ii) is carried out at about 150 - 300 °C to react the caustic soda and in particular the silicate impurity minerals and solubilize them under aqueous and weak acid conditions. The residence time of the caustic firing step is about 60 - 240 minutes, for example about 120 minutes. The amount of caustic soda added to the graphite material to be purified is calculated using a ratio of at least 1 mol of caustic soda per 1 mol of silicon, for example a ratio of 2.5 - 5.5 mol of caustic substance to silicon, in particular a ratio of 3.2 mol of caustic substance: 1 mol of silicon. The caustic firing step (ii) is carried out, for example, in a rotary kiln.

[0056] The water leaching step (iii) is carried out at about 5 - 60 °C, for example about 35 °C ± 5 °C. The water leaching step (iii) is carried out in a single leaching step, but depending on the situation, it may be carried out in multiple, for example three, countercurrent leaching stages. The water leaching step (iii) has a holding time of about 30 minutes - 240 minutes.

[0057] The first sulfuric acid leaching step (iv) is carried out at about 5 to 60 °C, for example about 40 °C ± 5 °C, and the holding time is about 30 to 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 oxide and iron hydroxide, and titanium mineral phases not removed in step (iii). More preferably, the residual free acid at the end of the first sulfuric acid leaching step (iv) is H2SO4 in the range of 5 to 75 g / L, for example about 50 g / L ± 5 g / L of H2SO4. The first sulfuric acid leaching step (iv) is preferably carried out with 5 to 25% solids, for example 10% solids.

[0058] The impurities leached in the first sulfuric acid leaching step (iv) include sodium silicate, sodium alum, iron oxide and iron hydroxide mineral phases formed in the caustic firing step, together with residual caustic substances.

[0059] It is envisaged that all or part of the product of the first sulfuric acid leaching step (iv) is recycled to step (i) for further treatment in the second firing step (ii). Since the firing step (ii) is the stage of the step of the present invention where titanium minerals (for example, titanates and rutile) are "decomposed", it is understood that this can be advantageous in dealing with titanium levels.

[0060] The hydrofluoric acid leaching step (v) is carried out at about 5 to 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 anorthite, biotite, and pyrophyllite. The residual free acid at the end of the hydrofluoric acid leaching step (v) is HF in the range of about 5 to 75 g / L, for example in the range of about 25 g / L ± 5 g / L of HF. The hydrofluoric acid leaching step (v) is carried out with 5 to 25% solids, for example 10% solids.

[0061] The hydrofluoric acid added to the acid leaching step (v) has a concentration in the range of about 20 to 70%. The concentration of hydrofluoric acid in the acid leaching step (v) depends on the grade and mineralogical composition of the starting graphite material, but is preferably in the range of 15 to 50 g / L. The leached solids from the hydrofluoric acid leaching step (v) have substantially no or only trace amounts of silicon remaining.

[0062] The second sulfuric acid leaching step (vi) is carried out at about 5 to 60 °C, for example about 40 °C ± 5 °C. The impurities leached in the second sulfuric acid leaching step (vi) include the precipitated fluoride phase, such as calcium fluoride, and the remaining base metals. The second sulfuric acid leaching step (vi) is carried out at 5 to 25% solids, for example 10% solids. The holding time of the second sulfuric acid leaching step (iv) is about 30 minutes to 240 minutes, for example about 120 minutes.

[0063] 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 to 75 g / L of H2SO4, for example about 50 g / L ± 5 g / L of H2SO4. The acid solution from the second sulfuric acid leaching step (vi) is recovered and recycled to the first sulfuric acid leaching step (iv) and the second sulfuric acid leaching step (vi).

[0064] The washing stage of step (vii) includes a plurality of countercurrent repulping filtration stages using deionized water, for example 5 plurality of countercurrent repulping filtration stages. The washing stage of step (vii) is carried out at 5 to 25% solids, for example 10% solids, using 3 stages of countercurrent repulping filtration stages. The liquid, residual salts, and / or acidity from the residual solids of the second sulfuric acid leaching step (vi) are recovered in the washing stage of step (vii) and returned to one or both of the sulfuric acid leaching steps (iv) and (vi). It is assumed that the liquid, residual salts, and / or acid from the residual solids of the second sulfuric acid leaching step (vi) may also be returned to the water leaching step (iii).

[0065] The first waste liquid treatment plant receives waste liquids from the water leaching step (iii) and the two sulfuric acid leaching steps (iv) and (vi). The first waste liquid treatment plant also receives lime or caustic soda, and iron sulfate as the ferric salt or ferrous salt. The first waste liquid treatment plant produces a mixed product of silicate - hydroxide - limestone when the first waste liquid and lime are added.

[0066] The first waste liquid treatment plant receives the waste liquid discharged from the first sulfuric acid leaching step (iv) at a rate determined by the silicon level in that leaching step. This level is about 5 g / L of silicon in the first sulfuric acid leaching step (iv).

[0067] The second waste liquid treatment plant receives the waste liquid discharged from the hydrofluoric acid leaching step (v). The second waste liquid treatment plant also receives lime and ferrous sulfate or ferric sulfate, and produces the second waste liquid and calcium fluoride product.

[0068] In one aspect of the present invention, the second waste liquid treatment plant receives aluminum hydroxide, thereby producing the second waste liquid and aluminum fluoride product.

[0069] The second waste liquid treatment plant receives the waste liquid discharged from the hydrofluoric acid leaching step (v) at a rate determined by the silicon level in that leaching step.

[0070] The first effluent and the second effluent are combined to provide a combined waste liquid product.

[0071] The formation of silica gel in the leaching steps (iii), (iv) and (vi) is avoided by discharging the leachate to the waste liquid treatment step. The silicon content in the leaching steps (iii), (iv) and (vi) is thus maintained in the range of 2.5 - 7.5 g / L, for example, about 5 g / L or less, by discharging the leachate in this way.

[0072] Dehydration is carried out using a filter and / or a centrifuge decanter between the leaching stages.

[0073] The carbon recovery rate of the purification process of the graphite material is greater than about 87%, for example about 87.3% - 96.0%. The loss on ignition (LOI) of the product of the purified graphite material of the process is about 99.90% or more, for example about 99.90 - 99.97%, or 99.96 - 99.97%.

[0074] The carbon content of the product of the purified graphite material of the process as graphite is 99.5% w / w or more.

[0075] The surface area (BET) of the product of the purified graphite material of the process is about 5 - 10 m 2 / g, for example about 7.0 m 2 / g ± 2.0 m 2 / g, but it should be understood that the surface area (BET) depends to some extent on the concentrate of the initial starting graphite material. The d 50 of the product of the purified graphite material of the process is in the range of about 5 - 10 μm, for example about 7.0 μm ± 2.0 μm, but it should be understood that d 50 depends to some extent on the concentrate of the initial starting graphite material.

[0076] Optionally, the concentrate of the graphite material can be ground before the pelletization step (i), thereby making it possible to obtain a purified graphite material having a surface area (BET) of about 25 m 2 / g or more.

[0077] The present invention further provides a purified graphite material product manufactured according to the purification process of the graphite material described herein and having a purity suitable for use in the manufacture of LiB.

[0078] FIG. 1 shows a purification process 10 of a graphite material according to the present invention, and this process 10 (i) Passing the concentrate 12 of the graphite material to be purified to a pelletizing step 14 that provides a pelletized concentrate; (ii) Firing the pelletized concentrate of step (i) in a caustic firing step 16 under caustic conditions to provide a sintered product, thereby solubilizing one or more impurity minerals; (iii) Passing the sintered product of step (ii) to a water leaching step 18, whereby at least a portion of the impurity minerals from step (ii) are solubilized, sent to waste liquid treatment, and separated from the leached solids; (iv) Passing the leached solids of step (iii) to a first sulfuric acid leaching step 20, whereby the impurity minerals that were partially leached in step (iii) are solubilized, sent to waste liquid treatment, and separated from the leached solids; (v) Passing the leached solids of step (iv) to a hydrofluoric acid leaching step 22, whereby the partially leached impurity minerals are solubilized, sent to waste liquid treatment, and separated from the leached solids; (vi) Passing the leached solids of step (v) to a second sulfuric acid leaching step 24, whereby the impurity minerals or components that precipitated during step (v) and were not leached in the previous step are solubilized, sent to waste liquid treatment, and separated from the leached solids; (vii) Passing the leached solids of step (vi) to one or more washing stages 26 to separate at least a portion of the remaining soluble impurities, thereby producing a purified graphite material 28.

[0079] This process further includes a drying step 30 of drying the purified graphite material 28 of step (vii) to provide a dried purified graphite material 32 (herein also referred to as Talcite C®). The purified graphite material 28 of step (vii) contains about 40% moisture before the drying step, but the dried purified graphite material is intended to contain 0 to 2.5% moisture, for example less than about 0.1% moisture. The purified graphite material 28 of step (vii) has a pH of 7 ± 2.5 when repulped in water, whereby the purified graphite material is suitable for direct use in the calendaring of electrodes (not shown).

[0080] The purified graphite material 28 of step (vii) is classified into at least two fractions in drying step 30, for example using cyclone classification. These two fractions typically include a fine fraction and a coarse fraction.

[0081] The concentrate 12 of graphite material has a moisture content of up to about 26 - 28% w / w. This concentrate 12 is first passed to a concentrate drying step 34, for example an instant drying stage or a rotary drum dryer. A portion of the raw material 12 is discharged into the exhaust gas but is recovered and reintroduced into the dried concentrate sent to the pelletizing step 14.

[0082] The pelletizing step 14 includes the stepwise addition of caustic soda in the form of caustic prills and water to the graphite material to be purified. The pellets produced in the pelletizing step 14 are micropellets with a diameter of about 2 - 10 mm, for example 5 mm ± 2 mm.

[0083] The dry fines of the purified graphite material are added during the pelletizing step 14, for example dry fines on the order of about 50 kg / t are added. The dry fines of the purified graphite material are supplied from the drying step 30. The pellets produced in the pelletizing step 14 have a moisture content of about 13 - 24% w / w, for example about 20% w / w.

[0084] The caustic firing step 16 is carried out at about 150 - 300 °C to react sodium hydroxide and especially silicate impurity minerals and solubilize them in water. The caustic firing step 16 has a residence time longer than about 60 minutes, for example about 120 minutes. The amount of sodium hydroxide added to the graphite material to be purified is calculated using a ratio of at least 1 mol of sodium hydroxide to 1 mol of silicon, for example a ratio of 3.2 mol of caustic substance to 1 mol of silicon. The caustic firing step 16 is carried out, for example, in a rotary kiln.

[0085] The water leaching step 18 is carried out at about 5 - 60 °C, for example about 35 °C. The water leaching step 18 is carried out in a single - stage or multi - stage, for example counter - current leaching steps up to 3 stages, and has a retention time of about 30 - 240 minutes.

[0086] The first sulfuric acid leaching step 20 is carried out at about 25 - 50 °C, for example about 40 °C, and has a retention time of about 30 - 240 minutes, for example 120 minutes. Concentrated sulfuric acid is added in the first sulfuric acid leaching step 20, and the residual free acid at the end of the first sulfuric acid leaching step (iv) is about 50 g / L of H2SO4. The first sulfuric acid leaching step (iv) operates at 5 - 25% solids, for example 10% solids.

[0087] The impurities leached in the first sulfuric acid leaching step 20 include sodium silicate, sodium alum, iron oxide and iron hydroxide mineral phases, together with the remaining caustic substances.

[0088] The hydrofluoric acid leaching step 22 is carried out at about 30 - 45 °C. The impurities leached in the hydrofluoric acid leaching step 22 include quartz, titanium mineral phases, and residual amounts of anorthite, biotite, and pyrophyllite. The residual free acid at the end of the hydrofluoric acid leaching step 22 is about 25 g / L of HF. The hydrofluoric acid leaching step (v) operates at 5 - 25% solids, for example 10% solids.

[0089] The hydrofluoric acid added to the leaching step 22 is in the range of about 20 - 70% concentration, and the concentration of the hydrofluoric acid 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 a trace amount of silicon remains.

[0090] The second sulfuric acid leaching step 24 is carried out at 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, the precipitated fluoride phase, for example calcium fluoride, and the remaining base metals. The second sulfuric acid leaching step 24 has a holding time of about 30 - 240 minutes, for example about 120 minutes.

[0091] Concentrated sulfuric acid is added in the second sulfuric acid leaching step 24, and the residual free acid at the end of the second sulfuric acid leaching step 24 is about 50 g / L. The second sulfuric acid leaching step (vi) operates at 5 - 25% solids, for example 10% solids.

[0092] The washing stage of step 26 includes a plurality of countercurrent repulping filtration stages, for example three countercurrent repulping filtration stages, using deionized water. The washing stage of step 26 operates at 5 - 25% solids, for example 10% solids. Water, residual salts, and / or acidic substances from the residual solids of the second sulfuric acid leaching step 24 are recovered in the washing stage of step 26 and returned to one or both of the sulfuric acid leaching steps 20 and 24. It is assumed that the liquid, residual salts, and / or acidic substances from the residual solids of the second sulfuric acid leaching step (vi) may be further returned to the water leaching step (iii).

[0093] It is assumed that carbonation is incorporated during the washing stage of step 26 through the addition of sodium bicarbonate or bubbling of carbon dioxide using caustic soda for pH control. This helps to neutralize the carry - over acid from the second sulfuric acid leaching step 24 and reduce the number of required countercurrent washing steps.

[0094] The first waste liquid treatment plant 36 receives the waste liquid from the water leaching step 18 and the two sulfuric acid leaching steps 20 and 24. The first waste liquid treatment plant 36 also receives lime and iron sulfate, such as ferric sulfate, and produces the first waste liquid 38 and the calcium carbonate product 40. The precipitation or residue of calcium carbonate can be minimized by the use of caustic soda rather than lime in this step.

[0095] The second waste liquid treatment plant 42 receives the waste liquid discharged from the hydrogen fluoride leaching step 22. The second waste liquid treatment plant 42 also receives lime and iron sulfate, such as ferric sulfate, and produces the second waste liquid 44 and the calcium fluoride product 46.

[0096] In one aspect of the present invention, the second waste liquid treatment plant receives aluminum hydroxide, thereby producing the second waste liquid and the aluminum fluoride product.

[0097] The second waste liquid treatment plant 42 receives the waste liquid discharged from the hydrogen fluoride leaching step 22 at a rate determined by the silicon level in the leaching step 22.

[0098] The first effluent 38 and the second effluent 44 may then be combined to provide a combined waste liquid product 48.

[0099] The formation of silica gel in the leaching steps 18, 20 and 24 is avoided by discharging the leachate to the waste liquid treatment step. The silicon content in the leaching steps 18, 20 and 24 is maintained below about 5 g / L by discharging the leachate by this method.

[0100] Dehydration is performed, if necessary, using a filter and / or a centrifuge decanter between multiple leaching stages.

[0101] The carbon recovery rate of the purification process 10 of the graphite material of the present invention is greater than about 87%, for example, about 87.3% to 96.0%. The loss on ignition (LOI) of the product of the purified graphite material of the process is about 99.90% or more, for example, about 99.90 to 99.97%, or 99.96 to 99.97%.

[0102] The carbon content of the product of the purified graphite material of the process 10 of the present invention as graphite is greater than 99.5% w / w.

[0103] The surface area (BET) of the product of the purified graphite material 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 product of the purified graphite material 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, but it should be understood that d 50 depends to some extent on the concentrate of the initial starting graphite material.

[0104] The process of the present invention can be better understood by referring to the following non-limiting examples.

[0105] (Example) The natural graphite precursor or ore used in the investigation of the present invention was extracted from the Vittangi graphite mine in Norrbotten County, northern Sweden. This natural graphite source is characterized by hard particles with a very narrow distribution containing microcrystalline flakes. The mineral phases are divided into two main categories. (i) Minerals dispersed in the graphite matrix host rock, and (ii) Discrete minerals and / or vein minerals present as free minerals or composite minerals at the grain boundaries.

[0106] The mineral phases classified into these two categories are summarized in Table 1 below, together with an approximate relative abundance.

Table 1

[0107] The concentrate was prepared by the applicant from the above ore and used as the basis for the computer model (using METSIM® software) of the process of the present invention. The assumed mineral composition of the purified plant feedstock employed in the METSIM modeling is summarized in Table 2 below, showing all carbon present in the form of graphite-quality carbon (C g ).

Table 2

[0108] The graphite concentrate is caustic calcined in a caustic calcination step that converts gangue minerals to sodium salts, and then, through multiple stages of water and acid leaching, repulping / washing, the gangue species are solubilized and removed from the solid graphite phase. The more dilute process water produced in the latter stages of the washing step is recycled to the upstream repulping and filter cake washing operations that flow countercurrent to the graphite material or concentrate within the process to maximize the washing efficiency of the raw water input to the process.

[0109] The intended functions of each stage of the process of the present invention are described below. The information on the described solution and slurry flows is presented for illustrative purposes only.

[0110] (Concentrate drying stage) This stage receives the wet concentrate filter cake in bulk bags and produces a loose solid dried to 0.5% w / w moisture, which is transferred by a screw feeder to the caustic calcination step.

[0111] The flash dryer feed bin equipped with a bag breaker receives the bags of wet filter cake from a suitable delivery pad by hoist. The loose filter cake is transferred from the bottom of the feed bin to the flash dryer by a screw feeder operating at a constant rate.

[0112] The concentrate is flash dried and conveyed by a screw feeder to a dry concentrate bin, from where it is sent by a screw feeder to the caustic firing step / roasting. An estimated 12.5% of the concentrate exits the dryer in the exhaust gas (post-dust cyclone) and is passed to the baghouse. An estimated 99.5% of the solids passed to the baghouse are captured and sent to the dry concentrate bin.

[0113] It is assumed that it is possible to control the final moisture to a higher value (close to but below the pellet moisture) to avoid the inefficiency of having to add the evaporated moisture again.

[0114] (Caustic firing step and pelletizing step) The caustic firing / roasting step combines the dry concentrate with sodium hydroxide to form pellets with an average diameter of about 5 mm and feeds these to a kiln. At high temperature, the silicate and other gangue minerals are converted to sodium salts.

[0115] The dry concentrate, caustic (sodium hydroxide) prill and water are fed to a pelletizing package and pellets with a target moisture of 15% w / w suitable for feeding to the roasting kiln are produced. Fine powder of the dry graphite product from the product dry baghouse bin is also added to the formed pellets to reduce the tendency to agglomerate in a step called "curing". The addition of the graphite fine powder is carried out at a rate of 5% w / w based on the uncured pellets.

[0116] The cured graphite pellets are transferred directly to a calcination rotary kiln, where the temperature is raised to 200 °C over 2 hours. According to the applicant's test research, about 95% of gangue minerals are converted into sodium salts, and about 13.7% of the graphite is lost in this process due to reaction with caustics. It is assumed that 5% of the solids are passed to the exhaust gas as dust.

[0117] The exhaust gas is led to a baghouse where 99.5% of the solids are assumed to be captured. The solids from the baghouse are put into a clinker bin together with the kiln discharge solids (clinker), from where a screw feeder transfers the clinker to the next processing area.

[0118] (Water leaching step) In the water leaching step, the sodium salts are solubilized and separated from the remaining solids in three stages: leaching, filtration, washing, and repulping.

[0119] The sintering material is transferred by a screw feeder to the first-stage repulping tank, where it is mixed with the second-stage filtrate. Another first-stage repulping tank is operated in continuous supply mode, and a duty supply pump discharges the graphite slurry into the first tank of two baffled stirred first-stage leaching tanks connected in series by gravity overflow. The precipitated salts dissolve, and the slurry overflows from the final leaching tank to the first-stage filter feed tank.

[0120] The first-stage batch press filter is supplied from the filter feed tank by a centrifugal slurry pump. The filter cake is washed with the second-stage filtrate supplied by a dedicated pump. The first-stage primary filtrate and washing filtrate are collected in one tank before being transferred by pump to the first waste liquid treatment plant.

[0121] The filter cake of the first stage is transferred by a screw feeder to the second stage obligatory repulping tank, where it is mixed with the filtrate of the third stage. Another second stage repulping tank is operated in continuous supply mode, and the obligatory supply pump discharges the graphite slurry into the first of two baffled stirred leaching tanks connected in series by gravity overflow. The precipitated salts dissolve, and the slurry overflows from the final leaching tank to the second stage filter supply tank.

[0122] The second stage batch press filter is supplied from the second stage filter supply tank by a centrifugal slurry pump. The filter cake is washed with the filtrate of the third stage supplied by a dedicated pump. The second stage primary filtrate and wash filtrate are collected in the second stage filtrate tank before being transferred by dedicated pumps to the first stage repulping and filter cake washing operations as required.

[0123] The second stage filter cake is transferred by a screw feeder to the third stage obligatory repulping tank, where it is mixed with raw water. Another third stage repulping tank is operated in continuous supply mode, and the obligatory supply pump discharges the graphite slurry into the first of two baffled stirred leaching tanks connected in series by gravity overflow. The precipitated salts dissolve, and the slurry overflows from the final leaching tank to the third stage filter supply tank.

[0124] The third stage batch press filter is supplied from the third stage filter supply tank by a centrifugal slurry pump. The filter cake is washed with raw water. The third stage primary filtrate and wash filtrate are collected in the third stage filtrate tank before being transferred by dedicated pumps to the second stage repulping and filter cake washing operations as required.

[0125] The third stage filter cake is transferred by a screw feeder to the next processing area.

[0126] (First sulfuric acid leaching step) The first sulfuric acid leaching step area partially solubilizes gangue minerals and separates them from the remaining solids.

[0127] The filter cake from the third stage of water leaching is transferred by a screw feeder to an obligatory acid leaching repulping tank, where it is mixed with leach filtrate and raw water to a pulp density of 12% w / w solids. Another repulping tank is operated in continuous feed mode, and an obligatory feed pump discharges acidic graphite slurry to the first of three baffled stirred 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. Gangue minerals dissolve and the slurry overflows from the final leaching tank to the filter feed tank.

[0128] The acid leaching batch press filter is fed from the filter feed tank by a centrifugal slurry pump. The filter cake is washed with water leaching filtrate supplied by a dedicated pump. The acid leaching primary filtrate and wash filtrate are collected in one tank, from which a portion of the solution is recycled by a dedicated pump to the acid leaching repulp tank, and the remainder is transferred by a pump to a first waste liquid treatment plant activated by a level controller in the transfer tank.

[0129] The acid leaching filter cake is transferred by a screw feeder to a water leaching obligatory repulp tank, where it is combined with a mixture of raw water and the final water repulp filtrate. Another water leaching repulping tank is operated in continuous feed mode, and an obligatory feed pump discharges graphite slurry to the first of two baffled stirred leaching tanks connected in series by gravity overflow. Precipitated salts dissolve and the slurry overflows from the final leaching tank to the water leaching filter feed tank.

[0130] The water leaching batch press filter is supplied from the water leaching filter supply tank by a centrifugal slurry pump. The filter cake is washed with raw water. The primary filtrate and the washing filtrate are collected in the water leaching filtrate tank before being transferred by a dedicated pump to the acid leaching filter cake washing as required, and the surplus water is sent to the first waste liquid treatment plant.

[0131] The finally washed filter cake is transferred to the next processing area by a screw feeder.

[0132] (Hydrofluoric acid leaching step) The hydrofluoric acid leaching step further solubilizes the silicate gangue minerals and separates them from the remaining solids.

[0133] The sulfuric acid leaching filter cake is transferred by a screw feeder to the obligatory acid leaching repulping tank, where it is mixed with the leaching filtrate and raw water to form a pulp with a solids concentration of 11% w / w. Another repulping tank is in continuous supply mode, and the obligatory supply pump discharges the acidic graphite slurry by gravity overflow into the first of three baffled stirred acid leaching tanks connected in series. 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 supply tank.

[0134] The acid leaching batch press filter is supplied from the filter supply tank by a centrifugal slurry pump. The filter cake is washed with the water leaching filtrate supplied by a dedicated pump. The acid leaching primary filtrate and the washing filtrate are collected in one tank, from which a part of the solution is recycled to the acid leaching repulping tank by a dedicated pump, and the rest is transferred to the second waste liquid treatment plant by a pump while being operated by a level controller in the transfer tank.

[0135] The acid leaching filter cake is transferred by a screw feeder to the water leaching duty repulping tank, where it is combined with raw water. Another water leaching repulping tank is operated in continuous supply mode, and the duty supply pump discharges the graphite slurry by gravity overflow into the first of two baffled stirred leaching tanks connected in series. The precipitated salts dissolve, and the slurry overflows from the final leaching tank into the water leaching filter feed tank.

[0136] The water leaching batch press filter is fed from the water leaching filter feed tank by a centrifugal slurry pump. The filter cake is washed with raw water. The primary filtrate and wash filtrate are collected in the water leaching filtrate tank before being transferred by dedicated pumps to the acid leaching filter cake wash as required, and the surplus water is sent to the second waste liquid treatment plant.

[0137] The finally washed filter cake is transferred to the next processing area by a screw feeder.

[0138] (Second sulfuric acid leaching step) The second sulfuric acid leaching step mainly solubilizes the calcium fluoride precipitate produced in the previous step. An important consideration in this area is to ensure that the solubility of calcium sulfate, which causes the formation of gypsum precipitate and dilution of graphite, is not exceeded. This is achieved by carefully controlling the parameters of the water balance and pulp density.

[0139] The washed hydrofluoric acid leached filter cake is transferred by a screw feeder to the repulping tank of the obligatory second sulfuric acid leaching step, 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 continuous feed mode and the obligatory feed pump discharges the acidic graphite slurry by gravity overflow to the first of three baffled stirred leaching tanks connected in series. 70% sulfuric acid is added to the leaching tanks to maintain the background / residual acid concentration at 25 g / L. The fluoride precipitate dissolves and the slurry overflows from the final leaching tank to the filter feed tank.

[0140] The batch press filter is fed from the filter feed tank by a centrifugal slurry pump. The filter cake is washed with process water supplied by a dedicated pump. The acid leach primary filtrate and the wash filtrate are collected in one tank, from where a portion of the solution is recycled by a dedicated pump to the acid leach repulp tank, a portion is recycled to the first sulfuric acid leach obligatory repulp tank, and the remainder is pumped to the first waste liquid treatment step.

[0141] The filter cake is transferred to the next processing area by a screw feeder.

[0142] (Water repulp washing step) The final water repulping step consists of three stages: repulping, continuous mixing, and filtration. This gives a final opportunity to remove the dissolved gangue components from the liquid contained in the pores of the graphite filter cake and the liquid film surrounding each graphite particle. The dissolved species remaining after this stage become part of the solid phase by evaporation of the water in the product drying stage.

[0143] The acid leaching filter cake is transferred by a screw feeder to the first-stage obligatory repulping tank, where it is mixed with the filtrate of the second stage. Another first-stage repulping tank is in continuous supply mode, and the obligatory supply pump discharges the graphite slurry into the first of two baffled stirred first-stage stirring tanks connected in series by gravity overflow. Dissolved solids migrate to the bulk solution by diffusion, and the slurry overflows from the final mixing tank to the first-stage filter supply tank.

[0144] The first-stage batch press filter is supplied from the filter supply tank by a centrifugal slurry pump. The filter cake is washed with demineralized water supplied by a dedicated pump. The first-stage primary filtrate and washing filtrate are collected in a single process water tank prior to transfer by dedicated pumps to upstream repulping and washing operations.

[0145] The first-stage filter cake is transferred by a screw feeder to the second-stage repulping tank, where it is mixed with the filtrate of the third stage. Another second-stage repulping tank is operated in continuous supply mode, and the obligatory supply pump discharges the graphite slurry into the first of two baffled stirred mixing tanks connected in series by gravity overflow. Dissolved solids migrate to the bulk solution by diffusion, and the slurry overflows from the final mixing tank to the second-stage filter supply tank.

[0146] The second-stage batch press filter is supplied from the second-stage filter supply tank by a centrifugal slurry pump. The filter cake is washed with demineralized water supplied by a dedicated pump. The second-stage primary filtrate and washing filtrate are collected in the second-stage filtrate tank prior to partial recycling to the first-stage repulping by dedicated pumps, and the remainder is sent to the process water tank.

[0147] The filtration cake of the second stage is transferred to the third stage repulping tank by a screw feeder and mixed with demineralized water there. Another third stage repulping tank is in continuous supply mode, and the duty supply pump discharges the graphite slurry first into the first of two baffled stirred mixing tanks connected in series by gravity overflow. Dissolved solids migrate to the bulk solution by diffusion, and the slurry overflows from the final mixing tank to the third stage filter feed tank.

[0148] The third stage batch press filter is fed from the third stage filter feed tank by a centrifugal slurry pump. The filter cake is washed with demineralized water. The third stage primary filtrate and wash filtrate are collected in the third stage filtrate tank prior to partial reuse by the second stage repulping dedicated pump, and the remainder is sent to the process water tank.

[0149] The third stage filter cake is transferred to the next processing area by a screw feeder.

[0150] (Product drying step) In the drying step, the purified graphite filter cake is dried in a pneumatic dryer to 0.5% w / w moisture to produce a loosely dried purified graphite suitable for supply to subsequent plants for anode production.

[0151] The pneumatic dryer receives the wet purified graphite filter cake by a screw feeder. The concentrate is pneumatically dried and conveyed to the dry product bin by a screw feeder. An estimated 12.5% of the concentrate is discharged from the dryer into the exhaust gas (post-dust cyclone) and sent to the baghouse. An estimated 99.5% of the solids sent to the baghouse are captured and mainly sent to the dry product bin.

[0152] (First waste liquid treatment plant) The first waste liquid treatment plant treats a sulfate waste solution to produce a liquid waste mainly containing sodium sulfate and calcium sulfate, and a wet filter cake of solids mainly containing gypsum and metal hydroxides for waste disposal.

[0153] The waste solution is led into a stirred neutralization tank with baffles, and the pH is equilibrated to ~pH6 by adding sulfuric acid if necessary to maintain the desired pH set value.

[0154] The solution with stabilized pH overflows from the neutralization tank into the ferric iron addition tank. A stirred ferric sulfate solution with baffles is introduced into this tank so that the iron in the slurry is 1 g / L. Depending on the natural pH after neutralization, ferric iron may precipitate in this tank or at a later stage.

[0155] The slurry with added ferric iron overflows from the ferric iron addition tank and enters the first of three stirred settling tanks with baffles. Lime slurry is dosed into each tank as necessary 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 produced by the reaction of lime and sulfuric acid, and gypsum precipitates at the solubility limit of calcium sulfate. The slurry overflows from the last settling reactor into the thickener. A dilute flocculant is introduced when the slurry enters the feed well, mixed with the slurry, and fast-settling flocs are formed. The precipitate of mixed gypsum and metal hydroxides settles, while the clear solution overflows from the thickener into the overflow tank.

[0156] The precipitation train of the first waste liquid treatment plant is operated as a high-density sludge plant to assist in the formation of fast-settling solids. The solids production rate is low, and it is necessary to increase the recycle rate of the thickener underflow to maintain the target solids of 10% w / w in the thickener feed slurry. Therefore, it is assumed that the duty underflow pump operates in full recycle mode for approximately 85% of the plant operating time, and discharges to the filter feed tank for the remaining time to lower the thickener bed level.

[0157] The batch press filter is periodically fed from the filter feed tank by a centrifugal slurry pump, and the filtrate is sent to the thickener overflow tank for discharge.

[0158] (Second waste liquid treatment plant) Treats fluoride waste liquid to produce a waste liquid mainly containing calcium sulfate and a filter cake mainly containing calcium fluoride, gypsum and metal hydroxides, and disposes of them.

[0159] The waste liquid is led to a baffled stirred ferric addition tank, and a ferric sulfate solution is added so that the iron in the slurry reaches 1 g / L. Since the pH of this tank is expected to be low, the ferric iron remains soluble.

[0160] The slurry with added secondary iron overflows the secondary iron addition tank and enters the first of three baffled stirred settling tanks. Lime slurry is introduced into each tank as needed to maintain a target pH of 12.0 in the last tank. Dissolved salts other than sodium sulfate are almost completely hydrolyzed and precipitate as hydroxides. Insoluble calcium fluoride is produced by the reaction of lime and hydrofluoric acid, calcium sulfate is produced by the reaction of lime and sulfuric acid, and gypsum precipitates at the solubility limit of calcium sulfate. The slurry overflows from the last settling reactor to the thickener. A dilute flocculant is introduced when the slurry enters the feed well, mixed with the slurry, and fast-settling flocs are formed. The mixture of calcium fluoride, gypsum, and metal hydroxide precipitates, while the clear solution overflows from the thickener to the overflow tank.

[0161] The precipitation train of the second waste liquid treatment plant is operated as a high-density sludge plant to assist in the formation of fast-settling solids. The solids production rate is low, and it is necessary to increase the recycle rate of the thickener underflow to maintain 10% w / w of the target solids in the thickener feed slurry. Therefore, it is assumed that the duty underflow pump will operate in full recycle mode for approximately 85% of the plant operating time and discharge to the filter feed tank to lower the thickener bed level for the remaining time.

[0162] The batch press filter is periodically fed from the filter feed tank by a centrifugal slurry pump, and the filtrate is sent to the thickener overflow tank for discharge.

[0163] Further tests were conducted regarding aspects of the process of the present invention.

[0164] The production data of Talphyte C (registered trademark) material with an LOI of over 99.9% final purity is summarized in Table 3 below. This data also suggests a decrease in surface area (BET) after purification, and the applicant believes that it is highly likely that this is the result of the removal of impurity fines through the purification process.

Table 3

[0165] (Baseline purification of selected GTK concentrated samples) Three types of graphite material concentrate samples were purified in the laboratory according to the following conditions. (i) Caustic firing - 4 hours at 250 °C, a NaOH:Si molar ratio of 5.2. (ii) Water leaching - 2 hours at 15 °C, three consecutive water leaching steps of 1 hour and 30 minutes. (iii) Sulfuric acid leaching (first stage) - 4 hours at 15 °C with an acid addition of 250 kg / t. (iv) Hydrofluoric acid leaching - 4 hours at 15 °C with an acid addition of 300 kg / t. (v) Sulfuric acid leaching (second stage) - 4 hours at 15 °C with an acid addition of 250 kg / t. (vi) Water repulping - 7 stages, each for 30 minutes, operating at 15 °C.

[0166] The main metallurgical data is summarized in Table 4 below.

Table 4

[0167] When scaled up to production scale (~150 kg scale), the carbon recovery rate improved from 87.4% in the laboratory to 95.7% in Sample 1. The carbon loss was less in larger-scale production operations compared to laboratory tests. The surface area of the final purified product was 6.4 m 2 / g.

[0168] (Optimization of the acid leaching stage) It has been shown that by optimizing the acid leaching conditions, it is possible to significantly shorten the residence time of these steps while maintaining high purity. The test results are summarized in Table 5. The firing, water leaching, and repulping washing steps remained the same as the baseline conditions described herein, while the acid leaching step was carried out at 15 °C.

Table 5

[0169] Reducing the acid addition to 50% and the residence time to 25% resulted in a decrease in purity below the acceptable level.

[0170] (Further Optimization of the Acid Leaching Stage) Under the baseline purification conditions, the minimum target value of the LOI purity of a certain concentrate sample was not obtained, and an optimization test operation focusing on the temperature of the leaching step of this sample was carried out. This test operation also overlapped with the period during the production execution for processing the concentrate raw material when the temperature conditions inside the building were 5 - 10 °C due to winter conditions. Under such conditions, two batches showed LOI values of 99.88% and 99.89%. However, when the solution was heated to about 20 °C and the batch was returned, the purity target was restored. From this observation, it became apparent that the purification process is sensitive to temperature changes. The results are summarized in Table 6 below.

Table 6

[0171] In the large-scale production purification of this material, by applying high-temperature leaching conditions (25 - 35 °C), the final LOI purity reached 99.9% and the overall carbon recovery rate was 91.3%.

[0172] (HF Acid Leaching Using Recycled Solution) To evaluate the effect on purification efficiency, a series of tests were completed to simulate the recycling of HF leaching solutions with various compositions.

[0173] These tests confirmed that it is possible to achieve an LOI purity target > 99.90%, even with high levels of silicon, potassium, titanium, aluminum, and iron in the starting leachate. To achieve the purity target when recycling the leachate, a recycle solution with a fluoride ion concentration of 55 g / l or higher is required. The main test results are summarized in Table 7 below.

Table 7

[0174] (Characterization of Purified Graphite Samples) Detailed analysis and characterization information was collated and summarized in Table 8 below for the talc C (R) product generated by the applicant in laboratory tests.

Table 8

[0175] (Larger-Scale Purification Trials) The applicant successfully purified a larger-scale graphite material concentrate sample (~150 kg batch of wet filter cake) and confirmed the laboratory-scale test results and scale-up of the process. The carbon recovery rate was improved from 90% to 96% compared to laboratory tests while achieving an LOI purity target ≥ 99.90%.

[0176] Table 9 below summarizes the production data.

Table 9

[0177] (Pelletization and Rotary Kiln Firing Pilot Tests) Pilot tests of pelletization and rotary kiln firing were conducted by the applicant.

[0178] To prevent the formation of clusters, reduce the adhesiveness of the pellets, and establish operating conditions targeting pellets in the range of 2 - 10 mm, a pelletization test was carried out using a 5L Eirich Intensive Mixer (Model R01).

[0179] Tests have shown that adding dry fines at the pelletization operation stage coats the surface of the pellets and reduces their adhesiveness, thereby improving the properties of the final pellet mixture. The addition of 50 kg / t of dry concentrated fines resulted in pellets with good fluidity having a final moisture content of 13% w / w.

[0180] Further test work to explore the influence of moisture in the feed and the addition of water has shown that feeding wet filter cake to the Eirich mixer results in the formation of suitable pellets. The maximum feed moisture content appears to be in the range of 26 - 28% w / w. Above this, even with the addition of a large amount of dry fines, large aggregates and / or paste were formed.

[0181] In the scale-up test using a 75L Eirich mixer (Model R08W), it was confirmed that by adding 50 kg / t of fines, pellets with excellent particle size and fluidity can be produced with a final moisture content of approximately 24%. The pelletization raw materials obtained from these tests proceeded to the rotary kiln pilot test.

[0182] The results of the pelletization tests and the conditions tested are summarized in Table 10 of Figure 2. These results suggest that it may be possible to omit the drying of the concentrate before pelletization or at least reduce the obligation to dry.

[0183] The bulk density of the pellets produced by the 75L Einrich device was 1.10 t / m 3 and the angle of repose was 40°.

[0184] Caustic roasting pilot test Loaded and stored fresh "green" pellets in a hopper equipped with a variable-speed belt conveyor that supplies them to a rotary kiln with the following specifications. (i) Kiln length - 2.5 m (ii) Kiln diameter - 300 mm (iii) Kiln inclination - 2.3 (iv) Kiln rotation - 0.5 rpm (v) Measurement of residence time - 50 minutes (tracer) (vi) Electric heating of the inner wall - In terms of the sintered product bed, the difference between the outer wall temperature sensor and the inner wall is 30 °C (vii) Countercurrent heating air flow

[0185] The residence time of the kiln was measured to be 50 minutes, providing a longer firing time. To investigate the effect of the residence time, 2 passes were made per campaign. Two campaigns were completed, and the operating conditions along with the main metallurgical data are summarized in Table 11 below.

Table 10

[0186] For the purification of the Pass 1 and Pass 2 samples of both campaigns (room temperature leaching, i.e., ~15 °C), the LOI purity was 99.88% regardless of the firing conditions. The material handling data was measured only for the products of Campaign 1.

[0187] In a further leaching test carried out at 45 °C on the Pass 1 material of Campaign 2, the final purity was not improved, and the LOI value was 99.88%.

[0188] For further investigation, the pelletized feedstock of Campaign 2 was fired in a static oven for 4 hours and leached at 15 °C, 30 °C, and 45 °C in the laboratory. The LOI values for these tests were 99.89%, 99.81%, and 99.92% respectively, suggesting that the leaching temperature is important. However, more importantly, when comparing the leaching results at 45 °C with the pilot-fired product, the residence time of the firing time is also important. The residence time of 100 minutes (50 minutes × 2 passes) in the pilot kiln seems insufficient to complete the reaction of the caustic soda and silicate minerals required to achieve the final purity requirements.

[0189] (Pilot Test of Concentrate Dryer) The concentrate drying test work using a DryTech (equipment supplier) pneumatic dryer was completed, and it was confirmed that the wet filter cake was easily processed using the process of the present invention, and a final dried product with a moisture content of < 0.2% w / w was obtained.

[0190] Filter cake samples with moisture levels in the range of 39% to 55% generated were tested. The use of a back mixer and a disintegration stage used by DryTech for other commercial graphite drying applications has proven successful in processing and feeding concentrated materials containing such high levels of moisture. Reusing the dried raw material in the back mixer yielded a product with a moisture content of ≦ 43% w / w. This material was found to be suitable for feeding into the pneumatic dryer unit.

[0191] The characteristics of the measured final dried concentrate are summarized below. (i) Final moisture: < 0.2% w / w (ii) Angle of repose: 36° (iii) Flow characteristics: Free flow

[0192] (Talcofite C® Drying and Classification Pilot Test) The test work on the drying and product classification of Talcite C (registered trademark) was completed using a DryTech pneumatic dryer, and it was confirmed that the dried Talcite C (registered trademark) material could be separated into three product streams with different PSD and surface area characteristics. The off-gas from the pneumatic dryer was classified using a two-stage cyclone and a baghouse to capture the fines exiting from the overflow stream of the paired secondary cyclone.

[0193] From the above description, it can be seen that the purification process of the graphite material of the present invention provides an improved purification process of graphite material that reduces carbon loss and / or reduces the dependence on large amounts of highly concentrated acids, at least in certain aspects, compared to the prior art processes.

[0194] Modifications and variations as would be apparent to one of ordinary skill in the art are considered to be within the scope of the present invention.

Claims

1. A process for refining graphite materials, (i) A step of providing pelletized material, and passing a concentrate of the graphite material to be purified to the pelletizing step, (ii) A step of firing the pelletized material from step (i) under caustic conditions to provide a sintered product, thereby making one or more impurity minerals soluble, (iii) The sintered product of step (ii) is passed to a water leaching step, thereby solubilizing at least a portion of the impurity minerals from step (ii), which are sent to wastewater treatment and separated from the leached solids, (iv) The leached solids from step (iii) are passed to the first sulfuric acid leaching step, and the impurity minerals partially leached in step (iii) are solubilized and sent to wastewater treatment to be separated from the leached solids. (v) The leached solids from step (iv) are passed to a hydrofluoric acid leaching step, and the partially leached impurity minerals are solubilized and sent to wastewater treatment to be separated from the leached solids. (vi) The leached solids from step (v) are passed to the second sulfuric acid leaching step, and any impurity minerals or components that precipitated during step (v) and did not leach in the previous step are solubilized and sent to wastewater treatment to be separated from the leached solids. (vii) The leached solids from step (vi) are passed to one or more washing steps, wherein at least a portion of the remaining soluble impurities are separated, thereby producing a purified graphite material. The refining process for graphite materials.

2. The pelletizing step (i) is: (i) The process comprising the stepwise addition of caustic soda and water to the graphite material to be purified, (ii) To produce pellets which are micropellets with a diameter of approximately 2 to 10 mm, and / or (iii) Generates pellets that are micropellets of 5 mm ± 2 mm. The process according to claim 1.

3. (i) The dried fine powder of the purified graphite material is added during the pelletizing step (i), or (ii) A dry fine powder of the purified graphite material in an order of approximately 50 kg / t ± 25 kg / t is added during the pelletizing step (i). The process according to claim 1.

4. The pellets produced in the pelletizing step (i) are (i) Approximately 10-25% w / w, or (ii) Approximately 20% w / w Having a moisture content, The process according to any one of claims 1 to 3.

5. The aforementioned caustic calcination step (ii) is carried out at approximately 150 to 300°C, in which caustic soda and silicate impurity minerals are reacted and solubilized under water and weak acid conditions. The process according to claim 1.

6. The amount of caustic soda added to the graphite material to be purified in the caustic calcination step (ii) is (i) The ratio of at least 1 mol of caustic soda to 1 mol of silicon, (ii) The ratio of 2.5 to 5.5 mol of caustic substance to silicon, or (iii) Ratio of 3.2 mol of caustic substance to 1 mol of silicon Calculated using, The process according to claim 1.

7. The impurities leached in the first sulfuric acid leaching step (iv) include the sodium silicate, sodium alum, iron oxide, and iron hydroxide mineral phases formed during the caustic calcination step (ii), along with residual caustic material. The process according to claim 1.

8. Concentrated sulfuric acid is added in the first sulfuric acid leaching step (iv). The process according to claim 1.

9. The residual free acid at the end of the first sulfuric acid leaching step (iv) is, (i) H in the range of approximately 5 to 75 g / L ２ SO ４ ,or (ii) H of approximately 50 g / L ± 5 g / L ２ SO ４ That is, The process according to claim 1.

10. The impurities leached out in the hydrofluoric acid leaching step (v) include quartz, titanium mineral phase, and residual amounts of albite, biotite, and pyrophyllite. The process according to claim 1.

11. The residual free acid at the end of the hydrofluoric acid leaching step (v) is (i) In the range of approximately 5 to 75 g / L of HF, (ii) The HF is approximately 25 g / L ± 5 g / L. The process according to claim 1.

12. The hydrofluoric acid added in the acid leaching step (v) is at a concentration of approximately 20-70%. The process according to claim 1.

13. The concentration of the hydrofluoric acid in the acid leaching step (v) is in the range of approximately 15 to 50 g / L of HF. The process according to claim 1.

14. The leached solid from the hydrogen fluoride leaching step (v) contains substantially no silicon, or only trace amounts of silicon. The process according to claim 1.

15. The impurities leached out in the second sulfuric acid leaching step (vi) are (i) Precipitated fluoride phase, or (ii) Calcium fluoride and residual base metals including, The process according to claim 1.

16. Concentrated sulfuric acid is added in the second sulfuric acid leaching step (vi). The process according to claim 1.

17. The residual free acid at the end of the second sulfuric acid leaching step (iv) is, (i) H at approximately 5-75 g / L ２ SO ４ ,or (ii) H of approximately 50 g / L ± 5 g / L ２ SO ４ Within the range, The process according to claim 1.

18. The liquid, residual salt, and / or acidic matter from the residual solids in the second sulfuric acid leaching step (vi) is recovered in the washing step of step (vii) and returned to either or both of the sulfuric acid leaching steps (iv) and (vi). The process according to claim 1.

19. The first wastewater treatment plant receives wastewater from the water leaching step (iii) and the two sulfuric acid leaching steps (iv) and (vi). The process according to claim 1.

20. The second wastewater treatment plant receives the wastewater discharged from the hydrogen fluoride leaching step (v). The process according to claim 1.

21. The second wastewater treatment plant receives aluminum hydroxide and thereby produces a second wastewater and an aluminum fluoride product. The process according to claim 20.

22. The formation of silica gel in the leaching steps (iii), (iv), and (vi) is avoided by the discharge of the leachate to the wastewater treatment step. The process according to claim 19.

23. The silicon content in the aforementioned leaching steps (iii), (iv), and (vi) is maintained within a range selected by the discharge of the leachate. The aforementioned range is, (i) Approximately 2.5 to 7.5 g / L, (ii) Approximately 5 g / L or less, The process according to claim 22.

24. The carbon recovery rate in the aforementioned graphite material purification process is (i) greater than approximately 87%, or (ii) Approximately 87.3% to 96.0% The process according to claim 1.

25. The loss on ignition (LOI) of the product of the purified graphite material in the above process is, (i) Approximately 99.90% or more, (ii) Approximately 99.90-99.97%, or (iii) 99.96-99.97% The process according to claim 1.

26. The carbon content of the graphite in the product of the purified graphite material of the process is 99.5% w / w or more. The process according to claim 1.

27. The surface area (BET) of the product of the purified graphite material in the above process is (i) within the range of about 5 to 10 m ２ / g, or (ii) Approximately 7.0m ２ / g ±2.0m ２ / g is The process according to claim 1.

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