Method of producing purified graphite

Abstract

A two-stage method of producing purified graphite is described. The first stage of the method comprises the steps of subjecting graphite material to a caustic bake and releasing any remaining caustic using water. The graphite material is then subjected to a first acid wash. Neutralising and washing the acid washed graphite material is then performed to deliver an intermediate purified graphite product. In the second stage the intermediate purified graphite product is subjected to a low temperature caustic leach. Any remaining caustic in the intermediate purified graphite product is released using water, and the intermediate purified graphite product is subjected to a second acid wash. Finally, neutralising and washing the intermediate purified graphite product is performed to deliver a final purified graphite product with a purity of 99.95% C and above.

1 . A method of producing purified graphite, the method comprising the steps of:
 subjecting graphite material to a sodium hydroxide (NaOH) bake;   releasing any remaining NaOH using water;   subjecting the graphite material to a first acid wash;   neutralising and washing the acid washed graphite material to deliver an intermediate purified graphite product;   subjecting the intermediate purified graphite product to a NaOH leach;   releasing any remaining NaOH in the intermediate purified graphite product using water;   subjecting the intermediate purified graphite product to an acid wash; and,   neutralising and washing the intermediate purified graphite product to deliver a final purified graphite product.   
     
     
         2 . A method of producing purified graphite as defined in  claim 1 , wherein the step of subjecting the graphite material to a NaOH bake comprises mixing the graphite material with liquid NaOH (50%) and heating the mixture in a furnace. 
     
     
         3 . A method of producing purified graphite as defined in  claim 2 , wherein the mixture is heated to a temperature of between 450° C. and 550° C. 
     
     
         4 . A method of producing purified graphite as defined in  claim 3 , wherein the mixture is heated for between approximately 25 to 45 minutes. 
     
     
         5 . A method of producing purified graphite as defined in  claim 4 , wherein the mixture is heated to 500° C. for 30 minutes. 
     
     
         6 . A method of producing purified graphite as defined in  claim 1 , wherein the step of releasing any remaining NaOH comprises immersing the material in hot water. 
     
     
         7 . A method of producing purified graphite as defined in  claim 1 , wherein, after the step of releasing any remaining NaOH, the material is washed and filtered. 
     
     
         8 . A method of producing purified graphite as defined in  claim 7 , wherein the material is washed and filtered in a wash neutral step at ambient temperature, for about 5 to 10 minutes, using 2.0 to 7.0 parts H 2 O. 
     
     
         9 . A method of producing purified graphite as defined in  claim 1 , wherein the step of subjecting the material to a first acid wash comprises washing the material with a diluted acid mixture comprising water and H 2 SO 4 . 
     
     
         10 . A method of producing purified graphite as defined in  claim 9 , wherein the diluted acid mixture comprises between 2.0 to 5.0 parts H 2 O and between 0.15 and 0.25 parts H 2 SO 4  96%. 
     
     
         11 . A method of producing purified graphite as defined in  claim 10 , wherein the diluted acid mixture comprises 4.0 parts H 2 O and 0.17 parts H 2 SO 4  96%. 
     
     
         12 . A method of producing purified graphite as defined in  claim 9 , wherein the first acid wash is performed at elevated temperatures in the range of approximately 70° C. to 90° C. to increase reactivity. 
     
     
         13 . A method of producing purified graphite as defined in  claim 12 , wherein the first acid wash is performed at an elevated temperature of 80° C. for between about 25 to 45 minutes. 
     
     
         14 . A method of producing purified graphite as defined in  claim 1 , wherein the step of neutralising and washing the acid washed graphite material comprises filtering the material at ambient temperature and final washing with water at elevated temperatures respectively. 
     
     
         15 . A method of producing purified graphite as defined in  claim 14 , wherein the final washing with water occurs at 85° C. for 30 minutes using 20 parts H 2 O. 
     
     
         16 . A method of producing purified graphite as defined in  claim 1 , wherein the step of neutralising and washing the material comprises washing the acid washed graphite material in 3 to 7 parts H 2 O for 3 to 7 minutes while stirring, at ambient temperature. 
     
     
         17 . A method of producing purified graphite as defined in  claim 1 , wherein the step of subjecting the intermediate purified graphite product to a NaOH leach comprises immersing the intermediate purified graphite product in 0.1 to 0.3 parts NaOH (50%) with 2.0 to 4.0 parts H 2 O at low temperature. 
     
     
         18 . A method of producing purified graphite as defined in  claim 17 , wherein the NaOH leach takes place at temperatures in the range of 72° C. to 88° C. 
     
     
         19 . A method of producing purified graphite as defined in  claim 18 , wherein the residence time for the NaOH leach is about 1.5 to 2.5 hours. 
     
     
         20 . A method of producing purified graphite as defined in  claim 1 , wherein the intermediate purified graphite product is preferably neutralized and washed, before it is subject to the acid wash step. 
     
     
         21 . A method of producing purified graphite as defined in  claim 1 , wherein the only reagents used are NaOH in the NaOH bake and NaOH leach steps, and H 2 SO 4  in the acid wash steps. 
     
     
         22 . A method of producing purified graphite as defined in  claim 21 , wherein, the intermediate purified graphite product is finally washed in a water bath and neutralized with water after the acid wash step. 
     
     
         23 . A method of producing purified graphite as defined in  claim 1 , wherein the acid wash of the intermediate purified graphite product is performed with a diluted acid mixture comprising between 2.0 and 4.0 parts H 2 O and 0.01 to 0.04 parts H 2 SO 4  96%. 
     
     
         24 . A method of producing purified graphite as defined in  claim 23 , wherein the diluted acid mixture comprises 2.5 parts H 2 O and 0.03 parts H 2 SO 4  96%, and the acid wash is performed at elevated temperatures in the range of approximately 77° C. to 93° C. to increase reactivity. 
     
     
         25 . A method of producing purified graphite as defined in  claim 24 , wherein, the acid wash is performed at an elevated temperature of 80° C. for approximately 35 minutes. 
     
     
         26 . A graphite product produced according to the method of  claim 1 . 
     
     
         27 . The graphite product as defined in  claim 26 , wherein the graphite product has a purity of at least 99%. 
     
     
         28 . A battery or battery product including a graphite product, the graphite product produced according to the method of  claim 1 . 
     
     
         29 . The battery or battery product as defined in  claim 28 , wherein the graphite product has a purity of at least 99%.