Recovery of materials from lithium iron phosphate battery waste

Abstract

Methods are provided for forming iron phosphate. In a first stage, heat treating lithium iron phosphate black mass and selectively leaching lithium from the heat treated lithium iron phosphate black mass with an oxidative leaching solution forms a semi-delithiated iron phosphate black mass. In a second stage, the semi-delithiated iron phosphate black mass and a pre-leaching solution comprising dilute acid and an oxidizing agent are mixed, and in a third stage the remaining iron phosphate in the solid phase and an iron phosphate leaching solution are mixed to form a leachate comprising iron phosphate.

1 . A method for forming iron phosphate, comprising:
 in a first stage, heat treating lithium iron phosphate black mass to form a heat treated lithium iron phosphate black mass and selectively leaching lithium from the heat treated lithium iron phosphate black mass with an oxidative leaching solution to form a semi-delithiated iron phosphate black mass;   in a second stage, mixing the semi-delithiated iron phosphate black mass and a pre-leaching solution comprising an acid and an oxidizing agent to form a slurry, and separating the slurry into a solid phase and a liquid phase, the solid phase comprising iron phosphate and graphite and the liquid phase comprising lithium ions and leachate impurities; and   in a third stage, mixing the solid phase and an iron phosphate leaching solution to form a leachate comprising iron phosphate and a graphite solid phase.   
     
     
         2 . The method of  claim 1 , wherein the oxidative leaching solution includes at least one oxidant and at least one acid. 
     
     
         3 . The method of  claim 1 , wherein mixing to form the slurry in the second stage comprises mixing at a temperature range of from 20° C. to 80° C. 
     
     
         4 . The method of  claim 1 , wherein mixing the solid phase and the iron phosphate leaching solution in the third stage comprises mixing at a temperature range of from 20° C. to 90° C. 
     
     
         5 . The method of  claim 1 , further comprising, after the third stage, mixing the graphite remaining in the solid phase and a dilute acid to remove graphite impurities from the graphite. 
     
     
         6 . The method of  claim 1 , further comprising, after the second stage, separating the lithium ions and the leachate impurities of the liquid phase by one or more of hydrolysis, sodium sulfate precipitation, and ion exchange. 
     
     
         7 . The method of  claim 1 , wherein the leachate impurities comprise one or more of nickel, manganese, cobalt, copper, and aluminum. 
     
     
         8 . The method of  claim 1 , wherein the second stage removes at least 75% of the leachate impurities from the semi-delithiated iron phosphate black mass. 
     
     
         9 . The method of  claim 1 , wherein the acid of the pre-leaching solution is an inorganic acid. 
     
     
         10 . The method of  claim 1 , wherein the oxidizing agent of the pre-leaching solution is one or more of a peroxide, a persulfate, a hypochlorite, a perchlorate, a nitrate, a nitrous oxide, and a nitrogen dioxide. 
     
     
         11 . The method of  claim 1 , wherein a concentration of the acid comprising the pre-leaching solution is in a range of from 0.2 M to 0.6 M. 
     
     
         12 . The method of  claim 1 , wherein a molar ratio of lithium to iron in the heat treated lithium iron phosphate black mass is greater than a molar ratio of lithium to iron in the semi-delithiated iron phosphate black mass. 
     
     
         13 . The method of  claim 1 , wherein the iron phosphate leaching solution comprises a concentrated acid solution comprised of an inorganic acid in a range of from 2 M to 5 M. 
     
     
         14 . A method for forming iron phosphate, comprising:
 heat treating a lithium iron phosphate (LFP) black mass to form a heat treated LFP black mass;   mixing the heat treated LFP black mass and an oxidative leaching solution to form a lithium leachate and a semi-delithiated iron phosphate black mass;   separating the semi-delithiated iron phosphate black mass and the lithium leachate;   mixing the semi-delithiated iron phosphate black mass and a pre-leaching solution to form an impurity leachate and an iron phosphate black mass;   separating the impurity leachate and the iron phosphate black mass;   mixing the iron phosphate black mass and an iron phosphate leaching solution to form an iron phosphate leachate and graphite; and   precipitating iron phosphate from the iron phosphate leachate.   
     
     
         15 . The method of  claim 14 , wherein the impurity leachate comprises lithium ions. 
     
     
         16 . The method of  claim 14 , wherein the method further comprises removing impurities from the impurity leachate by one or more of hydrolysis, ion exchange, and/or sodium sulfate precipitation, and precipitating a lithium salt from the impurity leachate. 
     
     
         17 . A method for forming iron phosphate, comprising:
 selectively leaching a lithium iron phosphate black mass and an oxidative leaching solution to form a semi-delithiated iron phosphate black mass;   mixing the semi-delithiated iron phosphate black mass and a pre-leaching solution to pre-leach impurities from the semi-delithiated iron phosphate black mass and obtain an iron phosphate black mass;   leaching iron phosphate from the iron phosphate black mass to form an iron phosphate leachate; and   precipitating iron phosphate from the iron phosphate leachate to form an iron phosphate precipitate.   
     
     
         18 . The method of  claim 17 , wherein precipitating iron phosphate comprises chemically precipitating by adjusting a pH of the iron phosphate leachate by adding a base and an oxidizing agent. 
     
     
         19 . The method of  claim 17 , further comprising annealing the iron phosphate precipitate to form a crystalline iron phosphate. 
     
     
         20 . The method of  claim 17 , wherein precipitating iron phosphate comprises increasing a pH of the iron phosphate leachate and hydrothermally precipitating the iron phosphate leachate.