EXTRACTION OF RARE EARTH METALS FROM NdFeB USING SELECTIVE SULFATION ROASTING

Abstract

Sulfuric acid baking allows for the selective extraction of rare earth metals from scrap Nd 2 Fe 14 B magnets. This process has the advantage of making the high-value rare earth metals water soluble while converting the contained iron, around 70% of the magnet's mass, into stable and insoluble iron (III) oxide, eliminating the need for separating and precipitating iron from solution. The process also has the advantage of safely disposing of metalworking fluid contained in rare earth magnet machine waste, a troublesome contaminate from technical and environmental perspective.

What is claimed is: 
     
         1 . A method for extracting rare earth metals from a rare earth containing material, comprising:
 mixing the rare earth containing material with an acid and water to form a slurry, wherein the rare earth containing material comprises at least one rare earth metal and at least one other metal;   roasting the slurry under oxidizing conditions at temperatures between about 200° C. and about 900° C. to form a baked mixture and an off gas;   leaching the baked mixture in an aqueous solution to form a liquid leaching product comprising at least one soluble rare earth ion, and a solid leaching residue comprising at least one other insoluble metal oxide; and   separating the at least one soluble rare earth ion from the liquid leaching product by precipitation.   
     
     
         2 . The method of  claim 1 , wherein said slurry is comprised of at least about 1.5 gram of acid per 1 gram said rare earth bearing material. 
     
     
         3 . The method of  claim 1 , wherein the acid is sulfuric acid. 
     
     
         4 . The method of  claim 1 , wherein said precipitation is performed with oxalic acid as the precipitation agent. 
     
     
         5 . The method of  claim 1 , wherein said precipitation comprises a first a solvent extraction stage which separates individual rare earths into different process streams prior to precipitation 
     
     
         6 . The method of  claim 1 , wherein said baking is performed in a rotary kiln or a multiple hearth furnace. 
     
     
         7 . The method of  claim 1 , wherein the baked mixture comprises at least one rare earth sulfate 
     
     
         8 . The method of  claim 1 , further comprising preprocessing the rare earth containing material. 
     
     
         9 . The method of  claim 8 , wherein the preprocessing comprises removing a coating from the rare earth containing material. 
     
     
         10 . The method of  claim 8 , wherein the preprocessing comprises comminuting the rare earth containing material. 
     
     
         11 . The method of  claim 1 , wherein the rare earth containing material is selected from the group consisting of a rare earth magnet, a rare earth scrap, a rare earth swarf, and combinations thereof. 
     
     
         12 . The method of  claim 1 , wherein the other metal is at least one of iron, neodymium, dysprosium and praseodymium. 
     
     
         13 . The method of  claim 1 , further comprising evaporating excess moisture from the slurry prior to the roasting step. 
     
     
         14 . The method of  claim 1 , further comprising removing at least one volatile material from the off gas. 
     
     
         15 . The method of  claim 1 , further comprising scrubbing the off gas to remove SO 2  and form at least one compound of sodium sulfate and sodium sulfite. 
     
     
         16 . A method for extracting at least one rare earth metal from a rare earth scrap material, comprising:
 removing a coating from the rare earth scrap material to produce a bare rare earth scrap material;   comminuting the bare rare earth scrap material to produce a comminuted material;   mixing the comminuted material with an acid and water to form a slurry, wherein the comminuted material comprises at least one rare earth metal and at least one other metal;   roasting the slurry under oxidizing conditions at temperatures between about 200° C. and about 900° C. to form a baked mixture;   leaching the baked mixture in an aqueous solution to form a liquid leaching product comprising at least one soluble rare earth ion, and a solid leaching residue comprising at least one other insoluble metal oxide; and   separating the at least one soluble rare earth ion from the liquid leaching product by precipitation.   
     
     
         17 . The method of  claim 16 , wherein the coating is an aluminum coating, and wherein the coating is removed by subjecting the rare earth scrap material to a leaching solution comprising sodium hydroxide. 
     
     
         18 . The method of  claim 16 , wherein the coating is a nickel coating, and wherein the coating is removed by subjecting the rare earth scrap material to a nickel striping solution. 
     
     
         19 . The method of  claim 16 , wherein the acid is sulfuric acid. 
     
     
         20 . A method for extracting rare earth metals from a rare earth containing material, comprising:
 removing a coating from the rare earth scrap material to produce a bare rare earth scrap material;   comminuting the bare rare earth scrap material to produce a comminuted material;   mixing the comminuted material with an acid and water to form a slurry, wherein the comminuted material comprises at least one rare earth metal and at least one other metal;   evaporating residual moisture from the slurry to form an evaporated slurry;   roasting the evaporated slurry under oxidizing conditions at temperatures between about 200° C. and about 900° C. to form a baked mixture and an off gas;   scrubbing the off gas to form at least one of sodium sulfate and sodium sulfite;   leaching the baked mixture in water to form a liquid leaching product comprising at least one soluble rare earth ion, and a solid leaching residue comprising at least one other insoluble metal oxide; and   precipitating the at least one soluble rare earth ion from the liquid leaching, wherein the precipitating agent is at least one of sodium sulfate and oxalic acid, wherein at least a portion of the sodium sulfate is formed by scrubbing the off gas.