Selective sulfation roasting of rare earth magnet waste

Abstract

The present invention relates to a sulfation method which processes a rare earth containing material. The material is roasted and exposed to a sulfur gas, then an aqueous leach to produce an insoluble metal oxide and a soluble rare earth sulfide. The insoluble and soluble material are separated utilizing a solid/liquid separator. Advantageously, the process eliminates the need for additional steps to precipitate the metal oxide in order to separate the metal from the rare earth. A system is also disclosed.

1 . A method to selectively separate at least one rare earth metal from magnetic waste, comprising:
 roasting the magnetic waste in a sulfur gas environment at a temperature between about 300° C. and about 1000° C. to produce a roasted magnetic waste;   leaching the roasted magnetic waste with an aqueous fluid to produce a rare earth liquid containing stream and an insoluble material, wherein the rare earth liquid containing stream comprises less than about 1 wt. % of a total weight of at least one metal, and wherein the insoluble material comprises the at least one metal of iron, cobalt, aluminum; and   separating the rare earth liquid containing stream and the insoluble material.   
     
     
         2 . The method of  claim 1 , wherein the sulfur gas environment comprises air and sulfur dioxide. 
     
     
         3 . The method of  claim 1 , wherein a ratio of the aqueous fluid to the roasted magnetic waste is between about 1:50 and about 1:10. 
     
     
         4 . The method of  claim 1 , wherein the roasted magnetic waste comprises a metal oxide and an at least one stable rare earth sulfate. 
     
     
         5 . The method of  claim 1 , wherein temperature is between about 600° C. and about 800° C. 
     
     
         6 . The method of  claim 1 , wherein the at least one metal is an iron, a cobalt, aluminum and combinations thereof. 
     
     
         7 . The method of  claim 2 , wherein the sulfur dioxide is recycled. 
     
     
         8 . The method of  claim 1 , wherein a metal sulfide is not formed following the roasting of the magnetic waste. 
     
     
         9 . The method of  claim 1 , further comprising comminuting the magnetic waste prior to the roasting step. 
     
     
         10 . The method of  claim 1 , further comprising removing a coating from the magnetic waste prior to the roasting step. 
     
     
         11 . The method of  claim 9 , further comprising processing the comminuted magnetic waste to form a pellet or a briquette. 
     
     
         12 . The method of  claim 1 , further comprising combining the magnetic waste and an additive prior to the roasting step. 
     
     
         13 . The method of  claim 12 , wherein the magnetic waste further comprises between about 10 wt. % and about 50 wt. % of the additive. 
     
     
         14 . The method of  claim 12 , wherein the additive is an alkali metal sulfate, an ammonium carbonate, an ammonium bicarbonate, a cellulose, and combinations thereof. 
     
     
         15 . The method of  claim 14 , wherein the additive is the alkali metal sulfate comprising potassium sulfate. 
     
     
         16 . The method of  claim 1 , further comprising substantially purifying the at least one rare earth containing stream by oxalic acid precipitation to form a purified rare earth metal, wherein the purified rare earth metal comprises at least 90% of the at least one rare earth. 
     
     
         17 . A method to recover at least one rare earth metal, comprising:
 roasting a metal material with a sulfur gas to produce a roasted metal, wherein the metal material comprises at least one rare earth metal, and at least one metal comprising iron;   leaching the roasted metal to produce a rare earth containing stream and an insoluble metal, wherein the rare earth containing stream does not comprise the insoluble metal; and   separating the rare earth containing stream and the insoluble metal.   
     
     
         18 . A system to recover at least one rare earth metal, comprising:
 a furnace for receiving material containing the at least one rare earth metal, wherein the furnace is capable of operating at a temperature between about 300° C. and about 1000° C.;   a sulfur gas inlet, wherein the sulfur gas inlet provides a sulfur gas to the furnace;   a leaching tank, wherein the leaching tank receives a roasted material from the furnace, and wherein the leaching tank combines water and the roasted material to produce an insoluble material and a liquid, wherein the liquid comprises the at least one rare earth metal; and   a separator, wherein the separator separates the liquid from the insoluble material.   
     
     
         19 . The system of  claim 18 , wherein the furnace is selected from the group comprises at least one of a rotary kiln, a rotary hearth, and a fluidized bed. 
     
     
         20 . The system of  claim 18 , wherein the leaching tank is a stirred tank reactor.