Method for thiosulfate leaching of precious metal-containing materials

Abstract

Processes are provided for recovering precious metals from refractory materials using thiosulfate lixiviants. The processes can employ lixiviants that include at most only small amounts of copper and/or ammonia and operate at a relatively low pH, reduction of polythionates, inert atmospheres to control polythionate production, and electrolytic solutions which provide relatively high rates of precious metal recovery.

1 - 106 . (canceled) 
     
     
         107 . A method, comprising:
 (a) contacting a precious metal-containing material with a thiosulfate lixiviant to dissolve the precious metal and form a pregnant thiosulfate leach solution containing the dissolved precious metal and a polythionate;   (b) contacting the pregnant thiosulfate leach solution with at least one of a sulfite-containing reagent and a sulfide-containing reagent to convert at least most of the polythionates into thiosulfate;   (c) thereafter contacting the pregnant leach solution with an extraction agent to collect at least most of the dissolved precious metal on the extraction agent and form a barren thiosulfate leach solution for recycle to step (a); and   (d) recovering the collected precious metal from the precious metal loaded extraction agent.   
     
     
         108 . The method of  claim 107 , further comprising, after step (b) and before step (c):
 conditioning the pregnant leach solution in an oxidizing atmosphere to redissolve any precipitated precious metal sulfides.   
     
     
         109 . The method of  claim 107 , wherein polythionates compete with dissolved precious metal complexes for loading on the extraction agent. 
     
     
         110 . The method of  claim 108 , wherein the at least one of a sulfite-containing reductant and sulfide-containing reductant is the sulfite-containing reductant and wherein the sulfite-containing reductant is at least one of a metabisulfite and sulfur dioxide. 
     
     
         111 . The method of  claim 108 , wherein the at least one of a sulfite-containing reductant and sulfide-containing reductant is the sulfide-containing reductant and wherein the sulfide-containing reductant is at least one of a bisulfide, sulfide, hydrogen sulfide gas, and a polysulfide. 
     
     
         112 . A method, comprising:
 (a) contacting a precious metal-containing material with a thiosulfate lixiviant to dissolve the precious metal and form a pregnant thiosulfate leach solution containing the dissolved precious metal;   (b) recovering the dissolved precious metal from the pregnant thiosulfate leach solution to form a barren leach solution; and   (c) sparging an at least substantially non-oxidizing gas through at least one of the pregnant thiosulfate leach solution and barren leach solution to inhibit the formation of polythionates.   
     
     
         113 . The method of  claim 112 , wherein the substantially non-oxidizing gas is substantially free of oxidants. 
     
     
         114 . The method of  claim 112 , wherein the substantially non-oxidizing gas comprises at least about 85 vol. % of an inert gas and no more than about 5 vol. % oxidants. 
     
     
         115 - 134 . (canceled) 
     
     
         135 . The method of  claim 114 , wherein the inert gas in the substantially non-oxidizing gas is nitrogen gas. 
     
     
         136 . The method of  claim 112 , wherein the substantially non-oxidizing gas comprises a reducing gas. 
     
     
         137 . The method of  claim 113 , wherein the substantially non-oxidizing gas comprises no more than about 5 vol. % oxidants.