Recovery of precious metals

Abstract

A process for leaching precious metals from material containing precious metals, such as oxidic and sulfidic gold-bearing ores, is disclosed. The process includes the steps of: (i) leaching the precious metal with a leach solution containing a thiosulfate-based lixiviant; (ii) treating the material by oxidising precious metal in the material into a form that is leachable in a subsequent leaching step; and thereafter as a separate step.

1 . A process for leaching precious metals from material containing precious metals, which process includes the steps of: 
 (i) treating the material by oxidising precious metal in the material into a form that is leachable in a subsequent leaching step; and thereafter as a separate step    (ii) leaching the precious metal with a leach solution containing a thiosulfate-based lixiviant.    
     
     
         2 . The process defined in  claim 1  wherein the material is in the form of ores and concentrates of the ores.  
     
     
         3 . The process defined in  claim 2  wherein the ores and concentrates are gold-bearing ores and concentrates.  
     
     
         4 . The process defined in any one of the preceding claims wherein treatment step (i) includes forming agglomerates of the precious metal-bearing material and an oxidant.  
     
     
         5 . The process defined in  claim 4  wherein the agglomerates are formed by contacting the material and a solution containing the oxidant.  
     
     
         6 . The process defined in  claim 5  includes forming agglomerates of the material, a binder, and the oxidant.  
     
     
         7 . The process defined in  claim 6  includes forming agglomerates by mixing the material (such as an ore or concentrate of the ore) and the binder and thereafter contacting the mixture with a solution containing the oxidant.  
     
     
         8 . The process defined in any one of  claims 4  to  7  includes curing the agglomerates.  
     
     
         9 . The process defined in  claim 8  includes curing the agglomerates in air for a period of at least 24 hours.  
     
     
         10 . The process defined in any one of  claims 4  to  9  wherein the treatment step (i) includes forming agglomerates of the precious metal-bearing material and an oxidant and a thiosulfate-based lixiviant.  
     
     
         11 . The process defined in any one of  claims 1  to  3  wherein treatment step (i) includes forming agglomerates of the precious metal-bearing material (with or without a binder) and thereafter contacting the agglomerates with a solution containing the oxidant.  
     
     
         12 . The process defined in  claim 11  wherein treatment step (i) includes contacting the agglomerates with a solution containing a thiosulfate-based lixiviant.  
     
     
         13 . The process defined in any one of  claims 1  to  3  wherein treatment step (i) includes contacting the material (without agglomerating the material first) with a solution containing the oxidant.  
     
     
         14 . The process defined in  claim 13  wherein treatment step (i) includes contacting the material with a solution containing a thiosulfate-based lixiviant.  
     
     
         15 . The process defined in any one of  claims 5  to  14  wherein the amount of the solution of the oxidant is between 10 and 20% by weight of the weight of the precious metal-bearing material.  
     
     
         16 . The process defined in  claim 15  wherein the amount of the solution of the oxidant is between 12 and 15% by weight of the weight of the precious-metal bearing material.  
     
     
         17 . The process defined in any one of the preceding claims includes treating the material with ammonia or an ammonium salt, such as ammonium carbonate, to stabilise the oxidant.  
     
     
         18 . The process defined in any one of the preceding claims wherein the oxidant is a soluble source of copper ions.  
     
     
         19 . The process defined in  claim 18  wherein the oxidant is selected from the group consisting of copper sulfate, copper salt, and ammonium complex of divalent copper.  
     
     
         20 . The process defined in any one of the preceding claims wherein the thiosulfate lixiviant is selected from the group consisting of sodium thiosulfate and ammonium thiosulfate.