Process for liberating metals using direct production of leach grade acid solutions

Abstract

A system which uses available waste acid process streams from hydrometallurgical extraction processes as absorption media for the direct production of leach grade acid solutions for return to the hydrometallurgical processing circuit for use in liberating metals from metal-bearing materials. The produced acid may have a concentration in the range suitable for processing of metal-bearing materials

What is claimed is: 
     
         1 . A process for metal recovery, the process comprising the steps of:
 (a) drawing a first stream of aqueous sulfuric acid solution from a hydrometallurgical extraction circuit, said first stream of aqueous sulfuric acid solution selected from the group consisting of leach solution, solvent extraction raffinate, electrowinning electrolyte and combinations thereof;   (b) providing a gas stream comprising sulfur dioxide;   (c) converting a first portion of said sulfur dioxide to sulfur trioxide in a catalytic converter;   (d) reacting a first portion of said sulfur trioxide with at least a portion of said first stream of aqueous sulfuric acid solution to produce a leach grade acid solution comprising not less than about 5% by weight sulfuric acid;   (e) introducing at least a portion of said leach grade acid solution back to said hydrometallurgical extraction circuit for contact with a metal bearing material to yield a pregnant solution having a metal content; and   (f) extracting at least a portion of said metal content from said pregnant solution.   
     
     
         2 . The process as recited in  claim 1 , wherein during the reacting step an enhanced concentration acid stream is recirculated through a heat exchanger and absorption unit. 
     
     
         3 . The process as recited in  claim 2 , wherein the heat exchanger is cooled by an aqueous solvent extraction raffinate solution to produce a heated aqueous solvent extraction raffinate solution. 
     
     
         4 . The process as recited in  claim 3 , wherein the heated aqueous solvent extraction raffinate solution is delivered to a leaching process. 
     
     
         5 . The process as recited in  claim 1 , wherein said catalytic converter is a multi-pass catalytic converter. 
     
     
         6 . The process as recited in  claim 5 , wherein said multi-pass catalytic converter is a four pass converter. 
     
     
         7 . The process as recited in  claim 1 , wherein said aqueous sulfuric acid solution is characterized by an acid concentration of not greater than about 60 grams per liter. 
     
     
         8 . The process as recited in  claim 1 , wherein said leach grade acid solution comprises about 5% to about 50% by weight sulfuric acid. 
     
     
         9 . The process as recited in  claim 1 , wherein said gas stream comprises not less than about 2% by volume of sulfur dioxide. 
     
     
         10 . The process as recited in  claim 1 , comprising the further steps of absorbing a second portion of said sulfur dioxide into a second stream of aqueous sulfuric acid solution recovered from the hydrometallurgical extraction circuit to produce an SO 2 -bearing acid solution, and delivering said SO 2 -bearing acid solution to an ore leaching process, said second stream of aqueous sulfuric acid solution selected from the group consisting of leach solution, solvent extraction raffinate, electrowinning electrolyte and combinations thereof. 
     
     
         11 . A process for metal recovery, the process comprising the steps of:
 (a) drawing a first stream of aqueous sulfuric acid solution from a hydrometallurgical extraction circuit treating a metal bearing material, the hydrometallurgical extraction circuit including ore leaching, solvent extraction and electrowinning stages, said first stream of aqueous sulfuric acid solution selected from the group consisting of leach solution, solvent extraction raffinate, electrowinning electrolyte and combinations thereof;   (b) providing a gas stream comprising sulfur dioxide;   (c) converting a first portion of said sulfur dioxide to sulfur trioxide in a catalytic converter;   (d) reacting a first portion of said sulfur trioxide with at least a portion of said first stream of aqueous sulfuric acid solution to produce a leach grade acid solution comprising about 5% to about 50% by weight sulfuric acid;   (e) introducing at least a portion of said leach grade acid solution back to said hydrometallurgical extraction circuit within at least one of the ore leaching stage and the solvent extraction stage to yield a pregnant solution having a metal content; and   (f) extracting at least a portion of said metal content from said pregnant solution.   
     
     
         12 . The process as recited in  claim 11 , wherein during the reacting step an enhanced concentration acid stream is recirculated through a heat exchanger and absorption unit. 
     
     
         13 . The process as recited in  claim 12 , wherein the heat exchanger is cooled by an aqueous solvent extraction raffinate solution to produce a heated aqueous solvent extraction raffinate solution. 
     
     
         14 . The process as recited in  claim 13 , wherein the heated aqueous solvent extraction raffinate solution is delivered to a leaching process. 
     
     
         15 . The process as recited in  claim 11 , wherein said catalytic converter is a multi-pass catalytic converter. 
     
     
         16 . The process as recited in  claim 15 , wherein said multi-pass catalytic converter is a four pass converter. 
     
     
         17 . The process as recited in  claim 11 , wherein said aqueous sulfuric acid solution is characterized by an acid concentration of not greater than about 60 grams per liter. 
     
     
         18 . The process as recited in  claim 11 , wherein said gas stream comprises not less than about 2% by volume of sulfur dioxide. 
     
     
         19 . A process for production of leach grade sulfuric acid, the process comprising the steps of:
 (a) drawing a first stream of aqueous sulfuric acid solution from a hydrometallurgical extraction circuit, said first stream of aqueous sulfuric acid solution selected from the group consisting of leach solution, solvent extraction raffinate, electrowinning electrolyte and combinations thereof;   (b) providing a gas stream comprising sulfur dioxide;   (c) converting a first portion of said sulfur dioxide to sulfur trioxide in a catalytic converter; and   (d) reacting a first portion of said sulfur trioxide with at least a portion of said first stream of aqueous sulfuric acid solution to produce a leach grade acid solution comprising not less than about 5% by weight sulfuric acid.   
     
     
         20 . A system for producing leach grade sulfuric acid having about 5% to about 70% by weight sulfuric acid, the system comprising:
 a sulfur furnace adapted to combust a sulfur feed to produce a gaseous sulfur dioxide stream comprising not less than about 5% by volume sulfur dioxide;   a catalytic converter adapted to receive said gaseous sulfur dioxide stream and to convert at least a portion of said sulfur dioxide to sulfur trioxide;   a sulfur trioxide absorber in fluid communication with said multi-pass catalytic converter, said sulfur trioxide absorber being adapted to react said sulfur trioxide with an aqueous absorption media to produce an enhanced concentration acid stream; and   a heat exchanger in circulating fluid communication with said sulfur trioxide absorber to cool and return said enhanced concentration acid stream to said sulfur trioxide absorber.