Patent ID: 8070850

Claim:
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 including a solvent extraction stage in series with and an electrowinning stage, said first stream of aqueous sulfuric acid solution comprising a process fluid normally used in the hydrometallurgical extraction circuit and 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 by absorptive contact reaction in a sulfur trioxide absorption unit in fluid communication with a heat exchanger to produce a leach grade acid solution wherein during this reacting step an enhanced concentration acid stream is withdrawn from the sulfur trioxide absorption unit and is recirculated through the heat exchanger for cooling and back to the absorption unit in a circulation loop to produce a controlled target acid concentration for said leach grade acid solution of not less than about 5% to 50% 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.