Process for gold and silver leaching with thiourea solutions

Abstract

A solution composition that permits the use of thiourea is provided. The process is to form a solution that improves, on one hand, the velocity of gold and silver extraction, from minerals and other materials that contain them, improving the stability of the thiourea in the leaching solution and, on the other, the direct electrorecovery of the metals from the solution. The leaching solution, beforehand or simultaneously, has been subjected to a controlled electro-oxidation to produce formamidine disulfide (FADS) which acts as an oxidizing agent for the mineral phases that contain the gold and silver. In a preferred mode, the FADS is present as 10 to 30% of the total thiourea contained in the solution and the electrodeposition of the metals is performed in the same cell (cathodic compartment) in which the FADS is formed (anodic compartment).

1 . Improvement of the thiourea solutions to leach silver and gold characterized by containing a quantity of partially electro-oxidized thiourea. 
     
     
         2 . Improvement of the thiourea solutions to leach silver and gold according to  claim 1 , characterized additionally by a solution which contains formamidine disulfide (FADS) produced in-situ by a controlled electro-oxidation in a proportion of 10 to 30% of the total amount of thiourea contained in the solution. 
     
     
         3 . Improvement of the thiourea solutions to leach silver and gold, according to  claim 1  wherein the composition of the thiourea leaching solution is formulated in the same process in which the leaching solution is placed in contact with the mineral from which silver and gold values are to be leached. 
     
     
         4 . Improvement of the thiourea solutions to leach silver and gold, according to  claim 2  wherein the composition of the thiourea leaching solution is formulated in the same process in which the leaching solution is placed in contact with the mineral from which silver and gold values are to be leached. 
     
     
         5 . Gold and silver leaching and recovery process with partially oxidized thiourea characterized as consisting of the thiourea oxidation by the application of an electrical current in a membrane cell, where the anodic and cathodic compartments are separated, before sending the product to the leaching stage and that after leaching is concluded, the pregnant solution, separated from the mineral residue (gangue), enters the cathodic compartment of the same electrolytic cell in which the thiourea was partially oxidized in the anodic part, where the metals are reduced and electrodeposited.