Patent ID: 7559973

Claim:
A method for processing precious metal-containing mineral material to recover precious metal from the mineral material using a circulating thiocyanate leach solution, the method comprising: thiocyanate leaching the mineral material with the thiocyanate leach solution, the thiocyanate leach solution comprising dissolved thiocyanate and dissolved ferric iron and during the thiocyanate leaching at least a portion of the precious metal from the mineral material is dissolved into the thiocyanate leach solution in the form of precious metal-thiocyanate complex; supplying feed of the thiocyanate leach solution to the thiocyanate leaching, the feed of the thiocyanate leach solution comprising a pH in a range of from pH 1 to pH 3 and comprising a molar ratio of the dissolved ferric iron to the dissolved thiocyanate of at least 2, wherein the molar ratio of the dissolved ferric iron to the dissolved thiocyanate is determined by dividing molar concentration of the dissolved ferric iron by molar concentration of the dissolved thiocyanate, and wherein during the thiocyanate leaching at least a portion of the dissolved ferric iron in the feed of the thiocyanate leach solution is reduced to dissolved ferrous iron; recovering at least a portion of the precious metal from the thiocyanate leach solution, to produce a barren effluent of the thiocyanate leach solution comprising concentration of the dissolved ferric iron that is smaller than a concentration of the dissolved ferric iron in the feed of the thiocyanate leach solution; conditioning the thiocyanate leach solution to prepare the feed of the thiocyanate leach solution, at least a portion of the barren effluent of the thiocyanate leach solution being supplied to the conditioning for use to prepare the feed of the thiocyanate leach solution, and the conditioning comprising increasing a concentration of the dissolved ferric iron in the thiocyanate leach solution relative to the concentration of the dissolved ferric iron in the barren effluent of the thiocyanate leach solution supplied to the conditioning; wherein the recovering comprises introducing dissolved cyanide into the thiocyanate leach solution and transferring at least a portion of the precious metal in the thiocyanate leach solution from the precious metal-thiocyanate complex to precious metal-cyanide complex.