Silver Production
Silver Production
First stage of the silver production is ore enrichment: flotation and gravitational separation. Further extraction methods depend on the ore type and pyrometallurgical or hydrometallurgical. Polymetallic sulphide ores are not convertible by hydrometallurgical methods. For this reason they are first submitted to oxidizing and reducing or chlorinating roasting. During the lead ores roasting Ag2S is concentrated in Pb oxide and, then, in Pb metal. Two methods may be applied for lead ores processing. To recover silver from ores, the Parkes and Pattison method is used. In this method, the lead ore is heated with Zinc until it becomes molten. A method of separating lead from silver and to concentrate silver from a lead melt by the Pattison method, in which method a lead bath which contains silver is allowed to solidify partially, therewith to separate out the lead in a purer form, while the silver is concentrated in the molten residue. Subsequent to tapping of this residue, the residue is repeatedly subjected to the same process until a eutectic lead-silver alloy containing about 2.5% of silver is obtained, from which pure silver can be produced after expelling the lead. The purer lead crystals are melted and treated in a similar manner, so that after repeating the process a number of times, a lead free from silver is obtained.
Most of the silver produced worldwide from silver ores is extracted by the cyanidation process. The recovery of the precious metals involves two distinct operations: the oxidative dissolution of silver by an alkaline cyanide solution NaCN or KCN in Oxygen, and the reductive precipitation of metals from the solution by reducing or using anionites. Another method is amalgamation process of silver recovery in which the ore is passed over a surface of liquid Mercury and chlorides to form an amalgam that is subjected to fire-refining processes for the recovery of the silver.
Silver is also recovered during electrolytic refining in AgNO3 solution with silver precipitation on cathode is commercially applied. Fine silver contains at least 99.9% silver. Purities of 99.999 are available.