Nitric acid leaching of the copper-bearing arsenic sulphide concentrate of Akzhal

Abstract

This paper examines the possibility of using the hydrometallurgical process of nitric acid leaching to process the refractory sulphide concentrate of Akzhal. The study that looked at the structure and composition of this material confirmed that the studied material has a complex mineralogy due to dissemination of gold-bearing sulphides (mainly pyrite and arsenopyrite) in the gangue and their interpenetration, as well as the presence of finely dispersed gold (10 μm) in tight assemblage with the host minerals. A series of laboratory tests, as well as mathematical experimental design techniques, helped identify the most critical parameters governing the leaching efficiency. The following process parameters are recommended: nitric acid concentration — 5 mol/dm3, L/S = 5:1,  = 1 h. A high recovery into solution can be achieved in the above conditions, %: >98 Fe; >96 As; >90 S. The authors propose to use atmospheric deposition of scorodite to dispose of leach liquors. This is achieved by means of staged neutralization until the concentration of arsenic in the liquor reaches 20 mg/dm3. Sorption techniques are applied to recover copper and zinc from leach liquors. Leach cakes are subjected to sorption cyanidation with the total recoveries of gold and silver of >94 and >64%, correspondingly. The nitrous gas recovery stage proved highly efficient — >90%. A series of pilot tests was carried out to verify the findings. Thus, the developed hydrometallurgical process was applied to the copper-bearing arsenic sulphide concentrate of Akzhal at the testing facility of KazGidroMed, a research centre for innovative technology. The tests enabled to conduct a feasibility study, which proved the proposed processing techniques to be efficient and feasible.This research study was funded by the Russian Science Foundation (Project no. 18-19-00186).The study of arsenic precipitation from leach liquor was funded by the Russian Foundation for Basic Research under the Research Project no. 18-38-00914\18.