<Original Papers>A Hydrometallurgical Treatment of Arsenic-Bearing Intermediate Products in Smelters : Recovery of Valuable Metals and Arsenic Trioxide

A hydrometallurgical treatment of speiss and some arsenic-bearing sulphide mixtures was tested. The principal steps of the process examined here are oxidative ammoniacal leaching, separation of arsenic as MgNH_4AsO_4・6H_2O from the leach solution, acid dissolution of the precipitate and the reduction of the arsenic to produce As_2O_3. The thermodynamic consideration and the leaching test with arsenic sulphide showed that oxidative ammoniacal leaching was applicable to arsenic sulphide and speisses of some metals having a tendency to form their own ammine complexes. The formation of MgNH_4AsO_4・6H_2O was proved to be an efficient way to separate arsenic from the ammoniacal solution containing ammine complexes of nickel, cobalt and copper. Finally, the reduction of As(V) in sulphuric acid solution with (NH_4)_2SO_3,Na_2SO_3 and SO_2 gas was determined. The optimum condition for the reduction of As(V) with the sulphites was at pH of about 1.0 and at approximately 40℃. With SO_2 gas, the reaction slowed down when the acid concentration was 1.0 mol/l or more, and the reaction rate was at a constant level up to the initial As(V) concentration of 15 g/l at a given acid concentration. Based on the data obtained in this work, it was concluded that by this method the materials under consideration could be hydrometallurgically treated with the final product of As_2O_3 and ammoniacal solution of the metals originally contained in speisses