THE LEACHING OF SILVER SULFIDE IN FERRIC ION MEDIA

The leaching of synthetic Ag2S in FeCl3-HCl and Fe2(SO4)3-H2SO4 media was investigated using the rotating disk technique. The Ag2S dissolved relatively rapidly in FeCl3-HCl media over the temperature range 40-9 5-degrees-C, and with predominantly elemental sulphur formation. The d issolution kinetics consistently obeyed the parabolic rate law. The ra te is independent of the disk rotation speed and of FeCl3 concentratio ns > 0.03 M. The addition of chlorides such as NaCl, HCI or FeCl2, whi ch enhances the solubility of AgCl, also increases the rate of Ag2S di ssolution. The presence of AgCl, however, sharply reduces the leaching rate. Hence, it is concluded that the rate of dissolution of Ag2S is controlled by the outward diffusion of the AgCl reaction product, as v arious Ag-Cl complexes, through the solution trapped in the pores of t he constantly thickening layer of elemental sulphur formed on the surf ace of the sulphide. In contrast to the relatively rapid rates observe d in chloride solutions, leaching in the corresponding Fe2(SO4)3-H2SO4 system results in negligible silver dissolution under comparable cond itions of concentration, Eh and temperature.