The leaching of galena in cupric chloride media

The kinetics of dissolution of galena (PbS) in CuCl₂-HCl-NaCl media have been investigated using the rotating disk technique. Rapid nonlinear kinetics are observed over the temperature range 45 °C to 90 °C and for NaCl concentrations from 0 to 4.0 M. The leaching rate is in-dependent of CuCl₂ concentrations >0.1 M but increases with increasing concentrations of either HC1 or NaCl. The leaching rate decreases with the accumulation of either the PbCl₂ or CuCl reaction product in the leaching medium but is insensitive to the disk rotation speed. The apparent activation energy for the rate controlling process is 33 kJ/mol, and this value falls to about 15 kJ/mol when interpreted as a dissolution rate for PbCl₂, whose solubility increases with temperature. The above observations are shown to be consistent with rate control by the outward diffusion of the PbCl₂ and CuCl reaction products through the solution trapped in the pores of the constantly thickening elemental sulfur layer which forms on the surface of the galena. CANMET, Energy, Mines, and Resources Canada, 555 Booth Street, Ottawa, ON, K1A 0G1, Canada.