THE EFFECT OF THE ELEMENTAL SULFUR REACTION-PRODUCT ON THE LEACHING OF GALENA IN FERRIC-CHLORIDE MEDIA

The dissolution of galena in 0.3 M FeCl3-0.3 M HCl solutions containing 0 to 6 M LiCl was studied at 80-degrees-C, and parabolic kinetics were observed at all LiCl concentrations. The leaching rate increases gradually with increasing LiCl concentrations to almost-equal-to 4 M LiCl; the presence of > 4 M LiCl results in a rapid increase in the leaching rate. The solubility of PbCl2 in 0.3 M FeCl3-0.3 M HCl solutions containing 0 to 6.5 M LiCl was measured over the temperature range of 50-degrees-C to 90-degrees-C. The solubility increases systematically with increasing temperature and LiCl concentration. The parabolic kinetics, coupled with the correlation between the leaching rate and the solubility of PbCl2, suggest that the dissolution of galena is controlled by the outward diffusion of the PbCl2 reaction product through the constantly thickening layer of elemental sulfur formed during leaching. This conclusion is also supported by various morphological studies which consistently indicated a thin layer of PbCl2 between the corroding galena and the porous elemental sulfur reaction product.