The leaching of galena in ferric sulfate media

The leaching of galena (PbS) in ferric sulfate media was investigated over the temperature range 55 degrees C to 95 degrees C and for various Fe(SO4)(1.5), H2SO4, FeSO4, and MgSO4 concentrations. Relatively slow kinetics were consistently observed; in most instances, the 1 - 2/3 alpha - (1 - alpha)(2/3) vs time relationship, indicative of a diffusion-controlled reaction, was closely obeyed. The diffusion-controlled kinetics were attributed to the formation of a tenacious layer of PbSO4 and S-0 on the surface of the galena. The generation and morphology of the reaction products were systematically determined by scanning electron microscopy, and complex growth mechanisms were illustrated. The leaching rate increased rapidly with increasing temperature, and the apparent activation energy is 61.2 kJ/mol. The rate increases as the 0.5 power of the ferric ion concentration but is nearly independent of the concentration of the FeSO4 reaction product. The rate is insensitive to H2SO4 concentrations <0.1 M but increases at higher acid levels. The presence of neutral sulfates, such as MgSO4, decreases the leaching rate to a modest extent.