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 variou s Fe(SO4)(1.5), H2SO4, FeSO4, and MgSO4 concentrations. Relatively slo w kinetics were consistently observed; in most instances, the 1 - 2/3 alpha - (1 - alpha)(2/3) vs time relationship, indicative of a diffusi on-controlled reaction, was closely obeyed. The diffusion-controlled k inetics were attributed to the formation of a tenacious layer of PbSO4 and S-0 on the surface of the galena. The generation and morphology o f the reaction products were systematically determined by scanning ele ctron microscopy, and complex growth mechanisms were illustrated. The leaching rate increased rapidly with increasing temperature, and the a pparent 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 t he concentration of the FeSO4 reaction product. The rate is insensitiv e to H2SO4 concentrations <0.1 M but increases at higher acid levels. The presence of neutral sulfates, such as MgSO4, decreases the leachin g rate to a modest extent.