Abstract

Some sedimentary minerals have attractive contents of gold and silver, like a sedimentary exhalative ore available in the eastern of Hidalgo in Mexico. The gold and silver contained represent an interesting opportunity for processing by non-toxic and aggressive leaching reagents like thiosulfate. The preliminary kinetic study indicated that the leaching process was poorly affected by temperature and thiosulfate concentration. The reaction order was -0.61 for Ag, considering a thiosulfate concentration between 200-500 mol.m(-3), while, for Au, it was -0.09 for a concentration range between 32-320 mol.m(-3). By varying the pH 7-10, it was found that the reaction order was n = 5.03 for Ag, while, for Au, the value was n = 0.94, considering pH 9.5-11. The activation energy obtained during the silver leaching process was 3.15 kJ.mol(-1) (298-328 K), which was indicative of a diffusive control of the process. On the other hand, during gold leaching, the activation energy obtained was of 36.44 kJ.mol(-1), which was indicative that this process was mixed controlled process, first at low temperatures by diffusive control (298-313 K) and then by chemical control (318-323 K).