Leaching of Silver and Gold Contained in a Sedimentary Ore, Using Sodium Thiosulfate; A Preliminary Kinetic Study

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).

Keywords

• thiosulfate
• gold leaching
• silver leaching
• kinetic analysis
• sedimentary ore
• diffusion control
• mixed control