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

**Edmundo Roldán-Contreras 1, Eleazar Salinas-Rodríguez 1,\*, Juan Hernández-Ávila 1, Eduardo Cerecedo-Sáenz 1,\*, Ventura Rodríguez-Lugo 1, Ricardo I. Jeldres <sup>2</sup> and Norman Toro 3,4**


Antofagasta, Antofagasta 1240000, Chile; ricardo.jeldres@uantof.cl


Received: 11 December 2019; Accepted: 15 January 2020; Published: 21 January 2020

**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 <sup>−</sup>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 <sup>=</sup> 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−<sup>1</sup> (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
