Dissolution of Silver and Gold with Sodium Hypochlorite and Hydrochloric Acid in Refractory Minerals (Mangano-Argentiferous)

The present study examined a process for precious metal recovery (silver and gold) from difficult minerals which exhibit refractory characteristics to cyanidation and ammonium thiosulfate leaching (low extraction and high consumption of leaching agent). It is well known that mangano-argentiferous minerals are mainly composed of manganese, silver, gold, and iron. In this research, a mineral sample from Monte del Favor mine, located in Hostotipaquillo, Jalisco, Mexico, was physically and chemically characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), fire assay, and atomic absorption spectroscopy (AAS). Two-stage leaching was carried out: first to eliminate manganese from the sample using sodium sulfite (Na₂SO₃) as a reductive reagent and sulfuric acid (H₂SO₄) and a second stage to dissolve silver and gold with sodium hypochlorite (NaClO) and hydrochloric acid (HCl); the results show extraction around 96% for Mn and 98.73% and 83% of Ag and Au, respectively. The usefulness of high acidity and Na₂SO₃ to obtain good results in Mn and Ag leaching is discussed along with the roles that HCl and NaClO play in the dissolution of Ag and Au values.