Lixiviación de plata contenida en un mineral de pirargirita usando un sistema tiourea-FeS2-H2O

Pyrargyrite is a sulfosalt mineral containing Ag, S, and Sb also known as "red silver" that is considered refractory, meaning it is difficult to leach using cyanide. In this study, silver dissolution was investigated using a system consisting of thiourea (TU), pyrite (FeS2), and H2O, with separate tests using cyanide conducted for comparison. The results show poor silver dissolution in the presence of 500 ppm of free cyanide (CN⁻), with only 14.51% leached after 72h a finding that confirms the refractory nature of this mineral. A system containing 0.4 M TU at pH 1.6, with 1.5 g of FeS2, achieved 19% extraction over 24h. Lowering the pH to 1.4 significantly improved silver extraction, reaching 56.9%. Using smaller amounts of pyrite specifically 0.5 g and 1 g over a 24h period resulted in silver extraction rates of 75.7% and 62.4%, respectively. Thiourea is a leaching agent sensitive to redox conditions; an excess of charges generated by the oxidation of pyrite promotes the degradation of the formamidine disulfide (FDS) complex back into thiourea. This disrupts the bond between the silver and the FDS complex, reducing the amount of metal in solution and impairing leaching efficiency. FDS is responsible for the formation of stable, cationic aqueous silver bis(thiourea) complexes.