Dissolution Behavior of Gold in Alkaline Media Using Thiourea

Abstract

In this work the dissolutive behavior of gold in alkaline medium using thiourea (TU), under different variables, was studied in a theoretical and experimental way, in order to determine the conditions under which it is feasible to dissolve gold in thiourea-alkaline medium. A thermodynamic study was conducted by chemical speciation using the method of Ro-jas-Hernandez, together with an electrochemical study where the electric potential was swept in the anodic direction. The main results of the thermodynamic study were that formamidine disulfide (FDS) and sulfinic compounds (S.C.) prevail at alkaline pH; by increasing the initial concen-tration of thiourea at alkaline pH, the presence of the gold complex is al-most zero for any initial concentration of thiourea. By including sodium sulfite in the gold-thiourea system, it was possible to obtain the Au(I)-TU complex at alkaline pH, with a presence of 95.13%. Electrochemical tests allowed verifying that in the absence of sodium sulfite the dissolution of gold in an alkaline medium is very slow but adding sodium sulfite im-provements become evident in the dissolution of the metal. Therefore, sodium sulfite catalyzes the gold dissolution process and stabilizes the thiourea. With this study it was possible to establish the feasibility of using thiourea in an alkaline medium for the dissolution of gold, and the conditions under which it is possible to dissolve the gold in that medium. With these fundamentals and conditions, it is now possible to move forward to test this system for minerals and/or concentrates containing gold.