Abstract

In the last years, diverse studies about the cementation of gold with powder of zinc from thiosulphate and ammonia solutions have been carried out. The kinetic studies have concluded that during the process, the passivation of zinc particles takes place, causing the decrease of the gold cementation rate. For this reason, the anodic behavior of zinc in thiosulphate media was studied, using electrochemical techniques of linear potential sweep and potentiometry. The work was developed to different values of pH and thiosulphate concentrations, and the results were analyzed with scanning electronic microscopy. The polarization curves present 3 areas, an active dissolution area, a pseudo-passivation area and finally a reactivation area. The pseudo-passivation is caused by the formation of ZnS, which is dissolved for the action of OH-ions, originating the reactivation area.