Galvanic interactions during the dissolution of gold in cyanide and thiourea solutions
Galvanic interactions between gold and associated substances are amongst the many factors that could influence the rate of dissolution of gold in a cyanide or an acidic thiourea solution. Some of these galvanic influences were investigated here by short-circuiting two rotating disc electrodes either in the same container or in two separate containers linked by a salt bridge. In a cyanide solution it was established that the largest decrease in the rate of gold dissolution was obtained when gold was in contact with copper, chalcopyrite and pyrite in the same container. On the other hand, in an acidic thiourea solution, chalcopyrite and pyrite increased the rate of dissolution when both electrodes were in the same container. This was ascribed to sulphur species in solution that inhibited the degradation of thiourea to formamidine disulphide, one of the by-products of the dissolution of gold in thiourea. Galena produced a very marked increase in the rate of dissolution of gold in cyanide solutions when both electrodes were in the same container. This could be ascribed to the action of Pb(II) ions on the surface of the gold. However, galena had little or no effect on the rate of dissolution of gold when in the same container in an acidic thiourea medium. © 1990.