Thermodynamic and kinetic of iodine–iodide leaching in gold hydrometallurgy

The thermodynamic equilibria and kinetic aspect of gold dissolution in iodine–iodide leaching were studied with emphasis on the effects of pH value and temperature on the system. The results of thermodynamic analysis of iodine in aqueous solution were given and numerous forms of iodine exist mainly in the acid region of pH values. An increase of the potential of the system results in an increase of iodine speciation. The oxidizing potential of the system will increase by the addition of element iodine. The IO3– anions are stable in the potential range from –2.0 to –0.75 V and at pH value greater than 12.1. An increase of the temperature shifts boundaries of existence of various iodine species in the acid region of pH values. Some of them become unstable. The determined values of the diffusion coefficients and the thickness of the diffusion boundary layer, as well as the solvent concentration on the disc surface (14 mg/L) indicate that the process proceeds in the external diffusion region. Thus, while choosing the conditions of leaching from gold-containing materials of different origins of iodide solvents, it is necessary to carry out the process within the acidic region of pH values, where I−, I3− and IO4− ions are capable to form complex compounds with metals.