Reaction kinetics for gold dissolution in acid thiourea solution using formamidine disulfide as oxidant

Reaction kinetics for gold dissolution in acid thiourea solutions were investigated with the rotating disc technique using formamidine disulfide as an oxidant. For the conditions studied, it appears that a surface reaction limits the rate of gold dissolution. The rate was found to be first order with respect to thiourea concentration and half order with respect to the concentration of formamidine disulfide; the apparent activation energy for the reaction was 10.4 kcal/mol (43.4 kJ/mol); and the reaction rate was independent of pH for the pH range of 1.0–3.0. netics were found to be described by the following rate expression:dCAu(I)dt=k[Tu][FDS]0.5which was substantiated from electrochemical theory using the Butler–Volmer equation.