Dissolution kinetics of gold in iodide solutions

Of the halogens, the gold iodide complexes are the most stable in aqueous solutions. A series of experiments were performed to investigate the kinetics and mechanism of the leaching reaction between gold and iodide. Using a rotating disk technique, the effects of rotation speed, iodide and iodine concentration, temperature, pH and the presence of different electrolytes were measured. Oxygen and hydrogen peroxide were also examined as oxidants in the iodide system. A first order reaction rate was found with respect to I3− and half order reaction rate with respect to I−. A comparison of gold leaching between iodide and cyanide is also presented, in which a rate of about 2.6 × 10−9 mol/cm2 sec for 10−2M Nal and 5 × 10−3M I2 was obtained. This value is close to that for typical cyanidation.