The kinetics and mechanism of dissolution of gold in solutions of thiocarbamide with an oxidizer |
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| Authors: | L F Kozin E O Berezhnoi A K Bogdanova |
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| Institution: | (1) Vernadsky Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine, pr. Akademika Palladina 32/34, Kiev, 03680, Ukraine;(2) International Center Institute of Applied Optics, National Academy of Sciences of Ukraine, Kiev, 04053, Ukraine |
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| Abstract: | The kinetics and mechanism of dissolution of gold in solutions of thiocarbamide (T) in the presence of Fe2(SO4)3 as an oxidizer were studied. The dependences of the rate of dissolution of gold on the concentration ratio between iron(III) and T and pH were determined, and optimum solution compositions for the dissolution of gold were found. The compositions of gold(I) complexes formed in the boundary double layer (Au{(NH2)2C=S}2]+) and in the bulk (Au{(NH2)2C=S}3]+) were determined. The diffusion and kinetic components of the overall reaction of gold dissolution in solutions of T in the presence of the oxidizer were obtained by the rotating disc method. The first-order rate constants at 278–333 K, k Au = 3.5 × 10?5?2.73 × 10?4 s?1, and the activation energies at 278–295 K (E a = 13.4 kJ/mol, which is evidence that dissolution value characteristic of kinetically controlled reactions) were determined for the dissolution of gold in solutions of T. The composition of the adsorption sulfide-containing film on the surface of gold was studied by Auger electron spectroscopy. The film, which inhibited gold dissolution, consisted of gold(I) hydrosulfide (AuHS) and sulfide (Au2S). The solubility products of these compounds and their solubilities in aqueous solutions were calculated. |
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