Gold and palladium oxidation/complexation in water by a thioamide-iodine leaching system

This paper concerns the oxidative dissolution ability of a thioamide/iodine leaching system in water towards gold, palladium and silver metals in powder in view of a potential application in the recovery process of these metals from electrical and electronic waste equipment (E-waste). The leaching mixture composed of equimolar amounts of thioamide 3-methyl-benzothiazole-2-thione and I-2 in water can oxidize/complex gold and palladium metals in powder in order to form the complexes [Au-|(mbtt)(2)]I-3 and [Pd-||(mbtt)(3)I]I-3. Considering the mild conditions under which the processes were performed ([I-2] = 1.14 x 10(-3) M, T = 20 degrees C, pH = 5.0, leaching time = 24 h), the obtained oxidation yield of Au-0 and Pd-0 are to be considered satisfactory with values of 65% and 69%, respectively. No oxidation was observed for the silver powder. The oxidising/complexing properties of the leaching mixture mbtt + I-2 were interpreted considering the formation of the mbtt-I-2 adduct that features, as a consequence of the S-donor to I-2 interaction, a charge separation between the bridging and terminal iodine atoms in the fragment S-I-b-I-t. The feasibility of recovering gold from the complex [Au-|(mbtt)(2)]I-3 was verified by performing a cementation with magnesium powder.