Gold-enhanced Raman observation of chalcopyrite leaching

Gold decoration of chalcopyrite surfaces has been shown to stimulate surface enhancement of Raman scattering and this enables oxidation products, undetectable using normal Raman spectroscopy, to be investigated. Electroless deposition, sputtering and evaporative deposition facilitated SERS. In situ potentiodynamic investigations demonstrated similar oxidative product/s on the chalcopyrite surface in sulfate or chloride aqueous acid solutions. The product/s appeared to be amorphous and commenced SS bonding in the transpassive potential region. The νSS bands from the oxidized surface were broad and at a lower Raman shift than elemental sulfur, indicative of an aging metal-deficient remnant sulfide lattice. The oxidation product/s was not consistent with the formation of polysulfides or polythionates.Ex situ investigations of oxidised chalcopyrite surfaces and model systems corroborated in situ data, in that the species detected were oxidation products of the chalcopyrite, rather than artifacts of sample preparation.