A Density Functional Theory study on gold cyanide interactions: The fundamentals of ore cleaning

We have employed Density Functional Theory calculations to study the adsorption of CN, CN− and KCN on Au(111) and Au(211) surfaces and compare the obtained results to CO. The adsorption of CN, CN−, and KCN are exothermic with respect to the gas-phase moieties, and the adsorption energy increases at steps. Our results show that the binding mechanism of CN− is different from that of CO. The projected LDOS indicates that the bond between the flat surface and CN shows very small overlap between metal and CN states. This overlap increases provided that extra charge is present or low-coordinated Au atoms are available. Charge transfer is analyzed via the Bader method and the Electron Localization Function. Both suggest that Au-CN bonding resembles that in the gas-phase [Au(CN)2]−, which has been identified as covalent. The present study justifies the mechanism described in the literature involving a first CN− adsorption, electron transfer to form AuCN, and second adsorption of a CN− to form the soluble species and dissolve gold atoms from low grade ores.