Integration of Biosorption in Gold Cyanidation: A Study Using Density Functional Theory

Abstract

This research investigates the feasibility of integrating bio-adsorbents into the gold cyanidation process. Since bio-adsorbents favor gold(III) chloride relative to gold(I) cyanide, this research will study the possibility of substituting cyanide ligands in gold(I) cyanide complex with chloride. For the purpose of this study, several quantum mechanical calculations on AuCl2-, AuCN2-, AuCN2Cl2-, AuCl4- and AuCN4- complexes are performed to investigate their stabilities and bonding nature.

The study shows that Au-C bond in gold(I) and gold(III) complexes are stronger than Au-Cl bonds. Geometry optimization, frequency and thermodynamic calculations as well as natural bonding orbital (NBO) and local energy decomposition (LED) analyses have all reached a similar conclusion. It is shown that the stability of Au-C bond is attributed to better orbital overlap between gold and carbon orbitals. Moreover, the occurrence of pi back-bonding in Au-C bond also contributes to its strength.