Investigation on Gold–Ligand Interaction for Complexes from Gold Leaching: A DFT Study

Abstract

Gold leaching is an important process to extract gold from ore. Conventional alkaline cyanide process and alternative nontoxic lixiviants including thiosulfate, thiourea, thiocyanate, and halogen have been widely investigated. However, density functional theory (DFT) study on the gold complexes Au(CN)2−, Au(S2O3)23−, Au[SC(NH2)2]2+, Au(SCN)2−, and AuCl2− required for discovering and designing new highly efficient and environmentally friendly gold leaching reagents is lacking, which is expected to support constructive information for the discovery and designation of new high-efficiency and environmentally friendly gold leaching reagents. In this study, the structure information, electron-transferring properties, orbital interaction, and chemical bond composition for complexes Au(CN)2−, Au(S2O3)23−, Au[SC(NH2)2]2+, Au(SCN)2−, and AuCl2− depending on charge decomposition analysis (CDA), natural bond orbital (NBO), natural resonance theory (NRT), electron localization function (ELF), and energy decomposition analysis (EDA) were performed based on DFT calculation. The results indicate that there is not only σ-donation from ligand to Au+, but also electron backdonation from Au+ to ligands, which strengthens the coordinate bond between them. Compared with Cl−, ligands CN−, S2O32−, SC(NH2)2, and SCN− have very large covalent contribution to the coordinate bond with Au+, which explains the special stability of Au-CN and Au-S bonds. The degree of covalency and bond energy in Au–ligand bonding decreases from Au(CN)2−, Au(S2O3)23−, Au[SC(NH2)2]2+, Au(SCN)2−, to AuCl2−, which interprets the stability of the five complexes: Au(CN)2− > Au(S2O3)23− > Au[SC(NH2)2]2+ > Au(SCN)2− > AuCl2−.

Morphostructural, Chemical and Genetic Features of Native Gold in Brown Coals from the Yerkovetsky Deposit, Far East Russia

“…The deposition of submicron particles of gold associated with silver halides is based on the It is worth noting that part of the gold in brown coals can be found in a dissolved state in pore water in the form of sulfur-bearing complexes of the following types, AuSO 3 − , Au(SO 3 ) 2 3− , Au(S 2 O 3 ) 2 3− , Au(SO 3 )(S 2 O 3 ) 3− , Au(SO 3 )Cl 2− , AuHS, Au(HS) 2 − , AuS − , Au(SO 4 ) 2 − etc. [21][22][23][24][25], which could have been formed as a result of the dissolution of ultradisperse forms of gold in the acidic sulfur-saturated medium of coals. The confirmation of this form of gold in brown coals is the appearance of gold nanoparticles along the boundaries of cracks formed on the surface of the coal-polished section during this study.…”

Investigation on Gold Dissolution Performance and Mechanism in Imidazolium Cyanate Ionic Liquids

“…However, cyanide is highly toxic, and it not only threatens the user’s safety but also entails a high transportation risk [ 3 , 4 ]. The other leaching reagents such as thiourea, thiosulfate and chlorine all have their own advantages and disadvantages [ 5 ]. Up to now, there has been no reagent that can completely substitute cyanide to leach gold.…”