Interaction of HO with (CuS), (CuS), and (ZnS) small clusters (n = 1-4, 6): relation to the aggregation characteristics of metal sulfides at aqueous solutions.

The interaction of HO onto small CuS, CuS, and ZnS clusters was theoretically studied by Density Functional Theory computations to get insights into the aggregation characteristics of metal sulfides at aqueous solutions. The results show the charge-controlled interactions with polarized solvent molecules are favored on the ZnS clusters compared with CuS and CuS clusters. Moreover, the chemical adsorption of HO molecules is energetically favored onto ZnS clusters with higher interaction energies of up to 35.4 kcal/mol compared with CuS and CuS clusters (up to 31.3 kcal/mol), where the stability of HO adsorption decreases as the size of the clusters increases. However, thermochemical analysis shows that the adsorption of HO on copper sulfides is not a spontaneous process at room temperature. Additionally, the electrostatic energy of HO onto the CuS and CuS clusters is lower than that associated with the HO-HO interactions, suggesting that copper precipitates prefer to bind between them at early stages of the precipitation process due to an unfavorable solvent-solute interaction. Dispersion forces play a relative key role in the interaction of water on copper sulfides, while for zinc sulfide clusters, the adsorption energy is slightly influenced by dispersion contributions. Accordingly, the aggregation of zinc sulfides in a water environment is expected to be lower compared with copper sulfides, and where the aggregation characteristics are not determined by the binding energy of the sulfides, but of the ability to interact with the solvent molecules. These statements were confirmed by experimental optical microscopy analysis and settling tests during precipitation processes in water. Therefore, this work allows proposing a simple strategy to study the aggregation characteristics of metal sulfides, which turns useful for use in hydrometallurgical applications.