Interactions of xanthates of increasing chain length with pyrite surfaces: A DFT-D and microcalorimetry study

The theoretical technique of computational modelling and the experimental determination of the enthalpy of adsorption of a ligand molecule onto a mineral surface deliver the same output parameters and, therefore, complement each other in investigating the affinity of different ligand types for mineral surfaces. This study ran parallel experimental tests and computational calculations to determine the enthalpy of adsorption of a series of increasing chain length xanthates onto pyrite surfaces. We found that the vertical mode of adsorption was more exothermic than the flat mode adsorption. Most importantly we found that the flat mode adsorption for the 5C xanthate chain demonstrated the effect of van der Waals interaction of the hydrocarbons with the surface. Furthermore, the adsorption of charged xanthate both on hydrated and dry (1 0 0) surface gave inconsistent trends with experiments, except for charged xanthate flat adsorption on (1 1 1) surface. Significantly, the results of the adsorption of neutral xanthate both on dry and hydrated surfaces showed that although the absolute energy values were different; the trends were similar to the experimental approach. In particular the adsorption of neutral xanthate in water on the surface gave R2 = 0.96 and microcalorimetry gave R2 = 0.95, which indicated a linear correlation between the number of carbon atoms in the alkyl chain and the enthalpy of reaction for both computational and experimental data. The experimentally determined exothermic increase in heat of adsorption for the addition of each CH2 group was found to be −8.17 kJ.mol−1, while the contribution of the thiol head group was 34.9 kJ.mol−1. This study provides a rigorous experimental and computational approach which is intended to afford confidence in modelled data for the screening of new ligands for flotation processes. © 2022 Elsevier B.V.