Interactions of Acetylene-Derived Thioester Collectors with Gold Surfaces: A First-Principles Study

The high reactivity of acetylene group the formation of strong chemical bonds with active sites on mineral surfaces, thereby improving the flotation performance of gold minerals. This study utilized Density Functional Theory (DFT) to analyse the quantum chemical parameters of structure, Mulliken population, and the frontier orbitals of a thioester collector containing an acetylene group, PDEC (prop-2-yn-1-yl diethylcarbamodithioate). PDEC is compared with analogous thioester collectors Z-200 and Al-DECDT, and the interaction mechanism of PDEC on the Au(1 1 1) surface is simulated, followed by empirical validation through adsorption experiments. The findings indicate that S atom of PDEC in the carbon-sulfur group exhibit shorter covalent bond lengths, and reduced carbon-sulfur double bonds and Mulliken population, resulting in enhanced electron localization. This confers greater selectivity to PDEC during its adsorption on mineral surfaces. Frontier orbital analysis shows that the electrons of acetylene group possess a notable electron-accepting capacity, significantly influencing frontier orbital energy of PDEC and playing a pivotal role in the bonding interaction with mineral surfaces. Both the S atom in carbon-sulfur group and its acetylene group establish stable adsorption structures with the A(111) surface in a single coordination mode. The adsorption energy sequence is PDEC > Al-DECDT > Z-200. Partial density of states demonstrates that S 3p orbit of carbon-sulfur group hybridize with Au 5d orbit, while the C 2p orbit of the acetylene group engage in weaker back-donation bonding with Au 5d orbit. This is corroborated by electron density difference and post-adsorption Mulliken population analyses, revealing that S atom of carbon-sulfur group in PDEC donate electrons to Au atom, forming dominant positive coordination bonds, whereas the acetylene group accepts partial electrons from Au atom, resulting in weaker back-donation bonds. The adsorption experiments align with the DFT adsorption energy results.