Elucidating the mechanism of ball milling on surface reconstruction of arsenopyrite: XPS property and theoretical studies

The surface composition, coordination environment, and chemical state of arsenopyrite dictate the propensity of the mineral to undergo oxidation, leaching, and flotation separation. Because of this, it is of great significance to study the mechanism by which mechanical ball milling affects the composition and coordination of the surface atoms. In this study, the arsenopyrite powder was ground using ball milling under argon. Then, the composition and oxidation state of the Fe, As, and S atoms on the arsenopyrite surface were characterized by XPS after different ball milling durations. A surface reconstruction model was constructed using density functional theory (DFT) calculations by adsorption of single atoms and multiple atoms onto the (001) surface of arsenopyrite, and the atomic configuration, binding energy, and formation energy of the reconstructed surface were calculated. The results showed that the relative content of Fe atoms raised from 30.3 % to 36.3 % as the duration of ball milling increased from 0 to 2 h, while the relative content of S atoms reduced from 33.33 % to 28.47 % under the same conditions. Furthermore, as the duration of ball milling was extended, there was an enhancement in the oxidation state of the atoms on the surface. In particular, S atoms under prolonged ball milling were converted to S⁰ (S monomer polymer). The binding energy between S atoms and the ideal surface was significantly greater than the energies between Fe and As atoms and the surface. Furthermore, the binding energy between the reconstruction layer and the ideal surface was positively correlated with the ratio of Fe atoms, with the 1Fe + 3As + 2S structure having the lowest binding energy and the 3Fe + 1As + 2S and 3Fe + 2As + 1S structures having the highest binding energies. When the surface was rich in S atoms, the formation energy of the reconstructed surface was the most negative, indicating the highest surface stability.