The formulas for calculating the activity coefficient, ␥ i , in the binary system and the activity coefficient of a solute at infinite dilution, , as well as interaction parameters, and , in a metallichave been proposed on the basis of Miedema et al.'s model for the estimation of the heat of formation of binary alloys. The formulas can be used in both solid and liquid solutions and have been used in the calculation of both binary and ternary alloy systems taken from 75 elements. The results were compared with the experimental values.

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Both the reactivity and the removal capacity of zerovalent iron (ZVI) for the target contaminant are important for applying ZVI in wastewater treatment. In this study, the feasibility of combining sulfidation treatment and Fe2+ dosing (S-ZVI/Fe2+) to enhance the performance of ZVI for Se­(VI) removal was comprehensively investigated under aerobic conditions. Se­(VI) was first adsorbed on the surface of ZVI particles and then reduced to Se­(IV) and Se(0) with Se(0) being the final product in S-ZVI/Fe2+ system. This system bore the advantages of both sulfidation treatment (S-ZVI) and Fe2+ dosing (ZVI/Fe2+) for Se­(VI) removal. The amounts and rate constants of Se­(VI) removal in S-ZVI/Fe2+ system were increased by 1.8–32.8 times and 11.7–194.0 times, respectively, compared to those in pristine ZVI system. Sulfidation significantly accelerated the corrosion of Fe0 thus improved the removal rate of Se­(VI). The promoting effect of Fe2+ on Se­(VI) sequestration by S-ZVI should be mainly associated with the following facts: Fe2+ could maintain a relatively low pH level during Se­(VI) removal by S-ZVI; Compared to S-ZVI alone, the consumption of Fe0 in S-ZVI/Fe2+ by O2/H+ was slower, and thus the electron efficiency of S-ZVI was elevated; Fe2+ dosing facilitated electron transfer by forming semiconductive Fe3O4.