Mechanistic insights into the structure-activity relationship of FeS for arsenic removal in strongly acidic wastewater

Abstract

Sulfide precipitation is an efficient method for separation. However, its application is limited due to the significant H2S pollution caused by conventional reagents. The utilization of amorphous FeS lead to a substantial reduction in H2S escape, while concurrently enhancing the crystallization and settling characteristics of As-precipitates. Under the conditions of an initial arsenic and H2SO4 concentration in the solution of 2 g/L and 50 g/L, respectively, and a FeS dosage of 1.5 times the molar amount of S/As, the arsenic removal exhibited a significant decrease from 89.8 % to 40.8 % over a FeS aging period of 0 to 84 days. Notably, no H2S emissions were detected during the entire reaction process. XRD analysis revealed a transformation of FeS from its amorphous form to a crystalline state as it undergoes aging. This transition is primarily characterized by a reduction in interlayer spacing and FeS bond length within the FeS lattice. The lattice energy experienced a decrease from −3071 to −3688 kJ/mol, indicating the progressive stabilization of the FeS structure. FTIR and TG-DSC analyses have demonstrated the infiltration of water molecules into both the interlamellar spaces and the lattice of FeS during the process of crystallization. Additionally, As3+ ions were observed to initially adsorb onto the surface of aged FeS through the hydroxyl group, followed by their diffusion into the lattice. The products of arsenic removal undergone a transformation from As2S3 to predominantly FeAsS-like complexes, as the mechanism of arsenic removal shifted from precipitate transformation to adsorption and co-precipitation.