[Sodium Alginate Loading of Zero-Valent Iron Sulfide for the Reduction of Cr(Ⅵ) in Water]

In this study, the functional material SZVI-SA is successfully prepared to efficiently remove Cr(Ⅵ) from water. This composite, with micron zero-valent iron (ZVI) as its core, is sulfurized and loaded by sodium alginate (SA). Some parameters affecting the Cr(Ⅵ) removal are also tested, including the type and mass fraction of chelating agents as well as S/Fe. SEM-EDS, TEM, XRD, and XPS are used to characterize and analyze the material. The results show that 7% Fe³⁺ is most suitable as the chelating agent for sodium alginate, and a S/Fe ratio of 3.5 and drying temperature of 70℃ are the ideal formation conditions. The effect of SZVI-SA on the removal of Cr(Ⅵ) is in line with the secondary adsorption rate model, mainly affected by the availability of binding sites. The active ingredient was identified as FeS, and the specific surface area can reach 97.83 m²·g^-1. Many pores, especially micropores, are present in this material and in addition to Cr(Ⅵ), SZVI-SA was found to effectively remove Cr(Ⅲ) and Fe(Ⅲ) from the test solution. Overall, the Cr(Ⅵ)-removal efficiency was 92%; the removal mechanism is mainly via redox reactions; and the main reducing active substances are Fe²⁺, S^2-, and S₂^2-. Following the reaction of Fe(Ⅲ) and Cr(Ⅲ), Fe(OH)₃ and Cr(OH)₃ are formed and Cr₂O₃ precipitation separation occurs.