Synthesizing sulfidated zero-valent iron for enhanced Cr(VI) removal: Impact of sulfur precursors on physicochemical properties

Abstract

Sulfidated zero-valent iron (SZVI) samples were synthesized using different sulfur precursors, including sodium sulfide, sodium hydrosulfite, and potassium polysulfide. Sulfidation significantly increased the specific surface area and hydrophobicity of all SZVI samples, with SZVI-Na2S showing the highest specific surface area (21.7 m2/g) and optimal hydrophobicity (65.3°). Additionally, the free corrosion potential of SZVI after sulfidation was more negative than ZVI, indicating a stronger electron transfer. Furthermore, among the SZVI samples, SZVI-Na2S exhibited the highest Fe0 content (53.3%). The Cr(VI) removal efficiency was significantly enhanced by SZVI, with SZVI-Na2S, SZVI-K2S6, and SZVI-Na2S2O4 achieving removal efficiencies of 90.4%, 78.5%, and 49.9%, respectively. SZVI-Na2S exhibited the highest removal efficiency among the three SZVI samples, with a removal rate of up to 40.3 × 10−3 min−1. The enhanced removal of Cr(VI) by SZVI-Na2S was achieved through a combination of enhanced adsorption by FeS shell, rapid reduction of Cr(VI) to Cr(III) via electron transport, and precipitation of Cr(III) with S2- and Fe(II)/Fe(III) on the surface of SZVI, leading to its removal from water. These findings clarify the effects of different S precursors on the physicochemical properties of SZVI and provide insights for the rational design of an efficient Cr(VI) reducing agent.