Preparation of Dispersed Iron-Sulfur-Based Nanoparticle Slurry and Its Application in Remediating Cr(VI) Contamination
Hexavalent chromium (Cr(VI)) contamination in chromite ore processing residue (COPR) and associated soils poses a persistent environmental challenge. This study developed a dispersedly stabilized iron-sulfur-based slurry (DSS-ISB) modified with an inorganic dispersant to enhance nanoparticle suspension stability and interfacial reactivity. The slurry, with a particle size of approximately 200 nm, efficiently reduced and immobilized Cr(VI) without pH adjustment. Under optimal conditions (liquid-to-solid ratio of 5 mL:10 g, DSS-ISB dosage of 1.8 mg/g, reaction time of 20 h), the removal efficiency exceeded 97%, reducing the leaching concentration from 15.03 mg/L to 0.03 mg/L, well below the GB 5085.3—2007 limit of 5 mg/L. X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) analyses revealed a synergistic mechanism of chemical reduction (Fe2+/S2- as dual electron donors) and surface adsorption, converting toxic Cr(VI) to stable Cr(III). Compared with traditional reductants ferrous sulfate (FeSO4) and sodium sulfide (Na2S), DSS-ISB increased removal efficiency by 28.24% and 6.23%, respectively, and unit mass removal capacity by 92.43% and 77.08%. The reagent cost per ton of COPR was reduced to RMB 36.40, achieving savings of 33.82% and 26.02% versus FeSO4 (RMB 55.00) and Na2S (RMB 49.20). The process eliminates pH adjustment and subsequent passivation, simplifying remediation. DSS-ISB offers an economical and green solution for Cr(VI) remediation in both industrial residues and contaminated soils.