Key Takeaways & Executive Findings
- •• • DSS-ISB achieved >97% Cr(VI) removal efficiency at a dosage of 1.8 mg/g and liquid-to-solid ratio of 5 mL:10 g, reducing leachate concentration from 15.03 mg/L to 0.03 mg/L, far below the 5 mg/L regulatory limit (GB 5085.3—2007). • • The slurry's particle size of ~200 nm and inorganic dispersant modification ensure stable suspension and high reactivity, overcoming aggregation and passivation issues common in nano iron-sulfur materials. • • Compared with FeSO4 and Na2S, DSS-ISB increased unit mass removal capacity by 92.43% and 77.08%, respectively, while reducing reagent cost per ton of COPR to RMB 36.40—a 33.82% and 26.02% cost saving. • • The remediation mechanism combines chemical reduction (Fe2+/S2- dual electron donors) and surface adsorption, converting Cr(VI) to stable Cr(III) precipitates, as confirmed by XPS and BET analyses.
Abstract
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.
1. Introduction
Chromium chemical industries generate vast quantities of chromite ore processing residue (COPR) laden with hexavalent chromium (Cr(VI)), a known carcinogen and mobile groundwater contaminant. Traditional remediation approaches, such as using ferrous sulfate (FeSO4) or sodium sulfide (Na2S), often require pH adjustment, produce secondary wastes, and suffer from incomplete reduction due to particle aggregation and surface passivation. These limitations escalate operational costs and complicate in-situ soil treatment, leaving a critical gap for efficient, cost-effective, and environmentally benign remediation technologies.
This study introduces a dispersedly stabilized iron-sulfur-based slurry (DSS-ISB) engineered with an inorganic dispersant to maintain nanoparticle suspension stability and enhance interfacial reactivity. The slurry's dual electron donor system (Fe2+/S2-) enables rapid Cr(VI) reduction under ambient pH conditions, while its mesoporous structure, confirmed by BET analysis, augments adsorption capacity. By achieving >97% removal efficiency and reducing reagent costs by up to 33.82% compared to FeSO4, DSS-ISB directly addresses the bottlenecks of legacy reductants, offering a scalable and simplified remediation pathway for both COPR and contaminated soils.
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XING Ningning, ZHANG Hongling, JIANG Hui, XU Hongbin (2026). Preparation of Dispersed Iron-Sulfur-Based Nanoparticle Slurry and Its Application in Remediating Cr(VI) Contamination. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202606011
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Frequently Asked Questions
What is the long-term stability of DSS-ISB under field conditions, particularly regarding re-oxidation of Cr(III) back to Cr(VI)?
The study indicates that DSS-ISB converts Cr(VI) to stable Cr(III) precipitates (e.g., FexCr(1-x)(OH)3), which are resistant to re-oxidation under typical environmental conditions. However, long-term field data are not provided; further monitoring would be required to confirm stability over extended periods.
How does the performance of DSS-ISB scale from laboratory batch tests to pilot-scale or industrial applications, considering mixing and injection logistics?
The slurry's improved permeability and stability facilitate in-situ injection, as noted in the paper. However, scale-up would require optimization of injection rates and distribution in heterogeneous soils. The cost estimate of RMB 36.40 per ton of COPR suggests economic feasibility, but pilot trials are necessary to validate performance under field conditions.
What is the environmental footprint of DSS-ISB production, including energy and raw material sourcing?
The production cost breakdown shows raw materials account for 80.13% of total cost (RMB 402.05 per m3), with energy costs at 0.71%. The use of iron and sulfur precursors is relatively benign, but a full life-cycle assessment would be needed to quantify environmental impacts.
Can DSS-ISB be regenerated or reused, or is it a one-time application?
The paper does not discuss regeneration. Given the chemical reduction mechanism, the slurry is likely consumed during the reaction, making it a one-time reagent. However, the high removal capacity (92.43% improvement over FeSO4) reduces the required dosage, mitigating waste generation.
How does DSS-ISB perform in the presence of competing ions or organic matter commonly found in contaminated soils?
The study does not address interference from co-contaminants. Further research would be needed to evaluate selectivity and potential passivation effects in complex matrices.
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