Characteristics, kinetics, thermodynamics and long-term effects of zerovalent iron/pyrite in remediation of Cr(VI)-contaminated soil

• Published in: Environmental pollution (1987) 2021-11, Vol.289, p.117830-117830, Article 117830
• Main Authors: Min, Xiaobo, Li, Qi, Zhang, Xiaoming, Liu, Lu, Xie, Yan, Guo, Lili, Liao, Qi, Yang, Zhihui, Yang, Weichun
• Format: Article
• Language: English
• Subjects: Hexavalent chromium contaminated soil; Kinetics and thermodynamics; Long-term stability; Reductive remediation; ZVI/FeS2
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2021.117830

Development of efficient, green and low-cost natural mineral-based reductive materials is promising to remediation of hexavalent chromium(Cr(VI))-contaminated soil. Considering the synergetic effect between pyrite and zerovalent iron (ZVI), an activated pyrite supported ZVI(ZVI/FeS2) with high reducing activity was developed by ball milling activation of natural pyrite and sulfidation of ZVI. The remediation property of ZVI/FeS2 for Cr(VI)-contaminated soil was evaluated with different ZVI/FeS2 dosage, soil-water ratio, initial pH, time and temperature, as well as the stability of Cr. The results showed that ZVI/FeS2 possessed high reduction activity with soil Cr(VI) removal rate up to 99 % even under alkaline condition, and soil with different pH values eventually converged to neutral after 90 days, indicating that ZVI/FeS2 has a good self-regulating alkaline ability. The reduction process conformed to Langmuir-Hinshelwood first-order kinetics and was a spontaneous and endothermic process. The lower activation energy of 17.97 kJ mol−1 (usually 60–250 kJ mol−1) indicated that the reduction reaction of Cr(VI) was particularly easy to occur. The speciation change of Cr in soil within 30 days demonstrated that the Cr in the soil was converted from a readily migratable state to a more stable state, where the Fe–Mn oxide bound fraction reached 85.03 % due to the generation of Cr(III)/Fe(III) co-precipitation. The results of long-term stability experiments showed that the leaching concentrations of Cr(VI) and total Cr decreased significantly after the ZVI/FeS2 treatment and remained stable at very low levels for 180 days. This study provided a sustainable way to fully utilize natural pyrite minerals to obtain iron-bearing reductive materials for feasible, effective and long-term stable immobilization of Cr(VI) in soil. [Display omitted] •Natural pyrite-based ZVI/FeS2 reductive material is developed by ball milling.•ZVI/FeS2 possesses high reduction activity with soil Cr(VI) removal rate > 99 %.•ZVI/FeS2 is suitable in a wide pH range with good self-regulating alkaline ability.•Reaction of ZVI/FeS2 with Cr(VI) is easy to occur due to the low activation energy.•ZVI/FeS2 has excellent long-term stability in Cr(VI)-contaminated soil remediation.