Constructing the active surface soil layer with ZVI-biochar amendment for simultaneous immobilization of As and Zn in both contaminated soil and groundwater: Continuous versus intermittent infiltration mode

• Published in: Journal of hazardous materials 2023-03, Vol.445, p.130518, Article 130518
• Main Authors: Chen, Xiang, Xu, Xiaoyun, Wei, Yaqiang, Wang, Xinbing, Cao, Xinde
• Format: Article
• Language: English
• Subjects: Active soil layer; As and Zn; Charcoal; Ferric Compounds; Groundwater; Immobilization; Soil; Soil Pollutants - analysis; Zinc
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2022.130518

In this study, the zero valent iron-biochar composite (ZVI-BC) was applied to construct an active surface soil layer for the simultaneous remediation of As-Zn contaminated soil and groundwater, focusing on the influence of the infiltration mode of pumped-up groundwater into soil. The active surface soil treated more contaminated groundwater for As (4.45-5.46 L kg-1 soil) than that for Zn (2.52-3.13 L kg-1 soil) under both continuous and intermittent infiltration modes, with about 98% As and 95% Zn removed from groundwater and retained in the soil. As(V) precipitated with Fe(III) due to ZVI oxidation, which was responsible for the As immobilization. The soil under the intermittent infiltration mode was enriched by the Sphingomonas with arsenate reductase gene, which promoted more reduction of As(V) into As(III) and facilitated coprecipitation of As(III) with Fe(III). The Mn oxide determined the sorption of Zn in the active soil layer, where the Hyphomicrobium, one type of manganese oxidizing bacteria, was much higher under the continuous infiltration mode, which accounted for the more Zn immobilization. After the remediation, both As and Zn immobilized in the active surface soil showed high stability, with the average downward migration rate of only 0.207-0.368 cm year-1 within 20-year rainfall exposure. Our findings indicate that this active surface soil layer is applicable for simultaneous immobilization of As and Zn in both contaminated soil and groundwater, and the groundwater intermittent infiltration could be a better option considering the remediation effectiveness, the immobilization mechanism, the long-term stability, and the energetic efficiency. [Display omitted] •The active surface soil was constructed with zero valent iron-biochar composite.•As was adsorbed by ZVI-BC and finally transformed into As-Fe coprecipitates.•The sorption and immobilization of Zn was dominated by Mn oxide in soil.•The downward migration rates of As and Zn immobilized in soil were low.•Intermittent infiltration was optimal for simultaneous immobilization of As and Zn.