Enhanced remediation of Cr(VI)-contaminated soil by modified zero-valent iron with oxalic acid on biochar

Lihong Xie; Qingjun Chen; Yiyang Liu; Qiyan Ma; Jinlan Zhang; Chenliu Tang; Guilan Duan; Aijun Lin; Tingting Zhang; Shangyi Li

doi:10.1016/j.scitotenv.2023.167399

Enhanced remediation of Cr(VI)-contaminated soil by modified zero-valent iron with oxalic acid on biochar

Sci Total Environ. 2023 Dec 20:905:167399. doi: 10.1016/j.scitotenv.2023.167399. Epub 2023 Oct 2.

Authors

Lihong Xie¹, Qingjun Chen², Yiyang Liu¹, Qiyan Ma¹, Jinlan Zhang¹, Chenliu Tang³, Guilan Duan⁴, Aijun Lin¹, Tingting Zhang¹, Shangyi Li⁵

Affiliations

¹ Department of Environmental Science and Engineering, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
² China National Petroleum and Chemical Planning Institute, Beijing 100013, China.
³ Department of Environmental Science and Engineering, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China. Electronic address: tangchenliu@mail.buct.edu.cn.
⁴ State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
⁵ Department of Environmental Science and Engineering, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China. Electronic address: lishangyi@mail.buct.edu.cn.

PMID: 37793443
DOI: 10.1016/j.scitotenv.2023.167399

Abstract

Hexavalent chromium (Cr(VI)) is carcinogenic and widely presented in soil. In this study, modified zero-valent iron (ZVI) with oxalic acid on biochar (OA-ZVI/BC) was prepared using wet ball milling method for the remediation of Cr(VI)-contaminated soil. Microscopic characterizations showed that ZVI were distributed on the biochar uniformly and confirmed the enhanced interface interaction between biochar and ZVI by wet ball milling. Electrochemical analysis indicated the strong electron transfer ability and enhanced corrosion behavior of OA-ZVI/BC. Moreover, inhibitory efficiencies of Cr(VI) removal with the addition of 1,10-phenanthroline suggested abundant Fe²⁺ generation in OA-ZVI/BC, which might facilitate the reduction of Cr(VI) to Cr(III). Theory calculation further demonstrated the ZVI modified by oxalic acid was more susceptible to solid-solid interfacial reactions with Cr(VI), and more electrons were transferred to Cr(VI). When applied to Cr(VI)-contaminated soil, OA-ZVI/BC could passivate 96.7 % total Cr(VI) and maintained for 90 days. The toxicity characteristic leaching procedure (TCLP) and simple based extraction test (SBET) were used to evaluate the leaching toxicity and bioaccessibility of Cr(VI), respectively. The TCLP-Cr(VI) decreased to 0.11 mg·L^-1 after OA-ZVI/BC treatment, much lower than that of soils with ZVI/BC and OA-ZVI remediation (1.5 mg·L^-1 and 4.1 mg·L^-1). The bioaccessibility of Cr(VI) reduced by 93.5 % after 3-month remediation. Sequential extraction showed that Cr fractions in the soil after OA-ZVI/BC remediation was converted from acetic acid-extractable (HOAc-extractable) to more stable forms (e.g., residual and oxidizable forms). Benefiting from the synergies of oxalic acid, biochar and wet ball milling, OA-ZVI/BC exhibited an excellent performance on the remediation of Cr(VI)-contaminated soil, whose mechanisms involved adsorption, reduction (Fe⁰/Fe²⁺, Fe²⁺/Fe³⁺) and co-precipitation. This study herein develops a promising ZVI technology in the remediation of heavy metal-contaminated soil.

Keywords: Cr(VI)-contaminated soil; Electron transfer; Oxalic acid modification; Wet ball milling; Zero valent iron.