Effect and mechanism of kaolinite loading amorphous zero-valent iron to stabilize cadmium in soil

Jieling Ren; Chunli Zheng; Yingying Yong; Zishen Lin; Aibin Zhu; Chi He; Hua Pan

doi:10.1016/j.scitotenv.2023.166319

Effect and mechanism of kaolinite loading amorphous zero-valent iron to stabilize cadmium in soil

Sci Total Environ. 2023 Dec 15:904:166319. doi: 10.1016/j.scitotenv.2023.166319. Epub 2023 Aug 15.

Authors

Jieling Ren¹, Chunli Zheng², Yingying Yong¹, Zishen Lin¹, Aibin Zhu³, Chi He¹, Hua Pan⁴

Affiliations

¹ Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, PR China.
² Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, PR China; Shaanxi Qingling Chunchuang Environmental Protection Industry Technology Co., Ltd., Xi'an 710049, PR China. Electronic address: clzheng@mail.xjtu.edu.cn.
³ Institute of Robotics & Intelligent Systems, Xi'an Jiaotong University, Xi'an 710049, PR China.
⁴ Key Laboratory of Pollution Exposure and Health Intervention of Zhejiang Province, College of Biological and Environment Engineering, Zhejiang Shuren University, Hangzhou 310015, PR China. Electronic address: panhua@zjsru.edu.cn.

PMID: 37586509
DOI: 10.1016/j.scitotenv.2023.166319

Abstract

Amorphousness effectively improves the electron transfer rate of zero-valent iron. In this study, a novel kaolinite loading amorphous zero-valent iron composite (K-AZVI) was prepared and applied to the remediation of soils with cadmium (Cd) pollution concentrations of 20, 50, and 100 mg/kg respectively. The results showed that the application of K-AZVI increased the pH and cation exchange capacity (CEC) of soil, and decreased the dissolved organic carbon (DOC) and organic matter (OM) of soil, thus indirectly promoting the adsorption of Cd in the soil. After 28 days of stabilization, the stabilizing efficiency of K-AZVI on the water-soluble Cd content in soil reached 98.72 %. Under the amendment of 0.25 %-1.0 % (w/w), the available Cd content in 20-100 mg/kg contaminated soil decreased by 46.47 %-62.23 %, 24.10 %-41.52 %, and 16.09 %-30.51 % respectively compared with CK. More importantly, the addition of K-AZVI promoted the transformation of 33.18 %-48.42 % exchangeable fraction (EXC) to 10.09 %-20.14 % residual fraction (RES), which increased the abundance and diversity of soil bacterial communities. Comprehensive risk assessment showed that adding 1.0 % K-AZVI provided the best remediation on contaminated soil. In addition, the results of scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) of K-AZVI before and after the reaction showed that the stabilization mechanism of K-AZVI to Cd in soil is mainly the stable metal species (Cd(OH)₂, CdO and CdFe₂O₄) formed by the direct complexation and coprecipitation of a large number of iron oxides formed by the rapid corrosion of amorphous zero-valent iron (AZVI). Overall, this work provides a promising approach to the remediation of Cd-contaminated soil using K-AZVI composites.

Keywords: Amorphous zero-valent iron; Cd-contaminated soil; Immobilization; Kaolinite; Removal mechanism.