Reduction, mineralization, and magnetic removal of chromium from soil by using a natural mineral composite

Xiang Ji; Chuanye Zhou; Liangxi Chen; Yanzhang Li; Tianci Hua; Yan Li; Changqiu Wang; Song Jin; Hongrui Ding; Anhuai Lu

doi:10.1016/j.ese.2022.100181

Reduction, mineralization, and magnetic removal of chromium from soil by using a natural mineral composite

Environ Sci Ecotechnol. 2022 Apr 9:11:100181. doi: 10.1016/j.ese.2022.100181. eCollection 2022 Jul.

Authors

Xiang Ji¹, Chuanye Zhou¹, Liangxi Chen¹, Yanzhang Li¹, Tianci Hua¹, Yan Li¹, Changqiu Wang¹, Song Jin^{2

3}, Hongrui Ding¹, Anhuai Lu¹

Affiliations

¹ Beijing Key Laboratory of Mineral Environmental Function, School of Earth and Space Sciences, Peking University, Beijing, 100871, China.
² Advanced Environmental Technologies LLC, 4025 Automation Way, Unit F4, Fort Collins, CO, 80525, USA.
³ Department of Civil and Architectural Engineering, University of Wyoming, Laramie, WY, 82071, USA.

Abstract

Reductive immobilization has been a commonly used technique to detoxify Cr(VI) from soil; however, it's challenging to remove the reduced Cr from soil to prevent its re-oxidation. This work explored a natural magnetic composite for the remediation, mineralization, and magnetic removal of Cr(VI) from the soil. It consists of 77% magnetite and 23% pyrrhotite with strong magnetic properties. A series of characterization tests show that composites of magnetite and pyrrhotite are interlaced and closely bonded, and contain no other heavy metals. The Cr(VI) removal rate increases with the decrease in composite particle size. A kinetics study shows that removing Cr(VI) by the composite is likely through both adsorption and reduction. Acidic conditions are more favorable for the immobilization of Cr(VI), at 45.8 mg Cr(VI) removal per g of composite at pH 2. After 100 days of in-situ treatment by the composite, the leaching concentration (TCLP) of Cr(VI)-contaminated soil was 1.95 mg L^-1, which was below the EPA limit (5 mg L^-1) for hazardous waste. After reduction, the composite was separated from soil by magnetic characteristics, and 58.2% of Cr was found mineralized. The post-treatment Cr-containing composite was analyzed by SEM-EDS, Raman spectra, and XPS. It was found that Cr was mineralized on the surface of the composite in the form of Cr(OH)₃, Cr₂O₃, and FeCr₂O_4. This indicates that reduction and mineralization of Cr(VI) in the soil can be accomplished through natural magnetic mineral composites and easily separated and removed from the soil, achieving a complete soil cleanup.

Keywords: Cr; Magnetic; Mineral composite; Mineralization; Soil remediation.