Distinct chromium removal mechanisms by iron-modified biochar under varying pH: Role of iron and chromium speciation

Lecheng Liu; Ping Sun; Youyuan Chen; Xiaochen Li; Xilai Zheng

doi:10.1016/j.chemosphere.2023.138796

Distinct chromium removal mechanisms by iron-modified biochar under varying pH: Role of iron and chromium speciation

Chemosphere. 2023 Aug:331:138796. doi: 10.1016/j.chemosphere.2023.138796. Epub 2023 May 2.

Authors

Lecheng Liu¹, Ping Sun², Youyuan Chen³, Xiaochen Li⁴, Xilai Zheng¹

Affiliations

¹ College of Environmental Science and Engineering, Ocean University of China, Qingdao, 266100, China; Key Laboratory of Marine Environment and Ecology, Ministry of Education of China, Ocean University of China, Qingdao, 266100, China; Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, Ocean University of China, Qingdao, 266100, China.
² College of Environmental Science and Engineering, Ocean University of China, Qingdao, 266100, China.
³ College of Environmental Science and Engineering, Ocean University of China, Qingdao, 266100, China; Key Laboratory of Marine Environment and Ecology, Ministry of Education of China, Ocean University of China, Qingdao, 266100, China; Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, Ocean University of China, Qingdao, 266100, China. Electronic address: youyuan@ouc.edu.cn.
⁴ China Institute for Radiation Protection, Taiyuan, 030000, China.

PMID: 37142103
DOI: 10.1016/j.chemosphere.2023.138796

Abstract

Iron-modified biochar (Fe-biochar) has been widely developed to attenuate Cr(VI) pollution in both acid and alkaline environments. However, there are few comprehensive studies on how the iron speciation in Fe-biochar and chromium speciation in solution influencing the removal of Cr(VI) and Cr(III) under varying pH. Here, multiple Fe-biochar containing Fe₃O₄ or Fe(0) were prepared and applied to remove aqueous Cr(VI). Kinetics and isotherms suggested that all Fe-biochar could efficiently remove Cr(VI) and Cr(III) via adsorption-reduction-adsorption. The Fe₃O₄-biochar immobilized Cr(III) by forming FeCr₂O₄, while amorphous Fe-Cr coprecipitate and Cr(OH)₃ was formed when using Fe(0)-biochar. Density functional theory (DFT) analysis further indicated that pH increase caused more negative adsorption energies between Fe(0)-biochar and the pH-dependent Cr(VI)/Cr(III) species. Consequently, the adsorption and immobilization of Cr(VI) and Cr(III) species by Fe(0)-biochar was more favored at higher pH. In comparison, Fe₃O₄-biochar exhibited weaker adsorption abilities for Cr(VI) and Cr(III), which were in consistent with their less negative adsorption energies. Nonetheless, Fe(0)-biochar merely reduced ∼70% of adsorbed Cr(VI), while ∼90% of adsorbed Cr(VI) was reduced by Fe₃O₄-biochar. These results unveiled the importance of iron and chromium speciation for chromium removal under varying pH, and might guide the application-oriented design of multifunctional Fe-biochar for broad environmental remediation.

Keywords: Chromium removal; Density functional theory; Iron speciation; Iron-modified biochar; pH-dependent.

MeSH terms

Adsorption
Charcoal
Chromium* / analysis
Hydrogen-Ion Concentration
Iron*
Water Pollutants, Chemical* / analysis

Substances

biochar
Charcoal
Chromium
chromium hexavalent ion
Iron
Water Pollutants, Chemical