Mechanistic insight into Cr(VI) retention by Si-containing ferrihydrite

Ying Hu; Qiang Xue; Honghan Chen; Huaming Guo; Kenneth C Carroll; Song Wang

doi:10.1016/j.jes.2023.05.040

Mechanistic insight into Cr(VI) retention by Si-containing ferrihydrite

J Environ Sci (China). 2024 May:139:217-225. doi: 10.1016/j.jes.2023.05.040. Epub 2023 Jun 3.

Authors

Ying Hu¹, Qiang Xue², Honghan Chen¹, Huaming Guo³, Kenneth C Carroll⁴, Song Wang⁵

Affiliations

¹ MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China; Beijing Key Laboratory of Water Resources and Environmental Engineering, School of Water Resources and Environment, China University of Geosciences, Beijing 100083, China.
² MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China; Beijing Key Laboratory of Water Resources and Environmental Engineering, School of Water Resources and Environment, China University of Geosciences, Beijing 100083, China. Electronic address: xueqiang@cugb.edu.cn.
³ MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China; State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China. Electronic address: hmguo@cugb.edu.cn.
⁴ Plant & Environmental Science, New Mexico State University, NM 88003, USA.
⁵ Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130023, China.

PMID: 38105049
DOI: 10.1016/j.jes.2023.05.040

Abstract

Hexavalent chromium [Cr(VI)] causes serious harm to the environment due to its high toxicity, solubility, and mobility. Ferrihydrites (Fh) are the main adsorbent and trapping agent of Cr(VI) in soils and aquifers, and they usually coexist with silicate (Si), forming Si-containing ferrihydrite (Si-Fh) mixtures. However, the mechanism of Cr(VI) retention by Si-Fh mixtures is poorly understood. In this study, the behaviors and mechanisms of Cr(VI) adsorption onto Si-Fh with different Si/Fe molar ratios was investigated. Transmission electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and other techniques were used to characterize Si-Fh and Cr(VI)-loading of Si-Fh. The results show that specific surface area of Si-Fh increases gradually with increasing Si/Fe ratios, but Cr(VI) adsorption on Si-Fh decreases with increasing Si/Fe ratios. This is because with an increase in Si/Fe molar ratio, the point of zero charge of Si-Fh gradually decreases and electrostatic repulsion between Si-Fh and Cr(VI) increases. However, the complexation of Cr(VI) is enhanced due to the increase in adsorbed hydroxyl (A-OH-) on Si-Fh with increasing Si/Fe molar ratio, which partly counteracts the effect of the electrostatic repulsion. Overall, the increase in the electrostatic repulsion has a greater impact on adsorption than the additional complexation with Si-Fh. Density functional theory calculation further supports this observation, showing the increases in electron variation of bonding atoms and reaction energies of inner spherical complexes with the increase in Si/Fe ratio.

Keywords: Cr(VI) Adsorption; Ferrihydrite; Hexavalent chromium; Si/Fe ratio.

MeSH terms

Adsorption
Chromium* / chemistry
Ferric Compounds* / chemistry
Silicates

Substances

ferric oxyhydroxide
chromium hexavalent ion
Ferric Compounds
Chromium
Silicates