Effect of groundwater ions (Ca2+, Na+, and HCO3-) on removal of hexavalent chromium by Fe(II)-phosphate mineral

Sungjun Bae; Sunho Yoon; Ugras Kaplan; Hyungjun Kim; Seunghee Han; Woojin Lee

doi:10.1016/j.jhazmat.2020.122948

Effect of groundwater ions (Ca²⁺, Na⁺, and HCO₃^-) on removal of hexavalent chromium by Fe(II)-phosphate mineral

J Hazard Mater. 2020 Nov 5:398:122948. doi: 10.1016/j.jhazmat.2020.122948. Epub 2020 May 25.

Authors

Sungjun Bae¹, Sunho Yoon¹, Ugras Kaplan², Hyungjun Kim³, Seunghee Han⁴, Woojin Lee⁵

Affiliations

¹ Department of Civil and Environmental Engineering, Konkuk University, Seoul 05029, South Korea.
² Institute for Nuclear Waste Disposal, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany.
³ Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 34141, South Korea.
⁴ School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, South Korea.
⁵ Department of Civil and Environmental Engineering, Green Environment and Energy Lab., National Laboratory Astana, Nazarbayev University, Nur-Sultan 010000, Kazakhstan. Electronic address: woojin.lee@nu.edu.kz.

PMID: 32497861
DOI: 10.1016/j.jhazmat.2020.122948

Abstract

A systematic study was conducted to investigate the effect of major groundwater ions (i.e., Ca²⁺, Na⁺, and HCO₃^-) on removal of hexavalent chromium (Cr(VI)) by an Fe(II)-phosphate mineral (i.e., vivianite). The batch experiments revealed that the second-order rate constant for Cr(VI) removal by vivianite with Ca²⁺ + CO₃^2- (0.076-1.90 mM) and Na⁺ + HCO₃^- (0.26-6.50 mM) was 1.5-5.2 times lower than that without these ions. The removal kinetics of Cr(VI) by vivianite was abruptly slowed down with the increased ion concentration, which showed their inhibitory effect on the reaction. The results of the geochemical modeling and density functional theory calculations showed that the presence of Ca²⁺ + HCO₃^- and Na⁺ + HCO₃^- can form less favorable Cr(VI) species (i.e., CaCrO_4(aq) and NaCrO₄^-) on the Fe-B site of vivianite surface, leading to the inhibitory effect observed in this study. Finally, the X-ray absorption spectroscopy results showed that reductive immobilization of Cr(VI) to Cr(III) occurred by structural Fe(II) oxidation of vivianite to amorphous mixed-valence Fe-phosphate via an inner-sphere complexation. The results suggest that the presence of Ca²⁺, Na⁺, and HCO₃^- in phosphorous-enriched iron-reducing environments may lower the remedial efficiency of Cr(VI) removal.

Keywords: Cr(VI); DFT, XAS; groundwater ions; vivianite.

Publication types

Research Support, Non-U.S. Gov't