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Article

Competing Sorption of Se(IV) and Se(VI) on Schwertmannite

1
Department of Hydrology, University of Bayreuth, BayCEER, Universitaetsstr.30, 95440 Bayreuth, Germany
2
Canadian Light Source, Saskatoon, SK S7N 2V3, Canada
3
Experimental Biogeochemistry, BayCEER, University of Bayreuth, Dr.-Hans-Frisch-Str. 1-3, 95448 Bayreuth, Germany
*
Author to whom correspondence should be addressed.
Academic Editors: Sergey Churakov and Fulvio Di Lorenzo
Minerals 2021, 11(7), 764; https://doi.org/10.3390/min11070764
Received: 14 June 2021 / Revised: 10 July 2021 / Accepted: 12 July 2021 / Published: 15 July 2021
Schwertmannite (SHM) is a naturally occurring mineral that has been shown to effectively scavenge oxyanions from contaminated water. In this study, Fourier-transform infrared spectroscopy and X-ray absorption spectroscopy techniques in combination with wet-chemical techniques were used to study the competitive sorption of Se(IV) and Se(VI) at pH 3. The experiments were conducted with three types of schwertmannite obtained from oxidative synthesis, biogenic synthesis and high-pressure compaction at different initial Se concentrations and mixing ratios for 48 h and 56 days, respectively. A threshold value for the uptake mechanisms was identified, which reflects the amount of easily exchangeable sulphate (~0.5 mmol/g). At adsorbate concentrations below this threshold, an inner-sphere corner-sharing bidentate binuclear complex forms upon exchange with sulphate. At higher concentrations, both oxyanions become bound to SHM through co-occurrence of mainly inner-sphere and partly outer-sphere corner-sharing bidentate binuclear complexes with Fe(III) containing surface sites. Single species experiments clearly indicate a higher affinity of SHM for Se(IV). However, in mixed species experiments, competitive sorption occurs with equal or even preferential uptake of Se(VI) at concentrations much lower than the threshold value, presumably due to geometrical similarity between selenate and sulphate, and increasing preference for Se(IV) at high Se concentrations. View Full-Text
Keywords: schwertmannite; selenite; selenate; adsorption mechanism; XAS schwertmannite; selenite; selenate; adsorption mechanism; XAS
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MDPI and ACS Style

Marouane, B.; Chen, N.; Obst, M.; Peiffer, S. Competing Sorption of Se(IV) and Se(VI) on Schwertmannite. Minerals 2021, 11, 764. https://doi.org/10.3390/min11070764

AMA Style

Marouane B, Chen N, Obst M, Peiffer S. Competing Sorption of Se(IV) and Se(VI) on Schwertmannite. Minerals. 2021; 11(7):764. https://doi.org/10.3390/min11070764

Chicago/Turabian Style

Marouane, Bouchra, Ning Chen, Martin Obst, and Stefan Peiffer. 2021. "Competing Sorption of Se(IV) and Se(VI) on Schwertmannite" Minerals 11, no. 7: 764. https://doi.org/10.3390/min11070764

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