Abstract
Selenium (Se) is an essential and crucial micronutrient for humans and animals, but excessive Se brings negativity and toxicity. The adsorption and oxidation of Se(IV) on Mn-oxide surfaces are important processes for understanding the geochemical fate of Se and developing engineered remediation strategies. In this study, the characterization of simultaneous adsorption, oxidation, and desorption of Se(IV) on δ-MnO2 mineral was carried out using stirred-flow reactors. About 9.5% to 25.3% of Se(IV) was oxidized to Se(VI) in the stirred-flow system in a continuous and slow process, with the kinetic rate constant k of 0.032 h−1, which was significantly higher than the apparent rate constant of 0.0014 h−1 obtained by the quasi-level kinetic fit of the batch method. The oxidation reaction was driven by proton concentration, and its rate also depended on the Se(IV) influent concentration, flow rate, and δ-MnO2 dosage. During the reaction of Se(IV) and δ-MnO2, Mn(II) was produced and adsorbed strongly on Mn oxide surfaces, which was evidenced by the total reflectance Fourier transform infrared (ATR-FTIR) results. The X-ray photoelectron spectroscopy (XPS) data indicated that the reaction of Se(VI) on δ-MnO2 produced Mn(III) as the main product. These results contribute to a deeper understanding of the interface chemical process of Se(IV) with δ-MnO2 in the environment.
Highlights
Selenium (Se) is a redox-sensitive element that could be both deficient and excessive in the environment [1,2]
We investigated the dynamic process of Se(IV) oxidation and adsorption on manganese oxide via a stirred-flow method
The objectives of the study were as follows: (1) to investigate the simultaneous kinetics process of adsorption and oxidation of Se(IV) on manganese oxide by the stirredflow method; (2) to explore selenium adsorption and oxidation affected by flow rate, initial
Summary
Selenium (Se) is a redox-sensitive element that could be both deficient and excessive in the environment [1,2]. Se is highly irregularly distributed, with Se content of 0.01–2 mg kg−1 in most soils and over 1200 mg kg−1 in Se-rich or Secontaminated soils [3,4]. As Se cycling and transport in the near-surface soil zone leads to detailed interaction between Se in the environment and the health of living things, the study of the environmental behavior of Se in soil has received tremendous attention in recent decades. The mobility of Se is strongly governed by its speciation [7]. The main forms of Se in the environment are selenite (Se(IV)) and selenate (Se(VI)), and
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