Kinetics and mechanism of selenate and selenite removal in solution by green rust-sulfate

Abstract

This work investigated the removal of selenite and selenate from water by green rust (GR) sulfate. Selenite was immobilized by simple adsorption onto GR at pH 8, and by adsorption–reduction at pH 9. Selenate was immobilized by adsorption–reduction to selenite and zero valent selenium (Se 0 ) at both pH 8 and 9. In the process, GR oxidized to a mixture of goethite (FeOOH) and magnetite (Fe 3 O 4 ). The kinetics of selenite and selenate sorption at the GR–water interface was described through a pseudo-second-order model. X-ray absorption spectroscopy data enabled to elucidate the concentration profiles of Se and Fe species in the solid phase and allowed to distinguish two removal mechanisms, namely adsorption and reduction. Selenite and selenate were reduced by GR through homogeneous solid-phase reaction upon adsorption and by heterogeneous reaction at the solid–liquid interface. The selenite reduced through heterogeneous reduction with GR was adsorbed onto GR but not reduced further. The redox reaction between GR and selenite/selenate was kinetically described through an irreversible second-order bimolecular reaction model based on XAFS concentration profiles. Although the redox reaction became faster at pH 9, simple adsorption was always the fastest removal mechanism.

Influence of Silica Coatings on Magnetite-Catalyzed Selenium Reduction

“…4a) revealed the presence of Se IV and Se 0 , indicating that either all Se VI was reduced to Se IV and Se 0 ; or that adsorbed Se VI is washed away from solids during the filtration and washing procedures (Se VI is generally presumed to form outer-sphere complexes 82 ). Similarly, Onoguchi et al 37 recently reported the reduction of selenate into selenite and elemental Se 0 catalyzed by green rusts (GR) through two different mechanisms: i) after adsorption (homogeneous redox reaction); and ii) without adsorption (heterogeneous redox reaction), where dissolved Se VI could be reduced upon contact with GR. Our attempts to detect Se IV in solution by ionic chromatography (IC) analysis…”

“…In reductive precipitation processes, Fe II -bearing minerals catalyze the reduction of Se IV forming predominantly Se 0 , but also Fe selenides (FeSe, and FeSe2) depending on the experimental conditions. 36,37,39,77,78 In adsorption processes, sorbed Se IV may form inner-sphere (FeSeO3) and outer-sphere (Na2SeO3 electrostatic sorption) complexes. 77,[79][80][81] Although Se IV is generally sorbed by bidentate inner-sphere complexation, 78 the exact Se IV solid species in our system are hard to describe by our XANES measurements.…”

“…29 In this context, selenium represents an ideal probe to evaluate electron transfer because iron oxides are effective scavengers of selenite (SeO3 2-, Se IV ) and selenate (SeO4 2-, Se VI ) via adsorption processes [30][31][32][33][34][35] and reductive precipitation. [36][37][38][39] In the latter, iron oxides containing Fe II , like magnetite, catalyze the reduction of Se oxyanions to produce non-soluble Se 0 and Fe selenides. The redox reactivity of MNPs towards Se oxyanions (mainly Se IV ) makes Se an ideal molecular probe to study the influence of silica surface coatings on sorption and redox processes.…”

Forecast of AMD Quantity by a Series Tank Model in Three Stages: Case Studies in Two Closed Japanese Mines

“…The general treatment for AMD is neutralization and sedimentation by addition of a neutralizer, such as lime, calcium carbonate, and sodium hydroxide [2], and solid/liquid separation [3] of the produced sludge from the neutralized effluents. In these treatments, all toxic elements are concentrated into the sludge by precipitation [4][5][6] and adsorption [7][8][9][10][11][12], and the sludge is controlled in a tailing pond at a mine site or final disposal site. For these last several decades, AMD has been treated properly in Japan and has not caused severe pollution.…”

酸化マグネシウムおよび第一鉄を用いた層状複水酸化物による多元素含有排水の除去性能の検討

“…有効 確認 (Sasaki et al, 2011;Li et al, 2014;Fukushi et al, 2019) ．Sasaki et al(2011 et al, 2019) ．α-FeOOH 30 g dm −3 pH 6-9 7.8 mg dm −3 Se (VI) 90% 以上除去 (Hayes et al, 1987) 内圏錯体 形 成 吸着 知 (Zhang and Sparks, 1990;Favorito et al, 2018) ，green rust 同 吸着機構 確認 (Onoguchi et al, 2019;Refait et al, 2000 (Izawa et al, 2014;Fukuda et al, 2020;Sasaki et al, 2015) (Morimoto et al, 2011;Das et al, 2002) ，green rust…”