Abstract
Schwertmannite is an environmental mineral material that can promote the natural passivation of heavy metal elements, thereby reducing environmental pollution from toxic elements. However, the fundamental reason for the difference between the chemically (H2O2-FeSO4) and biologically (Acidithiobacillus ferrooxidans-FeSO4) synthesized schwertmannite is still unclear. In this study, X-ray diffraction, scanning electron microscopy, the Brunauer–Emmett–Teller method, and X-ray fluorescence spectrometry were used to compare the structure, specific surface area, and elemental composition of schwertmannite synthesized by biological and chemical methods. The removal capacity of As(III) by the two kinds of schwertmannite and the effects of extracellular polymeric substances (EPS) on biogenetic schwertmannite were also investigated. At a consistent Fe2+ oxidation efficiency, the chemical method synthesized more schwertmannite than the biological method over a 60-h period. The biosynthesized schwertmannite had a “chestnut shell” shape, with a larger particle size and specific surface than the chemically synthesized schwertmannite, which was relatively smooth. The saturated adsorption capacities of the biologically and chemically synthesized schwertmannite were 117.0 and 87.0 mg·g−1, respectively. After exfoliation of the EPS from A. ferrooxidans, the biosynthesized schwertmannite displayed a “wool ball” shape, with rough particle surfaces, many microporous structures, and a larger specific surface area. The schwertmannite yield also increased by about 45% compared with that before exfoliation, suggesting that the secretion of EPS by A. ferrooxidans can inhibit the formation of schwertmannite.
Highlights
Schwertmannite is a widely used adsorbent material with a chemical composition ofFe8 O8 (OH)8−2x (SO4 )x (1≤ x ≤1.75) [1]
The schwertmannite yield increased by about 45% compared with that before exfoliation, suggesting that the secretion of extracellular polymeric substances (EPS) by A. ferrooxidans can inhibit the formation of schwertmannite
This study is the first to investigate the differences between the chemical (H2O2-FeSO4) and biological methods (A. ferrooxidans-FeSO4) for the synthesis of schwertmannite at the same Fe2+
Summary
Schwertmannite is a widely used adsorbent material with a chemical composition ofFe8 O8 (OH)8−2x (SO4 )x (1≤ x ≤1.75) [1]. Schwertmannite is a widely used adsorbent material with a chemical composition of. The SO4 2− groups in the mineral’s pores can be replaced by anions with similar ionic radii (PO4 3− , CrO4 2− , etc.), which allows schwertmannite to adsorb or coprecipitate toxic and harmful elements in water. This process can be used to remove heavy metal (metalloid) ions from wastewater [4,5]. Many studies have shown that schwertmannite can promote the natural passivation of heavy metal (metalloid) elements, thereby reducing or eliminating
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