Abstract
Cr(VI) is considered as a priority pollutant, and its remediation has attracted increasing attention in the environmental area. In this study, the driving of pyrite-based Cr(VI) reduction by Acidithiobacillus ferrooxidans was systematically investigated. The results showed that pyrite-based Cr(VI) reduction was a highly proton-dependent process and that pH influenced the biological activity. The passivation effect became more significant with an increase in pH, and there was a decrease in Cr(VI) reduction efficiency. However, Cr(VI) reduction efficiency was enhanced by inoculation with A. ferrooxidans. The highest reduction efficiency was achieved in the biological system with a pH range of 1–1.5. Pyrite dissolution and reactive site regeneration were promoted by A. ferrooxidans, which resulted in the enhanced effect in Cr(VI) reduction. The low linear relevancy between pH and Cr(VI) dosage in the biological system indicated a complex interaction between bacteria and pyrite. Secondary iron mineral formation in an unfavorable pH environment inhibited pyrite dissolution, but the passivation effect was relieved under the activity of A. ferrooxidans due to S/Fe oxidization. The balance between Cr(VI) reduction and biological activity was critical for sustainable Cr(VI) reduction. Pyrite-based Cr(VI) remediation driven by chemoautotrophic acidophilic bacteria is shown to be an economical and efficient method of Cr(VI) reduction.
Highlights
Hexavalent chromium [Cr(VI)] is an important raw material that is widely applied in various industries including in metallurgy, electroplating, and leather tanning
Pyrite dissolution was mainly caused by two factors, Fe(III)/Cr(VI)-dominated chemical oxidation and A. ferrooxidans-mediated biological oxidation (Demoisson et al, 2005, 2007; Lara et al, 2015)
In the BS system, the Fe(II) concentration remained at 80 mg/L in the middle and later periods, significantly higher than that in the chemical group (CI) system, which indicated that proton compensation promoted pyrite dissolution
Summary
Hexavalent chromium [Cr(VI)] is an important raw material that is widely applied in various industries including in metallurgy, electroplating, and leather tanning. Two forms of Cr with different oxidation states, Cr(VI) and Cr(III), usually exist in the natural environment. Cr(VI) is considered a priority pollutant, and its remediation has attracted increasing attention in the environmental area (Jiang et al, 2015). The toxicity of Cr(III) is far lower than that of Cr(VI), and it can be precipitated as Cr(OH), while Cr(VI) is soluble over a wide pH range. The potential of sulfide minerals such as pyrite or reduced sulfur in redox-sensitive contaminant remediation has attracted great interest in recent years (He and Traina, 2005). The pyrite surface is usually passivated due to the formation of Fe-Cr compounds, resulting pyrite
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