Electron transfer at the mineral/water interface: Selenium reduction by ferrous iron sorbed on clay

Charlet, Laurent; Scheinost, Andreas C.; Tournassat, Christophe; Grenèche, Jean‐Marc; Géhin, Antoine; Fernández-Martı́nez, Alejandro; Coudert, Sylvie; Tisserand, Delphine; Brendlé, Jocelyne

doi:10.1016/j.gca.2007.08.024

Cited by 185 publications

(138 citation statements)

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“…Previous research indicated that aqueous Fe(II) sorbed on solid in heterogeneous solution could quickly reduce Se(IV) to Se(0). 14,40 We propose that the first electron transfer for pyrite-Se(IV) reaction is from Fe 2þ that is adsorbed on pyrite surface to HSeO 3 -, which produces a Fe 3þ . Subsequently, the Fe 3þ receives an electron, at a cathodic site, from Fe 2þ in the mineral surface.…”

Section: Articlementioning

confidence: 99%

Effect of pH on Aqueous Se(IV) Reduction by Pyrite

Kang

Chen

et al. 2011

Environ. Sci. Technol.

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104

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International audienceInteraction of aqueous Se(IV) with pyrite was investigated using persistently stirred batch reactors under O2-free (<1 ppm) conditions at pH ranging from 4.5 to 6.6. Thermodynamic calculations, an increase in pH during the experiments, and spectroscopic observation indicate that the reduction of aqueous Se(IV) by pyrite is dominated by the following reaction: FeS2 + 3.5HSeO3− + 1.5H+ = 2SO42− + Fe2+ + 3.5Se(0) + 2.5H2O. The released Fe(II) was partitioned between the bulk solution and pyrite surface at pH ≈ 4.5 and 4.8, with the Fe2+ density at pyrite-solution interface about 4 orders of magnitude higher than that in the bulk solution, while iron oxyhydroxide precipitated at pH ≈ 6.6, resulting in the decrease of dissolved iron. In the Se(IV) concentration range of the experiments, aqueous Se(IV) reduction rate follows the pseudofirst order which is in the form of ln mSe(IV) = −k′t + ln mSe(IV)0, where k′ is apparent rate constant combining the rate constant k and pyrite surface area to mass of solution ratio (A/M). And the aqueous Se(IV) reduction rate constant for a standard system (k) with 1 m2 pyrite surface area per 1 kg solution was obtained to be 1.65 × 10−4 h−1, 3.28 × 10−4 h−1, and 4.76 × 10−4 h−1 at pH around 4.5, 4.8, and 5.1, respectively. The positive correlation between reaction rate and pH disagrees with the theories that protons are consumed when HSeO3− is reduced to Se0, and negative charge density on pyrite surface increases as pH increases. Thus, a ferrous iron mediated electron transfer mechanism is proposed to operate during the reduction of aqueous Se(IV) by pyrite. pH and iron concentration affect significantly on Se(IV) reaction rate and reaction product

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Section: Articlementioning

confidence: 99%

Effect of pH on Aqueous Se(IV) Reduction by Pyrite

Kang

Chen

et al. 2011

Environ. Sci. Technol.

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104

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“…Many researchers have reported that Fe(II) is an important factor for inorganic and organic pollutant removal in a ZVI system (Charlet et al 2007;Huang and Zhang 2006). Most of the pollutants can be reduced through redox reactions involving Fe(II) on the Fe(0) surface.…”

Section: Introductionmentioning

confidence: 99%

Selenate removal by zero-valent iron in oxic condition: the role of Fe(II) and selenate removal mechanism

Yoon

Bang²,

Kim

et al. 2015

Environ Sci Pollut Res

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In this study, batch experiments were conducted to investigate the effect of the concentration of ferrous [Fe(II)] ions on selenate [Se(VI)] removal using zero-valent iron (ZVI). The mechanism of removal was investigated using spectroscopic and image analyses of the ZVI-Fe(II)-Se(VI) system. The test to remove 50 mg/L of Se(VI) by 1 g/L of ZVI resulted in about 60% removal of Se(VI) in the case with absence of Fe(II), but other tests with the addition of 50 and 100 mg/L of the Fe(II) had increased the removal efficiencies about 93 and 100% of the Se(VI), respectively. In other batch tests with the absence of ZVI, there were little changes on the Se(VI) removal by the varied concentration of the Fe(II). From these results, we found that Fe(II) ion plays an accelerator for the reduction of Se(VI) by ZVI with the stoichiometric balance of 1.4 (=nFe(2+)/nSe(6+)). Under anoxic conditions, the batch test revealed about 10% removal of the Se(VI), indicating that the presence of dissolved oxygen increased the kinetics of Se(VI) removal due to the Fe(II)-containing oxides on the ZVI, as analyzed by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) spectra also showed that the reductive process of Se(VI) to Se(0)/Se(-II) occurred in the presence of the both ZVI and Fe(II). The final product of iron corrosion was lepidocrocite (γ-FeOOH), which acts as an electron transfer barrier from Fe(0) core to Se(VI). Therefore, the addition of Fe(II) enhanced the reactivity of ZVI through the formation of iron oxides (magnetite) favoring electron transfer during the removal of Se(VI), which was through the exhaustion of the Fe(0) core reacted with Se(VI).

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“…Iron oxides such as magnetite [6], hematite [7][8] and goethite [9] are known to be capable of binding selenite with high distribution coefficients in groundwater without significantly influencing the ionic strength [9]. Moreover, the presence of Fe(II) in magnetite has shown to help the reduction of selenium oxides to a lower oxidation state [5,10] in a pH range of 3~8. However, X-ray absorption spectroscopy (XAS) indicated that the oxidation state of selenium did not change when selenite adsorbed onto magnetite at pH=4.45~7.46 [11].…”

Section: Introductionmentioning

confidence: 99%