Properties and mechanism of Cr(VI) adsorption and reduction by K₂FeO₄ in presence of Mn(II)

ABSTRACT

To efficiently treat hexavalent chromium (Cr(VI)) wastewater, K₂FeO₄ was used to remove and reduce Cr(VI) in presence of Mn(II) in this paper. Batch removal experiments were carried out to study the effect of Fe/Mn molar ratios, initial pH, in-situ and ex-situ and co-existing ions on Cr(VI) removal. The results showed the removal efficiency of Cr(VI) was 97.7% for the initial Cr(VI) concentration of 10.0 mg/L at Fe/Mn molar ratio of 2:3 and initial pH 8.0. Meanwhile, the high removal efficiency of Cr(VI) had been maintained throughout the pH range of 3.0–8.0 in the experimental study. Moreover, the removal process was relatively stable regardless of in-situ and ex-situ, and co-existing ions such as Ca²⁺ and low concentration of ${\mathrm{HCO}}_3^{-}$ had no intense effect on Cr(VI) removal, while ${\mathrm{SO}}_4^{2-}$ inhibited Cr(VI) removal in the reaction system. To investigate the removal mechanism of Cr(VI) by K₂FeO₄ in presence of Mn(II), the reaction products were characterized by the Fourier transformed infrared spectrometer, X-ray powder diffraction, Transmission electron microscopy and the high-resolution X-ray photoelectron spectroscopy. The results indicated the ferrate decomposition products of γ-FeOOH/γ-Fe₂O₃ had the ability to adsorb Cr(VI) and react with Mn(II) to form γ-Fe₂O₃-Mn(II) complex to adsorb and reduce Cr(VI).

GRAPHICAL ABSTRACT

KEYWORDS:

• K₂FeO₄
• Cr(VI) adsorption
• Fe(VI) reduction products
• MnO_x
• mechanism

Acknowledgments

This research is supported by National Natural Science Foundation of China (No. 51978174), and Natural Science Foundation of Guangdong Province (No. 2018A030313099).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research is supported by National Natural Science Foundation of China [grant number 51978174], and Natural Science Foundation of Guangdong Province [grant number 2018A030313099].