[Removal of Cr(VI) by iron filings with microorganisms to recover iron reactivity]

The reduction of Cr(VI) by iron filings and microorganisms was carried out during our investigation. Effects of factors (e. g. temperature, initial pH, iron filings loadings, inoculum size, initial concentration of Cr(VI) and other ions) on Cr(VI) reduction were studied, and the X-ray photoelectron spectroscopy (XPS) was applied to explore elements composition on the surface of iron filings. Experimental results revealed a promotion of Cr(VI) reduction by iron filings with the presence of microorganisms, and the Cr(VI) removal was complete within 18 h. Results showed the Cr(VI) reduction preferred a higher temperature within the range of 25-42 degrees C and the optimum initial pH was supposed to be 5.8. The efficiency of Cr(VI) reduction was increased with increasing amounts of iron filings and microorganisms, and was decreased with the increasing initial concentration of Cr( VI). Mn2+, Zn2+, Co2+, Cu2+ and Ni2+ ions could cause varying degrees of inhibition of Cr(VI) reduction, and among these ions, the effect of Mn2+ was the smallest and that of Ni2+ was the highest. Characterizations with XPS indicated the deposition of Cr element on iron filings surface in forms of Cr(III) and Cr(VI), as the Cr2p3/2 region could be decomposed into two peaks at (576.8 +/- 0.1) eV and (578.1 +/- 0.1) eV. Furthermore, Cr(III) was most likely to be in the form of Cr(OH)3 or Fe(x)Cr(1-x)(OH)3.