XPS study of the reaction of chromium (VI) with mackinawite (FeS)

In this study, the ability of mackinawite (FeS) to reduce Cr(VI) was investigated as a function of the initial aqueous Cr(VI) concentration (1 × 10−4–5 × 10−3 M) at pH 5 and fixed ionic strength under a nitrogen atmosphere. X‐ray photoelectron spectroscopy was used to characterize the surface after reaction and to identify the oxidation products. Aqueous Cr(VI) concentration removed from solution was determined using the diphenylcarbazide colorimetric method. Mackinawite was found to act as an efficient Cr(VI) removal material. Surface analysis revealed that all detectable chromium occurred as Cr(III), even at the highest initial Cr(VI) concentration. Strong attenuation of the Fe 2p and S 2p signals from mackinawite counterbalanced the increase of the Cr 2p and O 1s levels when the initial Cr(VI) concentration increased. Clear evidence for the oxidation of Fe(II) to Fe(III), as well as hydroxylation of the surface, was provided by the Fe 2p and O 1s levels, respectively. Furthermore, the S 2p level indicated that S(‐II) was the main component, whatever the initial Cr(VI) concentration, with small amounts of polysulphides and elemental sulphur at the surface. These observations at pH 5 show that the mechanism of removal of Cr(VI) is through the reduction of Cr(VI) to Cr(III) and results in the formation of oxidation products such as Cr(OH)3 and/or FexCr(1−x)(OH)3 precipitates at the reacted mackinawite surface. Copyright © 2002 John Wiley & Sons, Ltd.

[1]  M. Abdelmoula,et al.  Surface chemistry and structural properties of mackinawite prepared by reaction of sulfide ions with metallic iron , 2002 .

[2]  E. Thornton,et al.  Chromium(VI) reduction by hydrogen sulfide in aqueous media: stoichiometry and kinetics. , 2001, Environmental science & technology.

[3]  P. Liu,et al.  Spectroscopic study of the reaction of aqueous Cr(VI) with Fe3O4 (111) surfaces , 2000 .

[4]  D. Banerjee,et al.  Oxidation of aqueous Cr(III) at birnessite surfaces: constraints on reaction mechanism , 1999 .

[5]  P. Behra,et al.  Surface Oxidation of Pyrite as a Function of pH , 1998 .

[6]  D. Blowes,et al.  Surface chemistry and morphology of poorly crystalline iron sulfides precipitated in media containing sulfate-reducing bacteria , 1998 .

[7]  K. Hayes,et al.  Effects of Solution Composition and pH on the Reductive Dechlorination of Hexachloroethane by Iron Sulfide , 1997 .

[8]  D. Blowes,et al.  Products of Chromate Reduction on Proposed Subsurface Remediation Material , 1997 .

[9]  J. Barnhart.  Occurrences, uses, and properties of chromium. , 1997, Regulatory toxicology and pharmacology : RTP.

[10]  S. Fendorf,et al.  Reduction of Hexavalent Chromium by Amorphous Iron Sulfide , 1997 .

[11]  Hesham S. Abdel-Samad,et al.  An XPS study of the adsorption of chromate on goethite ( α-FeOOH) , 1997 .

[12]  N. McIntyre,et al.  Comment on ‘Curve Fitting of Cr 2p Photoelectron Spectra of Cr2O3 and CrF3’ , 1996 .

[13]  E. Kemnitz,et al.  Curve fitting of Cr 2p photoelectron spectra of Cr2O3 and CrF3 , 1995 .

[14]  D. Vaughan,et al.  Synthesis and Rietveld crystal structure refinement of mackinawite, tetragonal FeS , 1995, Mineralogical Magazine.

[15]  H. Nesbitt,et al.  Generation of acids from mine waste: Oxidative leaching of pyrrhotite in dilute H2SO4 solutions at pH 3.0 , 1994 .

[16]  C. Palmer,et al.  Processes affecting the remediation of chromium-contaminated sites. , 1991, Environmental health perspectives.

[17]  L. Eary,et al.  Kinetics of chromate reduction by ferrous ions derived from hematite and biotite at 25 degrees C , 1989 .

[18]  J. Murday,et al.  An XPS study of passive film formation on iron in chromate solutions , 1988 .

[19]  Rajendra P. Gupta,et al.  Calculation of multiplet structure of core p -vacancy levels. II , 1974 .

[20]  G. C. Allen,et al.  X-Ray photoelectron spectroscopy of chromium–oxygen systems , 1973 .