Reduction of Hexavalent Chromium by Amorphous Iron Sulfide

Abstract

The reduction of Cr(VI) to Cr(III) decreases the toxicity and mobility of chromium contaminants in soils and water. In addition, the formation of a highly insoluble Cr(III) product would decrease the likelihood of future Cr(III) re-oxidation. Amorphous iron sulfide minerals like mackinawite (FeS1 - x ) have the potential to reduce large quantities of Cr(VI) and in the process form very stable [Cr, Fe](OH)3 solids. In this study, we examine the effectiveness of amorphous FeS as a reductant of Cr(VI) by identifying the solution and solid-phase products of the reaction between FeS suspensions and chromate. Iron sulfide suspensions at pH 5.0, 7.0, and 8.0 were reacted with a range of Cr(VI) solutions from 50 to 5000 μM in a N2 atmosphere glovebox for 3 d. Solutions were analyzed using ICP−AES, IC, and colorimetric methods; solids were analyzed using XRD, TEM, EDS, and XANES spectroscopy. Iron sulfide removed all of the added Cr(VI) from solution for the reaction conditions studied and reduced between 85% and 100% of the Cr(VI) to Cr(III). Chromate reduction occurred dominantly at the FeS surface and resulted in [Cr0.75,Fe0.25](OH)3; while less extensive, reduction of Cr(VI) by Fe(II) (aq) was noted and produced a solid with the opposite Cr:Fe ratio, [Cr0.25,Fe0.75](OH)3.

Laboratory Study of Simulated Atmospheric Transformations of Chromium in Ultrafine Combustion Aerosol Particles

“…The baseline subtracted height of the pre-edge peak in a given spectrum with the post-edge normalized to unity is equal to the fraction of total chromium that is present as Cr(VI), that is, the value for Cr(VI)/Cr(total) in each sample is determined directly as the baseline-subtracted height of the normalized pre-edge peak. This procedure has been previously shown to be accurate within a few percent (Patterson et al 1997;Peterson et al 1997). Because of the small differences between many of our not-aged and aged FIG.…”

Adsorption of chromium(VI) onto electrochemically obtained magnetite nanoparticles

“…Several processes have been developed to eliminate the chromium present in industrial wastewater (Singh and Prasad 2015). The most commonly used methods to reduce the concentration of Cr(VI) in aqueous solutions are ion exchange, polymer resins, coagulation-flocculation, activated carbon adsorption and the reduction/chemical precipitation/sedimentation process (Boddu et al 2003;Hu et al 2004;Patterson et al 1997). Although the last method is probably the most commonly employed, it is very inefficient because a large amount of sludge is produced and the chromium cannot be recovered from the precipitate, making this strategy very expensive (Leyva Ramos et al 1994).…”

Molecular-Level Processes Governing the Interaction of Contaminants with Iron and Manganese Oxides - Final Report

“…In acidic solutions, Cr 2 O 7 2-is the dominant Cr(VI) aq species, whereas in basic solutions, CrO 4 2-is dominant (49). A number of past studies have shown that Cr(VI) can be reduced to Cr(III) on such oxides via abiotic pathways (e.g., (50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61)(62)(63)(64)(65)(66)(67)(68)). Eary and Rai (53) reviewed some of the most commonly used abiotic reductants and their efficiencies in reducing Cr(VI) aq to Cr(III) under a range of conditions in aqueous wastes.…”