Reduction and immobilization of chromate in chromite ore processing residue with nanoscale zero-valent iron

Abstract

Keywords:Chromite ore processing residue (COPR) Nanoscale zero-valent iron (nZVI) X-ray absorption near edge structure (XANES) spectroscopy Chromate leachability Speciation a b s t r a c t Chromite ore processing residue (COPR) poses a great environmental and health risk with persistent Cr(VI) leaching. To reduce Cr(VI) and subsequently immobilize in the solid matrix, COPR was incubated with nanoscale zero-valent iron (nZVI) and the Cr(VI) speciation and leachability were studied. Multiple complementary analysis methods including leaching tests, X-ray powder diffraction, X-ray absorption near edge structure (XANES) spectroscopy, and X-ray photoelectron spectroscopy (XPS) were employed to investigate the immobilization mechanism. Geochemical PHREEQC model calculation agreed well with our acid neutralizing capacity experimental results and confirmed that when pH was lowered from 11.7 to 7.0, leachate Cr(VI) concentrations were in the range 358-445 mg L −1 which contributed over 90% of dissolved Cr from COPR. Results of alkaline digestion, XANES, and XPS demonstrated that incubation COPR with nZVI under water content higher than 27% could result in a nearly complete Cr(VI) reduction in solids and less than 0.1 mg L −1 Cr(VI) in the TCLP leachate. The results indicated that remediation approaches using nZVI to reduce Cr(VI) in COPR should be successful with sufficient water content to facilitate electron transfer from nZVI to COPR.

Chromate Reduction in Highly Alkaline Groundwater by Zerovalent Iron: Implications for Its Use in a Permeable Reactive Barrier

“…22,23 Much work has already been done to investigate the use of ZVI and nZVI to reduce Cr(VI) over the common environmental pH range of mildly acidic to moderately alkaline conditions. [22][23][24][25][26][27] In acidic conditions the reaction is relatively fast, but the rate of reaction is slower in neutral and mildly alkaline conditions. 28 The primary objective of this study is to extend understanding of the reaction between ZVI and Cr(VI) to alkaline conditions characteristic of COPR leachate.…”

Simultaneous removal of trichloroethylene and hexavalent chromium by green synthesized agarose-Fe nanoparticles hydrogel

“…4(h) presents two signals for Cr 2p 1/2 and Cr 2p 3/2 centering at 586.6 and 576.9 eV, respectively. According to the literature [38], spin-orbit splitting of 9.7-9.9 eV and 9.2-9.4 eV are the characteristic parameters of the Cr(III) and Cr(VI) compounds, respectively, and the Cr (VI) compounds have higher binding energy (579.0-579.8 eV). Herein, the spin-orbit splitting of 9.7 eV and no higher binding energy revealed the reduction of Cr(VI) to Cr(III) was complete.…”

Field methods for rapidly characterizing paint waste during bridge rehabilitation

“…These processes cannot be quantitatively captured in the statistical modeling effort. In addition, although Cr(III) is the dominant form leached, a small percent may be present as Cr(VI) (Peterson et al, 1996(Peterson et al, , 1997Du et al, 2012). Again as a result, these precipitation and complexation reactions were poorly captured in the statistical model.…”