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

Abstract

It is not currently known if the widely used reaction of zero valent iron (ZVI) and Cr(VI) can be used in a permeable reactive barrier (PRB) to immobilise Cr leaching from hyper alkaline chromite ore processing residue (COPR). This study compares Cr(VI) removal from COPR leachate and chromate solution by ZVI at high pH. Cr(VI) removal occurs more rapidly from the chromate solution than from COPR leachate. The reaction is first order with respect to both [Cr(VI)] and the iron surface area, but iron surface reactivity is lost to the reaction.Buffering pH downwards produces little change in the removal rate or the specific capacity of iron until acidic conditions are reached. SEM and XPS analysis confirm that reaction products accumulate on the iron surface in both liquors, but that other surface precipitates also form in COPR leachate. Leachate from highly alkaline COPR contains Ca, Si and Al that precipitate on the iron surface and significantly reduce the specific capacity of iron to reduce Cr(VI). This study suggests that although Cr (VI) reduction by ZVI will occur at hyper alkaline pH, other solutes present in COPR leachate will limit the design life of a PRB. 4

Reductive sequestration of chromate by hierarchical FeS@Fe0 particles

“…Figure 5a shows performance of Cr(VI) uptake by FeS@Fe 0 particles at various initial pHs in the range of 3.0~11.0. Overall, the removal rate of Cr(VI) increases with decreasing pH, similar as previously described in different nFe 0 systems (Hoch et al 2008, Lv et al 2014, Fuller et al 2013. Complete removal of Cr(VI) can be achieved under acidic conditions.…”

Progress in Understanding the Mechanism of CrVI Removal in Fe0-Based Filtration Systems

“…For instance, XPS analysis carried out on reacted Fe-Ni nanoparticles revealed that ratio between adsorbed Cr III and Cr VI was 7.87 [92]. Therefore, in addition to the heterogeneous reduction mechanism occurring at the surface of Fe 0 , dissolved Fe II and H/H 2 , both products of Fe 0 corrosion, may also be involved in the mechanism of Cr VI removal in Fe 0 /H 2 O system [62,67,86,91,[102][103][104][105][106][107][108]. Even though these reduction pathways have been suggested much earlier by several pioneering works in this field [15,18,21], they were often overlooked in articles describing the removal of Cr VI with Fe 0 -based PRBs, as well as in numerous more recent papers.…”

Negative impact of oxygen molecular activation on Cr(VI) removal with core–shell Fe@Fe2O3 nanowires

“…The reductive reactions of Cr(VI) by Fe 0 and Fe(II) are thermodynamically favorable (Eqs. (1)(2)(3)(4)) in both acidic conditions (Eq. (5)) and neutral pH conditions (Eq.…”

“…environments. Cr(VI) species in aquatic systems with strong oxidizing ability are highly soluble, mobile, and toxic and has drawn worldwide attentions [1][2][3]. In contrast, Cr(III) species are relatively stable, less-toxic, and have low solubility (<10 −5 M) in water over a wide pH range.…”

“…Nanoscale zero-valent iron (nZVI) with large surface area and electron donor ability offered great potentials for its in-situ immobilization of chromium-contaminated groundwater through simultaneous adsorptive and reductive sequestrations [1,2,5,[10][11][12][13]. According to nZVI's environmental benignancy, Cr(VI) sequestration by nZVI has been widely studied [1,[8][9][10][11][14][15][16][17][18].…”