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>Biogenic nano-magnetite and nano-zero valent iron treatment of alkaline Cr(VI) leachate and chromite ore processing residue
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Biogenic nano-magnetite and nano-zero valent iron treatment of alkaline Cr(VI) leachate and chromite ore processing residue
Highly reactive nano-scale biogenic magnetite (BnM), synthesized by the Fe(III)-reducing bacterium Geobacter sulfurreducens, was tested for the potential to remediate alkaline Cr(VI) contaminated waters associated with chromite ore processing residue (COPR). The performance of this biomaterial, targeting aqueous Cr(VI) removal, was compared to a synthetic alternative, nano-scale zero valent iron (nZVI). Samples of highly contaminated alkaline groundwater and COPR solid waste were obtained from a contaminated site in Glasgow, UK. During batch reactivity tests, Cr(VI) removal from groundwater was inhibited by ∼25% (BnM) and ∼50% (nZVI) when compared to the treatment of less chemically complex model pH 12 Cr(VI) solutions. In both the model Cr(VI) solutions and contaminated groundwater experiments the surface of the nanoparticles became passivated, preventing complete coupling of their available electrons to Cr(VI) reduction. To investigate this process, the surfaces of the reacted samples were analyzed by TEM-EDX, XAS and XPS, confirming Cr(VI) reduction to the less soluble Cr(III) on the nanoparticle surface. In groundwater reacted samples the presence of Ca, Si and S was also noted on the surface of the nanoparticles, and is likely responsible for earlier onset of passivation. Treatment of the solid COPR material in contact with water, by addition of increasing weight % of the nanoparticles, resulted in a decrease in aqueous Cr(VI) concentrations to below detection limits, via the addition of ⩾5% w/w BnM or ⩾1% w/w nZVI. XANES analysis of the Cr K edge, showed that the % Cr(VI) in the COPR dropped from 26% to a minimum of 4–7% by the addition of 5% w/w BnM or 2% w/w nZVI, with higher additions unable to reduce the remaining Cr(VI). The treated materials exhibited minimal re-mobilization of soluble Cr(VI) by re-equilibration with atmospheric oxygen, with the bulk of the Cr remaining in the solid fraction. Both nanoparticles exhibited a considerable capacity for the remediation of COPR related Cr(VI) contamination, with the synthetic nZVI demonstrating greater reactivity than the BnM. However, the biosynthesized BnM was also capable of significant Cr(VI) reduction and demonstrated a greater efficiency for the coupling of its electrons towards Cr(VI) reduction than the nZVI.
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机译：测试了由还原Fe（III）的细菌Geobacter sulfreducens合成的高反应性纳米级生物磁铁矿（BnM）修复与铬铁矿矿石加工残留物（COPR）相关的碱性Cr（VI）污染水的潜力。将该生物材料的目标性能为去除水中的Cr（VI）与合成的替代纳米级零价铁（nZVI）进行了比较。高污染的碱性地下水和COPR固体废物的样品是从英国格拉斯哥的一个污染场地获得的。在批处理反应性测试中，与处理化学性质较弱的模型pH 12 Cr（VI）溶液相比，从地下水中去除Cr（VI）的能力被抑制了约25％（BnM）和约50％（nZVI）。在模型Cr（VI）溶液和受污染的地下水实验中，纳米颗粒的表面均被钝化，从而阻止了其可用电子与Cr（VI）还原的完全耦合。为了研究该过程，通过TEM-EDX，XAS和XPS对反应样品的表面进行了分析，确认了Cr（VI）还原为纳米颗粒表面上溶解度较低的Cr（III）。在与地下水反应的样品中，纳米颗粒的表面上还注意到了Ca，Si和S的存在，这很可能是造成钝化较早发生的原因。通过添加重量百分比增加的纳米颗粒来处理与水接触的固态COPR材料，通过添加⩾5％w / w BnM或⩾将水的Cr（VI）浓度降低至检测极限以下。 1％w / w nZVI。 XANES对Cr K边缘的分析表明，通过添加5％w / w BnM或2％w / w nZVI，COPR中Cr（VI）的百分比从26％降至最低4-7％。较高的添加量无法减少剩余的Cr（VI）。经处理的材料通过与大气中的氧气重新平衡，可溶的Cr（VI）的重新迁移最少，而大部分Cr保留在固体馏分中。两种纳米颗粒均具有相当大的补救COPR相关的Cr（VI）污染的能力，合成的nZVI具有比BnM更高的反应活性。但是，生物合成的BnM还具有显着的Cr（VI）还原能力，并且其电子向Cr（VI）还原的耦合效率高于nZVI。
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