Watts Mathew P, Coker Victoria S, Parry Stephen A, Pattrick Richard A D, Thomas Russell A P, Kalin Robert, Lloyd Jonathan R
School of Earth, Atmospheric and Environmental Sciences and Williamson Research Centre for Molecular Environmental Science, The University of Manchester, Manchester M13 9PL, UK.
Diamond Light Source, Chilton, Didcot, Oxfordshire OX11 ODE, UK.
Appl Geochem. 2015 Mar;54:27-42. doi: 10.1016/j.apgeochem.2014.12.001.
Highly reactive nano-scale biogenic magnetite (BnM), synthesized by the Fe(III)-reducing bacterium , 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 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.
通过铁（III）还原细菌合成的高活性纳米级生物源磁铁矿（BnM），被用于测试其修复与铬铁矿加工残渣（COPR）相关的碱性六价铬污染水体的潜力。将这种以去除水体中六价铬为目标的生物材料的性能，与一种合成替代品——纳米级零价铁（nZVI）进行了比较。高度污染的碱性地下水和COPR固体废物样本取自英国格拉斯哥的一个污染场地。在批量反应测试中，与处理化学复杂性较低的pH 12六价铬模型溶液相比，从地下水中去除六价铬时，BnM使去除率降低了约25%，nZVI使去除率降低了约50%。在模型六价铬溶液和受污染地下水实验中，纳米颗粒表面都发生了钝化，阻止了其可用电子与六价铬还原的完全耦合。为了研究这个过程，通过透射电子显微镜 - 能量色散X射线光谱（TEM - EDX）、X射线吸收光谱（XAS）和X射线光电子能谱（XPS）对反应后样品的表面进行了分析，证实了六价铬在纳米颗粒表面还原为溶解度较低的三价铬。在与地下水反应的样品中，还在纳米颗粒表面发现了钙、硅和硫的存在，这可能是钝化提前开始的原因。通过添加重量百分比不断增加的纳米颗粒来处理与水接触的固体COPR材料，通过添加⩾5% w/w的BnM或⩾1% w/w的nZVI，使水体中六价铬浓度降至检测限以下。对铬边缘的X射线吸收近边结构（XANES）分析表明，通过添加5% w/w的BnM或2% w/w的nZVI后，COPR中六价铬的百分比从26%降至最低为4 - 7%；添加量更高时无法进一步降低剩余的六价铬。处理后的材料通过与大气中的氧气重新平衡，可溶性六价铬的再迁移极小，大部分铬保留在固体部分。两种纳米颗粒都对与COPR相关的六价铬污染表现出相当大的修复能力，合成的nZVI比BnM表现出更高的反应活性。然而，生物合成的BnM也能够显著还原六价铬，并且在将其电子耦合到六价铬还原方面比nZVI表现出更高的效率。
