Digiacomo Flavia, Tobler Dominique J, Held Thomas, Neumann Thomas
ARCADIS Germany GmbH, Griesbachstraße 10, 76185, Karlsruhe, Germany.
Institute of Applied Geosciences, Karlsruhe Institute of Technology, Adenauerring 20b, Building 50.40, 76131, Karlsruhe, Germany.
Geochem Trans. 2020 Aug 14;21(1):8. doi: 10.1186/s12932-020-00073-9.
Chromate, Cr(VI), contamination in soil and groundwater poses serious threat to living organisms and environmental health worldwide. Sulphate green rust (GR), a naturally occurring mixed-valent iron layered double hydroxide has shown to be highly effective in the reduction of Cr(VI) to poorly soluble Cr(III), giving promise for its use as reactant for in situ remedial applications. However, little is known about its immobilization efficiency inside porous geological media, such as soils and sediments, where this reactant would ultimately be applied. In this study, we tested the removal of Cr(VI) by GR in quartz sand fixed-bed column systems (diameter × length = 1.4 cm × 11 cm), under anoxic conditions. Cr(VI) removal efficiency (relative to the available reducing equivalents in the added GR) was determined by evaluating breakthrough curves performed at different inlet Cr(VI) concentrations (0.125-1 mM) which are representative of Cr(VI) concentrations found at contaminated sites, different flow rates (0.25-3 ml/min) and solution pH (4.5, 7 and 9.5). Results showed that (i) increasing Cr(VI) inlet concentration substantially decreased Cr(VI) removal efficiency of GR, (ii) flow rates had a lower impact on removal efficiencies, although values tended to be lower at higher flow rates, and (iii) Cr(VI) removal was enhanced at acidic pH conditions compared to neutral and alkaline conditions. For comparison, Cr(VI) removal by sulphidized nanoscale zerovalent iron (S-nZVI) in identical column experiments was substantially lower, indicating that S-nZVI reactivity with Cr(VI) is much slower compared to GR. Overall, GR performed reasonably well, even at the highest tested flow rate, showing its versatility and suitability for Cr(VI) remediation applications in high flow environments.
土壤和地下水中的铬酸盐（Cr(VI)）污染对全球生物和环境健康构成严重威胁。硫酸绿锈（GR）是一种天然存在的混合价态铁层状双氢氧化物，已证明其在将Cr(VI)还原为难溶性Cr(III)方面非常有效，有望用作原位修复应用的反应物。然而，对于这种反应物最终将应用的多孔地质介质（如土壤和沉积物）内部的固定化效率知之甚少。在本研究中，我们在缺氧条件下，在石英砂固定床柱系统（直径×长度 = 1.4 cm×11 cm）中测试了GR对Cr(VI)的去除效果。通过评估在不同进水Cr(VI)浓度（0.125 - 1 mM，代表污染场地中发现的Cr(VI)浓度）、不同流速（0.25 - 3 ml/min）和溶液pH值（4.5、7和9.5）下进行的穿透曲线，确定了Cr(VI)去除效率（相对于添加的GR中可用的还原当量）。结果表明：（i）增加进水Cr(VI)浓度会大幅降低GR对Cr(VI)的去除效率；（ii）流速对去除效率的影响较小，尽管在较高流速下数值往往较低；（iii）与中性和碱性条件相比，酸性pH条件下Cr(VI)的去除得到增强。为作比较，在相同柱实验中，硫化纳米零价铁（S-nZVI）对Cr(VI)的去除率要低得多，这表明S-nZVI与Cr(VI)的反应性比GR慢得多。总体而言，即使在测试的最高流速下，GR的表现也相当不错，显示出其在高流量环境中用于Cr(VI)修复应用的通用性和适用性。
