Chromate, Cr(VI), contamination in soil and groundwater poses serious threat to living organisms and environmental health worldwide. Sulphate green rust (GRSO4), 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 GRSO4 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 GRSO4) 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 GRSO4, (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 GRSO4. Overall, GRSO4 performed reasonably well, even at the highest tested flow rate, showing its versatility and suitability for Cr(VI) remediation applications in high flow environments.

中文翻译：

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硫酸盐铁锈和硫化的纳米级零价铁在沙子介质中固定Cr（VI）的研究：分批和柱研究。

铬酸盐，六价铬，土壤和地下水的污染严重威胁着全世界的生物和环境健康。硫酸盐生铁锈（GRSO4）是一种天然存在的混合价铁层状双氢氧化物，已显示出将Cr（VI）还原为难溶性Cr（III）的高度有效的特性，从而有望将其用作原位修复剂应用程序。但是，关于其在多孔地质介质（例如土壤和沉积物）中的固定效率知之甚少，最终将在该介质中使用该反应物。在这项研究中，我们测试了缺氧条件下GRSO4在石英砂固定床色谱柱系统（直径×长度= 1.4 cm×11 cm）中对Cr（VI）的去除。通过评估在不同进口Cr（VI）浓度（0.125–1 mM）下执行的突破曲线来确定Cr（VI）去除效率（相对于所添加GRSO4中可用的还原当量），该曲线代表了在以下位置发现的Cr（VI）浓度。被污染的部位，不同的流速（0.25-3 ml / min）和溶液的pH值（4.5、7和9.5）。结果表明（i）增加Cr（VI）入口浓度会大大降低GRSO4的Cr（VI）去除效率，（ii）流速对去除效率的影响较小，尽管在较高流速下该值往往较低，并且（ iii）与中性和碱性条件相比，在酸性pH条件下提高了六价铬的去除率。为了进行比较，在相同的色谱柱实验中，硫化的纳米级零价铁（S-nZVI）去除的Cr（VI）较低，表明S-nZVI与Cr（VI）的反应性比GRSO4慢得多。总体而言，即使在最高测试流速下，GRSO4仍表现良好，显示出其多功能性和适用于高流量环境中的Cr（VI）修复应用。