School of Environmental Science and Engineering, Sun Yat-sen University, University Town, Guangzhou, China.
Chemosphere. 2012 Feb;86(8):809-16. doi: 10.1016/j.chemosphere.2011.11.042. Epub 2011 Dec 23.
Cr(VI) was often reported to oxidize soil organic matter at acidic environments due to its high ORP, probably thus changing cationic metal species bound to soil organic matter, and influencing their electro-migration patterns. However, such an effect on the electro-migration was not confirmed in most previous studies. Therefore, this study applied a fixed voltage direct current field on an aged electroplating contaminated clayed soil, with a special interest in the direct or indirect influence of Cr(VI) on the electro-migration of other coexisting metals. After 353 h electrokinetic process, 81% of Zn, 53% of Ni and 22% of Cu in the original soil were electro-migrated into the electrolyte, and most of the remaining concentrated near the cathode. The Cr(VI) oxidized some soil organic matter along its migration pathway, with a pronounced reaction occurred near the anode at low pHs. The resulting Cr(III) reversed its original movement, and migrated towards the cathode, leading to the occurrence of a second Cr concentration peak in the soil. Metal species analyses showed that the amount of metals bound to soil organic matter significantly decreased, while a substantial increase in the Cr species bound to Fe/Mn (hydro-)oxides was observed, suggesting an enhancement of cationic metal electro-migration by the reduction of Cr(VI) into Cr(III). However, the Cr(VI) may form some stable lead chromate precipitates, and in turn demobilize Pb in the soil, as the results showed a low Pb removal and an increase in its acid-extractable and residual fractions after electrokinetic remediation.
六价铬由于其高氧化还原电位（ORP），常被报道在酸性环境中氧化土壤有机质，可能因此改变与土壤有机质结合的阳离子金属物种，并影响它们的电动迁移模式。然而，在大多数先前的研究中，并没有证实这种对电动迁移的影响。因此，本研究在老化的电镀污染粘性土壤上施加固定电压直流电场，特别关注六价铬对其他共存金属电动迁移的直接或间接影响。在 353 小时的电动过程后，原始土壤中 81%的锌、53%的镍和 22%的铜被电动迁移到电解质中，大部分剩余的金属则集中在阴极附近。六价铬在其迁移路径上氧化了一些土壤有机质，在低 pH 值下靠近阳极处发生了明显的反应。由此产生的三价铬逆转了其原来的运动方向，向阴极迁移，导致土壤中出现第二个铬浓度峰值。金属物种分析表明，与土壤有机质结合的金属量显著减少，而与铁/锰（氢）氧化物结合的铬物种大量增加，这表明六价铬还原为三价铬增强了阳离子金属的电动迁移。然而，六价铬可能会形成一些稳定的铬酸铅沉淀，从而使土壤中的铅失活，因为结果显示电动修复后铅的去除率较低，其酸可提取和残留分数增加。
