Thoming J, Kliem BK, Ottosen LM
Department of Environmental Science and Technology, Technical University of Hamburg-Harhurg, Hamburg, Germany.
Sci Total Environ. 2000 Oct 16;261(1-3):137-47. doi: 10.1016/s0048-9697(00)00636-7.
For remediation of soils contaminated with heavy metals, the electrodialytic remediation (EDR) method is a highly relevant method, see e.g. Hansen et al. (Hansen HK, Ottosen LM, Kliem BK, Villumsen A. Electrodialytic remediation of soils polluted with Cu, Cr, Hg, Pb, and Zn. J Chem Tech Biotechnol 1997;70:67-73). During the process the heavy metals are transferred to the pore water in dissolved form or attached to colloids and move within the applied electric field. The method is found to be useful in many soil types, but has its strength in fine-grained soils. It is exactly in such soils that other remediation methods fail. Four cell experiments were made in order to investigate how relevant the method is for a more sandy soil and if it is suitable for non-ionic heavy metals such as elemental mercury. The duration was 27 days for two of the experiments and two experiments lasted 54 days, and the mercury within the soil was initially 1200-1900 mg kg(-1), of which 84% was elemental Hg. To monitor the process the pseudo-total mercury concentration was distinguished between elemental mercury and non-metallic mercury species by thermodesorption. During the electrodialytic treatment an increase of the content of non-metallic mercury occurred and a corresponding decrease of the content of elemental mercury which indicates a transformation of the latter species into any other non-metallic species. Generally, oxidation of Hg by dissolved oxygen in a solution is kinetically inhibited and thus quite slow. The redistribution of Hg was closely connected to a decrease of soil pH during the experiments. This corresponds very well to the thermodynamic calculations from which it was found that a decrease in the pH of the soil will result in an increase in the oxidation rate of elemental Hg. Results from this investigation show that the electrodialytic remediation method alone is not efficient in situations with sandy soils containing elemental mercury. As a solution for this problem it is suggested to add chloride to the soil system. Chloride would act as a complexing agent avoiding precipitation and enhancing the dissolution of precipitates as well as elemental mercury.
对于修复受重金属污染的土壤，电渗析修复（EDR）方法是一种高度相关的方法，例如参见汉森等人（汉森HK、奥托森LM、克利姆BK、维卢姆森A。铜、铬、汞、铅和锌污染土壤的电渗析修复。《化学技术与生物技术杂志》1997年；70：67 - 73）。在该过程中，重金属以溶解形式转移到孔隙水中或附着在胶体上，并在施加的电场中移动。该方法在许多土壤类型中都很有用，但在细粒土壤中优势明显。恰恰是在这类土壤中，其他修复方法效果不佳。进行了四项细胞实验，以研究该方法对于砂质更多的土壤的相关性，以及它是否适用于诸如元素汞之类的非离子重金属。其中两项实验持续27天，另外两项实验持续54天，土壤中的汞初始含量为1200 - 1900毫克/千克（-1），其中84%为元素汞。为监测该过程，通过热脱附区分了元素汞和非金属汞物种的伪总汞浓度。在电渗析处理过程中，非金属汞含量增加，元素汞含量相应减少，这表明后一种物质转化为了其他非金属物种。一般来说，溶液中溶解氧对汞的氧化在动力学上受到抑制，因此相当缓慢。汞的重新分布与实验过程中土壤pH值的降低密切相关。这与热力学计算结果非常吻合，根据该计算发现土壤pH值的降低会导致元素汞氧化速率增加。本研究结果表明，仅电渗析修复方法在含有元素汞的砂质土壤情况下效率不高。针对这个问题，建议向土壤系统中添加氯化物。氯化物将作为络合剂，避免沉淀并增强沉淀物以及元素汞的溶解。
