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Abstract: While the feasibility of using electrokinetics to decontaminate soils has been studied by several authors, the effects of soil composition on the efficiency of this method of decontamination has yet to be fully studied. This study focuses its attention on the effect of “calcite or carbonate” (CaCO3) on removal efficiency in electrokinetic soil remediation. Bench scale experiments were conducted on two soils: kaolinite and natural-soil of a landfill in Hamedan, Iran. Prescribed quantities of carbonates were mixed with these soils which were subsequently contaminated with zinc nitrate. After that, electrokinetic experiments were conducted to determine the efficiency of electrokinetic remediation. The results showed that an increase in the quantity of carbonate caused a noticeable increase on the contaminant retention of soil and on the resistance of soil to the contaminant removal by electrokinetic method. Because the presence of carbonates in the soil increases its buffering capacity, acidification is reduced, resulting in a decrease in the rate of heavy metal removed from the contaminant soil. This conclusion was validated by the evaluation of efficiency of electrokinetic method on a soil sample from the liner of a waste disposal site, with 28% carbonates. [Copyright &y& Elsevier]

Abstract: Wetting and water uptake by partly saturated smectite clays are expected when such clays are used as buffer material surrounding embedded high level nuclear waste (HLW). Nuclear waste canisters in a repository impose elevated temperatures on the surrounding smectite buffer material for thousands of years. Generally, the behaviour of clays is markedly influenced by the type of minerals present in the clay, the nature of the exchangeable ions, and the type of clay microstructure present. Because of the different microstructures of clay soils, the corresponding macrostructure will result in different hydraulic conductivities. The published literature reveals that research has failed to pay adequate attention to the effect of temperature on the re-structuring of the microstructure of smectite, specifically after the re-hydration process. Therefore, this paper is concerned with the impact of temperature on the re-structuring of microstructure and its consequences on smectite geo-environmental performance. The effect of temperature changes on the re-structuring of interlayer-distance, micropores, macropores and the sorption forces associated with the development of the micro- and macrostructures of smectite was examined. For this purpose, the variations of position and intensity of XRD major basal spacing of smectite have been studied over a range of different temperatures and re-hydration process. In addition, a series of buffering capacity tests, and permeability tests were performed to assess the impact of heat treatment on some of the geo-environmental properties of smectite. This paper illustrates different aspects of the influence of high temperature (up to 200 °C) on the performance of smectite in respect to the temperature effects on the re-structuring of the microstructures constituting the bulk smectite clay, as evidenced by the XRD response and permeability performance. The application of XRD analyses on smectite and homoionized Ca-smectite has shown that heating the smectite sample up to 200 °C will expel the water from its basic unit layers. This causes a reduction in the basal spacing of smectite. This reduced basal spacing might be mistaken for illite''s major basal spacing. Such a decrease in the position of major basal spacing of smectite after heat treatment is attributed to the reduction in distance between its basic unit layers. It is shown that this change in the microstructure of smectite has an irreversible impact on its cation exchange capacity and permeability. However, within the temperature range and conditions studied, the geo-environmental properties of smectite remain favorable. [Copyright &y& Elsevier]