Evaluation of formation of solubility-limited solid phase of calcium- and magnesium-bearing immobilizers by microscopic observation and element mapping analysis.

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  • 不溶化処理後のカルシウム系・マグネシウム系資材の固相観察および元素マッピング分析による溶解度制限固相の評価

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<p>To estimate the lifetime of an immobilizer used for countermeasures for disposing of excavated rocks containing hazardous trace elements such as arsenic, the appropriate method for evaluating the solubility of the immobilizer is required. In our previous study, the solubility-limiting solid phase that governs the solubility of the immobilizer, was assumed based on the saturation index (SI) of each mineral calculated using water chemistry of the leachate obtained by batch immobilization experiments. In this study, the formation of the solubility-limiting solid phases was confirmed by electron microscopic (EPMA) observation and elemental mapping analysis by using the residues of batch immobilization experiments. The results observed by EPMA showed that brucite as a solubility-limiting solid phase of Mg-bearing immobilizers, formed surrounding magnesium oxide. In case of using Ca-bearing immobilizers containing Mg, Mg ion was sorbed on calcite and dolomite-like secondary mineral was formed, which could behave as the solubility-limiting solid phase. These results indicate that the prediction of the solubility-limiting solid phase by SI based on the results of batch immobilization experiments was also consistent with and supported by the results of microscopic observations and elemental mapping analysis of the solid phase.</p>

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