Remediation of Heavy-Metal-Contaminated Soil with Chelating agent and Treatment of Waste Solution

概要

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Experiments were performed to elute and remove contaminants from artificially contaminated soil using chelating agents such as citric acid, which exists in nature, and N,N-dicarboxymethyl glutamic acid(GLDA), which is biodegradable. The soil was artificially contaminated with heavy metals such as lead, copper, and cadmium. The most effective conditions for batch elution operation using citric acid alone were determined to be 0.1 mol/dm3, pH 3-4, and 30 min shaking time. Because the elution of Pb tended to be slower than that of the other heavy metals, it was determined that this process could be accelerated by adding GLDA to the citric acid. This mixed chelating agent was then used in the column continuous test which was carried out in order to obtain the elution speed and flow amount required to satisfy the environmental quality standard values regarding contaminated soil. Based on the elution speed obtained from the column operation, guidelines for designing a heap leaching type treatment of contaminated soil are proposed. Treatment of waste solution was investigated using sulfide and hydroxide precipitation methods to remove heavy metal ions. Metal sulfide precipitation method is superior for the removal of metal ions in the presence of citric acid and there seems possibility to reuse chelating agents after removal of metal ions.