An Attempt to Remediation of Heavy-Metal-Contaminated Soil with Chelating Agent

Experiments to remove heavy metals such as lead, cadmium and copper from artificially contaminated soil were carried out using (S,S)-ethylenediaminedisuccinic acid (EDDS), N,N-dicarboxymethylglutamic acid (GLDA) and citric acid as chelating agents. The chelating agents were tested both separately and in admixture. Elution behavior in a batch operation was investigated by changing the concentration of chelating agents and the treatment time. Since the chelating agents have distinct acid dissociation constants and stability constants in metal ion-complexes, these values provide guidelines for selecting a suitable chelating agent. EDDS has a large stability constant, but dissociation takes place at high pH corresponding to metal hydroxide precipitation, making it difficult to use as a chelating agent for removing heavy metals from the contaminated soil. The mixture of GLDA and citric acid allows lead, cadmium and copper to be eluted at similar velocities and in similar amounts. Based on the batch elution experiments, column continuous tests were carried out to obtain the value of elution velocity. From the elution velocity, calculations and estimates were made as a model for the removal of heavy metals by heap leaching type treatment.