Column extraction of heavy metals from soils using the biodegradable chelating agent EDDS.

A possible remediation strategy for metal polluted soils is washing with chelants. Here, we compare the efficiency of batch and column extraction of Cu, Zn, and Pb from three soils using the biodegradable chelant EDDS. A total of 53-80% of Cu was extracted in batch and 18-26% in column extraction. For Zn, the extractability was 16-50% in batch and 20-64% in columns and for Pb 25-52 and 18-91%, respectively. Column leaching was therefore equally or better suited for Zn and Pb removal. The longer extraction time in the column resulted in more formations of Fe(III)EDDS by slow dissolution of iron oxides. Zn was uniformly washed from the column, while Cu and Pb were extracted in the top layers and deposited in the bottom layers, presumably by biodegradation of the metal-EDDS complexes and slow dissolution of iron oxides. Between 18 and 42% of the applied EDDS was lost through biodegradation after 7 weeks. In short time experiments, only 6% of EDDS was degraded. Using EDDS concentrations in excess of available heavy metals caused pronounced leaching of organic matter and clogging of the column. Our results prove that heap leaching using EDDS is a promising approach to reduce the heavy metal content of polluted soils.