Effects of remediation train sequence on decontamination of heavy metal-contaminated soil containing mercury

Abstract

When a contaminated site contains pollutants including both nonvolatile metals and Hg, one single remediation technology may not satisfactorily remove all contaminants. Therefore, in this study, chemical extraction and thermal treatment were combined as a remediation train to remove heavy metals, including Hg, from contaminated soil. A 0.2 M solution of ethylenediamine tetraacetic acid (EDTA) was shown to be the most effective reagent for extraction of considerable amounts of Cu, Pb, and Zn (>50%). Hg removal was ineffective using 0.2 M EDTA, but thermogravimetric analysis suggested that heating to 550°C with a heating rate of 5°C/min for a duration of 1 hr appeared to be an effective approach for Hg removal. With the employment of thermal treatment, up to 99% of Hg could be removed. However, executing thermal treatment prior to chemical extraction reduced the effectiveness of the subsequent EDTA extraction because nonvolatile heavy metals were immobilized in soil aggregates after the 550°C treatment. The remediation train of chemical extraction followed by thermal treatment appears to remediate soils that have been contaminated by many nonvolatile heavy metals and Hg.

Implications

A remediation train conjoining two or more techniques has been initialized to remove multiple metals. Better understandings of the impacts of treatment sequences, namely, which technique should be employed first on the soil properties and the decontamination efficiency, are in high demand. This study provides a strategy to remove multiple heavy metals including Hg from a contaminated soil. The interactions between thermal treatment and chemical extraction on repartitioning of heavy metals was revealed. The obtained results could offer an integrating strategy to remediate the soil contaminated with both heavy metals and volatile contaminants.

Acknowledgment

The authors greatly acknowledge Dr. Gregory Jacobson from the University of Waikato for his help correcting syntax errors and refining this paper.

Additional information

Notes on contributors

Zeng-Yei Hseu

Zeng-Yei Hseu is a professor at the Department of Environmental Science and Engineering, National Pingtung University of Science and Technology, Taiwan.

Yu-Tuan Huang

Yu-Tuan Huang is a doctoral student at the Department of Earth and Ocean Sciences, University of Waikato, New Zealand.

Hsing-Cheng Hsi

Hsing-Cheng Hsi is an associate professor at the Graduate Institute of Environmental Engineering, National Taiwan University, Taiwan.