Evaluation of newly designed flushing techniques for on-site remediation of arsenic-contaminated excavated debris

Excavated debris (soil and rock) contaminated with geogenic arsenic (As) is an increasing concern for regulatory organizations and construction stakeholders. Chelator-assisted soil flushing is a promising method for practical on-site remediation of As-contaminated soil, offering technical, economic, and environmental benefits. Ethylenediaminetetraacetic acid (EDTA) is the most prevalent chelator used for remediating As-contaminated soil. However, the extensive environmental persistence and potential toxicity of EDTA necessitate the exploration of eco-compliant alternatives. In this study, the feasibility of the conventional flushing method pump-and-treat and two newly designed immersion and sprinkling techniques were evaluated at the laboratory scale (small-scale laboratory experiments) for the on-site treatment of As-contaminated excavated debris. Two biodegradable chelators, L-glutamic acid-N,N′-diacetic acid (GLDA) and 3-hydroxy-2,2′-iminodisuccinic acid (HIDS), were examined as eco-friendly substitutes for EDTA. Additionally, this study highlights a useful post-treatment measure to ensure minimal mobility of residual As in the chelator-treated debris residues. The pump-and-treat method displayed rapid As-remediation ( t , 3 h), but it required a substantial volume of washing solution (100 mL g −1 ). Conversely, the immersion technique demonstrated an excellent As-extraction rate using a relatively smaller washing solution (0.33 mL g −1 ) and shorter immersion time ( t , 3 h). In contrast, the sprinkling technique showed an increased As-extraction rate over an extended period ( t , 48 h). Among the chelators employed, the biodegradable chelator HIDS (10 mmol L −1 ; pH, 3) exhibited the highest As-extraction efficiency. Furthermore, the post-treatment of chelator-treated debris with FeCl 3 and CaO successfully reduced the leachable As content below the permissible limit.