Biodegradable Chelator-Assisted Washing and Stabilization of Arsenic-Contaminated Excavated Soils
2022
Rahman, Shafiqur | Jii, Naoyuki | Ni, Shengbin | Harada, Yasuhiro | Mashio, Asami S. | Begum, Zinnat Ara | Rahman, Ismail M. M. | Hasegawa, Hiroshi
Excavated soils from construction activities contaminated with geogenic arsenic (As) are increasing concerns owing to after disposal impact on ecosystem and human health. Washing remediation with chelators, e.g., ethylenediaminetetraacetic acid (EDTA), has been evaluated widely to treat contaminated soil. However, prolonged persistence and noxiousness of EDTA and its homologs evoke eco-concerns. Herein, the efficiency of ethylenediamine N,N'-disuccinic acid (EDDS) and 3-hydroxy-2,2'-imino disuccinic acid (HIDS) was evaluated to treat As-contaminated excavated soil as eco-compliant alternatives to EDTA. Besides, the post-treatment preferences for the chelator-washed suspension and soil residue were also assessed to immobilize eluted-As and suppress subsequent As-leaching, respectively. The efficiency of chelators toward the extraction of As was positively correlated with washing variables (e.g., washing time, solution pH, chelator concentration, liquid-to-soil ratio, and shaking speed) and optimized for maximum As-removal. Biodegradable chelator, HIDS (10 mmol L–¹, pH 11) showed better washing effectiveness among the tested chelators (duration, 12 h). The eluted-As in chelator-washed suspension was better immobilized with combined Feᴵᴵᴵ and Caᴵᴵ salt application blended with organic coagulant and polymer flocculant. Stabilization/solidification (S/S) of As-content in soil residues with cement-based binders was examined with or without the addition of Feᴵᴵᴵ. The cement amendments, except the ordinary Portland cement, Tuff-rock ace, and GS225, showed superior As-stabilization capability without Feᴵᴵᴵ-additives. The proposed combined remediation approach can be a green solution to recycle As-contaminated surplus soils for extensive geotechnical applications.
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