Simultaneous remediation of co-contaminated soil by ball-milled zero-valent iron coupled with persulfate oxidation

Abstract

The problem of co-contaminated soil at e-waste dismantling sites is serious and constitutes a critical threat to human health and the ecological environment. Zero-valent iron (ZVI) has been proven to be effective in the stabilization of heavy metals and the removal of halogenated organic compounds (HOCs) from soils. However, for the remediation of co-contamination of heavy metals with HOCs, ZVI has disadvantages such as high remediation cost and inability to take into account both pollutants, which limits its large-scale application. In this paper, boric acid and commercial zero-valent iron (cZVI) were used as raw materials to prepare boric acid-modified zero-valent iron (B-ZVIbm) through a high-energy ball milling strategy. B-ZVIbm coupled with persulfate (PS) to achieve simultaneous remediation of co-contaminated soil. The synergistic treatment of PS and B-ZVIbm resulted in the removal efficiency of 81.3% for decabromodiphenyl ether (BDE209) and the stabilization efficiencies of 96.5%, 99.8%, and 28.8% for Cu, Pb, and Cd respectively in the co-contaminated soil. A series of physical and chemical characterization methods showed that the oxide coat on the surface of B-ZVIbm could be replaced by borides during ball milling. The boride coat facilitated the exposure of the Fe0 core, promoted the corrosion of ZVI and the orderly release of Fe2+. The analysis of the morphological transformation of heavy metals in soils revealed that most of the heavy metals in the exchangeable, carbonate-bound state were transformed into the residue state, which was the key mechanism for the remediation of heavy metal-contaminated soils with B-ZVIbm. The analysis of BDE209 degradation products showed that BDE209 was degraded to lower brominated products and further mineralized by ZVI reduction and free radical oxidation. In general, B-ZVIbm coupled with PS is a good recipe for synergistic remediation of co-contaminated soils with heavy metals and HOCs.