Sediments nearby harbors are dredged regularly, and the sediments require the stringent treatment to meet the regulations on reuse and mitigate the environmental burdens from toxic pollutants. In this study, FeCl3 was chosen as an extraction agent to treat marine sediment co-contaminated with Cu, Zn, and total petroleum hydrocarbons (TPH). In chemical extraction process, the extraction efficiency of Cu and Zn by FeCl3 was compared with the conventional one using inorganic acids (H2SO4 and HCl). Despite the satisfactory level for extraction of Cu (78.8%) and Zn (73.3%) by HCl (0.5 M) through proton-enhanced dissolution, one critical demerit, particularly acidified sediment, led to the unwanted loss of Al, Fe, and Mg by dissolution. Moreover, the vast amount of HCl required the huge amounts of neutralizing agents for the post-treatment of the sediment sample via the washing process. Despite a low concentration, extraction of Cu (70.1%) and Zn (69.4%) was done by using FeCl3 (0.05 M) through proton-enhanced dissolution, ferric-organic matter complexation, and oxidative dissolution of sulfide minerals. Ferric iron (Fe3+) was reduced to ferrous iron (Fe2+) with sulfide (S2-) oxidation during FeCl3 extraction. In consecutive chemical oxidations using hydrogen peroxide (H2O2) and persulfate (S2O82-), the resultant ferrous iron was used to activate the oxidants to effectively degrade TPH. S2O82- using FeCl3 solution (molar ratio of ferrous to S2O82- is 19.8-198.3) removed 42.6% of TPH, which was higher than that by H2O2 (molar ratio of ferrous to H2O2 is 1.2-6.1). All experimental findings suggest that ferric is effectively accommodated to an acid washing step for co-contaminated marine sediments, which leads to enhanced extraction, cost-effectiveness, and less environmental burden.
Keywords: Chemical oxidation; Chemical-enhanced washing; Ferric chloride; Oxidative dissolution; Sediment remediation.
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