Mechanism of carbon tetrachloride reduction in ferrous ion activated calcium peroxide system in the presence of methanol.

Highlights • CT degradation in CaO 2 /Fe(II) system is promoted by MeOH addition. • The leading species for CT degradation are O 2 −, CO 2 −. • CHCl 3 , C 2 Cl 4 , and C 2 Cl 6 were the intermediates of CT. • A reduction mechanism for CT degradation was proposed. • Efficient removal of CT in groundwater was attained. Abstract This study investigated the reductive initiation for the depletion of highly oxidized/perhalogenated pollutants, specifically the degradation of carbon tetrachloride (CT) was induced by adding methanol (MeOH) into a ferrous ion (Fe(II)) activated calcium peroxide (CaO 2) system. The results indicated that CT could be completely degraded within 20 min at CaO 2 /Fe(II)/MeOH/CT molar ratio of 30/40/10/1 in this system. Scavenging tests suggested that both superoxide radical anion (O 2 −) and carbon dioxide radical anion (CO 2 −) were predominant reactive species responsible for CT destruction. Hydroxymethyl radicals (CH 2 OH), an intermediate in the transformation of MeOH, could also initiate CT degradation by reducing C Cl bond. GC/MS analysis identified CHCl 3 , C 2 Cl 4 , and C 2 Cl 6 as the intermediates accompanied by CT destruction, and a reduction mechanism for CT degradation was proposed accordingly. In addition, the impact of solution matrix and initial solution pH were evaluated, and the results showed that Cl−, NO 3 −, and HCO 3 − had adverse effects on CT degradation. Moreover, the alkaline condition was unfavorable to CT depletion. In conclusion, the results obtained in the actual groundwater tests encouragingly demonstrated that the CaO 2 /Fe(II)/MeOH process is a highly promising technique for the remediation of CT-contaminated groundwater. [ABSTRACT FROM AUTHOR]