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

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 CaO2/Fe(II)/MeOH process is a highly promising technique for the remediation of CT-contaminated groundwater.