Utilization of formic acid in nanoscale zero valent iron-catalyzed Fenton system for carbon tetrachloride degradation

Although the utilization of formic acid (FA) as a target compound for modeling the kinetic and mechanism in several Fenton processes has been previously reported, this study explored the potential of FA as an efficient hydroxyl radical (HO center dot) scavenger to generate reductive carbon dioxide radical (CO2 center dot-) for carbon tetrachloride (CT) degradation in nanoscale zero valent iron (nZVI) suspension in the presence and absence of oxidant. The results showed that the presence of 3.12 mM FA enhanced CT removal from 11.4% to 85.0% within 60 min in oxygenated 0.5 g/L nZVI suspension. Meanwhile, the presence of 3.12 mM FA improved Fe2+ elution by 5 folds under pH = 3. The generation of H2O2 in oxygenated nZVI suspension was also monitored. Hence, it was hypothesized that the rapid CT degradation in nZVI/FA system was initiated by reductive CO2 center dot- radical. In anaerobic nZVI/oxidant/FA system, CT degradation of 69.3% and 75.1% was achieved when using H2O2 or calcium peroxide (CP) as the oxidant, respectively. The addition of oxidant at 10 min reaction performed the best for CT removal as enough Fe2+ has been released after the dissolution of nZVI. These results demonstrated that a suitable dose of released Fe2+ was the key factor to enhance HO center dot and CO2 center dot- radical generation in nZVI/oxidant/FA system. This study provided new information about effective usage of nZVI and FA for enhancing CT degradation in heterogeneous Fenton system.