(86g) The Formation of Peroxymonocarbonate (HCO4-) and Its Impact on the Degradation of Organic Contaminants during Hydrogen Peroxide (H2O2) in Situ chemical Oxidation (ISCO)

Hydrogen peroxide (H₂O₂) reacts with iron and manganese adsorbed on surfaces and on minerals to produce hydroxyl radical and other reactive oxygen species during in situ chemical oxidation of contaminated groundwater. Under the conditions used for remediation, high concentrations of hydrogen peroxide (e.g. up to ~10 M) are encountered. Using ¹³C NMR we have shown that under these conditions, an alternative pathway for H₂O₂ loss occurs in which H₂O₂ reacts with HCO₃^- to produce HCO₄^-, at a HCO₃^- concentration of 10~1000 mM, HCO₄^- was formed and quickly reacted with phenol to produce di- and tri-hydroxyl phenols. The rate of transformation of phenol was determined by the concentration of HCO₃^-. HCO₄^- also reacted with substituted phenols in an electrophilic behavior. Results of this study indicate that HCO₄^- is a potentially important but previously unrecognized oxidative species generated during H₂O₂ ISCO and that it may be possible to adjust treatment conditions to enhance its formation as a means of accelerating rates of contaminant removal.