Impact of Peroxymonocarbonate on the Transformation of Organic Contaminants during Hydrogen Peroxide in Situ Chemical Oxidation

Under the conditions employed when in situ chemical oxidation is used for contaminant remediation, high concentrations of H₂O₂ (e.g., up to ~10 M) are typically present. Using ¹³C NMR, we show that in carbonate-rich systems, these high concentrations of H₂O₂ result in a reaction with HCO₃ ^- to produce peroxymonocarbonate (HCO₄ ^-). After formation, HCO₄ ^- reacts with phenol to produce di- and tri-hydroxyl phenols. HCO₄ ^- reacts with substituted phenols in a manner consistent with its electrophilic character. Exchanging an electron-donating substituent in the para position of a phenolic compound with an electron-withdrawing group decreased the reaction rate. Results of this study indicate that HCO₄ ^- is a potentially important but previously unrecognized oxidative species generated during H₂O₂ in situ Chemical Oxidation (ISCO) that selectively reacts with electron-rich organic compounds. Under conditions in which HO· formation is inefficient (e.g., relatively high concentration of HCO₃ ^-, low total Fe and Mn concentrations), the fraction of the phenolic compounds that are transformed by HCO₄ ^- could be similar to or greater than the fraction transformed by HO·. It may be possible to adjust treatment conditions to enhance the formation of HCO₄ ^- as a means of accelerating rates of contaminant removal.