Impact of Peroxymonocarbonate on the Transformation of Organic Contaminants during Hydrogen Peroxide <i>in Situ</i> Chemical Oxidation

Abstract

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 <i>para</i> 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 <i>in situ</i> 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.