Perchlorate Formation by Ozone Oxidation of Aqueous Chlorine/Oxy-Chlorine Species: Role of Cl_xO_x Radicals

摘要

The environmental occurrence of perchlorate (CIO_4~-) can be related to either natural or anthropogenic sources. Recent studies highlighted the ubiquitous occurrence of natural CIO_4~- in the environment including wet deposition in the United States. Limited studies have investigated potential mechanisms responsible for natural CIO_4~- production in the environment These studies have neither addressed the influence of relevant reaction conditions nor have they evaluated the rates of CIO_4~- production. The purpose of this study was to determine the comparative yields and rates of CIO_4~- production from O_3 mediated oxidation of CI~-, OCI~-, CIO_2~-, CIO_3~-, and CIO_2. The influence of reactant (O_3 and CIO_x~-) concentration and pH were evaluated. The comparative rate and efficiency of CIO, production is generally greater for higher oxidation states of CI (2.7 to 0.5% for CIO_2~- / CIO_2 and 0.02 to 0.005% for OCI /HOCI oxidation) with the notable exception of CIO_3~- which does not react with O_3. The very slow rate of CIO_4~- production from CI~- (～20 × 10~(-9) mM min~(-1)) even at elevated O_3 and CI~- concentrations implies negligible potential for anthropogenic CIO_4~- formation in process units of water/wastewater systems that use O_3 for treatment Based on results of CIO_4~- formation from tested CI species and available literature, we propose a potential formation pathway for CIO_4~- from CI~- with emphasis on the role of CIO_2 and higher oxy-chlorine radicals/intermediates (e.g., CI_2O_6) in its formation.