Electrochlorination of pyridine in ultrahigh salinity water: Reactive species and mechanism

The reactive species of electrochlorination (E-Cl) in the ultrahigh salinity water (1 %-15 % NaCl) were investigated using pyridine (Pyr) as the model pollutant. No • OH signal can be detected for the E-Cl process in the ultrahigh salinity water. The free radicals are dominantly composed of the reactive chlorine species (RCS) such as Cl • , Cl 2 •− and ClO • . Moreover, the steady concentrations of Cl 2 •− and ClO • , and thus their contributions to the Pyr removal, are higher than that of Cl • . In 15 % NaCl solution, at the current density lower than 3 mA cm −2 , the RCS cannot be generated. Compared with the RCS species, the contribution of free chlorine (FC) to the Pyr removal is slightly higher due to the abundant FC generated during the E-Cl process. However, the reactivity of RCS to Pyr is much higher than that of FC. The second-order reaction rate constants of Cl • , Cl 2 •− , ClO • and FC with Pyr are 4.1 × 10 9 M −1 s −1 , 8.0 × 10 6 M −1 s −1 , 2.2 × 10 5 M −1 s −1 and 1.9 × 10 −3 M −1 s −1 , respectively. Among the background substances, SO 4 2- ions shows the significantly inhibitory effect on the Pyr degradation. Furthermore, the degradation pathway of Pyr was also proposed in the study.