Destruction of EDTA by mediated electrochemical oxidation process: Monitoring by continuous CO 2 measurements

Abstract

The mediated electrochemical oxidation (MEO) process with cerium(IV) in nitric acid as the oxidizing medium was employed for the destruction of ethylenediaminetetraacetic acid (EDTA) in batch and continuous feeding modes. A complete mineralization of EDTA to CO 2 and water was achieved. The system parameters studied were the temperature (343, 353 and 368 K), concentration of nitric acid (2, 3 and 4 M), Ce(IV) concentration (0.7–0.95 M), aqueous EDTA concentration (67–268 mM) , flow rate of EDTA addition (3.0–7.5 ml/min), and feeding time (30 min and 2 h). The batch process CO 2 pattern clearly showed two distinct kinetic regimes. Accordingly the overall CO 2 formation rate constants were evaluated for fast and slow processes using pseudo first-order kinetics. In case of continuous organic feeding, the CO 2 formation rate constant was obtained using a new proposed mathematical procedure based on geometrical progression. The only parameter in the calculations was the first-order rate constant. The theoretical CO 2 evolution pattern was fitted on to the experimental data to obtain the formation rate constants. The activation energy was calculated based on the CO 2 formation constants and presented. The application of mathematical procedure predicted a steady-state attainment of CO 2 evolution for the destruction process during a long-term organic feeding and observed experimentally.