Electrochemical Oxidation of Carboxylic Acids in the Presence of Manganese Chloride

Carboxylic acids are the main byproducts in effluents after treating source pollutants with advanced oxidation processes (AOPs). This work developed a feasible electrochemical method for mineralizing oxalic acid and citric acid (50 ppm, pH(i); = 3). A reactor was mounted with RuO2/IrO2 coated Ti-DSA electrodes (titanium dimensional stable anode). The selected chloride electrolytes (NaCl, MgCl2 and MnCl2, [Cl-] = 20 mM) mineralized completely oxalic acid through the production of active chlorine. However, the highest total organic carbon (TOC) removal efficiency was obtained using MnCl2 and was aided by the MnO2 deposited electrochemically on the anode. In the chlorine-free electrolysis process, the performance in terms of TOC removal of the Ti-DSA electrodes that had MnO2 on the anode depended on the electrical conditions. Without electricity, MnO2 directly mineralized oxalic acid; with electricity, TOC removal from the citric acid solution improved substantially. The changes in the Mn2+ concentration suggest that MnO2 dissolved by organic compounds could be recovered and reused through formation of electrolytic manganese dioxide (EMD). (C) 2013 The Electrochemical Society. All rights reserved.