Anodic oxidation of tartaric and oxalic acids in the presence of halides

Several methods, biological, chemical, physicochemical, can be used to detoxify industrial wastewaters containing organic pollutants. In particular, during the last decade, electrochemical incineration has drawn much attention, often affording interesting alternatives to already existent processes. The electrochemical abatement of organic pollutants in a given wastewater can be carried out directly or indirectly, by electrochemical oxidation. The main goal in this process is the complete oxidation of the organic substrate to CO2, or its conversion to biocompatible compounds. For the optimization of the electrochemical oxidation method, the role of the anodic material is clearly important; traditional electrode materials, such as Pt, PbO2, IrO2, Pt-SnO2 and Ti/SnO2-Sb2O5, have been taken into consideration. More recently, highly boron-doped diamond (BDD) electrodes have been also suggested, potentially representing an important alternative, because of their very high oxygen overpotential. Aim of the present communication is to show experimental results, and related conclusions, on the electrochemical oxidation of tartaric acid (TA), which has been carried out at Ti/PbO2, Pt and BDD electrodes, as a function of process parameters like current density and temperature. TA complete mineralization has been achieved only at BDD and PbO2, faradaic efficiency being higher at the latter electrode. At Pt, the electroxidation was found to be extremely slow, both in acidic and alkaline media. The experimental evidence has shown that the main factor is the interaction of the organic substrate and hydroxyl radicals with the electrode surface. In the case of oxalic acid, better results were obtained at the Pt electrode, supporting the idea that the interaction of organic substrate with the electrode surface must be considered.