DEVELOPMENT OF ELECTROCHEMICAL OXIDATION USING DIAMOND - COATED ELECTRODES FOR THE TREATMENT OF WASTE LUBRICANTS: PART 1 ASSESSMENT OF POTENTIAL

Electrochemical oxidation using electrodes coated with boron-doped diamond is a potential treatment process for waste oils contaminated with radioactive materials. If it could be applied to destroy the waste oils without resorting to the use of aggressive chemicals, it would facilitate the disposal of the radioactive contaminants. Accordingly AWE has examined the oxidation of various non-radioactive oils in a laboratory scale electrochemical cell equipped with diamond-coated electrodes with the objective of initiating the development of a disposal process. Before starting the experimental work with the oils, the equipment was commissioned with sucrose. Oxidation of at least 98% of the added sucrose was achieved. The current efficiency for the oxidation depended on the sucrose concentration. It was concluded that the rate of oxidation was limited by the applied current at high concentrations and by the rate of sucrose diffusion at low concentrations. The electrodes were found to lose their diamond coating during operation, but this did not appreciably affect the oxidation of sucrose. The process was capable of oxidising an aqueous emulsion of a cutting oil, but mineral oils resisted oxidation. It was thought that this might have been due to a poor contact between the oil suspended in the electrolyte and the electrode surface. Accordingly, a surfactant system was devised to emulsify the mineral oils, but this did not lead to a significant improvement in performance. When sucrose was added to the electrolyte containing an emulsified mineral oil, the oxidation of the sucrose was inhibited. This indicated that there could be some property of the emulsified mineral oil that inhibits the electro-oxidation of its organic components. Further work is required to understand the system before the process can be developed. It is expected that the activity of the electrodes will be influenced by the loss of the diamond coating, and that successful development of the technology will require a supply of stable