Developments of electrochemistry in Environmental Technology
Uses of electrochemical systems in environmental control technology are described for the removal and separation of metals from solution and the destruction of dye molecules in effluents. A novel concentrator cell system for the removal of lead and cadmium from solution is developed. The operation of this system permits the pH-independent recovery of metals from solution by electrodeposition. The formation of complexes with suitable ligands is exploited to achieve the separation of metals by electrochemical methods. The separations of tin, lead and indium from each other, the separation of nickel from cobalt and the separation of copper and palladium from cobalt are used to illustrate the benefits of complex formation. A three-compartment electrodialysis cell for removal of nickel from cobalt exploiting the greater stability of the nickel-EDTA complex compared with the Co-EDTA complex is described. Efficient removal of nickel from cobalt can be achieved but there is a compromise between cobalt purity and the percentage of cobalt transferred to the catholyte chamber for recovery. The anodic oxidation of a number of dye molecules including methylene blue, acid blue 25, reactive blue 2 and reactive blue 15 in chloride solution has been studied. The anodic oxidation of methylene blue results in the formation of seven neutral and two charged intermediates. The main intermediate is identified by X-ray diffraction crystal structure determination and accurate mass spectrometry as the novel compound 4,6-dichloro-7-dimethylamino-3H-phenothiazin-3 -one, (C14HjoCI2N20S) formed by replacement of one of the diirnethylamino groups of methylene blue with oxygen accompanied by regiospecific chlorination of the carbocylic system. The mass spectra of other intermediates formed are interpreted in terms of this structure. An electroadsorption system combining adsorption and electrolytic processes to achieve the elimination of the chlorinated compounds that are formed during the electro-oxidation of methylene blue is also reported.