Electrochemical reduction of dilute chromate solutions on carbon felt electrodes

Carbon felt is a potential material for electrochemical reduction of chromates. Very dilute solutions may be efficiently treated due to its large specific surface area and high porosity. In this work, the up-scaling of this technology is investigated using a new type of separated cell and once-through flow of industrial rinse water. A significant enhancement of the process is obtained due to copper deposition during long-term operation. The co-deposition and re-solution of copper occurs depending on the inlet chromate concentration. When previously deposited copper is present a current-free reduction of chromate takes place resulting in current efficiencies apparently above 100%. Very high space time yields are obtained even for effluents at low concentration and optimised conditions (high flow rates and pH 2). The economic feasibility of the technology is also considered. Continuous, single-pass operation results in lower energy requirements than batch processing. The economic potential of the process is also evaluated in comparison with chemical detoxification of chromate. The operating costs for the electrochemical treatment of very dilute effluents on a carbon felt electrode are 30% lower than for the chemical method.