Electrochemical reduction of dilute chromate solutions on carbon felt electrodes

Abstract

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.

Electrochemically-mediated selective capture of heavy metal chromium and arsenic oxyanions from water

“…Not only does water oxidation at the anode provide the electrons for reduction of both PVF + and Cr(VI), but the protons produced are crucial in that they regulate the pH towards a range in which the cationic species are soluble (see the E -pH diagram in Fig. 2b ), and, conveniently, act as co-reagents in the reduction of Cr(VI) to Cr(III) species 30 , 31 . A charge balance on the electrochemical system for electrons transferred to the cathode for Cr(VI) and PVF + reduction, and from the anode, with the production of protons, gives a cathode current efficiency of around 100%; the calculated value of ~1.27 Coulomb transferred to the cathode, based on the assumption of full Fc reduction coupled with the equivalent Cr(VI) transformation, agreed well with the experimentally determined value of 1.24 Coulomb of charge transferred during regeneration (Supplementary Figure 9 ).…”

Effect of the Ultrasonic Irradiation on the Cr(VI) Electroreduction Process in a Tubular Electrochemical Flow Reactor

“…These effects make it possible that the insoluble oxide films of iron and chromium deposited on the electrodes surface 25 can be removed. Moreover, it is possible that localized pH zones on the electrode are reduced due to fluid motion that takes place at the electrode surface/solution, reducing the passivation and increasing the mass transfer 26 between the electrodes and the solution, which also enhanced the reduction rate of Cr(VI) on the cathode, 27 as shown in reaction 2. These effects caused the Cr(VI) reduction rate to increase, in comparison to the process without ultrasonic radiation.…”

Evaluation of the Effect of the Rotational Electrode Speed in an Electrochemical Reactor Using Computational Fluid Dynamics (CFD) Analysis

“…Electrochemical treatment is presented as an alternative method to achieve low Cr(VI) concentration 3,4 in wastewaters. This treatment has been carried out with different electrode materials, such as carbon felt electrodes 5 and polypyrrole-coated aluminum electrodes; however, the treatment time is too long and, in some cases, the achieved Cr(VI) concentration is quite high (∼50 mg/L). In this work, carbon steel electrodes were used, because they have the following advantages: the water treated is recyclable; a low amount of nonhazardous sludge is generated; and they contain chromite (FeCr 2 O 4 ), 6 which has refractory 7 Because of these process reactions, an oxide film grows on the surface of electrodes (passivation effect), reducing both the Fe(II) transfer to the bulk liquid and the process efficiency, increasing the energy consumption.…”