Modeling an electrochemical process to remove Cr(VI) from rinse-water in a stirred reactor

Experimental studies were developed in a batch reactor (16 dm3), to obtain the kinetic model of Cr(VI) removal by means of an electrochemical process. An overall kinetic model was obtained and experimentally validated in a continuous stirred electrochemical reactor (16 dm3) with synthetic and industrial wastewater. To develop the mathematical model of the continuous reactor in relation to the Cr(VI) and Fe(II) concentration in the solution, a classical mass balance procedure was performed. The Cr(VI) concentration in the electrochemically-treated waters was less than 0.5 mg/dm3. In the electrochemical process the Cr(VI) reduction is caused by the Fe(II) released from the anode due to the electric current applied, by the Fe(II) released for the dissolution (corrosion) of the electrodes due to the acidic media, and by reduction at the cathode. During the process, reduction from Fe(III) to Fe(II) occurs. All of these different reactions cause a diminution in the quantity of sludge generated. Finally, it was found that due to the slow rate of reduction of Cr(VI) during the first part of the process it is necessary to develop a method of control to apply the process in a continuous industrial system.