Removal of Cr (VI) by electrochemical reduction

Removal of Cr (VI) from aqueous solutions by electrochemical reduction was studied using steel rods connected in unipolar mode. An aqueous solution of potassium dichromate was used as the model contaminant. Three different supporting electrolytes, viz. NaCl, NaNO3 and Na2SO4 were used during electrolysis. Only NaCl was found to be effective to arrest the passivation of electrodes by Cr (VI). The effect of initial concentration of Cr (VI) and current density on chromium removal was investigated. The rate of conversion of Cr (VI) to chromite is fast at higher current densities and the sludge is contaminated with more iron oxide. X-ray diffraction studies have revealed the formation of chromite (FeCr2O4) as main product in the electrochemically precipitated sludge. Though chromite is a predominant species other products such as Cr2O3, Fe2O3 are also formed during the process. At low current densities the electrochemical reduction of Cr (VI) was found to be initially under current control and turns to diffusion control after certain time. (c) 2007 Elsevier B.V. All rights reserved.