Electrochemical depassivation for recovering Fe(0) reactivity by Cr(VI) removal with a permeable reactive barrier system.

A new electrochemical permeable reactive barrier (Electro-PRB) system for removal of hexavalent chromium [Cr(VI)] using Fe(0) meshes was developed. Electro-PRB was found to be effective for electrochemical depassivation of Fe(0) to remove Cr(VI) during treatment. During initial treatment, Cr(VI) removal rates decreased with time, due to loss of Fe(0) reactivity by mineral fouling. After Fe(0) was passivated, electrochemical depassivation was introduced for different electrolysis times to recover Fe(0) reactivity. It was found that there was approximately 100.4-131.3% initial removal rate recovery, due to the electrochemical break down of precipitates on the Fe(0) surfaces. During the treatment, the decreasing pH and increasing oxidation-reduction Potential (ORP) of the effluent implied the passivation of Fe(0) surfaces. Scanning electron microscope analysis of acid-washed, electrochemically depassivated, and passivated Fe(0) confirmed the efficiency of Elecro-PRB in the recovery Fe(0) reactivity. The results indicate that the Electro-PRB system proposed here is capable of recovering the reactivity of Fe(0), which may prolong the operation of Cr(VI) removal processes.