A novel approach to sustain Fe0-electrocoagulation for Cr(VI) removal by optimizing chloride ions

Abstract Chloride (Cl − ) is widely used for depassivation in electrocoagulation using metallic iron (Fe 0 -EC). However, its optimization is still on a pragmatic approach and thus of limited success. This study proposed a novel approach based on a systematic investigation of Cl − –induced pitting dissolution behavior of Fe 0 with the evolution of pH and Cr(VI) (0 ⩽ Cr(VI) (mg/L) ⩽ 520) in Fe 0 -EC. The depassivation behavior was characterized by potentiodynamic polarization, cyclic voltammograms (CVs), galvanostatic measurements, and scanning electron microscope (SEM) analysis. The proposed approach to optimize Cl − for depassivation was as follows: (1) Build a database of minimum Cl − concentrations for pitting dissolution (MCPD) as a function of pH and Cr(VI) in passivation region III (MCD =  f (pH, Cr(VI))); (2) Record the curve function ( g ) of pH and Cr(VI) evolution ( g  = {(pH i , Cr(VI) i ), …, (pH f , Cr(VI) f )}) without passivation in the Fe 0 -EC process; (3) Obtain the optimal concentration of Cl − for depassivation (OCD) by selecting the maximum MCDs by combining the curve ( g ) and the database of MCPD (OCD =  Max {MCPD 1 , MCPD 2 , … MCPD n }). This method was more accurate and stable compared with RSM.