Efficient Removal of Hexavalent Chromium from Wastewater with Electro-Reduction

Abstract

Removal of hexavalent chromium had attracted much attention as it is a hazardous contaminant. An electrocoagulation-like technology electro-reduction was applied. The chromium (VI) in the wastewater was reduced to chromium (III) by the electron supplied by electricity power and Fe2+, formed from corrosion of steel electrodes in acidic conditions. The mechanism and parameters affecting the reaction were investigated. The results optimized by response surface methodology indicated that the influence of single factor on the reduction efficiency followed the order: A: dosage of H2SO4 > C: reaction time > D: reaction temperature > B: current intensity. The reduction efficiency was hardly affected by current intensity, while it was increased with the increasing of reaction time and acid concentration. The reducing agent, Fe2+ an and extra free electron, acted as a reducing agent and could easily reduce hexavalent chromium to trivalent chromium at high temperatures in an acidic medium.

Electrochemical Removal of Chromium (VI) from Wastewater

“…The effect of reaction temperature on the reduction efficiency was conducted while other conditions kept constant: initial concentration of chromium (VI) of 1.000g/L, current density of 50 A/m 2 , concentration of H2SO4 of 100 g/L and stirring rate at 500 rpm. The results showed in Figure 3 indicated that the reduction of chromium (VI) could be easily achieved at higher reaction temperature (≥50 ℃), which was partial consistent with recent study [8]. High temperature would decrease the diffusion resistance and favor the contact of free electron and chromium (VI) resulting in high reduction efficiency.…”

“…The reduction of chromium (VI) in the process was acid-dependent and higher chromium (VI) reduction efficiency could be achieved at high acid concentration. The acceleration of Cr(VI) reduction in the system at the high acid concentration could be attributed to that the chromium (VI) species were more easily being reduced in acidic conditions than in neutral/ alkaline conditions according to Equation (7) and (10) [8]. And the molar fraction of the Cr2O7 2-was drastically increased with increasing acid concentration according to Equation (9).…”

“…During the process, reaction temperature is an important parameter affected the reaction during the diffusion process [8,10,22,30,31]. The effect of reaction temperature on the reduction efficiency was conducted while other conditions kept constant: initial concentration of chromium (VI) of 1.000g/L, current density of 50 A/m 2 , concentration of H2SO4 of 100 g/L and stirring rate at 500 rpm.…”

“…Many methods have been demonstrated efficient for Cr(VI) removal, such as: ion exchange [5,6], electrochemical treatment [7][8][9], chemical precipitation [10], coagulation [11], chemical reduction [12,13], and adsorption [3,[14][15][16][17].Also some biological treatments [18,19] (phytoremediation [20])are also applied to remove chromium (VI) in wastewater and groundwater. Lead sulfate as a precipitation is used to precipitate chromium (VI) and it can remove chromium (VI) from 0.2mol/L to 0.15 mmol/L [10], but lead sulfate is a second pollutant which is harmful for environment.…”

“…In recent study [8], an electro coagulation-like technology electro-reduction is applied to reduce hexavalent chromium to trivalent chromium. The results showed that the chromium (VI) was easily being reduced by Fe 2+ and free electron, while the current intensity had little effect on the reduction process.…”