Removal of hexavalent chromium from electroplating wastewater by electrocoagulation with iron electrodes

Abstract

The performance of electrocoagulation using iron electrodes for the removal of hexavalent chromium from synthetic aqueous solutions and actual industrial electroplating wastewater was studied. Parameters affecting the electrocoagulation process, such as initial pH, applied current density, initial metal ion concentration, COD and time of electroprocessing were investigated. The optimum pH was found to be in the range 4-8. Initial chromium concentrations of 200 -800 mg L -1 did not influence its removal rate. Higher concentrations were reduced significantly in relatively less time than lower concentrations. Increased current density accelerated the electrocoagulation process, however, on cost of higher energy consumption. Results revealed that best removal was achieved at a current density 40 mA cm -2 . The electrocoagulation process was successfully applied to the treatment of an electroplating wastewater sample. Its Cr (VI) ion concentration and COD were effectively reduced under the admissible limits in 50 minutes of electroprocessing.

Chromium Pollution in European Water, Sources, Health Risk, and Remediation Strategies: An Overview

“…Electrocoagulation is a process consisting of creating metallic hydroxide flocs inside the wastewater by electro dissolution of soluble anodes. Dermentzis et al (2011) [133] found that some affecting parameters are pH, applied current density, and time, while initial Cr (VI) did not influence its removal rate by electrocoagulation. By contrast, Zewail et al (2014) [130] as well as Genawi et al (2020) [132] found that the initial chromium concentration determines the efficiency of the treatment.…”

“…The most used pairs of electrodes are made by Fe-Fe, Al-Al, or Al-Fe [129]. In the case of iron anodes, the Fe (II) ions reduce Cr (VI) to Cr (III) in alkaline to neutral medium, while they are oxidized to Fe (III) ions, according to the following reaction: CrO 4 2− + 3Fe 2+ + 4H 2 O + 4OH − → 3Fe(OH) 3 + Cr(OH) 3 [133]. Consequently, both the Fe (III) and Cr (III) combine with OH-ions, forming insoluble hydroxides which precipitate.…”