Role of Iron Anode Oxidation on Transformation of Chromium by Electrolysis

Abstract

The potential for chemical reduction of hexavalent chromium Cr(VI) in contaminated water and formation of a stable precipitate by Zero Valent Iron (ZVI) anode electrolysis is evaluated in separated electrodes system. Oxidation of iron electrodes produces ferrous ions causing the development of a reducing environment in the anolyte, chemical reduction of Cr(VI) to Cr(III) and formation of stable iron-chromium precipitates. Cr(VI) transformation rates are dependent on the applied electric current density. Increasing the electric current increases the transformation rates; however, the process is more efficient under lower volumetric current density (for example 1.5 mA L(-1) in this study). The transformation follows a zero order rate that is dependent on the electric current density. Cr(VI) transformation occurs in the anolyte when the electrodes are separated as well as when the electrolytes (anolyte/catholyte) are mixed, as used in electrocoagulation. The study shows that the transformation occurs in the anolyte as a result of ferrous ion formation and the product is a stable Fe(15)Cr(5)(OH)(60) precipitate.

Figure 1

Schematic of experimental setup

Figure 2

Cr(VI) concentration in the anolyte using iron electrode under 15, 7.5, and 1.5 mA L⁻¹

Figure 3

Cr(VI) ratio as a function of charge density in the anolyte using iron electrode under 15, 7.5, and 1.5 mA L⁻¹.

Figure 4

ORP values during Cr(VI) reduction in anolyte solution using iron electrode.

Figure 5

Cr(VI) reduction in non-membrane redox cell under a current density of 15mA L⁻¹.

Figure 6

pH and ORP in the mixed electrolyte in non-membrane redox cell under a current density of 15mA L⁻¹.