Electrolytic Reduction of Chromic Anhydride in Dilute Solution

Abstract

For the purpose of disposing the industrial waste containing chromic anhydride, the electrolytic reduction of Cr₂O₇^2- into Cr³⁺ in the chromium plating solution diluted 200-fold is preliminarily examined on a small scale.
The reduction is effectively carried out by the use of the iron anode and cathode. On the cathode, the electrochemical reduction takes place mainly, while on the anode, iron dissolves into the solution in the form of Fe²⁺ which reduces Cr₂O₇^2-.
The pH of the solution must be kept less than 2.8 otherwise hydroxide will be formed that makes voltage high and time of electrolysis long.
The optimum range of current density should be from 1 to 2A/dm² from the viewpoint of the terminal voltage and reduction speed.
The current efficiency of the electrochemical reduction on the cathode is less than 52% in the range of current density from 0.5 to 3A/dm², where the current efficiency decreases with an increase of the current density.