複極式電解槽によるＣｒ（ＩＩＩ）のＣｒ（ＩＩ）への電解還元

Abstract

To examine the feasibility of electrolytic reduction of Cr (III) to Cr (II) using a titanium cathode, cathodic polarization characteristics of Cr (III) on a titanium cathode and batch-type electrolytic reduction of Cr (III) using a bipolar electrolytic cell were investigated with acidic aqueous solutions of CrCl3 and Cr2 (SO4)3. The reduction of Cr (III) to Cr (II) started at a cathode potential of about-0.7V vs SHE, and the reduction current of Cr (III) increased with a decrease in cathodic potential. The reduction current in CrCl3 solution was greater than that in Cr2 (SO4) 3 solutions under the same conditions. However, in CrC13 solutions, a remarkable decrease in the reduction current was observed at around-1.2V vs SHE, because of the hydrolysis of Cr (III). In the batch-type electrolytic reduction of Cr (III) using a bipolar electrolytic cell, complete reduction of aqueous 0.5-1.0kmol m-3 CrCl3 solution with a current efficiency of 70-50% could be achieved by keeping the catholyte pH at 2, to avoid hydrolysis of Cr (III). When using Cr2 (SO4) 3 solutions, the reduction of Cr (III) proceeded almost as fast as using CrCl3 solutions, at the same condition. Since the hydrolysis of Cr (III) is less significant in Cr2 (SO4) 3 solutions than in CrC13 solutions, the electrolytic reduction process can be operated at a higher current using Cr2 (SO4) 3 solutions. KEY WORDS: Electrolytic Reduction, Chromic Chloride, Chromic Sulfate, Bipolar Electrolysis Cell