Recovery of “Hard-to-Recover” Selenate Ions in Sulfuric Acid Solutions during Polarization of Titanium Electrodes by Industrial Alternating Current

Abstract

The article is devoted to the study of selenium (VI) reduction processes in sulfuric acid solutions when titanium electrodes are polarized by alternating current of industrial frequency (50 Hz). It was found that selenate ion reduction occurs on the surface of titanium electrodes in the cathode half-cycle of alternating current (practically at the cathode) by reaction: SeO42−+ 6e + 8H+ → Se + 4H2O. In addition, the recovery is carried out by titanium (III) ions: 6Ti3+ SeO42−+ 8H+ → Se + 6Ti4+ + 4H2O. It has been established that titanium (III) ions are products of dissolution of titanium during polarization by alternating current, so they can be formed by reaction: 2Ti + 6H+ → 2Ti3+ + 3H2. Reduction in selenate ions during polarization by alternating current can also occur due to the cementation reaction with titanium: 3Ti + 2SeO42− + 16H+ → 2Se + 8H2O + 3Ti4+. It was shown for the first time that the selenate ion is reduced to form a dispersed selenium powder with a high current efficiency. Depending on the conditions, both amorphous and crystalline selenium modifications are produced.