Electrochemical Reduction of Chromate in the Presence of H2O in Molten Lithium Chloride-Potassium Chloride Eutectic.

摘要

The chronopotentiometric reduction of K2CrO4 was studied in molten LiCl-KCl eutectic at 450 C in the presence of CaCl2 and/or water. The vapor pressure of H2O was varied in the range of 0-22.5 Torr. Under highly dehydrated conditions, a single wave occurs at -1.18V vs. Pt(II), 1M/Pt reference electrode, and Ca(II) ions have no effect on the reduction wave. However, in a moist melt and in the presence of insufficiently dehydrated CaCl2, two reduction waves are observed. The first reduction wave occurs at -0.6V and the second at -1.18V. LiCrO2 is formed as an insoluble product at the first reduction step. The same product is produced chemically by decomposition of synthesized Li3CrO4 in a moist melt. Coulometry and chronopotentiometry revealed that three electrons and two water molecules are consumed per chromate ion and the first step is controlled by H2O diffusion. A reduction path consistent with these observations is proposed. (Author)