Clean preparation of Cr2O3 by direct molten salt electrolysis of sodium chromate

• Published in: Journal of cleaner production Vol. 467; p. 143028
• Main Authors: Feng, Baoyan, Jia, Yongzheng, An, Jialiang, Jia, Yadong, Wang, Mingong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.08.2024
• Subjects: Chromate; Chromium trioxide; Current efficiency; Molten salt electrolysis; Molten salt electrolysis; Current efficiency; Chromate; Chromium trioxide
• ISSN: 0959-6526
• DOI: 10.1016/j.jclepro.2024.143028

Chromium oxides, such as Cr2O3 and CrO3, are important raw materials in the fields of metallurgy, chemical industry et al. At present, sodium roasting-water leaching followed by two-step acidification is a common route to produce chromium oxides. Complex process and enormous discharge of H2SO4-containing wastewater are serious issues. Herein, a clean and short-process separation method to prepare Cr2O3 is proposed by direct molten salt electrolysis of soluble sodium chromate (Na2CrO4) as an intermediate in conventional chromium separation route. The theoretical decomposition voltages of Na2CrO4 to various low-valence chromium oxides were calculated. The solubility, melting point and electrical conductivity of Na2CrO4 in molten salt were analyzed. It is confirmed that the molten salt electrolysis of soluble Na2CrO4 to Cr2O3 is feasible due to high solubility and low decomposition voltage. The dependence of Na2CrO4 electrolysis on cell voltage, molten salt system, temperature, Na2CrO4 content and cathode material is systematically studied. At optimal conditions, the current efficiency and electricity consumption are 59.71% and 4.43 kW h·kg−1, respectively. A long-term electrolysis for 50 h is also carried out. High-purity Cr2O3 is obtained. The work provides a promising and clean route to prepare Cr2O3. [Display omitted] •A novel and clean method for the preparation of Cr2O3 is proposed by molten salt electrolysis of Na2CrO4.•The decomposition thermodynamics and solubility of Na2CrO4 are analyzed.•Optimum preparation of Cr2O3 from Na2CrO4 by molten salt electrolysis is studied.•Long-term electrolysis for Cr2O3 preparation from Na2CrO4 is carried out.