Direct electrolytic preparation of chromium metal in CaCl2-NaCl eutectic salt
(1. CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China;
2. National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China;
3. University of Chinese Academy of Sciences, Beijing 100049, China;
4. Hubei Zhenhua Chemical Co., Ltd., Huangshi 435001, China)
Abstract: The electro-reduction of chromium oxide (Cr2O3) was investigated in an equimolar mixture of CaCl2-NaCl molten salt at 800 °C for developing a more efficient process for chromium preparation. Cyclic voltammetry and potentiostatic electrolysis were used to study the electro-reduction of the Cr2O3-loaded metallic cavity electrode. In addition, a number of parameters affecting the rate and extent of Cr2O3 electrolysis were considered to better understand the electrolysis process. The results demonstrate that CaCl2-NaCl molten salt is applicable for preparing Cr directly from Cr2O3 and the electrolysis parameters exert great influence on the cathode product. Under optimal experimental conditions, nodular Cr with an oxygen content of 0.5% (mass fraction) was obtained without any chromium carbides detected by XRD. Furthermore, the relatively high solubility of CaO and quite rapid crystal growth result in the formation of large platelet CaCr2O4, and the addition of NaCl to CaCl2 results in several variations on the electrolysis process and the product morphology from pure CaCl2 molten salt.
Key words: electrolysis; chromium; chromium oxide; CaCl2-NaCl molten salt