Preparation of Cr₂O₃ precursors by hydrothermal reduction in the abundant Na₂CO₃ and Na₂CrO₄ solution

Guang-ye Wei1), Jing-kui Qu2,3), Yu-dong Zheng1), Tao Qi2,3), and Qiang Guo2,3) 1) School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China 2) National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Beijing 100190, China 3) Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China

摘 要：Precursors of chromium oxide （p-Cr2O3） were prepared by reducing hexavalent chromium in the presence of sodium carbonate solution under hydrothermal conditions. Methanal was used as the reductant, and carbon dioxide was the acidulating agent. The influences of reaction temperature, initial pressure of carbon dioxide, isothermal time and methanal coefficient on Cr（Ⅵ） reduction were investigated. Experimental results showed that Cr（Ⅵ） was reduced to Cr（Ⅲ） with a yield of 99%. Chemical titration, thermogravimetry （TG）, X-ray diffrac-tion （XRD） analysis, and scanning electron microscopy （SEM） were used to characterize the p-Cr2O3 and Cr2O3. The series of p-Cr2O3 were found to be multiphase even if they presented different colors, from gray green to lavender. After these p-Cr2O3 samples were calcined, the product of rhombohedral Cr2O3 with a purity of 99.5wt% was obtained.

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