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

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 diffraction (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