A series of cerium zirconium mixed oxides were prepared by two co-precipitation methods using magnesium hydrogen carbonate （MHC） and mixed ammonia-ammonia hydrogen carbonate （AAHC） as precipitant respectively. The crystal structure, BET surface area and morphology of the produced cerium zirconium mixed oxides were characterized by X-ray diffraction （XRD）, Bru- mauer-Emmett-Teller （BET） and scanning electron microscopy （SEM） techniques. The reduction-oxidation behavior and oxygen storage capacity （OSC） performance were also studied by temperature programmed reduction （TPR） and oxygen pulse chemical adsorption methods. The XRD results demonstrated that the cerium zirconium mixed oxides obtained by both methods possessed struc ture of cubic solid solution phase. The fresh surface area calcinated at 600 ℃, aged surface area after 1000 ℃and OSC at 500 ℃ of cerium zirconium mixed oxides were determined to be 89.337, 34.784 ma/g, and 567 pmol O2/g for MHC method and 122.010, 46.307 m2/g, and 665 pmol O2/g for AAHC method, respectively.
In view of the problem of ammonia-nitrogen wastewater pollution in rare earths extraction and separation, the novel saponification agent of organic phase, which is magnesium bicarbonate solution, was prepared with the natural rich and cheap dolomite as raw material through carbonation process. The behavior and purification of main impurities ions in the carbonation process as well as the application effect of the novel saponification agent in the extraction and separation was researched. The results showed that the concentration of Fe, A1, Si im- purities ions was.less than 5 ppm in the saponification agent through the development of effective removal technology, respectively. When the novel saponification agent was used in the extraction and separation, magnesium utilization rate was more than 95%, and rare earths extrac- tion rate above 99.5% has achieved. Therefore, the technology could replace ammonia-water to saponify the organic phase in rare earth ex- traction and separation process.
The effects of magnetic field intensity, roasting temperature and roasting time on digestion rate and settling performance of bauxite with different iron contents were investigated systematically. The results indicate that such magnetic treatment can profoundly change the microstructure and digestion performance of bauxite. For the two samples carrying different iron contents, phase transformation of the aluminum oxide phase proceeds faster in the high iron bauxite than the low one. The optimal pretreatment conditions of low iron bauxite are roasting temperature 550 ℃ and magnetic field intensity 6 T, while for high iron bauxite are 500 ℃ and 9 T. The digestion rate of alumina can reach 95% and 92% at digestion temperature of 190 ℃ and 250 ℃. The settling performances of roasted ore by intense magnetic field after digestion are enhanced through pretreatment.
