Roasting Kinetics Of Bastnasite And Preparation Of Superfine Polishing Powder

ROASTING KINETICS OF BASTNASITE AND PREPARATION OF SUPERFINE POLIISHING POWDERChinese rare earth resource, occupying 53.5% in industrial reserve, is at the top of the world. Rare earth elements, applied in many parts of modem industry, enjoy the honor of precious resource of new material. Now the serious problem is that all kinds of rare earth elements are used unequally. In order to transferring the rich in resource to dominance in economics, it is a key project to explore and make the best use of the high containment rare earth, especially the research of cerium for its high containment among the rare earth.Cerium dioxide, a kind of cheap rare earth, is used extensively in the world. The cerium utilization was concisely introduced in this paper. For the special electron configuration, the cerium representsâ…¢andâ…£valence. According the unique chemical property, the cerium chloride was prepared by leaching with hydrochloric acid in two steps, followed by producing the super fine cerium dioxide powder by precipitation with ammonium bicarbonate.The main achievements of the dissertation are shown as the following:(1) Roasting kinetics of bastnasite with sodium carbonateAs amount of HF was produced by traditional technology with sulfuric acid, the new roasting processing of removing fluorine by adding sodium carbonate, a typical solid phase's reaction, was absorbed by lots of researcher. The kinetics equation which characterized the roasting process was given by TG analyzing. The result was shown that the roasting process is a first order kinetics reaction and the active energy decreases slightly with the dosage of sodium carbonate increasing.(2) The preparation of enriched cerium chloride solution with hydrochloric acid by two stepsWhen the bastnasite was roasted in the air condition, 95 percent of cerium appears tetra-valence existed as CeO₂. The term does not resolved in diluted hydrochloric acid, while the other rare earth and impurities such as iron et al. could solute in diluted hydrochloric, which guarantees the cerium separated from impurities. The roasted was firstly washed with water to remove fluorine existed as sodium fluoride. Then tri-valence rare earth and soluble impurities were extracted with 1 mol/L hydrochloric acid. Finally the tri-valence cerium, being cerium chloride solution, was obtained by leaching with 6 mol/L hydrochloric acid under hydrogen peroxide, in which the containment of cerium was over 95%. The percent recovery of cerium is up to 90% by this technology.(3) The cerium chloride solution was precipitated with ammonium bicarbonate adding PEG as dispersant agent. The cerium carbonate, precursor of cerium dioxide, was obtained. By roasting the super fine cerium dioxide was produced. The optimal technology of precipitation and roasting was presented.(4) The super fine cerium dioxide was characterized by XRD (x-ray diffraction) and SEM (scan electronic microscope). It was found that the particle size of single cerium dioxide crystal is about 20.5 nm and the particle size of powder is smaller than 100 nm.