Study On Preparation Of CeO₂from Bastnaesite Directly

Rare earth, known as the” monosodium glutamate in industry”, is called the“treasure house” of new materials by people. Bastnaesite, as a major industrialmineral, has the largest reserves in all the world’s rare earths. At present, thepreparation of CeO2is mainly based on cerium compounds by precipitation andsol-gel method. Reports referring to the extraction and preparation of ceria directlyfrom bastnaesite are rare seen. And the current method of preparing CeO2directlyfrom bastnaesite is incomplete with long and complex experimental process and highdemand for the equipment. The usage of large amounts of acid leads the discharge ofwaste water containing large amounts of acid and alkali, which causes great damageto the environment. However, with cerium widely used in the field of modernhigh-tech and cutting-edge technology, it requires us continually improve and explorenew technology of preparation of ceria.In order to extract rare earth CeO2from bastnaesite effectively. This thesis firststudied the chemical composition and phase composition features of bastnaesiteconcentrate. Through the analysis by X-ray fluorescent (XRF), the majorcompositions of bastnaesite concentrate are Ce, La, Ca, Fe, Nd, Si, S,etc. And othertraces are Ti, Mg, Pb, Th, Mn, etc. The major mineral compositions are bastnaesite,quartz, fluorite, chevkinite, cerianite, celestite, parisite, cordylite, allanite, etc. Themajor basic phase composition are bastnaesite though the determination by X-raydiffraction (XRD).According to the composition of raw materials and phase analysis results, thestudy extracts CeO2directly from bastnaesite. The experimental process could bedivided into the following steps:(1) Conduct the oxidizing roasting experiment. In thepresence of fluoride retention additive, CeO2and NaF will be obtained by theoxidative decomposition of bastnaesite. The experimental result shows that with the NaHCO3as fluoride retention additive, when the mass ratio of bastnaesite to NaHCO3is10:4, roasting temperature and time are respectively550℃and2hours, oxidizingroasting could make bastnaesite decomposed to target product CeO2completely.(2)Wash the roasted ore after roasting, remove the water-soluble substances such as NaFin the roasted ore, remain the CeO2left in the residue. The experimental result showsthat the NaF left in the roasted ore could be removed effectively when the liquid-solidratio is6:1, and water-wash temperature and time are respectively65℃and60minutes.(3) Adopt roasted ore washed by dilute hydrochloric acid could remove theother rare earth (REE), some oxide impurities (Ca, Fe, Al, etc.) and some incompletedecomposition of carbonates in the process of roasting. The experimental result showsthat when the liquid-solid ratio is5:1, concentration of hydrochloric acid is3mol/L,the acid leaching temperature and time are respectively45℃and100minutes, CeO2could be separated from other elements completely. The purity of CeO2could reachmore than72%.(4) Lastly, heat-treat the acid slag under the temperature of600℃for2hours. The ultra-fine powders CeO2with structural integrity and particle size isbetween20~100nm, the average particle size of50nm could be obtained. Onlyusing diluted hydrochloric acid in the experimental process, this paper applies simpleexperimental method, which reduces the demand for production equipment andexperimental process with less emissions of "three wastes" and lower environmentalpressure.