A Study Of Clean Process Decompose Bastnaesite Concentrate With Anhydrous Magnesium Chloride

This dissertation presents a new process for chlorination and decomposition of Sichuan Mianning bastnaesite concentrate with anhydrous magnesium chloride.The first part introduces the factors affecting the decomposition of bastnaesite concentrate under the heating of muffle furnace.The reaction mechanism of chlorination decomposition of bastnaesite concentrate was explored with anhydrous magnesium chloride by Thermogravimetry differential thermal analysis(TG-DSC),X-ray diffraction(XRD)and other detection methods.Meanwhile,the micro morphology and surface element distribution of mineral particles were investigated by scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).Finally,it is determined that bastnaesite concentrate is converted into rare earth oxychloride(REOCl)and magnesium fluoride(Mg F₂)under the chlorination of anhydrous magnesium chloride.And,optimum roasting parameters of the new process are roasting temperature 500?,roasting time 90 min and mineral salt ratio 1:0.25,in which the decomposition rate of REO can reach 97.23%,and the leaching rate of fluorine is 52.47%.In order to promote the development of green and clean rare earth metallurgy,based on the new process of chlorination and decomposition of Sichuan Mianning bastnaesite concentrate with anhydrous magnesium chloride,the second part introduces that microwave heating technology is used to replace the traditional heating(muffle furnace).In the process of decomposing bastnaesite concentrate by microwave chlorination roasting,anhydrous magnesium chloride is used as chlorination agent and activated carbon is used as auxiliary agent to enhance microwave absorption,which makes the bastnaesite concentrate decompose efficiently and realizes the non oxidation of cerium element in roasted ore in air atmosphere.About the second part,through the simple theoretical calculation of chemical thermodynamics and the application analysis of a series of above-mentioned detection methods,the phase transformation of anhydrous magnesium chloride and bastnaesite concentrate in microwave field is revealed,and the reason for the non oxidation of cerium element in microwave roasted ore is explained.Then,a large number of experiments are carried out to obtain optimum process parameters of microwave chlorination roasting,which are microwave power 1200W,roasting temperature 800?,roasting time 30 min,and mineral salt ratio 1:0.25.And the amount of activated carbon is 15%,which is in the mass of mixed materials(anhydrous magnesium chloride and bastnaesite concentrate).Under this roasting condition,the decomposition rate of REO is 96.23%,the leaching rate of fluorine is only 23.35%,and the oxidation rate of cerium in roasted ore is less than 0.36%.Finally,the energy-saving gap between microwave roasting and muffle furnace roasting is compared,which shows that the microwave chlorination of anhydrous magnesium chloride to decompose bastnaesite concentrate has the advantages of energy conservation.Also,there are mang advantages about the microwave chlorination decomposition,such as emission reduction,high efficiency,cost reduction and efficiency increase of clean and green.In order to ensure the rare earth leaching rate of microwave roasted ore and realize the goal of decomposition bastnaesite concentrate and recovery of magnesium fluoride,the optimum conditions of hydrochloric acid leaching of microwave roasted ore were explored about the third part of this paper.The optimum acid leaching conditions are as follows:acid leaching temperature 50?,initial acidity of hydrochloric acid 4 mol/L,liquid-solid ratio 10 ml/g,leaching time 20 min and stirring rate300 rpm.Under this acid leaching condition,the rare earth leaching rate of microwave roasted ore is94.21%,and the leaching rate of fluorine in acid leaching solution is only 20.52%.Finally,according to a large number of experimental data and from the perspective of leaching kinetics theory,the apparent activation energy of hydrochloric acid leaching and sintering process is calculated to be13.545 k J/mol.It is determined that the reaction rate is jointly controlled by interfacial mass transfer and product layer diffusion.The semi empirical equation of leaching kinetics is obtained to describe the process of hydrochloric acid leaching microwave roasted ore,which verifies the feasibility of hydrochloric acid leaching microwave roasted ore.