Non-oxidative Micriwave Radiation Roasting Of Bastnasite Concentrate And Leaching Kinetics Of Hydrochloric Acid

Herein,a new clean extraction technology for the decomposition of bastnasite concentrate by utilizing microwave radiation is proposed,which prevented Ce(III)from being oxidized to its tetravalent form.This paper focuses on the investigation of the dielectric properties of bastnasite concentrate,mechanism analysis of Ce(III)not being oxidized to Ce(IV),the response surface methodology(RSM)to optimize the microwave non-oxidative roasting process,hydrochloric acid leaching of the non-oxidative roasted ore,and kinetics analysis of the leaching process.The analysis of the dielectric properties of bastnasite concentrate has a key role in guiding the development of microwave roasting treatments for bastnasite concentrate.The dielectric properties are correlated to the information such as TG-DSC analysis and temperature rise curve.This combination permits a targeted study of the mechanism of the microwave roasting process,providing new evidence about the unique conditions of this microwave roasting process.The roasting experiments were carried out concentrating on the effect of roasting temperature,holding time,and the contents of activated carbon on the decomposition rate of the bastnasite concentrate and the oxidation rate of cerium.This work also explores the response surface methodology(RSM)based on Central Composite Design(CCD)to optimize the microwave non-oxidative roasting process.The optimal roasting temperature,contents of activated carbon,and holding time were1100°C,20%,and 21.5 min,respectively.Under these conditions,the decomposition rate of bastnasite concentrate and oxidation rate of cerium was 99.8%,less than 0.3%,respectively.The new non-oxidizing roasting method significantly shortens the roasting time,reduces energy consumption,and has great significance for industrial applications.The leaching experiments were carried out concentrating on the effect of acidity,liquid-solid ratio,leaching temperature,and stirring rate on the leaching kinetics of the non-oxidative roasting ore.When the roasting temperature is 1100°C,the holding time is 21.5 min,and the m(C)/m(REFCO₃)ratio is 20%,the results show that the leaching efficiency of rare earths can reach 85.45%under the conditions 3 mol/L HCl,90°C,60 min,9 m L/g liquid-solid ratio,and 300 rpm stirring rate.The apparent activation energies of leaching rare earths were calculated as14.326 k J/mol,and the HCl leaching process can be described by a shrinking-core model,in which both the interfacial transfer and the diffusion through the product layer influenced the reaction rate.Furthermore,a semiempirical rate equation was created to describe the leaching process of the non-oxidative roasted ore.The X-ray diffraction and scanning electron microscopy analyses of the samples before and after acid leaching show that the rare earth oxides were completely leached and Ce(III)was not oxidized to its tetravalent form.The acid leaching residue was mainly composed of rare earth fluoride that is not easily soluble in dilute hydrochloric acid,which effectively avoids fluorine ions from entering the rare earth chloride solution and leading to emulsification during extraction.