Synergistic Extraction Of Rare Earth Elements From Coal-Series Kaolin By Alkali Fusion And Sulfamic Acid Leaching

As an important non-renewable tri-rare metal mineral resource,rare earths play an important role in energy production,national defense and security applications.With the increased exploitation of traditional rare earth mines,rare earth deposits were becoming increasingly scarce and the conflict between supply and demand of rare earth resources was gradually intensifying,so there was an urgent need to find alternative non-traditional rare earth resources.As a traditional solid waste resource,coal-series kaolin has become an important alternative source of rare earths and has great potential for recovery and extraction of rare earth elements.In this thesis,coal-series kaolin was taken as the research object,the modes of occurrence of rare earth elements in coal-series kaolin was studied by sequential chemical extraction,floating and sinking,and other methods,the optimal conditions of each factor in the process of alkali fusion activation were explored,and the activation mechanism of alkali fusion was analyzed by XRD,FT-IR,FESEM,etc.Besides,the influence of various operating factors of the acid leaching process on the leaching of rare earth elements in coal-series kaolin was studied,and the kinetics of acid leaching process was analyzed,so as to realize the efficient extraction of rare earth elements from coal-series kaolin.The total rare earth element content of coal-series kaolin was 590.51μg/g,and the high-density sample(+1.8 g/cm~3)contained more rare earth elements,in which the coal-series kaolin with a density fraction of 2.5-2.6 g/cm~3 had the highest rare earth element content.The results of sequential chemical extraction,correlation analysis and FESEM test showed that the rare earth elements in coal-series kaolin were mainly in the silicate/aluminosilicate state,and the light rare earth elements were more inclined to be in the inorganic fraction than the heavy rare earth elements,and had more significant correlation with Al and Si elements.The surface of coal-series kaolin contained a large number of Al,Si and other elements,the silicon-aluminum ratio was closed to the theoretical value of kaolinite,and rare earth elements were detected at the same time,indicating that silicate/aluminosilicate minerals were the main carriers of rare earth elements.The direct acid leaching efficiency of rare earth elements from coal-series kaolin was low,and the Na OH alkali fusion method was used to activate the coal-series kaolin.The optimal conditions for alkali fusion were determined:alkali fusion temperature of300°C,a mass ratio of coal-series kaolin to Na OH(coal-alkali mass ratio)of 1:1.5 and alkali fusion time of 1 h.After alkali fusion,the leaching rates of REE,LREE and HREE in coal-series kaolin increased to 74.37%,76.99%and 64.02%,respectively.The analysis results of XRD,FT-IR and FESEM showed that when the alkali fusion temperature was 300℃,the diffraction peaks of mineral crystals in coal-series kaolin disappeared basically,the original stretching vibration peaks of kaolinite and quartz weakened,the crystal structure had been completely destroyed,the surface morphology changed dramatically,and the structure showed a melt-like substance,which formed a loose porous structure.The results of leaching reaction kinetics showed that the leaching process of rare earth elements in coal-series kaolin was controlled by both chemical reaction and diffusion.The optimum leaching conditions were determined:sulfamic acid of 0.5mol/L,hydrogen peroxide of 0.2 mol/L,sodium chloride of 0.2 mol/L,solid-liquid ratio of 1:50,stirring speed of 300 r/min,leaching temperature of 50℃,leaching time of 15min,and the leaching rates of REE,LREE and HREE were 83.66%,87.37%and69.02%,respectively,which realized the efficient extraction of rare earth elements from coal-series kaolin.There are 48 figures,20 tables and 120 references in this thesis.