Activation of Kaolinite-Rich Coal Gangue and Synthesis of NaY Molecular Sieve
Using coal gangue as raw material,NaY molecular sieve was synthesized by a hydrothermal process of"high-temperature calcination,alkali melting,alkali dissolution and crystallization"under the conditions of no templates or additives.Moreover,the high-temperature heat-treated coal gangue and synthesized NaY molecular sieve were characterized using methods such as XRF,TG,XRD,SEM,N2 adsorption-desorption curve,and NH3-TPD.The results show that the kaolinite phase in the coal gangue can form the amorphous metakaolinite phase at 600-800 ℃.With the increase of the mass ratio of sodium carbonate to coal gangue or the increase of alkali melting temperature,the crystal phase content of sodium aluminosilicate first increases and then decreases;the addition of NaY molecular sieve seeds(mass fraction 0.1％-2.0％)has increased the relative crystallinity and specific surface area of the product molecular sieve sample;increasing the concentration of NaOH leads to a decrease in the silicon/aluminum ratio of NaY molecular sieve;increasing the silicon/aluminum molar ratio(n(SiO2)/n(Al2O3)=6-30)of the feeding results in an increase and then a decrease in the silicon/aluminum ratio and relative crystallinity of NaY molecular sieve.When the mass fraction of the crystal seed is 0.5％,n(SiO2)/n(Al2O3)=20,and the NaOH concentration is 3 mol/L,the synthesized NaY molecular sieve has a silicon/aluminum molar ratio of 4.3,a relative crystallinity of 87.4％,a specific surface area of 584 m2/g,a pore size mainly distributed at 3.4 nm,and a particle size of about 100 nm.
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