Abstract:

The NaApellets composed of kaolin and NaA molecular sieve were calcinated,and the small pellets were successivelytreated with alkali solutionand exchanged with Ca2+solution. Samples were characterized and evaluated by TG-DTA, XRD, 27Al-NMR, methanol adsorption, nitrogen physical adsorption and pulse test. The results showedthat kaolininNaApelletswas changedintometakaolinduring calcinations at 500-700 ℃, and the latter was converted to NaAmolecular sieve after alklitreatment.When calcinated at 750 ℃,NaA molecular sieve in pellets was changed in structure and lost adsorption capacity of methol, however,afteralkali treatment, not only kaolin in pellets was converted to NaA molecular sieve, but alsothe destroyedNaA molecular sieve was repairedandhad higher adsorption capacity than uncalcinedNaA. When calcination temperature was above 800 ℃, NaAwas transformed into more stable carnegeiteand nepheline. Physical analysis and mercury intrusion showed that, NaApelletscalcinatedat750 ℃ had larger apparent bulk density and crush strength compared to thatcalcinatedbelow 700 ℃。This was because particlesin pelletsbindsmore tightly during higher temperature.

Key words: NaA pellet, NaA molecular sieve, 5A pellet adsorbent, calcination temperature, alkali treatment