Study On Synthesis Of NaX Zeolite From Coal Kaolin

Coal-series kaolin is a natural non-metallic mineral, which is associated with the coal. The coal-series kaolin is a raw material for the synthesis of NaX zeolite. It can not only make better use of solid resources but also form high added value product. Moreover, the synthesis of NaX zeolite with coal-series kaolin has the characteristics of low cost, making it greatly competitive on the market.In this paper, NaX zeolite was prepared by hydrothermal and microwave-assisted heating methods respectively using calcined kaolin, NaOH, silicon sol and distilled water as raw materials when the n(Si)/n(Al) of reaction mixture was 4. The synthesis conditions were optimized by the single factor method. The NaX zeolite was characterized by static water absorption, XRD, IR and SEM. The water absorption performance of NaX zeolite could reach the industrial standard.These were the optimization conditions of hydrothermal: the dosage seeds was 2%, the dosage of alkalinity R(R=n(Na2O)/n(Al2O3), molar ratio) was 5.3, pre-crystal temperature was 65℃, pre-crystal time was 3h, crystal temperature was 100℃, crystal time was 24h. The Static water absorption ratio and relative crystal were 33.19% and 91.18% respectively. These were the optimization conditions of microwave-assisted heating: the dosage of alkalinity R was 4.7, the pre-crystal time was 30min in 120W, the crystal time was 105min in 700W. The Static water absorption ratio and relative crystal were 33.91% and 88.43% respectively.The process of crystallization synthesized NaX zeolite by microwave heating was discussed. In the reaction process, the concentration of Al₂O₃ almost was the same in the liquid phase. It was found from SEM that kaolin particles converted to octagonal zeolite crystals in the soild phase.Compared with hydrothermal, microwave heating exhibited faster crystallization speed, less consumption of alkali and better inhibition miscellaneous crystalling phase formation.