PRODUCTION OF HIGH GRADE SODIUM SILICATE AND SILICA SOL FROM KANKARA KAOLIN FOR ZSM-5 SYNTHESIS

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Department of Engineering

ABSTRACT
This research work utilized the silica obtained from locally sourced kaolin (from Kankara in Katsina State) to produce zeolite grade sodium silicate as a raw material for the preparation ofsilica sol for ZSM-5 synthesis. The work also involved development of sodium silicate pilot plant. Of the various dealumination routes considered, double dealumination, specifically 2.5/2.5 fold was regarded the best for its economic advantage and capability to completely remove alumina (Al2O3) alongside with the major trace contaminants like CaO and Fe2O3 associated with silica from kaolin. When the resulting silica was employed for sodium silicate preparation, 6.0M concentration of sodium hydroxide solution gave the highest dissolution (95%). However, it was not suitable for the preparation of the targeted silica sol due to its high silica content, hence 2.5 and 3.0M concentration of sodium hydroxide solution both with lower percentage dissolutions (77 and 78) were selected as the two that yielded the desired results for the silica sol preparation. Kinetics of silica dissolution in sodium hydroxide were studied and it was found that it followed first order reaction law with specific rate constant of 1.7798min-1. Although, three types of silica sols were prepared via peptization and ultra-sonication methods, basic sol produced by ultra-sonication method was the best for its superior qualities (stability and suitability for ZSM-5 preparation). Despite the fact that commercial zeolite grade silica sol was more concentrated, the prepared Kankara kaolin based silica sol was purer and the X-ray diffraction patterns of all the zeolites synthesized from these sols were purely crystalline and conformed well with both the standard and the commercial XRD patterns of Na-ZSM-5. The X-ray fluorescence of the powder products further classified the materials as high silica zeolites (silica to alumina ratio equal to 10 to several thousands). Though, Na-ZSM-5 from commercial silica sol has higher silica to alumina ratio theNa-ZSM-5 produced from Kankara kaolin showed fewer impurities. Based on the information from the kinetics study at 90oC, a sodium silicate pilot plant of approximately 10 liters capacity for a single batch in 3hrs was developed with a batch requirement of 5kg silica sand which gave a percentage yield of 88.4%.