Preparation of analcime from local kaolin and rice husk ash

Analcime zeolite was synthesized using a hydrothermal technique with rice husk ash and metakaolin as sources of silica and alumina respectively. Both the raw materials and the final product were characterized using XRD, FTIR, SEM and atomic absorption spectroscopy. XRD diffractogram of the rice husk exhibited α-quartz as a dominant and critobalite as a minor component. Metakaolin consisted of alumina, with minor amounts of α-quartz. Analcime was obtained after 72 h aging and 24 h reaction time at temperature of 180 °C. Longer reaction time led to a decrease in the amount of analcime phase with corresponding increase in zeolite-p. SEM of the analcime crystals showed formation of trapezohedral morphology of sizes ranging from 15 to 25 μm. The analcime was tested in the adsorption of phenol from its aqueous solutions (50–400 ppm). Among the adsorption isotherms tested, the Langmuir model was found to give better representation of the data. The ultimate amount of phenol adsorbed on analcime (12.5 mg/g) was lower compared with a commercial zeolite (33.1 mg/g) used as reference. However, in terms of adsorption per surface area, the analcime (3.88 mg/m2) exhibited better performance than the other sample (0.01 mg/m2). The value of the constant related to free energy of adsorption in the Langmuir model was used to evaluate a dimensionless equilibrium parameter, RL. At high phenol concentrations (100–400 ppm), the RL values for the commercial sample (0.73–0.40) were higher than for analcime (0.50–0.20). The results show that the readily available raw materials could be used to prepare analcime zeolite with a good and favourable adsorptive capacity.

Figure 6 SEM micrographs of analcime samples: A (scale bar 50 μm) and B (scale bar 10 μm).Figure optionsDownload as PowerPoint slideHighlights
► Analcime zeolite was synthesized using local clays sources of silica and alumina.
► Rice husk ash and metakaolin were used as sources of silica and alumina.
► Reaction time is important in determining the amount of the analcime phase.
► The analcime crystals formed trapezohedral morphology with size of 15 to 25 μm.
► The samples exhibited high adsorptive capacity for the removal of aqueous phenol.