Diffusion Kinetic Modeling of Fluoride Removal from Aqueous Solution by Charge-Reversed Zeolite Particles

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In this study, zeolite particles were charge-reversed by chemically modifying them with aluminum and it was verified by EDXS that aluminum replaced sodium from the zeolite structure. The charge-reversed zeolite particles were subsequently used in fluoride removal from aqueous solution. The influence of the experimental variables such as particle size, initial fluoride concentration and temperature on the fluoride diffusion kinetics, was investigated using a batch adsorber. A model that lumps internal mass transfer phenomenon, i.e. pore and surface diffusion, was used to describe the uptake kinetics. From the model, a diffusional time constant and a corresponding effective diffusion coefficient were determined. Results demonstrate that the internal mass transfer rate is enhanced with an increase in temperature and decreases in particle size and initial concentration. It is also found that the diffusional time constant correlates well with the reciprocal of the square of zeolite particle radius corroborating that internal mass transfer plays a limiting role in fluoride sorption. An examination of the thermodynamic parameters reveals that the interaction between fluoride and charge-reversed zeolite particles is endothermic and spontaneous in nature.
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