Investigations on the batch and fixed-bed column performance of fluoride adsorption by Kanuma mud

The removal of fluoride from water by Kanuma mud using batch and fixed-bed column adsorption techniques was investigated. In a batch study, maximum fluoride removal was achieved within the pH range 5.0–7.0, taking about 2 h to attain equilibrium. Equilibration time did not depend upon the initial fluoride concentration. Kinetics data were fitted with a pseudo-second-order model. The experimental data fitted well to a Freundlich adsorption isotherm. Fixed-bed column experiments were carried out for different influent fluoride concentrations, bed depths, and various flow rates. The breakthrough time and exhaustion time decreased with increasing flow rate, decreasing bed depth and increasing influent fluoride concentration. The bed depth service time model and the Thomas model were applied to the experimental results. Both model predictions were in good agreement with the experimental data for all the process parameters studied, indicating that the models were suitable for Kanuma mud fix-bed column design. Column adsorption was reversible and the regeneration operation was accomplished by pumping 0.1 M NaOH through the loaded Kanuma mud column.

Research highlights
► Adsorption process followed the pseudo-second-order kinetic model.
► Maximum adsorption of fluoride was achieved within the pH range 5.0–7.0.
► Adsorption capacity was 3.067 mg/g calculated by the Freundlich isotherm model.
► The data obtained from column study fit BDST model well.
► Kanuma mud can be eluted with 0.1 M NaOH.