Optimization study of adsorption parameters for removal of fluoride using aluminium-impregnated potato plant ash by response surface methodology

High fluoride level is a major threat to drinking water availability in many countries worldwide. Therefore, knowledge of its removal, using the best technique with optimal efficiency, is needed. In the present study, aluminium-impregnated potato plant ash (Al-IPPA) was used for removal of fluoride from synthetic fluoride solution. The Al-IPPA has high specific area and strong affinity towards fluoride. Synthesized Al-IPPA was characterized by point of zero charge, Fourier Transform infrared, scanning electron micrograph and XRD (X-ray diffraction) studies. Adsorption kinetics indicated that the adsorption equilibrium was reached within 30 min and the adsorption process followed the pseudo second-order model better. The equilibrium data were analysed using Langmuir, Freundlich, D-R and Temkin isotherm models. The Langmuir and D-R isotherm models could fit the experimental data well. Thermodynamic parameters such as Gibbs free energy (a dagger GA degrees), enthalpy (a dagger HA degrees) and entropy (a dagger SA degrees) changes of sorption were also evaluated, which indicated that the adsorption process was spontaneous, feasible and endothermic in nature. Furthermore, the coexisting anions had significant effect on fluoride adsorption. Finally, process parameters were optimized using response surface methodology. The desirability study highlighted the optimized process parameters: initial concentration 94.02 mg/l; pH 4.64; adsorbent dose 2.8 g/l; and contact time 57.0 min. On the other hand, perturbation study revealed that the process parameters such as contact time and initial fluoride concentration are the dominating factors. The desorption study with Al-IPPA showed that nearly 99 % of fluoride could be leached out at pH 12. However, up to pH 8.5, there is no leaching of fluoride. The reusable properties of material supported the possibility of its commercial use.