Kinetics and thermodynamics of defluoridation of drinking water using high performance hybrid zirconium (IV)-hexamethylenediamine: A comparative aspect with ion-exchanger amorphous zirconium (IV) phosphate

The present investigation reports the synthesis and fluoride removal characteristics of zirconium (IV)-hexamethylenediamine (ZrHMDA). The ion-exchanger was prepared using environment friendly sol-gel method by mixing of molar proportion of aqueous solution of zirconium oxychloride (0.1 M) and aqueous solution of hexamethylenediamine (0.1 M). The organic-inorganic hybrid sorbent ZrHMDA shows enhanced fluoride removal capacity in comparison to amorphous zirconium phosphate (AZrP) ion-exchanger. All prepared materials were characterized and defluoridation kinetics were studied with variation of solution parameters. The experimental results indicate efficient fluoride adsorption (>99%) by ZrHMDA with quick attainment of adsorption equilibrium. A pseudo second order kinetic model, with both theoretical adsorption capacity (qe,cal, mg g−1) and experimental adsorption capacity (qe,exp, mg g−1) found close value to each other, fitted well to experimental data, thus explaining defluoridation kinetics. Evaluation of thermodynamic parameters indicated feasibility and spontaneity of material-anion interaction. Reusability of ZrHMDA was tested up to 10th consecutive cycles of operation without significance loss of adsorption efficiency. It was found that almost 94% fluoride could be desorbed from fluoride adsorbed ZrHMDA using dilute (0.001 M) aqueous solution of NaOH.