• Adsorbent was prepared by calcination at 500 °C.
  • Jamum leaf ash (JLA) rich in calcium and calcium minerals favoured F adsorption.
  • F adsorption was a complex process involving both boundary layer effect and intraparticle diffusion.
  • Adsorption process of fluoride by JLA was spontaneous, feasible and exothermic.

Removal of fluoride was done by adsorbent prepared from leaves of Syzygium cumini. Adsorbent preparation was done by calcination (500 °C) and characterized by multiple physiochemical, and micro-analytical techniques including EDS, FT-IR, TGA and XRD. The adsorbent was mainly composed of calcium carbonate and calcium oxide/hydroxide. Adsorption study revealed a maximum fluoride removal efficiency of 77.8% with uptake capacity 4.56 mg g-1, within 60 min of contact time from an initial 6 mg L-1 fluoride solution with adsorbent dose 6.5 g L-1 at pH 6.5 and temperature 300 K. Fluoride adsorption data obtained best fitted to the Freundlich isotherm model, signified a multilayer adsorption process. Additionally, the mean calculated adsorption energy (1 kJ mol-1) from the Dubinin-Radushkevich model suggested a physical adsorption process. The kinetic adsorption data showed agreement to the pseudo-second-order and intraparticle diffusion model, both signifying that the removal of fluoride involved boundary layer effect and intraparticle diffusion. Spontaneous and exothermic nature of the adsorption process was revealed by the thermodynamic parameters. Finally, the adsorbent successfully purified two real water samples contaminated with fluoride. The results suggested that physical adsorption with some effect of electrostatic interaction and anion exchange was also involved in the fluoride adsorption. This study will be useful in designing new calcium based low-cost adsorbent from biological wastes for removing fluoride from contaminated water.

Graphical abstract