Standardization of bone char preparation for drinking water defluoridation of community waters.

Different bone char (BC) preparation methods can affect its physical and chemical properties and therefore its capacity to remove fluoride. Fluoride removal capacities of BC prepared at three controlled temperatures, with particle grain sizes of 250 - 500 µm, 500 - 1000 µm and 1000 - 1800 µm were determined in column experiments. The initial water fluoride concentration was 8.55 mg/L. The sorbents were calcined at 400oC, 500oC and 600oC. BC calcined at 400oC had better fluoride removal performance compared to those calcined at 500oC and 600oC. The adsorbent pore volume and surface area decreased as the calcination temperature was increased. There was a reduced mass transfer effect to the adsorption sites in pores as the BC particle size was increased. Langmuir equilibrium adsorption isotherm maximum monolayer coverage (Q) was determined to be 3.512 mg/g, and the value of separation factor (r) obtained was 0.1394 indicating favourable adsorption as it lies between 0 and 1. The Freundlich governing equilibrium adsorption isotherm model gave a value of 1/n equal to 0.445. This indicates favourable adsorption process since the bond energies increase with surface density of the adsorbent. The determination coefficient (R2) for pseudo first order ranged between 0.822 and 0.921 whereas the same values for the second order model range between 0.999 to 0.99998. This indicates that the experimental data best fitted the pseudo second order adsorption reaction. The findings therefore concluded that the bone char calcined at 400oC at heating rate of 8oC/min with particle size of 250 -500 µm developed the best physical and chemical properties for fluoride removal and hence recommended for application in to column defluoridation filters used for community defluoridation units.