Standardizing defluoridation of community waters using bone char

Different bone char (BC) preparation methods affect the physical chemical properties and therefore the capacity to remove fluoride. Fluoride removal capacities of BC prepared at three controlled temperatures, with particle grain sizes of 250–500 μm, 500–1,000 μm and 1,000–1,800 μm were determined in column experiments with an initial fluoride concentration of 8.55 mg/L. The sorbent was calcined at 400°C, 500°C and 600°C. BC calcined at 400°C had better fluoride removal performance compared to those calcined at 500°C and 600°C due to decreased pore volume and surface area 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. The equilibrium adsorptions Langmuir and Freundlich isotherms were tested. For the Langmuir equilibrium adsorption isotherm, maximum monolayer coverage (Q) was determined to be 3.512 mg/g, and the value of the separation factor (r) obtained was 0.1394 indicating favorable 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 a favorable adsorption process, since the bond energies increase with surface density of the adsorbent.