Adsorption of fluoride from aqueous solution by a new low-cost adsorbent: thermally and chemically activated coconut fibre dust

Fluoride is a persistent and non-biodegradable pollutant that accumulates in soil, plants, wildlife and human beings. Therefore, knowledge of its removal, using the best technique with optimum efficiency, is needed. In the present study, the potential usage of coconut fibre (Cocos nucifera), which is an agricultural waste, in the adsorption of fluoride from aqueous solutions was evaluated with respect to various experimental parameters including pH, adsorbent dose, contact time, agitation speed, initial fluoride concentration and temperature. The objective is to expand upon research of new and existing fluoride removal technologies or promote a new, alternative process. In the present study, the maximum adsorption capacity was recorded as 12.66, 25.64 and 38.46 mg/g for CFD-1, CFD-2 and CFD-3, respectively. From the kinetic study, it was found that fluoride adsorption by coconut fibre dust followed pseudo-second-order kinetics with an average constant of 0.002, 0.003 and 0.004 g/mg min for CFD-1, CFD-2 and CFD-3, respectively. Intraparticle diffusion model was studied to determine the rate-limiting step of the adsorption process. Thermodynamic parameters such as Gibb's free energy (a dagger GA degrees), enthalpy (a dagger HA degrees) and entropy (a dagger SA degrees) changes were determined for the adsorption process. Negative a dagger HA degrees value signified that the adsorption process was exothermic in nature. Results from this study demonstrated potential utility of CFD adsorbent which could be developed into a suitable method for fluoride removal from aqueous solution.