Adequate fluoride intake is necessary in developing health bones and teeth and for the prevention of dental caries. Too much fluoride intake, however, leads to dental, skeletal and soft tissue damage, an irreversible condition that has no cure; prevention is the only remedy for this menace. Today fluorosis remains an important clinical and public health problem in many parts of the world. In Kenya native fluorosis has been problematic for several years and as a result there is a serious concern over the destiny of fluoride (F) in the environment especially the ground and sources of water underground, especially in areas associated with the Great Rift Valley and the Central Highlands. People get exposed to excessive fluoride through food, soil and water. However, drinking water with excessive fluoride remains the primary pathway of human exposure to hazardous levels of fluoride from the environment. Providing water, with optimal fluoride concentration is, therefore one of the ways by which the future generation can be protected against the disease. Defluoridation is the conventional and widely tested method for supplying safe water to the fluorosis affected communities. In the current study a number of low cost materials, which included sulphonated polystyrene (SPS), fish scales and chicken feathers single and combined forms were investigated for fluoride adsorption. These materials were ground and tested for fluoride removal in water using both simulated solutions and natural high Fluoride water from Lake Elementaita. The adsorbents were also modified using solutions containing Ca2+, Mg2+ and Al3+ ions. Characterization of the adsorbents was done by use of FTIR and SEM. The fluoride adsorption properties of the adsorbents were then assessed with respect to changes in adsorbent dosage, contact time, agitation rate, solution pH, temperature and initial fluoride concentration. Batch and column tests were carried out using natural high-fluoride water in order to assess the efficacy of the adsorbents to adsorb fluoride. Solution parameters and chemical composition of the adsorbents were found to control fluoride adsorption onto the adsorbents. According to the batch tests, aluminium modified feathers showed the highest maximum fluoride adsorption capacities of 285 mg/g. The fish scales had a capacity of 133 mg/g, while SPS had 22 mg/g fluoride adsorption and combined adsorbents 34 mg/g. The fluoride adsorption equilibrium data for the adsorbents were fitted by the Giles, the Langmuir and the Freundlich isotherms. The Al feathers, SPS and fish scales showed a similarity with the C isotherm classification by Giles, while the combined adsorbents curve showed a resemblance with the S Giles classification of isotherms. Basing on the Langmuir and Freundlich isotherms, fluoride adsorption onto the adsorbents was therefore based on mixed reactions. However, the SPS did not fit on both the Langmuir and Freundlich isotherms. Additionally, the fluoride adsorption data for the adsorbents were correlated to pseudo-first order, pseudo second order and Weber-Moris intraparticle diffusion kinetic models. For the pseudo first-order plots were found linear with good correlation coefficients (>0.9) indicating the applicability of pseudo first-order model in this study. However, the correlation coefficient (R2) values for pseudo second-order adsorption model had high values; hence the adsorption kinetics of fluoride onto the adsorbents could be better described by pseudo second order model. The fluoride adsorption onto the adsorbents described by Weber-Moris intraparticle diffusion model, had all the R2 values greater than 0.9. The fluoride adsorption data based on the column experiments were analyzed using the Thomas model. The adsorbent were regeneratated using 1 M NaOH. The adsorbents showed good fluoride adsorption capacities and they could be utilized as low cost adsorbents to defluoridate high fluoride drinking waters and help to alleviate endemic fluorosis

University of Eldoret



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