Dissertation (MSc. Chemistry)This study aims to assess the fluoride adsorption characteristics of the two clay minerals categorized into ten groups i.e bentonite alone (B), bentonite impregnated with 1% sodium hydroxide (BS), thermally activated bentonite (800 0C) (BAA), bentonite impregnated with iron (BI), bentonite impregnated with aluminum (BA), mica alone (M), mica impregnated with 1% sodium hydroxide (MS), thermally activated mica (800 0C) (MAA), mica impregnated with iron (MI) and mica impregnated with aluminum (MA) on the fluoride contaminated water from Hai District of Kilimanjaro region of Tanzania. Characterization done by XRF for B and M, showed that highest percentage composition of SiO2, CaO, P2O5, Fe2O3, Al2O3, MgO, K2O and Na2O before impregnation and after impregnation showed higher composition of Fe2O3, SiO2, CaO, Al2O3, K2O, and P2O5. XRD showed higher composition of illite, calcite, quartz and albite for B and M. Batch experiments were conducted to see the fluoride removal efficiency by the use of homogeneous mixture of water having 16 mg/L of fluoride using fluoride ion selective electrode. The removal efficiencies obtained in this study were 83.73%, 92.70%, 94.98%, 76.02, 90.21%, 94.40%, and 96.88% for BAA, BI, BA, M, MAA, MI and MA respectively. The best ratio of impregnation was 7.9:0.1 g, 6.9:0.1 g, 8.9:0.1 g and 7.9:0.1 g for BI, BA, MI and MA, The optimum pH were found to be 8, 3, 7, 7.3, 4.4 and 7.5 and the optimum doses of 9, 8, 7, 10, 9 and 8 g, optimum contact time of 70, 60, 50, 40, 35 and 30 minutes for the BAA, BI, BA, MAA, MI and MA with the batch volume of 50 mL. The materials were regenerated and reused by using 1%NaOH and 1% HCl. The adsorption process obeyed Langmuir adsorption model for BAA and BI; and Freundlich model for MA. BA, MAA and MI agreed with both Langmuir and Freundlich models. For the kinetics perspective, the fluoride adsorptive reaction followed the pseudo-second order model. Therefore the activated and impregnated bentonite and mica are the best for water defluoridation.