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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/2645

Authors: Fentahun, Adeno
Advisors: Feleke Zewge (Ph.D)
Yonas Chebude (Ph.D)
Keywords: nano-scale AlOOH
Fluoride removal efficiency
Adsorption kinetics
Copyright: Mar-2010
Date Added: 6-May-2012
Publisher: AAU
Abstract: Fluoride generates effects on skeletal tissues (bones and teeth) and has a narrow range between intakes that cause beneficial and detrimental health effects. Elevated levels of fluoride (>1.5 mg/L) in drinking water supply based on groundwater is a problem in a number of countries and resulting in an increase in the occurrence of dental and skeletal fluorosis in the affected people. Even though there are numerous effective methods to remove fluoride ion from water most of them are not feasible for developing countries due to their high cost. Adsorption is one of the techniques for the removal of fluoride from water. So far, studies explored the efficiency of various substances such as activated carbon, activated alumina, bone char and clay minerals as adsorbents for the removal of fluoride from water. The most desirable properties of the adsorbent are strong affinity for fluoride and high adsorption capacity. The present study has concentrated on investigating the fluoride removal potential of nano-scale aluminum oxide hydroxide (nano-AlOOH) produced by controlled precipitation method from aluminum nitrate and ammonium bicarbonate, from aqueous solution. A series of batch adsorption experiments were carried out to assess parameters that influence the adsorption process. The parameters considered were contact time and adsorbent dose, thermal treatment of adsorbent, initial fluoride concentration, pH and water temperature. Result showed that most of the adsorption took place during the first 30 min; and the adsorption equilibrium reached at one hour contact time with an optimum adsorbent dose of 1.6 g/L for initial fluoride concentration of 20 mg/L. The removal efficiency of fluoride was increased with adsorbent dosage. Fluoride adsorption efficiencies increase with increase in the thermal treatment temperature up to 300 °C, however further increase in temperature resulted in decreased removal efficiency. The fluoride removal efficiency raise as the pH of the solution increase from pH 3 to 8, but further increase in pH the adsorption efficiency decreased; may be due to the hydroxide ion competition ix with fluoride ion. Fluoride adsorption capacity increases linearly with increase in fluoride concentration. The adsorption data were well fitted to the Langmuir isotherm model with a maximum capacity of 62.5 mg F-/g. The kinetic studies showed that the adsorption reaction of fluoride removal by nano-AlOOH obeys a pseudo-second-order rate equation. Therefore, nano-AlOOH possesses a maximum fluoride adsorption capacity and maximum adsorption occurred at around pH 7 with initial fluoride concentration of 20 mg/L, which makes nano-AlOOH a potential adsorbent for drinking water treatment. The intra-particle diffusion was not a rate-controlling step for the adsorption process. The thermodynamic studies revealed that the adsorption of fluoride by nano-AlOOH was an endothermic and the adsorption process is spontaneous. Thus the adsorbent needs further investigation or characterization in order to initiate projects to conduct pilot study and develop defluoridation unit at different level.
URI: http://hdl.handle.net/123456789/2645
Appears in:Thesis - Environmental Sciences

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