Abstract
The ability of lateritic soils to remove fluoride from water has been studied. Important issues considered in the study include the relation between the mineral composition of soils and their ability to remove fluoride, the effect of thermal treatment of the soil on fluoride removal; the predominant fluoride containing species remain in the treated water and the possible mechanism of fluoride removal by lateritic soils. The fluoride removal capacity of thermally treated lateritic soils used in this study is in the range of 22 to 47 mmol/kg. The maximum capacity of 47 mmol/kg was obtained for RGS fired at 500 o C. The results obtained indicate that there is strong correlation between fluoride removal capacity and gibbsite content of the soil. From this it can be concluded that gibbsite is the active component in lateritic soils that strongly influence the fluoride removal capability. Speciation analysis reveals that at low initial fluoride concentrations the dissolution of gibbsite is facilitated by the adsorption of fluoride onto gibbsite. This may result in the formation of aluminum fluoro complexes in water. KEY WORDS : Fluoride removal, Laterite soils, Speciation analysis, Adsorption capacity, Thermal treatment Bull. Chem. Soc. Ethiop. 2012 , 26(3), 361-372. DOI: http://dx.doi.org/10.4314/bcse.v26i3.5
Highlights
Fluoride ion exists in natural waters and it is an essential micronutrient in humans in preventing dental caries and in facilitating the mineralization of hard tissues, if taken at a recommended range of concentration
The soil samples were characterized by X-ray diffraction (XRD) spectrometry and X-ray fluorescence (XRF) spectrometry at the University of Caliary, Italy and the University of Karlsuhe, Germany
The results of XRD spectroscopic analysis of the soil samples show that all the samples contained quartz, which has hardly any defluoridating capacity
Summary
Fluoride ion exists in natural waters and it is an essential micronutrient in humans in preventing dental caries and in facilitating the mineralization of hard tissues, if taken at a recommended range of concentration. Excess fluoride in drinking water is prevalent in all of the Rift Valley regions of the country [2, 3]. According to the Ministry of Water and Energy of Ethiopia, rural drinking water supply in the Rift Valley region is, to a large extent, dependent on groundwater [4, 5]. It becomes necessary to reduce the fluoride concentration within permissible limit of 1.5 mg/L according to the Ethiopian Standard for drinking water [4]. For communities in developing countries like the Rift Valley regions of Ethiopia where the groundwater is fluoride rich and provision of alternative water supply is difficult, treatment of contaminated water is the only option to provide safe drinking water
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