DEFLUORIDATION OF DRINKING WATER BY USING CALCIUM LOADED BENTONITE

Abstract

BACKGROUND: Endemic fluorosis is a serious problem due to ground water contamination by fluoride. In Ethiopia the distribution of fluorosis extents outside the region of the rift valley to some highland regions. The concentration of fluoride level in rift valley region is above 5.0mg/L in hot springs and other water sources. Hence, it is very much essential to supply safe drinking water to the consumers in these regions. Therefore this study examined, a newer ecofriendly defluoridation method was developed by using bentonite clay minerals. METHODS: The experimental solution was prepared by using analytical grade NaF. The concentration of the stock solution was 0.1M. Pure bentonite C obtained from the Department. of Geology, University of Caliary, Italy. The main mineral present in bentonite is montmorillonite, having a formula of (Na, Ca)(Al, Mg) 6 (Si 4 O 10 ) 3 (OH) 6.nH2O and modified chemically by using 0.5M CaCl 2 solution to enhance the ion – exchange capacity. The chemically modified bentonite formula is (Na, Ca)(Al, Mg) 6 (Si 4 O 10 ) 3 (OH) 6 . (CaCl 2 ). nH2O. Red clay samples were collected from the local study area (Akaki region). The experiment was conducted during the period 2003. Ion – exchange experiments and adsorption experiments were conducted in batch processes. Finely graded samples of bentonite minerals and red clay were used for this purpose. The free fluoride concentration was determined by using potentiometric method and atomic adsorption spectroscopic method. All the defluoridation experiments were performed at room temperature 22±2 0 C. RESULTS: The ion exchange capacity of the calcium-loaded bentonite was found to be 0.275mmol Ca 2+ /g of bentonite. The ion exchange capacity of untreated bentonite was 0.013 mmol Ca 2+ /g. This results indicate that calcium loaded bentonite mineral have good defluoridation capacity. The concentration – time dependency of defluoridation of calcium loaded and raw bentonite mineral showed a good decreasing trend. The rise in free fluoride concentration was due to the influence of dissolved Ca 2+ ions, because this ion is originally present on the surface of solid bentonite minerals. After proper stirring, the free fluoride ions precipitated as CaF 2 and intern removed from the solutions. Further, the fluoride removal efficiency between calcium loaded, original bentoniteshowed that the percentage removal of 44 for calcium loaded, and 25 for original bentonite. CONCLUSION: The defluoridation efficiency of Calcium-loaded bentonite is excellent. Hence, this process can be recommended for the water treatment. The untreated bentonite clay minerals have less efficiency in fluoride removal. The red clay can also be used in removal of fluoride effectively. These methods are economically feasible for providing safe drinking water.