Fluoride Removal by Lateritic Soil and Electrochemically Formed Al(Oh)3

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Addis Ababa Universty


The ability of lateritic soils to remove fluoride from water was studied to clarify some basic issues a) is there a correlation between the mineral composition of the soils and their ability to remove fluoride? b) which processes account for the fluoride removal? c) is the fluoride removal ability increased by a thermal treatment of the soils? and d) which kind of fluoride containing species remain in the soil treated water? The results obtained indicate that fluoride removal and gibbsite content of the soils are correlated. From this it can be concluded that gibbsite is the active component in lateritic soils in the fluoride removal. Speciation analysis reveals that at low free fluoride concentrations the dissolution of gibbsite facilitated by the adsorption of fluoride onto gibbsite accompanied by the formation of aluminum fluoro complexes can explain the mechanism of fluoride removal. The question to which extent the exchange of hydroxide ion with fluoride ion in gibbsite takes place in the defluoridation process cannot be answered with certainty. The electrochemical investigations of aluminum electrodes by cyclic voltammetry, impedance spectroscopy and potentiometry have shown that passivation of the aluminum electrodes is a drawback of the defluoridation of low fluoride solutions by electrochemically generated Al(OH)3 but it might be possible at higher fluoride concentrations. Key words: Fluoride removal, lateritic soils, speciation analysis, complexed fluoride, Alzheimer’s disease, electrochemical behaviors, passivation, votammogram, impedance spectroscopy, removal capacity and adsorption isotherm.



Fluoride removal; lateritic soils; speciation analysis; complexed fluoride; Alzheimer’s disease; electrochemical behaviors; passivation votammogram; impedance spectroscopy; removal capacity and adsorption isotherm.