We studied fluoride sorption by montmorillonite and kaolinite dominated by either Ca2+ or K+ as a function of F solution concentration, pH, and solution-to-clay ratio. Within an F concentration rate of 0 to 180 μM and at pHs between 4 and 9, F concentration in the solution of the studied suspensions was governed by adsorption. Adsorption decreased with increasing pH values and was negligible at pH > 8.5. A competitive Langmuir model simulated satisfactorily F retention by the adsorbents under the studied experimental conditions. The maximum adsorption capacity parameter was greater for kaolinite than for montmorillonite and greater for Ca-dominated clays than for K-clays. The affinity of the F species to the surface was maximum in K-kaolinite and minimal in Camontmorillonite.
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