Abstract:
Adsorption of fluoride (F) ions from water using acid treated lateritic mineral (LM-1) from Kenya was
studied by batch experiments. The effect of acid-treatment of adsorbent and change in temperature,
mass of LM-1, pH and selected competing ions was evaluated. The adsorption process was strongly
influenced by temperature, pH and adsorbent dosage. The percentage F removal increased the
presence of the nitrate and the chlorate ions but decreased the presence of sulphates, chloride and
phosphate ions. Adsorption isotherms were classified according to Giles’ classification and the
adsorption data validated using Langmuir and Freundlich isotherms. The data correlated to both the
Langmuir and Freundlich isotherms although the data fit to the Freundlich model was somehow better.
This showed that F adsorption onto LM-1 followed a mixed adsorption mechanism in which
physisorption reactions involving intra-particle diffusion of F into mesoporous sites in LM-1 became
increasingly important at higher concentrations and temperatures whereas ion-exchange mechanism
involving surface OH
appear to dominate at low surface coverage in more alkaline conditions. With
maximum adsorption capacity of 10.5 mg/g, LM-1 could be used to remove F water.
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