Fluoride Adsorption onto Acid-Treated Diatomaceous Mineral from Kenya

Enos W. Wambu, Charles O. Onindo, Willis J. Ambusso, Gerald K. Muthakia

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DOI: 10.4236/msa.2011.211220                

Abstract

Acid treated diatomaceous earth (ATDE) from a mining site in Kenya was evaluated for its removal of F from aqueous solutions using adsorption batch experiments. The effect of initial F concentration, adsorbent dosage, contact time, temperature, pH and competing anions was studied. The adsorption process was very fast reaching an initial equilib- rium in just 10 min. Fluoride adsorption onto ATDE increased strongly from just about 40% to over 92% when the solution temperature was raised from 293 to 303 K. The process was however, almost unresponsive to pH changes drop- ping by a margin of < 1% from 98.8% to 98% when the solution pH was raised from 1.59 to 6.89. It was obvious therefore that increase in concentration of OH^- ions does not affect F adsorption onto ATDE. More so apart from the Cl^- ions which marginally reduced F adsorption onto ATDE, there was no obvious effect of the SO₄^2- , NO₃^- and PO₄^3- ions on F uptake by ATDE. Complete F removal (100% adsorption) could be achieved at 400 mg/L initial F concentra- tions using 0.5 g/mL ATDE batch loading ratio at 303 - 313 K and pH = 3.4 ± 0.2. The F adsorption iso- therm was well correlated to the Freundlich and Langmuir models and could be classified as H-Type according to Giles classification of isotherms. The maximum Langmuir F adsorption capacity of ATDE was 51.1 mg/g. It has been demonstrated that a diatomaceous mineral from Kenya could be use as an inexpensive adsorbent for the removal of F ions from aqueous streams.

Keywords

Acid Activated Diatomaceous Earth, Competing Anions, Fluoride Adsorption Isotherms

Conflicts of Interest

The authors declare no conflicts of interest.

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