World Bank assisted National Agricultural Research Project (NARP) - University of Port Harcourt
Doi
Abstract
African countries along the Great Rift Valley are among areas of the
world where excess fluoride in water sources is a major public health
problem. In this work, the removal of fluoride (F) from water solutions
using a ferric poly-mineral (FPM) from Kenya was therefore studied
using batch adsorption experiments. The effect of change in solution
pH, temperature, initial concentration of F, mass of FPM, contact time
and presence of various competing ions on F adsorption onto FPM was
evaluated. Adsorption isotherms were then applied to the adsorption
data to characterize and establish the adsorption capacity of the
mineral. The adsorption of F onto FPM was found to be a fast process
and, at 1000 mg/L initial F concentration at pH 3.32 and 293 K and
using 0.2 g/mL adsorbent dosage, over 90% F removal from solution could
be achieved in 30 min. Based on Giles system of classification of
adsorption isotherms, F adsorption isotherm conformed to L4
Langmuir-type isotherms. This indicated that FPM is composed of a
heterogeneous surface consisting of sites which, during adsorption,
filled-up with F ions in succession. The adsorption data also
correlated to Langmuir and Freundlich models indicating that F
adsorption onto FPM was a mixed process involving chemisorption onto
surface sites followed by gradual intra-particle penetration of F into
mesoporous structure of the mineral. High mean Langmuir adsorption
capacity of 10.8 mg/g, indicate that the mineral could be of use as an
inexpensive substrate for the removal of F from aqueous streams