Abstract:
The fate of excessive fluoride in water is cause for serious public health concerns worldwide. Water
defluoridation using various technologies therefore continues to attract disproportionate research
interest from around the world. Defluoridation studies using soil adsorbents, in particular, have
remained the focus of intense research efforts since the last few decades. So as to assess the
research status in this area, soil adsorbents commonly reported for water defluoridation over the last
few decades were reviewed. This paper presents a compilation of defluoridation capacities and a
summary of requisite parameters for water defluoridation using soil adsorbents. Comparison of
defluoridation efficiencies of soil adsorbents is also presented, and the fluoride adsorption kinetics
and adsorption equilibrium characteristics of adsorbents discussed. The results indicate that the soil
adsorbents that have attracted highest research interest in this regard include hydroxyapatites,
montmorillonites, hydrotalcite, zeolites, pumice and kaolinites. On average, however, the minerals
that have shown the highest capacities for water defluoridation are: ferrihydrites, hydrotalcite,
palygorskites, boehmite/bauxite, and pumice. Fluoride adsorption for most soil adsorbents is fitted
by the Langmuir and Freundlich isotherms. Most of the kinetic data, in contrast, were described by
the pseudo-second order kinetics model. Water pH and temperature were the dominant solution
factors that controlled fluoride adsorption onto soil adsorbents.
|