Abstract:
The fluoride and phosphate adsorption capacity of Fe3O4/Al2O3/ZrO2 ternary oxide synthesized
by chemical coprecipitation method was studied because, excess amounts of fluoride and
phosphate in water bodies lead to fluorosis and eutrophication problems, respectively. The
practically obtained percentage composition of Fe, Al and Zr in the synthesized nanocomposite
was 72.3, 23.9 and 3.8, respectively. The surface structure of the material was investigated by
means of X-ray diffraction (XRD), Fourier transform-infrared (FTIR) and Brunauer- emmerteller
(BET) to understand the effect of surface properties on the adsorption behavior of fluoride
and phosphate. The specific surface area of this ternary oxide was found to be high (205.16
m2/g). The effects of different experimental parameters, namely, solution pH, dosage, contact
time, speed of agitation and initial fluoride and phosphate concentration were also investigated.
The optimum values of these parameters were obtained as, 4, 0.5 g, 12 h, 100 rpm and 20 ppm,
respectively for fluoride and 5, 0.1 g, 8 h, 100 rpm and 10 ppm for phosphate. The experimental
results showed that the adsorbed amounts of fluoride and phosphate tend to decrease with
increase in pH. Fluoride adsorption best fit with Freundlich isotherm model and phosphate
adsorption fit well with Langmuir isotherm model. Kinetic data of both ions correlated well with
the pseudo-second-order kinetic model. The desorbability of these ions from the adsorbent is
very low when pH of the solution is below 8. Maximum desorption was achieved at pH 12 for both ions. The thermodynamics study shows that the value of ΔG and ΔH are positive in case of
fluoride adsorption. Thus, the interaction of fluoride with the adsorbent is nonspontaneous and
endothermic where as phosphate adsorption is spontaneous and exothermic as indicated by
negative values of ΔG and ΔH.
