Synthesis and characterization of Fe-Al-Mn nanocomposite sorbent for phosphate sorption-desorption study

In this work, we evaluated the potential application of a ternary nanosorbent for predicting phosphate desorption kinetics from soil. Accordingly, ternary mixed oxide nanosorbents with Fe:Al:Mn mole ratios of 3:3:1; 6:3:1 and 2:4:1 were prepared using simultaneous oxidation and coprecipitation methods. The adsorbents were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, scanning electron microscope (SEM) coupled with EDX (energy dispersive X-ray) and Furrier transform infrared spectroscopy (FT-IR). The results indicated that the as-synthesized ternary oxides were either amorphous or crystalline depending on the composition from which the composite was formed, with specific surface area ranging from 41.2 to 243 m2g-1. Among the three proportions considered, the one with Fe:Al:Mn in 3:3:1 mole ratio exhibited the highest surface area and was selected for P sorption-desorption studies. Phosphate removal gradually decreased with the increasing of pH from 4 to 10.5. Adsorption isotherms on the adsorbent at pH 6.5 followed the order: Freundlich > Temkin > Dubinin-Radushkevich > Langmuir. At 35 °C, the maximum adsorption capacity for the adsorbent was found to be 49.95 mg g-1. The effect of coexisting anions on phosphate sorption followed the order: SiO32- > CO32– > SO42– > NO3- and this is closely correlated with charge-to-radius ratios of the anions. The kinetic data were described better by the pseudo-second-order adsorption model. The as-obtained nanocomposite sorbent with good specific affinity towards phosphate is a promising adsorbent for soil P desorption studies.