Abstract:
In this study, ternary mixed oxide, Fe3O4/Al2O3/MnO2 adsorbents where synthesized for
desorption of phosphorus with ratios of NC1 (90:5:5), NC2 (80:15:5) and NC3 (70:15:15)
interms of percentage composition of Fe, Al, and Mn, respectively from its precursor, ferric
chloride hexahydrate and ferrous chloride tetra hydrate, aluminum nitrate nonahydrate and
manganese oxide by co-precipetation method under nitrogen atmosphere in basic condition and
investigated for their phosphorus (P) desorption capacity. Among these NC2, which was found to
have high surface area and small size was selected and used for long-term P desorption and
kinetic studies. The as-sythesized adsorbents were characterized with XRD, FTIR, FAAS, BET,
SEM and EDX. Crystal structure of selected nanocomposite was slightly amorphous with a
particular of size 22.75 nm and 203.69+1.34 m2
/g surface area. The study of phosphorus
desorption were carried out on four different acidic soil samples, which were incubated for three
months and twenty two days with four different concentration of (0,50,100 and 150 mg/kg) P.
The simulation of P desorption from soil to plant was predicted by dialysis membrane tube filled
with hydrous iron-aluminum-manganese oxide. DMT-HFAMO was found to be a promising
adsorbent to simulate the plant–P relation in acidic soil or to estimate the properties of soil for P
desorption to the soil solution. The observed desorbed P was significant in the order of Boji
Dirmaji < Kiltu Kara < Mene Sibu < Nedjo and order of treatments P0 (0) < P1 (50) < P2 (100) < P3 (150) mg/kg for all soil samples. The releasing rate of P from soil to solution
followed first order kinetics having rate constant (0.021-0.028 h-1
) and rapid release of P with in
the first two weeks followed by a slower release and it was still continuing after 28 days of
desorption. The physicochemical properties like available P, total P, organic carbon, bulk
density, iron extracted by dithionite, iron extracted by oxalate, and manganese extracted by
dithionite were correlated with cumulative desorbed P positively or negatively.
