Phosphate Adsorption by Aluminous Hematites of Different Shapes
The phosphate adsorption capacity of 43 synthetic hematites having widely different shapes, specific surface areas and Al2O3 mole fractions ranged between 0.19 and 3.33 µmol P m−2, with a mean value of 0.97 µmol P m−2. There was a significant decrease in the adsorption capacity when the diameter/thickness ratio of the particles increased; this agrees with the hypothesis that, because of the distribution and type of surface hydroxyls, the basal faces of hematites are not able to adsorb phosphate, in contrast with some of the nonbasal faces. The low adsorption capacity of the hematites studied here, as compared to many natural and synthetic goethites, gives a reason why, as reported in the literature, red (hematitic) soils adsorb less phosphate than similar yellow (goethitic) soils.
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