Kafkafi, U.
Sposito, G.

Phosphate reactions in soils are affected by various factors operating simultaneously. The objective of this work was to study specific effects of total P concentration, pH, ionic strength, and equilibration time on P partitioning between solid and solution phases of Ca- and K-kaolinite and -montmorillonite suspensions as model systems of soils containing these minerals decreased Cp in both clay systems. Phosphorus adsorption by Ca-clay exceeded that by K-clay. This, and the effect of EC on Cp are suggested to operate via their effect on the extent of the diffuse double layer, which determine the accessibility of P to adsorption sites on clays' edges. Phosphorus solution concentration as a function of pH was minimal in the studied clays around pH 6. In the investigated pH range (5-9), P partitioning was controlled by adsorption, which could be described by a modified Langmuir model. The model accounts for effects of Cp and pH on adsorption and considers retention of individual P species by the adsorbent. -from Authors