Phosphorus adsorption by kaolinite and montmorillonite. I. Effect of time, ionic strength, and pH
1988
Bar-Yosef, B. | Kafkafi, U. | Rosenberg, R. | Sposito, G.
Phsophate 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. Phosphorus concentration in the solution phase (Cp) stabilized within 24 to 48 h after introducing P into the system. Increased electrolyte concentration, which elevated the electrical conductivity (EC) from 0.2 to 5.0 dS/m, decreased Cp in both clay systems. Futher increase to about 40 dS/m had a negligible effect on Cp. 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.
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