Phosphate Sorption-Desorption Behavior of Some Acidic Soils of South and Southeast Asia
- S. K. Sanyal,
- P. Y. Chan and
- S. K. De Datta
The equilibrium phosphate sorption and release behavior and the kinetics of adsorption were studied in some acidic soils of South and Southeast Asia. Phosphate sorption data at 25 °C were fitted to the Tempkin, Freundlich, and Langmuir adsorption isotherms. The soils varied widely in their capacity to sorh and retain P. During desorption, the amount of sorbed P at a given equilibrium P concentration was always higher than that during sorption, indicating low desorbability of the sorbed P. The kinetic P sorption data at 21 and 35 °C were fitted to a modified Freundlich type of kinetic equation to obtain a parameter related to the sorption rate coefficient. The effect of temperature on the kinetics of sorption was small, suggesting the process is diffusion controlled. Equilihrium and kinetic P sorption parameters were found to he closely correlated with clay and organic matter contents and surface area of soils. A negative correlation between specific P sorption by clay or organic matter and clay or organic matter content of the soils suggests an association between the two colloidal components of the soils, causing loss of effective P-sorhing surface area. An attempt was further made to evaluate the differential change in free energy of P sorption at infinite dilution from the corresponding thermodynamic equilibrium constant for P sorption by the given soils. The results suggest that the stability of the P sorption reaction products in the given soils contribute to the P-fixing characteristics of these soils.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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