A LANGMUIR TWO‐SURFACE EQUATION AS A MODEL FOR PHOSPHATE ADSORPTION BY SOILS

Abstract

Summary For forty‐one soils (pH > 5.0) from southern England and eastern Australia, the Langmuir equation was an excellent model for describing P adsorption from solutions < 10 ‐3 M P, if it was assumed that adsorption occurs on two types of surface of contrasting bonding energies. For most of these soils, which were relatively undersaturated with P, this equation may be written as: image where x = adsorption, k = adsorption/desorption equilibrium constant, x m = monolayer adsorption capacity, and c = equilibrium solution concentration. The relative magnitude of the parameters for each surface were approximately: x m = 0.3 x ″ m =0.3 and k′= 100 k. More than 90 per cent of the native adsorbed P occurs on the high‐energy surface in most soils.