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A mechanistic model for describing the sorption and desorption of phosphate by soil
Author(s) -
BARROW N. J.
Publication year - 1983
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1983.tb01068.x
Subject(s) - phosphate , desorption , sorption , adsorption , diffusion , chemistry , inorganic chemistry , phosphorus , divalent , chemical engineering , thermodynamics , organic chemistry , physics , engineering
Summary A model of phosphate reaction is constructed and its output compared with observations for the sorption and desorption of phosphate by soil. The model has three components: first, the reaction between divalent phosphate ions and a variable‐charge surface; second, the assumption that there is a range of values of surface properties and that these are normally distributed; third, the assumption that the initial adsorption induces a diffusion gradient towards the interior of the particle which begins a solid‐state diffusion process. The model closely describes the effects on sorption of phosphate of: concentration of phosphate, pH, temperature, and time of contact. It also reproduces the effects on desorption of phosphate of: period of prior contact, period and temperature of desorption, and soil: solution ratio. The model is general and should apply to other specifically adsorbed anions and cations. It suggests that phosphate that has reacted with soil for a long period is not ‘fixed’ but has mostly penetrated into the soil particles. The phosphorus can be recovered slowly if a low enough surface activity is induced.