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A Chemical Model of Phosphate Adsorption by Soils: I. Reference Oxide Minerals: II. Noncalcareous Soils
Author(s) -
Goldberg Sabine,
Sposito Garrison
Publication year - 1984
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1984.03615995004800040056x
Subject(s) - soil water , citation , phosphate , chemistry , adsorption , library science , mineralogy , computer science , geology , soil science , biochemistry
The Constant Capacitance model is shown to provide a quantitative description of o-phosphate adsorption by a variety of aluminum and iron hydrous oxides, including the effect of varying pH values. This model, based on a ligand exchange mechanism for ophosphate adsorption, comprises six adjustable parameters: two surface protonation-dissociation constants, three o-phosphate surface complexation constants, and a capacitance density parameter. The five surface equilibrium constants can be obtained from potentiometric titration data and o-phosphate adsorption data. These constants are independent of pH but, in principle, can depend on the composition of the background electrolyte solution. The capacitance density parameter cannot be obtained directly from experiment. A working value can be chosen on the basis of previous applications of the Constant Capacitance model and other model parameters are not sensitive to this choice. Additional Index Words: anion adsorption, ligand exchange, surface chemistry, o-phosphate. Goldberg, S., and G. Sposito. 1984. A chemical model of phosphate adsorption by soils: I. Reference oxide minerals. Soil Sci. Soc. Am. J. 48:772-778. T REACTIONS between o-phosphates and soils often have been described mathematically with adsorption isotherm equations (Olsen and Watanabe, 1957; Syers et al., 1973; Holford et al., 1974; Fitter andSutton, 1975; Barrow, 1978;Berkheiseretal., 1980; 1 Contribution from the Dep. of Soil and Environmental Sciences, Univ. of California, Riverside, CA 92521. Received 25 Oct. 1983. Approved 14 Mar. 1984. 2 Former Graduate Research Assistant and Professor of Soil Science, respectively. The senior author is presently Soil Scientist, U.S. Salinity Lab., 4500 Glenwood Drive, Riverside, CA 92501. Harter and Smith, 1981; Travis and Etnier, 1981; Mead, 1981). These equations usually are special cases of the expression: