Modifications to the Freundlich equation to describe anion sorption over a large range and to describe competition between pairs of ions

• Published in: European journal of soil science Vol. 56; no. 5; pp. 601 - 606
• Main Authors: Barrow, N. J., Cartes, P., Mora, M. L.
• Format: Journal Article
• Language: English
• Published: Oxford, UK; Malden, USA Blackwell Science Ltd 01.10.2005; Blackwell Science
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Geochemistry; Mineral components. Ionic and exchange properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Soil and rock geochemistry; Soil science; Competition; Modification; computer programs; Physical chemistry; mathematical models; Andisols; Ionic interaction; sorption; selenites; Freundlich isotherm; Soil science; soils; anions; Soil chemistry; geochemistry; Ion pair; Property of soil; Inorganic ion; Equation; Mineral soils; Earth science; Inorganic anion; physicochemical properties; phosphates; Selenium compound; Phosphorus compound
• ISSN: 1351-0754; 1365-2389
• DOI: 10.1111/j.1365-2389.2005.00700.x

Summary We measured sorption of selenite and phosphate, both separately and in competition, in a Chilean Andisol. We also used previously published data for competitive sorption of arsenate and phosphate by a clay subsoil. We wrote computer programs that allowed us to compare the fits of differing versions of equations to describe individual sorption and competitive sorption. For the selenite–phosphate data, the index term of the Freundlich equation decreased as concentration increased. This was described using the Sibbesen modification of the Freundlich equation. This modification was then included in competition equations. For both the selenite–phosphate and the arsenate–phosphate data, competition was not ‘symmetrical’, that is, the competition terms were not reciprocals of each other. We think this occurred because competition between ions is not only competition for adsorption sites but also involves electrical effects that follow penetration of the surface.