Describing the effect of time on sorption of phosphate by iron and aluminium hydroxides

N. S. BOLAN, N. J. BARROW, A. M. POSNER

Research output: Contribution to journalArticle

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Abstract

Iron and aluminium hydroxides were precipitated both in the presence and absence of kaolinite. The reaction between phosphate and these hydroxides was measured for periods which ranged from 5 min to 72 h. The effect of time on phosphate sorption was examined by plotting the sorption data according to different, simple, kinetic equations such as the first order, second order, the parabolic diffusion equation, the Elovich equation and the modified Freundlich equation. The effect of time on sorption was also examined by the mechanistic model recently developed by Barrow (1983b) for the sorption and desorption of phosphate by soils. The sorption of phosphate by iron and aluminium hydroxides increased with time and the reaction continued through the period of observation without reaching a true equilibrium. Curvilinear relationships were obtained when the data were plotted according to the simple kinetic equations. These simple kinetic equations fail to describe the effect of time on sorption partly because the mechanism is different from that postulated and partly because they do not consider electrostatic effects when phosphate ions react with a charged surface. The mechanistic model of Barrow (1983b), which takes this effect into account, described effect of both concentration and time on phosphate sorption. According to this model, the increase in phosphate sorption with time was caused by a redistribution of adsorbed phosphate into the interior of the particles of iron and aluminium hydroxides by solid‐state diffusion.

Original languageEnglish
Pages (from-to)187-197
Number of pages11
JournalJournal of Soil Science
Volume36
Issue number2
DOIs
Publication statusPublished - 1 Jan 1985
Externally publishedYes

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iron hydroxides
Aluminum Hydroxide
aluminum hydroxide
sorption
hydroxide
Iron
aluminum
Phosphates
phosphate
phosphates
iron
mechanistic models
barrows
kinetics
Hydroxides
Kaolin
hydroxides
effect
kaolinite
Static Electricity

Cite this

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abstract = "Iron and aluminium hydroxides were precipitated both in the presence and absence of kaolinite. The reaction between phosphate and these hydroxides was measured for periods which ranged from 5 min to 72 h. The effect of time on phosphate sorption was examined by plotting the sorption data according to different, simple, kinetic equations such as the first order, second order, the parabolic diffusion equation, the Elovich equation and the modified Freundlich equation. The effect of time on sorption was also examined by the mechanistic model recently developed by Barrow (1983b) for the sorption and desorption of phosphate by soils. The sorption of phosphate by iron and aluminium hydroxides increased with time and the reaction continued through the period of observation without reaching a true equilibrium. Curvilinear relationships were obtained when the data were plotted according to the simple kinetic equations. These simple kinetic equations fail to describe the effect of time on sorption partly because the mechanism is different from that postulated and partly because they do not consider electrostatic effects when phosphate ions react with a charged surface. The mechanistic model of Barrow (1983b), which takes this effect into account, described effect of both concentration and time on phosphate sorption. According to this model, the increase in phosphate sorption with time was caused by a redistribution of adsorbed phosphate into the interior of the particles of iron and aluminium hydroxides by solid‐state diffusion.",
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Describing the effect of time on sorption of phosphate by iron and aluminium hydroxides. / BOLAN, N. S.; BARROW, N. J.; POSNER, A. M.

In: Journal of Soil Science, Vol. 36, No. 2, 01.01.1985, p. 187-197.

Research output: Contribution to journalArticle

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