Testing a mechanistic model. I. The effects of time and temperature on the reaction of fluoride and molybdate with a soil

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Abstract

A mechanistic model that had been developed to describe the reaction of phosphate with soil was applied to the reactions of fluoride and molybdate with soil. The model assumes that: there is an initial adsorption reaction between ions and charged surfaces; that the surfaces are not uniform in their properties; and that the initial adsorption is followed by diffusive penetration. The model was developed beyond that previously published to permit the rate of the initial adsorption reaction to be included. The model reproduced the effects of solution concentration, and of increasing period and temperature of incubation, on the retention of both fluoride and molybdate. Increasing the temperature of incubation increased the retention, or decreased the solution concentration, and this was reproduced by the effect of temperature on the rate of diffusive penetration. Desorption of fluoride was also reproduced. This supports the argument that slow desorption is mostly due to the need to reverse the diffusive penetration. After incubation at constant temperature, increasing the temperature at which solution concentration of molybdenum was measured, increased the concentration. The direction of this effect of temperature was also reproduced. It arises because of the effect of temperature on the position of the equilibrium between adsorbed molybdate (in the strict sense of the term) and molybdate in solution.

Original languageEnglish
Pages (from-to)267-275
Number of pages9
JournalJournal of Soil Science
Volume37
Issue number2
DOIs
Publication statusPublished - 1 Jan 1986

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molybdates
mechanistic models
fluorides
Fluorides
fluoride
Soil
Temperature
soil
temperature
Adsorption
testing
adsorption
penetration
incubation
desorption
Molybdenum
molybdenum
effect
molybdate
Phosphates

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abstract = "A mechanistic model that had been developed to describe the reaction of phosphate with soil was applied to the reactions of fluoride and molybdate with soil. The model assumes that: there is an initial adsorption reaction between ions and charged surfaces; that the surfaces are not uniform in their properties; and that the initial adsorption is followed by diffusive penetration. The model was developed beyond that previously published to permit the rate of the initial adsorption reaction to be included. The model reproduced the effects of solution concentration, and of increasing period and temperature of incubation, on the retention of both fluoride and molybdate. Increasing the temperature of incubation increased the retention, or decreased the solution concentration, and this was reproduced by the effect of temperature on the rate of diffusive penetration. Desorption of fluoride was also reproduced. This supports the argument that slow desorption is mostly due to the need to reverse the diffusive penetration. After incubation at constant temperature, increasing the temperature at which solution concentration of molybdenum was measured, increased the concentration. The direction of this effect of temperature was also reproduced. It arises because of the effect of temperature on the position of the equilibrium between adsorbed molybdate (in the strict sense of the term) and molybdate in solution.",
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N2 - A mechanistic model that had been developed to describe the reaction of phosphate with soil was applied to the reactions of fluoride and molybdate with soil. The model assumes that: there is an initial adsorption reaction between ions and charged surfaces; that the surfaces are not uniform in their properties; and that the initial adsorption is followed by diffusive penetration. The model was developed beyond that previously published to permit the rate of the initial adsorption reaction to be included. The model reproduced the effects of solution concentration, and of increasing period and temperature of incubation, on the retention of both fluoride and molybdate. Increasing the temperature of incubation increased the retention, or decreased the solution concentration, and this was reproduced by the effect of temperature on the rate of diffusive penetration. Desorption of fluoride was also reproduced. This supports the argument that slow desorption is mostly due to the need to reverse the diffusive penetration. After incubation at constant temperature, increasing the temperature at which solution concentration of molybdenum was measured, increased the concentration. The direction of this effect of temperature was also reproduced. It arises because of the effect of temperature on the position of the equilibrium between adsorbed molybdate (in the strict sense of the term) and molybdate in solution.

AB - A mechanistic model that had been developed to describe the reaction of phosphate with soil was applied to the reactions of fluoride and molybdate with soil. The model assumes that: there is an initial adsorption reaction between ions and charged surfaces; that the surfaces are not uniform in their properties; and that the initial adsorption is followed by diffusive penetration. The model was developed beyond that previously published to permit the rate of the initial adsorption reaction to be included. The model reproduced the effects of solution concentration, and of increasing period and temperature of incubation, on the retention of both fluoride and molybdate. Increasing the temperature of incubation increased the retention, or decreased the solution concentration, and this was reproduced by the effect of temperature on the rate of diffusive penetration. Desorption of fluoride was also reproduced. This supports the argument that slow desorption is mostly due to the need to reverse the diffusive penetration. After incubation at constant temperature, increasing the temperature at which solution concentration of molybdenum was measured, increased the concentration. The direction of this effect of temperature was also reproduced. It arises because of the effect of temperature on the position of the equilibrium between adsorbed molybdate (in the strict sense of the term) and molybdate in solution.

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