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This article in SSSAJ

  1. Vol. 37 No. 6, p. 847-850
     
    Received: May 24, 1973
    Published: Nov, 1973


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doi:10.2136/sssaj1973.03615995003700060018x

The Interaction of Phosphate with Calcite1

  1. R. A. Griffin and
  2. J. J. Jurinak2

Abstract

Abstract

Adsorption isotherms of phosphate on calcite were shown to be described by a two-region Langmuir isotherm equation, i.e., the plot showed two distinct linear portions. The break in the slope of the Langmuir plot was found, on a solubility diagram of the calcium phosphates, to correspond closely to the division between octocalcium phosphate and hydroxylapatite.

The adsorption data were also found to be described by the BET equation. The monolayer capacity computed from the BET equation was found to correspond closely with the adsorption maximum computed from the initial solpes of the Langmuir plots. Comparison of monolayer capacities with the total surface area of the calcite indicated that only approximately 5% of the total surface was covered with phosphate ions.

The differential isosteric heat of adsorption, was computed from the adsorption data. A plot of as a function of phosphate sorbed revealed a discontinuity at the region 1 boundary of the adsorption data.

 
 

Kinetics of phosphate reaction with calcite were found to be consistent with heterogeneous nucleation theory and are discussed in terms of the previous adsorption data.

It was concluded that the interaction of phosphate with the calcite surface could be described as a heterogeneous nucleation process.

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