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Relative Solubility of Corundum, Gibbsite, Boehmite, and Diaspore at Standard State Conditions

Published online by Cambridge University Press:  02 April 2024

F. J. Peryea  and
J. A. Kittrick
F. J. Peryea*
Affiliation:
Department of Agronomy and Soils, Washington State University, Pullman, Washington 99164
J. A. Kittrick
Affiliation:
Department of Agronomy and Soils, Washington State University, Pullman, Washington 99164
*
2Present address: Washington State University, Tree Fruit Research Center, 1100 North Western Avenue, Wenatchee, Washington 98801.
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Abstract

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The solubilities of HCl-treated samples of corundum, gibbsite, boehmite, and diaspore in aqueous solutions at 298 K and one atmosphere pressure were determined from undersaturated and supersaturated initial conditions. Solution characteristics at apparent equilibrium were measured and used to calculate equilibrium constants (Kr) for mineral dissolution reactions:

$$\begin{array}{l} A{l_2}{O_3}\left( {corundum} \right) + 3{H^ + } = A{l^3} + 1.5\,{H_2}O,\\ Al{\left( {OH} \right)_3}\left( {gibbsite} \right) + 3{H^ + } = A{l^3} + 3\,{H_2}O,\\ and\\ AlOOH\left( {boehmite\,or\,diaspore} \right) + 3{H^ + } = A{l^3} + 2{H_2}O, \end{array}$$
Assuming solid phase and water activities of unity, log Kr = 3pH - pAl3+ for all three equations. The calculated log Kr values were: 9.01 ± 0.05 (corundum), 7.76 ± 0.14 (gibbsite), 7.49 ± 0.09 (boehmite), and 6.75 ± 0.24 (diaspore), indicating that the relative thermodynamic stabilities under the experimental conditions were: corundum < gibbsite < boehmite < diaspore. The gibbsite value agreed well with that determined independently by another research group using acid-treated subsamples of the same source mineral (7.70 ± 0.02). The calculated Gibbs free energies of formation (kJ/mole) were: -1587.4 ± 2.1 (corundum), -1156.7 ± 1.6 (gibbsite), -921.0 ± 1.5 (boehmite), and -925.1 ± 2.0 (diaspore). The Δ Gfo values of the acid-treated minerals were 1.8 to 12.4 kJ/mole more negative than values recently compiled for untreated mineral samples. This result is attributed to the removal of reactive surface coatings that isolated the bulk mineral phases from the solution phase.

Keywords

Acid solubilityAluminumBoehmiteCorundumDiasporeGibbsite
Type
Research Article
Information
Clays and Clay Minerals , Volume 36 , Issue 5 , October 1988 , pp. 391 - 396
Copyright
Copyright © 1988, The Clay Minerals Society

Footnotes

1

Scientific Paper 7888, Project 0747, College of Agriculture and Home Economics Research Center, Washington State University, Pullman, Washington 99164.

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