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Aqueous dissolution, solubilities and thermodynamic stabilities of common aluminosilicate clay minerals: Kaolinite and smectites

January 1, 1986

Determinations of the aqueous solubilities of kaolinite at pH 4, and of five smectite minerals in suspensions set between pH 5 and 8, were undertaken with mineral suspensions adjusted to approach equilibrium from over- and undersaturation. After 1,237 days, Dry Branch, Georgia kaolinite suspensions attained equilibrium solubility with respect to the kaolinite, for which Keq = (2.72 ± 0.35) × 107. The experimentally determined Gibbs free energy of formation (ΔGf,2980) for the kaolinite is −3,789.51 ± 6.60 kj mol−1. Equilibrium solubilities could not be determined for the smectites because the composition of the solution phase in the smectite suspensions appeared to be controlled by the formation of gibbsite or amorphous aluminum hydroxide and not by the smectites, preventing attempts to determine valid ΔGf0 values for these complex aluminosilicate clay minerals. Reported solubility-based ΔGf0 determinations for smectites and other variable composition aluminosilicate clay minerals are shown to be invalid because of experimental deficiencies and of conceptual flaws arising from the nature of the minerals themselves. Because of the variable composition of smectites and similar minerals, it is concluded that reliable equilibrium solubilities and solubility-derived ΔGf0 values can neither be rigorously determined by conventional experimental procedures, nor applied in equilibriabased models of smectite-water interactions.

Citation Information

Publication Year 1986
Title Aqueous dissolution, solubilities and thermodynamic stabilities of common aluminosilicate clay minerals: Kaolinite and smectites
DOI 10.1016/0016-7037(86)90129-8
Authors Howard M. May, D.G. Klnniburgh, P.A. Helmke, M.L. Jackson
Publication Type Article
Publication Subtype Journal Article
Series Title Geochimica et Cosmochimica Acta
Series Number
Index ID 70015666
Record Source USGS Publications Warehouse
USGS Organization Toxic Substances Hydrology Program