Dissolution kinetics of kaolinite in acidic aqueous solutions at 25 C
- Inst. for Water Resources and Water Pollution Control, Duebendorf (Switzerland) Swiss Federal Inst. of Tech., Zuerich (Switzerland)
The dissolution of kaolinite is interpreted in terms of the surface complexation model. Acid/base properties of the terminal OH groups and ion exchange reactions occurring at the kaolinite surface have been investigated. A three-site model incorporating solid-solution equilibria at aluminol groups of the edge and gibbsite surfaces and at negatively charged XO groups of the siloxane surface account for the protonation of kaolinite platelets in acidic solutions. The dissolution kinetics of kaolinite at 25 C has been studied as a function of solution pH. The dissolution of kaolinite is nonstoichiometric in the pH range 2-6.5 with a preferential release of silicon. Stoichiometry of the dissolution reaction is achieved, however, in the presence of oxalate as Al-complexing ligand. The detachment of aluminium from the lattice structure of the kaolinite surface and its readsorption on distinct surface sites occur simultaneously during the dissolution process causing the experimentally observed nonstoichiometry. The proton-promoted dissolution of kaolinite occurs at the edge surface (pH < 6.5) and the gibbsite surface (pH < 4). The pH-dependence of the dissolution rate R[sub H](Si) reflects sequential protonation of terminal OH groups on both surfaces. The dissolution reaction can be interpreted as a coupled release of Al and Si with the detachment of the Al center from the surface lattice structure as the rate-limiting step. The aluminium:proton stoichiometry of the activated complex is 1:3 at the gibbsite surface and 1:1 at the edge surface.
- OSTI ID:
- 6893699
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 56:9; ISSN GCACAK; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CRYSTAL LATTICES
CRYSTAL MODELS
CRYSTAL STRUCTURE
DISSOLUTION
ION EXCHANGE
KAOLINITE
MATHEMATICAL MODELS
MINERALS
MOLECULAR MODELS
OXYGEN COMPOUNDS
PH VALUE
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
STOICHIOMETRY
SURFACE PROPERTIES
THERMODYNAMIC ACTIVITY