Kinetic aspects of basaltic glass dissolution at 90°C: role of aqueous silicon and aluminium

Steady-state dissolution rates of a synthetic basaltic glass were measured in an open-system mixed flow reactor as a function of solution composition at a temperature of 90°C and over the pH range 7.8 to 8.3. The dissolution is a two-step process. The first of these steps involves the release of the...

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Bibliographic Details
Published in:Chemical geology 1997-10, Vol.142 (1), p.109-126
Main Authors: Daux, Valérie, Guy, Christophe, Advocat, Thierry, Crovisier, Jean-Louis, Stille, Peter
Format: Article
Language:English
Subjects:
chemical affinity
dissolution
Earth Sciences
Geochemistry
glass
kinetic
Sciences of the Universe
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Summary:Steady-state dissolution rates of a synthetic basaltic glass were measured in an open-system mixed flow reactor as a function of solution composition at a temperature of 90°C and over the pH range 7.8 to 8.3. The dissolution is a two-step process. The first of these steps involves the release of the cation modifier elements leading to the formation of a hydrated surface gel (HBG) of which the solubility controls the overall dissolution reaction. The glass steady-state dissolution rates were found to be independent of aqueous aluminium and silicium concentration but to depend on the chemical affinity for the overall hydrolysis reaction. The glass is a rapidly reacting solid, whose dissolution induces a dramatic change in solution concentration, which results readily in small chemical affinities for the dissolution reaction. Consequently, conditions of great undersaturation have not been investigated (affinity max. 9.8 kJ/mol). However, our results strongly suggest that the dissolution rates are controlled by the decomposition of a stoichiometric silico-aluminous surface precursor. The variation of the steady-state dissolution rates can be described using a simple expression based on the concept that the precursor is formed by the simple absorption of reactants: R (mol cm −2s −1) = 3 × 10 −10 (OH −) 0.39 (1− Q/8.2 × 10 −5), where Q, the ion activity quotient is equal to: Q = (H 4SiO 4) (Al(OH) 4 −) 0.36 (Fe(OH) 3) 0.18 (OH −) −0.36.
ISSN:0009-2541
1872-6836
DOI:10.1016/S0009-2541(97)00079-X