Experimental determination of rhyolitic glass dissolution rates at 40–200 C and 2 pH 10.1.

The steady-state dissolution rates of O¨ raefajo¨kull rhyolitic glass were measured in titanium mixed-flow reactors as a function
of aqueous Al, Si, and oxalic acid concentration at temperatures from 40 to 200 C and pH from 2 to 10.1. Measured
dissolution rates at were found to be consistent with
rþ ¼ Ae EA
RT   a3
Hþ
aAl3þ
1=nbr /> where r+ refers to the specific dissolution rate, A represents a pre-exponential factor equal to 1.4nbsp; 105 mol/cm2br /> /s, EA denotesbr /> an activation energy equal to 55.15 kJ/mol, n represents a stoichiometric factor equal to 11.1, R designates the gas constant,br /> T corresponds to the absolute temperature and ai defines the activity of the subscripted aqueous species. In accord withbr /> this equation, aqueous organic ligands will enhance rates by complexing with aqueous Al3+, thus lowering aAl3thorn; . The observedbr /> variation of rhyolite dissolution rates with solution chemistry and temperature is similar to that previously observed for basalticbr /> glass. This similarity suggests that all natural Al-silicate volcanic glasses have similar dissolution mechanisms consisting ofbr /> the sequential removal of metals from the glass structure via proton exchange reactions. The overall dissolution rate withinbr /> this mechanism is controlled by the detachment of Si tetrahedral that have been partially liberated from the glass structurebr /> through the removal of adjoining Al.br /> nbsp;2012 Elsevier Ltd. All rights reserved.br /> 1. IN/p>