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

The steady-state dissolution rates of Öraefajökull 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 withr+=Ae-EARTaH+3aAl3+1/nwhere r+ refers to the specific dissolution rate, A represents a pre-exponential factor equal to 1.4 × 10−5 mol/cm2/s, EA denotes an activation energy equal to 55.15 kJ/mol, n represents a stoichiometric factor equal to 11.1, R designates the gas constant, T corresponds to the absolute temperature and ai defines the activity of the subscripted aqueous species. In accord with this equation, aqueous organic ligands will enhance rates by complexing with aqueous Al3+, thus lowering aAl3+aAl3+. The observed variation of rhyolite dissolution rates with solution chemistry and temperature is similar to that previously observed for basaltic glass. This similarity suggests that all natural Al-silicate volcanic glasses have similar dissolution mechanisms consisting of the sequential removal of metals from the glass structure via proton exchange reactions. The overall dissolution rate within this mechanism is controlled by the detachment of Si tetrahedral that have been partially liberated from the glass structure through the removal of adjoining Al.