Dissolution kinetics of basaltic glass: The effect of temperature, dissolved oxygen and silica concentrations under circum-neutral to basic pH

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This study investigates the dissolution kinetics of synthetic basaltic glass under circum-neutral to basic conditions (pH 20 °C from 6 to 10) and temperatures of 30, 60 and 90 °C, with a particular focus on the roles of dissolved oxygen (O 2 (aq)) and silica (SiO 2 (aq)) concentrations. Surface retreats were measured using vertical scanning interferometry, and the thickness of alteration layers (amorphous silica-rich surface layer, referred to as ASSL) using X-ray reflectivity and transmission electron microscopy performed on focused ion beam-milled lamellae. As expected, the dissolution rate of basaltic glass increases with increasing pH from neutral to basic conditions. A modest influence of O 2 (aq) concentrations was observed, attributed to Fe(II) oxidation and the associated formation of a passivating Fe(III)–Si-rich surface layer. Most strikingly, the dissolution rate was found to decrease exponentially with increasing SiO 2 (aq) concentrations, which is inconsistent with the transition state theory. Instead, this behavior is consistent with a mechanism governed by classical nucleation theory in the studied conditions, resulting in the following overall dissolution rate law: r = k 0 . 10 n . pH T . exp − Ea RT . exp k 1 − k 2 ln SiO 2 aq / K eq T , with r being the dissolution rate (in mol/m 2 /s), k 0 = 552 mol/m 2 /s, n = 0.35, Ea = 84 kJ/mol, k 1 = 0.40, k 2 = 3.87, pH T is the pH value at the considered temperature T , R the gas constant, and K eq T the solubility constant of amorphous silica at the considered temperature. Taken together, these findings provide new insights into the coupled effects of pH, O₂(aq), and SiO₂(aq) on basaltic glass reactivity, offering a refined kinetic framework for modeling glass weathering in natural and engineered environments. • Basaltic glass dissolution rate was measured using Vertical Scanning Interferometry. • The dissolution rate decreases exponentially with SiO 2 (aq) concentration. • Dissolved oxygen has only a modest effect on the dissolution kinetics. • VSI-derived rates match literature data normalized to geometric surface area.

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