Albite feldspar dissolution kinetics as a function of the Gibbs free energy at high pCO_2

TL;DR

This study investigates how the dissolution rate of albite feldspar varies with Gibbs free energy at high CO2 levels, revealing a non-linear, sigmoidal relationship crucial for geochemical modeling.

Contribution

It provides new experimental data on albite dissolution kinetics as a function of Gibbs free energy under high pCO2 conditions, highlighting a non-linear rate relationship.

Findings

Dissolution rate plateaus at far-from-equilibrium conditions.

Rates sharply decrease as Gibbs free energy approaches equilibrium.

Data fit a sigmoidal, non-linear rate versus free energy relation.

Abstract

We are currently measuring the dissolution kinetics of albite feldspar at 100 deg C in the presence of high levels of dissolved CO_2 (pCO_2 = 9 MPa) as a function of the saturation state of the feldspar (Gibbs free energy of reaction, \Delta G). The experiments are conducted using a flow through reactor, thereby allowing the dissolution reactions to occur at a fixed pH and at constant, but variable saturation states. Preliminary results indicate that at far-from-equilibrium conditions, the dissolution kinetics of albite are defined by a rate plateau, with R \approx 5.0 x 10^{-10} mol m^{-2} s^{-1} at -70 < \Delta G < -40 kJ mol^{-1}. At \Delta G > -40 kJ mol^{-1}, the rates decrease sharply, revealing a strong inverse relation between the dissolution rate and free energy. Based on the experiments carried out to date, the dissolution rate-free energy data correspond to a highly non-linear and sigmoidal relation, in accord with recent studies.