Dissolution of olivine in the presence of oxalate, citrate, and CO2 at 90 °C and 120 °C

In this article, we report the results from a study of olivine dissolution kinetics under operating conditions suitable for ex situ aqueous mineral carbonation for CO2 storage. We studied the effect of oxalate and citrate ions on the dissolution of gem-quality San Carlos olivine (Mg1.82Fe0.18SiO4). Flow-through experiments were performed at 90 degrees C and 120 degrees C, at f (CO2) between 4 and 81 bar, with a solution containing either sodium oxalate or sodium citrate in a molality range between 10(-3) and 10(-1). The pH was varied between 2 and 7 by adding HCl, LiOH, and adjusting f(CO2). At all investigated temperatures and for pH values in a broad range, both sodium oxalate and sodium citrate increased dissolution rate with the strongest effect up to one order of magnitude in presence of 0.1 m of oxalate, at 120 degrees C, and above pH 5. The enhancement effect was primarily ascribed to the oxalate or citrate ions that are the dominant species in this pH range. The overall dissolution process was described using the population balance equation (PBE) coupled with a mass balance equation to account for the evolution of the particle size distribution (PSD) of olivine. Far from equilibrium conditions for dissolution were established in all the experiments in order to achieve a surface-reaction controlled mechanism. We described the reaction with a surface complexation model, which assumes adsorption of a proton and of an oxalate (citrate) ions (proton and oxalate) on adjacent sites in order to enhance dissolution, and we derived a dissolution rate equation in presence of oxalate: r=r*/1+K(H)a(H)(n) (1+beta K(X)a(X)/1+K(X)a(X)), where r* is the specific dissolution rate commonly used in absence of organic compounds, and K-H, K-X, and beta are thermodynamic and kinetic parameters. The values of these parameters have been estimated from the experimental data and the agreement between the model results and the experiments is very good. (C) 2011 Elsevier Ltd. All rights reserved.