Dissolution rate of dawsonite from pH 2 to 12

摘要

Dawsonite (NaAl(OH)2CO3) has been suggested to play an important role as a storage host for CO2 (Hellevang, 2006). To understand the significance ofdawsonite during CO2 storage, both the thermodynamic and kinetic stability must be known. The thermodynamic value is well established, whereas little information is known about the dissolution/precipitation rate of dawsonite. The first data from Hellevang et al. (2005) was obtained in a narrow range of pH and temperature (80°C, pH 4 to 9) and suggests that rate was pH independent and slower than the other carbonates. In order to have a better understanding of the dissolution mechanism we have extended the experimental conditions from a pH of 2 to 12 and a temperatures range between 25 to 150°C. We have used an artificial mineral with the same habitus as the natural dawsonite and with a far greater homogeneity.In order to cover a large range of temperature we used two different experimental setups, a titanium ParrTM mixed flow reactor for temperature range from 80 to 150°C and a shaker bath reactor for the lower temperatures (25 to 80°C). The two sets of experiments overlap at 80°C in order to have a common reference. The dissolution rate of dawsonite was calculated from the outlet concentrations of Na. The previous study by Hellevang et al. stated that the dawsonite dissolution rate was independent of pH, but the use of a mixed flow reactor and extension to a wider range of experimental conditions shows a very strong pH dependence of the dissolution rate at low pH. The pH dependence under basic conditions is currently under study.