The dissolution rates of dawsonite at pH 0.9 to 5 and temperatures of 22, 60 and 77 °C

Occurrences of the mineral dawsonite (NaAl(OH)2CO3) after natural CO2 accumulation support suggestions that this mineral may contribute to long-term storage of CO2 in geological formations. Knowledge of the reactivity of dawsonite is crucial to better understand its role as a CO2 storage host. Here the results of free-drift batch dissolution rate experiments at 22, 60 and 77 °C performed on synthesized dawsonite are presented. Based on previously reported dawsonite dissolution rate data at circumneutral conditions and the present experiments, it is suggested that the dissolution rates can be expressed by two parallel mechanisms according to r + = k 1 a H + v + k 2 , where a H + denotes the proton activity. The rate coefficient k1 (22 °C) and order with respect to the proton activity v were estimated from the 22 °C dataset to be 10−4.48 ± 0.48 and 0.982 ± 0.15, respectively, at the 95% confidence level. The rate coefficient for the pH-independent region k2 (77 °C) was found to be approximately 10−6.89 from the maximum R2 = 0.95 for the rate equation using the 77 °C dataset. The k2 value was however uncertain because of the few data points in the transition into the pH-independent region. The apparent activation energy Ea for the proton-promoted mechanism was estimated to 49.43 kJ/mol, increasing to 63.82 kJ/mol for the data points approaching pH independence. From the trends of data points for the 22 and 77 °C data series, it is likely that the difference in rates between 22 and 77 °C increases further at higher pH.