Dissolution of beidellite in acidic solutions: Ion exchange reactions and effect of crystal chemistry on smectite reactivity

• Published in: Geochimica et cosmochimica acta 2016-05, Vol.180, p.97-108
• Main Authors: Robin, Valentin, Tertre, Emmanuel, Regnault, Olivier, Descostes, Michael
• Format: Article
• Language: English
• Subjects: Earth Sciences; Sciences of the Universe
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/j.gca.2016.02.009

The dissolution rate of beidellite, a dioctahedral smectite with tetrahedral charge that is a common swelling clay mineral in surface and subsurface natural environments, was studied in acidic solutions at 25°C under far from equilibrium conditions. A 1.1, and the presence of an amorphous Si-enriched layer can be reasonably assumed in some cases from the interpretation of the aqueous concentrations and the characterization of the solid phase (X-ray diffraction and FTIR spectroscopy). Beidellite dissolution rates normalized to the sample mass (molg−1s−1) were obtained from Si and Al concentrations under steady state dissolution conditions. Calculated rates were compared with those previously reported for montmorillonite in several publications. The beidellite dissolution rates are, on average, ten times lower than those of montmorillonite. This implies that the smectite crystal chemistry (i.e., amount of Al3+ versus Mg2+ or Fe3+ substitution in the structure) has a strong effect on its stability and should be considered in reactive transport models in which the dissolution properties of smectites are taken into account.