The role of the viscous sublayer in calcium carbonate dissolution

Remineralization is a key component of post-treatment of desalinated water, particularly that obtained by thermal desalination, to avoid corrosion in distribution systems and address human health concerns. Dissolution of limestone under an elevated pressure of carbon dioxide is a common remineralization procedure. Prompted by the desire to optimize this process, we examined literature data on its kinetics and found that there was no consensus on the mechanism of dissolution or the nature of the rate-controlling step. We propose a steady-state model, where there is a locally constant concentration of solute in a surface layer of solvent, with the rate of dissolution controlled by transport into and out of this surface layer. This model can explain the wide variation reported in experimental rate coefficients for calcium carbonate dissolution and fit experimental data obtained under very different systems with physically reasonable values for the dimensions of the viscous sublayer.