Effect of variable solubility on reactive convective dissolution

Abstract

Chemical reactions can influence convective dissolution arising from density changes when a solute A dissolves into a host phase containing a reactant B. In this theoretical study, we examine the conditions that optimize the convective dissolution of A into the host phase when A reacts with B via an A + B → C reaction and the compositional change by the reaction reduces the solubility of A in the solution. Through numerical simulations, we explore how this variable solubility affects the reaction–diffusion–convection (RDC) concentration distributions and the flux of A at the interface. We classify the different density profiles based on key parameters such as the ratio of the initial concentration of B and the initial solubility of A, the individual contributions of each species to the total solution density and a parameter quantifying the influence of the reaction on the solubility of A. Taking into account the variable solubility of A allows to reach new regimes where, for instance, there is no longer any influence of the initial concentration of B on the mass transfer when B is in excess. We also show that, if C strongly decreases the solubility of A, the flux can even be lower than its nonreactive counterpart. These results contribute to understand the conditions where reactions can enhance or reduce the transfer of solutes into a host phase, a question relevant to many applications such as carbon dioxide storage in geological formations.