The Evaporation-Driven Growth Law of Porous Salt Structures

The development of porous salt structures from an evaporating salt solution at the surface or within a porous medium is a major problem in connection with civil engineering, agriculture, CO2 injection into saline aquifers, the durability of building materials, and the preservation of our cultural heritage. The salt structure growth mechanisms are qualitatively understood, but quantitative predictions of the growth and the salt structure development are challenging. Herein, the salt structure local growth law is obtained from the analytical solution to the dissolved salt transport problem in the growing salt structure. The obtained law is quite simple and easy to use. It shows that the local growth rate is linearly proportional to the local evaporation flux at the salt structure surface. The obtained law depends on a Damköhler number involving the porosity and the specific surface area of the growing structure as well as the precipitation reaction coefficient and the salt structure effective diffusion coefficient. The derived growth law is successfully tested against experimental data. It opens up the road toward the prediction of the development of salt structures of complex shape and, thereby, the deeper analysis of the numerous situations in which the evaporation-driven development of salt structures is a key issue.