Evaporation-driven growth of large crystallized salt structures in a porous medium

Abstract

Subflorescence refers to crystallized salt structures that form inside a porous medium. We report a drying experiment revealing major development of subflorescence in the dry region of the porous medium away from the liquid zone. Using a combination of image analyses and numerical computations, we show that the growth is directly correlated to the evaporation flux distribution along the boundary of the growing salt structure. This indicates that the salt is transported into the domain occupied by the salt structure in the porous medium up to the structure periphery, where salt deposition takes place. This is confirmed when a growing salt structure encounters dry subflorescence formed earlier during the drying process. The dry subflorescence is reimbibed and resumes its growth. The analysis also suggests that the solution within the growing subflorescence is in equilibrium with the crystallized salt wall. These results shed light on the growth mechanisms of subflorescence, a phenomenon that can play a fundamental role in several important issues such as carbon dioxide sequestration or salt weathering.

Pore-Scale Controls on Reaction-Driven Fracturing

“…The upward fl uid fl ow and enhanced evaporation that is created by this crystallization leads to accelerated drying of the salt solution. A similar effect has been shown for salt crystallization due to evaporation in a hydrophobic porous medium (Sghaier et al 2014). …”

Modelling evaporation processes in soils from the Huasco salt flat basin, Chile

“…This crystallization decreases the pore space in the soil matrix and therefore decreases the K s (Nachshon et al, ; Vásquez et al, ), reduces the vapour flow (Nachshon and Weisbrod, ), and also modifies the water retention characteristics (as described below) (Fierro, ). Although subflorescent precipitation has been widely investigated in other disciplines, few investigations have reported this type of precipitation in soils under drying conditions (Sghaier et al, ; Weisbrod et al, ). To our best knowledge, the present work is the first one reporting probable subflorescence precipitation in laboratory columns designed to study water movement in soils where the water table is rising.…”

Temperature gradient induced double stabilization of the evaporation front within a drying porous medium

“…Control of the final distribution of these species after drying can be essential. For instance, in the case of salts, the drying process leads to the formation of salt crystals either within the porous medium [8,9] or on its surface [10]. This in turn can greatly affect the drying process depending on the properties of the crystallized salt layers [10].…”

“…IV [see Eqs. (5)- (8)]. The first experimental proof of the formation of the IPSG pattern in presence of a negative temperature gradient (by convention, negative means that the temperature decreases with depth) can be found in [31] where a visualization experiment with a quasi-two-dimensional etched network is presented.…”