Effects of Grain and Pore Size on Salt Precipitation During Evaporation from Porous Media

Salt precipitation in saline porous media during evaporation is important in many processes including CO2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {CO}_{2}$$\end{document} sequestration, soil salinity which is a global problem as well as the preservation of monuments and buildings. In this study, X-ray micro-tomography was used to investigate the evolution of salt precipitation during evaporation to study the effects of particle and pore sizes on salt precipitation patterns and dynamics. The packed beds were saturated with NaCl solution of 3 Molal, and the time-lapsed X-ray imaging was continued for one day to obtain pore- scale information associated with the evaporation and precipitation dynamics and patterns. The results show that the presence of preferential evaporation sites (associated with fine pores) on the surface of the sand columns influences significantly the patterns and dynamics of NaCl precipitation. They confirm the formation of an increasingly thick and discrete salt crust with increasing grain size in the sand column due to the presence of fewer fine pores (preferential precipitation sites) at the surface compared to the sand packs with finer grains. Fewer fine pores on the surface also result in shorter stage-1 precipitation for the columns with larger grain sizes. A simple model for the evolution of salt crust thickness based on this principle shows a good agreement with our experiments. The findings of this study offer new insights about the dynamics and patterns of salt precipitation in drying porous media.