Evaporation from porous media in the presence of dissolved salts is an important topic in relation to several environmental issues. In this study, we investigated the interaction of evaporation, salt crystallization and the internal structure of the porous material. Porous columns with different internal structures were generated through random packing of angular quartz sand and round glass beads. Evaporation-induced salt efflorescence on the surface of porous media was recorded by a camera with micro lens. The internal pore structure before and after salt crystallization was visualized using the x-ray computed tomography and quantified by the extracted pore networks. Hydraulic properties in the absence/presence of salt crystals were simulated numerically using the pore-network approach and partially measured experimentally. The evaporative water loss ratio in the angular quartz sand was greater than that in the glass beads with the same sieving size. The evaporation of saline water in angular quartz sand and round glass beads can be separated into three stages similar to water evaporation. Salt efflorescence was generated a crust dome architecture on the surface of the angular sand, but was in tight patchy contact with the round glass beads. The presence of salt crust interrupted the exchange of vapor between the porous media and atmosphere, hindering evaporation. Salt subflorescence clogged some of the pores, and the pore size distribution shifted to smaller sizes part. The porosity decreased and the geometric tortuosity of the porous materials increased owing to salt subflorescence. The presence of subflorescence salt crystals decreased the intrinsic permeability and relative diffusion coefficient of different porous media. The relationship between the vapor diffusion coefficients and porosity is linear in the presence/absence of salt crystallization, considering the geometric tortuosity. The findings indicate that the feedback of salt precipitation on hydraulic properties and vapor diffusion must be considered to accurately quantify hydrological processes, particularly in arid and semi-arid areas where intensive evaporation is accompanied by soil salinization and water shortage.

在存在溶解盐的情况下，从多孔介质中蒸发是与几个环境问题相关的重要主题。在这项研究中，我们研究了蒸发，盐结晶和多孔材料内部结构的相互作用。通过随机填充有角的石英砂和圆形玻璃珠产生具有不同内部结构的多孔柱。用带微透镜的照相机记录在多孔介质表面上蒸发引起的盐的风化。使用X射线计算机断层扫描可以看到盐结晶前后的内部孔结构，并通过提取的孔网络对其进行定量。使用孔网方法对存在/不存在盐晶体的水力学性质进行了数值模拟，并通过实验进行了部分测量。在相同的筛分尺寸下，角石英砂中的蒸发失水率大于玻璃珠中的蒸发失水率。角质石英砂和圆形玻璃珠中的盐水蒸发可以分为三个阶段，类似于水蒸发。盐的风化在角砂的表面上形成了一个硬壳圆顶结构，但与圆形玻璃珠紧密地，不规则地接触。盐皮的存在中断了多孔介质与大气之间的蒸汽交换，从而阻碍了蒸发。盐亚花序阻塞了一些孔，并且孔尺寸分布转移到较小尺寸的部分。由于盐的亚开花，孔隙率降低，多孔材料的几何曲折度增加。亚花期盐晶体的存在降低了不同多孔介质的固有渗透性和相对扩散系数。考虑到几何曲折度，在存在/不存在盐结晶的情况下，蒸气扩散系数与孔隙率之间的关系是线性的。研究结果表明，必须考虑盐分沉淀对水力特性和蒸汽扩散的反馈，才能准确地量化水文过程，特别是在干旱和半干旱地区，这些地区大量蒸发伴随着土壤盐碱化和缺水。