Experimental Investigation of Salt Precipitation in a Free-Flow/Porous-Media Microfluidic System

Shujie Guo, Wenqian Zhang, and Bo Guo

Department of Hydrology and Atmospheric Sciences

University of Arizona

Salt precipitation is an important process in many environmental and technical applications such as soil salinization and precipitation in building material. Driven by intense evaporation, dissolved salts migrate with water toward the surface, where they accumulate and precipitate upon exceeding solubility limits. This process contributes to soil degradation, reduced plant growth, and significant economic losses. A fundamental understanding of the mechanisms governing salt precipitation in porous media is essential for developing effective mitigation strategies in agriculture and environmental management. 

While mathematical models at different scales have been developed, persistent discrepancies between simulations and experimental observations indicate critical gaps in current knowledge. Microfluidic experiments conducted under well-controlled conditions with high-resolution visualization offer a powerful approach to elucidating the key processes governing salt precipitation. We present initial microfluidic experiments investigating evaporation and salt precipitation in a free-flow/porous-media-flow system under controlled conditions. Using a heterogeneous two-layer micromodel and NaCl solutions, we systematically observe and quantify the pore-scale evaporation and salt precipitation processes. The experimental data will serve as a benchmark for refining and validating pore-network models for simulating evaporation and salt precipitation in such systems.