Mechanisms of salt rejection at the ice-liquid interface during the freezing of pore fluids in the seasonal frozen soil area

Abstract

Seasonal frozen soil accounts for about 53.50% of the land area in China. Frozen soil is a complex multiphase system where ice, water, soil, and air coexist. The distribution and migration of salts in frozen soil during soil freezing are notably different from those in unfrozen soil areas. However, little knowledge is available about the process and mechanisms of salt migration in frozen soil. This study explores the mechanisms of salt migration at the ice-liquid interface during the freezing of pore fluids through batch experiments. The results are as follows. The solute concentrations of liquid and solid phases at the ice-liquid interface (CL*, CS*) gradually increased at the initial stage of freezing and remained approximately constant at the middle stage. As the ice-liquid interface advanced toward the system boundary, the diffusion of the liquid phase was blocked but the ice phase continued rejecting salts. As a result, CL* and CS* rapidly increased at the final stage of freezing. The distribution characteristics of solutes in ice and the liquid phases before CL* and CS* became steady were mainly affected by the freezing temperature, initial concentrations, and particle-size distribution of media (quartz sand and kaolin). In detail, the lower the freezing temperature and the better the particle-size distribution of media, the higher the solute proportion in the ice phase at the initial stage of freezing. Meanwhile, the increase in concentration first promoted but then inhibited the increase of solutes in the ice phase. These results have insights and scientific significance for the tackling of climate change, the environmental protection of groundwater and soil, and infrastructure protection such as roads, among other things.© 2021 China Geology Editorial Office.