Laboratory studies on nitrate redistribution during the freezing process of a water-saturated sand system.

The process of ice crystal formation by ejecting salt into a pore solution increases the solution's concentration. However, the redistribution law of solutes in ice-containing soils is not well understood. We designed new equipment to obtain the unfrozen solution and study the nitrate redistribution. Our work investigates the mechanism of nitrate redistribution during the freezing of a saturated medium system. The results showed that the polysized grain samples had a higher freezing rate and lower salt discharge efficiency than the monosized grain samples. The influence of the freezing temperature and the initial concentration on the nitrate redistribution was dependent on the medium's particle size. For the samples with particle sizes between 150 and 250 um, the ejection efficiency decreased with the increase of the freezing temperature and decreased with the increase of the initial concentration at the same frozen ratio. However, for the samples with particle sizes between 250 and 500 um, the two factors had no significant effect on the nitrate expulsion. These results will provide a theoretical basis for the treatment of nitrate in groundwater.