Salt redistribution during freezing of saline sand columns at constant rates

Columns of sand with grain sizes from about 250 to 600 μm were saturated with a sodium chloride solution with a concentration of 35 parts per thousand (ppt) and frozen at constant rates ranging from 1 to 20 mm d −1 . Electrical conductivity of the soil solution, water content, and temperature were measured during the experiments. The interface between the frozen and unfrozen regions was sharply defined and mechanically hard with no evidence for a soft, ice‐bearing transition region thicker than a millimeter. Ice content near the interface was less than 50%. Substantial salt redistribution occurred with downward freezing but not with upward freezing. For downward freezing, the amount of salt rejected near the interface decreased with increasing freezing rate and increased with the salinity of the soil solution in the unfrozen region. Salt redistribution consisted of salt rejection and brine drainage from an extended partially frozen region just above the interface. Brine drained from this partially frozen region until the ice content reached about 900–950 ppt. Brine drained through the interface and mixed rapidly in the unfrozen region, apparently by salt fingering. No evidence could be found for a salt‐enriched layer just below the interface. There was a layer just above the interface, moving with it, which was undersaturated at low and oversaturated at high freezing rates. An effective distribution coefficient may be useful in describing salt redistribution during freezing of saline sands.