Final answer:
In brine rejection during the freezing of seawater, salts are expelled while forming sweetwater ice, and dissolved gases such as CO2 tend to escape due to their decreased solubility at lower temperatures. This process is different from methods like reverse osmosis or distillation that are used for desalination.
Step-by-step explanation:
When seawater freezes, it experiences a phenomenon called freezing point depression, where the solution freezes at a lower temperature than pure water. This is because the dissolved salts disrupt the ability of the water molecules to form a solid lattice structure at 0 °C. As ice forms, it expels the salts, resulting in 'sweetwater' ice and a residual brine that is more concentrated in salts. However, this brine rejection process is also influenced by the solubility of gases in the liquid phase.
Brine rejection doesn't necessarily enrich brine in CO2 the same way it would with dissolved salts. Gases such as CO2 have different solubility characteristics compared to non-volatile solutes like salt. Generally, the solubility of gases decreases with lower temperatures, so as seawater freezes, the ability of the ice to hold dissolved gases also decreases, and dissolved gases tend to escape back into the atmosphere.
It's important to note that while brine rejection can increase the concentration of certain dissolved substances, not all processes that lead to the purification of water—like reverse osmosis or distillation—work in the same way or are suitable for all circumstances. For example, whereas brine rejection is a natural process that can occur in polar regions, reverse osmosis is a technological solution that involves applying pressure to force water through a semipermeable membrane, separating pure water from dissolved substances.