How to Separate Salt and Water

Have you ever wondered how you could purify seawater to drink it or how you could separate salt from water in saltwater? It's really very simple. The two most common methods are distillation and evaporation, but there are other ways to separate the two compounds.

Separate Salt and Water Using Distillation

You can boil or evaporate the water and the salt will be left behind as a solid. If you want to collect the water, you can use distillation. This works because salt has a much higher boiling point than water. One way to separate salt and water at home is to boil the salt water in a pot with a lid. Offset the lid slightly so that the water that condenses on the inside of the lid will run down the side to be collected in a separate container. Congratulations! You've just made distilled water. When all of the water has boiled off, the salt will remain in the pot.

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Separate Salt and Water Using Evaporation

Evaporation works the same way as distillation, just at a slower rate. Pour the salt water into a shallow pan. As the water evaporates, the salt will remain behind. You can speed up the process by raising the temperature or by blowing dry air over the surface of the liquid. A variation of this method is to pour the salt water onto a piece of dark construction paper or a coffee filter. This makes recovering the salt crystals easier than scraping them out of the pan.

Other Methods to Separate Salt and Water

Another way to separate salt from water is to use reverse osmosis. In this process, water is forced through a permeable filter, causing the concentration of salt to increase as the water is pushed out. While this method is effective, reverse osmosis pumps are relatively expensive. However, they can be used to purify water at home or when camping.

Electrodialysis can be used to purify water. Here, a negatively-charged anode and a positively-charged cathode are placed in water and separated by a porous membrane. When an electric current is applied, the anode and cathode attract the positive sodium ions and negative chlorine ions, leaving behind the purified water. Note: this process does not necessarily make the water safe to drink, since uncharged contaminants may remain.

A chemical method of separating salt and water involves adding decanoic acid to salt water. The solution is heated. Upon cooling, salt precipitates out of the solution, falling to the bottom of the container. The water and decanoic acid settle into separate layers, so the water can be removed.

Sources

• Fischetti, Mark (September 2007). "Fresh from the Sea." Scientific American. 297 (3): 118–119. doi:10.1038/scientificamerican0907-118
• Fritzmann, C; Lowenberg, J; Wintgens, T; Melin, T (2007). "State-of-the-art of reverse osmosis desalination." Desalination. 216 (1–3): 1–76. doi:10.1016/j.desal.2006.12.009
• Khawaji, Akili D.; Kutubkhanah, Ibrahim K.; Wie, Jong-Mihn (March 2008). "Advances in seawater desalination technologies." Desalination. 221 (1–3): 47–69. doi:10.1016/j.desal.2007.01.067