How to Purify Sodium Chloride From Rock Salt

Two techniques to remove impurities from rock salt to get table salt

Rock salt often contains impurities that color the mineral. Pure sodium chloride is clear or white.
Rock salt often contains impurities that color the mineral. Pure sodium chloride is clear or white.

Magone/Getty Images

Rock salt or halite is a mineral the contains sodium chloride (table salt) as well as other minerals and impurities. You can remove most of these contaminants using two simple purification techniques: filtration and evaporation.


  • Rock salt
  • Water
  • Spatula
  • Filter paper
  • Funnel
  • Evaporating dish
  • Beaker or graduated cylinder
  • Tripod
  • Bunsen burner


  1. If the rock salt is one large chunk, grind it into a powder using a mortar and pestle or a coffee grinder.
  2. Add 30-50 milliliters of water to six heaping spatula scoops of rock salt.
  3. Stir to dissolve the salt.
  4. Place the filter paper in the mouth of the funnel.
  5. Place the evaporating dish under the funnel to collect the liquid.
  6. Slowly pour the rock salt solution into the funnel. Make sure you don't over-fill the funnel. You don't want the liquid to flow around the top of the filter paper because then it isn't getting filtered.
  7. Save the liquid (filtrate) that comes through the filter. Many of the mineral contaminants did not dissolve in the water and were left behind on the filter paper.


  1. Place the evaporating dish containing the filtrate on the tripod.
  2. Position the Bunsen burner under the tripod.
  3. Slowly and carefully heat the evaporating dish. Be careful! If you apply too much heat, you might break the dish.
  4. Gently heat the filtrate until all the water is gone. It's okay if the salt crystals hiss and move a little.
  5. Turn off the burner and collect your salt. Although some impurities will remain in the materials, many of them will have been removed simply by using the difference in solubility in water, mechanical filtration, and by applying heat to drive off volatile compounds.


If you want to further purify the salt, you can dissolve your product in hot water and crystallize the sodium chloride from it.