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How Is Rock Salt Purified?

Updated February 21, 2017

Rock salt, also known as the mineral halite, comes from underground mines where it occurs naturally, but this rock salt has the same composition and origin as sea salt. When purified, rock salt becomes table salt, both with the chemical composition of sodium chloride. Salt deposits underground resulted from the evaporation of oceans which covered the area of the mines millions of years ago. Layers of salt remained and later became buried by sediments.

How Salt Got Underground

Rock salt, also known as the mineral halite, comes from underground mines where it occurs naturally, but this rock salt has the same composition and origin as sea salt. When purified, rock salt becomes table salt, both with the chemical composition of sodium chloride. Salt deposits underground resulted from the evaporation of oceans which covered the area of the mines millions of years ago. Layers of salt remained and later became buried by sediments.

Mining Halite

Miners dig large holes over areas of rock salt (halite) deposits. Dynamite blows chunks of salt out of the hole. These chunks get crushed down into smaller pieces in grinders. The broken pieces of rock salt crush into small enough pieces to dissolve in water to produce a brine. During the grinding, magnets pull out metal particles from the halite. Other impurities get removed from the rock salt by first creating a brine. This allows the rock salt to be used as edible table salt.

Purifying Halite

The salt and water brine mixture passes through a filter to remove dirt particles. Crystallising the brine to get salt either happens through evaporation of the water naturally in the sun or by boiling the water away in a series of heating pots. As the water evaporates out of the brine, the water remains behind. Producers who make ionised salt add potassium iodide to the purified rock salt. Other producers will add minerals such as magnesium carbonate or calcium carbonate to enhance the flowing capabilities of the table salt.

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