The sketch below illustrates a GEA Messo Standard Salt Wash (see, also,
Fig. 6 of the article mentioned earlier).
The GEA Messo Standard Salt Wash consists of unit operations selected to
separate the soluble and particulate impurities from the sodium chloride
crystals by simple and separate mechanical means.
The feed crude salt
first is first ground to a size distribution which is appropriate for market
use. The step combines fulfilling a market specification with the removal of
impurities that are typically trapped within the salt solids.
Following
the size reduction, both soluble and particulate impurities are subsequently
separated by means of dissolution and hydro-mechanical classification steps. By
addition of water to the salt, soluble impurities are washed out and purged
with a liquid effluent stream, which may be fed to a solar pond to improve the
total process yield. Taking advantage of the different particle sizes of sodium
chloride crystals and particulate impurities, the two are separated by
hydro-mechanical classification: gypsum, sand and dirt and other solid
particles can be separated from the sodium chloride crystals because their
settling velocity is lower. The separated solid impurities are concentrated and
discharged.
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