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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