The GEA Messo Standard Salt Wash can achieve a product purity of
99.3 - 99.7% NaCl (dry basis), if the crude salt has close to
typical composition. Purity is defined as follows:
K+ and others (e.g. HCO3-) are neglected.
In handling crude salt of
lower purity than the typical range, the GEA Messo Standard Salt Wash may
produce washed salt with somewhat lower purity than the range noted above.
Lower purity crude salt is usually generated by solar ponds that operate
poorly, and allow, in the salt, particulate matter that has settling velocity
similar to that of salt. Without a settling rate difference, it is not possible
to separate these impurities, and one can either accept their presence in the
product, or take additional steps for increased purification efficiency.
If gypsum is the major component of the impurities in the salt, a
flotation step may be integrated in the salt wash system. This can reduce the
gypsum content in the salt markedly, but has the drawback of a decrease in
washed salt yield.
If particulate matter is the problem impurity one
needs to modify the solar pond operation or the harvesting. In general, there
are no acceptable flotation agents that can be used for such impurities. If
pond improvements cannot be effective, one may wish to consider vacuum
re-crystallization as an alternative to salt wash.
Crude Salt Crystal Size
The plant can be designed to handle crude salt with a particle size
distribution in the approximate range of 0.1-3 mm.
Surface Mother Liquor on Washed Salt
The plant can be designed for an adherent moisture of 4 - 5% for industrial
salt and 0,1% for table salt.
Yield
Depending on the crude salt composition, the Salt Wash system yield is
between 90-95%.
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