Process for separating off calcium nitrate tetrahydrate by crystallization
AssigneeUnie van Kunstmestfabrieken B.V.
InventorsGijsbertus H. M. Calis, Matheus H. G. Jennekens
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Abstract
Separating Ca(NO.sub.3).sub.2.4H.sub.2 O from a nitrophosphate digestion liquor by crystallization, wherein Ca(NO.sub.3).sub.2.4H.sub.2 O seeding material with a particle size smaller than 100 .mu.m is added to this liquor at a temperature of 0.degree.,1.degree.-2.degree. C. lower than the saturation temperature, the resulting liquor is batchwise cooled, and the Ca(NO.sub.3).sub.2.4H.sub.2 O crystallized out is separated from the cooled liquor. The Ca(NO.sub.3 ).sub.2.4H.sub.2 O is substantially crystallized out without excessive cooling as very coarse and uniform particles which can be easily separated out.
Claims8
A process for separating calcium nitrate tetrahydrate by crystallization during batchwise cooling from a digestion liquor obtained by digesting phosphate rock with nitric acid, which process comprises;
- initially cooling the digestion liquor using a cooling medium having a temperature higher than the nucleation temperature of the digestion liquor and adding about 50,000 to 200,000 calcium nitrate tetrahydrate seeds per kg of the digestion liquor to be cooled to the digestion liquor, said seeds having a particle size less than 100 .mu.m wherein the temperature of the digestion liquor is between 0.1.degree. C. and 2.degree. C. below the saturation temperature of the digestion liquor whereby calcium nitrate tetrahydrate crystals grow from said seeds, the initial cooling continuing as long as the concentration of calcium nitrate tetrahydrate crystals in the digestion liquor is less than about 20%,
- thereafter, when the concentration of said crystals in the digestion liquor has increased to above about 20%, subsequently cooling the digestion liquor using a cooling medium having a temperature lower than the nucleation temperature of the digestion liquor;
- and
- separating out the calcium nitrate tetrahydrate crystallized out in this process from the thus-cooled digestion liquor.
Dependencies are inferred from the claim text.