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Abstract

This invention comprises a method for removing fluorine from natural phosphates, superphosphate materials and wet process phosphoric acids starting materials comprising (a) admixing rock phosphate having a fluorine content above that desired with an acid mixture within the range of rock:acid mixture of about 0.8 to 1 and 1:1.4 by weight; (b) said acid mixture being substantially concentrated phosphoric acid and concentrated sulfuric acid in a range of phosphoric:sulfuric of about 1:1 to 5:1 by weight; (c) said admixing being at a temperature in the range of 215.degree. to 265.degree. F. while adding water in an amount of up to about 12% by weight of the total mixture and then subjecting the above charge; (d) in a first heating stage adding (1) recycle in an amount substantially of recycle to charge of 1:1 to 10:1 by weight (2) and water while heating to a temperature in the range of 300.degree. F. to 400.degree. F. for a period of time up to about 6 minutes; (e) and in a second heating stage, maintaining the temperature in the range of 400.degree. to 600.degree. F. for a period of time of up to about 6 mimutes, and then; (f) quickly cooling the resulting product above to a temperature range below about 300.degree. F. to 200.degree. F. while neutralizing to about 1 to 6% free acid and with addition of at least sufficient amount of water to have water of hydration of substantially 2 to 9% by weight in the final product; (g) and, crushing the above resulting product to a desired granular size and separating and returning smaller fine particles as recycle.

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First Claim