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Occidental Chemical Corporation

Occidental Chemical Company

Thomas E Richards

James P Harvey

Michael A Daigle

Fernando N Ore

P.sub.2 O.sub.5 values occluded in the crystals which are precipitated during the hemihydrate process for manufacturing phosphoric acid are recovered by dissolving and recrystallizing the hemihydrate crystals as dihydrate crystals in an acidic environment having a P.sub.2 O.sub.5 concentration of from about 0.1% to about 10% and a free sulfate concentration in the range of about 0.1% to about 10%. Water is used to wash the dihydrate filter cake, and the filtrate from this wash is used to redissolve the hemihydrate crystals. The free sulfate values are preferably supplied to the dihydrate crystallizer as sulfuric acid.

Recovery of P.sub.2 O.sub.5 values from phosphoric acid hemihydrate

A process, for removing solid impurities from impure phosphoric acid containing solids, comprising: (a) passing said acid at an elevated temperature through a filter cake of a phosphoric acid-resistant filter aid supported on a porous medium, thereby to cause at least a portion of said solid impurities of said acid to be filtered therefrom and to be retained by said filter cake; (b) contacting at least a portion of said filter cake with a displacing liquid, maintained at a temperature and in an amount sufficient to cause at least a portion of the acid which remains in said filter cake to pass through said filter cake without fracturing said filter cake; (c) collecting said filtered acid which passes through said filter cake; and (d) removing an impurity-containing portion of said filter cake after contact with said acid and displacing liquid, thereby to present a fresh surface for subsequent filtration.

Process for removing fine solids from phosphoric acid by vacuum

An improved rotary vacuum precoat filter apparatus comprises a nozzle positioned for spraying a displacing liquid on the outer surface of the filter cake. Connected to the nozzle is a supply conduit for delivering the displacing liquid under pressure to the nozzle. Included along the supply conduit is a temperature control for regulating the temperature of the displacing liquid. The temperature of the displacing liquid is regulated for providing a spray of the displacing liquid about the temperature of the filter cake. Such temperature regulation minimizes thermal shock to the precoat of filter aid forming the filter cake.

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Jennings, FL, United States of America

Thomas E Richards