Occidental Research Corporation

Occidental Petroleum

Occidental Petroleum Company

Fernando N Ore'

James L Bradford

Magnesium and aluminum impurities are removed from aqueous phosphoric acid by treatment with a fluorine material and an alkali metal containing material in such a manner that the atomic ratio of fluorine to aluminum is adjusted so that it is greater than about 2 and the alkali metal plus magnesium to aluminum atomic ratio to a value no greater than about 2. In one embodiment the fluorine to aluminum ratio is below about 11, preferably between about 4 and about 8. By controlling such atomic ratios in the limits prescribed, a more purified aqueous phosphoric acid can be produced having a substantial reduction in the magnesium and aluminum content thereof. The process is useful for wet-process phosphoric acids. The process is also particularly useful for acids having low P.sub.2 O.sub.5 content and/or high aluminum concentration. The purification process does not require evaporation for the removal of impurities, as for example fluorine as silicon tetrafluoride.

Removal of magnesium and/or aluminum values from impure aqueous

A process for producing low aluminum content phosphoric acid from high aluminum matrix comprises digesting the matrix in phosphoric acid; adding a flocculant to consolidate gelatinous or fine undigested solids; separating the flocculated solids from the mother liquid comprising monocalcium phosphate; acidifying the monocalcium phosphate with sulfuric acid to precipitate solid calcium sulfate and simultaneously adding at least one sodium or potassium compound or both to co-precipitate some of the soluble fluoride with the gypsum; separating the product phosphoric acid from the precipitated solids; recycling part of the lower fluoride content phosphoric acid back to the digestion step; and, aging the remainder of the product phosphoric acid until a precipitate of aluminum fluorophosphate forms and separating the precipitate to produce a low aluminum content phosphoric acid. Additional fluorine (e.g., a fluoride compound) can be added to accellerate formation of the aluminum fluorophosphate.

Process for producing low aluminum content phosphoric acid from high

When sulfate ions and a solution of monocalcium phosphate are reacted under conditions which result in the formation of a slurry comprising calcium sulfate hemihydrate and phosphoric acid of about 35% to about 55% P.sub.2 O.sub.5, filtration is improved when a sulfonic acid, a sulfonic acid salt, tall oil fatty acid or alkoxylated or esterified tall oil fatty acid and mixtures thereof is present in the slurry (preferably at 1-1000 ppm). Preferably a two vessel reaction system is used in which the reaction slurry undergoes intra- and inter- vessel circulation (preferably through a draft tube). The solution portion of the slurry in the first vessel (the 'dissolver') is preferably maintained at a negative sulfate concentration (i.e. excess Ca.sup.+2) and the solution in the second vessel (the 'crystallizer') is preferably maintained at a positive sulfate ion concentration, most preferably at a reduced pressure, (e.g. to provide evaporative cooling). Better filtration rates can thus be obtained due to the lower viscosity of the slurry and/or favorable shape, dominant size and size distribution of the hemihydrate crystals.

Hemihydrate type process for phosphoric acid manufacture using additive

Water immiscible organic acid phosphates used in conjunction with water immiscible organic sulfonic acids results in an improved process for the purification of phosphoric acid. An increase in the extraction of ionic metallic impurities and a decrease in the extraction of P.sub.2 O.sub.5 values from the aqueous phosphoric acid phase is observed in the improved solvent extraction process.

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Whittier, CA, United States of America

Fernando N Ore'