Occidental Research Corporation

Howard Winterbottom

Subhas K Sikdar

Donald E Adam

In a process for purifying an aqueous phosphoric acid containing up to about 55% P.sub.2 O.sub.5 by weight and dissolved magnesium, iron and aluminum ions, wherein (a) said phosphoric acid is contacted with an organic extractant containing a water immiscible organic sulfonic acid to form: a loaded organic extractant phase containing the organic sulfonic acid, extracted ionic metallic impurities and extracted P.sub.2 O.sub.5 values, and a purified aqueous phosphoric acid; (b) the purified aqueous phosphoric acid phase is separated from the loaded organic extractant phase; (c) the separated loaded organic extractant phase is contacted with a solution phase containing calcium ions (e.g., calcium nitrate), under conditions whereby at least some of said extracted ionic metallic impurities (e.g., Mg.sup.+2, Al.sup.+3, Fe.sup.+3) are replaced by calcium and are transferred to said solution phase; and (d) the solution phase is separated from the contacted extractant phase; the improvement wherein the separated solution phase from step (d) is made basic, preferably with lime, to cause a solid precipitate to form, said solid precipitate comprising at least some of the metallic impurities and/or P.sub.2 O.sub.5 values from phosphoric acid which was entrained in the organic extractant. The separated solid precipitate is useful as a nutrient (e.g., as a fertilizer or as an animal feed supplement). Where sulfuric acid is used for the acidification, solid calcium sulfate forms, which can be separated from the 'used' acid. The sulfuric acid can be strengthened with fresh, more concentrated, acid and recycled.

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Pomona, CA, United States of America

Howard Winterbottom