Purification of wet-process phosphoric acid with methanol and ammonia

Claim 1

The improved method for the partial purification of crude phosphoric acid prepared from phosphate rock and sulfuric acid and containing 50 to 55 percent P 2 O 5 with co-production of solid fertilizer material, said solid fertilizer material containing 44-55 % P 2 O 5 and 4-7% nitrogen and containing the substantial portion of the metallic and fluorine impurities originally present in the crude phosphoric acid, which improved method consists essentially of the steps of: 1. mixing said crude acid with methanol and ammonia while maintaining the temperature of the resulting mixture between 35°C and the boiling point for a period of time from 15 minutes to 90 minutes, wherein the mole ratio NH 3 :P 2 O 5 of said mixture is maintained from 0.26 to 0.40 and the weight ratio methanol:P 2 O 5 of said mixture is maintained from 2.5 to 4.2; 2. subsequently separating the reaction mixture into a clarified liquid fraction consisting of aqueous phosphoric acid and ammonium phosphate dissolved in methanol and a solid fraction containing 44-55% P 2 O 5 and 4-7% nitrogen and containing the major portion of the metallic and fluorine compounds originally present in the crude phosphoric acid; 3. subsequently separating the methanol from said clarified liquid fraction to obtain partially purified concentrated phosphoric acid; 4. subsequently removing phosphoric acid adhering to said solid fraction by washing with methanol and then evaporating methanol from washed solids to recover said solid fertilizer material.