METHOD FOR PURIFYING WET-PROCESS PHOSPHORIC ACID Russian patent published in 1998 - IPC

FIELD: chemical industry; production of wet-process phosphoric acid, in particular, for production of alimentary and fodder phosphate additives. SUBSTANCE: first, crude wet-process phosphoric acid is produced. Extraction is carried out with tributyl phosphate in presence of sulfuric acid, followed by re-extraction into aqueous phase and by recirculating portion of re-extract back to process. Extraction is carried out in counter-current continuous process mode and sulfuric acid is added after producing mixture containing 1-40% of free phosphoric acid. Extract is directed to two-step washing in counter-current mode. Washing is conducted first with water and/or with phosphoric acid which is not concentrated by evaporation. Finally, washing is conducted with concentrated phosphoric acid. Washed reaction mass is subjected to fractioned re-extraction in aqueous medium, followed by separating 10-20% of total amount of product acid containing 75-86-% strong H₃PO₄ in first process step. Product acid containing 60-75-% strong H₃PO₄ is separated as finished product in second process step. Remaining acid is directed in third process step for concentration until ortho-phosphoric concentration in it reaches 85-94%. Optionally, acid separated in first re-extraction step can be recycled back to recirculation circuit for production of super-high-purity acid. Acid produced in third re-extraction step, after concentrating it up to 85-94% H₃PO₄ content, can be recycled back to second washing step. EFFECT: higher efficiency. 2 cl, 1 tbl