Purification of wet process phosphoric acid - by treating cooled reaction mixture with oxidising absorbent coagulant compn, filtering ageing and concentrating filtrate

摘要

Removal of org. and inorg. impurities from phosphoric acid is new in which phosphate, rock or uncalcined natural calcium phosphate is reacted with sulphuric acid to give a phosphoric acid broth, CaSO4 and impurities, then evaporating instantaneously, the brew contg. the acid and CaSO4 so as to cool it, treating the cooled stirred brew with an oxidising, adsorbent, and coagulant compsn. to remove the uncalcined impurities, filtering the brew, concentrating the filtrate, ageing the concentrate to precipitate inorg. impurities and concentrating once more the impurity-free phosphoric acid to give a clarified product having a solid content of 2%. Phosphoric acid may be made by the wet process from phosphate, rock etc. to give a prod. sufficiently free from colour and with a low enough solid content to be used for preparing calcium phosphate or sodium tripolyphosphate. Smaller reaction vols. may be employed and H2SO4 of only 93% concn. is needed.