Purifying phosphoric acid-nitrate solns. - obtd. by nitric acid digestion of phosphorite, gives prods. suitable for fertilisers

摘要

Aq. solns. of H3PO4 and NH4NO3 or KNO3 obtd. by (a) digesting phosphorite with HNO3, (b) opt. sepg. off part of the CaNO3 and (c) subjecting to double decompsn. with (NH4)2SO4 or K2SO4 in an amt. such that after pptn. of CaSO4 the proportion of Ca equivalents to Fe equivalents in soln. is 0.60-0.99, are purified by sepg. off the CaSO4, treating at 100-120 degrees C. with NH4OH until pH is 4.0-6.5 and sepg. off the CaSO4, treating at 100-120 degrees C. with NH4OH until pH is 4.0-6.5 and sepg. off pptd. impurities. The procedure gives quantitative pptn. of undesired impurities, esp. Fe+++, Al+++, Mg++, F- and SiF6-- in a form which is readily separable and washable. The pptd. impurities contain only a small amt. of the P2O5 and N present in the soln. Subsequent treatment of the mother liquor gives high-purity prods. such as ammonium phosphates and NH4NO3 which can be used as technical prods. or as high-grade fertilisers.