Mono:ammonium phosphate and ammonium nitrate prodn. - from phosphate ore via digestion with nitric acid, used as fertilisers etc.

摘要

Prodn. of moammonium phosphate (MAP) and ammonium nitrate (AN) is carried out by (a) digesting phosphate ore with HNO3 to form a mixt. of H3PO4 and Ca(NO3)2, and opt. partially crystallising the Ca(NO3)2 by cooling; (b) adding (NH4)2SO4 to ppte. CaSO4; (c) neturalising the resulting soln. with ammonia to form MAP and AN; (d) crystallising the MAP; and (e) adding a Ca cpd. and ammonia to the remaining AN soln. to ppte. residual phosphate as tricalcium phosphate (TCP). The improvement comprises precipitating the TCP in coarse-crystalline form by adding part of the liquor obtd. during digestion. The crystalline MAP can be used as a fertiliser or converted to (NH4)2HPO4. The AN soln. can be used as a liq. fertiliser or used to produce solid AN or calcium ammonium nitrate. The coarsely crystallie TCP i s readily sepd. from an AN soln. (e.g. in a hydrocyclone) without entraining intert fines, so there is no build up of fines when the TCP is recycled to the digestion step.