Wet-process phosphoric acid prodn. - with calcium sulphate recovery as hemi:hydrate via di:hydrate

摘要

Prodn. of H3PO4 and CaSO4.1/2H2O is carried out by (a) reacting a phosphate ore with H2SO4 under conditions such that the CaSO4 pptes as hemihydrate; (b) separating the hemihydrate and washing it under conditions such that the hemihydrate is not converted to dihydrate, while cpds. which migh inhibit the conversion of hemihydrate to dihydrate are removed by decompsn. and/or dissolution, (c) removing free moisture from the hemihydrate, (d) converting the hemihydrate to dihydrate by direct cooling, and (e) converting the dihydrate to hemihydrate in known manner. The process permits simultaneous prodn. of conc. aq. H3PO4 (e.g. with a P2O5 content of 40-54 wt.%) and high-purity CaSO4,1/2H2O, which is a more useful by-prod. than CaSO4.2H2O.