GB745551A - Improvements in or relating to the manufacture of sodium and potassium phosphates - Google Patents

Abstract

Aqueous solutions of sodium or potassium phosphate are prepared by feeding phosphoric acid and a slurry of sodium or potassium carbonate or bicarbonate to a closed reaction vessel to react there under pressure and thereafter discharging the reaction mixture as a stream, preferably atomized to a receiver, preferably a closed vessel, maintained at a lower gaseous pressure than the reaction vessel thereby disengaging the carbon dioxide and steam formed in the reaction, from the solution. The proportions of the slurry and phosphoric acid fed are preferably such that a phosphate of mean empirical formula MaH3-aPO4 is formed in which <FORM:0745551/III/1> is from 0.5 to 2, M being Na or K. The phosphoric acid solution suitably contains 50 to 60 per cent by weight of available P2O5 and the slurry may contain about 50 per cent by weight of soda ash. As shown in the Figure, phosphoric acid and soda ash solution are fed by pumps 4 and 3 to a reaction vessel 5 in the form of a pipe 10 to 20 feet long. An outlet valve 6 is adjusted to maintain a reaction vessel pressure of 10 to 30 p.s.i. above that of the vessel 9 into which the reaction mixture is discharged through nozzle 7. A flow rate of 3 to 7 feet per second may be maintained in vessel 5. The reaction mixture, discharging from nozzle 7 may be atomized by inpingement <PICT:0745551/III/1> on the walls or on a plate 8 and evolved gas is withdrawn at 13. The vessel 9 is provided with an agitator to assist disengagement of gases and the phosphate liquor leaves through pipe 14, if desired after being passed by pipe 17 to a vessel 12 similar to and operating at a lower pressure than, vessel 9. Further evolved gas is removed at 15 and the phosphate liquor leaves by pipes 16 and 14. The carbon dioxide is air free. The process may be adjusted to produce orthophosphates of empirical formula M2HPO4,M3 PO4 and MH2PO4 in which the ratio of metal atoms to hydrogen atmos is 2 : 1, 5 : 3, 1 : 1 and 1 : 2 and intermediate values.