Coarsely crystalline trisodium phosphate dodecahydrate prodn. - in form of free-flowing cubic or spheroidal crystals

摘要

Prodn. of Na3PO4. 12H2O having a cubic or spheroidal crystal form by cooling crystallisation is improved in that phosphoric acid produced by the thermal method is treated at 70-80 degrees C with NaOH soln. in an amt. corresp. to an atomic Na:P ratio of 3.1-3.3:1 and such a concn. that the P2O5 content is 11-13 wt.%, and the density of the soln. si 1.310-1.340 g/cm3; the soln is gradually cooled to 30-40 degrees C (over 16-23 hr.) whilst turbulent conditions are maintained (Froude number 2.6-6. 2x10-2). Coarsely crystalline Na3PO4. 12H2O (in cubic or spheroidal form) is produced in a simple manner with low energy consumption. The prod. is free-flowing and has good storage stability (in contrast to the acicular or columnar crystals of Na3PO4. 12H2O obtd. by the convetional process which tend to cake on storage). The purity of the prod. is high; chloride ions are nearly absent.