The present paper deals with proper separation of trisodium phosphate as a valuable by product from the associated excess caustic soda of the reaction filtrate of controlled alkali breakdown of Rosetta monazite. Two procedures are applied for this purpose; namely a direct crystallization procedure of the phosphate product or else its salting out by using methanol. XRD and IR analysis of the separated by-product indicated a structural formula of Na₃PO₄.12H₂O. Analysis of the latter was revealed about 100 ppm uranium in the product separated by crystallization while that separated by methylation was completely exempt of uranium.