A process for the preparation of granular
fertilizer grade DAP (a product composed of
ammonium phosphates, principally
diammonium phosphate, resulting from the ammoniation of
phosphoric acid, as defined in Official Publication No. 52 of the Association of American
Plant Food Officials, dated 1999) comprising partially preneutralizing orthophosphoric acid with
ammonia, completing the ammoniation of the orthophosphoric acid with
ammonia in a rotary ammoniator-granulator to provide granular DAP,
sizing the granular DAP to provide the granular DAP product, reducing the particle size of the oversized granular DAP, and recycling the undersized granular DAP and the sized-reduced oversized granular DAP to the ammoniator-granulator. The
ammoniacal nitrogen concentration of the granular DAP recycle, hence the granular DAP product, is enhanced by subjecting the finely-divided recycled granular DAP to
anhydrous gaseous ammonia which is at a super
atmospheric pressure and which is at a temperature sufficient to maintain said
anhydrous ammonia in the gaseous state. The increase in the
ammoniacal nitrogen concentration is a function of the absolute ammonia pressure, the initial
moisture content of the granular DAP recycle, and the
contact time of the
ammonium with the granular DAP recycle.