Synthesis of Hydrated Aluminum Phosphate, AlPO4·1.5H2O (AlPO4−H3), by Controlled Reactive Crystallization in Sulfate Media

A new method for the synthesis of hydrated aluminum phosphate, AlPO 4 ·1.5H 2 O, in a semibatch reactor is reported. The synthesis involves direct reactive crystallization induced by pH adjustment to a predetermined supersaturation level. Precipitation was conducted in sulfate-based solutions with Al(III):P(V) molar ratio of 1 and at 95 °C. Homogeneous precipitation tests led to the definition of the metastable zone of aluminum phosphate. This zone was used to design the supersaturation-controlled seeded test. XRD, TGA, and chemical analysis confirmed the product to be AlPO 4 ·1.5H 2 O. SEM and particle size analysis revealed the product to consist of aggregates of submicron-size crystallites of 3.5 μm average size (homogeneously formed product) grown to 16.5 μm after three cycles of seeded crystallization.