Phosphorous recovery by means of fluidized bed homogeneous crystallization of calcium phosphate. Influence of operational variables and electrolytes on brushite homogeneous crystallization

Phosphate recovery from wastewaters is one of the major engineering challenges to securing the worldwide food production. Fluidized-bed heterogeneous crystallization of struvite has been one of the most considered technologies. Nevertheless, the recovery of other phosphate products could be of the major interest at industrial level. Thus, in this work we present the recovery of calcium phosphate salts as brushite by a novel fluidized-bed homogeneous crystallization (FBHC) process. The no requirement of seeds in FBHC reactor allows obtaining high-purity crystals. The operational parameters of the FBHC process have been optimized in order to achieve the higher degree of granulation and to obtain the most homogeneous distribution of granules sizes. Thus, the treatment of 1500 mg/L of phosphate at pH 9.0 with a ratio of 1.2:1.0 of [Ca²⁺]:[PO₄³⁻]_T leads to the obtaining of ca. 90% of granulation with crystals of 0.5 mm of diameter. The influence of electrolytes typically found in TFT-LCD industry has been further considered. The characterization of the spheroidal crystals obtained allowed identifying brushite (calcium hydrogenphosphate salt) as unique crystal phase.