Recovery of phosphate as hydroxyapatite by fluidized bed homogeneous crystallization technique

Phosphorous recovery from aqueous solutions gained substantial attention and this not only secure the food demand but also curtail the pollution of freshwater courses. In the current study, authors employed novel fluidized bed homogeneous crystallization (FBHC) technique to granulate the phosphorous as hydroxyapatite (HAP). FBHC technique nurtures the formation of high pure HAP crystals without seed addition and potential technique to recover phosphorous compared to other techniques. The key operational parameters influencing the HAP crystallization were analyzed prior to FBHC by batch analysis. From the batch study results, the range of pH and calcium to phosphorous molar ratio fixed for FBHC studies. Maximum phosphate removal and granulation efficiencies obtained were 91.25% and 82.55%, respectively, at 500 mg/L phosphate concentration, pH 12, and calcium to phosphorous molar ratio 1.65. Box-Behnken design of response surface methodology was employed for evaluating interaction impact of process parameters on granulation efficiency. Granulation efficiency of 79.74% was attained at pH 11.83, calcium to phosphorous molar ratio 1.637, and reaction time 70.73 h.