Precipitation flotation of phosphate from water

The removal of phosphate from water by precipitation flotation was examined. Calcium chloride (CaCl2) was added to induce precipitates. Effects of both molar ratio ([Ca2+]:[HPO42−]) and pH on precipitation were examined, and experimental results were compared with those from equilibrium modeling by PHREEQC. Molar ratio and pH were the key parameters in determining the residual phosphate concentration, and monetite (CaHPO4), hydroxyapatite (Ca5(PO4)3OH), and amorphous calcium phosphate precipitates (Ca3(PO4)2·xH2O) were found to be the dominant solid species. Dispersed air flotation was utilized for the removal of precipitates from water using various collectors. Anionic collector, sodium dodecyl sulfate (SDS) and sodium oleate (NaOl) could become adsorbed onto solid surfaces and facilitated the flotation removal of calcium phosphate precipitates. Neither nonionic collector Brij 35 nor cationic cetyltrimethyl ammonium bromide (CTAB) were effective collector. The ionic strength and the presence of anions affected the removal efficiency of calcium phosphate precipitate when SDS was the collector. However, it increased by increasing the concentration of SDS or by adding SOl.