Wastewaters can contain residual phosphorus concentrations above the recommended limiting values, and it could have a high environmental impact. The discharge of such effluents is undesirable and can cause excessive nutrients and eutrophication in the receiving water. In order to produce an effluent suitable for stream discharge, chemical precipitation of phosphate based on a sequential experimental design has been explored. The influence of factors [pH, type of salt (calcium or iron)] involved in the co-precipitation of phosphate ions was studied by a complete factorial design. It was established that the optimal parameter values obtained from a second-order model allowed conclusion to be drawn on the effectiveness of the removal. So in the best conditions (pH 8.41 and a dose of 97.07 mg/L Ca(OH)2 with 10 mg/L FeSO4·7H2O), 95.80 % (removal rate) of the phosphate ion were removed from the synthetic solution. A second-order mathematical model of the removal of phosphate ions, depending on two parameters which are pH and Ca(OH)2 concentration, was finally proposed. Moreover, on the basis on the pH solution, it was shown that the precipitate formed was hydroxyapatite Ca10(PO4)6(OH)2 and the scanning electron microscopy views revealed the amorphous and homogeneous aspect of the precipitates.