Elimination of Pb²⁺ ion from aqueous solution by using calcium hydroxide solution or ammonium phosphate solution

The elimination of Pb²⁺ ion front aqueous solution was performed by adding calcium hydroxide solution or ammonium phosphate solution to a solution containing Pb²⁺ ion. The concentration of the filtrate was measured and the data were compared with those of the ferrite formation method. In the case of Ca(OH)₂ addition, the concentration of Pb²⁺ ion in the filtrate was affected by the Ca²⁺/Pb²⁺ ratio. The minimum concentration of 0.58 mg/dm³ was obtained when the Ca²⁺/Pb²⁺ ratio was 1, where pH of the solution was 11.74. In the case of (NH₄)₃PO₄ addition, ill-crystallized Pb-hydroxyapatite was precipitated, and the concentration of Pb²⁺ ion in the filtrate was 0.01 mg/dm³. The well-crystallized Pb-hydroxyapatite was obtained by the hydrothermal treatment of ill-crystallized one by using solution with pH of 12 at 150°C for Ih. This Pb-hydroxyapatite has lower solubility than lead hydroxide over a wide pH range. It is concluded that the method for elimination of Pb²⁺ ion from aqueous solution by using calcium hydroxide or ammonium phosphate were more effective than the ferrite formation method.