Immobilization of Pb2+ with ordinary portland cement - The method using lead hydroxyapatite

Lead hydroxyapatite was synthesized hydrothermally at 150 degrees C under saturated vapor pressure for 1h. This apatite or lead nitrate solution was added to ordinary portland cement (OPC) in order to immobilize the Pb2+. In this paper, the effect of Pb2+ on the hydration of OPC, mechanical properties of OPC pastes and the leaching characteristic of Pb2+ from hardened pastes were investigated. An addition of lead hydroxyapatite did not affect the hydration of OPC significantly, while that of lead nitrate solution affected the hydration of OPC. Therefore, a larger amount of Pb2+ could be immobilized by cement paste with lead hydroxyapatite than that with lead nitrate solution. The strength for hardened paste with lead hydroxyapatite was larger than that with nitrate solution. According to the leaching test for pastes, the apparent diffusion coefficient of Pb2+ in the paste with lead hydroxyapatite was smaller than that of Pb2+ in the paste with addition of lead nitrite solution.