Inertization of lead by using blended cement pastes

Inertization of lead nitrate Pb(NO3)2, a representative of soluble lead compound, with five cements pastes based on either ordinary Portland cement (OPC) or blended Portland cement with granulated blast-furnace slag (GBFS) or metakaolin (MK) was studied. Various mixes were prepared by using a water/solid ratio (W/S) of 0.28 (by weight). Two ratios of Pb ions (1.0% and 2.0% of the solid binder) was used by adding to the mixing water. Hydration characteristics of the different cement pastes were investigated via the examination of chemically combined water content, compressive strength, X-ray diffraction analysis and thermal analysis (DTA/TGA). Leaching of lead ions from various hardened cement pastes was examined. The results showed that lead nitrate retards cement hydration through the formation of plumbate salt CaPbO3. The obtained results of leaching showed a high degree of immobilization of Pb ions in the various cement pastes. Moreover, partial replacement of Portland cement by MK is more efficient than granulated blast-furnace slag GBFS.