Solidification/stabilization of Ni(II) by various cement pastes

The immobilization of Ni(II) in various cement matrices was investigated using the solidification/stabilization (S/S) technique. The different cement pastes used in this study were neat Portland cement in absence and presence of water reducing- and water repelling-admixtures as well as blended cement with kaolin. Two ratios of Ni(II) were used (0.5% and 1.0% by weight of the solid binder). The hydration characteristics of the used cement pastes were tested via the determination of the combined water content, phase composition and compressive strength at different time intervals from 1 up to 180 days. The results show that the presence of NiCl2 caused retardation for the hydration of Portland cement paste in absence and presence of water-reducing agent. But NiCl2 caused acceleration rather than retardation on the hydration of the mixes containing calcium stearate and/or clay. The degree of immobilization of the added heavy metal ions was very high in the different investigated cement pastes.