Immobilization of co %28ii%29 ions in cement pastes and their effects on the hydration characteristics

J. Mater. Sci. Technol., 2011, 27(1), 74-80.

Immobilization of Co (II) Ions in Cement Pastes and Their Effects on the Hydration Characteristics
Eisa Hekal1)† , Essam Kishar2) , Wafaa Hegazi2) and Maha Mohamed2)
1) Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt 2) Chemistry Department, Women s College for Arts, Science and Education, Ain Shams University, Cairo, Egypt
[Manuscript received May 14, 2009, in revised form January 30, 2010]

The immobilization of Co (II) in various cement matrices was investigated by using the solidification/stabilization (S/S) technique. The different cement pastes used in this study were ordinary Portland cement in absence and presence of water reducing- and water repelling-admixtures as well as blended cement with kaolin. Two ratios of Co (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 up to 180 d. The degree of immobilization of the added heavy metal ions was evaluated by determining the leached ion concentration after time intervals extended up to 180 d. The leachability experiments were carried out by using two modes: the static and the semi-dynamic leaching processes. It was noticed that the concentration of the leached Co2+ ions in the static mode of leachability was lower than the solubility of its hydroxide in all the investigated cement pastes. KEY WORDS: Hydration characteristic of cement; Admixtures; Immobilization; Heavy metals

1. Introduction The protection of public health and environment from hazardous pollutants is a major concern of industrialized nations. As the quantity of hazardous industrial wastes increases significantly owing to rapid industrialization, its appropriate management is required to reduce adverse impacts on humans and ecosystems[1,2] . Various technologies have