Development of improved systems for the cement-based solidification of metal hydroxide sludges

The addition of cement and other pozzolanic materials to many types of industrial wastes can be an effective treatment method to reduce the leaching rates of hazardous components. Many wastes normally treated by this type of process have a deleterious effect on cement hydration and the resulting solidified waste is often a relatively weak, highly variable, poorly characterized material. The effect of individual waste components on cement hydration has been studied by analyzing solutions extracted from hydrating cements and using conduction calorimetry, X-ray diffraction, DTA and SEM. Particularly problematic metal hydroxide species have been identified, and the effects of additives which accelerate cement hydration, such as CaCl2, on the microstructure and leaching of solidified waste mixes which are normally retarded have been investigated. Leach testing studies emphasize the importance of controlling the acid neutralization capacity of mixes in order to achieve long term retention of most heavy metals. This factor together with the minimization of connected porosity are seen as key parameters in determining the quality of a solidified waste