Mechanisms of metal stabilization by cement based fixation processes

The mechanism of zinc and mercury fixation by cement/silicate stabilization processes has been assessed from leaching, scanning electron microscopy, X-ray diffraction and porosimetry studies. The results of these tests correlate closely and suggest two separate mechanisms operating in the interaction between these metals and the cement/silicate system. The presence of zinc has a significant effect upon the hydration and final physical properties of cement. The chemical interaction between mercury and cement/silicate is minimal and the hydration process of cement proceeds normally. Zinc appears to be chemically stabilized by cement based fixation processes through the formation of insoluble compounds at high pH. Mercury and related metals which do not form precipitates at elevated pH levels are held in pore solution. Mobility depends largely upon physical encapsulation by the cement matrix and leachability of these materials is expected to be closely related to porosity of the final product.