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Solidification/Stabilization (S/S) of cadmium by Portland Type V cement (OPC) and its leaching mechanism have been investigated by Fourier Transform Infrared Spectroscopy (FTIR). Effects of carbonation on cadmium S/S systems have also been investigated. Evidence is presented from FTIR results that the hydration of OPC is retarded due to the formation of calcium hydroxycadmiates, which result from the surface reaction of [Cd(OH) 4 ] 2-with calcium ions at or on the surface of the cement grains. Considerable insight has been gained concerning the nature of hydration reactions in the presence of carbon dioxide and in its absence. The results reveal the nature of the hydroxylated surface compounds formed by cadmium -doped Portland cement. Carbonation has been found to play an important role in the hydration and polymerization of silicates. The leaching process leads to higher degree of polymerization of the silicate components due to the attack of C-S-H by the acidic leaching solution. This is facilitated by the dissolution of calcium hydroxide, sulfates and cadmium complexes from the surface of the cement grains. † Visiting Professor,