HEXAVALENT CHROMIUM IN TRICALCIUM SILICATE - PART II - EFFECTS OF CR-VI ON THE HYDRATION OF TRICALCIUM SILICATE

The composition and structure of hydrated tricalcium silicate (C3S) p astes admixed with Cr-VI have been studied. The resultant mixture simu lates Cr-VI waste forms stabilized in ordinary Portland cement. Scanni ng electron microscopy and transmission electron microscopy were used to identify the microstructural changes accompanying the addition of C r-VI solutions to C3S. Energy-dispersive X-ray spectroscopy was used t o probe the distribution of chromium in the phases within the hazardou s waste forms. Elucidation of the molecular structure of the reaction products was accomplished with Fourier transform infrared and nuclear magnetic resonance spectroscopies. Cr-VI was found to be contained in the waste form as soluble Ca2CrO5 . 3H(2)O and partially VI chemically bonded within the calcium silicate hydrate (C-S-H) phase. Cr was also found to increase the condensation of C-S-H and porosity of the waste form.