CONTAINMENT MECHANISM OF TRIVALENT CHROMIUM IN TRICALCIUM SILICATE

Trivalent chromium admixtures in ordinary Portland cement (OPC) have a pronounced effect on the structure of the hydration products of trica lcium silicate (C3S). (I) Cr-III compounds, added as dopants to C3S, s imulate chromium waste forms that might be stabilized in a Portland ce ment matrix. Scanning electron microscopy (SEM) and transmission elect ron microscopy (TEM), were used to identify the microstructural change s accompanying the addition of Cr-III solutions to C3S. Energy dispers ive spectroscopy (EDS) was used to probe the distribution of chromium in the stabilized hazardous waste forms. Fourier transform infrared (F TIR) and Si-29 nuclear magnetic resonance (NMR) spectroscopies were em ployed to provide structural information about the crystalline and amo rphous products of C3S hydration. In monolithic waste forms containing trivalent chromium, chromium was found to be stabilized both through the formation of insoluble calcium chromium hydroxide nitrate complexe s, and localized chemical incorporation of chromium in the stable calc ium silicate hydrate (C-S-H) phase. (C) 1998 Elsevier Science B.V.