CHARACTERIZATION OF CHROMIUM-DOPED TRICALCIUM SILICATE USING SEM/EDS, XRD AND FTIR

The containment of chromium in tricalcium silicate (C3S1) has been investigated. Tricalcium silicate is a major component in ordinary Portland cement (OPC), and chromium compounds used as dopants simulate chromium wastes that might be stabilized in a cement matrix. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to probe the distribution of chromium in the stabilized waste form and also to identify the microstructural changes in the normal hydration products of C3S accompanying the addition of chromium as Cr(III) and Cr(VI). X-ray diffraction (XRD) was used to monitor the hydration reaction of C3S and formation of crystalline calcium hydroxide (CH). The effect of chromium addition on the condensation of the orthosilicate units in C3S was followed with Fourier transform infrared spectroscopy (FTIR). Standard acetic acid leaching tests were carried out to evaluate the mobility of chromium in the Cr(III)/C3S and Cr(VI)/C3S systems. Probable mechanisms of chromium containment in the amorphous calcium silicate hydrate (C-S-H) phase are discussed.