An NMR and XRD study of solidification/stabilization of chromium with portland cement and beta-C2S

Abstract

Solidificalion/stabilization of chromium with Portland cement Type I and P-dicalcium silicate (beta-C2S) was investigated by means of the Si-29 solid stale Magic Angle Spinning/Nuclear Magnetic Resonance (Si-29 MAS/NMR) and X-ray Diffraction (XRD) techniques. It is found that chromium nitrate can increase the extent of beta-C2S hydration. It is also confirmed that the chromium ion is easily incorporated into the beta-C2S paste and hydrated Portland cement, and that it affects the characteristics of hydration and hydration products. Formation of beta-calcium chromium oxide hydrate (beta-CaCrO4 . 2H2(O)) during the hydration of chromium-doped beta-C2S and calcium chromium oxide hydrate (CaCrO4 . 2H(2)O) during the hydration of chromium-doped Portland cement indicates the substitution of chromium for silicon in hydration products. The chromium ion, Cr3+, is thus stabilized and solidified through this mechanism.