Mechanisms of metal stabilization in cementitious matrix: Interaction of dicalcium silicate (C₂S) paste and copper oxide

There are relatively few published studies describing the microstructural and microchemical interaction, of metal‐containing wastes and solidifying agents in solidification systems. An understanding of such interactions would be useful to predict the ability of fixation systems to retard the solubility and/or mobilitty of the incorporated metal species. Thus, solidification systems could be designed to exert a minimal environmental impact. For the present study, the interactions between dicalcium silicate (C2S) paste and CuO were characterized using X‐ray diffractometer (XRD) and scanning electron microscopy (SEM) equipped with energy‐dispersive X‐ray analysis (EDAX). The results of XRD analysis indicated that the C2S paste/CuO fixation system provided a mild alkaline environment during hydration reaction. The interfacial microanalysis by SEM/EDAX of C2S paste and CuO showed a significant difference between hydrated β‐ and non‐hydrated γ‐C2S systems. The interfacal zone is in about 1 μm thickness and the concentration gradient of calcium and silicon observed in the CuO region is due to the interaction of hydrated β‐C2S and CuO. It is suggested that the CuO was stabilized in the C2S paste by two major mechanisms; Ca and Si from hydrated β‐C2S diffuse and form a solid solution in the CuO region, and CuO is in well contact with C2S paste.