An X-ray diffraction (XRD) and Fourier transform infrared spectroscopic (FT-IR) investigation of the long-term effect on the solidification/stabilization (S/S) of arsenic(V) in Portland cement type-V

The long-term effects on solidification/stabilization (S/S) of As 5+-bearing oxyanions (AsO 3− 4) in Portland cement type-V (OPC) have been investigated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopic (FT-IR) techniques. The results of this study confirm our previous results that the early hydration of cement is inhibited by the presence of AsO 3− 4, and that the inhibition is mainly caused by the formation of highly insoluble Ca 3(AsO 4) 2 on the surface of hydrating cement particles. Arsenate analog of ettringite [Ca 6(Al 2O 6)(SO 4) 3·32H 2O] was identified in the early stages of hydration of pure Portland cement and As(V)-treated Portland cement [OPC-As(V)], but not in 10-year-old similar samples. The XRD and FT-IR results indicated interactions of oxyanions and cement particles to produce minor quantities of As 5+-bearing compounds in fresh as well as in 10-year-old samples. New As 5+-bearing phases, NaCaAsO 4·7.5H 2O and Ca 5(AsO 4) 3OH were identified in the 10-year-old OPC-As(V) samples by XRD analyses. Based on these results it is concluded that Portland cement may be considered as a potential matrix to immobilize As 5+-bearing wastes.