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

摘要

The long-term effects on solidification/stabilization (S/S) of As~(5+)-bearing oxyanions (AsG_4~(3-)) 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_4~(3-), 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.