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 As5+-bearing oxyanions (AsO43-) in Portland cement type-V (OPC) have been investigated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopic (FTIR) techniques. The results of this study confirm our previous results that the early hydration of cement is inhibited by the presence of AsO43-, and that the inhibition is mainly caused by the formation of highly insoluble Ca-3(AsO4)(2) on the surface of hydrating cement particles. Arsenate analog of ettringite [Ca-6(Al2O6)(SO4)(3).32H(2)O] was identified in the early stages of hydration of pure Portland cement and As(V)-treated Portland cement [OP-CAs(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 As5+-bearing compounds in fresh as well as in 10-year-old samples. New As5+-bearing phases, NaCaAsO4.7.5H(2)O and Ca-5(AsO4)(3)OH 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 As5+-bearing wastes. (C) 2003 Elsevier B.V. All rights reserved.