Vibrational spectroscopy of functional group chemistry and arsenate coordination in ettringite

Satish Chandra Babu Myneni, Samuel J. Traina, Glenn A. Waychunas, Terry J. Logan

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179 Scopus citations

Abstract

The functional group chemistry and coordination of AsO43-sorption complexes in ettringite [Ca6Al2(SO4)3(OH)12·26H2O] were evaluated as a function of sorption type (adsorption, coprecipitation) and pH using Raman and Fourier Transform infrared (FTIR) spectroscopies. The reactive functional groups of ettringite, ≡Al-OH, ≡Ca-OH2, and ≡Ca2-OH exhibit broad overlapping OH bands in the range 3600-3200 cm-1, prohibiting separation of component vibrational bands. The SO42- polyhedra of the channels are present in three crystallographically different sites and exhibit weakly split S-O asymmetric stretch at 1136 cm-1 (with several components) and symmetric stretch at 1016, 1008, and 989 cm-1. During AsO43- adsorption, the vibrational spectra of SO42- were least affected, and the OH stretching intensities around 3600 cm-1 decreased with an increase in AsO43- sorption. In contrast, the S-O symmetric stretch at 1016 and 1008 cm-1 were almost completely removed, and the OH vibrations were relatively unaffected during AsO43-coprecipitation. The As-O asymmetric stretch of sorbed AsO43- are split and occur as overlapping peaks around 870 cm-1. The As-O(complexed) stretching vibrations are at ~800 cm-1. The low pH samples (pH = 10.3-11.0) exhibit distinct As-OH stretching vibrations at 748 cm-1, indicating that some of the sorbed AsO43- ions are protonated. These spectral features demonstrate that AsO43- directly interacts with ettringite surface sites during adsorption and substitute inside the channels during coprecipitation (preferentially for two of the three sites). The energy position of the As-O symmetric stretch vibrations suggest that the AsO43- polyhedra interacts predominantly with ≡Ca-OH2 and ≡Ca2-OH sites rather than with ≡Al-OH sites. Sorption of more than one type of As species was evident in low pH (<11.0) samples.

Original languageEnglish (US)
Pages (from-to)3499-3514
Number of pages16
JournalGeochimica et Cosmochimica Acta
Volume62
Issue number21-22
DOIs
StatePublished - Nov 1998

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology

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