Vibrational spectroscopy of functional group chemistry and arsenate coordination in ettringite

Journal Article · Sun Nov 01 04:00:00 EST 1998 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(98)00221-X· OSTI ID:338619

Myneni, S C.B.; Traina, S J; Logan, T J ^[1]; Waychunas, G A ^[2]

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1. Ohio State Univ., Columbus, OH (United States). School of Natural Resources
2. Lawrence Berkeley National Lab., CA (United States). Earth Sciences Div.

The functional group chemistry and coordination of AsO{sub 4}{sup 3{minus}}-sorption complexes in ettringite [Ca{sub 6}Al{sub 2}(SO{sub 4}){sub 3}(OH){sub 12}{center_dot}26H{sub 2}O] 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, {triple_bond}Al-OH, {triple_bond}Ca-OH{sub 2}, and {triple_bond}Ca{sub 2}-OH exhibit broad overlapping OH bands in the range 3,600--3,200 cm{sup {minus}1}, prohibiting separation of component vibrational bands. The SO{sub 4}{sup 2{minus}} polyhedra of the channels are present in three crystallographically different sites and exhibit weakly split S-O asymmetric stretch at 1,136 cm{sup {minus}1} (with several components) and symmetric stretch at 1,016, 1,008, and 989 cm{sup {minus}1}. During AsO{sub 4}{sup 3{minus}} adsorption, the vibrational spectra of SO{sub 4}{sup 2{minus}} were least affected, and the OH stretching intensities around 3,600 cm{sup {minus}1} decreased with an increase in AsO{sub 4}{sup 3{minus}} sorption. In contrast, the S-O symmetric strength at 1,016 and 1,008 cm{sup {minus}1} were almost completely removed, and the OH vibrations were relatively unaffected during AsO{sub 4}{sup 3{minus}}-coprecipiation. The As-O asymmetric stretch of sorbed AsO{sub 4}{sup 3{minus}} are split and occur as overlapping peaks around 870 cm{sup {minus}1}. The As-O{sub complexed} stretching vibrations are at {approximately}800 cm{sup {minus}1}. The low pH samples (pH = 10.3--11.0) exhibit distinct As-OH stretching vibrations at 748 cm{sup {minus}1}, indicating that some of the sorbed AsO{sub 4}{sup 3{minus}} ions are protonated. These spectral features demonstrate that AsO{sub 4}{sup 3{minus}} 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 AsO{sub 4}{sup 3{minus}} polyhedra interacts predominantly with {triple_bond}Ca-OH{sub 2} and {triple_bond}Ca{sub 2}-OH sites rather than with {triple_bond}Al-OH sites. Sorption of more than one type of As species was evident in low pH (<11.0) samples.

• Sponsoring Organization: Geological Survey, Reston, VA (United States); Lawrence Berkeley Lab., CA (United States); USDOE, Washington, DC (United States); Ohio State Univ., Columbus, OH (United States)
• OSTI ID: 338619
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 21-22 Vol. 62; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ADSORPTION
ALUMINIUM HYDROXIDES
ALUMINIUM SULFATES
AQUATIC ECOSYSTEMS
ARSENATES
CALCIUM HYDROXIDES
CALCIUM SULFATES
COPRECIPITATION
HYDRATES
VIBRATIONAL STATES