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The formation of Sr silicates at low temperature and the solubility product of tobermorite-like Sr (sub 5) Si (sub 6) O (sub 16) (OH) (sub 2) 5H (sub 2) O

Andrew R. Felmy, Marvin J. Mason, Paul L. Gassman and David E. McCready
The formation of Sr silicates at low temperature and the solubility product of tobermorite-like Sr (sub 5) Si (sub 6) O (sub 16) (OH) (sub 2) 5H (sub 2) O
American Mineralogist (January 2003) 88 (1): 73-79

Abstract

The aqueous phase interaction of divalent Sr with silicate-containing solutions was studied over a range of pH values, dissolved silica, and Sr concentrations, and extending to basic solution (0.2 M NaOH) at room temperature (22-23 degrees C). Formation of an amorphous Sr silicate phase of variable composition was observed, beginning at approximately pH 10. The precipitate became quasi-crystalline at higher base concentrations and with aging time. The phase that formed at high base concentration (beginning at pH 11.5-12.0) was identified by total chemical analysis. X-ray diffraction, and thermogravimetric analysis to have a chemical formula of Sr (sub 5) Si (sub 6) O (sub 16) (OH) (sub 2) .5H (sub 2) O, with a tobermorite-like structure. The Sr (sub 5) Si (sub 6) O (sub 16) (OH) (sub 2) .5H (sub 2) O phase has not been previously reported. Scanning electron microscopy (SEM) analysis of alcohol-washed precipitates showed a fine granular structure similar to Ca silicate hydrates. De-ionized water washing of the precipitates resulted in dissolution and growth of surface phases with the classical "sheaf of wheat" nucleation structure previously identified only for Ca silicate hydrates. Solubility studies of the precipitates, which extended to 286 days of equilibration, yielded an estimate of the solubility product of quasicrystalline, tobermorite-like Sr silicate of Log K = -38.0+ or -0.7 for the overall reaction, 5H (sub 2) O + Sr (sub 5) Si (sub 6) O (sub 16) (OH) (sub 2) . 5H (sub 2) O = 5Sr (super 2+) + 6H (sub 3) SiO (super -) (sub 4) + 4OH (super -) . The first estimate of the association constant for the species SrH (sub 2) SiO (sub 4) (aq) of Log K = 2.86 was also made.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 88
Serial Issue: 1
Title: The formation of Sr silicates at low temperature and the solubility product of tobermorite-like Sr (sub 5) Si (sub 6) O (sub 16) (OH) (sub 2) 5H (sub 2) O
Affiliation: Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory, Richland, WA, United States
Pages: 73-79
Published: 200301
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 29
Accession Number: 2003-024302
Categories: General geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200309
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