Common opal was dissolved in NaOH lyes in rotating autoclaves. The starting material was characterized by X-ray diffraction and adsorption spectroscopy, thermal and chemical analysis, electron and atomic force microscopy. The opal proved to be an Opal-CT with a microstructure consisting of microcrystalline tridymite, traces of low-quartz, and amorphous parts built up by random packings of size distributed amorphous silica colloids. The dissolution conditions have been inspired by the technological process of hydrothermal water glass synthesis by dissolving silica. Temperature and time of the dissolution process as well as initial molar SiO2:Na2O (Rm) ratios of the starting materials were varied systematically. The particle size of the samples was varied, too, but due to the nanoscopic microstructure without greater impact on dissolution kinetics. The process products were analyzed chemically. Additionally, some of them were characterized by X-ray diffraction, viscosimetry and dynamic light scattering. Already after short dissolution times, water glasses with quite high silica concentrations of up to 27 wt.% and SiO2:Na2O ratios of up to 3.7 were obtained. At longer dissolution times low-quartz and analcime precipitated and the SiO2 contents were reduced to about 22 wt.% and Rm to about 2.7. The silica contents in equilibrium with low-quartz were almost independent on temperature.
References
[1]
Weldes, H.H. and Lange, K.R. (1969) Properties of Soluble Silicates. Journal of Industrial and Engineering Chemistry, 61, 29-44. https://doi.org/10.1021/ie50712a008
[2]
Iler, R.K. (1979) Chemistry of Silica. Wiley-Interscience, New York.
[3]
Stober, W. (1966) Physical and Chemical Properties of Coesite and Stishovite Compared to Quartz (Translated from German). Beitr. Silikoseforschung, 89, 1-113.
[4]
Dove, P.M. and Rimstidt, J.D. (1994) Silica-Water Interactions. In: Prewitt, P.J., et al., Eds., Reviews in Mineralogy, Vol. 29, Silica-Physical Behavior, Geochemistry and Materials Applications, Mineralogical Society of America, Washington DC, 259-308.
[5]
Fleming, B.A. and Crerar, D.A. (1982) Silicic Acid Ionization and Calculation of Silica Solubility at Elevated Temperature and pH Application to Geothermal Fluid Processing and Reinjection. Geothermics, 11, 15-29. https://doi.org/10.1016/0375-6505(82)90004-9
[6]
Gunnarsson, I. and Arnorsson, S. (2000) Amorphous Silica Solubility and the Thermodynamic Properties of H4SiO4 in the Range of 0° to 350°C at Psat. Geochimica et Cosmochimica Acta, 64, 2295-2307. https://doi.org/10.1016/S0016-7037(99)00426-3
[7]
Tuttle, O.F.A. and Friedmann, I.I. (1948) Liquid Immiscibility in the System H2O-Na2O-SiO2. Journal of the American Chemical Society, 70, 919-926.
https://doi.org/10.1021/ja01183a011
[8]
Jones, J.B. and Segnit, E.R. (1971) The Nature of Opal. I. Nomenclature and Constituent Phases. Journal of the Geological Society of Australia, 18, 57-68.
https://doi.org/10.1080/00167617108728743
[9]
Florke, O.W., Graetsch, H., Martin, B. and Wirth, R. (1991) Nomenclature of Micro- and Non-Crystalline Silica Materials—Based on Structure and Microstructure. Neues Jahrbuch für Mineralogie Abhandlungen, 163, 19-42.
[10]
Avakov, V.A. and Vinogradow, B.N. (1974) Comparative Solubility of Silica and Some Alumosilicates (Title Translated from Russian). Izvestiya Vysshikh Uchebnykh Zavedenii, Khimiya i Khimicheskaya Tekhnologiya, 17, 879-882.
[11]
Ordiales, E. (1969) Production of Alkali Silicates from Opal and Similar Minerals (Translated from German). German Patent DE 1969-1900066.
[12]
DIN EN 896 (2012) Chemicals Used for Treatment of Water Intended for Human Consumption-Sodium Hydroxide. Beuth Verlag, Berlin.
[13]
Oelkers, E.H., Helgeson H.C., Shock, E.L., Sverjensky, D.A., Johnson, J.W.A. and Pokrovskii, V.A. (1994) Summary of the Apparent Partial Molal Standard Gibbs Free Energies of Aqueous Species, Minerals, and Gases at Pressures 1 to 5000 Bars and Temperatures 25 to 1000 °C. Journal of Physical and Chemical Reference Data, 24, 1401-1560.
[14]
Patterson, A.L. (1939) The Scherrer Formula for X-Ray Particle Size Determination. Physical Review, 56, 978-982. https://doi.org/10.1103/PhysRev.56.978
[15]
Brunauer, S., Emmet, P.H. and Teller, E. (1938) Adsorption of Gases in Multimolecular Layers. Journal of the American Chemical Society, 60, 309-319.
https://doi.org/10.1021/ja01269a023
[16]
Roggendorf, H., Grond, W. and Hurbanic, M. (1996) Structural Characterization of Concentrated Alkaline Silicate Solutions by 29Si-NMR Spectroscopy, FT-IR Spectroscopy, Light Scattering, and Electron Microscopy—Molecules, Colloids and Artefacts. Glass Science and Technology, 69, 216-231.
[17]
Boschel, D., Janich, M. and Roggendorf, H. (2003) Size Distribution of Colloidal Silica in Sodium Silicate Solutions Investigated by Dynamic Light Scattering and Viscosity Measurements. Journal of Colloid and Interface Science, 267, 360-368.
https://doi.org/10.1016/j.jcis.2003.07.016
[18]
Diedrich, T., Dybowska, A., Schott, J., Valsami-Jones, E. and Oelkers, E.H. (2012) The Dissolution of SiO2 Nanoparticles as a Function of Particle Size. Environmental Science & Technology, 46, 4909-4915. https://doi.org/10.1021/es2045053
[19]
Azizi, S.N. and Yousefpour, M. (2011) Isomorphous Substitution of Iron and Nickel into Analcime Zeolite. Zeitschrift für anorganische und allgemeine Chemie, 637, 759-765.
https://doi.org/10.1002/zaac.201100059
[20]
Jannagadha Rao, M. and Gopal Krishna, B. (2013) Naturally Engineered Analcime for Water Treatment Process and Its Calorimetric Properties. International Journal of Science and Research, 160-166.
[21]
La Mer, V.K. (1952) Nucleation in Phase Transitions. Industrial & Engineering Chemistry, 44, 1270-1277. https://doi.org/10.1021/ie50510a027
