Modeling Alkaline Silicate Solutions at 25 °C

Weber, C.F.; Hunt, Rodney D.

doi:10.1021/ie0303449

Cited by 16 publications

(25 citation statements)

References 14 publications

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“…It has previously been hypothesized [21] that the presence of highly soluble NO 3 − in the geopolymerization process may have some effect on the alkaline solution. The presence of a large quantity of nitrate is known to suppress silica solubility [24], although it is not clear if this is due to a simple 'salting-out' effect or an ion-specific behavior. However, at the very low levels of nitrate addition used here, any effect observed will most likely be an ion-specific one, as the effect on the ionic strength of a geopolymer pore solution of adding a small amount of NaNO 3 will be negligible.…”

Section: Compressive Strengthmentioning

confidence: 99%

Geopolymers for immobilization of Cr6+, Cd2+, and Pb2+

Zhang

Provis

Feng

et al. 2008

Journal of Hazardous Materials

322

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Section: Compressive Strengthmentioning

confidence: 99%

Geopolymers for immobilization of Cr6+, Cd2+, and Pb2+

Zhang

Provis

Feng

et al. 2008

Journal of Hazardous Materials

322

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“…In Figure 4, predicted solubilities of amorphous silica are compared with experimental data in NaOH solutions at 25 °C from Alexander et al (1954), and in NaOH + NaNO 3 mixtures at 25 °C from Weber and Hunt (2003). From Figure 4, it is obvious that solubilities predicted by the model are in good agreement with model-independent experimental data over the entire ionic strength range from very dilute to ∼4.5 m in alkaline solutions.…”

Section: Model Validationmentioning

confidence: 73%

“…The log K for reaction 20, is -25.81 from Weber and Hunt (2003). In Figure 4, predicted solubilities of amorphous silica are compared with experimental data in NaOH solutions at 25 °C from Alexander et al (1954), and in NaOH + NaNO 3 mixtures at 25 °C from Weber and Hunt (2003).…”

Section: Model Validationmentioning

confidence: 99%

“…Experimental data in NaOH + 1.0 m NaNO₃ (Weber and Hunt, 2003) Experimental data in NaOH + 3.3 m NaNO₃ (Weber and Hunt, 2003) Experimental data in NaOH (Alexander et al, 1954) Model predicted values silica. In the pH range from 8 to 14, H 5 Si 3 O 10 3-can account for up to ∼40% of the total dissolved silica, and H 4 Si 2 O 7 2-can account for up to ∼10% of the total dissolved silica.…”

Section: Molality Of Naoh (M Naoh )mentioning

confidence: 99%

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A thermodynamic model for silica and aluminum in alkaline solutions with high ionic strength at elevated temperatures up to 100 C: Applications to zeolites

Xiong

2012

American Mineralogist

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In this study, a thermodynamic model for silica and aluminum in high ionic strength solutions at elevated temperatures up to 100 °C is constructed. Pitzer equations are utilized for the thermodynamic model construction. This model is valid up to ionic strengths of ∼24 molal (m) in NaOH solutions with silicate concentrations up to ∼1.5 m. The speciation of silica (including monomers and polymers) and aluminum at elevated temperatures is taken into account. Also, the equilibrium constants for silicic acid and its polymer species (H 4 SiO 4 , H 5 Si 2 O 7 -, H 4 Si 2 O 7 2-, and H 5 Si 3 O 7 3-) at elevated temperatures up to 100 °C, are obtained based on theoretical calculations. Using this thermodynamic model, thermodynamic properties, including equilibrium constants, and respective reaction enthalpies are obtained for sodium silicates, zeolite A, and the amorphous form of zeolite A, based on solubility experiments at elevated temperatures. The equilibrium constants for zeolite A and amorphous precursor of zeolite A regarding the following reactions up to 100 °C, NaAlSiO 4 ⋅2.25H 2 O(cr) + 4H + = Na + + Al 3+ + H 4 SiO 4 (aq) + 2.25H 2 O(l) (1) and NaAlSiO 4 ⋅2.25H 2 O(am) + 4H + = Na + + Al 3+ + H 4 SiO 4 (aq) + 2.25H 2 O(l) (2) can be expressed as follows K T log 7963 327 16.46 0.96 1 = ± − ± (3) and K T log 12971 160 30.80 0.50 2 = ± − ±where T is temperature in Kelvin. The enthalpy of formation from elements, Gibbs free energy of formation from elements, and standard entropy derived for zeolite A and the amorphous form of zeolite A with the chemical formulas mentioned above at 25 °C and 1 bar are -2738 ± 5 kJ/mol, -2541 ± 2 kJ/mol, 373 ± 10 J/(K⋅mol); and -2642 ± 3 kJ/mol, -2527 ± 2 kJ/mol, and 648 ± 10 J/(K⋅mol), respectively. The enthalpy of formation from elements for zeolite A derived in this study based on solubility experiments in hydrothermal solutions agrees well with those obtained by calorimetric measurements and by theoretical calculations.

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“…[7] Many studies have been carried out recently to identify silicate molecules which participate directly in the pre-nucleation, nucleation and crystal growth of zeolites (microporous solids used for heterogeneous catalysis, separations and ion-exchange processes), based on the premise that a zeolites unique properties are encoded at its earliest stages of formation in hydrothermal solution. [8][9][10][11] Additionally, research has been conducted to determine the mechanistic pathways employed by organisms such as diatoms, grasses and sponges to produce hierarchically ordered biosilica, with the goal of developing novel biomimetic ceramics.…”

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confidence: 99%

Aqueous Alkali‐Metal Silicate Anions Containing Fully Condensed Four‐Coordinate Sites

2012

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The chemistry of aqueous silicates has long been investigated owing to its geochemical significance [1,2] and its numerous industrial applications in fields as diverse as cements and geopolymers, [3,4] pulp/textile bleaching, [5] sol-gel derived ceramics, [6] and waste/water treatment. [7] Many studies have been carried out recently to identify silicate molecules which participate directly in the pre-nucleation, nucleation and crystal growth of zeolites (microporous solids used for heterogeneous catalysis, separations and ion-exchange processes), based on the premise that a zeolites unique properties are encoded at its earliest stages of formation in hydrothermal solution. [8][9][10][11] Additionally, research has been conducted to determine the mechanistic pathways employed by organisms such as diatoms, grasses and sponges to produce hierarchically ordered biosilica, with the goal of developing novel biomimetic ceramics. [6,[12][13][14][15] The first 29 Si NMR spectrum of a concentrated alkalimetal silicate solution (commercial "waterglass") was reported in 1973, [16,17] and revealed broad resonance bands which were assigned to end (Q 1 ), middle (Q 2 ) and branching (Q 3 ) silicate centers by analogy to the 29 Si NMR spectra of polyalkylsiloxanes. [18] A broad peak at the low-frequency end of the spectrum, centered at À35 ppm with respect to the orthosilicate (Q 0 ) signal, was assigned to tetrafunctional (Q 4 ) units in colloidal silica. Improvements in spectrometer technology, combined with attention to factors such as solution composition and 29 Si NMR relaxation phenomena, have resulted in the ability to resolve signals from the individual spin sites of silicate anions. By employing materials that are highly 29 Si enriched together with structure elucidation techniques such as COSY, it thus becomes possible to characterize the parent anions. [19][20][21][22][23][24] To date, the structures of 48 different silicate anions have been determined in this manner. [25] They are all compact, containing no more than nine Si sites, and are largely based on three-, four-and fivemembered silicate rings. [26] They exist in dynamic equilibrium with one another [27,28] and their relative abundances are highly dependent on solution pH, concentration and temperature. [24] Conspicuous by their absence, however, are 1) specialized building units that appear in zeolite frameworks ("secondary building units") [8,11,29] and 2) pre-nucleation or protomineral species which contain fully condensed Q 4 sites. Indeed, only two Q 4 -containing structures have ever been found in solution and then only in the presence of tetraalkylammonium (TAA) cations, both being derivatives of the TAA-stabilized cubic octamer species. [30] We report herein the existence of aqueous silicate ions containing fully condensed Q 4 sites in alkali-metal hydroxide solution, thereby providing the first definitive evidence of the chemical nature of protomineral species in such systems.Surprisingly, little direct mechanistic information has so far been obtained...

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Modeling Alkaline Silicate Solutions at 25 °C

Cited by 16 publications

References 14 publications

Geopolymers for immobilization of Cr6+, Cd2+, and Pb2+

Geopolymers for immobilization of Cr6+, Cd2+, and Pb2+

A thermodynamic model for silica and aluminum in alkaline solutions with high ionic strength at elevated temperatures up to 100 C: Applications to zeolites

Aqueous Alkali‐Metal Silicate Anions Containing Fully Condensed Four‐Coordinate Sites

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