Adsorption sodium silicate

Zeolites are naturally occurring hydrous aluminum-sodium silicates in porous granule form. They are capable of exchanging their sodium base for calcium or magnesium and of expelling these alkaline earth metals for sodium by treatment with salt. Thus, they are a type of ion-exchange media. (Some zeolites act as molecular sieves by adsorption of water and polar compounds.)... 

Figurel. Nitrogen adsorption isotherms (A) and pore size distributions (B) of samples synthesized with different silica source, a TMOS, pH = 10, b TMOS, pH =2 and c sodium silicate, pH = 10...

Powdered, particulate MCM-41 molecular sieves (Si/Al = 37) with varied pore diameters (1.80, 2.18, 2.54 and 3.04 nm) were synthesized following the conventional procedure using sodium silicate, sodium aluminate and C TMAB (n = 12, 14, 16 and 18) as the source materials for Si, A1 and quaternary ammonium surfactants, respectively [13]. Each sample was subjected to calcination in air at 560 °C for 6 h to remove the organic templates. The structure of the synthesized material was confirmed by powder X-ray diffraction (XRD) and by scanning/transmission electron microscopy. Their average pore sizes were deduced from the adsorption curve of the N2 adsorption-desorption isotherm obtained at 77 K by means of the BJH method (Table 1). 

Starch can be enzymically converted in the presence of pigment. The conversion follows a similar time-temperature cycle as in neat starch conversion. The pigment will adsorb a portion of the enzyme adsorption can be minimized by the addition of sodium silicate to the mixture prior to the addition of the enzyme (Vanderbilt process). Even with silicate treatment, a higher quantity of enzyme will be required to reach a specific viscosity target. Other coating components, such as latex and lubricants, have to be added after the conversion. The Vanderbilt process is now rarely used for the preparation of coating binder. 

Following the investigations of Schiith, Stucky and Unger and their co-workers, various procedures have been proposed for the preparation of M41S and other related materials. For example, Edler and White (1995) have described a method for the low-temperature synthesis of a pure silica form of MCM-41. An essential stage in their preparative route was the controlled ageing of the mixed solution of sodium silicate and cetyltrimethylammonium bromide (CTAB) before the intermediate product was filtered, washed, dried and finally calcined in air at 350°C. Comparison with standard hydrother-mally produced material revealed no significant difference in the adsorption properties. 

Another method to refine oils using milder silicate refining agent was recently reported. This process combines neutralization and adsorption and eliminates the use of centrifuges to remove free fatty acids from crude oils (it involves the addition of sodium silicate instead of sodium hydroxide, which allows for the removal of free fatty acids and protein-like materials by adsorption and filtration and avoids the use of more expensive centrifuges). The combined agglomerating and adsorptive characteristics of silicates allow for the removal of these impurities (81). 

Silica-Aluminas. Amorphous. These are generally considered to be cationic exchangers owing to their protonic character. The adsorption character may also vary depending upon whether they were prepared by acid side precipitation (e.g., by adding sodium silicate to aluminium sulphate in which case the alumina tends to precipitate last giving more of an alumina type of surface) or whether conversely if prepared by a base side precipitate (in which case the surface tends towards that of silica). There is no published information that differentiates what effects, if any, this may have. 

The membranes obtained after adsorption of sodium silicate have a non-uniform composition with a high percent of the amorphous phase. Pretreatment with NH4OH solution conducts to membranes with low uniformity. The zeolite or amorphous nickelsilicate with very small particles form these membranes. 

I d ous glass and quartz are also basically similar, but tb i lwo.a sorbents h ive not been used much in adsorption chromatography. Chromato-I l aphic silicas are amorphous, porous solids which can be prepared in a wide range of surface areas and average pore diameters Variation Of solution pH during the acid gelation of sodium silicate yields silicas with... 

T-H Hsia, S-L Lo, C-F Lin, D-Y Lee. Characterization of arsenate adsorption on hydrous iron oxide using chemical and physical methods. CoU Surf 85 1-7, 1994. RB Robinson, GD Reed, B Frazier. Iron and manganese sequestration facilities using sodium silicate. J Am Water Works Assoc 84 77-82, 1992. 

A similar effect is shown in Figure 3 where surfactant was titrated into dispersions of a montmorilIonite clay. In each case the surfactant activity in solution was reduced, but the amount of reduction was least when sodium silicate was present in the clay dispersion. The mechanism at work is probably the displacement of surfactant or preferential adsorption of silicate anions at the edges and discontinuities in the sand, as well as on clay minerals where cations are exposed. 

This shows the sacrificial nature of the silicates. Also some work by Somasundaran (30) has shown that the sodium silicates are more effective than the other alkaline chemicals in reducing surfactant adsorption on rock surfaces. 

An explanation of the anomalous stability of Iler s silica sols in terms of steric stabilization effects requires that oligomeric or polymeric silicate species are present at the silica-water interface and that steric repulsion results during overlap of such layers. This mechanism is appealing in that soluble silicates, usually sodium silicates, are universal dispersants of many electrostatic colloids. Again, well-hydrated silicas [2] and other colloids exposed to aqueous silicate [18] acquire high adsorption densities of aqueous silica. 

In this study, a cost-effective CO2 adsorbent has been prepared by impregnating PEI onto precipitated silica, which was synthesized by acidizing sodium silicate solution using sulfuric acid. The prepared adsorbent possesses a relatively high CO2 adsorption capacity and stability. 

The model consists of a concentrated suspension of monodisperse silica in squalene. The silica was prepared from sodium silicate [1] and treated as described by Philipse and Vrij [2]. Its particle size was about 50 nm. In the preparation of monodisperse silica samples, the silane was added in the squalene solvent phase. To assess the completeness of the silane treatment, adsorption was followed by recording the compacted silica density against silane addition. This provided evidence that the silane/silica reaction had reached completion at silane concentrations of about 2 %. However, silica samples were treated with 8 % silane throughout the study. 

The most common preparation is by the acidification of sodium silicate solutions to a pH of less than 10. The precipitate is usually provided in granular form although beaded forms are available. Fine powders are also occasionally us in some adsorptive applications. 

Silica gels with porous amorphous beads, the specific surface area in the 25-800 m /g range and the pore volume of 0.05-1.5 cm /g, are typically produced from sodium silicate (tetraethyl orthosilicate [TEOS]). Silica gels are widely used in adsorption applications as a desiccant (to control local humidity), chromatographic adsorbents (unmodified and functionalized), drug and catalysts carriers, etc. (Her 1979, Bergna 1994, 2005, Legrand 1998,). Surface chemistry of... 

Alkaline inorganic chemicals such as sodium silicates, sodium hydroxides, sodium carbonate, and sodium phosphates have been added to injection fluids used in enhanced oil recovery systems. These chemicals can, in varying degrees, affect various rock and fluid parameters such as interfacial tension, interfacial viscosity, emulsion stability, rock wettability, hardness-ion content, ion-exchange capacity or equilibria, surfactant adsorption, phase equilibria, etc., in order to improve recovery efficiency for residual oil remaining after waterflooding. 

The data from these tests show that sodium orthosilicate is more effective than sodium hydroxide in recovering residual oil under the conditions studied, both for continuous flooding and when 0.5 PV of alkali was injected. The mechanisms through which sodium orthosilicate produced better recovery than sodium hydroxide in this system have not been completely elucidated. Reduction in interfacial tension is similar for both chemicals, so other factors must play a more important role. Somasundaran (26) has shown that sodium silicates are more effective than other alkaline chemicals in reducing surfactant adsorption on rock surfaces. Wasan (27,28) has indicated that there are differences in coalescence behavior and emulsion stability which favor sodium orthosilicate over sodium hydroxide. Further work is being done in this area in an attempt to define the limits of physically measurable parameters which can be used for screening potential alkaline flooding candidates. 

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