Sodium aluminosilicate gels

Table 3. Some Synthetic Zeolites Prepared from Sodium Aluminosilicate Gels...

Sodium aluminate, 2 345t, 358-359 analysis, 2 275-276 economic aspects, 2 275 health and safety factors, 2 276 manufacture, 2 274-275 neutralization, 2 424 physical and chemical properties of, 2 273-274 uses of, 2 276-277 in water treatment, 26 111 Sodium aluminosilicate gels, synthetic zeolites prepared from, 16 831t Sodium aluminosilicates, 12 578 Sodium aluminum hydride, 13 621, 623-624... 

Flanigen monitored the changes in the IR spectra that occur during the synthesis of NaX zeolite from a sodium aluminosilicate gel. The appearance of absorption bands due to the formation of structural units in the zeoUte as the crystallization of NaX proceeded were observed [93]. In particular, the growth of a band around 575 cm indicated the formation of double six-rings which is one of the structural sub-units of X zeolite. 

Zeolite Na-A was synthesized in our laboratory. After crystallization from the sodium aluminosilicate gel, the zeolite was carefully washed with deionized water in order to remove occluded impurities without causing H30+ ion exchange. It was then stored in a desiccator containing saturated NH4CI solution. 

This paper is aimed at clarification of the change of concentration with time in the liquid phase before crystallization starts. To find optimum conditions for the commercial production of pure zeolites of the types A and faujasite, the reaction of fine-particle amorphous silica with sodium alu-minate solution was studied at 20°, 40°, and 75°C. The liquid phase separated by filtration nucleates the zeolite types Ay sodalite, phillipsite, and faujasite, depending on stirring time before liquid-solid separation. Quite similar conditions are observed in precipitated sodium aluminosilicate gels and mother liquor. 

Zeolites. A large and growing industrial use of aluminum hydroxide and sodium aluminate is the manufacture of synthetic zeolites (see Molecular sieves). Zeolites are aluminosilicates with Si/Al ratios between 1 and infinity. There are 40 natural, and over 100 synthetic, zeoUtes. All the synthetic stmctures are made by relatively low (100—150°C) temperature, high pH hydrothermal synthesis. For example the manufacture of the industrially important zeolites A, X, and Y is generally carried out by mixing sodium aluminate and sodium silicate solutions to form a sodium aluminosilicate gel. Gel-aging under hydrothermal conditions crystallizes the final product. In special cases, a small amount of seed crystal is used to control the synthesis. 

Sodium aluminosilicate gel. This experiment illustrates the preparation of a different type of gel. Prepare a sodium alumi-nate solution that is 0.5-molar in aluminum, either by dissolving powdered sodium aluminate, NaA102 H20, in water and filtering or by adding sodium hydroxide solution to a solution of aluminum sulfate until the aluminum hydroxide first precipitated has just dissolved. Mix 30 ml of the 20 per cent sodium silicate solution used for silica el with 20 ml of water in a 400-ml beaker ... 

Cowley AR, Chippindale AM (1996) J Chem Soc Chem Commun 673 Chippindale AM,Cowley AR (1997) Zeolites 18 176 Flanigen EM, Lok BMT, Patton RL, Wilson ST (1988) U.S. Patent 4,737,353 Harvey G, Meier WM (1989) In Jacobs PA, Van Santen RA (eds) Zeolites Facts, Figures, Future. Elsevier, Amsterdam, Studies in Surface Science and Catalysis 49 411 The faujasite zeolite X crystallizes at low temperatures (100 °C) from sodium aluminosilicate gels. Higher temperatures or longer crystallization times result in the formation of the gismondine structure Gier TE, Stucky GD (1991) Nature 349 508... 

Our synthetic routes to ZK4 were modifications of those described by Kerr (21). An amorphous, basic aluminosilicate gel containing tetramethylammonlum (TMA) Ion was heated at 100°C to promote formation of ZK4 crystals. Preparation of the gel Involved the vigorous mixing at room temperature of one component acting as a source of sodium and alumina, with another component acting as a source of TMA and silica. The alumina used was sodium... 

The manufacture of the industrially important zeolite types A, X and Y is generally carried out by mixing sodium aluminate and sodium silicate solutions, whereupon a sodium aluminosilicate get is formed. In this gel Si02- and Al203-containing compounds pass into the liquid phase, from which the zeolites are formed by cry.stallization. As the zeolite growth components are removed from the solution more gel dissolves. The reaction mechanism for zeolite formation is presently not yet fully understood. There is experimental evidence that, depending upon the reaction conditions, different mechanisms are possible. 

Direct microscopy shows that crystals of zeolites are sometimes formed from sodium aluminosilicate solutions at 70 °C without intermediate gel formation. When a gel is formed, it acts as a reservoir of reagent, and nucleation is favoured by the presence of zeolite crystals. ... 

Silicates and aluminosilicates, including hydrated and dehydrated silica and aluminosilicate gels, represent other examples of noncrystalline condensation structures. Silica gels form in the course of a sol-gel transition in which the new amorphous phase is formed due to the reaction of sodium silicate with an acid ... 

The fourth mechanism for the corrosion of ceramics is incongruent dissolution with the formation of noncrystalline layer. Here, the chemical reaction between the solvent and the solid leaves a noncrystalline layer on the surface. It happens in the case of sodium aluminosilicate. When it is allowed to react with an acid, Na+ ions go into the solution along with some silicon tetrahedral units. On the surface, a noncrystalline gel layer of combined aluminum octahedral-silicon tetrahedral imits are formed. The reaction is shown in Equation 5.3. 

---