Abstract: Crystalline aluminosilicate Type Y zeolite is prepared by reacting silica, alumina, sodium hydroxide and water to produce a slurry of Type Y zeolite and excess silicate containing mother liquor. Silicate is recovered from the mother liquor as precipitated silica/alumina hydrogel by the addition of an acid aluminum salt such as aluminum sulfate. The precipitated silica/alumina hydrogel is used in the zeolite reaction step as a source of silica and alumina.

Abstract: Faujasitic-type crystalline zeolites X and Y are produced. In one embodiment, sodium sulfide is added to the reaction mixture as a source of sodium and as a buffer. The buffering action of the sodium sulfide provides the basicity required to maintain the alumina hydrate component of the reaction mixture in solution but not a basicity whereby zeolite crystallization is retarded. In another embodiment, a nucleating mixture having the formula3-10 Na.sub.2 S: 5-15 Na.sub.2 O: 5-50 SiO.sub.2 : 0.4-4.0 Al.sub.2 O.sub.3 : 50-500 H.sub.2 Ois added to the reaction mixture to promote crystalline zeolite formation.

Abstract: Methods of increasing the thermal stability of crystalline zeolites are disclosed. The methods are characterized by the steps of either (i), treating the crystalline zeolite first in at least one step with a dilute solution of a fluorine compound whereby a very small amount of fluoride is incorporated in the zeolite with a subsequent exchange with an ammonium ion, rare earth ion, or other metal ion solution, (ii), first exchanging the zeolite with an ammonium ion, rare earth ion or other metal ion solution followed by a treating with a dilute fluoride solution, or (iii), concurrently treating the zeolite with the fluoride ion and exchanging the zeolite in a simultaneous operation.