The subject of the invention is a process for the continuous preparation of x-ray amorphous sodium aluminosilicates of small particle size, capable of conversion into zeolitic sodium aluminosilicates of smallest particle size, by mixing an aqueous sodium aluminate solution with an aqueous sodium silicate solution in the presence of excess sodium hydroxide solution above room temperature.
On mixing sodium aluminate solutions with sodium silicate solutions under the mentioned conditions, particularly at temperatures above 60.degree. C., a precipitate of x-ray amorphous sodium aluminosilicate is formed instantaneously at all starting and concentration levels of the reaction partners commonly used in the technology. Of technological significance is especially the mixing solutions which give the following molar ratios of the reaction partners:
1.5 to 9 Na.sub.2 O:1 Al.sub.2 O.sub.3 :1 to 7 SiO.sub.2 :40 to 400 H.sub.2 O. PA1 1 to 5 Na.sub.2 0:1 Al.sub.2 O.sub.3 :1.8 to 4 SiO.sub.2. PA1 0.9 to 1.1 Na.sub.2 O:1 Al.sub.2 O.sub.3 :1.8 to 4 SiO.sub.2 PA1 1.5 to 9 Na.sub.2 O:1 Al.sub.2 O.sub.3 :1 to 7 SiO.sub.2 :40 to 400 H.sub.2 O
An alkalinity exceeding this, a higher silicate content or a greater dilution of the precipitation batch are not technologically meaningful. A water content of the batch lower than that given above results in especially pronounced formation of lumps in the precipitate as well as nonhomogeneous products.
Within the mentioned batch ratios, an amorphous sodium aluminosilicate precipitates always primarily from a large excess of sodium hydroxide solution, which precipitate has a chemical composition corresponding to the molar ratios of:
After rinsing out the excess alkali, x-ray amorphous products are obtained with a chemical composition corresponding to the molar ratios of:
with a moisture content depending on the degree of drying. The silicate content of the precipitate depends largely on the molar ratio of SiO.sub.2 :Al.sub.2 O.sub.3 in the precipitation batch.
The instantaneously forming precipitates of amorphous sodium aluminosilicate upon mixing of aluminate solutions with silicate solutions above room temperature lead to the formation of a gel-like reaction mixture that has no fluidity at first. This, in the one hand, makes a thorough and complete mixing of the two reaction components and thus also the obtaining of a homogeneous reaction product difficult and, on the other hand, delays also a subsequent crystallization of the amorphous product, if this is desired. Beyond this, the effect causes the formation of a relatively coarse-grained product containing large proportions with a particle diameter exceeding 50.mu.. With a batch precipitation of sodium aluminosilicate, the no longer fluid reaction mixture usually can be liquefied again by a sufficiently long application of strong shear forces. Until now, however, a continuous precipitation of amorphous sodium aluminosilicate was made impossible by the brief available time, due to the continuous process at technologically significant rates, which was inadequate to break up or crush the nonfluid reaction mixture sufficiently to reliquefy it.