Process for the continuous conversion of meta-kaolin into very finely-divided zeolitic sodium alumino-silicate

In a continuous process for the conversion of metakaolin into an aqueous alkaline suspension of low-grit, water-containing, zeolitic sodium aluminosilicate of the smallest particle size having the molar composition:

• 0.9 to 1.1 Na.sub.2 O:1 Al.sub.2 O.sub.3 :1.8 to 2.3 SiO.sub.2
• with a water content depending on the degree of drying, which contains at least 99.8% by weight of a particle size of less than 25.mu. and has a high cation exchange capability comprising:
• (a) reacting meta-kaolin with sodium hydroxide at elevated temperatures,
• (b) in a first aqueous alkaline suspension having a composition corresponding to the molar ratios of:
• 1.5 to 5 Na.sub.2 O:1 Al.sub.2 O:1.8 to 2.3 SiO.sub.2 :40 to 200 H.sub.2 O,
• and
• (c) recovering said aqueous, alkaline suspension of zeolitic sodium aluminosilicate, the improvement consisting of:
• (d) slowly heating said first suspension from a charging temperature of 50.degree. C. or below to a zeolitization temperature in the range of from 70.degree. C. to 100.degree. C., with a temperature rise averaging 20.degree. C. within a period of from two to ten minutes,
• (e) feeding the first suspension continuously into a reactor heated to said zeolitization temperature and having progressively, separately zoned mixing areas with a stage-like effect and having at least seven stages while mixing said suspension sufficiently in the respective stages to avoid sedimentation,
• (f) passing said heated suspension through the reactor at a preselected temperature in the range of from 70.degree. C. to 100.degree. C. at such a rate and time until the degree of crystallization of the zeolitic sodium aluminosilicate, determined by X-ray, has reached at least 80% of the theoretically possible crystallinity, and
• (g) continuously removing an aqueous alkaline suspension of zeolitic sodium aluminosilicate from the end opposite of the intake end of the reactor, where said frist suspension is continuously fed into said reactor and said suspension of zeolitic sodium aluminosilicate is continuously removed at a throughput in the range of from 1 to 3 cubic meters of suspension per cubic meter of reactor volume and per hour, and said first suspension is at a charging temperature of from 25.degree. to 43.degree. C. and said heating step (d) is by steam injection and occurs at least by the time said suspension leaves the first third of said reactor.