WO1992021612A1

WO1992021612A1 - Process for the production of high-swelling layer silicates

Info

Publication number: WO1992021612A1
Application number: PCT/EP1992/001091
Authority: WO
Inventors: Willi WÜST; Harald Liebs; Claus-Peter Herold; Heinz Müller; Stephan Von Tapavicza; Britta Liesenfeld; Hans Dolhaine
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1991-05-27
Filing date: 1992-05-18
Publication date: 1992-12-10
Also published as: DE4117323A1; MX9202517A

Abstract

The invention concerns a simplified process for the production of fluoride-containing, swellable magnesium layer silicates of the smectite type, in particular compounds of this type with the hectorite structure, the process including a hydrothermal reaction step between the layer-silicate-forming reactants at elevated pressures and temperatures. The new process is characterized in that a hydroxidic coprecipitate of magnesium and silicon, optionally virtually free of foreign salts, in alkaline aqueous suspension, and in the presence of dissolved MgSiF6 and/or other salts supplying fluoride ions, is subjected to a hydrothermal reaction and the solid formed is optionally separated, after cooling, from the aqueous phase and from any foreign salts dissolved in it. The moist product thus obtained does not swell significantly in water. The invention calls, as the last process step, for this moist product to be dried at moderately temperatures, thus forming in this step the crystalline, high-swelling layer silicate. The invention also concerns the use of layer silicates produced in this way in the thickening of liquid aqueous phases. When layer silicates produced by the process proposed are provided, using prior art methods, with oleophilic groups, these modified thickening agents are suitable for use in organic phases.

Description

Process for the production of swellable swelling silicates

The invention relates to a simplified synthesis process for the production of water-swellable smectite clays and describes in particular a possibility in a simple manner to master the difficulties which arise in the production of highly swellable hectorites, saponites and / or saponite-hectorite hybrids.

The synthesis of phyllosilicates, especially hectorites, has been widely described in the literature (H. Strese and U. Hoffmann, Z. Anorg. Allg. Chem. 247 (1941) 65-95; WI Crandquist and SS Pollack in "Gays and Clay Minerals "Natl. Acad. Sci., Natl. Res. Council Publ. 8 (1960) 150-169; DE-AS 1 667 502). A recent literature section deals extensively with the knowledge available today on the structure, genesis and production of hectorite, cf. Karl-Heinz Bergk et a. Chem. Techn. 41 vol., Issue 6, 245-251.

Highly swellable layered silicates of the Smectit type (in particular Hectorite, Saponite and / or Saponite-Hectorite hybrids) are widely used, for example, in the fields of cosmetics, lacquers, paints, waste water treatment and drilling fluids. The pronounced swelling capacity of the representatives of this class of compounds in water and / or - after suitable dressing - in organic liquid phases is used in almost all applications. The use of naturally occurring materials of the type concerned here often stands in the way of their limited purity, so that the synthesis of corresponding materials with predeterminable material properties is of great importance. In this context, hydrothermal synthesis at high temperatures is of paramount importance in practice. Details of the synthesis can be found in particular in the last-mentioned reference Karl-Heinz Bergk et al. , see. here in particular the flow diagrams from Figures 3 and 4 on page 247 op. , as well as the information on page 250 for oleophilic equipment.

An industrially significant application area of highly swellable synthetic layered silicates of the type concerned here is their use as a means of increasing viscosity in aqueous and / or organically based drilling fluid and borehole treatment agents in the exploration and development of deposits of, for example, petroleum and natural gas, but also in geothermal drilling , water drilling, geoscientific drilling and mining. From the relevant literature, EP-A 260 538 should be mentioned here in particular. The use of selected synthetic swellable sheet silicates of the hectorite and / or saponite type for such water-based drilling fluid systems is described here. The last-mentioned literature reference describes in its example 1 a typical process for the production of the synthetic sheet silicates of the hectorite type to be used there. An aqueous suspension is prepared from magnesium sulfate, sodium hydroxide solution, sodium silicate solution and lithium carbonate, which is then reacted for about 4 hours at 180 ° C. in a stirred autoclave. The resulting product must then be filtered off from the mother liquor and the filter cake thus obtained must be washed with deionized water before the material is dried. These decisive steps of filtering a primarily formed hectorite slurry with subsequent washing of the separated solid phase are also integral components of the flow diagrams 3 and 4 from the cited literature reference Karl-Heinz Bergk et al. (loc. cit.) Page 247 shown method. This filtering and washing is necessary to separate foreign constituents which have been introduced into the reaction mixture via the reactants and / or reaction auxiliaries used. As a rule, these are water-soluble salts such as sulfates, carbonates, nitrates or chlorides and the excess of free alkali used in the hydrothermal synthesis. This apparently simple step of separating the aqueous phase containing dissolved salts and then washing the synthetic smectite clay brings considerable difficulties for the practical process. This is immediately understandable from the following: the formed highly swellable layered silicate stubbornly holds onto at least parts of the aqueous reaction phase and requires special intensity for the subsequent cleaning by water washing. The economy of the overall process is unduly burdened by the processing steps mentioned here. Older proposals by the applicant address this difficulty and are based on the task of designing the known process for the production of synthetic and in particular highly swellable smectite clays in such a way that the crude reaction product can no longer be purified by filtration and subsequent washing the previously known difficulties. In this context, reference is made to the older German patent applications P 40 10 878.3, P 40 15 857.8 and P 40 10 879.1.

The technical teachings of these three older proposals by the applicant are based on the concept of avoiding the need to remove swellable reaction intermediates or the desired highly swellable reaction end product from an undesired electrolyte content by filtration and water washing. The absence of such electrolyte foreign salts in the final reaction product is known to be necessary in order to ensure the desired high swellability while forming the desired thixotropic behavior in aqueous phases, cf. the detailed description in the already cited reference Karl-Heinz Bergk et al. a .a. O.

The technical teaching of the further development described below and now found by the applicant essentially frees one another from the concept of the three older applications mentioned. The technical teaching according to the invention is based on the surprising finding that if the synthetic route now depicted is followed, electrolyte-forming foreign salts can be tolerated as reaction intermediates. The reac- tion stages before the hydrothermal reaction, but possibly also the reaction product from the hydrothermally carried out reaction stage, in each case allow a solid / liquid phase separation, for example by filtration or comparable conventional treatments without undue work. The reaction product obtained as wet material after the hydrothermal stage does not yet show any pronounced swellability. Although it is no longer completely X-ray amorphous, it does not yet show any characteristic structural data for Smectϊt types of the type affected here in the X-ray diagram. Surprisingly, however, the desired conversion into the highly swellable and now X-ray-specific crystalline layered silicate occurs, if the moist product obtained primarily from the hydrothermal reaction is subjected to subsequent drying at preferably moderately elevated temperatures. This formation of the highly swellable layered silicate of the desired structure and nature only in the last stage of the synthesis process thus allows the use of comparatively cheap synthetic chemicals and simple work steps known per se, including the intermediate formation of foreign salts with their subsequent removal by washing.

Accordingly, the invention relates in a first embodiment to the process for the preparation of selected fluoride-containing swellable magnesium layer silicates of the smectite type, in particular corresponding compounds with hectorite structure, which are suitable for use in aqueous or - after oleophilic finishing - in organic systems are suitable, including a hydrothermal reaction stage of the layer silicate-forming reactants at elevated pressures and elevated temperatures. The new process is characterized in that a hydroxide coprecipitate of magnesium and silicon in alkaline aqueous suspension and in the presence of dissolved MgSiF _fi and / or other salts providing fluoride ions, which is practically freed from external salts, is subjected to the hydrothermal reaction, if necessary, the solid formed Cooling from the aqueous phase and any foreign substances dissolved therein salts separated and converted to highly swellable layered silicate by drying.

The method according to the invention can be understood as a sequence of three method stages, which can be defined as follows:

Production of a hydroxide coprecipitate of magnesium and silicon in an aqueous alkaline suspension and - if necessary or desired - its purification of foreign salts which may have been formed.

Carrying out the hydrothermal reaction with the addition of compounds providing fluoride ions. If necessary, separation of the solid phase formed in this second reaction stage from the aqueous reaction medium and any electrolyte salts still present to obtain a moist material which does not yet have a pronounced swellability in the aqueous phase, and

Conversion of the moist material from the second reaction stage into the desired highly swellable layered silicate by drying under the conditions specified below. Oleophilic equipment can be connected for use in organic phases.

The process according to the invention is particularly important for the production of synthetic swellable sheet silicates as described in EP-A 260 538 and are accordingly characterized by the following general formula (I)

MgO. aMA. bAI ₂ 0 ₃ . cSi0 ₂ . nH ₂ 0 (I)

in the mean

M = Na and / or Li with a Na / Li ratio equal to or greater than 1

- 2-

A = F or partly OH and / or 1/2 0 as well as a, b, c and n numbers are according to a = 0 *, 1 to 0.6 b = 0 to 0.3, preferably 0 c = 1.2 to 1.7 n = 0 to 3.0.

The process according to the invention, which is particularly suitable for the production of aluminum-free, fluoride-containing layered silicate compounds of the hectorite type, is described below in the sequence of the three reaction stages.

Formation and, if desired, desalting of the hydroxide coprecipitate of magnesium and silicon

Water-free compounds of magnesium and silicon free of fluoride ions are dissolved in the desired molar ratios in dilute aqueous acid. The aqueous acidic phase is used in a comparatively large excess, so that solids contents below 30% by weight and preferably below 20% by weight are preferably present in this reaction stage. Suitable acids are conventional mineral acids, for example hydrochloric acid, sulfuric acid and the like. Electrolyte salts are not taken into account. The layered silicate-forming magnesium and silicon components can be used here as any soluble, in particular water-soluble, compounds, so that in this embodiment of the process according to the invention the selection of particularly inexpensive materials is possible. Particularly suitable components as water-soluble silicon compounds are sodium water glasses, which can be used as a solid or, preferably, in the form of commercially available aqueous solutions. The magnesium is used as an inexpensive salt, for example as magnesium chloride.

The amount of acid specified in this process stage is such that, after the silicon and magnesium components have been mixed in, water-thin reaction mixtures with a comparatively strongly acidic pH value are obtained, which is preferably in the range from pH 1 to 3. So it has proven to be useful, for example, in a reactor Submit aqueous acids diluted at normal pressure and, at temperatures in the range from 20 to 100 ° C., with intensive mixing, for example, first metering in the aqueous water glass solution and then dissolving the magnesium salt in the required amount. The aqueous solution of the reactants, which is still in the acidic pH range, is raised in pH using alkali hydroxide and in particular using aqueous sodium hydroxide solution. The working conditions in this neutralization reaction and subsequent alkalization can be coordinated with one another in the course of professional action in such a way that spontaneous gelling can be observed, depending on the temperature, in the pH range from about 3.5 to 6.3, but this occurs during the course the further addition of NaOH collapses again.

The addition of sodium hydroxide solution is continued until a pH in the range from 8 to 12, preferably about 8 to 9, has been established in the aqueous medium. The material held during this neutralization and the subsequent alkalization, for example in the temperature range from about 50 to 100 ° C., can subsequently be separated off by filtration - preferably also within this temperature range. The solid is isolated in this way and can also be washed free of electrolytes. Methods suitable for separating the solid are, for example, micro-filtration, working up on vacuum belt filters, the use of inverting filter centrifuges, so-called candle filters and the like. Good cleaning results are also achieved by decanting and repeatedly resuming the sediment in deionized water. Finally, filter cakes with residual electrolyte salt contents below 100 ppm and preferably below 50 ppm can be obtained. The residual moisture levels in such solid phases are in the range from 70 to 90% by weight, depending on the filtration method selected. If desired and / or necessary, additional dewatering can be carried out using known pressing devices.

The X-ray structure examination of the magnesium / silicon precipitate thus produced shows an X-ray amorphous good. The cleaning of the coprecipitate from co-formed electrolyte salts by washing them out of the precipitate is a preferred, but not a mandatory measure in the context of the synthesis according to the invention. The subsequent stage of hydrothermal synthesis can also be carried out without disadvantages in the presence of foreign salts. They are then separated off after the hydrothermal reaction, ie before the intermediate dries. Such a process control will always be possible if the solids concentration in the subsequent second process step is not chosen too high and is, for example, below 15% by weight and in particular below 10% by weight. YJϊe described below, however, it is possible in the context of an important variant of the process according to the invention to carry out this subsequent second process stage at comparatively increased solids concentrations, which then lead to a primary reaction product from the hydrothermal stage of such a nature that electrolyte salts are carried along here can only be washed out with difficulty or only incompletely. In cases of this type, it is expedient or even necessary to wash out the accompanying electrolyte salts which arise in the first working step from the coprecipitate formed in the first place. The same applies to the modification of the method according to the invention which will be described later, in which the subsequent second and third method stages are carried out at different times, but are carried out in the same device. Here too, the carryover of disruptive electrolyte salts from the reaction product of the first process stage into the subsequent reaction stages would be an unnecessary hindrance.

Hydrothermal implementation of the second stage of the process

To carry out the hydrothermal reaction, the reaction product of the first process stage is first mixed with the fluoride reactant. Fluoride compounds that are sufficiently soluble at least under the conditions of the hydrothermal reaction stage and fluoride ions are available for incorporation into the layered silicate structure put. Those fluorine-containing reactants are preferred which, with regard to their other constituents, in particular with regard to their cation content, do not lead to any undesired interactions with the reaction material. Suitable fluoride compounds are, for example, alkali fluorides, which can also be prepared in situ from hydrofluoric acid and alkali hydroxide, in particular sodium hydroxide. MgSiF is particularly suitable as a fluoride source. proven, that is, a representative of such fluorides, in which the other constituents are also incorporated into the layered silicate structure.

The procedure and the sequence of operations of this second reaction stage are determined as follows by the specific batch conditions chosen:

The invention here provides the possibility of working in the stage of the hydrothermal synthesis with comparatively limited solids contents which are, for example, in the range below 10% by weight. The resulting reaction product then allows the primary reaction product from this second stage of the process to be washed sustainably and thus the removal of undesirable proportions of electrolyte foreign salts formed and / or entered in this stage of the process.

On the other hand, it has been found that in this second process stage it is also possible to work at comparatively elevated solids concentrations, which are, for example, in the range from about 14 to 30% by weight of solids. The primary reaction product of the hydro-thermal conversion is then a viscous-plastic material which, although not yet swellable, is nevertheless not or only to a limited extent accessible to intensive washing. Accordingly, in order to carry out a process in the sense of this synthetic route, it is in any case expedient or even necessary to wash off electrolyte foreign salts from the reaction product of the first process step before the hydrothermal synthesis of the second reaction step is carried out. The following then applies in detail: -10

The filter cake obtained from the first reaction stage and, if desired, washed free of salt is redispersed in deionized water if necessary. The amount of the aqueous liquid phase is adapted to the particular synthetic route chosen in the sense of the information given above, so that either low solids contents are present in the suspension, which are preferably about 10% by weight and in particular about 5% by weight. not exceed or that there are solid contents of the coprecipitate in the range above 10% by weight and in particular in the range up to approximately 30% by weight.

The stoichiometrically required amounts of the fluoride supplier are then added to the aqueous suspension. As already stated, the preferred reaction component here is MgSiF, the stoichiometrically required amounts being derived from the fluoride content of this reaction component (s), taking into account the structural formula according to the general formula (I) given above. At the same time, to accelerate the subsequent hydrothermal reaction, aqueous alkali, in particular dilute aqueous NaOH, is added and the pH is raised in the range from about 8.0 to 12.5.

The reaction mixture is then subjected to the hydrothermal reaction. Suitable reaction temperatures are usually in the range from about 150 to 300.degree. C., it being possible to choose working temperatures in the range from 170 to 250.degree. C. and in particular in the range from about 180 to 230.degree. The reaction is advantageously carried out in a manner known per se under the autogenous pressure of the reaction mixture at the process temperature chosen in each case. The reaction time is - depending on the specified working temperature - in the range of about 0.5 to 20 hours and in particular in the range of about 1 to 10 hours.

The reaction mixture can be worked up in various ways after the hydrothermal reaction phase has ended. First of all, the problem of any electrolyte foreign salts that are present, which are components of the mixture in the highly swellable reac- -11 -

end product are undesirable. As previously indicated, such a reaction procedure requires comparatively limited solids contents in the primary reaction product of the second reaction stage. The following then applies, for example, to the processing of such a good:

After the hydrothermal reaction phase has ended, the reactor contents are cooled. A low-viscosity aqueous suspension of the mineral reaction product is obtained, which can be filtered and washed. Suitable here are, for example, the auxiliaries or working means mentioned in connection with the filtration and washing of the reaction product from the first process stage.

The residual moisture content of the filter cake separated in this second process stage is, for example, in the range up to about 90%, preferably in the range from about 10 to 50%, in each case again as% by weight based on the moist product. The reaction product thus shows considerable water retention, but no tendency towards extensive swelling, as is known from layered silicates of the smectite type. In the X-ray diffraction diagram of the still moist, that is to say not yet dried, reaction product, no bands typical for crystalline smectites dominate. However, the solids separated off in this reaction stage are not completely X-ray amorphous.

Filtration and washing of the primary reaction product from the hydrothermal synthesis can be dispensed with if this primary reaction product does not have a disruptive content of foreign electrolyte salts due to the chosen reaction procedure and / or the consistency of this reaction product is such that filtration does not occur seems reasonable.

Activation and drying of the third stage of the process

The primary reaction product or the filter cake containing residual moisture from the previous process step is dried in the last process step. It is not necessary to drive the water removal particularly far before this drying step, so that residual moisture contents in the process product of the second process stage in the range up to 98% by weight are also quite possible. -% by weight based on moisture - may be suitable.

The drying of the third process stage here leads to the desired conversion into the highly swellable layered silicate even at room temperature. However, this drying is preferably carried out at elevated temperatures, the temperature range below 180 ° C. being preferred. Drying temperatures in the range of approximately 80 to 150 ° C. are suitable, for example. The drying step can be carried out under normal pressure or under reduced pressures. In general, drying is carried out to constant weight.

In an important embodiment of the invention, the working steps of the second and third stages are connected as follows: The particularly highly concentrated reaction product from the hydrothermal reaction stage - for example the correspondingly formed viscous-plastic mass - is the hot reaction product Relieved of pressure so that substantial drying already takes place using the thermal energy present in the reaction material. The hydrothermal reaction stage and the subsequent complete drying can be carried out in the same reaction vessel, so that these two process stages lead directly to the dry product.

A usually colorless, crumbly solid product is obtained, which, however, has now proven to be the desired valuable material with high swellability. Advantageously, the primary dry matter is a fine distribution, e.g. B. Grinding, subjected.

Examination of this material by X-ray diffraction shows that a crystalline layered silicate of the smectite type is present after drying. The extensive swelling behavior of the product in water in the presence of small amounts of electrolyte and the ability to form transparent and thixotropic gels are appropriately designed. In a further embodiment, the invention finally relates to the use of the swellable sheet silicates produced by the process according to the invention, in particular the compounds of the general formula (I), as thickeners or. Gel formers for aqueous preparation of active substances of any kind. Particularly important fields of use are, for example, corresponding cosmetic preparations, lacquers and / or paints and the field of dishwashing detergents and / or cleaning agents. Other areas of application are the production of refractory non-conductive coatings or moldings, the use as binders for foundry sands or to improve the hardening behavior of thin mortar. Corresponding types of smectite can also be used in crop protection formulations in a manner known per se, an extension of the retention capacity being brought about here. In particular, here again the publication Karl-Heinz Bergk et al. aa. O. referenced there in particular page 249.

A particularly important area of application for the materials produced according to the process according to the invention is their use as agents for increasing viscosity in aqueous drilling mud and / or borehole treatment agents in the exploration and development of deposits, for example of petroleum and natural gas, in geothermal drilling. when drilling water, performing geoscientific drilling and drilling in the mining area. The use of the highly swellable sheet silicates produced according to the invention in the context of the teaching of EP-A 260 538 falls within the scope of the present invention.

If the crystalline phyllosilicate compounds prepared according to the invention are to be used in organic phases, in particular in organic liquid phases, for example as viscosity formers, gel formers or in general thickeners, then the above-mentioned finishing of the primary water-swellable layer silicate compounds with oleophilic auxiliaries is necessary commanded. Quaternary ammonium compounds, which in turn are sufficiently oleophilic in character, are particularly suitable for this purpose, for example at least have a longer-chain hydrocarbon radical as a substituent on the nitrogen.

With regard to the mechanism of the application of the quaternary ammonium compounds to the clay mineral to be finished in each case, reference can also be made to the extensive state of the art in printed form, as described in detail in H. van Olphen's literature reference "Clay Colloid Chemistry", John Wiley and Sons. 2nd edition (1977), 171 - 173 and in particular the publications on paragraphs 15 - 36 from the reference list of this subchapter.

B e i s p i e l e

In the following, the production of a highly swellable layered silicate of the hectorite type in the three stages of

Sol / gel production and desalination,

Hydrothermal implementation

Activation / drying

described. The following applies in detail:

1. Sol / gel production and desalination

Molar ratio Mg: Si = 1.00: 1.36

3 In a 0.5 m reactor equipped with a 4-stage Intermig stirring system

(d = 0.9) was equipped with 268.8 kg of fully demineralized water

(Demineralized water) and 10.2 kg (0.105 kMol) of 65% nitric acid, the dilute acid is heated to 70 ° C and circulated via a pump.

3 run pumped. The delivery rate of the pump was set to 5 m / h.

On the suction side of the pump, 38.7 kg of water glass solution with an SiO 2 content of 28% (corresponding to 0.180 kMol) and a Na 0 content were then in 30 minutes via a coaxial tube immediately in front of the hub of the impeller of 8.4% (corresponding to 0.052 kMol). A colorless, water-thin reaction mixture with a pH of 1 to 2 is obtained, which can be used for further processing without additional cleaning steps.

The measures taken certainly prevent the formation of gel bodies which are not or only insufficiently accessible to the intended subsequent reaction. In the solution obtained in this way, 37.0 kg of MgNO, * 6 H_0 (0, 133 kMol) are dissolved in the reactor and the pH is brought to 8 by adding 53, 0 kg of 20% sodium hydroxide solution (0, 265 kMol) , 8 raised. Intermediate, namely in the pH range from 5 to 6, a spontaneous gelation is observed, which breaks down in the course of the further addition of NaOH.

The solid is isolated in a manner known per se mainly by filtration in the temperature range from 50 to 90 ° C. and washed free of electrolytes. A filter cake material with a residual moisture content of 80 to 85% by weight and a NO_ content below 50 ppm can be obtained by working up the solid on an invertible filter centrifuge from Heinkel. Comparable results are also obtained on a vacuum belt filter from BHS.

The Mg / Si-containing precipitate produced is X-ray amorphous.

2. Hydrothermal implementation

The filter cake obtained in the first stage of the process was suspended in deionized water. The amount of demineralized water was chosen so that the solids content in the suspension is 4% by weight.

In 3.59 kg of this suspension, which contains 143.6 g of Mg / Si compound, 17.8 g of MgSϊF _ß - dissolved in 100 g of demineralized water - and 290 g of 2% NaOH were then added and the reaction mixture 4 h implemented at 220 ° C hydro-thermal under the autogenous pressure of the reaction mixture. After cooling to 25 ° C., a low-viscosity suspension was obtained, from which the solid was separated off as described in the first process step.

The residual moisture in the filter cake is in the range from 85 to 90% by weight. The reaction product shows no tendency to swell in water, as is known from layered silicates of the smectite type. In the X-ray diffraction diagram of the still moist, that is to say not yet dried, reaction product, no bands typical for crystalline smectites dominate; however, the connection is not completely X-ray amorphous.

3. Activation / drying

350 g of the filter cake obtained from the second stage with a residual moisture of 85 wt. % were dried to constant weight at 120 ° C. There are 51.8 g of a colorless, crumbly solid which can be pulverized in a simple manner, for example on a micro-impact mill from Jahnke S Kunkel.

The X-ray diffraction analysis of this dried material shows that a crystalline layered silicate of the smectite type is now present, as is shown by the comparison of the X-ray diffraction diagram of the dried solid mass produced according to the invention with the X-ray diffraction diagram of a commercially available, highly swellable layered silicate based on hectorite.

The product dried according to the invention shows extensive swelling behavior in water in the presence of small amounts of electrolyte and the ability to form transparent and thixotropic aqueous gels. It can, for. B. can be modified by reaction with oleophilic quaternary ammonium compounds and is then suitable for thickening organic liquid phases.

Claims

Patent claims

1 . Process for the preparation of fluoride-containing swellable magnesium layer silicates of the smectite type, in particular corresponding compounds with hectorite structure, which are suitable for use in aqueous or - after oleophilic finishing - in organic systems, including a hydro-thermal reaction stage of the layered silicate-forming reactants at elevated pressures and temperatures, characterized in that a hydroxide coprecipitate of magnesium and silicon in alkaline aqueous suspension and in the presence of dissolved MgSiF _fi and / or subjecting further fluoride ion salts to the hydrothermal reaction, if necessary separating the solid formed after cooling from the aqueous phase and any foreign salts dissolved therein and converting it to highly swellable sheet silicate by drying.

2. The method according to claim 1, characterized in that one works with an X-ray amorphous hydroxide coprecipitate of magnesium and silicon, which has been prepared as follows:

Water-soluble compounds of magnesium and silicon, in particular water glass and water-soluble magnesium salts, are dissolved in an aqueous acidic medium, preferably at moderately elevated temperatures,

by adding alkali metal hydroxide, in particular aqueous NaOH, the mixture is expediently alkalized with thorough mixing, a final pH in the range from about 8 to 12 being preferred, whereupon the solid phase formed is separated from the excess of the aqueous reaction medium and, if necessary, washed free of electrolytes.

3. Process according to Claims 1 and 2, characterized in that the hydrothermal reaction of the X-ray amorphous coprecipitate with the MgSiF _fi and / or alkali metal fluoride in an alkaline aqueous phase is carried out either at low solids contents of the redispersed material, which is preferably below about 10% by weight. %, which can also be carried out in the presence of intermediate electrolyte salts, or that a coprecipitate washed free of electrolyte salts at solids contents above 10% by weight, preferably in the range up to about 30% by weight, of the hydro-thermal reaction with formation a tough-plastic, not yet swellable reaction material is subjected.

4. The method according to claims 1 to 3, characterized in that the hydrothermal reaction at temperatures of about 150 to 300 ° C, preferably from about 170 to 250 ° C, for a period of 0, 5 to 20 hours, preferably of about 1 up to 10 hours.

5. Process according to Claims 1 to 4, characterized in that the autogenous pressure of the aqueous reaction mixture is carried out at working temperature.

6. Process according to Claims 1 to 5, characterized in that a reaction product is obtained in the hydrothermal reaction stage, but which after cooling has no substantial swelling capacity in the not yet dried state.

7. Process according to Claims 1 to 6, characterized in that the moist reaction product from the hydrothermal reaction stage is dried at temperatures below 180 ° C, preferably at or above 100 ° C, the reaction mixture in the converts crystalline layered silicate with a pronounced swelling capacity from aqueous phases and, if desired, mechanically comminutes the dry material, whereupon, if desired, an oleophilic finish - e.g. B. by reaction with quaternary ammonium compounds.

Process according to Claims 1 to 7, characterized in that synthetic swellable sheet silicates of the following general formula (I) are prepared

MgO. aMA. bAI 0,. cSiO. nH 0 (I) in the mean

MM == NNaa ⁺ and / or Li with a Na / Li ratio equal to or greater than 1

- 2-

A = F or partly OH and / or 1/2 0 as well as a, b, c and n numbers are according to a = 0, 1 to 0, 6 b = 0 to 0.3 c = 1, 2 to 1, 7 n = 0 to 3.0.

Use of the water-swellable crystalline layered silicates produced by the process of claims 1 to 8, in particular of the general formula (I), as thickeners or gel formers with thixotropic thickening action in the fields of aqueous active substance preparations, for example from the fields of cosmetics, lacquers and Paints and dishwashing detergents and / or cleaning agents, in particular, however, as agents for increasing the viscosity in aqueous drilling mud and borehole treatment agents for the exploration and development of geological deposits, for example of petroleum and / or natural gas, or according to oleophilic equipment the crystalline layered silicates in a corresponding manner as a thickening additive in systems on an organic basis, in particular oil and / or solvent based.