EP1891191B1 - Fast-dissolving bentonite granulate - Google Patents

Abstract

A process is disclosed for preparing fast-dissolving bentonite granulates, as well as a bentonite granulate prepared by this process. To prepare the bentonite granulate, an overactivated bentonite overactivated with at least 110 % of its cation exchange capacity with alkali metal ions is preferably used as starting material, and is preferably granulated with a water glass solution having a SiO<SUB>2</SUB>:X<SUB>2</SUB>O modulus of more than 3.2, X being selected from sodium and potassium.

Description

The invention relates to a process for the production of rapidly disintegrating bentonite granules and bentonite granules which can be obtained by this process.

Detergent formulations use bentonites to create a built-in soft-grip effect. These bentonites have a high swelling capacity, especially when activated as sodium bentonite. In the application, however, difficulties arise because rapidly forms a gel layer on the surface of the bentonite particles in contact with water, which hinders the further access of water. After a rapid initial formation of the gel layer, therefore, the decay of the bentonite granules slows down in the water, because the core of the particles remains stable for a long time and is only very slowly swollen by the penetrating water and thus decays. Ultimately, this means that a significant portion of the bentonite granules is discharged with the wash liquor or that larger bentonite particles remain on the fibers of the washed fabrics. In both cases, therefore, go considerable Shares of bentonite used lost and can not contribute to the soft grip effect.

Highly swelling bentonites can potentially also be used in detergent tablets, where they can also act as a disintegrating agent. However, this is only possible if the disintegration of the bentonite particles takes place rapidly. Detergent tablets have even higher requirements for disintegration compared to normal powder detergents to ensure that no coarser particles remain on the washed laundry. So here it is particularly important that the detergent tablets disintegrate as quickly as possible in the wash liquor.

In the EP 1 102 729 B1 The problem of defective disintegration of the bentonite granules is attempted by reducing the swelling capacity of the bentonite granules without interfering with the disintegration of the bentonite into individual lamellae, so that the bentonite present in the wash liquor can be used to a considerable extent to form a soft-grip effect Available. In this case, a bentonite with a montmorillonite content of at least 85 wt .-% is first dried to a moisture content of 25 to 35 wt .-%. The dried bentonite is then comminuted and processed by adding water to an extrudable paste having a moisture content of 25 to 40 wt .-%. This paste is then extruded through a 4 to 10 mm diameter orifice and the extrudate is dried to a moisture content of 10 to 14% by weight. After drying, the extrudates are calcined at 120 to 250 ° C until they have an ignition loss of less than 4% at 190 ° C. The bentonite extrudates are then comminuted again. For the preparation of this bentonite with a low swelling capacity a bentonite is already used as starting material, which even after activation with sodium ions in contact with water only in proportion swells small extent or shows only a slight tendency to form a gel.

In the US 4,746,445 Bentonite agglomerates are described, which are prepared by spraying finely divided bentonite with sodium silicate as a binder. The agglomerates contain 1 to 5% binder. Although they have a different bulk density, the agglomerates do not separate from the other detergent ingredients after incorporation into detergent powder because they have an irregular surface. The agglomerates have an increased stability, so that they do not disintegrate in the further production steps of the detergent production. Nevertheless, they dissolve easily on contact with water. For the production of the bentonite agglomerates, a clay is used which has large proportions of montmorillonite. Particular preference is given to using a sodium bentonite. This can be obtained from natural sources, such as a Wyoming or Western bentonite. However, it is also possible to use a calcium bentonite which has been activated with alkali compounds, such as sodium carbonate. The Na ₂ O content of the agglomerates should be at least 0.5%, preferably at least 1%, particularly preferably at least 2%. For binding the bentonite agglomerates, a water glass with a modulus Na ₂ O: SiO ₂ of 1: 1.6 to 1: 3.2, preferably 1: 2 to 1: 2.8 or 1: 3.0 is used. The bentonite agglomerates are prepared by spraying an aqueous solution of the binder onto finely divided bentonite while it is being agitated. In the examples, the binder used is a water glass solution having a solids content of 7% and a Na ₂ O: SiO ₂ module of about 1: 2.4. Furthermore, it is described that when using water glass solutions with another module Na ₂ O: SiO ₂ , which is chosen within a range of 1: 2 to 1: 3, a good agglomeration can be achieved, non-dusting agglomerates are obtained.

Similar bentonite agglomerates are used in the US 4,767,546 . US 4,851,137 , such as US 4,488,972 described, wherein the examples are each selected identically. The bentonite agglomerates contain 1 to 5% sodium silicate as binder. To produce the agglomerates, a water glass solution having a solids content of from 2 to 4% by weight and a modulus of Na ₂ O: SiO _{2 of} from 1: 2 to 1: 3 is used in each case. The content of sodium oxide in the bentonite can be selected in the range of 0.5 to 10 wt .-%. However, detailed data is not executed in the examples. Here in each case commercially available sodium bentonites are used. However, exact details of the degree of activation are missing.

In the DE 33 11 568 C2 describes a particulate and softening laundry detergent for textiles, which contains, inter alia, sodium bentonite. The sodium bentonite is present as an agglomerate of smaller particles of ground sodium bentonite from which the attendant Grus has been removed after milling and before agglomeration. The bentonite agglomerates are coated with a silicate or partially coated to prevent the bentonite agglomerates from sticking to surfaces. The agglomeration of the bentonite takes place with the addition of dilute sodium silicate solution. In the example, bentonite particles are described which consist of 82.3 parts by weight of anhydrous bentonite, 16.1 parts by weight of water, 1.5 parts by weight of sodium silicate and 0.06 parts by weight of a blue dye, based on the Surface of the particles is applied, exist. The bentonite used is a sodium carbonate-treated bentonite which, after the sodium carbonate treatment, is freed from its Grus contents by centrifugation.

In the US 4,699,729 there is described a process for preparing a detergent composition containing a small amount of finely divided bentonite powder. The bentonite is agglomerated on the surface of a particulate granule. The binder used is a sodium silicate solution which has a Na ₂ O: SiO ₂ module of 1: 2.4. Generally, sodium silicate solutions having a modulus Na ₂ O: SiO _{2 of} from 1: 1.6 to 1: 3.2, preferably 1: 2 to 1: 3, more preferably 1: 2.35 or 1: 2.4, may be used.

As bentonite sodium bentonite is preferably used, wherein both a natural sodium bentonite as well as a Na ₂ CO ₃ activated calcium bentonite can be used. Typically, the bentonite has a content of Na ₂ O of 0.8 to 2.8%.

In the US 4,609,473 Agglomerates of bentonite and sodium sulfate are described, which textiles can give a soft touch effect. The agglomerates are prepared by agglomerating the finely divided bentonite and the sodium sulfate with the aid of a binder. In the simplest case, moisture can be used for this purpose. However, it is also possible to use sodium silicate as an inorganic binder, but more accurate values for amount and modulus are not specified. As bentonite, preferably natural sodium bentonites are used. It is also possible to use calcium bentonites which have been activated with sodium carbonate. In Example 1, an agglomerate of finely divided sodium bentonite and sodium sulfate is prepared using water as the binder. If the resulting agglomerates are compared in their softening properties with agglomerates obtained by agglomeration of the same bentonite with dilute sodium silicate solution, the agglomerates described first have much better properties.

In the DE 39 42 066 A1 A process for the preparation of a granular, avivating detergent additive is described. The detergent additive contains (A) 30 to 90% by weight of a layered silicate, (B) 1 to 40% by weight of fine crystalline synthetic Zeolite NaA, (C) 0 to 30% by weight of water-soluble salts from the class of sulphates, carbonates, silicates and phosphates of sodium or potassium, and (D) the remainder to 100% by weight of water. Preferably, however, the detergent additives are free of phosphates and alkali silicates. Preferred components of group (C) are sodium sulfate and sodium carbonate, both of which are used as anhydrous salts individually or in admixture. The components are dry blended, then mixed with an aqueous component containing a portion of the zeolite. Granulate formation thus takes place without the addition of water glass.

In the DE 34 19 571 there is described a fabric softening mixture useful as an additive to a particulate detergent. The softener mixture contains discrete softening particles containing at least about 75% by weight of a smectite-type clay and less than about 5% by weight of anionic, nonionic, ampholytic and zwitterionic surfactants. The plasticizer particles are prepared by spraying the smectite clay with a solution containing a quaternary ammonium compound. Since there is no exchange reaction with the clay, as long as the ammonium compound is adsorbed only on the surface of the clay, the amount of the ammonium compound can be remarkably reduced. The clays used are preferably sodium bentonites. However, it is also possible to use calcium bentonites which have been activated by treatment with sodium carbonate. The plasticizer particles may optionally contain, in addition to the smectite-type clay, substances which soften the desired fabric or do not adversely affect washing, examples of suitable materials being binder or agglomerating agents, e.g. For example sodium silicate. A suitable sodium silicate has a modulus Na ₂ P: SiO ₂ of, for example, 1: 2.4. In the EP 0 387 426 A2 a detergent additive for producing a soft handle effect is described, which contains a natural hectorite of certain composition. The agglomeration of the natural hectorite is carried out in Example 1 with water as the agglomerating agent. The wet agglomerates are dried and sieved to the desired particle size.

In the DE 42 43 389 A1 For example, a process is described for the preparation of sorbents which are used, for example, as animal litter. For this purpose, a weakly swelling bentonite, preferably a calcium bentonite, with a Montmorrilonitgehalt of about 40 to 65 wt .-% with a basic reacting alkali metal compound homogenized by intimate kneading and transferred under ion exchange in a swellable bentonite. The alkali metal compound, preferably the corresponding sodium compound, is used in an amount of from 0.1 to 1.5% by weight, preferably from 0.25 to 1.5% by weight, based on the dried crude bentonite. In the examples, as the alkali metal compound, among others, a water glass solution is used. The added amounts correspond to a Na ₂ O content of 0.5%, 1.0% and 1.5%. In this process, however, the crude calcium bentonite is not first activated with an alkali metal compound, and then the activated bentonite is granulated.

The CH 656 394 A5 describes a particulate, bleaching and softening laundry detergent. The detergent contains 5 to 25 wt .-% of an agglomerated bentonite. The starting material used is a swellable bentonite. This can also be provided by treating calcium or magnesium bentonite with alkali carbonate so that 5 to 100% or 10 to 90% or 15 to 50% of the exchangeable calcium and / or magnesium is replaced by sodium or potassium, respectively becomes. The bentonite particles can be agglomerated using water glass.

The use of water glass as a binder for the production of bentonite agglomerates, as are customary in detergent additives, has been known for some time. Typically, water glasses with a modulus of Na 2 O: SiO 2 of about 2.4 are used. The water glasses must be strongly alkaline to prevent premature polymerization of the water glass. This would lead to a solidification of the granules and thus to a poor disintegration in the wash liquor. The bentonite granules become detergent compositions further processed, for which the bentonite granules must first be packaged after production and then, for example, transported to the detergent producer. In the process, workers come into contact with the bentonite granules or the dust they produce. Because of the highly alkaline properties of the water glass, especially when used in higher amounts, the bentonite granules are irritating, ie when handling the bentonite granules appropriate safety precautions must be taken.

The invention was based on the object to provide a process for the production of bentonite granules are available, which are obtained with which bentonite granules that can be handled without major safety precautions. The granules should be able to be stored for a long time and show rapid disintegration in the wash liquor.

The object is achieved by a method having the feature of patent claim 1. Advantageous developments of the method are the subject of the dependent claims.

Surprisingly, it has been found that when using bentonite which has been overactivated with alkali metal ions, it is possible to obtain granules which show a very rapid decomposition in water. The bentonite introduced into the water or a wash liquor can therefore dissolve completely during periods of time available in a washing machine at the end of a normal washing cycle and is therefore completely available for the production of a good softening effect when applied to textiles. The losses due to the discharge of undissolved bentonite particles with the wash water can be minimized and there are no residues of larger bentonite agglomerates on the washed textiles.

The best swelling properties of bentonites in water are achieved per se with stoichiometrically activated with alkali metal ions bentonite. If the amount of alkali used to activate the bentonite is further increased, the volume of the source decreases again. Therefore, one expects the best swelling properties and thus a rapid disintegration of the granules when using a stoichiometrically activated bentonite. Surprisingly, however, it has been shown that in the granulation with waterglass, the granules containing a more than stoichiometrically activated with alkali metal ions bentonite, show a faster disintegration, than granules, which were prepared from a stoichiometrically activated bentonite.

Without wishing to be bound by this theory, the inventors believe that addition of ions beyond the amount needed for activation results in electrostatic shielding of the bentonite plate negative charges.

In the production of rapidly disintegrating bentonite granules, the procedure is such that

provided with alkali metal ion overactivated bentonite which is overactivated with at least 110% of its cation exchange capacity with alkali metal ions; and

the over-activated with alkali metal ions bentonite is granulated with a water glass solution.

By a bentonite overactivated with alkali metal ions is meant a bentonite which has been reacted with a larger amount of an alkali metal compound, for example soda or potassium oxalate, than corresponds to its cation exchange capacity. The cation exchange capacity is determined on the starting material, ie the non-activated bentonite, by first exchanging the exchangeable cations for ammonium ions and then the nitrogen content of the washed and dried bentonite is determined by elemental analysis. From the found amount of exchangeable cations then the amount of alkali metal compounds to be used can be calculated. The molar excess of the amount of alkali metal ion used is at least 110%, preferably at least 120%, particularly preferably at least 140%, based on the cation exchange capacity of the bentonite. Preferably, the excess is selected in the range of 140% to 200%, more preferably in the range of 150% to 180% of the cation exchange capacity.

The activation of the bentonite used as starting material takes place in a manner known per se. The wet bentonite, which usually has a water content of 20 to 40 wt .-%, is kneaded with a suitable alkali metal compound, for example. Soda or potassium oxalate, and then dried. The obtained with alkaline metal ions overactivated bentonite may optionally be ground again. Usually, the bentonite overactivated with alkali metal ions before granulation has a dry sieve residue on a sieve with a mesh size of 75 μm, preferably less than 15% of the weighed amount.

In addition to the described activation method, other conventional methods can be used. For example. the activation can also be carried out by first slurrying the bentonite used as starting material in water and then activating it by adding a solid or dissolved in water alkali metal compound. The concentration of the reaction components is chosen so that an activated with alkali metal ions bentonite is obtained, which has the required overactivation.

For the granulation of the over-activated bentonite with alkali metal ions, a water glass solution is used, which has a modulus SiO ₂ : Na ₂ O of more than 3.2. The waterglass solution preferably has a modulus SiO ₂ : Na ₂ O of more than 3.3, particularly preferably a modulus in the range of 3.3 to 4.0. In the production of the granules, therefore, it is advantageous to use a water glass which has a higher modulus SiO ₂ : Na ₂ O than that of the water glasses conventionally used. This means that the alkali content of the water glass, and thus also the bentonite granules, can be significantly reduced in comparison to the previously available bentonite granules. When using a water glass with a modulus SiO ₂ : Na ₂ O of more than 3.2, the irritant effect of the granules decreases significantly, which is why the granules are easier to transport and handle. For example, the granules no longer have to be classified as "irritating". In addition to the sodium water glass solution described above, a potassium water glass solution or a sodium / potassium water glass solution having the above-mentioned modulus can be used in the same manner. The modulus here is based on potassium oxide or the mixture of potassium oxide and sodium oxide, but has the abovementioned range of values.

The granulation preferably uses a water glass solution which has a solids content of at least 10% by weight, preferably at least 15% by weight, particularly preferably at least 30% by weight, particularly preferably at least 40% by weight, particularly preferably at least 50 % By weight.

Another advantage of the use of bentonite overactivated with alkali metal ions is that very small amounts of waterglass can be used, yet granules are obtained showing on the one hand high mechanical stability and on the other hand rapid disintegration. Preferably the water glass solution is added in such an amount to the over-activated sodium bentonite that the bentonite granules at a water content of 8 wt .-% of alkali metal silicate, preferably sodium silicate, of less than 4.0 wt .-%, preferably less than 3, 5 wt .-%, particularly preferably less than 3.0 wt .-%, preferably less than 2.6 wt .-%, in particular less than 2.0 wt .-%.

Preferably, the bentonite overactivated with alkali metal ions is prepared from a bentonite having a pH of more than 7, preferably a pH of more than 8, more preferably a pH of more than 9 in an aqueous slurry containing 2% by weight of bentonite , in particular has a pH in the range of 8-10.

Preferably, the over-activated with alkali metal ions bentonite has a swelling capacity in water of at least 15 ml / 2 g. Due to the high swelling capacity of the rapid disintegration of the granules is supported. In spite of the high swelling capacity of the bentonite overactivated with alkali metal ions, no delay in the disintegration of the granules due to gelation on the bentonite grains is observed.

The over-activated alkali metal ion bentonite is preferably prepared by activation of a calcium bentonite. Common calcium bentonites can be used. Such calcium bentonites usually have cation exchange capacities in the range of 50 meq / 100 g to 120 meq / 100 g. However, it is also possible to use a sodium bentonite for overactivation.

The alkali metal ions with which the bentonite is overactivated are preferably selected from the group of sodium ions and Selected potassium ions, with sodium ions being particularly preferred.

When activated with sodium ions, the bentonite used as starting material, in particular calcium bentonite, is activated preferably with a compound from the group of sodium carbonate, sodium bicarbonate, sodium phosphate, sodium oxalate and sodium citrate. Suitable sodium phosphates are, for example, trisodium monophosphate and trisodium polyphosphate. When activated with potassium ions, the potassium compound is preferably selected from the group of potassium carbonate, potassium hydrogencarbonate, potassium phosphate, potassium citrate and potassium oxalate. The activation of the bentonite, in particular calcium bentonite, is carried out in a conventional manner. For this purpose, the bentonite, which may have a moisture in the range of 20 to 40 wt .-%, is kneaded with the calculated amount of the alkali metal compound. Subsequently, the over-activated with alkali metal ions bentonite can be dried, ground and optionally sifted to adjust the desired grain size.

The granulation of the over-activated with alkali metal bentonite, particularly preferably sodium bentonite, takes place per se by conventional methods. For example. the waterglass solution can be sprayed onto the agitated bentonite which has been overactivated with alkali metal ions. For this purpose, for example, free-fall mixers can be used, in which a curtain of falling particles of the overactivated bentonite is formed, on which the water glass solution is then sprayed.

After granulation, the water content of the granules can be lowered, for example, by introducing heated air to the desired value. Usually, the water content of the finished bentonite granules is 6 to 14 wt .-%, preferably 7 to 12 wt .-%, particularly preferably 8 to 10 wt .-%. Preferably, however, the granulation of the over-activated alkali metal ion bentonite, in particular sodium bentonite, but in such a way that the overactivated bentonite is placed in a high-speed mixer and the water glass is added within a short period of time in its entirety. The granulation can be carried out both in a batch process and in a continuous process. For granulation in the batch process, a so-called Eirich mixer and for continuous granulation, for example, a continuously operating ploughshare mixer, as offered for example by the company Lödige, or a ring layer mixer, such as a Lödige CB mixer, can be used.

Another object of the invention is a bentonite granules, as it can be obtained, for example, with the method described above. Such Bentonitgranulat is characterized by the fact that it dissolves very quickly in water or disintegrates very quickly.

• ein Quellvolumen von mindestens 15 ml/2g
• einen Zerfall in Wasser nach 30 Sekunden von zumindest 80 %.

The bentonite granules according to the invention have the following properties:

• a swelling volume of at least 15 ml / 2g
• a decay in water after 30 seconds of at least 80%.

The bentonite granules preferably have a decomposition in water after 90 seconds of at least 90%, particularly preferably of at least 95% and especially preferably of at least 99%.

The granulated overactivated bentonite preferably has a pH of more than 10 in an aqueous slurry containing 2% by weight of granules.

The invention will be explained in more detail by means of examples.

Used measuring methods Cation exchange capacity

Principle: The clay is treated with a large excess of aqueous NH ₄ Cl solution, washed out and the amount of NH ₄ ⁺ remaining on the clay determined by elemental analysis.

Me ⁺ (clay) ^- + NH ₄ ⁺ - NH ₄ ⁺ (clay) ^- + Me ⁺

(Me ⁺ = H ⁺ , K ⁺ , Na ⁺ , 1/2 Ca ²⁺ , 1/2 Mg ²⁺ ....)

Equipment: sieve, 63 μm; Erlenmeyer grinding flasks, 300 ml; Analytical balance; Membrane filter chute, 400 ml; Cellulose nitrate filter, 0.15 μm (Sartorius); Drying oven; Reflux condenser; hot plate; Distillation unit, VAPODEST-5 (Gerhardt, No. 6550); Volumetric flask, 250 ml; Flame AAS.

Chemicals: 2N NH ₄ Cl solution Nessler's reagent (Merck, item No. 9028); Boric acid solution, 2%; Caustic soda, 32%; 0.1 N hydrochloric acid; NaCl solution, 0.1%; KCl solution, 0.1%.

Procedure: 5 g of clay are sieved through a 63 μm sieve and dried at 110 ° C. Then weigh exactly 2 g on the analytical balance in differential weighing into the Erlenmeyer grinding flask and add 100 ml of 2N NH ₄ Cl solution. The suspension is boiled under reflux for one hour. In the case of strongly CaCO ₃ -containing bentonites, ammonia development may occur. In these cases, as long as NH ₄ Cl solution must be added until no ammonia smell is perceived. Additional control can be done with a wet indicator paper. After a service life of about 16 h, the NH ₄ ⁺ bentonite is filtered through a membrane filter and until For extensive freedom from ions washed with demineralized water (about 800 ml). Detection of the ionic freedom of the wash water is performed on NH ₄ ⁺ ions with the sensitive Nessler's reagent. The washing time can vary between 30 minutes and 3 days, depending on the key. The leached NH ₄ ⁺ clay is removed from the filter, dried at 110 ° C for 2 h, ground, sieved (63 micron sieve) and dried again at 110 ° C for 2 h. Thereafter, the NH ₄ ⁺ content of the clay is determined by elemental analysis.

Calculation of the CEC: The CEC (cation exchange capacity) of the clay is conventionally determined by the NH ₄ ⁺ content of the NH ₄ ⁺ clay, which was determined by elemental analysis of the N content. For this purpose, the device Vario EL 3 of the company Elementar-Heraeus, Hanau, DE, was used according to the manufacturer's instructions. The data are given in mval / 100 g clay (meq / 100g).

Example: nitrogen content = 0.93%;

CEC = 66,4 meq/100 g NH₄ ⁺-BentonitMolecular weight: N = 14.0067 g / mol $$\mathrm{CEC}=\frac{0.93x1000}{14.0067}=66.4\mathrm{meq}/100\mathrm{G}$$

CEC = 66.4 meq / 100 g NH ₄ ⁺ bentonite

Determination of water content

The water content of the products at 105 ° C is determined using the method DIN / ISO-787/2.

Determination of the pH of a bentonite sample

2 g of the sample are dispersed in 98 ml of distilled water. Thereafter, the pH is determined with a calibrated glass electrode.

Determination of the dissolution rates of granules

The dissolution rate of the granules is investigated by a method as described in US Pat WO 99/32591 is described.

The granules are first screened with a sieve of mesh size 200 microns. 8 g of the sieved material are placed in one liter of water, which is heated to 30 ° C and 21 ° German hardness. With a paddle stirrer is for 90 sec. At 800 revolutions / min. touched. The remaining residue of the granules is sieved with a sieve of mesh size 0.2 mm and then dried to constant weight at 40 ° C. The residue is weighed and the solubility determined as the difference to the weighed-in amount of granules.

Determination of mechanical stability

105 to 115 g of the granules are placed on a sieve of mesh size 0.15 mm and sieved finely divided portions of the granules.

100 g of the freed of fines granules are placed on a sieve of mesh size 0.15 mm, which is mounted on a drip tray. On the granules 3 rubber balls are given, which have a diameter of 2.9 mm. The sieve is covered with a lid, with a distance of 25 mm between sieve and lid. The device composed of drip tray, sieve and lid is placed on a rotary shaker and shaken there for 15 min. Subsequently, the collected in the drip tray granules is weighed. This number corresponds to the refractive index for 15 min. Shaking time.

The sieve is shaken again for 15 minutes and again the material is weighed, which accumulates in the drip tray Has. From the sum of the sieve passes results Brechbarkeitszahl for 30 min.

Determination of the source volume

A graduated 100 ml graduated cylinder is filled with 100 ml of distilled water or an aqueous solution of 1% soda and 2% trisodium polyphosphate. 2 g of bentonite are added slowly and in portions, each about 0.1 to 0.2 g, with a spatula on the surface of the water. After a drop of added portion, the next portion is added. After the 2 g of bentonite have been added and dropped to the bottom of the graduated cylinder, the cylinder is allowed to stand for one hour at room temperature. Then the height of the swollen substance in ml / 2g is read on the graduation of the measuring cylinder.

Determination of dry residue

About 50 g of the air-dry clay material to be examined are weighed out on a sieve of the corresponding mesh size. The sieve is connected to a vacuum cleaner, which sucks all parts, which are finer than the sieve through the sieve through a suction slot circulating under the sieve bottom. The strainer is covered with a plastic lid and the vacuum cleaner is switched on. After 5 minutes, the vacuum cleaner is switched off and the amount of remaining on the screen coarser fractions determined by differential weighing.

X-ray:

The X-ray images are taken on a Philips high-resolution powder diffractometer (X'-Pert-MPD (PW3040)) equipped with a CO anode.

Determination of montmorillonite content via methylene blue adsorption

1. a) Herstellung einer Tetranatriumdiphosphat-Lösung
   5,41 g Tetranatriumdiphosphat werden auf 0,001 g genau in einen 1000 ml Messkolben eingewogen und unter Schütteln bis zur Eichmarke mit dest. Wasser aufgefüllt.
2. b) Herstellung einer 0,5 %-igen Methylenblaulösung
   In einem 2000 ml Becherglas werden 125 g Methylenblau in ca. 1500 ml dest. Wasser gelöst. Die Lösung wird abdekantiert und auf 25 1 mit dest. Wasser aufgefüllt.
   0,5 g feuchter Testbentonit mit bekannter innerer Oberfläche werden in einem Erlenmeyerkolben auf 0,001 g genau eingewogen. Es werden 50 ml Tetranatriumdiphosphatlösung zugegeben und die Mischung 5 Minuten zum Sieden erhitzt. Nach dem Abkühlen auf Raumtemperatur werden 10 ml 0,5 molare H₂SO₄ zugegeben und 80 bis 95 % des zu erwartenden Endverbrauchs an Methylenblaulösung zugegeben. Mit dem Glasstab wird ein Tropfen der Suspension aufgenommen und auf ein Filterpapier gegeben. Es bildet sich ein blau-schwarzer Fleck mit einem farblosen Hof. Es wird nun in Portionen von 1 ml weitere Methylenblaulösung zugegeben und die Tüpfelprobe wiederholt. Die Zugabe erfolgt solange, bis sich der Hof leicht hellblau färbt, also die zugegebene Methylenblaumenge nicht mehr vom Testbentonit absorbiert wird.
3. c) Prüfung von Tonmaterialien
   Die Prüfung des Tonmaterials wird in der gleichen Weise durchgeführt wie für den Testbentonit. Aus der verbrauchten Menge an Methylenblaulösung lässt sich die innere Oberfläche des Tonmaterials berechnen.
   381 mg Methylenblau/g Ton entsprechen nach diesem Verfahren einem Gehalt von 100 % Montmorillonit.

The methylene blue value is a measure of the inner surface of the clay materials.

1. a) Preparation of a tetrasodium diphosphate solution
   5.41 g tetrasodium diphosphate are weighed to 0.001 g exactly in a 1000 ml volumetric flask and shaking to the mark with dist. Water filled up.
2. b) Preparation of a 0.5% methylene blue solution
   In a 2000 ml beaker, 125 g of methylene blue in about 1500 ml dest. Water dissolved. The solution is decanted off and distilled to 25 l with dist. Water filled up.
   0.5 g of wet test bentonite with a known internal surface are weighed to the nearest 0.001 g in an Erlenmeyer flask. Add 50 ml of tetrasodium diphosphate solution and heat the mixture to boiling for 5 minutes. After cooling to room temperature, 10 ml of 0.5 molar H ₂ SO _{4 are} added and 80 to 95% of the expected final consumption of methylene blue solution is added. With the glass rod, a drop of the suspension is taken and placed on a filter paper. It forms a blue-black spot with a colorless yard. It is then added in portions of 1 ml more Methylenblaulösung and repeated the dot sample. The addition takes place until the yard turns slightly light blue, so that the added Methylenblaumenge is no longer absorbed by the test bentonite.
3. c) Testing of clay materials
   The test of the clay material is carried out in the same way as for the test bentonite. From the used amount of methylene blue solution, the inner surface of the clay material can be calculated.
   381 mg methylene blue / g clay correspond to a content of 100% montmorillonite according to this method.

Example 1:

The bentonite used was a natural Ca bentonite which has the following properties: <u> Table 1: Properties of the bentonite </ u> property value Montmorillonite content via methylene blue adsorption 75% Minor mineral content via X-ray measurements quartz <1% by weight cristobalite <5% by weight feldspar <12% by weight Cation exchange capacity via the NH ₄ method 75 meq / 100g

This bentonite was activated with different proportions of soda. As a comparison, a sample of the bentonite which had not been subjected to activation. The bentonite samples obtained are summarized in Table 2. <u> Table 2: Level of activation of the bentonites used </ u> bentonite activation Added amount of soda (% by weight Concentration of Na ⁺ in the eluate (meq / 100 g) Share Na ⁺ in the total CEC (%) 1 none 0 15 20 2 stoichiometric 3 76 100 3 hyperstoichiometrically 4.3 96 126

The bentonites listed in Table 2 were each granulated with water glass using two grades of waterglass that differed in modulus. The data of the water glass used are summarized in Table 3. <u> Table 3: Properties of water glasses used for granulation </ u> water glass Module SiO ₂ : Na ₂ O A 2.65 B 3.2

Activation of the bentonite

Each 350 g of bentonite, which had been dried to a water content of about 30%, is placed in a Werner & Pfleiderer mixer type LUK 050 T and kneaded for 1 min. Thereafter, while continuing to run the mixer, the appropriate amount of soda is added and the mixture is kneaded for a further 10 minutes. The dough is crushed by hand into small pieces and dried in a convection oven at about 75 ° C for 2 to 4 hours to a water content of 10 ± 2%. The dry goods is then ground in a rotary rotor mill Retsch type SR 3 with a 0.12 mm sieve.

Production of granules

In each case 1000 g of the characterized in Table 2 bentonite were placed in an Eirich Intensive Mixer R02E and metered via a funnel as an agglomerating agent water or water glass solution (water glass A or B). Each of water glass solutions having a solids content of 10%, 20% and 40% was used. Here, the low setting for the rotational speed of the plate and the maximum rotational speed for the swirler was selected. Unless otherwise indicated, the agglomeration parameters were each chosen below such that more than 50% of the granules were in a particle size range of 0.4 to 1.4 mm. For this purpose, the granules were sieved off appropriately after granulation and drying.

Investigation of the dispersion rate

The granules were examined for their dispersion rate in the manner described above. The data obtained are summarized in Table 4 for a granulation with a water glass with a modulus SiO ₂ : Na ₂ O of 2.65 and in Table 5 for a granulation with a water glass with a modulus SiO ₂ : Na ₂ O of 3.2 , In addition to the data on the disintegration of the granules, the swelling volumes of the granules obtained and the pH during dissolution of the granules in water are also included in Tables 4 and 5. <u> Table 4: Properties of granules containing different amounts of water glass Modulus SiO </ u>_{<u> 2 </ u>}<u>: Na </ u><sub><u> 2 </ u></u><u> O of 2.65 were granulated (comparison) </ u> bentonite Agglomeration smittel swelling volume solubility PH value Water glass content ml / 2 mg 90 s 30 s (%) 1 water 12 70 52 9.5 - 1 296 g A (10%) 12 75 61 1.2 1 313 g A (20%) 18 91 83 2.6 1 426 g A (40%) 18 99 98 10.6 7.2 2 314 g of water 20 66 30 10.7 - 2 352 g A (10%) 14 63 44 10.7 1.5 2 364 g A (20%) 14 98 91 10.6 3.1 2 430 g A (40%) 14 > 99.5 > 99.5 10.6 7.3 3 450 g of water 15 90 74 10.5 - 3 284 g A (10%) 20 100 100 10.5 1.2 3 330 g A (20%) 19 100 99.5 10.6 2.8 3 352 g A (40%) 17 > 99.5 > 99.5 10.5 6.0

Considering initially the granules which were granulated with water only, it can be seen that the swelling volume of the unactivated bentonite is 12 ml / 2 mg, increases in stoichiometrically activated bentonite to 20 ml / 2 g, and then the overactivated bentonite back to 15 ml / 2 g to fall off.

Considering the solubility, the overactivated bentonite 3 is already at a water glass content of 1.2% after 30 s achieved a complete resolution, while the stoichiometrically activated bentonite 2 a much higher water glass content of 7.3% is required within 30 s to achieve a complete dissolution of the granules.

All granules showed a high mechanical stability and the abrasion according to the previously described test method was ≤ 2%. Even at low concentrations of waterglass granules were obtained, which had sufficient mechanical stability for technical use. <u> Table 5: Properties of granules containing different amounts of water glass modulus SiO </ u>_{<u> 2 </ u>}<u>: Na </ u><sub><u> 2 </ u></u> O of 3.2 were granulated </ u> bentonite agglomeration agent swelling volume solubility PH value Water glass content ml / 2 mg 90 s 30 s (%) 1 water 12 70 52 9.5 - 1 252 g B (10%) 11 77 62 0.9 1 275 g B (20%) 13 96 84 1.9 1 341 g B (40%) 16 97 93 4.8 2 314 g of water 20 66 30 10.7 - 2 519 g B (10%) 13 99 94 10.4 1.5 2 410 g B (20%) 13 98 94 10.4 3.0 2 457 g B (40%) 18 > 99.5 > 99.5 10.1 6.6 3 258 g of water 15 90 74 10.5 - 3 305 g B (10%) 16.5 > 99.0 97.0 10.7 0.85 3 330 g B (20%) 17.0 > 99.5 > 99.5 10.6 1.8 3 352 g B (40%) 19.0 > 99.5 > 99.5 10.5 3.9

If one uses a water glass with a modulus SiO ₂ : Na ₂ O of 3.2, which thus has a lower proportion of strong bases, a water glass content of 1.8% is sufficient to give the overactivated bentonite 3 within 30 s a practical to achieve complete dissolution of the granules. The stoichiometrically activated bentonite in turn have higher levels of Water glass required to achieve a quick dissolution of the granules.

All granules showed a high mechanical stability and the abrasion according to the previously described test method was ≤ 2%. Even at low concentrations of waterglass granules were obtained, which had sufficient mechanical stability for technical use.

Claims (13)

1. Process for preparing fast-dissolving bentonite granulates, wherein:

   a bentonite overactivated with alkali metal ions, which is overactivated with at least 110 % of its cation exchange capacity with alkali metal ions, is provided; and

   the bentonite overactivated with alkali metal ions is granulated with a water glass solution, wherein the water glass solution has a SiO₂:X₂O modulus of more than 3.2, wherein X is selected from sodium and potassium.
2. Process according to claim 1, wherein the water glass solution has a solids content of at least 10 wt.%.
3. Process according to one of the previous claims, wherein the alkali metal ion is selected from the group of sodium ions and potassium ions.
4. Process according to one of the previous claims, wherein the water glass solution is added to the bentonite overactivated with alkali metal ions, in a quantity such that the bentonite granulate, containing 8 wt.% water, has a proportion of alkali metal silicate, in particular sodium silicate, of less than 3.0 wt.%.
5. Process according to one of the previous claims, wherein the bentonite overactivated with alkali metal ions is prepared from a bentonite which, in an aqueous solution containing 2 wt.% bentonite, has a pH greater than 8.
6. Process according to one of the previous claims, wherein the bentonite overactivated with alkali metal ions has a swelling capacity in water of at least 15 ml/2 g.
7. Process according to one of the previous claims, wherein the bentonite overactivated with alkali metal ions is prepared by the activation of a calcium bentonite.
8. Process according to claim 7, wherein the calcium bentonite is activated with a compound from the group of sodium carbonate, sodium citrate, sodium bicarbonate as well as sodium phosphates.
9. Process according to one of the previous claims, wherein the bentonite granulate is dried to a water content in the range of from 6 to 14 wt.%.
10. Fast-dissolving bentonite granulate, obtained with a process according to one of claims 1 to 9, which has the following properties:

    - swelling volume of at least 15 ml/2g;

    - at least 80 % dissolution in water after 30 seconds, determined according to the process given in the description for determining the dissolution rate of granulates.
11. Fast-dissolving bentonite granulate according to claim 10, wherein the bentonite granulate exhibits at least 90% dissolution in water after 90 seconds, determined according to the process given in the description for determining the dissolution rate of granulates.
12. Fast-dissolving bentonite granulate according to claim 10 or 11, wherein the bentonite granulate, in an aqueous solution containing 2 wt.% granulate, has a pH greater than 10.
13. Fast-dissolving bentonite granulate according to one of claims 10 to 12 wherein the granulate, containing 8 wt.% water, has a sodium silicate content of less than 3 wt.%.