WO2008077877A2

WO2008077877A2 - Method for processing crude bentonite

Info

Publication number: WO2008077877A2
Application number: PCT/EP2007/064312
Authority: WO
Inventors: Matthias Buri; Beat Karth; Daniel Gantenbein; A.C. Patrick Gane
Original assignee: Omya Development Ag
Priority date: 2006-12-22
Filing date: 2007-12-20
Publication date: 2008-07-03
Also published as: WO2008077877A3; DE102006061046A1; CA2688084A1; EP2144850A2

Abstract

The present invention relates to a method for processing crude bentonite, process bentonite obtainable by the method according to the present invention, use of this bentonite in papermaking and/or finishing, in particular, as a filler, coating pigment, retention agent or rheological additive, as a pitch control agent, for the control of sticky deposits in the paper machine or to mask and/or reduce the residual chemicals in pigments.

Description

Method for Processing Crude Benlonitc

The present invention relates to a method for processing crude benlonilc, processed bcntonitc obtainable by the method according to the present invention, the use of this benlonitc in paper making and/or paper finishing, in particular as a filler, a coating pigment, a retention agent or a rheological additive, as a pilch control agent, to control sticky deposits in the paper machine or to mask and/or reduce residual chemicals in pigments.

Bcntonitc is a mineral comprising a mixture of various clay minerals and containing as the most important component moπlmorilϊonitc, which explains its high water absorbency and swcliabϋity. Other concomitant minerals include quart/, mica, feldspar, pyrite or calcitc. Montmorillonite is a highly dispersed layered aluminum silicate in which negative excess charges appear due to the nonstoichiomctric substitution of cations in the crystal lattice, compensating for the exchange cations in the interstitial space. This is the explanation for the high water absorbency of bcntonitc. Water penetrates into the interstitial space of montmorillonite, hydrates its surface and the exchange cations. This causes swelling of the mineral, A different composition of the exchange cations produces a different swelling behavior. With further dissolving in water, such bentonites form a stable viscous suspension. A special group of bentonites is formed when a portion of the exchange cations are fatty amines. We then speak of organophilic bentonites, which swell in organic solvents.

Due to these properties, benlonitc is used in various ways in a wide variety of areas, e.g., in paper production or paper finishing. Due to its flocculation properties and high adsorption capacity, bentonite increases fiber and filler retention and improves the dcwatcring behavior during the sheet-forming process.

It is also used for adsorption of interfering substances during waste paper recycling and to prevent problems with resins or sticky residues in the machine cycle. O 7185/VT However, before bentonitc can be used in the above processes, it must be recovered from crude benlonite, which is comprised of a mixture of numerous clay minerals or other unwanted constituents, as mentioned above.

Therefore, the processing of the crude benlonile determines not only whether the bentonite will have the desired properties but also whether, for example, any abrasive constituents are still present which could damage the paper or the equipment, e.g., the wire of a papermaking machine or the blade of a coating unit, as well as having a negative effect on the efficiency of the product.

The processing of the crude bentonitc which may comprise, depending on the area of use, the separation of the bentonite or montmorillonite from unwanted constituents, activation with alkali salts, e.g., sodium salts, size reduction and homogcnization, etc., is a multistage process which is time-consuming, expensive and involves a high consumption of raw materials; optimization of this process has often been the subject of efforts at further development.

Various methods have been proposed for improving the properties of bentonite and/or montmorillonite in various applications.

DE 197 28 503 Cl relates to an improved method for delamination of calcium montmoriilonitcs with the object of increasing the surface area of montmorillonite agglomerates to such an extent that the efficiency values of the typical parameters that are relevant from the standpoint of application technology arc altered in the sense of increasing them, e.g., the adsorption capacity for albumins in stabilization of wine, thixotropy in application of a gelation agent and the opacity in use as a coating pigment in the paper industry. The raw material is suspended in water, optionally purified and adjusted to a preselectable solids content, whereupon the concentrated suspension is exposed to high shearing forces with preselectable dwell times and layer thicknesses. Concentrating the suspension before shearing causes the development of a thixotropic system, which is necessary for the desired dclamination, and in which the free mobility of the particles is suppressed to such an extent that particles of different sizes can no longer separate as a result of the influence of gravity. It is pointed out that the concentrated suspension should preferably not be treated with shearing equipment in which mainly compressive and impact forces occur in addition to frictional forces because the former also lead to an unwanted reduction in the size of the lamellae across the surface, e.g., in vibration mi lls or oscillating mills or in agitated ball mills. According to DE 197 28 503, it may also be advantageous to activate calcium bentonite because of technical requirements pertaining to applications, e.g., the increase in thixotropic properties. This activation is accomplished by adding sodium carbonate with a forced-feed mixer upstream from the dispersion machine. Thus, a process which still involves multiple steps for delamination of concentrated montmorillonite, optionally previously activated, is described for altering the properties of the montmorillonite.

US 4,483,934 describes the processing of crude bentonite, again in multiple steps, by treating an aqueous suspension of crude bentonite to provide a bentonite that is whiter and has a greater purity by preventing discoloration of same by iron oxide. The bentonite suspension, which is essentially free of iron oxide due to mechanical or chemical methods, is treated with a base, dewatered, washed, rcsuspended in water, subjected to shearing forces in a homogenizer, dried and optionally dry- ground with an alkali metal salt to adjust properties that are not defined in greater detail. The resulting product has a good whiteness and is therefore used as a tablet disintegrant, emulsifier, thickener or thixotropic gelation agent in cleaning compositions, pharmaceutical formulations or cosmetic compositions. The relatively complex multistage method of US 4,483,934 thus serves primarily to improve the aesthetic appearance of bentonite in addition to achieving an increased bacteriological resistance due to its heating in treatment with a base. Additional suggestions for improvement in work-up and processing of bcntonite pertain to the poor handleability of bentonitc because of its high swcllability plus the associated problems in shipping and storage.

For example, EP 0 485 124 A 1 describes a papermaking process comprising the preparation of a cellulose suspension, admixture of a bentonitc swelling clay to the suspension, where the clay is present in the form of an aqueous slurry, and then dcwatcring of the cellulose half-slock, where the bentonite swelling clay is prepared as a fluid concentrated dispersion containing at least 15 wt% bentonitc, based on dry weight, in a nonswollen form and a certain amount of dissolved monomcπc electrolytes sufficient to prevent swelling of the bentonite. The amount of electrolyte which may also be an activator such as sodium carbonate, is much greater than the amount usually used for activation, which leads to inhibition of swelling. By diluting the concentrate before addition Io the half-stock suspension or in the half-stock suspension, the electrolyte concentration is also diluted, so that the bentonitc can swell. Then the pulp contains a conventional mixture of bentonitc and electrolyte and/or optionally an activator. Thus, better handling of the swollen clay, which would otherwise be difficult to process, is achieved.

The same thing is also true in principle for the systems described in

WO 97/33041 Al in which a concentrate of alkaline earth bentonite with water and alkali metal citrate, ammonium citrate or sodium citrate as the activator and stabilizing agent is prepared and added to the pulp, optionally after prior dilution.

The concentrates according to EP 0 485 124 Al and WO 97/33041 Al arc thus conventional activated bentonites, except that they are initially present in a concentrated form to simplify handling. Ultimately they do not differ functionally from known products as soon as they enter the pulp. There, they can be used as resin dispcrsanis, as is already known for these mixtures, or with the addition of a retention aid to the pulp before admixture of the benlonitc. No improvement in the properties in this regard is described there.

US 5,266,538 and US 5,391 ,228, which have the same object, describe a method for preparing a stable aqueous bentonitc slurry, preferably a sodium bentonitc slurry having a low viscosity and a high solids content. Bcntonitc is mixed with a nondispcrsing salt, in particular sodium chloride, with the least possible shearing, and/or with a sodium or lithium salt in combination with a potassium salt to prevent swelling of the bcntonite and to improve the shipping and storage properties. The inhibition of swelling is reversible and can be canceled by diluting the concentrate before its use as intended, e.g., as a conventional retention aid in papeπnaking, without having any effect on the known function.

Moreover, approaches for simplifying the processing of bcntonite arc also described.

US 5,248,641 , for example, relates to a method for increasing the viscosity of bcntonitc in aqueous media by a simplified procedure in comparison with the state of the art. In this process, the crude bentonitc in the form of a slurry is subjected to shearing in a mixing drum and then dried. Next, by adding an activating metal salt such as sodium carbonate, a dry mixture is prepared and then pulverized. The simplification of the method thus consists of the fact that the complex aging and activation method described in the prior art is no longer necessary to improve the viscosity properties of the bcntonite but instead activation is possible by dry mixing the sheared and dried bentonite with the activator.

However, none of the aforementioned documents describes a simpli fication of the method with a simultaneous improvement in the functional properties of the bentonitc in papeπnaking and/or paper finishing with good handling properties at the same time, One of lhc greatest problems in the papermaking or paper finishing process, for example, is lhc abrasivcncss of lhc substances used, which leads Io increased wear on the wire or abrasion on lhc coaling blade in coating and thus to a reduction in production output which may even lead to machine downtime and consequently not only reduces production efficiency but also results in considerable costs.

The desired low abrasiveness cannot be achieved under practical conditions with the known dry grinding methods without prior processing steps such as prcdrying. The problem is the high water content of the crude bcntonile of up to 35 wl% naturally associated with it. This imparts a greasy slippery consistency to the products. It is therefore impossible to mill such crude bentonites to a high degree of fineness in a dry mill without prcdrying to <20 wt% residual moisture content or, better yet, to 8 to 12 wt%. This prcdrying is accomplished primarily by thermal means, the first by solar exposure and secondly by electric heat and/or heat generated by combustion. The former has the disadvantage of the long duration required while the latter yields increased CCb emissions and therefore is not consistent with the Kyoto Protocol.

These disadvantages can be greatly reduced by the method according to the present invention and the bentonites thereby obtainable.

The object of the present invention is thus first to provide a simplified method for processing crude benlonite. The object is to reduce the individual process steps required, which are very time-consuming and energy-intensive. The object of the present invention is to reduce the process steps and/or finishing steps for crude bcπlonitc to the end use to two steps or three steps at most.

In addition, another object in this method is to avoid the use of organic complexing agents such as NTA, EDTA, DTPA and salts of poiyacrylic acid to support the activation, first to reduce environmental pollution and secondly to prevent problems caused by such chemicals in subsequent applications. For example, it is known that complcxing agents are capable of dissolving heavy metals such as mercury out of sediments in natural bodies of water and can therefore lead to elevated levels in drinking water.

Another object of the present invention is to provide a bentonite having improved properties, in particular with regard to abrasiveness, without having a negative effect on the functionality of the bentonite that is otherwise necessary and/or even supporting this in use in papcrmaking and/or paper finishing as well as its use as an aid in the papcrmaking process and paper finishing process.

The features defined in the independent claims serve to achieve these objects.

Advantageous embodiments of the present invention can be taken from the subclaims and the following description.

The object of the present invention is achieved by the method for processing crude bentonite according to the present invention.

According to this method, an aqueous slurry comprising crude bentonite with a solids content of max. 19 wt% is provided, which is wet-ground to a mean particle si/c of less than 1 μm.

Crude bentonite occurs throughout the world, e.g., in the United States, Uruguay, Argentina, New Zealand, China, Russia, Morocco, Turkey and Europe, e.g., Greece and Germany. According to the present invention, all commercially available crude bcntonitcs can be used, in particular the bentonite from Morocco, Milos (Greece), Bakirgol (Turkey) and New Zealand.

The bentonite contained in crude bentonite is preferably bentonite containing alkaline earth, in which the smectite group is occupied almost exclusively with calcium and/or magnesium ions in the interstitial layers. Such benlonitcs occur in Germany and Greece, for example. However, crude bentonite containing bentonite in which the smectite group is occupied primarily by sodium ions in the interstitial spaces may also be used. Such bcntonites occur in the United States, for example. Use of crude bentonite whose interstitial layers arc occupied with sodium as well as calcium and/or magnesium ions is also possible. Such bcntonites occur in Morocco, for example. In addition, other alkali ions such as potassium ions may also be present.

Λs mentioned in the introduction, the crude bentonite usually contains various clay minerals such as in particular montmorillonite as the main component, but also quartz, mica, feldspar, pyrite, calcite and/or cristobalite. These minerals may be present in variable amounts, as well as other components, depending on the site of origin.

Benlonitcs with a montmorillonite content of >60 wt%, preferably >80 wt%, e.g., between 85 and 95 wt% are especially suitable for the method according to the present invention.

The crude bentonite is slurried in an aqueous medium, preferably using a traditional stirrer or dispersion apparatus.

During the slurrying and grinding step, the temperature of the mixture may be increased from room temperature to 40 to 100⁰C₅ preferably 50 to 80⁰C. The heating especially preferably comes about due to the internal frictional energy and needs not be supplied externally. This has the advantage, for example, that the dispcrsibility and millability are further increased and any chemical reaction with inorganic chemicals such as activating reagents is accelerated. The crude bcntonitc solids content in the aqueous slurry amounts to max. 19 wt%. In a special embodiment it may be 2 to 19 wt%, preferably 5 to 15 wt%, more preferably 7 to 12 wt%, in particular 8 to 10 wt%, e.g., 9 wt%.

The concentration of the solids is selected so that the viscosity of the slurry is optimal for efficiency in grinding, i.e., between 10 and 5000 mPa-s, preferably 100 to 1000 mPa-s, and especially in the range of 1 50 to 600 mPa.s, measured with a Brookficld viscometer (as described in the examples). The optimal concentration depends on the occurrence, i.e., the chemical and mineralogical composition of the crude bcntonitc and its swcllability, which in turn influences (he viscosity.

If the crude bcntonitc slurry has the desired consistency, it is subjected to wet grinding in which even abrasive impurities are ground until they arc so small that they no longer have an abrasive effect in the subsequent application.

The viscosity can be regulated by dilution with water and optimizing the solids content.

The bcntonitc solids content in the aqueous slurry after wet grinding preferably amounts to 2 to 19 wt%, more preferably 5 to 18 wt%, especially preferably 6 to 12 \vt%, e.g., 7 wt%.

The abrasive impurities that may occur in crude bcntonitc and be ground include for example silicates such as quartz, feldspar and chlorites.

In wet grinding, the crude bcntonitc slurry is ground to a mean particle diameter of preferably less than 1 μm, especially less than 0.8 μm, in particular less than 0.5 μm, e.g., in the range of 0.05 μm to 0.3 μm, more preferably 0.1 to 0.2 μm, e.g., 0.15 μm, as determined by sedimentation analysis (on a Micromeπtics Sedigraph 51 00). In an especially preferred embodiment, after wet grinding, >50 wt%, preferably >80 wt%, especially >90 wt% of the particles have a spherically equivalent diameter of <0.2 μm (determined by sedimentation analysis on a Micromeritics Scdigraph 5100).

When using bcntonites with a high calcium and/or magnesium content, there is still the possibility of activating them with inorganic activating agents such as alkali carbonate salts. Examples include sodium carbonate, potassium carbonate or mixtures thereof.

In an especially preferred embodiment according to the present invention, the activation is performed in wet grinding by grinding one or more of the aforementioned activating substances together with the bentonite.

To this end, these substances arc preferably added io the bentonite slurry in an amount of 0.5 to 10 wt%, more preferably in an amount of 1 to 8 wt%, especially in an amount of 3 to 6 wt%, e.g., 5 wt%, based on the weight of the montmorillonitc present in the bentonite.

The molar concentration of exchangeable alkali metal ions in the aqueous phase preferably amounts to only >0. i mol/L, more preferably 0.01 to 0.05 mol/L, especially 0.02 to 0.04 mol/L. Despite this very low concentration, the exchange is much more efficient and more rapid than is the case with the conventional dry and semidry activation methods.

The grinding may be performed in any grinding equipment with which those skilled in the art arc familiar for wet grinding of minerals. For example, the conventional horizontal or vertical ball mills, jet plate mills, colloid mills or attritor mills, such as those distributed by the Dynomill Co., for example, are especially suitable for this purpose. The grinding media used are preferably grinding beads with a diameter of 0.1 to 5 mm. more preferably 0.2 to 3 mm, especially 0.5 to 2 mm, e.g., 1 mm, but also sand, e.g., quartz sand, with a diameter of 0.1 to 2 mm, for example, may be used.

The grinding beads arc preferably made of a material selected from the group comprising zirconium, cerium-stabilized zirconium or yttrium-stabilized zirconium and zirconium silicate.

Λ suitable weight ratio of bcnlonitc to grinding beads is, for example, 1 :3 to I : I 00, preferably 1 : 10 to 1 :90, especially preferably 1 :20 to 1 :80, most preferably 1 :30 to 1 :60, e.g., 1 :50.

After wet grinding, the bentonite slurry may be concentrated. It may be concentrated to a solids content of up to 30 wt%, preferably to the range of 12 to 17 wt%. After grinding, the concentration is preferably increased by 3 to 15 wt%, especially preferably by approximately 10 wt%, e.g., from 7 wt% to 17 wt%.

Concentration is especially advantageous, e.g., in an external production to optimize storage and shipping properties. In the case of an "on-side" system at the end user's location, for example, the slurry may be used directly.

Concentration may be performed with the conventional equipment used for this purpose, e.g., by means of a centrifuge or filter press. It may also be performed as a thermal process.

The inventive process thus constitutes a greatly simplified process for work-up of crude bentonite, especially for a reduction of its abrasivencss by grinding the bentonite together with its unwanted abrasive constituents, optionally after first separating out the very coarse constituents. Due to the fact that the drying, grinding and subsequent rcsuspcnding steps which arc otherwise conventional and necessary in the state of the art can be replaced by a single step, namely that of wet grinding, the method according to the present invention is therefore also an energy-saving and cost-saving new development because activation, which is usually also a separate step, may additionally be integrated into the wet grinding step, if necessary, and the method may be performed without the use of organic complexing agents.

Moreover, the method according to the present invention supplies bcntonite that is not only equivalent to the bcntonites of the state of the art but is actually superior to them in many regards.

Another aspect of the present invention thus consists of a processed bcntonite which is obtainable by the method according to this invention.

This bcntonite has various advantages, e.g., a much lower abrasion than that of bentonitcs customarily used in papermaking and/or finishing, e.g., as a filler or coating pigment.

The abrasion of this bcntonite, measured on the AT 2000 abrasion tester from the company Einlchner, Germany, which simulates the wear on the wire in the paper machine is less than 3 mg, for example, preferably less Chan 2 mg, e.g., 1 mg, The abrasion measured on the AT 1000, likewise by the company Einlehncr, Germany, which simulates a measure of the wear on the blade in coating, is preferably less than 30 mg, more preferably less than 20 mg, especially preferably less than ! 5 mg, in particular less than 10 mg, e.g., 7 to 9 mg, but also less (ban 5 mg, e.g., 4 or 2 mg.

In view of these excellent low abrasion properties, another aspect of the present invention therefore involves the use of the bcntonites obtainable by the method of the present invention in papermaking and in the paper finishing processes such as coating, where they can be advantageously used as additives.

It may be used here in particular as a filler, coating pigment, retention aid, in 5 particular filler aid and overall retention aid or as a rheological additive, as shown by the excellent swelling volumes in the examples.

Another application of the bentonite obtainable by the method of the present invention is to use it for masking and/or reducing residual chemicals. H)

In this case, the bentonite is wet-ground together with other minerals and/or the residual chemicals or minerals containing residual chemicals by the method according to this invention.

1 5 In addition, the bentonite obtainable by the method of the present invention also exhibits special advantages when used as a pitch control agent, in particular in controlling colloidal wood resin.

Pitch is a term used to refer to organic hydrophobic material that is released as fine 0 droplets into water in processing wood to wood fibers. Pitch consists of fats and fatty acids, sterols and sterol esters, tcrpenes and waxes. Colloidal stabilization of pitch particles is accomplished by iignosuifonatcs and polysaccharides. If pitch particles arc destabilized, they can agglomerate and form deposits on the paper machine. These can lead to an inferior paper quality and tears in the paper sheets. 5

The deposits may develop in the files of the wire section and press section as well as on the rolls in the dry section, For an effective reduction in pitch deposits, it is important for the pitch particles to be already adsorbed in colloidal form and thereby passivatcd. 0 In addition to these species of pitch, there arc also problems with so-cailed while pitch. These deposits arc often caused by binders such as slyrene-acrylates or styrcnc-butadicne latex and other additives. The combination with fillers and pigments from the coated brokes may lead to what is called white pitch.

However, white pitch may already be formed in the coating station, eg,, due to shearing. The resulting agglomerates are removed by the screen. I f the pressure in the screen baskets is too high, the screen is backwashed. The washing water then often gets back into the water circulation and therefore is also returned to the paper machine water cycle. Here again, it is important for the problem-causing particles such as latexes to be adsorbed in an unagglomeratcd state as much as possible. Another problem with deposits in the paper machine is caused by latexes to be absorbed in an unagglomeratcd state as much as possible.

Another problem with deposits in the paper machine is caused by stickies. Stickies arc sticky impurities from recycled paper processing and include hot-melt adhcsives, binders and other thermoplastic materials. The chemical components arc mainly adhesivcs, styrcnc-butadicne binders, rubber, vinyl acrylatcs, polyisoprcnc, polybutadienc, polyvinyl acetate, etc..

Especially good results are achieved with the combination of bentonitc with talc due to its lubricant properties and its chemical inertia and the resulting lack of sensitivity with regard to changes in pH and conductivity. In addition, when combined with the bentonites obtainable by the method of the present invention, talc contributes toward less adhesion of pre-existing agglomerates due to its adhesion releasing property.

The talc may be simply added to the benlonilc obtainable by the method of the present invention or ground together with it, preferably in the wet grinding step of the method according to the present invention. The method according to the present invention thus not only constitutes a simplification and therefore also an improvement in comparison with processing methods for bcnlonitc known in the prior art, but also the resulting bcntonite has improved properties with respect to bcnlonilcs processed by traditional methods and it can be used economically and in a variety of ways in various steps m the papcrmaking and/or finishing process.

The figures, examples and experiments described below arc used to illustrate the present invention and should not restrict it in any way.

Description of the figures:

Figure 1 shows the x-ray diffraction diagrams of the samples (3/2) and sample (3/4).

Figure 2 shows the turbidity of the TMP filtrate treated with mineral in NTU as a function of the bentonitc sample used.

Figure 3 shows the COD analysis of the TMP filtrate treated with the mineral in mg

Cb per liter as a function of the bentonitc sample used.

Figure 4 shows the turbidity of the TMP filtrate treated with the mineral in NTU as a function of the amount of bentonitc added per liquid filtrate.

Figure 5 shows the turbidity of the TMP filtrate treated with the mineral in NTU as a function of the quantity of benionite added per dried filtrate.

Figure 6 shows the COD analysis of the TMP filtrate treated with the mineral in mg O₂ per liter as a function of the quantity of bentonitc added per liquid filtrate. Figure 7 shows the COD analysis of the TMP filtrate treated with the mineral in mg OT per liter as a function of the quantity of bentonite added per dried nitrate.

Figure 8 shows the turbidity of a polyacrylalc containing sample and a polyvinyl acetate containing sample treated with bentonite obtained by the method of the present invention.

Figure 9 shows the COD analysts of a polyacrylate containing sample and a polyvinyl acetate containing sample treated with bentonite obtained by the method of the present invention.

EXAMPLES:

1. Examples of the method according to the present invention

1 .1 Materials/comparative materials used

To perform the experiments, the known commercially available raw materials listed and characterized in Table 1 were used.

The grain size distribution was determined using a Sedigraph 5100.

The moisture was determined by using a Mettler dry balance (Mettler AG, Grci fcnsee, Switzerland).

The swelling volume was determined according to the following procedure:

A 100 niL graduated cylinder was filled accurately up to the measurement mark with 100 niL deionized water. 2.0 g of the sample is weighed onto a sample boat (accuracy of the weight: 10 mg). Using a spatula or working directly from the weighing boat, the sample is added slowly in portions onto the surface of the water, so that contact between the wall of the graduated cylinder and the meniscus edge is avoided. After a portion added has sunk, the next portion is added, being sure that no air is entrained downward. If entrained air cannot be removed by tapping on the graduated cylinder, the measurement must be repeated. After the 2 g sample has been added and dropped to the bottom of the graduated cylinder, the height of the swollen solid phase is read 2 hours after filling the cylinder.

Analysis:

The swelling volume was determined immediately after adding the 2 g sample, after 2 hours and after 24 hours. The swelling volume is calculated according to the following formula. When expressing the swelling volume, the water content of the weighed sample must be taken into account:

Weight (g) x Volume reading (mL)

Swelling volumc_{{coi l}ccic₍i):

Weight minus Water content (g)

The abrasion was determined on the AT 2000 and AT 1000 abrasion testers from the company Einfchncr, Germany.

The following results were obtained from the materials used:

Table 3 :

* Range within diffcicnt samples.

"" Mcasuied after drying in a spiay diyci to 11 wt% icsidυal moisiuic.

"^{' "} Can be delci mined only to the slated value because of a high coaise content m oidci not to damage the test msliumcnt. y^~'^'- ^[ Hie .samples wcie screened at 2 mm Then the samples weie -still loo coaise to be measiued on the Sedigiaph 5100 Thcieibic, a picliminasy SOO μm soeening was pci formed.

.2 Method according to the present invention

a) The respective crude bentonite from Table 1 (sample no.3-6) was slurried at a solids content of approx.12%. The crude products were each screened at 3 mm before use to avoid damage to the mill that was used due to an excessively high coarse fraction. b) The slurry was pumped with a hose pump (pump brand PindcR; tubing internal diameter 7 mm) at a rate of 150-240 L/h through the Dynomill ball mill (capacity 1.4 L; distribution: Willy A. Bachofen, Basel). The pressure at the mill inlet was 0.2-0.5 bar. The slurry was diluted with water with an increase in pressure to >1 bar. Grinding was performed in circulation until achieving the desired grain si/e distribution.

Optionally at the start of grinding sodium carbonate (5 wt%. based on the dry bcntonitc) or Potassium carbonate (6.5 wt%, based on the dry bcnionitc) was added as an activation agent. It may be added as a solid or as liquid prcdissolvcd in water.

Λ portion of the slurry was then dried using a GEA NlRO Λ/S spray dryer (Mobil Minor 3247 model, year of construction 2005) for samples (3/1 ) to (3/4) or a Biichi spray dryer (Typ 190 Mini Spray Dryer) for sample (3/6), respectively, to determine the swcllability in water.

The sample (3/4) listed in Table 2 which had a solids content of 7.2 \vt% after grinding was concentrated by 10 wt% to 17.3 wt% by means of a pressure filter at 6 bar. The Brookfleld viscosity of the concentrated slurry, measured at 100 rpm, spindle 7, was 17000 mPas. 2. Properties of the bciitonites produced by the method according to the present invention

2.1 Abrasiveπess, swelling volume, activation ability

Bentonitcs produced by the method described above were first tested for their properties with regard to abrasiveness, swelling volume and activation ability.

The corresponding results are given in Tables 2 and 3. The measurements of the individual parameters were performed as described above:

Table 2:

* ι After drying to 10 wt% moisture in a spray drier Table 3:

* After drying So 10 wt% moisture in a spray drier a) Abrasivcncss

The abrasivcncss of the samples according to the present invention is much lower than that of the starting materials. It is originally more than 15 mg (AT 2000) or more than 25 mg (AT 1000), whereas with the inventive samples, even those that have been activated, the abrasiveness is in a range of <1 to 5.4 mg (AT 2000) or 2 to 1 3 mg (AT 1000).

In comparison with the dry-ground comparative sample 1 (Rbeobenl SF white; activated with 5 wt% NaCO₃ at a water content of 18 wt% and then dry-ground at 10 wl% ± 2 wt% solids content using a ball mil! with an integrated classifier) and comparative sample 2, the inventive samples (3/1) through (3/4) show definitely reduced abrasion values. b) Activation ability, swelling volume

The x-ray diffraction patterns of sample (3/2) shown in Figure 1 in comparison with sample (3/4) show clearly that the activation of calcium bcntonitc to sodium bcntonite was extremely successful in only 120 minutes at the low concentration of only approx. 0.03 mol Na₂CCVL.

The comparison of the swelling volume of sample (3/4) with commercially available dry-ground sodium bcntonitc (sample (I )) also shows that the activation has resulted in better swcllability. The same thing is also true for the inventive sample (3/2) in comparison with the dry-ground sample (2).

It can be taken from the results of sample (3/5) that also the use of potassium carbonate as an activation agent provides for an increased swcllability, although it is not as strong as in the case of Na₂CO-_?, which is due to the bigger si/c of the potassium cations.

The swelling volume is important inasmuch as it is an important property for use as a rhcological additive. In view of the results obtained, the bcntonites obtainable by the method according to the present invention arc at icast equivalent if not superior to the known bentonites while having a greatly reduced abrasion and arc therefore excellent for use as a rheo logical additive.

2.2 Experiments regarding the support of the retention behavior of calcium carbonate by the bentonttes obtainable by the method according to the present invention

a) Materials

For testing the retention aid effect of the bcntonites obtainable by the method according to the present invention, a fiber substance having the following composition was prepared:

Table 4

The known samples (1) and (2) (sec Table 1 ) and the inventive bcntonitc samples (3/1 ), (3/3) and (3/4) (see Table 2) as well as mixtures thereof with the known retention aid Percol 47 from the company ClBA, based on poiyacrylamidc were used as retention aids. b) Measurement of retention:

The experiments were conducted using the DFS 03 (Dynamic Filtration System) from the company BRG, Mϋtcc, Germany, following the general operating procedure described by Mϋtcc.

The following stirring speeds and times were used according to the general operating instructions from Mϋtec:

fable 5

c) Results

The following results were obtained with regard to the retention aid properties of the inventive products for calcium carbonate in comparison with the known bcntonitcs.

Table 6

Table 7

Tables 6 and 7 show lhal the filler retention and total retention (i.e., filler and fiber retention) with the inventive Ca bcnlonites (3/1 ) and (3/3) were in the same range as those of comparative sample (2). The primary goal of preventing abrasion thus does not have a negative effect on the retention aid properties of the bcntonitcs.

For sample (3/4), the maximum filler retention level was reached with an addition of only 0.1 wt%. When using comparative sample (1 ), this level is reached only by adding 0.2 wl%.

The bcntonitcs obtainable by the method according to the present invention thus not only excellently fulfill the primary task of reducing abrasivcness but also have at least an equivalent efficacy as retention aids, or in the case of activated bentonites even have a significantly improved efficacy.

2.3 Experiments regarding the adsorption properties of the bentonite co-ground with marble contaminated with residual chemicals by the method according to the present invention

To test the adsorption properties of the bentonite produced by the method according to the present invention with regard to residual chemicals, e.g., the calcium carbonate present as marble, which is used as a filler or coating pigment in papeπnaking/finishing, the marble was ground together with the crude bcntoπitc by the method according to the present invention and then the free residual chemical content was determined.

5 a) Materials

The following samples were used for the experiments in the adsorption of residual chemicals:

I O - 5 kg each of an Austrian, Spanish and Norwegian marble having a mean particle diameter of approx. 45 μm each and a residual chemical content of 15 to 25 ppm dicoco dimethyl ammonium chloride (mainly Cj₂-Ci₄ alky!)

- 2.5 g each of sample (5) (crude Ca bentonitc from Turkey) as the starting material 15 b) Procedure

5 kg samples each of Austrian, Spanish and Norwegian marble were slurried in water using 2.5 g sample (5) at 75 wt% solids content, based on the marble and bentonite 0 content and then pumped at a rate of 150 to 240 L/h through a Dynomill ball mill (capacity 1 .4 L) using a hose pump (brand name FindcR; tubing internal diameter 7 mm). The pressure at the mill inlet was 0.2-0.5 bar. Co-grinding was performed in circulation until 80 wt% of the particles had a spherical equivalent diameter of less than 1 μm (75 wt% less than 0.2 μm) (the grain si/c distribution was determined 5 using the Scdi graph 5100). Zirconium silicate beads with a diameter of approx. 0.7- 1 .5 mm were used as the grinding media.

After 24 hours, the residual dicoco dimethyl ammonium chloride in the samples was determined in comparison with a blank sample. The blank sample was produced in0 the same way but without the addition of bentonitc. The quaternary ammonium compounds were determined by coloπmctry according to the following procedure:

ϊ%st, the following standard solutions were prepared:

Standard buffer solution fpH 5.6):

- 1 OO mL aqueous solution with 0.1 wt% bromophenol blue + 0.1 wt% bromocrcsol green in ethanol

- 420 mL 0.1 M aqueous citric acid solution

- 580 mL 0.2M disodium hydrogen phosphate solution

Standard solution of dicoco dimethyl ammonium chloride

For this solution, 200.0 mg dicoco dimethyl ammonium chloride was placed in a 1000 mL plastic flask and topped off with distilled water.

Ca²' standard solution:

7.3 g CaCI₂-2H₂O (corresponding to 5.0 g CaCO-!, see below) was dissolved in approx. 20 mL demineralized water.

To this solution was added 20.00 mL buffer solution and increasing amounts of standard solution of dicoco dimethyl ammonium chloride and the respective extinction was measured to plot a comparative measurement curve (VlS spectrophotometer: Lambda 1 (Pcrkin-Eimcr); wavelength: 425 nm; cuvette thickness (d): 1 cm). The sample solutions were prepared as follows:

5.0 g CaCOi or a weight of slurry corresponding to this amount was dissolved in 10% excess of 25% hydrochloric acid. To this solution was added 20.00 ml of the buffer solution by pipette. The pH was adjusted with 2N NaOH while stirring, where the final volume should be approx. 70 niL.

The sample was transferred to the PTFE agitator funnel with approx. 10 ml, water. Then 20.0 ml methylene chloride was added and extraction was performed. As soon as only a slight excess pressure had developed, the mixture was agitated intensely for 2 minutes.

The measurement sample was poured into a centrifuge glass and ccntri fugcd for 1 5 minutes at 4000 io 4500 rpm. Then the bottom yellow phase was drawn off using a 20 in L syringe with a long needle, being sure that no contaminates were entrained from the upper phase.

Λn auto zero adjustment was performed on the photometer at 425 nm using methylene chloride. Then the methylene chloride solution was dosed into the cuvette and the extinction was measured. Before reading the extinction, the signal must remain constant. There is often an initial weak turbidity (excessively high extinction) which disappears after a few minutes.

Calculation of the dicoco dimethyl ammonium chloride content:

From the standard solutions, the calibration curve was calculated by means of linear regression (extinction E; slope a; axis intercept b):

ing dicoco dimethyl ammonium chloride - a- E + b mg . dscoco dimethyl ammonium chioi idc 1000 ppm dicoco dimethyl ammonium chϊoiidc h (g 100%)

c) Results

The results of adsorption experiments arc given in Table 8.

Table 8:

Free Reduction dicoco dimethy I ammonium chloride content

Blank sample After grinding with sample (5)

Marble from Austria 22 ppm 10 ppm 55%

Marble from Spam 1 3 ppm 9 ppm 31 %

Marble from 12 ppm 9 ppm 25% Norway

These results show clearly that a great \ eduction in residual chemicals by 25 to 55 wt% can be achieved. Crude Ca bcntonitc co-ground with calcium carbonate by the method according to the present invention has very good adsorption properties with respect to quatcrnaled fatty amines.

2.4 Experiments regarding pitch control in thcrmomechanical pulp (TMP) Λvith the bentoπite obtained by the method according to the present invention

2.4.1 Materials

Comparative example - Sample (2)

- Finnlalc P05, MONDO minerals

- Fmntalc P60, MONDO minerals Inventive examples

- Sample (3/3)

- Sample (3/6): Sample (3/6) was obtained by co-grinding 50 wt% Finntalc P60 with 50 wt % sample (3), each based on the total weight of Finntalc P60 and sample (3), by a method like that used to prepare sample (3/3) (grinding lime: 180 min)

2,4.2 Qualitative determination

a) Procedure

2 kg thermomcchanical pulp (TMP) with a solids content of 3.7 w(% was filtered through a 2 μm filter, yield 2 L of filtrate. 200 g portions of this filtrate were each placed in eight glass bottles and each was mixed with 20 g of a 10 wt% slurry of the materials listed above.

Then the bottles were sealed and stirred for 2 hours and next the suspension was ccntπfugcd for 30 minutes (C312 IG from Jυoan, Winchester, USA; at 3500 rpm).

The upper and lower phases were separated from one another. The upper liquid phase was analyzed as follows:

- 45 ml for measurement of turbidity

- 2 niL for determination of the total organic constituent content - chemical oxygen demand (COD)

b) Analyses

Turbidity

All minerals and mineral mixtures investigated were capable of reducing the turbidity of the TMP filtrate (Figure 1 ). The fillcrcd TMP had a turbidity of 412 NTU.

The talc treatment reduced turbidity to 187 NTU.

Sample (2) (state of the art) reduced the colloidal particles to 18 NTU, i.e., to <10% of the original value of 412 NTU.

The inventive sample (3/3) also yielded a comparable reduction in the colloidal particles to <] ()% of the original value (28 NTU).

The inventive sample (3/6) had the same good adsorption effect as the samples (2) and (3/3), namely likewise a reduction to <10% of the original value of 412 NTU (38 NTU). As both, talc and bentonitc were reduced in size by co-grinding, the coarse crude Ca bcntonite (sample (3)) and the coarse talc were used as the starting materials for co-grinding.

The results show clearly that the primary goal of the invention, namely reducing the abrasion of benloπilcs, had no negative effect on the elimination of colloidal resin.

The presence of talc in grinding bcnlonite neither has any negative effect on the use in colloidal resin reduction.

Therefore, co-grinding of benlonile and talc is advantageous because talc has a positive effect on sticky hydrophobic deposits such as pitch, white pitch and stickies and thus helps eliminating such interfering substances, if present, and also leads to fewer tears in rolling up the paper and less abrasion on the paper machine because of its lubricant properties, Furthermore, the adsorption potential depends on the specific surface area of the talc and it is therefore advantageous to increase the surface area of the talc to that of the bcntonite in the same grinding operation. This combination of benlonite and talc is a highly potent adsorbent that not only has a lower abrasion than other customary adsorbents, but also has other positive properties in the production and finishing of paper.

COD:

The original untreated TMP filtrate had a COD of 4291 mg O₂ per liter. Fmntalc P05 reduced the COD to 3616 mg Oj per liter. Λll the forms of bentonitc tested as well as the bentonitc/talc mixture had a similar reduction potential, reducing the COD value to approx. 2700 ± 100 mg O2 per liter (Figure 2), with the values of the inventive samples being better than those of the untreated sample (2).

2.4.3 Quantitative determination

The following experiments were conducted to determine the minimum effective concentration of the bcntonites obtainable by the method according to the present invention.

a) Procedure

2 kg of a thcπnomcchanical pulp (TMP) with the same solids content of 3.5 wt% was filtered through a 2 μm filter, yielding 2 L of filtrate. Then 200 g portions of this filtrate each were placed into eight glass bottles and each was mixed with different amounts of a 10 wt% slurry of the sample (3/3).

Then the bottles were closed and stirred for 2 hours and next the suspension was ccnlrifugcd for 30 minutes (C312 IG from Juoan, Winchester, USΛ; at 3500 rpm). The upper and lower phases were separated from one another. The upper liquid phase was analyzed by taking 100 mL for quantification of the total amount of material in 100 mL filtrate.

To determine the minimum effective concentration of bcnlonile mineral per dry solids, the filtrate liquid was added to a weighed aluminum container ( 125 mL; diameter 96 mm, height 24 mm) to obtain dry fibers; then the filtrate was dried in an oven (95⁰C; 24 h) and the residue was weighed.

b) Analysis

Turbidity

Figures 4 and 5 show that the minimum effective concentration is approx. 0.01 wt% clear filtrate or 0.2 wl%, based on the dry fiber substance.

The optimum range for the paper industry on the basis of these results is between 0.5 and 2 wt%, based on the dry fiber substance.

COD

The trend is also support by the COD measurements, where 1 to 5 wt% based on dry fiber substance is preferred.

2.5 Experiments regarding control of white pitch and stickies with the bentonite obtained by the method according to the present invention

2,5 1 Provision of the bentonite by the method of the present invention

a) 1000 g Omya calcium bentonite from Morocco (sample (2)), was screened as an aqueous slurry with a soiids content of 9 wl% through a screen with a 3 mm mesh to prevent damage to the mill. b) The slurry was pumped through the Dynomill ball mill (capacity 1 .4 L; distribution: Willy A. Bachofcn, Basel) using a hose pump at the rate of 60 to 70 IVh (pump brand name FindcR; tubing internal diameter 7 mm), using 2700 g zirconium grinding beads with a diameter of 0.6 to 1 .0 mm. The pressure at the mill inlet was 0.1 to 0.3 bar. The slurry temperature rose m the course of the grinding process from room temperature at the beginning of grinding to 55°C at the end. The resulting product had the following features: The Scdigraph grain size distribution yielded 98% <2 μm, 97% <1 μm and 94% <0.2 μm. Abrasion values AT 2000 of 1 mg and AT 1000 of 7 mg. Corresponds to sample (3/3).

The resulting bentonite is used in various adsorption experiments with various polymers thai arc responsible for producing sticky deposits.

2L5_2_. Stickics/white pitch: styrene polyacrylatc binder

a) Procedure

Styrcnc polyacrylatc binder (Acronai V 212, BASF) was diluted to a solids content of 0.05 wl%. The pH was adjusted to 7.0-7.2 using 0.1 M hydrochloric acid or 0.1 M sodium hydroxide solution. The conductivity was adjusted to 1200 μS-cm ' by using I M sodium chloride solution. To 200 g of this latex suspension was added 4.04 g of the bentonite slurry described above, which was then stirred for 2 hours at room temperature. Next the sample was ccntrifuged for 30 minutes at 2580 g. The resulting supernatant was removed, and the turbidity and chemical oxygen demand (COD) were measured.

b) Results

The turbidity was reduced from 470 NTU to 222 NTU. This corresponds to a 53% reduction (cf. Figure 8). The COD value was reduced from 740 mg Oi per dm³ to 290 (cf. Figure 9).

The bcntonilc obtained by the method of the present invention had a good adsorption effect for polystyrene polyacrylatc binder which occurs in stickics and white pitch.

2.5.2 Stickics: polyvinyl acetate

a) Procedure

O. I 01 g Polyvinyl acetate (PVAc) (Vinnapas B17, Wackcr) was dissolved in 2 ml, acetone. The dissolved PVAc was added to a solution of 0.1 g polyvinyl alcohol and 200 g dcioni/ed water while stirring vigorously. The acetone was removed by evaporating overnight at 60⁰C. The suspension was filtered through a filter of Schlcichcr & Schuell No. 589 (Schlcichcr & Schucll AG, 8714 Fcldbach,

Switzerland). The pH was adjusted with 0.1 M I ICI and 0.1 M NaOH to 7.41. The conductivity was adjusted with IM NaCl solution to 141 1 μS-cirf '.

To 200 g of the polyvinyl acetate suspension, 4.04 g of the bcntonitc slurry described above was added and the mixture was stirred for 2 hours. Then the sample was centrifuged for 30 minutes at 2580 g. The upper liquid phase was separated and the turbidity and chemical oxygen demand (COD) were measured.

h) Results

The turbidity was reduced from 175 to 52 NTU. This corresponds (o a 70% reduction (cf. Figure 8). The COD value was reduced by 36% from 8170 mg O₂ per dm³ to 5230 mg. The bcntonite obtained by the method of the present invention had a good to very good adsorption tendency for sticky compounds such as polyvinyl acetate (cf. Figure 9).

Claims

1 . A method for processing crude bentonitc, comprising the steps

- preparing an aqueous slurry containing crude bcntonite with a solids content 5 of max. 19 wt%,

- wet grinding the resulting benlonilc slurry to a mean particle si/e of less (ban 1 μm.

2. The method according to claim I ,

10 characterized in that the crude bentonitc comprises mainly bcntonite whose smectite group is occupied primarily with calcium and/or magnesium ions.

3. The method according to claim 2, characterized in that the smectite group of the crude bcntonite is occupied with a i 5 minority of sodium and/or potassium ions.

4. The method according to any one of claims 1 through 3, characterized in that the crude bcnlonile comprises various clay minerals selected from the group comprising montmorillonitcs and concomitant minerals such as 0 quartz, mica, feldspar, pyrile, calcite and cristobalitc.

5. The method according to any one of claims 1 through 4, characterized in that the crude bentonitc has a monlmorillonitc content of >60 wl%, preferably >80 wt%, e.g., between 85 and 95 wt%. 5

6. The method according to any one of claims 1 through 5, characterized in that the crude bcntonite solids content in the aqueous slurry before wet grinding amounts to 2 to 19 wt%, preferably 5 to 15 wt%, especially preferably 7 Io 12 wt%, in particular 8 to 10 wt% e.g., 9 wt%. 0

7. The method according Io any one of claims 1 through 6, characterized in that the crude bentonite solids content in the aqueous slurry is selected so that the viscosity of the slurry is m a range of l 0 to 5000 inPa-s, preferably 100 to 1000 mPa-s and especially in the range of 150 to 600 mPa-s.

8. The method according to any one of claims 1 through 7, characterized hi that the bentonite solids content in the aqueous slurry after wet grinding is from 2 to 19 wt%, preferably 5 to 1 8 wl%, especially preferably 6 to 12 wt%₃ e.g., 7 wl%.

9. The method according to any one of claims 1 through 8, characterized in that in the production and grinding of the crude bentonite slurry, the temperature in the slurry step and/or grinding step is raised from room temperature up to a range of approximately 40 to 100⁰C, preferably 50 to 80⁰C

10. The method according to claim 9, characterized in that the heat is not supplied externally but instead comes from the grinding operation itself.

1 1 . The method according to any one of claims 1 through 10, characterized in that the wet grinding of the bentonite slurry is performed to a mean particle size of less than 0.8 μm, in particular Jess than 0.5 μm, e.g., in the range of 0.05 to 0.3 μm, more preferably 0.1 to 0.2 μm, e.g., 0.15 μm.

12. The method according to any one of claims 1 through 1 1 , characterized in that after wet grinding of the bentonite slurry, >50 wt% of the particles, preferably >80 wt%, in particular >90 wt% of the particles have a spherical equivalent diameter of <0.2 μm, based on the tola! weight of the bentonite slurry.

13. The method according Io any one of claims 1 through 12, characterized in that the wet grinding of the bcntonitc is performed in the presence of one or more inorganic activating agents such as alkali carbonate salts,

14. The method according to claim 13, characterized in that the alkali carbonate salt is selected from the group comprising sodium carbonate, potassium carbonate and mixture thereof.

15. The method according to any one of claims 13 or 14, characterized in that the alkali carbonate salts are present in an amount of 0.5 to 10 wt%, preferably 1 to 8 wt%, more preferably 3 to 6 wi%, e.g., 5 wt%, based on the weight of the montmorillonitc present in the benlonite.

16. The method according to any one of claims 13 through 1 5, characterized in that the molar concentration of exchangeable alkali metal ions in the aqueous phase amounts to less than 0.1 mol/L, preferably 0.01 to 0.05 mol/L, in particular 0.02 to 0.04 mol/L.

1 7. The method according to any one of claims 1 through 16, characterized in that the wet grinding of bcntonitc is performed in a mill, preferably a horizontal or vertical ball mill, a jet plate mill, an attritor mill or a colloid mill.

18. The method according to claim 17, characterized in that the wet grinding of bentoniie is performed using grinding beads with a diameter of 0.1 to 5 mm, preferably 0.2 to 3 mm, especially 0,5 Io 2 mm, e.g., 1 mm, or quartz sand with a diameter of 0.1 to 2 mm, for example, or mixture thereof.

] 9. The method according to any one of claims 17 or 18, characterized in that the wet grinding of benlonitc is performed using grinding beads made of a material selected from the group comprising zirconium, ccπum- siabili/cd zirconium or yttrium-stabilized zirconium and zirconium silicate.

20. The method according to any one of claims 18 or 19, characterized in that the weight ratio of bcntonite to grinding beads is 1 : Uo 1 : 100, more preferably 1 : 10 to 1 :90, especially preferably 1 :20 to 1 :80, most preferably 1 :30 to 1 :60, e.g., 1 :50.

21. The method according to any one of claims 1 through 20, characterized in that the viscosity of the benlonilc slurry is regulated by varying the solids content by adding water during wet grinding.

22. The method according to any one of claims 1 through 21 , characterized in that the bcntonite slurry is concentrated after wet grinding.

23. The method according to claim 22, characterized in that the bcntonite slurry is concentrated after wet grinding to a solids content of up to 30 wl%, preferably to a range of l 2 to 17 wt%.

24. The method according to any one of claims 1 through 23, characterized in that the wet-ground bcntonite slurry is concentrated by means of a centrifuge or a filter press or thermally,

25. The bcntonite obtainable by a method according to any one of claims 1 through 24.

26. The bcnlonilc according to claim 25, characterized in that the bcntonite has an abrasion AT 2000 of less than 3 mg, preferably less than 2 mg, in particular approximately 1 mg or less.

27. The bentonite according to any one of claims 25 or 26, characterized in that the bentonite has an abrasion AT 1000 of less than 30 mg, less than 20 mg, preferably less than 1 5 mg, more preferably less than 10 mg, e.g., from 7 to 9 mg but also less than 5 mg, e.g., 4 or 2 mg.

28. The use of the bentonite according to any one of claims 25 through 27 as an additive in papermaking and/or finishing.

29. The use of the bentonite according to claim 28 as a filler, coaling pigment, retention agent, in particular as a filler and total retention aid and/or as a rheological additive.

30. The use of the bentonite according to claim 25 for masking and/or reducing residua! chemicals.

31 . The use of the bentonite according to claim 30, characterized in that the bentonite is wet-ground together with other minerals and/or the residual chemicals or minerals containin ¹Og residual chemicals.

32. The use of the bentonite according to claim 25 as a pitch control agent.

33. The use of the bentonite according to claim 32, characterized in that the benlonite is used in a mixture with talc.

34. The use of the bentonite according to claim 33, characterized in that the bentonite is ground with talc.