FI115047B - Binder mix for use in manufacturing cast concrete products, contains pozzolanically reacting mixture comprising spherical, porous agglomerates consisting of metakaolin particles - Google Patents

Abstract

Binder mix contains hydraulically hardening binder and pozzolanically reacting mixture. The mixture comprises spherical, porous agglomerates consisting of metakaolin particles. The individual agglomerates have size of 2-200 Micro, have surface area with density of lower than that of the inner part, and have pore structures in the surface part and inner part that are the same. An independent claim is also included for a process for preparing a hydraulically hardened binder mass, comprising forming a paste-like composition from hydraulically hardening binder, pozzolanically reacting admixture and water, and optionally stone aggregate and filler; processing the paste-like composition, and allowing the worked composition to harden to form the binder mass.

Description

115047

Metakaolin agglomerates and processes for the preparation of calcined kaolin agglomerates and metakaolin agglomerates

The present invention relates to a process S for the preparation of calcined metakaolin agglomerates according to the preamble of claim 1.

The invention also relates to a process for the preparation of calcined kaolin agglomerates according to the preamble of claim 12 and to the metakaolin agglomerates according to claim 13 and their use.

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It has previously been known that certain drying methods, e.g. By spray drying, particle structures or granules are formed which are rotationally symmetrical and have a more compact particle structure formed during the drying process, which in turn has left the inside of the granule porous. A binder has been used to reinforce the structure of the chain, which naturally concentrates on the surface layer of the particle structure upon evaporation of the liquid phase, leaving less of the binder in the porous core. Because this membrane is usually formed before all of the water inside the granule has evaporated, the pressure of the water vapor inside the membrane can be increased and the pressure at the weaker point of the membrane, i.e. the granule 20, burst. Such a method is described e.g. FI patent application 20000929.

When individual slurries contained in the slurry to be dried have a sheet-like shape, they · ·: tend to minimize surface energy during granule formation, whereby * · 1: the sheet-like particles are positioned substantially parallel to the surface. The result is M t · * 25 with a substantially smooth, compact, rotationally symmetrical particle structure. Drying * * f "· · 'processes generally use a level of solids that is to be produced at a level that gives the slurry a relatively low viscosity.

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1 ;;; together. Such a method is described in Π Patent Application 20001250.

»» »> · '·' '30 Some patents disclose processes for the preparation of catalysts in the grand process.

•; · 'For their preparation it is typical that the granulated curd is calcined thoroughly; '' Followed by follow-up to achieve the functional properties necessary for their end use. Such methods are described e.g. U.S. Patent Nos. 5,023,220,5,395,809; and 5,559,067. In contrast to the present invention 11,115,47, both kaolin and separately calcined kaolin are used as the raw material in the above processes, and the granules are held together by a binder with a typically high dosage amount (2-40%).

5 Metakaolin pigment has been used as a compounding agent for concrete. The product gives many good properties to concrete, but its application rate is limited by the unfavorable Theology of calcined kaolin and the consequent increased water demand and slow start of pozzolanic reactions. Calcined kaolin is used both as a filler for paper and as a coating pigment. Usage rates are limited by its poor Theology as well as its paper strength reducing effect.

10 In granules, rheology has limited the amount. For product applications, granule is not the best structure in terms of optical properties. This is due to the unfavorable size distribution of the pore structure. If calcined kaolin is used as a raw material, it will result in low sludge solids (<40%), which will still result in high evaporation costs.

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The object of the present invention is to eliminate the drawbacks of the prior art and to provide a completely new type of kaolin particle product based on metakaolin composed of agglomerates of metakaolin particles.

The invention is based on the idea of forming a metakaolin agglomerate having a characteristic pore structure of homogeneous cross-section having a surface density of less than the inner portion. In such a structure, the pore structure opens up to its surface.

. *. The agglomerate according to the invention has good mechanical strength. The product can be: •: | further forms a calcined agglomerate, which in turn is characterized by: "': The degree of calcination corresponds to that of the crystalline structure formed after the exothermic reaction.

I t »* · | The products according to the invention may be used e.g. prepared by a process in which the agglomerate is produced. ' . a high solids slurry is used (more than 50% by weight of the slurry, preferably about 60-80%, typically about 70%).

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For the preparation of the calcined product, the agglomerate is preferably calcined in a fluid state using mainly heat which is transmitted as radiation. Agglomerates are preferably classified by the low mechanical stress ion-wind method. The heat treatment may be carried out in a radiation calcination furnace.

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Agglomerates can be produced by a process that combines gas phase methods and radiation drying. The post-calcination of the crystalline form of metakaolin produced by fluid radiation is carried out e.g. by the transfer of radiant heat. The product obtained according to the invention can be used, for example, as a concrete compounding agent, characterized in that: 1. The compounding agent is metakaolin having a porous agglomerate; calcium oxide (CaO) precipitated on the surface of the metakaolin particles 3. The above-mentioned porous agglomerate, the porous structure of which is filled with water in the manufacture of concrete 4. The above-mentioned porous agglomerate added to the porous structure, preferably by crystallization of water-soluble of the same order of magnitude as • t 20 cement particles.

• # * * · ...,: The paper filler product is characterized in that: 1. The agglomerate is calcined at a temperature where its structure is similar to that of metakaolin;;: 2. The agglomerate is calcined at a temperature where its structure corresponds to an exothermic: * * *; Crystalline structure formed after 25 modifications 3. The surface pores of the calcined agglomerate are closed •: · 4. Optical properties are achieved by a controlled interparticle pore structure: '': 5. The size of the agglomerate d50 is preferably 20 µm · · · ....: 30 customized for use as a coating material so that it has one. '. or more of the following features: • 1. The agglomerate is calcined at a temperature where its structure corresponds to the crystalline structure formed after the exothermic change 4 115047 2. The surface pores of the agglomerate are blocked 3. The size d50 of the agglomerate is preferably 10 is characterized in what is set forth in the characterizing part of claim 1.

The process for the preparation of calcined kaolin agglomerates 10, in turn, is characterized by what is disclosed in the characterizing part of claim 12 and the metakaolin agglomerates according to the invention by what is described in the characterizing part of claim 13.

The use of metakaolin agglomerates is disclosed in claim 15.

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The invention provides significant advantages. Thus, in the solution of the invention, the problems of the known solutions have been eliminated. The agglomerate is formed from kaolin and then calcined. This agglomerate settles into the voids between the fibers in the paper web and does not reduce the web strength. Calcined kaolin has traditionally been produced by technically sophisticated processes. In the solution according to the invention, manufacturing is considerably simpler and more economical with better: *: optimization of energy use. Thus, the production process according to the invention enables to produce: '': technically higher quality and economically cheaper calcined kaolin-based products.

: ··: 25 I I · • ... · In the following, the invention will be explored in greater detail with reference to the accompanying drawings.

Fig. 1a to le are schematic drawings of the shear agglomerate • · (Fig. 1a), the structure of the kaolin agglomerate (Fig. Ib) and the charges of the kaolin particle (Fig. Le); :. Figures 2a and 2b show corresponding views of the calcined agglomerate and its' surface; ; * ·. Fig. 3 is a flow chart of a first device unit of the apparatus used in the invention: '\:; Figure 4 is a flow chart of a drying unit used in the invention; and 35, Figures 5a and 5b are flow diagrams of the calcining unit used in the invention.

115047 In the process of this invention, the raw material is kaolin (natural kaolin) and any alloying agents, such as calcium carbonate or silica, and the binder content is typically very low (less than 1%). The process does not form granules but agglomerates. In granules, the film formed by the binder determines the size of the granule as well as 5 larger internal pore structures. In the agglomerates, the pore structure results from the locking of the particles to each other, which makes it possible to produce a solid agglomerate such that only the surface layer is sintered, whereby bonding necks are formed between the individual particles.

10 The agglomerates have a size range of 2-100 µm, so that they are distributed according to their intended use.

In the process of the invention for the preparation of metakaolin agglomerates, only the surface of the agglomerate is calcined to metakaolin, but the inner portion remains as kaolin. The Ca-carbonate as an alloying agent is calcined into Ca-oxide while liberating. 20 gaseous carbon dioxide. Alternatively, the agglomerate is formed only of * · »....: kaolin, whereby its surface is converted by heat treatment into metakaolin | with the crystal structure remaining kaolin.

The concepts of agglomerate and granulate overlap in different industrial sectors.

: '' ': 25 In connection with the invention there is a need to clarify these concepts with respect to the scope of the invention.

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Agglomerate »·» ·! 30 1. Shape indefinite but tending to spherical • 2. The pore structure extends substantially homogeneously throughout the agglomerate '' 3. Binder (<2%) or not at all, so '' * * · film formation during drying does not affect structure 4. Kaolin agglomerate the pore structure is affected by varying charges on the surfaces 35 and the edges of the plate-like particles 6 115047 5. The agglomerate has good strength due to the bonding forces caused by the charges 6. The structure is porous due to its low degree of organization 7. Agglomerate is formed high, typically about 70%, whereby the structure of the droplet resulting from spray drying is locked 5 before the internal assembly becomes substantially exposed to 8. The size of the agglomerate is strongly dependent on the droplet size. Only the capillary forces reduce its final size.

Granule: 10 1. The shape is most often a rotationally symmetric sphere 2. The pore structure can be described as having a granular center that is sparse or gas filled, the pore size decreases towards the surface, and the pores on the surface are substantially smaller than its inner portions. positioning such that their plate-like surface is parallel to the surface of the granule 4. When a binder is used in the granule, typically over 2%, but generally over 4%, it forms a film on the surface of the granule. This film becomes dense and slows down the drying process.

20 5. In the shell layer immediately below the surface, the orientation of the particles continues “*, essentially parallel to the surface. 6. The structural strength is concentrated on the surface and the underlying shell layer. . 7. A granular structure is formed during spray drying when the solids content of the slurry to be dried is typically less than 50%.

•, 25 8. Granule size is influenced by, among other things, the size of the droplet, its solids content, and the amount and composition of binder it contains

Calcined kaolin '. ': 30 Calcined kaolin is a generic term for kaolins whose crystal structure is modified by heat treatment. The final crystal form '·,' ·· is influenced by temperature and treatment duration. When the treatment temperature is below 1000 ° C (typically 500 ° C to 700 ° C), * * i of the kaolin crystal structure is already substantially removed from the water bound to the crystal structure (about 14%). A predominantly amorphous crystal structure is formed. The time required is 35, usually less than 5 seconds.

7 115047

As the heat treatment is continued, the temperature is raised and the treatment time is prolonged, allowing the amorphous structure to recrystallize, causing a slight exothermic effect. The resulting crystal structure differs from the original kaolin crystal structure and the intermediate metakaolin. The product is commonly called calcined kaolin.

Often contaminated with kaolin, the Ti compounds also change their crystalline form and turn white, raising the brightness of the product by about two ISO brightness units, which is relevant for commercial product applications. This change occurs at a temperature of about 1000-1200 ° C, especially about 1100-1200 ° C, with a residence time of about one hour. The product has a rough surface when flaky crystal scales open.

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Metakaolin Agglomerate 1. Agglomerate structure (see above).

2. The kaolin agglomerate is heat-treated at 600-1000 ° C for a treatment time of 15 0.1 to 5 s. This causes the crystalline water to leave the agglomerate and obtain pozzolanic properties. 3. In some products it is preferable to use a metakaolin agglomerate with only a small percentage have lost their crystalline water).

4. When acidic Ca carbonate, Ca (HCO3) 2, is used as a sintering agent, 20 oxide, CaO, which combines with water to form Ca hydroxide, Ca (OH) 2, and reacts with the metakaolin surface, is obtained on the anhydrous kaolin surfaces. other suitable substances such as silica sol, Na silicate: (eg water glass) or nepheline cyanide.

t * '' 25 kaolin agglomerate with exothermic crystal structure '· The kaolin agglomerate is first calcined to metakaolin »* · :: with a radiation temperature of n 1200 deg C and typically using a sintering agent to close the surface to the pore granulate time consuming (about 1 h)::: crystal structure change occurs at about 1200 ° C »I * <>> 8 115047

Kaolin is a natural product and quality variations must be taken into account. The final processing conditions are selected empirically based on experiments within the ranges mentioned in the invention.

5 In summary, the metakaolin agglomerates of the invention are characterized by: 1. A pore structure homogeneous in cross-section 2. The surface density is lower than the inner part 3. The pore structure opens up to the surface 10 4. The agglomerate has good mechanical strength

By comparison, the agglomerate of the agglomerates is generally characterized by: 1. The degree of calcination of the agglomerate corresponds to the 15 crystalline structures formed after the exothermic reaction 2. The pore structure of the surface is closed 3. The agglomerate has a constant cross-sectional density.

. . ·. 20 The use of kaolin as a metakaolin agglomerate and as an agglomerate with an exothermic region crystal structure provides a wider range of product applications for the use of kaolin •: · * ·.

• · II (* * · •: · ·: Note that the aggregate structure is generally characterized by 25 1. The pore structure can be constructed to the desired size of the particle size of the kaolin used as a raw material. '' 2. The pore structure can be constructed on an open surface up to or close the surface. '3. Strength without binders Generated by capillary forces *> ·. [t J 30 4. With a small amount of binder the agglomerate strength can be substantially increased * it · # 5. By rebelling to the sintering temperature, the strength increases substantially, especially when used; small amount of sintering aid 6. The same substance can be used as binder and sintering aid 9 115047 7. A preferred example of a substance that can act as both binder and sintering agent is acidic Ca carbonate Ca (HCO3) 2, which decomposes at high temperature to form Ca oxide CaO.

8. The open pore structure in the concrete application allows the reaction of water and 5 Ca-hydroxide dissolved therein with the metakaolin 9. The closed surface pore structure provides an increase in opacity in the paper application 10. The pore size can be adjusted to an optically more favorable size

Figures 3 to 5 of the accompanying drawings illustrate the method of the invention in more detail and the apparatus 10 that may be used to carry out the method.

Figure 3 shows a device for raising the dry solids content of a kaolin slurry to an area favorable for the formation of kaolin agglomerates.

Reference numeral 1 denotes an aqueous slurry from the kaolin (natural kaolin) plant, generally having a dry matter content of less than 10% by weight. The slurry is centrifuged to raise the solids content to about 40 wt%. Reference numeral 2 denotes a water separator based on the use of an electric field. The field voltage is typically about 1 to 20 V, preferably about 4 to 10 V, preferably about 6 V. The device raises the solids content from 40 wt% to 70 wt%. Reference numeral 3 denotes a rotor diffuser used for the screening of kaolin cakes having a high dry matter content. The resulting mass is pumped with a high pressure pump at a pressure of 200 to 500 bar to the drying apparatus shown in Figure 4.

'* .: A pre-feed pump (not having its own reference number) and a high pressure pump can handle slurry with a stiffness of 1000 cP.

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The device assembly shown in Figure 3 is continuous. It replaces, for example, the commonly used ..: 'pressure filtration method.

The tower dryer of Figure 4 produces kaolin agglomerate particles.

* · '· 30 The apparatus comprises a cylindrical tank space fed from 5 solids from the lifting device; _ j kaolin slurry. Under pressure, the slurry is fed to the nozzles 6, from which the slurry is sprayed into the tank space, where the droplets dry and form agglomerates. The high pressure slurry is sprayed with a droplet size of 2 to 50 micrometers and a solids content of 70%, whereupon the solids lock into agglomerates within a few milliseconds. 115047 drying air guides 7 are used for drying, through which air is introduced into the tank space, in particular fluid air 11 at about 400 ° C. The aqueous agglomerates fall onto wire 9 and the fluid gas is separated 12 and introduced into a jet shower. The temperature of the fluid gas is above 100 ° C and is passed to the jet condenser. The agglomerates are dried with radiant heat 10 and 5 by means of a blower 13 and transferred to the ion wind classifiers 14 and further through the transfer pipeline 15 to the intermediate storage silos.

The calcination of the kaolin agglomerates is carried out in the calcining apparatus of Figures 5a and 5b, respectively. The equipment first comprises intermediate storage (silos) 16-18, where 10 are stored separately for example agglomerates of three different particle sizes.

Typically, the first silo 16 holds agglomerates having an average size of less than 10 micrometers. Container 17 has agglomerates of 10 to 20 micrometers and intermediate storage 18 agglomerates of more than 20 micrometers.

From the intermediate stores 16, 17 and 18, respectively, the agglomerates are transferred by blower 19 to the calcining furnace dispenser 20, where the agglomerates are also mixed. The agglomerates are calcined to metakaolin in a radiation furnace 21. The calcined agglomerates are cooled by a blower 22 to 400 ° C and blown into an ion-wind classifier 23, from where they continue to either storage 27 or the exothermic calcination furnace 24. The calcined agglomerates are cooled. . ·. 20 blowers 25 to a temperature of about 400 ° C, and after the ion-wind classifier 26 is moved to storage, and the gas is blown at 400 ° C to a tumble dryer 28. Figure 5b *; The embodiment differs from the solution of Fig. 5a in that everything from the first calcination: * *, · the resulting metakaolin is calcined a second time 24, leaving the process ionic classifier 23;

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The method described above has considerable advantages: • '· »» teaspoon' '1. 1. Composite structure • ·. *. - agglomeration-calcination gives energy savings * = * ,, t, j 30 - Classification into different fractions increases product quality with accurate calcination temperature - product applications expand »·; ; 2. Quantities of binders and sintering aids can be minimized * * »* '3. Degree of calcination is differentiated between agglomerate surface and inner part 4. Adding gas phase heating to agglomerate formation with 35 radiant heat generates significant energy savings 11 115047 5. Use of high solids content 6. Calcination to the metakaolin step using the fluid-irradiation method gives accuracy for calcining (time 0.1-0.5 s) 5 7. Calcining to the exothermic crystal structure requires time (about 1 h) to make the metakaolin agglomerates eg in the grate furnace. The metakaolin step has removed the 'edges' from the agglomerates so that they do not sinter into each other. 8. The Ion Wind rating is more gentle on the agglomerates and contributes to saving the binder.

10 9. Ion Wind rating also saves energy compared to cyclones and other mechanical class teams

Products manufactured as described above are suitable for a variety of applications. These are discussed in more detail below:

Concrete compound

The tumble drier generates a large size distribution of agglomerates, of which sizes greater than 20 microns are very well suited as a concrete compound. These agglomerates, which are of the same order of magnitude as the cement particles, are ranked among the Portland cement particles. as a pozzolan and water donor in the cement autogenous reaction: · · J and as a precise stockpile of various cement additives.

Larger particles greater than 50 microns in size serve as pozzolanic: 25 filler and as a plasticizer for concrete.

• »». * Paper filler. | . According to the invention, the paper fill is intended to adhere a portion of the calcined kaolin to the fibers, but the majority of the agglomerates, which may be either * · • t metakaolin or calcined kaolin that has undergone an exothermic conversion step, settles; between the fibers to provide a flat web having favorable optical and mechanical paper technical properties.

35 5 115047 12

Paper coating material

Metakaolin or calcined kaolin that has undergone an exothermic conversion step can also be used for paper coating.

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Claims (15)

A process for preparing calcined metakaolin agglomerates, according to which the process of kaolin is treated at elevated temperature to produce a product with a desired crystal structure, characterized by - the kaolin first forms kaolin agglomerates, the average particle size of which ranges to about 2 - 100 microns, and - kaolin then to metakaolin, whereby agglomerates are obtained which exhibit an open pore structure, the surface portion density of which is lower than the inner portion and whose pore structure in the surface and inner portions is similar. 2. A process according to claim 1, characterized in that the calcination of the kaolin agglomerates into the metacoline phase is carried out in fluid state, at least mainly by means of radiant heat. Method according to Claim 1 or 2, characterized in that the heat treatment is carried out in a jet calcining furnace. 4. A process according to any one of claims 1-3, characterized in that the kaolin agglomerates are formed from a kaolin suspension whose dry matter content rises to over 50% by weight, preferably to about 60-75% by weight. 5. Process according to claim 4, characterized by the kaolin agglomerates: formed by spray drying the kaolin suspension. 25 * · «* j 6. Process according to claim 5, characterized in that the agglomerates are spray dried in a dryer. 7. A process according to claim 6, characterized in that the agglomerates are spray-dried in the dryer by thermal energy supplied with radiation. I »·> t * t t »'; The method according to any of claims 1-7, characterized by: The agglomerates are classified and different Large agglomerates are separately brought to the heat treatment. 115047 9. A method according to claim 8, characterized in that an ion wind classifier is used for the classification of the agglomerates. 10. A process according to any of claims 1-9, characterized in that in order to obtain an exothermic crystal structure, the agglomerates are calcined by radiant heat. 11. A process according to any one of claims 1-10, characterized in that the dry matter content of the kaolin suspension is installed using an electric field-based method for increasing the dry matter content. 10 Process for the preparation of calcined kaolin agglomerates, according to which the kaolin process is treated at elevated temperature to produce a product of the desired crystal structure, characterized in that - first of the kaolin is formed kaolin agglomerate, whose average particle size is up to about 2 - 100 microns - kaolin agglomerates calcined to metakaolin, and the calcination is continued until agglomerates with an exothermic crystal structure are obtained. 13. Metakaolin agglomerates, characterized in that their size ranges from 2 to 100 microns and exhibit an open pore structure, wherein the surface area density of the metakaolin agglomerates is lower than the inner portion and their pore structure in the surface and inner portions is the same. > «* · <'·: 25 14. Agglomerate according to claim 13, characterized in that the amount of: crystalline water on the outer surface of the metakaolin agglomerates accumulates to 0 to 8% by weight and to the inner, * crystal portion of water to 2 to 14% by weight. » The use of agglomerates according to any of claims 13 or 14 as a concrete mixing component. • »s * a