WO2014177767A1

WO2014177767A1 - Method of producing composite particles

Info

Publication number: WO2014177767A1
Application number: PCT/FI2014/050311
Authority: WO
Inventors: Pentti Virtanen
Original assignee: Kautar Oy
Current assignee: Kautar Oy
Priority date: 2013-04-29
Filing date: 2014-04-29
Publication date: 2014-11-06
Anticipated expiration: 2015-10-29
Also published as: FI126846B

Abstract

The present invention relates to a method of manufacturing composite particles that work as a binding agent, the composite particles containing a limestone portion, which is based on limestone particles or limestone silicate rock particles and which is mixed with a kaolin portion that comprises kaolin particles. In the method, the limestone portion or the kaolin portion is subjected to calcination before they are mixed with each other, or the mixture of these portions is subjected to calcination, whereby, the activated layer on the surfaces of the particles of, at least, one of the said portions that was formed in the calcination makes the particles of the portions to attach to each other into composite particles. The invention also relates to the composite particles thus produced, the concrete that is formed by these, and equipment that is suitable for the implementation of the said method.

Description

METHOD OF PRODUCING COMPOSITE PARTICLES

Background of the invention Field of the invention

The present invention relates to a method of manufacturing composite particles, which comprise a kaolin portion and a limestone portion and which are combined by activating the surfaces of the particles of the separate portions, for example, by means of calcination.

Description of the known technology

Concrete is the most common construction material in the world. It is made of stone aggre- gate and cement, the cement part, generally, consists of Portland cement. With the construction industry growing, larger and larger amounts of cement are also needed. Therefore, efforts have been made to replace, at least, part of it with other ingredients, or to add fillers thereto. The US patent specification 4588443, among others, describes a method of manufacturing concrete by using particles of different sizes, with which a surface-active dispersing agent has been mixed.

The raw materials of cement include calcium carbonate, iron oxide, aluminium, and silica, which react, forming different minerals, among others, such as silicates and aluminates. Cement also comprises small amounts of other materials, such as sodium and calcium oxides. When cement and the other ingredients of concrete come into contact with water, these materials are hydrated, making the concrete harden. The hydration of the different components, however, takes place at different stages and velocities and is, in large part, difficult to control.

In practice, the activation, i.e., hydration, of the Portland cement never occurs in full. Thus, water also remains in the concrete after the initial hardening. Efforts are often made to reduce the amount of water, to improve the strength and durability of the concrete. Conven- tionally, this is carried out, e.g., by means of plasticizers. Increasing the amount of plasti- cizers, however, causes problems in the quality of the concrete.

The challenges in replacing Portland cement include, among others, the formation of ce- ment that is economic, and, yet, works as an effective binder, with an advantageous strength.

One alternative binder that is often used is metakaolin, which is conventionally added to concrete, as such, in the form of a powder. Due to its pozzolanic property, metakaolin re- acts with the excess calcium hydroxide in the concrete, compacting the concrete by filling the empty spaces. It also protects the concrete structure against environmental effects, such as the corrosion of steel. Hence, the use of metakaolin can provide stronger and more durable concrete, improve its workability, and reduce the drying shrinkage, even without the use of separate additives. Metakaolin sinters have also been used.

In concrete products, it has been possible to replace about 1 /3 of Portland cement with metakaolin. The size of this portion is dependent on the amount of the above-mentioned excess calcium hydroxide produced by Portland cement, and on the time of its generation. As another alternative to the conventional Portland cement, different composite particles have been formed. One of these is described in the WO patent specification 2010/13051 1 A l , wherein the described composite consists of calcium carbonate and metakaolin. This is prepared by mixing together kaolin or another clay and fine calcium carbonate (CaCO. . and by heat-treating this composite at 750 °C for about 20 minutes.

The WO patent specification 2010/037903, again, describes a structured binder that comprises metakaolin sinters, on the surfaces of which, calcium carbonate and plasticizing organic polymers and Portland cement have been precipitated. This product is prepared, so that kaolin is calcined before it is brought into contact with the other ingredients. The me- takaolin sinter (in a spherical form) is fragile and large in size. When calcined, these spheres break, whereby, separate kaolin plates are formed. When metakaolin, as such, is used as part of the cement, high temperatures and alkalis stronger than Ca(OH)2, (e.g., NaOH) are needed for the activation. This has been the major obstacle to spreading the use of cements of this type. Geopolymers have also been formed to replace part of Portland cement. With these, the activation is neither dependent on the fonnation of hydrates, nor on high temperatures, nor do their manufacture cause as large carbon dioxide emissions as that of Portland cement. Geopolymer cements are formed by cross-linking silicates into 3D silico aluminate structures (J. Davidovits, Geopolymer Cement, a review, January 2013). A conventional geo- polymer, based on silicates, however, does not, yet, contain the components required to be suitable for use, as such, as the only binder of the concreting.

Short description of the invention

The object of the present invention is to provide a binding agent which is suitable for concrete or mortar and which can be mixed with the other dry ingredients of concrete, without the uncontrollable, premature implementation of a pozzolanic reaction, before adding separate concrete water.

A particular object of the invention is to provide a dry product, which is suitable for the manufacture of concrete or mortar and which works as a binding agent, containing the dry components required for the pozzolanic reaction, as such. Thus, the invention is based on the utilization of a new method in the manufacture of binder powder. The powder in question comprises composite particles or their precursors (the by-products described hereafter), the composite particles containing a kaolin portion and a limestone portion, the particles of which are attached to each other. By means of the calcination, a pozzolanically reacting layer is brought on the particle surfaces of the said portions, whereby, the invention makes it possible to produce a hydraulic binder portion by the pozzolanic reaction, either together with separate Portland cement or as such, and no separate hydraulic binder is, thus, needed. By means of these composite products, the addition of separate fillers into the end products that utilize hydraulic binders, such as concrete or mortar, can also be avoided.

The pozzolanic reaction is provided by means of metakaolin and the calcium oxide or cal- cium hydroxide that is mixed therewith, in particular.

The present invention, thus, relates to a method of manufacturing powder that comprises composite particles, which is formed from a limestone portion and a kaolin portion, by means of calcination. By means of the calcination, the different portions of the composite particles can be activated, at least on their surfaces, whereby, a 4D binder powder can be formed.

Hence, at least one portion of the composite particles is calcined to render it into a form that reacts pozzolanically. In the calcination, limestone, at least, partly changes into calci- um oxide (in a proportion defined by the calcination conditions with respect to the limestone), whereas kaolin, at least, partly changes into metakaolin.

The particles of the limestone portion can also be made to react into calcium hydroxide on their surfaces, already before the composite particles are utilized, e.g., in concrete or mor- tar. By means of the invention, agglomerates can also be formed from the limestone portion of this embodiment, whereby, the hydroxide on the surface of the particles first works as a binding agent in the formation of the agglomerate and, thereafter, possibly, as a sintering agent in the formation of sinter granules. To be more precise, the method of manufacturing the composite particles, according to the present invention, is characterized in that which is presented in the characterizing part of claim 1.

The thus manufactured composite particle is characterized in that which is presented in the characterizing part of claim 8; the intermediate product of the manufacturing method is characterized in that which is presented in claim 16; the concrete product is characterized in that which is presented in claim 17; and the equipment for implementing the method is characterized in that which is presented in claim 19. The invention provides considerable advantages. Among others, a means is provided of bringing, to the concrete or mortar, all of the components required by the pozzolanic reaction in one dry product. As the composite particles can be introduced into the manufacturing process of concrete in the form of dry powder, all of the dry ingredients of concrete can be mixed together effectively before adding water. In this way, the premature hydration can be decreased considerably. As the powder, according to the invention, can be produced separately, as a centralized industrial manufacturing process separate manufacturing of concrete is not needed.

The method, according to the invention, is neither dependent on the calcium hydroxide produced by the OPC, nor the time of its production, but the requirements made of con- crete are determined by what is called the number of composite particles produced.

The reaction of calcium oxide into calcium hydroxide (slaking) produces heat, by means of which, the pozzolanic reaction can be accelerated and, thus, influence the early strength of concrete. This early strength can also be increased by the invention by decreasing the need for water. As the concreting water can also contain calcium hydrogen carbonate

(Ca(HCO; 2), the invention can also decrease the so-called bleeding phenomenon.

Furthermore, the invention can improve the properties of cement and concrete without the high quality requirements of kaolin. In particular, the quality of concrete (such as chloride resistance) can be influenced be simply adjusting the mixing stage (among others, the turbulence and homogenization) during the manufacturing process.

The composite particle, according to the invention, can be formed continuously, in particular, by employing economic and compact equipment. The small size of the equipment makes it possible to also locate it in connection with the batching plant, whereby, the energy economy can be maximized.

In the following, the invention is described more precisely, by means of the appended drawings and a detailed description. Short description of the drawings Fig. 1 shows different possible structures of kaolin.

Fig. 2 shows microscopic images (figs. 2A and 2B) of kaolin, wherein kaolin packs have started to break into particles. Fig. 3 is a diagram of the calcination furnace, according to an embodiment of the invention, illustrating a possible connection to a pre-treatment section and a processing space as well.

Fig. 4 is a diagram of the pre-treatment section of the equipment, according to an embodiment of the invention, when connected to the processing space, the combination of the parts of the equipment being suitable for making calcium oxide react into hydroxide.

Fig. 5 is a more detailed diagram of the stator section of the pre-treatment section of the equipment (and its connection to the rotor section), according to an embodiment of the invention; wherein fig. 5A shows the positions of the rotor blade and the rotatable stator blade with respect to each other; fig. 5B shows the possible blade positions of the rotatable stator blade; and fig. 5C shows the differences between the rotatable and stationary stator blades.

Fig. 6 is a diagram of the pre-treatment section and the processing space of the equipment, according to a particularly advantageous embodiment of the invention, presenting an illustrated part of the auxiliary parts of the equipment that are described hereinafter, and their positions in the complex equipment.

Fig. 7 is a diagram, illustrating a way of connecting the parts of the equipment, according to the invention, to produce the composite products 1 - 3, according to the invention. Detailed description of the embodiments of the invention

The present invention relates to composite particles that work as a binding agent, the limestone portion of the particles being combined with the kaolin portion, whereby, at least, one portion of the composite is in a calcined form.

In practice, the composite particles are produced by combining limestone particles (or particles containing limestone and silicate rock), which, at least, on their surfaces have been calcined into calcium oxide (CaO), with kaolin particles, wherein kaolin has alternatively been calcined into metakaolin.

The limestone portion comprises particles that contain limestone, whereby, this portion preferably either comprises limestone particles or limestone silicate rock particles. In the following, these are simply called "limestone particles". It has been observed that, when particles containing both limestone and silicate rock are used in the calcination, the silicate rock also receives calcium oxide on its surface.

Thus, in connection with the invention, limestone refers to quarried limestone material that comprises calcium oxide.

Optionally, the composite particles or their calcined limestone portion (CaO) can be subjected to a slaking reaction, whereby, the calcium oxide in the limestone portion further changes into calcium hydroxide (Ca(OH)2). In connection with the invention, kaolin refers to a material that comprises different clay minerals, such as kaolinite, illite, vermiculite, smectite, and chlorite.

These clay materials have tetrahedral and octahedral portions, and the connections between these portions (in particular, the access of water and the ions contained therein into the structure) determine, whether the material is non-expandable or expandable.

Kaolinite, illite, and chlorite are non-expandable, whereas vermiculite is reasonably expandable and smectite strongly expandable (fig. 1 ). These expansion properties (and the particle sizes provided by this) can be utilized in the activation of the kaolin portion of the products of the invention. In the present invention, the kaolin to be exploited preferably comprises >50% of kaolinite. Optionally, sialates, such as polysialates, can also be formed from kaolinite, the most common of these comprising the different sialate structures of sodium, potassium, and calcium ions, such as poly(sialate), poly(disialate), poly(sialate-siloxo), and poly(sialate- disiloxo). These are found, particularly, with sodalite, sanidine, leucite, kalsilite, and anor- thite mineral structures.

The fonning of kaolinite can be carried out, for example, by polycondensing kaolinite at an elevated temperature and pressure, using an aqueous alkaline solution (such as a solution of NaOH). On the basis of the above, four different main products can be formed by means of the present invention:

Product 1 is a composite particle, wherein the calcination of the mixture has caused the limestone particle to convert into calcium oxide on its surface, and the same calcination has made the kaolin react into metakaolin. Instead of pure binding agent, this composite product 1 , as such, also comprises a small amount of aggregate that is required for concrete.

Product 2 is a conesponding composite particle, wherein the calcination of the mixture has caused the limestone to react entirely into calcium oxide, and the same calcination has caused the kaolin to react into metakaolin. The difference to product 1 is, thus, that all of the limestone is now calcium oxide. This can be implemented by selecting (in a manner known per se) small enough limestone particles or by enhancing the calcination.

One advantage of these composite products 1 and 2 is, among others, that they function, as such, as a pozzolanic binder.

Product 3 is a composite particle, wherein the metakaolin that is in an activated form is completely mixed with the limestone particles that were calcined into calcium oxide; however, the calcium oxide in the limestone particles was made to further react into calcium hydroxide before mixing. One advantage of this product, among others, isthat it is easy to transport to the desired use.

Product 4 is a composite particle, wherein the metakaolin that is in the activated form is mixed with the limestone particles, the surfaces of which were calcined into calcium oxide; however, the calcium oxide in the limestone particles was made to react into calcium hydroxide before mixing.

In addition to these main products, the present invention can be used to produce a compo- site product 5, which is spherical agglomerate that is formed from calcium hydroxide and metakaolin. One advantage of this product is, among others, that it is easy to mix, e.g., with the other dry ingredients of concrete.

In addition to the composite products, fractions can also be separated from the product and intermediate product flows, which are generated by the method of the invention, to be used, e.g., in the formation of the above-mentioned composite products in different uses. The most important of these are the following:

Intermediate product 1 comprises limestone particles that are calcined into calcium oxide on, at least, their surfaces.

Intermediate product 2 comprises limestone particles that are calcined into calcium oxide on, at least, their surfaces and, further slaked into calcium hydroxide. All of the product particles, preferably, have a size smaller than 2 mm. Naturally, the composite particles, wherein the limestone portion is still partly (at its core) in the original limestone form, have a larger size than those, the limestone portion of which is calcined completely (and, optionally, slaked). The said composite particles that have the original limestone (or the mixture of limestone and silicate rock) in their core, preferably, contain 50 - 95 % by volume, more preferably 75 - 95 % by volume, most preferably, about 90 % by volume of this core portion, while the rest comprises the surface portion that comprises calcium oxide (or calcium hydroxide) and the kaolin portion. In this surface portion, the ratio between calcium oxide and me- takaolin is, preferably, 1 : 1 - 3: 1 , most preferably about 2: 1 .

The said different composite products have in common that all of them contain a limestone portion and a kaolin portion. All of the said products and by-products, again, have in common that they can be recovered when dry, i.e., solid, in the form of powder, whereby, they can easily be transported and mixed with the other dry ingredients (and, of course, with water) and that they contain, at least, one calcined component. When the components contained in the composite products are brought together, said composite particles are formed, wherein kaolin particles and calcium oxide particles are attached to each other through hydroxide. The hydrates contained in the said composite products provide extremely good corrosion protection. Thus, the limestone portion of the composites is preferably based on limestone, the particles of which are obtained, e.g., by crushing the limestone that is obtained by quarrying, preferably, into particles of 50 μηι - 5 mm, whereby, the particles that are to be calcined completely are, preferably, crushed into a size category of 50 μιη - 2 mm. As presented above, the limestone particles can be converted into the form of burned lime, i.e., calcium oxide (CaO), at least, on their outer surfaces (possibly completely). This stage can be performed, e.g., by calcination.

If not otherwise presented, the calcined limestone particles, hereinafter, can be limestone particles, which either comprise calcium oxide or calcium hydroxide, at least, on their surfaces.

The layer of CaO that was made by calcination constitutes 5 - 100% by volume of the entire limestone-based particle. In relation to the diameter of the particles, which can be, e.g., 50 - 1000 μηι, the thickness of this layer is, most preferably, about 15 μιη.

Optionally, this calcium oxide is further made to react into slaked lime, i.e., calcium hydroxide (Ca(OH)₂). After the optional slaking reaction, the composite particle, according to the invention, thus, has a core particle, which, at least, on its surfaces is in the form of calcium hydroxide (although there might be some oxide left) and, at least, one other material is attached to its surface (the kaolin portion of the composite particle, in particular).

According to an embodiment of the invention, the quarried limestone is fractionated and the fractions that contain particles of different sizes are separately conducted to further treatments or, alternatively, large limestone particles (> 20 mm) are crushed into smaller sizes.

According to preferred embodiment, the method according to the invention includes stages, wherein the limestone that was crushed into particles of a suitable size is fractionated (e.g., by a sieve), the desired fraction is mixed with kaolin particles in a fluid state, whereby, the kaolin particles attach to the surface of the limestone, and this mixture is conducted to the calcination. By ad justing the size of the limestone particles and the conditions of the calcination, either one of the above-mentioned products 1 or 2 is obtained. Optionally, particles which are based on limestone and which, at least, on their surfaces are in the form of calcium hydroxide, can also be conducted to the same calcination (together with kaolin particles), because the calcination changes this hydroxide into oxide again, whereby the end products are the same.

According to another preferred embodiment, the method of the invention includes stages, wherein the limestone that was crushed into particles is ground into a finer particle size before the fractioning (e.g., by a sieve); the desired fraction is burnt into calcium oxide (CaO) and mixed with particles of kaolin or metakaolin in the fluid state, whereby, the kaolin particles attach to the surface of calcium oxide; and this mixture is conducted to slaking of CaO to obtain Ca(OH)2. The mixture that comprises kaolin (in the basic form) can then be conducted to calcination, whereby product 2 is obtained. The mixture that comprises metakaolin is already in the form of product 3 after slaking. In connection with the grinding, CaO surfaces in which there is no air are generated. Here the slaking reaction takes place quickly.

The crushing, optional grinding, and fractioning are preferably adjusted, so that particles within the size distribution of 0.01 - 2 mm are obtained. More preferably, two or more of the following fractions are collected, most preferably, all of the said fractions (according to the size of the largest particles that permeate the sieve):

2 mm, 1 mm, 0.5 mm, and 0.25 mm During the calcination, the surface of the limestone-based particle, at least, partly changes into calcium oxide, preferably by 1 - 10%, most preferably by 1 - 5%. In particular, the calcination is adjusted to achieve coverage of 10 - 100%, more preferably 10 - 85%, most preferably 40 - 80%. Generally, it can be assumed that in the fraction containing the smallest particles, a larger coverage of CaO is formed on the surface of the limestone than in the fraction containing the largest particles.

An optional slaking of CaO is implemented, so that water is added to the mixture formed from the limestone portion and the kaolin portion, preferably in the form of water vapour and/or mist in an amount that is stoichiometric with respect to the amount of water needed to slake the CaO. Kaolin and CaO are preferably mixed together in a ratio that corresponds to the combination of substances they produce which, in theory, is 1/1 .35 (kaolin/calcium oxide) and in practice about 1 /1. Thus, the present invention most preferably uses the ratio of 1/1 - 1 /1.4. Water vapour is preferably added during the mixing, so that an essentially homogeneous fluid is provided. Thereafter, the thus formed reaction mixture is conducted to processing, wherein the slaking reaction of CaO is completed while the nano- or micro-sized calcium hydroxide (Ca(OH)2) that is being formed is allowed to attach to the surface of the kaolin particle. During this processing, the temperature of the reaction mixture increases to close to 200 °C.

Due to the hydroxide that is formed, the kaolin portion of the reaction mixture particles and the calcium oxide portion of the particles attach to each other at their surfaces. The connection (or attachment ) of Ca(OH)2 to the surface of the kaolin particle takes place without a chemical reaction, by means of physical forces (such as on the basis of charges). The criterion for the amount of Ca(OH)2 on the surface of kaolin is the corrosion protection it gives to steel in the end product (concrete, in particular). For example, for a perfect pozzolanic reaction, 1 kg of metakaolin requires the same amount of Ca(OH)₂ as about 10 kg of Portland cement produces. Either due to the water that is added in slaking CaO, or to the quick temperature rise (in the calcination), the kaolin that is in pack form breaks into smaller particles (fig. 2) and, thus, changes into a form more suitable for the present invention.

The kaolin used as a raw material has to be in such a reactive form (in the form of kaolinite) that it can participate in the pozzolanic reaction. The final activation (i.e. , making the kaolin react into metakaolin), however, takes place during the optional calcination. During the calcination, the kaolinite mineral that is part of the kaolin is burnt at a high temperature, whereby it is activated, forming at least partly (particularly on its surfaces), metakaolin with a high reacting value, preferably, by > 40%, more preferably 40 - 60%, and most preferably about 50%. Al₂Si₂0₅(OH)4→ Al₂Oj^■ 2Si0₂ + 2H₂0

First, the high temperature causes (at 100 - 200 °C) absorbed water to exit (by evaporation), whereby, kaolinite starts to reorganise. Thereafter, with the temperature further rising, de- hydroxylation begins, whereby, also non-evaporable water exits. This burning causes the so-called activation of kaolin, i.e., the formation of metakaolin.

In the following, kaolin particles or the kaolin portion, thus, refer to the particles that are either in the form of kaolin or metakaolin (or to kaolin particles that have reacted into metakaolin on their surfaces).

The calcination of the invention is preferably carried out at a temperature of > 500 °C, more preferably 600 - 800 °C, most preferably about 700 °C.

The portions of the activated kaolin or limestone can be adjusted by decreasing the temper- ature, e.g., by 100 °C after reaching the highest calcination temperature, and by maintaining the decreased temperature for a certain time, which preferably is > 10 minutes, until the desired end result is achieved. Along with the limestone, some pulverised limestone always drifts from the crushing and optional grinding thereof, forming loose calcium oxide in the calcination.

As stated above, both limestone and kaolin can possibly react only partly in the calcination. Especially preferably, about 50% of kaolin is in the form of kaolin and about 50% is in the form of metakaolin, in the particles thus calcined, whereas 20 - 100% of the oxide of the calcium is in the form of calcium oxide, and 0 - 80% is in the form of calcium hydroxide.

In this way, a calcined composite particle is obtained, which makes it possible to produce a hydraulic binding agent by the pozzolanic reaction either together with separate Portland cement or as such, as the only pozzolanic binder. When the particle, according to the invention, is used as the only pozzolanic binder, the pozzolanic reaction induced by means of water takes place by means of metakaolin and the micro-sized (or nano-sized) calcium hydroxide and calcium oxide particles that are on its surface. Hence, the "pozzolanic prop- erty", in connection with the invention, refers to the ability of the silicate in the kaolin to react with calcium hydroxide, so that calcium silica hydrate is formed.

Al₂0₃ · 2SiO_: + 8Ca(OH)₂ + 7.34Η → 2(2CaO · Si0₂ · 1.17H₂0) + 4CaO · A1₂0, · 13H₂0 As a result of this pozzolanic reaction, the limestone particles obtain a corrosion-protection covering formed by a polymer network, which also helps to attach this limestone portion to the kaolin portion of the composite particles.

The composite particle, according to the invention, can also be rendered a concrete product that comprises one or more binders, of which at least part comprises this pozzolanic binder. Thus, 25 - 100% of the dry weight of the total binder comprises the composite particle mentioned above, and the rest is most preferably Portland cement.

The composite particles according to the invention provide the concrete in particular with early-stage strength and porosity, whereby its frost resistance is on an extremely good level. The reaction of the calcium oxide contained in the pozzolanic binder with water also forms larger-size calcium hydroxide, which compensates for the shrinkage in concrete. In the pozzolanic reaction, enough heat is also generated to raise the temperature of the concrete product by about 30 °C. Furthermore, the present invention relates to equipment for the manufacture of the products and intermediate products according to the invention. The equipment, according to the invention, comprises at least a calcining furnace 1 (fig. 3). Such a furnace preferably comprises vibrators 1 1 , which produce kinetic energy to the particles that are treated and which make it possible to convey them forward from the feeding end of the furnace 1 to its discharge end. A corresponding calcining furnace can also be used as the combustion furnace 23 of raw material, to make the limestone react, at least, on its surface, into calcium oxide (CaO).

The thermal or radiation energy required by the calcining or combustion reaction can be, preferably, provided by electric resistances or other thermoelectric cells 12 that are placed in the furnace I (or 23).

The calcining furnace 1 , preferably, also comprises a storage space 13, for storing the calcined or burned particles, wherein the temperature can be made lower than in the furnace 1 , and discharge screws 14, which are placed at the discharge end of furnace 1 , and through which the calcined particles are recovered.

The calcination (or combustion) temperature is, preferably, 500 - 800 °C, most preferably 600 - 800 °C, and the dwell time in the furnace is, generally, 10 - 20 min. By means of the calcination, activated particles are obtained from kaolin, which easily adhere, e.g., to calci- um hydroxide by means of simple physical forces, such as the van der Waals forces, or attach to matrices, such as rubber, and other polymers.

The raw limestone material can also be processed in the separate sections of the equipment, among others, to burn it into CaO, at least, on the surfaces of the particles. As a natural product (limestone), which is available in different size cateogries is used herein, it is subjected to a crushing stage before the actual processing, according to an embodiment. This stage is carried out, particularly, if the average diameter of the raw material particles is > 20 mm. Metals can also be removed from the raw material. Hence, according to a preferred embodiment of the invention, optional auxiliary parts are selected for the equipment from a group that includes:

- a batching and processing means 32 of raw material which is, generally, located before the other processing parts in the equipment and which includes, for example:

o a particle fractionator or crusher 21 (preferably, a crusher that is before the fractionator), which is preferably in the form of a slotted roller, for crushing the raw limestone material into smaller (<20 mm) particles or for separating the limestone particles of different sizes from each other and conveying them to separate further processing stages;

o a weighing appliance 22 for adjusting the batching of raw materials; or o a combustion furnace 23 of raw material for forming CaO, at least, on the surfaces of the limestone, or for converting kaolin into the form of me- takaolin;

o or more of these (e.g., both the crusher 21 and the weighing appliance 22);

- or a metal stripping means 3, which is, preferably, located in the equipment, so that it does not interrupt the flow of material that is being processed in the equipment, and which includes

o a metal detector 31 ; or

o a metal separator 32, to which a metal stripping device 33 is optionally connected;

o or both of these (both the detector 31 and the separator 32, to which the stripping device 33 can optionally be connected).

If limestone with a diameter of <20 mm is used, however, it can be conveyed to the grind- ing or fractioning without a separate crushing (after the quarrying).

It is also common practice to locate the limestone and kaolin containers 4, which are needed for the storage of the raw material, in connection with the equipment in question, whereby, they are preferably located right before the particle crusher 21 , if it is used.

The equipment, according to the invention, also comprises:

- a pre-treatment and mixing section 5 of particles, wherein the raw limestone material (particles of <20 mm) can be mixed with kaolin in a fluid state and converted into particles of a desired size, preferably, by means of an attrition impact disintegrator.

According to an embodiment of the invention, calcium hydroxide can be formed by an element of the equipment that is optionally connected to the pre-treatment section 5 and comprises (see fig. 4):

- a processing section 6, wherein the material that was conducted from the pre- treatment section 5 can be made to react, so that calcium oxide changes into hydroxide and attaches to the surface of kaolin or metakaolin; and

- optionally, one or more auxiliary parts.

The slaking reaction of burnt lime (i.e., calcium oxide) is implemented by the processing section 6 that is connected to the pre-treatment section 5: CaO + H₂0→Ca(OH)₂.

According to this embodiment, the particles, which are in the form of CaO, at least, on their surfaces, and which were obtained from the raw material, are ground in the pre- treatment section 5 into a micron grade, in particular, e.g., into particles with an average diameter of 1 - 20 μιη. At the same time, CaO particles receive water on their surfaces and, at least partly, inside their pore structures. As the amount of water is very small, the slaking reaction in this pre-treatment section 5 is not significant. The slaking reaction is, however, completed in the processing section 6 of the equipment. The reaction of kaolin under the influence of water is not substantial, but the kaolin packs that are possibly present can break into smaller parts, whereby, the desired particles are obtained. These particles also attach to the hydroxide that is formed.

The auxiliary parts of the equipment can also be used to adjust the process conditions or the properties, such as purity, of the product that is formed.

According to a preferred embodiment of the invention:

The pre-treatment section 5 of the equipment comprises these auxiliary parts:

rotor section 51 ; stator section 52; and

water vapour generator 53.

Hence, the pre-treatment section 5 comprises one rotor section 5 1 (with rotor blades 5 1 a), which, is preferably a polyelastomer and which functions by accelerating the calcium oxide particles (in water vapour) in the outermost rotor of the rotor section 5 1 , to a suitable velocity that is, preferably, 200 - 900 m/s. Its rotational speed and direction of rotation are adjustable, preferably, so that the radial velocity (the blade velocity) is adjusted to a value of 100 - 900 m/s, more preferably 100 - 300 m/s, and most preferably 300 m s.

Correspondingly, the pre-treatment section 5 comprises one stator section 52 that comprises stator blades 52a, b, which, preferably, consist of steel, have a V shape, and are arranged in circles, particularly, so that the outermost circle comprises a hinged blade 52a, by means of which the blade angle can be adjusted, while the other blades 52b are stationary. This stator section 52 is arranged, so that the CaO particles that are accelerated from the rotor section 51 can be made to collide with the said stator blades 52a, b at a suitably adjusted collision angle (see fig. 5). The purpose is, among others, to adjust the ratio of the radial and tangential velocities. The rotor section 1 and the stator section 52, combined so that particles can be conducted from the rotor section 51 to the stator section 52, are well suited to grinding the particles. The water vapour generator 53, such as a nozzle, can be used to spray water into this pre- treatment section 5, which, thus, works both as a grinder and a pre-hydration space. The large rotational speed of the rotors enables the use of rotors with a small diameter

(such as 250 - 600 mm), and the hinged blades 52a of the stator can be used to control the radial velocities and the magnitude of impact on the particle. Thus, high-speed motors are, preferably, used in the equipment of the invention, by means of which the rotors are accelerated to operating speeds of as high as 9000 rpm, or even 20000 rpm.

Particles stay in this pre-treatment section 5 for approximately < 1 sec, generally, 0.01 - 0. 1 sec. According to an especially preferred embodiment of the invention, optional auxiliary parts are selected for the equipment from a group of parts that are capable of advancing the operation or control of the pre-treatment section 5, these parts including:

- a dosing device 54 of water for adjusting the amount of water mist that is fed into the reaction mix, which is preferably, located in connection with the water mist generator 53 of the pre-treatment section 5; or

- an adjusting means 55 for controlling the rotational speed of the rotors of the rotor section 51 and the adjustment of the blade angles of the stator 52 of the pre- treatment section 5, which is, preferably, connected to the rotor section 5 1 and the stator section 52;

- or both of these (the dosing device 54 and the adjusting means 55).

According to a preferred embodiment of the invention, the processing space 6 of the equipment comprises the following auxiliary part:

- screw section 61 .

Calcium oxide, kaolin, and, e.g., the water needed for the slaking of calcium oxide are pre- treated by a strong turbulence in the pre-treatment section 5 described above. Now, the particles are subjected to strong attrition and they receive impacts (i.e., positive and nega- tive pressure pulses) from the blades 51 a/12a,b of the equipment, which continue to generate cavitation. As a result of the condensing water and the water mist (or steam) that hits the surface of CaO, the slaking reaction of CaO takes place, whereby, a thin Ca(OH)2 film is created, which is partly broken by the attrition. According to this preferred embodiment, the ground and pre-hydrated slurry (or fluid), thus, formed is conveyed from the pre-treatment section 5 of the equipment to the processing space 6, which comprises a screw section 61 that is formed by two screws, preferably, a screw conveyor 61 with two screws, especially preferably, a conveyor 61 formed by two helix screws. In this screw section 61 , the water that is bound to the surfaces and the pore structures of the calcium oxide particles causes a chemical reaction, whereby, the hydroxide formation reaction can be completed without essentially mixing the slurry that is fed thereto. At the same time, the Ca(OH): that is in the metaphase and the kaolin particles attach to each other. Optionally, the progress of the said reaction can be advanced by raising the temperature, e.g., to a value of > 100 °C, preferably 100 - 300 °C, most preferably 100 - 295 °C. In processing space 6, minor attrition is also created between the CaO particles, advancing the reaction. This attrition is adjusted by adjusting the rotational speed of the two screws in the screw section 61 .

Because of the variation in the amount of grits in the CaO that is processed (i.e., the particles of other materials in the raw material), inaccuracies are formed in the process, their adjustments having a minor delay (also by means of the equipment of the invention). This causes a slight release of steam. By means of the screws of the equipment processing section 6, the steam, thus, formed can be conveyed from the so-called discharge end of the space formed by the screws of the screw section 61 either to its so-called feeding end, or directly to the pre-treatment section 5 of the equipment. The rotational speed of the screws is, thus, adjusted according to the development of the process temperature. When conduct- ed to this feeding section of rotor crush, steam also reduces the amount of air that enters the processing space. If steam is condensed before the utilization, it is, preferably, carried out at a condensing temperature of < 120°C. Negative pressure is created, when this condensing temperature is < 100°C, and positive pressure must be used, when the temperature is > 100°.

It is also preferable to arrange the volume of the processing space 6 so as to increase toward its discharge end, whereby, the expansion of the material that is processed does not block the equipment. To maintain a suitable reaction speed, the temperature in the processing space 6 is, preferably, allowed to rise to a level of > 100°C, more preferably 100 - 3 10 °C, especially preferably 1 10 - 300 °C, and most preferably 260 - 290 °C.

According to an especially advantageous embodiment of the invention, optional auxiliary parts are selected for the equipment from a group of parts that can advance the control of the processing space 6, these parts including: - a temperature measuring means 62, which is, preferably, located in the processing section 6, more preferably, in its screw section 61 or below, and which is in contact with the rotor section 51 and the stator section 52 of the pre-treatment section 5, most suitably, through their adjusting means 55, so that the temperature of the cal- cium oxide that is being processed can be measured in the screw section 61 and used to control the rotational speed of the rotors and the blade angles of the stator; or

- a separate heating means 63 that is, preferably, located in the processing section 6;

- or both of these (the measuring means 22 and the heating means 63).

Part of the auxiliary parts of the preferred embodiments described above, and their mutual locations are illustrated in fig. 6.

One way of connecting the sections of the equipment described above for manufacturing the various products, according to the invention, is illustrated in fig. 7.

The particles, thus, produced can be used, e.g., as a binder in concrete, mortar or rubber, or as a filler in paper, in particular. The product, thus, made has good opacity and it includes various adhesion mechanisms, by which the good bonding ability in the final applications is accomplished.

The following examples are not meant to limit the scope of the invention but merely to illustrate the products achieved by specific embodiments, and their advantages.

Examples

Example 1 Product 2, according to the invention, was formed using an alternative method, wherein, limestone particles (0 < 0.25 mm) that had been calcined completely into the form of CaO were mixed with kaolin in the fluid state, a screw slaking was carried out (whereby, product 3 was obtained), and the composite particles, thus, formed were further conducted to calcination (whereby, the desired product 2 was obtained). An indirect analysis was carried out, determining the mutual relations of CaO and Ca(OH)₂ after the calcination.

The mixture that was used in the reaction:

Kaolin 5.6 kg

CaO 4.4 kg

In total 10.0 kg

1000 g of the mixture was taken to the analysis and a slaking reaction and calcination were carried out, whereby, a product mixture was obtained containing, in addition to kaolin, 440 g of the mixture of CaO and Ca(OH)₂ that was formed under the influence of water. This product mixture was titrated with 1000 N HC1, using phenolphthalein as an indicator, on the basis of which the mutual relations of CaO and Ca(OH)2 were calculated. The analysis results are in table 1 .

Table 1

Product mixture Calcination * % (CaO) % (Ca(OH)₂)

Limestone in pieces None 0 100.0

500°C 0 100.0

550°C 0 100.0

600°C 8.3 91 .7

650°C 10. 1 89.9

700°C 12.0 88.0 Fine limestone None 0 100.0

500°C 0 100.0

550°C 51 .4 48.6

600°C 61 .4 38.6

650°C 57.7 42.3

700°C 85.9 14. 1

Example 2 The calcination of limestone particles that had been collected in the different fractions was carried out at 800°C to obtain the intermediate product 1. These calcined intermediate products (the limestone particles, the surfaces of which at least, had turned into CaO) were titrated with 1000 N HC1, using phenolphthalein as an indicator, on the basis of which the amounts of CaO on the surfaces of the particles were calculated. The analysis results are in table 2.

Table 2

Example 3

Calcination was carried out at 800°C for mixtures that contained limestone particles that had been collected into different size fractions (5.00 g) and kaolin particles (2.00 g) that had permeated a 0.25 mm sieve, and the calcined composite particles were allowed to cool at 700°C for 10 minutes. The calcinations of corresponding mixtures were also carried out at lower temperatures. Thus, the composite products 1 and 2 were formed. These calcined products (about 50% of limestone particles, the surfaces of which, at least, had turned into CaO, and about 50% of silicate) were titrated with 1000 N HCl, using phe- nolphthalein as an indicator, on the basis of which, the amounts of CaO on the surfaces of the limestone particles were calculated. The analysis results are in table 3.

Table 3

Thus, about 90%, i.e., essentially the entire fraction of the smallest size category is cal- cined into CaO.

Claims

CLAIMS:

1. A method of manufacturing composite particles that work as a binding agent, the composite particles containing a limestone portion that is based on limestone particles or limestone silicate rock particles, characterized in that

- the limestone portion is mixed with a kaolin portion that comprises kaolin particles; and

- the limestone portion or the kaolin portion is subjected to calcination before they are mixed together, or the mixture of these portions is subjected to calcination; whereby, the activated layer that was formed in the calcination on the surface of the particles of, at least, one of the said portions, makes the particles of the portions attach to each other, forming the composite particle.

2. A method according to claim 1 , characterized in that the kaolin particles are formed from raw materials that contain kaolinite, illite, vermiculite, smectite, or chlorite, or two or more of the said minerals, preferably at least, kaolinite, most preferably, >50% of kaolinite.

3. A method according to claim 1 or 2, characterized in that at least the kaolin particles are calcined under conditions where they are activated into metakaolin at least on their surfaces, preferably by >40%, more preferably by 40 - 60% and, most preferably, by about 50%.

4. A method according to claim 1 or 2, characterized in that at least the limestone particles or limestone silicate rock particles are calcined under conditions wherein they react into calcium oxide at least on their surfaces, preferably by 10 - 100%, more preferably by 10 - 85% and, most preferably, by 10 - 50%.

5. A method according to claim 4, characterized in that a slaking reaction of calcium oxide is carried out by means of water mist, whereby calcium hydroxide is formed on the surface of the limestone particles or the limestone silicate rock particles.

6. A method according to claim 4 or 5, characterized in that the slaking reaction of calcium oxide is carried out, so that calcium hydroxide particles with an average diameter of <100 nm are fonned, at least on the surfaces of the limestone particles or limestone silicate rock particles.

7. A method according to any of the preceding claims, characterized in that the calcination is carried out at a temperature of >500°C, more preferably 600 - 800°C, and most preferably about 700°C.

8. Composite particles, which are intended to be used as a binding agent of concrete and which contain a limestone portion based on limestone particles or limestone silicate rock particles, characterized in that the limestone portion is attached to a kaolin portion that comprises kaolin particles, whereby at least one portion of the composite particles is at least partly in a calcined form.

9. Composite particles according to claim 8, characterized in that they areproduced by the method, according to any of claims 1 - 7.

10. Composite particles according to claim 8 or 9, characterized in that they have a size smaller than 2 mm.

1 1 . Composite particles according to any of claims 8 - 10, characterized in that the kaolin particles are selected from raw materials that include kaolinite, illite, vermiculite, smectite, or chlorite, or two or more of the said minerals, preferably at least kaolinite, most preferably >50% of kaolinite.

12. Composite particles according to any of claims 8 - 1 1 , characterized in that the kaolin particles are in a form wherein they are activated into metakaolin, at least on their surfaces, preferably by >40%, more preferably by 40 - 60% and most preferably by about 50%.

13. Composite particles according to any of claims 8 - 12, characterized in that the limestone particles or limestone silicate rock particles are in a form, wherein they have reacted into calcium oxide, at least, on their surfaces, preferably, by 10 - 1 0%, more preferably, by 10 - 85% and, most preferably, by 10 - 50%.

14. Composite particles according to claim 13, characterized in that the calcium oxide of the limestone particles or limestone silicate rock particles is in a slaked form, i.e., in the form of calcium hydroxide, which is preferably in the form of particles with an average diameter of < 100 nm.

15. Composite particles according to any of claims 8 - 14, characterized in that they are selected from the following:

- limestone particles or limestone silicate rock particles, on the surfaces of which, there are layers of calcium oxide that are attached to metakaolin particles;

limestone particles that have reacted completely into calcium oxide and are attached to metakaolin particles;

- limestone particles that have reacted completely into calcium oxide and, further, into calcium hydroxide, and are attached to metakaolin particles;

- limestone particles or limestone silicate rock particles, which on the surfaces thereof have reacted into calcium oxide and further into calcium hydroxide, and which are attached to metakaolin particles;

- agglomerates that are formed from limestone particles, which have reacted completely into calcium oxide and further into calcium hydroxide, and from metakaolin.

16. An intennediate product for manufacturing the composite products, according to any of claims 8 - 15, characterized in that it comprises:

- limestone particles or limestone silicate rock particles, on the surfaces of which there are layers of calcium oxide;

- limestone particles, which have reacted completely into calcium oxide;

- limestone particles or limestone silicate rock particles, which on the surfaces thereof have reacted into calcium oxide and further into calcium hydroxide; or

- limestone particles, which have reacted completely into calcium oxide and further into calcium hydroxide.

17. A concrete product comprising one or more binding agents of which at least part comprises a pozzolanic binder, characterized in that 25 - 100% of the dry weight of the total binder comprises the composite particles, according to any of claims 8 - 15.

18. A concrete product according to claim 17, characterized in that 0 - 75% of the dry weight of the total binder comprises Portland cement.

19. Equipment for implementing the method according to any of claims 1 - 7, characterized in that it comprises

- a calcining or combustion furnace ( 1 or 23), which is suitable for the calcination of limestone or the combustion of kaolin; and

- a pre-treatment section (5) of raw material, wherein the material that comprises the limestone and kaolin portions can be treated into smaller particles in a fluid state.

20. Equipment according to claim 19, characterized in that its furnace ( 1 or 23 ) comprises vibrators ( 1 1 ), which can generate kinetic energy in the composite particles and by which they can be conveyed forward from the feeding end of the furnace ( 1 ) to its discharge end and electric resistances or other thermoelectric cells ( 12), which can produce radiation energy or thermal energy.

21. Equipment according to claim 19 or 20, characterized in that its pre-treatment section comprises

- a rotor section (51), its number of rotations and direction of rotation being adjustable;

- a stator section (52) that comprises stator blades (52a, b), which, preferably, have a V shape and which are arranged in circles, particularly, so that the outermost circle comprises a hinged blade (52a), by means of which the blade angle can be adjusted, while the other blades (52b) are fixed;

the sections (51 , 52) being suitable for grinding the particles; and

- a water mist generator (53) that is, preferably, in the form of a sprayer.

22. Equipment according to any of claims 19 - 21 , characterized in that its auxiliary parts are selected from a group that includes:

- a dosing device (54) of water for adjusting the amount of water mist that is fed into the reaction mix, which is preferably located in connection with the water mist generator (53) of the pre-treatment section (5); or

- an adjusting means (55) for controlling the adjustment of the rotational speed of the rotor and the blade angles of the stator of the pre-treatment section (5), the ad justing means (55) being preferably connected to the rotor section (51 ) and the stator section (52);

- or both.

23. Equipment according to any of claims 19 - 22, characterized in containing a processing section (6), which comprises a screw section (61) that comprises two screws, wherein calcium oxide can be made to react into hydroxide and to attach to the surface of kaolin.

24. Equipment according to claim 23, characterized in that the velocity of the two screws of its screw section (61 ) is adjusted to adjust the reaction speed to convey steam from the tail of the space (61 ) formed by the screws to its forward end.