Mechanochemical activation of clay

Abstract

The present invention relates to a method for the mechanochemical activation of mineral materials, a) Drying and coarse grinding process of mineral materials, b) A step of transferring the mineral material to a first high-energy mill (40), c) The process of dry grinding and mechanical and chemical activation of the mineral material in the first high-energy mill (40), and d) The process includes a step of removing the activated mineral material from the first high-energy mill (40), In step c) above, the grinding is at least 100 kW / m 3 This relates to a method performed with energy input per unit volume of mill.

Description

[Technical Field]

[0001] This invention relates to a method for the mechanochemical activation of clay. [Background technology]

[0002] Activated clay is well-established as an additive, particularly in the cement industry. Currently, the standard method involves drying and firing the clay, i.e., thermal activation. This involves a two-step process: 1) A process of amorphousizing clay minerals by thermal activation (calcination) including pre-drying, and 2) The process requires increasing the surface area of ​​the amorphous clay mineral by grinding.

[0003] The purpose of thermal activation is to break down the crystalline structure of the clay minerals and convert them into an amorphous structure, so that individual chemical components such as aluminum oxide and silica can chemically react with the pulverized clinker during cement hydration. The purpose of the second step is further mechanical activation by grinding to increase the surface area of ​​the thermally activated clay and ultimately increase the kinetics of the cement hydration reaction.

[0004] The new mechochemical activation process is a one-step process using a high-energy-density mill that employs only mechanical energy, combining two activation steps (amorphization and mechanical activation).

[0005] Thermal activation requires energy for heating, and high temperatures can also cause undesirable changes to other materials. Furthermore, thermal methods require flue gas scrubbing to separate the resulting nitrogen oxide and sulfur oxide emissions. In addition, thermal methods may require the use of methods to separate and, if necessary, purify the carbon dioxide generated and released in the future.

[0006] International Publication No. 2017 / 008863 discloses methods and plant equipment for processing and activating raw materials.

[0007] European Patent Application Publication No. 3 909 682 discloses a method and roller mill for thermomechanical activation of clay mixtures.

[0008] German Patent Application Publication No. 10 2015 106 109 discloses a method for the tribochemical activation of binders and additives.

[0009] U.S. Patent No. 8,783,589 discloses a grinding method.

[0010] Russian Patent No. 2209824 discloses a method for producing slurry powder.

[0011] Chinese Patent No. 109954485 discloses a method for producing activated clay.

[0012] The paper on cement grinding is available at the following URL: https: / / e-pub.uniweimar.de / opus4 / files / 4279 / Dissertation_Reformat_Martin.pdf and is published as Martin Reformat: "Cement grinding," September 16, 2020 (2020-09-16), XP93163189.

[0013] VIZCAYNO C.ET AL: "Pozzolan obtained by mechanochemical and thermal treatments of kaolin," APPLIED CLAY SCIENCE, ELSEVIER, AMSTERDAM, NL, Vol.49, No.4, August 1, 2010 (2010-08-01), pages 405-413, XP027198140, ISSN:0169-1317 25 [found on 2009-10-03] describes the production of pozzolanes by mechanochemical and thermal treatments of kaolin.

[0014] Because clay constitutes a complex system (especially compared to the combustion of limestone), different activation methods produce different products (activated clays) with different properties. Kaolinite, in particular, can be easily activated by thermal activation, while other clay minerals such as muscovite cannot be activated at all, or are only insufficiently activated, even at high temperatures. Similarly, the diversity of usable clays means that not all methods can be used for all clays. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] International Publication No. 2017 / 008863 Brochure [Patent Document 2] European Patent Application Publication No. 3 909 682 [Patent Document 3] German Patent Application Publication No. 10 2015 106 109 [Patent Document 4] U.S. Patent No. 8,783,589 [Patent Document 5] Russian Patent No. 2 209 824 [Patent Document 6] Chinese Patent No. 109954485 Specification [Non-patent literature]

[0016] [Non-Patent Document 1] Martin Reformat:"Cement grinding," September 16, 2020 (2020-09-16), XP93163189, found at https: / / e-pub.uniweimar.de / opus4 / files / 4279 / Dissertation_Reformat_Martin.pdf [Non-Patent Document 2] VIZCAYNO C.ET AL:"Pozzolan obtained by mechanochemical and thermal treatments of kaolin,"APPLIED CLAY SCIENCE,ELSEVIER,AMSTERDAM,NL,Vol.49,No.4,August 1,2010(2010-08-01),pages 405-413,XP027198140,ISSN:0169-1317 25[Found on 2009-10-03]

Summary of the Invention

Problems to be Solved by the Invention

[0017] The object of the present invention is to provide an alternative activation method so that clays other than the currently considered suitable for clay firing can be used, or other product characteristics can be achieved. In particular, the possible raw material substrates should be able to be extended to muscovite clay, illite clay or chlorite clay.

Means for Solving the Problems

[0018] This object is achieved by a method having the features disclosed in claim 1. Advantageous further embodiments result from the dependent claims, the following description, and the drawings.

Embodiments for Carrying Out the Invention

[0019] The method according to the present invention is used for the mechanochemical activation of mineral materials, particularly clays. Thus, in contrast to conventional thermal activation, a heat treatment step after pulverization is unnecessary. The method according to the present invention comprises the following steps: a) a step of drying and coarsely pulverizing the mineral material, b) a step of transferring the mineral material to a first high-energy mill, c) a step of dry pulverization and mechanochemical activation of the mineral material in the first high-energy mill, and d) a step of removing the activated mineral material from the first high-energy mill.

[0020] In step a), a first drying and coarse grinding is performed. Here, the order of drying and coarse grinding may be arbitrary. They can also occur (partially) simultaneously. This is well known to those skilled in the art. Ultrafine mills, i.e., mills capable of producing particularly small particle sizes, are usually not suitable for materials that are too coarse. On the other hand, ultrafine mills are optimized for ultrafine grinding and are therefore unsuitable and uneconomical for coarse grinding. Therefore, it is customary and wise to perform coarse grinding before feeding the material into the ultrafine mill. Another main application is the activation of clay, but also, for example, the activation of slag stored in a storage facility. For this purpose, drying is necessary because the initial moisture content of the starting material is usually too high. Both are conventional before conventional thermal activation and can be carried out in a similar manner.

[0021] The first essential point is that the activated mineral material is simply extracted directly from the first high-energy mill, and therefore no thermal activation process follows. Thus, activation is already completely carried out in the first high-energy mill. In other words, amorphization and mechanochemical activation occur in step c), and therefore during the grinding procedure.

[0022] The second essential point is that, according to the present invention, the amorphization of mineral materials, particularly clay minerals, by mechanochemical activation requires an increased energy input that exceeds the energy input of normal fine grinding, and therefore requires a mill with a high energy density, and the grinding and mechanochemical activation in step c) requires at least 100 kW / m 3 This is performed with an energy input per unit volume of the grinding chamber. In this case, grinding is carried out as dry grinding without the addition of water, i.e., without the addition of water in a wet or slurry, as in step a), which differs from conventional wet grinding methods. A typical value for a ball mill, which is an example of an ultrafine grinding mill, is usually 20 kW / m³. 3It is close to and therefore remarkably low. In this regard, the grinding chamber volume is understood to be the volume available within the first high-energy mill, i.e., the free volume when there is no material and, for example, a grinding medium within the first high-energy mill. Therefore, components belonging to the mill, such as a shaft that is movable inside, are not part of the grinding chamber volume because this volume cannot be occupied by material.

[0023] Mechanochemical activation consists of three phases or stages: In the first stage, particle size decreases (almost linearly) with respect to energy input (Ritter zone). Simply put, the more it is ground, the finer the product becomes. However, there is a limit to this; below this particle size, it can hardly progress. After this point, there is a second stage where the particle size cannot be changed any further with additional energy input (activation and agglomeration zone). In this stage, the crystalline structure is destroyed by loosening of atomic bonds; individual atoms or entire groups of atoms are replaced by other atoms or other groups of atoms. Especially at the particle surface, high energy transfer and subsequent chemical reactions alter the initial crystalline structure, bond type, and oxidation state of atoms. Therefore, for economic reasons, the transition from the first to the second stage necessary for mechanochemical activation is avoided during normal grinding, where the only expectation is surface formation. Further increasing the energy input can lead to a third stage where an increase in particle size due to the aggregation of nanoparticles (agglomeration zone) can be observed again, which has a positive effect on the workability of activated clay cement concrete. Therefore, this zone is much more likely to be avoided during grinding, as better results in terms of particle size distribution can be achieved at a lower cost.

[0024] However, it has been found that high energy input, i.e., in the second stage, brings about a change in the material itself, and in the case of clay, this results in activation, i.e., reactivity that makes it possible to use it as a binder (and therefore as a clinker substitute), similar to thermal activation. Therefore, with such high energy input, it is possible to omit the subsequent heat treatment.

[0025] However, in this case, it has been found that the energy requirements for purely mechanochemical activation can be higher than those for thermal activation. Therefore, the method according to the present invention initially appears to be at a disadvantage compared to conventional thermal activation. However, despite perhaps relatively high, particularly electrical, energy requirements, the method according to the present invention has been found to be advantageous for activating clays that are particularly difficult to activate thermally. Thermal activation usually has several drawbacks, especially for complex starting materials such as clay. On the one hand, substances in gaseous form, for example, can escape from the clay at high temperatures, requiring more expensive exhaust gas treatment. This can be avoided by not using higher temperatures. On the other hand, coloring components such as iron compounds are often oxidized at high thermal activation temperatures, resulting in undesirable red coloration of the product in clays with high iron content. To avoid this, either a protective gas atmosphere or subsequent reduction is required, both of which are expensive from a process standpoint. This increases the energy requirements of the actual activation process in the method according to the present invention, but it simplifies exhaust gas treatment and avoids subsequent reduction. Furthermore, thermal activation methods also release carbon dioxide derived from fossil fuels or waste fuels, as does the deoxidation of carbonate minerals during calcination, ultimately requiring a carbon capture process. The method according to the present invention requires only electrical energy, and it has been found that carbonate minerals are not decomposed by the mechanochemical activation method but are retained in the activated clay product in the form of amorphous and reactive materials. This means that the entire activation procedure for producing marketable binders can be simplified and decarboxylated in an efficient manner. Moreover, different clay minerals have different optimal activation temperatures. For example, minerals of the kaolin and chlorite groups are activated at significantly lower temperatures than minerals of the mica group (muscovite, illite, etc.). If the optimal activation temperature of kaolinite is selected for the thermal activation of clay containing minerals from these groups, minerals such as muscovite and illite will not yet be activated. However, if the significantly higher activation temperatures of muscovite and illite are selected for thermal activation, the formation of new mineral phases, especially spinel, will result in the over-combustion and deactivation of kaolinite.However, this distinction in clay minerals regarding the optimal activation temperature is eliminated by mechanochemical activation.

[0026] According to the present invention, the first high-energy mill is a dry agitator bead mill. The dry agitator bead mill is operated at a peripheral speed of 2 m / s to 8 m / s.

[0027] In a further embodiment of the present invention, in step c), the grinding and mechanochemical activation are performed at a rate of at least 200 kW / m³ per volume of the grinding chamber. 3 It is performed with energy input.

[0028] In a further embodiment of the present invention, the first high-energy mill is operated continuously. This means that mineral material is continuously supplied to the first high-energy mill according to step b), and at the same time, activated mineral material is continuously removed according to step d). Therefore, preferably, the first high-energy mill operates as a continuous mill having an input side and an output side.

[0029] Alternatively, the first high-energy mill can be selected from the group including vibratory mills and planetary ball mills. Preferably, in this alternative configuration, the first high-energy mill is a planetary ball mill. These types of mills have proven particularly suitable for mechanochemical activation because they can introduce particularly high energy densities into the material.

[0030] In a further embodiment of the present invention, an agitator bead mill having a length-to-diameter ratio of 2.5:5 is selected.

[0031] In a further embodiment of the present invention, the first high-energy mill is filled with a grinding medium packing level of 50% to 95% volume, preferably 50% to 80% volume, and particularly preferably 60% to 70% volume. Here, the bulk volume of the grinding medium is related to the volume of the grinding chamber of the first high-energy mill. The packing level is about 64% for simple packing and only about 74% for the densest ball packing, so even a theoretical grinding medium packing level of 100% leaves a corresponding empty space that can be occupied, for example, by the mineral material to be activated. However, since the packing level of the grinding medium packing is highly dependent on the shape and uniformity of the grinding medium, it is simpler from a practical standpoint to relate the grinding medium packing level to the bulk volume rather than the actual (filled) volume.

[0032] In further embodiments of the present invention, a grinding medium made of iron or an iron alloy, or a grinding medium made of aluminum or an aluminum alloy is selected. Preferably, a grinding medium made of iron or an iron alloy is selected. In particular, a grinding medium made of steel is selected.

[0033] In further embodiments of the present invention, a ceramic grinding medium is selected.

[0034] In a further embodiment of the present invention, a grinding medium having a diameter of 1 mm to 10 mm is selected.

[0035] In a further embodiment of the present invention, the agitator bead mill is operated at a peripheral speed of 2 m / s to 6 m / s, preferably 3 m / s to 5 m / s, and particularly preferably 3.5 m / s to 4.5 m / s.

[0036] In a further embodiment of the present invention, the agitator bead mill operates with gas volume flow and material flow. The ratio of gas volume flow to material flow is 0.0001 m 3 / kg~5m 3 / kg, preferably 0.1m 3 / kg~2m 3 It is set to be / kg.

[0037] In a further embodiment of the present invention, drying and grinding in step a) are carried out to a residual moisture content of less than 1% by weight and a particle size of less than 2 mm.

[0038] In further embodiments of the present invention, the mineral material is selected from the group comprising clay, ash, particularly fly ash, lime cement clinker, spent concrete fine powder, slag, silicate sheets, and silicate skeletons. Particularly preferred mineral materials are clay or a mixture of clay and one or more additional materials selected from the group comprising ash, particularly fly ash, fine cement clinker, spent concrete fine powder, slag, silicate sheets, and silicate skeletons.

[0039] In further embodiments of the present invention, the mineral material is mechanically activated with 0.1 to 50% by weight of quartz or corundum.

[0040] In further embodiments of the present invention, after removing the activated mineral material in step d), the removed material is analyzed to determine its activation. For the analysis, one or more methods are selected from the group including IR spectroscopy, RAMAN spectroscopy, X-ray diffraction analysis, thermal flow differential calorimetry, thermogravimetric analysis, scanning electron microscopy, particle size and / or particle shape analysis, and NMR spectroscopy. One or more methods selected from the group including IR spectroscopy, RAMAN spectroscopy, X-ray diffraction analysis, and thermal flow differential calorimetry are particularly preferred for the analysis.

[0041] In further embodiments of the present invention, the gas selected and used for the gas flow through the first high-energy mill is a gas comprising one or more gases selected from the group comprising nitrogen, argon, carbon dioxide, water vapor, carbon monoxide, hydrogen, and hydrocarbons, particularly methane, ethane, propane, and butane. Particularly preferably, the gas comprises mainly nitrogen, carbon dioxide, or water vapor (more than 50% by volume). Particularly preferably, the gas comprises less than 1% by volume, preferably less than 0.1% by volume, of oxygen.

[0042] In further embodiments of the present invention, the mineral material is pulverized with a liquid or solid reducing agent in step c). For example, coal or coal dust can be used as the solid reducing agent. For example, liquid hydrocarbons can be used as the liquid reducing agent. On the one hand, the addition helps to prevent oxidation of iron, for example. At the same time, it can be used to achieve a desired neutral gray tone in the final product.

[0043] In a further embodiment of the present invention, the grinding in step c) is carried out at a material temperature of 100°C to 250°C. This high temperature is advantageous in order to avoid water condensation and to allow for the removal of additional water as needed.

[0044] In a further embodiment of the present invention, after step d), the activated mineral material is separated into a first fraction and a second fraction in step e), the first fraction is returned to step b), and the second fraction is removed as a product. Separation is performed, for example, using a separator. Here, since activation is associated with an increase in particle size, the finer first fraction is returned. This is fundamentally different from the usual separation and recirculation in mills where the coarse fraction is typically recycled.

[0045] In a further embodiment, the present invention relates to a binder manufactured according to the method of the present invention.

[0046] The method according to the present invention will be described in more detail below with reference to exemplary embodiments shown in the drawings. [Brief explanation of the drawing]

[0047] [Figure 1] A flowchart is shown.

[0048] A very schematic diagram of this method is shown in Figure 1. For example, clay is supplied to a hammer mill 10, where it is pulverized and then conveyed to a starting material silo 30 via a riser tube dryer 20. The clay pre-pulverized and dried in this way is transferred to a first high-energy mill 40, i.e., an agitator bead mill with a grinding media filling level of 65%, using steel balls with a diameter of 4 mm as the grinding media. The energy input is 350 kW / m 3 is. The agitator bead mill has a length-to-diameter ratio of 4 and is operated at a peripheral speed of 4 m / s. The ratio of the gas volume flow to the material flow is 0.01 m 3 / kg. The material removed from the first high-energy mill 40 is separated by a separator 50, the fine material is returned to the inlet of the first high-energy mill 40, and the coarse activated material is transferred to a product silo 60.

Explanation of symbols

[0049] 10 Hammer mill 20 Riser tube dryer 30 Starting material silo 40 First high-energy mill 50 Separator 60 Product silo

Claims

1. A method for the mechanochemical activation of mineral materials, a) Drying and coarse grinding process of mineral materials, b) A step of transferring the mineral material to a first high-energy mill, c) The process of dry grinding and mechanochemical activation of the mineral material in the first high-energy mill, and d) The process includes a step of removing the activated mineral material from the first high-energy mill, In step c) above, the dry grinding is at least 100 kW / m ３ A method in which the energy input per unit volume of the mill is performed, wherein the first high-energy mill is an agitator bead mill, and the agitator bead mill is operated at a peripheral speed of 2 m / s to 8 m / s.

2. In step c), the dry grinding and mechanochemical activation are performed at a rate of at least 200 kW / m ３ The method according to claim 1, wherein the energy input per unit volume of mills is used.

3. The method according to claim 1, wherein an agitator bead mill having a length-to-diameter ratio of 2.5:5 is selected.

4. The method according to claim 1, wherein the first high-energy mill is filled with a grinding medium at a filling level of 50% to 95% volume, preferably 50% to 80% volume, and particularly preferably 60% to 70% volume, and the bulk volume of the grinding medium is related to the volume of the grinding chamber of the first high-energy mill.

5. The method according to claim 1, wherein the grinding medium is selected from iron or an iron alloy, or aluminum or an aluminum alloy, or ceramic.

6. The method according to claim 1, wherein a grinding medium having a diameter of 1 mm to 10 mm is selected.

7. The method according to claim 1, wherein the agitator bead mill is operated at a peripheral speed of 2 m / s to 6 m / s, preferably 3 m / s to 5 m / s, and particularly preferably 3.5 m / s to 4.5 m / s.

8. The agitator bead mill is operated with gas volume flow and material flow, and the ratio of gas volume flow rate to material flow rate is 0.0001 m ３ / kg ~ 5m ３ / kg, preferably 0.1m ３ / kg ~ 2m ３ The method according to claim 1, wherein the value is set to be / kg.

9. The method according to claim 1, wherein the drying and grinding in step a) are carried out to a residual moisture content of less than 1% by weight and a particle size of less than 2 mm.

10. The method according to claim 1, wherein after removing the activated mineral material in step d), the removed material is analyzed to determine its activation, and one or more methods are selected for inspection from the group including IR spectroscopy, RAMAN spectroscopy, X-ray diffraction analysis, thermal flow differential calorimetry, thermogravimetric analysis, scanning electron microscopy, particle size and / or particle shape analysis, and NMR spectroscopy.

11. The method according to claim 10, wherein after removing the activated mineral material in step d), the removed material is analyzed to determine the activation, and for the analysis, one or more methods are selected from the group including IR spectroscopy, RAMAN spectroscopy, X-ray diffraction analysis, and thermal flow differential calorimetry.

12. The method according to claim 1, wherein the gas selected and used for the gas flow through the first high-energy mill is a gas comprising one or more gases selected from the group including nitrogen, argon, carbon dioxide, water vapor, carbon monoxide, hydrogen, and hydrocarbons, particularly methane, ethane, propane, and butane.

13. The method according to claim 1, wherein in step c), the mineral material is pulverized with a liquid or solid reducing agent and mechanically activated.

14. The method according to claim 1, wherein the dry grinding and mechanochemical activation in step c) are carried out at 100°C to 200°C.

15. The method according to any one of claims 1 to 14, wherein in step e), after step d), the activated mineral material is separated into a first fraction and a second fraction, the first fraction is recycled in step b), and the second fraction is removed as a product.

16. A binder manufactured using the method described in claim 1.

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