Combined mechanochemical and thermal activation of clays

Abstract

The present invention relates to a method for the combined thermal and mechanochemical activation of mineral materials, comprising the following steps: a) Coarse crushing and drying of mineral materials; b) a grinding and mechanochemical activation step in a first high-energy mill (40); and c) a thermal activation step in a heat treatment device (90); The method relates to a method in which step b) is performed before step c), or step c) is performed before step b).

Description

[Technical Field]

[0001] The present invention relates to a method for the combined thermal and mechanochemical activation of clays. [Background technology]

[0002] Activated clays are well established as additives, particularly in the cement industry. Currently, the usual method is to dry and calcinate the clay, i.e., heat activation.

[0003] On the one hand, this requires energy for heating and drying, and on the other hand, high temperatures can also cause other material changes that may be undesirable. Furthermore, thermal methods require flue gas scrubbing to separate the resulting nitrogen oxide and sulfur oxide emissions. Furthermore, thermal methods require the use of methods to separate and, if necessary, purify the carbon dioxide produced and released in the future.

[0004] WO 2017 / 008863 discloses a method and plant for treating and activating raw materials.

[0005] EP 3 909 682 A1 discloses a method and roller mill for the thermomechanical activation of clay mixtures.

[0006] DE 10 2015 106 109 A1 discloses a method for the tribochemical activation of binders and additives.

[0007] Russian Patent No. 2 209 824 discloses a method for producing a slurry powder.

[0008] US Patent Application Publication No. 2011 / 233314 discloses a grinding method.

[0009] Russian Patent No. 2 209 824 discloses a method for producing a slurry powder.

[0010] US Patent Application Publication No. 2011 / 233314 discloses a grinding method.

[0011] TOLE ILDA ET AL: "Mechanochemical activation of natural clay minerals: an alternative for the production of sustainable cementitious binders - Review," MINERALOGY AND PETROLOGY, SPRINGER VIENNA, VIENNA, Vol. 113, No. 4, May 8, 2019 (2019-05-08), pages 449-462, XP036833323, ISSN: 0930-0708, DOI: 10.1007 / S00710-019-00666-Y [discovered May 8, 2019] discloses the mechanochemical activation of clay.

[0012] Because clays constitute a complex system (especially compared to limestone combustion), different activation methods yield different products (activated clays) with different properties. Similarly, the variety of clays available means that not all methods can be used for all clays. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] International Publication No. 2017 / 008863 Brochure [Patent Document 2] European Patent Application Publication No. 3 909 682 [Patent Document 3] DE 10 2015 106 109 [Patent Document 4] Russian Patent No. 2 209 824 [Patent Document 5] US Patent Application Publication No. 2011 / 233314 [Patent Document 6] Russian Patent No. 2 209 824 [Patent Document 7] US Patent Application Publication No. 2011 / 233314 [Non-patent literature]

[0014] [Non-Patent Document 1] TOLE ILDA ET AL:"Mechanochemical activation of natural clay minerals:an alternative for the production of sustainable cementitious binders-Review,"MINERALOGY AND PETROLOGY,SPRINGER VIENNA,VIENNA,Vol.113,No.4,May 8,2019(2019-05-08),pages 449-462,XP036833323,ISSN:0930-0708,DOI:10.1007 / S00710-019-00666-Y[Discovered May 8, 2019] Summary of the Invention [Problem to be solved by the invention]

[0015] The object of the present invention is to provide an alternative activation method so that clays other than those currently considered suitable for clay calcination can be used or other product properties can be achieved. In particular, it should be possible to extend the range of possible raw material substrates to muscovite clays, illite clays or chlorite clays. [Means for solving the problem]

[0016] This object is achieved by a method having the features disclosed in claim 1. Advantageous further embodiments arise from the dependent claims, the following description and the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0017] The method according to the invention is used for the combined thermal and mechanochemical activation of mineral materials, which method comprises the following steps: a) the process of drying and coarse grinding of mineral materials; b) a step of dry grinding and mechanochemical activation in a first high-energy mill, and c) a step of thermal activation in a heat treatment device. Step b) is performed before step c), or step c) is performed before step b).

[0018] In step a), drying and coarse grinding are first performed. Here, the order of drying and coarse grinding can 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, usually cannot operate with 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 advisable to perform coarse grinding before the material is fed to the ultrafine mill. Another major application is the activation of clays, but also, for example, the activation of slag stored in reservoirs. For this, the initial moisture content of the starting material is usually too high, making drying necessary. Both are customary prior to conventional thermal activation and can be carried out in a similar manner.

[0019] In this case, the milling is carried out as dry milling without adding water, i.e. not wet or in a slurry, but without adding moisture following drying in step a), which differs from conventional wet milling methods.

[0020] Depending on the energy input, three stages can be identified in the grinding of materials. In the first stage, the particle size decreases (almost linearly) with the energy input. Simply put, the more you grind, the finer the product. However, there is a limit to this, below which particle sizes can hardly be reached (the Rittinger zone). After this point, a second stage is reached, below which the particle size does not change with additional energy input. Therefore, for economic reasons, the transition from the first to the second stage is avoided during normal grinding, since the additional cost does not achieve any additional observable grinding effect (the agglomeration zone). With a further increase in energy input, a third stage (the agglomeration zone) can be reached, where an increase in particle size can again be observed. Therefore, it is much more likely to avoid this zone during normal grinding, since better results can be achieved with less cost.

[0021] However, it has been found that a high energy input, i.e., the second stage, leads to a change in the material itself, which in the case of clays, for example, leads to activation, i.e., reactivity, which allows it to be used as a binder (and therefore as a clinker substitute), similar to thermal activation. Therefore, with such a high energy input, it is possible to dispense with subsequent heat treatment as far as possible.

[0022] However, in this case, it has been found that the energy requirements for purely mechanochemical activation can be higher than those for thermal activation. Thus, the method according to the invention may initially appear to be disadvantageous compared to conventional purely thermal activation. However, despite the potentially relatively high energy requirements, the method according to the invention has been found to be particularly advantageous for activating clays.

[0023] However, in this case, there are differences in the final product between mechanochemical activation and thermal activation, which are difficult to detect due to the highly complex materials and the highly localized modifications during activation, but which manifest themselves, for example, in specific differences in settling behavior. Therefore, it can be assumed that the two different activation methods activate different centers or activate them in different ways. This allows for the creation of new binders. Therefore, according to the present invention, the two activation methods are combined with each other. Here, it is essential that mechanochemical activation in step b) actually activates the material, not just as a grinding process to reduce particle size. When combining mechanochemical activation with thermal activation, it is also essential that the thermal activation substep can be carried out at a significantly lower temperature than in the case of pure thermal activation.

[0024] In a further embodiment of the invention, thermal activation is carried out at temperatures below 600°C, preferably below 500°C. For purely thermal activation, temperatures above 850°C are common. This saves energy and therefore at least partially reduces the energy requirements for mechanochemical activation. However, on the other hand, lowering the maximum temperature also has other positive effects, such as reducing the thermal formation of nitrogen oxides or avoiding undesirable product changes, such as color changes due to oxidation of coloring components.

[0025] In a further embodiment of the present invention, the mechanochemical activation of the mineral material in step b) causes an increase in the R3 value (7d) according to ASTM C1897-20 of at least 150 J / g, preferably at least 250 J / g. The activation is therefore high enough to allow the activated material to be used as a supplementary cementitious material (SCM). The ASTM C1897-20 standard is a standard commonly used in the cement industry to test reactivity and setting behavior.

[0026] According to the present invention, the mechanochemical activation of the mineral material in step b) causes an increase in the R3 value (7d) according to ASTM C1897-20 of at least 25%, preferably at least 33%, of the total activation of steps b) and c). This means that at least one-quarter, preferably at least one-third, of the total activation (increase in reactivity) is due to mechanochemical activation. For example, if the total increase in activity due to mechanochemical and thermal activation is 400 J / g and the proportion attributable to mechanochemical activation is 200 J / g, then the proportion is 50%. This value can be easily determined by recording a first measurement of the R3 value between steps b) and c) (regardless of the order) and a second measurement of the R3 value after steps b) and c) (i.e., after full activation).

[0027] In a further embodiment of the present invention, thermal activation is first performed in step c), followed by mechanochemical activation in step b). This allows color optimization during the mechanochemical activation in step b) to counteract undesirable discoloration caused by the thermal activation in step c). For this purpose, the grinding and mechanochemical activation in step b) are performed so that the mineral material is ground together with a reducing agent in a first high-energy mill. A metal with an electronegativity of less than 1.8, preferably less than 1.7, can be selected as the reducing agent. Alternatively, a hydrocarbon, preferably a gaseous hydrocarbon, most preferably propane, can be selected as the reducing agent.

[0028] In a further embodiment of the invention, the mechanochemical activation in step b) is at least 100 kW / m 3 , preferably at least 200 kW / m 3 The energy input per grinding chamber volume is typically 20 kW / m. 3is close to and therefore significantly lower (and more energy-efficient). In this context, the grinding chamber volume is understood to be the volume available in the first high-energy mill, i.e. the free volume when there is no material in the first high-energy mill, e.g. no balls. Components belonging to the mill, e.g. a shaft movably arranged inside, are therefore not part of the grinding chamber volume, since this volume cannot be occupied by material.

[0029] In a first embodiment of the present invention, mechanochemical activation is performed in step b) before thermal activation in step c). The advantage here is that mechanochemical activation goes beyond simple comminution and thus particle size reduction, already achieving activation and thus localized changes in the material. This significantly simplifies the subsequent thermal activation. For example, it can be assumed that a "predetermined breaking point" is created in the material during mechanochemical activation, so that thermal activation can be performed at significantly lower costs, especially at significantly lower temperatures.

[0030] In a second embodiment of the present invention, the mechanochemical activation in step b) is carried out after the thermal activation in step c). The advantage here is that the preceding thermal activation, especially the gaseous products generated during this process, results in a material that is easier to grind, which can then be more easily transferred to the second stage (activation during the grinding process), resulting in a lower residence time and therefore a lower energy input per amount of product. At the same time, the binder properties of this product are more similar to those of a purely mechanochemically activated binder, since no further changes occur after the mechanochemical activation.

[0031] In a further embodiment of the invention, the first high-energy mill is operated continuously, meaning that both the mineral material is continuously fed to the first high-energy mill and, at the same time, the activated mineral material is continuously removed. Preferably, therefore, the first high-energy mill operates as a continuous mill having an input side and an output side.

[0032] In a further embodiment of the present invention, the first high-energy mill is selected from the group consisting of a vibratory mill, a planetary ball mill, and an agitator bead mill. Preferably, the first high-energy mill is selected from the group consisting of a planetary ball mill and an agitator bead mill. These types of mills have proven to be particularly suitable for mechanochemical activation, as they are able to introduce particularly high energy densities. Particularly preferably, a dry agitator bead mill is used as the first high-energy mill.

[0033] In a further embodiment of the present invention, an agitator bead mill having a length to diameter ratio of 2.5 to 5 is selected.

[0034] In a further embodiment of the present invention, the first high-energy mill is filled with a grinding media fill level of 50% to 95% by volume, preferably 60% to 70% by volume. Here, the bulk volume of the grinding media relates to the volume of the first high-energy mill. Because the fill level is approximately 64% for simple packings and approximately 74% for the densest ball packings, even a theoretical grinding media fill level of 100% results in corresponding free space that can be occupied, for example, by the mineral material to be activated. However, because the fill level of the grinding media packing is highly dependent on the shape and uniformity of the grinding media, it is simpler from a practical standpoint to relate the grinding media fill level to the bulk volume rather than the actual (filled) volume.

[0035] In a further embodiment of the invention, grinding media made of iron or iron alloys or of aluminum or aluminum alloys are selected, preferably iron or iron alloys, and in particular steel.

[0036] In a further embodiment of the present invention, ceramic grinding media is selected.

[0037] In a further embodiment of the invention, grinding media are selected having a diameter of 1 mm to 10 mm.

[0038] In a further embodiment of the 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, particularly preferably 3.5 m / s to 4.5 m / s.

[0039] In a further embodiment of the invention, the agitator bead mill operates with a gas volumetric flow and a material flow, the ratio of the gas volumetric flow to the material flow being 0.0001 m 3 / kg~5m 3 / kg, preferably 0.1m 3 / kg~2m 3 / kg.

[0040] In a further embodiment of the invention, the drying and grinding in step a) is carried out to a residual moisture content of less than 1% by weight and a particle size of less than 2 mm.

[0041] In a further embodiment of the invention, the mineral material is selected from the group comprising clay, ash, in particular fly ash, lime cement clinker, used concrete fines, slag, silicate sheets and silicate frameworks. Particularly preferred mineral materials are clay or a mixture of clay with one or more additional materials selected from the group comprising ash, in particular fly ash, fine cement clinker, used concrete fines, slag, silicate sheets and silicate frameworks.

[0042] In a further embodiment of the invention, the mineral material is mechanochemically activated with 0.1 to 50% by weight of quartz or corundum.

[0043] In a further embodiment of the invention, after removal of the activated mineral material, the activated material is analyzed to determine activation. This can be done after just one activation step (mechanochemical or thermal) or after both activation steps. It is preferable to do this at both points so that activation can be determined at both successive steps. This allows both activation steps to be optimized. For analysis, one or more methods are selected from the group including IR spectroscopy, RAMAN spectroscopy, X-ray diffraction analysis, differential heat flow calorimetry, thermogravimetry, 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 differential heat flow calorimetry are particularly preferred for analysis.

[0044] In a further embodiment of the 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, in particular methane, ethane, propane, and butane. Particularly preferably, the gas comprises predominantly (more than 50% by volume) nitrogen, carbon dioxide, or water vapor. Particularly preferably, the gas comprises less than 1% by volume, preferably less than 0.1% by volume, of oxygen.

[0045] In a further embodiment of the present invention, the mineral material is ground in step b) with a liquid or solid reducing agent. For example, coal or coal dust can be used as a solid reducing agent. For example, liquid hydrocarbons can be used as a liquid reducing agent. On the one hand, the addition serves to prevent, for example, the oxidation of iron. At the same time, it can be used to achieve the desired neutral gray tone of the final product.

[0046] In a further embodiment of the invention, the grinding of step b) is carried out at a material temperature of 100°C to 250°C. This high temperature is advantageous in order to avoid condensation of water and to allow additional water to be removed if necessary. In particular, if the thermal activation of step c) is carried out before the mechanochemical activation of step b), this can already be achieved by the temperature at which the material is introduced.

[0047] In a further embodiment of the invention, after the mechanochemical activation in step b), the activated mineral material is separated into a first fraction and a second fraction, the first fraction being returned to the further mechanochemical activation in step b), and the second fraction being removed as product (if the thermal activation in step c) was carried out before the mechanochemical activation in step b) or being fed to the thermal activation in step c) (if the thermal activation in step c) was carried out after the mechanochemical activation in step b).

[0048] In a further embodiment of the invention, the thermal activation of step c) is carried out in an entrained flow reactor or a rotary kiln. Preferably, an entrained flow reactor is used.

[0049] In a further aspect, the present invention relates to a binder produced according to the method of the present invention.

[0050] The method according to the invention is explained in more detail below with reference to exemplary embodiments shown in the drawings. [Brief explanation of the drawings]

[0051] [Figure 1] 1 is a first exemplary flowchart. [Figure 2] 10 is a second exemplary flowchart.

[0052] A highly schematic illustration of the first method is shown in Figure 1 based on a first exemplary flow chart. For example, clay is fed to a hammer mill 10, where it is crushed and conveyed via a riser dryer 20 to a starting material silo 30. The clay thus pre-crushed and dried is transferred to a first high-energy mill 40 (a dry agitator bead mill using 4 mm diameter steel balls as grinding media with a grinding media filling level of 65%). The energy input is 350 kW / m 3 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 gas volume flow to material flow is 0.01 m 3 / kg. The material removed from the first high-energy mill 40 is separated in 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 heat treatment unit 90, preferably an entrained flow reactor, where it is thermally activated, for example at 450°C. The final product can then be removed from the heat treatment unit 90 and transferred to a product silo 60.

[0053] Figure 2 shows an alternative second method using the first exemplary flowchart. The difference with the first method shown in Figure 1 is that thermal activation occurs before mechanochemical activation. For example, clay is fed to a hammer mill 10, where it is crushed, and then conveyed via a riser dryer 20 to a starting material silo 30. The clay thus pre-crushed and dried is transferred to a thermal treatment device 90, preferably an entrained flow reactor, where it is thermally activated at 450°C. The partially activated clay is then transferred to a first high-energy mill 40 (a dry agitator bead mill using 4 mm diameter steel balls as grinding media and a grinding media loading of 65%). The energy input is 350 kW / m 3 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 gas volume flow to material flow is 0.01 m 3 / kg. The material removed from the first high energy mill 40 is separated in a separator 50. The fine material is returned to the inlet of the first high energy mill 40 and the coarse active material is transferred to a product silo 60. [Explanation of symbols]

[0054] 10. Hammer Mill 20 Rising tube dryer 30 Raw material silo 40 First High Energy Mill 50 Separator 60 Product Silo 90 Heat Treatment Equipment

Claims

1. 1. A method for combined thermal and mechanochemical activation of mineral materials, comprising the following steps: a) a step of drying and coarse grinding of the mineral material; b) a step of dry grinding and mechanochemical activation in a first high-energy mill, and c) a step of thermal activation in a thermal treatment device; Step b) is performed before step c), or step c) is performed before step b); A method wherein said mechanochemical activation of said mineral material in step b) causes an increase in the R3 value (7d) according to ASTM C1897-20 by at least 25% of the total activation of steps b) and c).

2. 2. The method of claim 1, wherein the thermal activation is carried out at a temperature below 600°C, preferably below 500°C.

3. 2. The method according to claim 1, wherein the mechanochemical activation of the mineral material in step b) causes an increase in the R3 value (7d) according to ASTM C1897-20 of at least 150 J / g, preferably at least 250 J / g.

4. 2. The method of claim 1, wherein the mechanochemical activation of the mineral material in step b) causes an increase in the R3 value (7d) according to ASTM C1897-20 by at least 33% of the total activation of steps b) and c).

5. The mechanochemical activation of the mineral material in step b) is performed at a power of at least 100 kW / m ３ , preferably at least 200 kW / m ３ 10. The method of claim 1, wherein the energy input per mill volume is

6. 10. The method of claim 1, wherein the first high energy mill is operated continuously.

7. 10. The method of claim 1, wherein the first high energy mill is selected from the group consisting of a vibratory mill, a planetary ball mill, and an agitator bead mill.

8. 10. The method of claim 1, wherein the first high energy mill is a dry agitator bead mill.

9. 10. The method of claim 1, wherein an agitator bead mill having a length to diameter ratio of 2.5 to 5 is selected.

10. 2. The method of claim 1, wherein the first high energy mill is filled at a grinding media fill level of 50% to 95% volume, preferably 60% to 70% volume, the bulk volume of the grinding media being related to the volume of the first high energy mill.

11. 8. The method according to claim 7, 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, particularly preferably 3.5 m / s to 4.5 m / s.

12. The agitator bead mill is operated with a gas volume flow and a material flow, and the ratio of the gas volume flow rate to the material flow rate is 0.0001 m ３ / kg to 5m ３ / kg, preferably 0.1m ３ / kg to 2m ３ The method of claim 7, wherein the saturation is set to be 1 / kg.

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

14. 2. The method according to claim 1, wherein the mineral material is selected from the group comprising clay, ash, in particular fly ash, lime cement clinker, post-consumer concrete fines, slag, silicate sheets and silicate frameworks.

15. 2. The method according to claim 1, wherein after the mechanochemical activation in step b), the activated mineral material is separated into a first fraction and a second fraction in step e), the first fraction is returned to further mechanochemical activation in step b), and the second fraction is either removed as a product or fed to the thermal activation in step c).

16. 16. The method according to any one of claims 1 to 15, wherein the thermal activation of step c) is carried out in an entrained flow reactor or a rotary kiln.

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