CN120981436A - Combined mechanochemical and thermal activation of clays - Google Patents

Abstract

The present invention relates to a method for thermal activation and mechanochemical activation of a combination of mineral materials, wherein the method comprises the following steps: a) coarsely crushing and drying the mineral materials, b) grinding and mechanochemical activation in a first high-energy mill (40), and c) thermal activation in a heat treatment apparatus (90), wherein step b) is performed before step c), or step c) is performed before step b).

Description

Mechanochemical and thermal activation of clay combinations

This invention relates to a method for the thermal and mechanochemical activation of clay compositions.

Activated clay has become an additive, especially in the cement industry. Currently, the commonly used method is the drying and calcination of clay, i.e., thermal activation.

On the one hand, this thermal activation requires energy for heating and drying; on the other hand, high temperatures may cause other potentially undesirable material changes. Furthermore, the thermal method requires flue gas cleaning to separate the generated nitrogen oxides and sulfur oxides. Additionally, future thermal methods will require the use of methods to separate and (if necessary) purify the generated and released carbon dioxide.

WO 2017/008 863A1 discloses a method and apparatus arrangement for processing and activating raw materials.

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

DE 10 2015 106 109 A1 discloses a method for tribochemical activation of adhesives and additives.

RU 2 209 824 C2 discloses a method for producing slurry powder.

US2011/233314 A1 discloses a grinding method.

Because clay constitutes a complex system (especially compared to the combustion of limestone), different activation methods produce different products (activated clay) with different properties. Similarly, the diversity of clays that can be used means that not every method can be used for every type of clay.

The object of this invention is to provide an alternative activation method that enables the use of clay qualities different from those currently considered suitable for calcined clay, or enables the achievement of other product properties. Specifically, the possible raw material matrices should be expanded to include muscovite, illite, or chlorite clay.

This objective is achieved by the characteristic method disclosed in claim 1. Further advantageous embodiments are derived from the dependent claims, the following description, and the accompanying drawings.

The method according to the present invention is used for the thermal and mechanochemical activation of combinations of mineral materials. The method comprises the following steps:

a) Dry and coarsely pulverize the mineral material.

b) Drying, grinding, and mechanochemical activation in a first high-energy grinding mill, and

c) Thermal activation in a heat treatment apparatus.

Step b) is performed before step c), or step c) is performed before step b).

In step a), a first drying and coarse grinding are performed. The order of drying and coarse grinding can be arbitrary; they can also be performed (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 generally not suitable for operating 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 reasonable to coarsely grind the material before feeding it into the ultrafine mill. Another major application is the activation of clay, but there is also, for example, the activation of slag stored in stockpiles. For this reason, the initial moisture content of the starting material is usually too high for drying to be necessary. Both are also routine before conventional thermal activation and can be carried out in a similar manner.

In this case, the grinding is carried out without the addition of water, i.e., not wet grinding or in a slurry, but as dry grinding without the addition of water according to the drying in step a), which distinguishes it from the classic wet grinding method.

Based on the energy input, three stages can be identified in the grinding of materials. In the first stage, the particle size decreases relative to the energy input (more or less linearly). Simply put, the more it is ground, the finer the product. However, there is a limitation: it is almost impossible to achieve a particle size lower than this (Rittinger zone). After this point, the second stage is reached, where the particle size does not change with further energy input. For economic reasons, the transition from the first to the second stage is therefore avoided during normal grinding, as the additional cost does not achieve any further observable pulverization effect (agglomeration zone). If the energy input is increased even further, a third stage can be reached, in which an increase in particle size can again be observed (agglomeration zone). Therefore, this zone is more likely to be avoided during normal grinding, as better results can be achieved with less cost.

However, it has been demonstrated that high energy input (i.e., in the second stage) leads to changes in the material itself, which in the case of clay, for example, results in activation, i.e., reactivity that enables it to be used as a binder (and thus as a clinker substitute). Therefore, in the case of such high energy input, subsequent heat treatment can be omitted to the greatest extent possible.

However, in this case, it has been shown that the energy requirement for purely mechanochemical activation can be higher than that for thermal activation. Therefore, the method according to the invention initially appears disadvantageous compared to conventional purely thermal activation. However, despite the potentially higher energy requirements, the method according to the invention has proven advantageous, particularly for the activation of clays.

However, in this case, differences exist between the finished product and the thermally activated material. These differences are difficult to detect due to the highly complex materials and the very localized modification during activation, but they manifest themselves, for example, as differences in coagulation behavior. Therefore, it can be assumed that the two different activation methods activate different centers or activate them in different ways. This combination thus makes it possible to obtain new binders. Therefore, according to the invention, these two activation methods are combined with each other. It is necessary here that the mechanochemical activation in step b) is not merely a grinding process to reduce particle size, but an actual material activation process. It is also necessary that when mechanochemical activation is combined with thermal activation, the thermal activation sub-step can be carried out at a temperature significantly lower than that of pure thermal activation.

In another embodiment of the invention, thermal activation is performed at a temperature below 600°C, preferably below 500°C. In pure thermal activation, temperatures of 850°C or higher are common. This saves energy and thus 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 unwanted product changes, such as color changes due to oxidation of coloring components.

In another embodiment of the invention, the mechanochemical activation of the mineral material in step b) increases the R3 value (7d) according to ASTM C1897-20 by at least 150 J/g, preferably at least 250 J/g. Therefore, the activation is sufficiently high to allow the activated material to be used as a supporting cementitious material (SCM). ASTM C1897-20 is a standard commonly used in the cement industry for testing reactivity and setting behavior.

In another embodiment of the invention, the mechanochemical activation of the mineral material in step b) increases the total activation of steps b) and c) by at least 25%, preferably at least 33%, according to the R3 value (7d) of ASTM C1897-20. This means that at least 1/4, preferably at least 1/3, of the total activation (increased reactivity) is attributable to mechanochemical activation. For example, if the total increase in activity achieved by mechanochemical and thermal activation is 400 J/g and the proportion attributable to mechanochemical activation is 200 J/g, then the proportion would be 50%. This value can be readily 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 complete activation).

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

In another embodiment of the invention, the mechanochemical activation in step b) is carried out with an energy input of at least 100 kW/ ^m³ , preferably at least 200 kW/ ^m³ per grinding chamber volume. Typical values for ball mills, which are examples of ultrafine grinders, are generally closer to 20 kW/ ^m³ and are therefore significantly lower (and more energy-efficient). In this regard, the grinding chamber volume is understood as the volume available inside the first high-energy grinder, i.e., the free volume when there is no material and, for example, no balls, in the first high-energy grinder. Therefore, components belonging to the grinder (e.g., shafts movably arranged inside) are not part of the grinding chamber volume because this volume cannot be occupied by material.

In a first embodiment of the invention, the mechanochemical activation in step b) occurs prior to the thermal activation in step c). The advantage here is that mechanochemical activation (which goes beyond simple grinding and thus reduces particle size) has already achieved activation and therefore a change at a local level in the material. This, in turn, significantly simplifies the subsequent thermal activation. For example, it can be assumed that a “predetermined break point” is generated in the material during mechanochemical activation, thus allowing thermal activation to be performed at a considerably low cost, particularly at significantly lower temperatures.

In a second embodiment of the invention, the mechanochemical activation in step b) occurs after the thermal activation in step c). The advantage here is that the preceding thermal activation, and particularly the gaseous product produced in this process, results in a more easily millable material, which can then be more readily transferred to the second stage (activation during milling), thus allowing for a shorter residence time and consequently lower energy input per unit volume of product. Simultaneously, the binder properties of this product are more similar to those of a purely mechanochemically activated binder, as no further changes occur after mechanochemical activation.

In another embodiment of the invention, the first high-energy mill operates continuously. This means that mineral material is continuously fed into the first high-energy mill, and simultaneously, activated mineral material is continuously removed. Preferably, the first high-energy mill thus operates as a continuous mill having an input side and an output side.

In another embodiment of the invention, the first high-energy grinding mill is selected from the group consisting of: vibratory mills, planetary ball mills, and agitator bead mills. Preferably, the first high-energy grinding mill is selected from the group consisting of planetary ball mills and agitator bead mills. These types of grinding mills have proven particularly suitable for mechanochemical activation because they can introduce particularly high energy densities. Dry-operated agitator bead mills are particularly preferred as the first high-energy grinding mill.

In another embodiment of the invention, a stirrer bead mill with an aspect ratio of 2.5 to 5 is selected.

In another embodiment of the invention, the first high-energy mill is filled with grinding media at a fill level of 50% to 95% by volume, preferably 60% to 70% by volume. Here, the total volume of the grinding media is related to the volume of the first high-energy mill. Since the fill level of simple filler is about 64% and the fill level of densest spherical filler is about 74%, even if the theoretical grinding media fill level is 100%, corresponding free space will be generated, which, for example, can be occupied by the mineral material to be activated. However, since the fill level of the grinding media is highly dependent on the shape and uniformity of the grinding media, it is simpler from a practical point of view to have the grinding media fill level related to the total volume rather than the actual (filled) volume.

In another embodiment of the invention, the abrasive media made of iron or an iron alloy, or made of aluminum or an aluminum alloy, are selected. Preferably, the abrasive media made of iron or an iron alloy are selected. Specifically, the abrasive media made of steel are selected.

In another embodiment of the invention, ceramic abrasive media are selected.

In another embodiment of the invention, an abrasive medium with a diameter of 1 mm to 10 mm is selected.

In another embodiment of the invention, the agitator bead mill operates at a circumferential 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.

In another embodiment of the invention, the agitator bead mill operates at a certain gas volumetric flow rate and material flow rate. The ratio of gas volumetric flow rate to material flow rate is set such that the ratio is between 0.0001 ^m³ /kg and 5 ^m³ /kg, preferably between 0.1 ^m³ /kg and 2 ^m³ /kg.

In another embodiment of the invention, the drying and pulverizing in step a) are carried out until the residual moisture content is less than 1% by weight and the particle size is less than 2 mm.

In another embodiment of the invention, the mineral material is selected from the group consisting of: clay; ash, particularly fly ash; lime cement clinker; used concrete powder; slag; flake silicates and framework silicates. Particularly preferred mineral materials are clay or mixtures of clay with one or more other materials selected from the group consisting of: ash, particularly fly ash; fine cement clinker; used concrete powder; slag; flake silicates and framework silicates.

In another embodiment of the invention, the mineral material is mechanically and chemically activated together with 0.1-50% by weight of quartz or corundum.

In another embodiment of the invention, after the activated mineral material is removed, the activated material is analyzed to determine activation. This can be performed after only one activation step (mechanical-chemical activation or thermal activation) or after two activation steps. Preferably, this is done at both points, so that activation can be determined in two consecutive steps. This allows for optimization of the two activation steps. For the analysis, one or more methods are selected from the group consisting of: IR spectroscopy, Raman spectroscopy, X-ray diffraction analysis, thermal flux calorimetry, thermogravimetric analysis, scanning electron microscopy, particle size and/or particle shape analysis, and NMR spectroscopy. For the analysis, one or more methods selected from the group consisting of: IR spectroscopy, Raman spectroscopy, X-ray diffraction analysis, and thermal flux calorimetry are particularly preferred.

In another 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 consisting of nitrogen, argon, carbon dioxide, water vapor, carbon monoxide, hydrogen, and hydrocarbons, particularly methane, ethane, propane, and butane. Particularly preferably, the gas primarily comprises (greater than 50% by volume) nitrogen, carbon dioxide, or water vapor. Particularly preferably, the gas contains less than 1% by volume, preferably less than 0.1% by volume, of oxygen.

In another embodiment of the invention, in step b), the mineral material is ground 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 one hand, additives are used to prevent, for example, the oxidation of iron. Simultaneously, the additives can be used to achieve the desired neutral gray tone of the finished product.

In another embodiment of the invention, the grinding in step b) is performed at a material temperature of 100°C to 250°C. This elevated temperature is advantageous to prevent water condensation and to allow for the removal of additional water if necessary. Specifically, this can already be achieved by introducing a higher temperature into the material if the thermal activation in step c) occurs prior to the mechanochemical activation in step b).

In another 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, wherein the first fraction is returned to step b) for further mechanochemical activation. The second fraction is removed as a product (if the thermal activation in step c) is performed before the mechanochemical activation in step b) or fed into step c) for thermal activation (if the thermal activation in step c) is performed after the mechanochemical activation in step b).

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

In another aspect, the present invention relates to adhesives produced according to the method of the present invention.

The method according to the invention will be described in more detail below with reference to the exemplary embodiments shown in the accompanying drawings.

Figure 1 First exemplary flowchart

Figure 2 Second Exemplary Flowchart

Based on the first exemplary flowchart, Figure 1 shows a very schematic illustration of the first method. For example, clay is fed into a hammer mill 10, where it is pulverized and conveyed through a riser dryer 20 to a starting material silo 30. The pre-pulverized and dried clay is then transferred to a first high-energy grinding mill 40 (a dry-operated agitator bead mill with a grinding media fill level of 65%, using steel balls with a diameter of 4 mm as the grinding media). The energy input is 350 kW/ ^m³ . The agitator bead mill has an aspect ratio of 4 and operates at a circumferential speed of 4 m/s. The ratio of gas volumetric flow rate to material flow rate is 0.01 ^m³ /kg. The material taken from the first high-energy grinding mill 40 is separated in a separator 50. The fine material is transported back to the inlet of the first high-energy grinding mill 40, and the coarse activated material is transferred to a heat treatment unit 90, preferably an entrained flow reactor, in which the coarse activated material is thermally activated at, for example, 450°C. The finished product can then be removed from the heat treatment unit 90 and transferred to a product silo 60.

Figure 2 illustrates an alternative second method using the first exemplary flow chart. The difference from the first method shown in Figure 1 is that thermal activation occurs prior to mechanochemical activation. For example, clay is fed into a hammer mill 10, where it is pulverized and conveyed through a riser dryer 20 to a starting material silo 30. The clay, already pre-pulverized and dried in this manner, is transferred to a heat treatment apparatus 90, preferably an entrained flow reactor, and thermally activated at 450°C. The partially activated clay is then transferred to a first high-energy grinding mill 40 (a dry-operated agitator bead mill with a grinding media filling degree of 65%, using steel balls with a diameter of 4 mm as the grinding media). The energy input is 350 kW/ ^m³ . The agitator bead mill has an aspect ratio of 4 and operates at a circumferential speed of 4 m/s. The gas volumetric flow rate to material flow rate ratio is 0.01 ^m³ /kg. The material removed from the first high-energy grinding mill 40 is separated in a separator 50. The fine material is transported back to the inlet of the first high-energy grinding mill 40, and the coarse activated material is transferred to the product silo 60.

Figure Labels

10 Hammer Mill

20 Ascending Pipe Dryer

30 Starting material silos

40 First High-Energy Grinding Machine

50 Separator

60 Product Silos

90 Heat treatment equipment

Claims (17)

1. A method for the thermal activation and mechanochemical activation of a combination of mineral materials, wherein the method comprises the following steps: a) Dry and coarsely pulverize the mineral material. b) Dry grinding and mechanochemical activation in a first high-energy grinding mill (40), and c) Thermal activation in heat treatment apparatus (90), Step b) is performed before step c), or step c) is performed before step b). 2. The method according to claim 1, wherein the thermal activation is carried out at a temperature of less than 600°C, preferably less than 500°C. 3. The method according to any one of the preceding claims, characterized in that the mechanochemical activation of the mineral material in step b) increases the R3 value (7d) according to ASTM C1897-20 by at least 150 J/g, preferably at least 250 J/g. 4. The method according to any one of the preceding claims, characterized in that the mechanochemical activation of the mineral material in step b) increases the total activation of steps b) and c) by at least 25%, preferably at least 33%, according to the R3 value (7d) of ASTM C1897-20. 5. The method according to any one of the preceding claims, characterized in that the mechanochemical activation of the mineral material in step b) is carried out at an energy input of at least 100 kW/ ^m³ per millimeter volume, preferably at least 200 kW/ ^m³ . 6. The method according to any one of the preceding claims, characterized in that the first high-energy grinding mill (40) operates continuously. 7. The method according to any one of the preceding claims, wherein the first high-energy grinding mill (40) is selected from the group consisting of: vibratory mills, planetary ball mills and agitator bead mills. 8. The method according to any one of the preceding claims, wherein the first high-energy grinding mill (40) is a dry-operated stirrer bead mill. 9. The method according to any one of the preceding claims, characterized in that a stirrer bead mill with an aspect ratio of 2.5 to 5 is selected. 10. The method according to any one of the preceding claims, characterized in that the first high-energy grinder (40) is filled horizontally with 50% to 95% by volume, preferably 60% to 70% by volume, of the grinding media, wherein the total volume of the grinding media is related to the volume of the first high-energy grinder (40). 11. The method according to any one of the preceding claims, characterized in that the agitator bead mill operates at a circumferential 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. 12. The method according to any one of the preceding claims, characterized in that the agitator bead mill is operated under certain gas volume flow rate and material flow rate, wherein the ratio of gas volume flow rate to material flow rate is set such that the ratio of gas volume flow rate to material flow rate is between 0.0001 ^m³ /kg and 5 ^m³ /kg, preferably between 0.1 ^m³ /kg and 2 ^m³ /kg. 13. The method according to any one of the preceding claims, characterized in that the drying and pulverizing in step a) are carried out until the residual moisture content is less than 1% by weight and the particle size is less than 2 mm. 14. The method according to any one of the preceding claims, characterized in that the mineral material is selected from the group consisting of: clay; ash, especially fly ash; lime cement clinker; used concrete fine powder; slag; flake silicates and framework silicates. 15. The method according to any one of the preceding claims, characterized in that, after the mechanochemical activation in step b), the activated mineral material is separated into a first fraction and a second fraction in step e), wherein the first fraction is returned to step b) for further mechanochemical activation and the second fraction is removed as a product or fed into step c) for the thermal activation. 16. The method according to any one of the preceding claims, wherein the thermal activation in step c) is carried out in an entrained flow reactor or a rotary kiln. 17. An adhesive produced using the method according to any one of the preceding claims.