Combined mechanochemical and thermal activation of clays

Abstract

The present invention relates to a method for the combined thermal and mechanochemical activation of mineral material, the method comprising the following steps: a) crushing and drying the mineral material, b) grinding and mechanochemically activating in a first high-energy mill (40), and thermally activating in a thermal treatment device (90), with step b) being carried out before step c) or step c) before step b).

Description

[0001] Combined mechano-chemical and thermal activation of clays

[0002] The invention relates to a process for the combined thermal and mechanochemical activation of clays.

[0003] Activated clays have established themselves as an additive, particularly in the cement industry. The current method is drying and calcining the clays, i.e., thermal activation. This requires energy for heating and drying, and the high temperature can also cause further, potentially undesirable, changes in the material. Furthermore, the thermal process requires flue gas purification to capture the resulting nitrogen oxide and sulfur oxide emissions. Furthermore, the thermal process will require the use of processes to capture and, if necessary, purify the carbon dioxide produced or released.

[0004] WO 2017 / 008 863 A1 discloses a method and a plant arrangement for processing and activating a raw material.

[0005] EP 3 909 682 A1 discloses a method and a roller mill for thermomechanically activating a clay mixture.

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

[0007] A process for producing sludge powders is known from Rll 2 209 824 C2.

[0008] A grinding process is known from US 2011 / 233314 A1.

[0009] Because clays are a complex system (especially compared to the firing of limestone), different activation processes result in different products (activated clays) with different properties. Likewise, the diversity of the clays that can be used means that not every process is suitable for every clay.

[0010] The object of the invention is to provide an alternative activation process to enable the use of clay qualities other than those currently considered suitable for clay calcination or to achieve different product properties. In particular, it should be possible to expand the possible raw material base to include muscovite, illite, or chloritic clays.

[0011] This object is achieved by the method having the features specified in claim 1. Advantageous further developments emerge from the subclaims, the following description, and the drawings.

[0012] The process according to the invention serves for the combined thermal and mechanochemical activation of mineral material. The process comprises the following steps: a) drying and coarse comminution of the mineral material, b) dry grinding and mechanochemical activation in a first high-energy mill, and c) thermal activation in a thermal treatment device.

[0013] Step b) is performed before step c) or step c) is performed before step b).

[0014] In step a), initial drying and coarse comminution take place. The sequence of drying and coarse comminution can be arbitrary; they can even occur (partially) simultaneously. This is well known to those skilled in the art. Micromills, i.e. mills capable of producing particularly small particle sizes, usually cannot be operated with material that is too coarse. Furthermore, micromills are optimized for ultrafine grinding and are therefore unsuitable and uneconomical for coarse comminution. Therefore, it is common and sensible to carry out coarse comminution before feeding the material to a micromill. Another main application is the activation of clays, but also, for example, slag stored in heaps. Therefore, the reactants usually have an excessively high initial moisture content, making drying necessary. Both processes are also common before conventional thermal activation and can be carried out in a similar manner.

[0015] Here, the grinding takes place without the addition of water, i.e. not wet or in a slurry, but as in step a) as dry grinding without the addition of moisture, which distinguishes it from the classic wet grinding processes.

[0016] When grinding a material, three stages can be observed depending on the energy input. In the first stage, the particle size decreases (more or less linearly) with the energy input. Put simply, the more you grind, the finer the product becomes. However, there is a limit to this, a particle size that can hardly be exceeded (Rittinger zone). From this point on, you enter a second stage 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 in normal grinding, as there is no further comminution effect for the additional effort (aggregation zone). If you increase the energy input even further, you can reach a third stage where an even further increase in particle size can be observed (agglomeration zone).This area will be avoided even more during normal grinding, as a better result can be achieved with less effort.

[0017] However, it has been shown that high energy inputs, i.e., in the second stage, lead to changes in the material itself. This, for example, leads to activation, just as thermal activation does in clays, i.e., to a reactivity that allows for use as a binder (and thus as a clinker substitute). Therefore, with such high energy inputs, subsequent thermal treatment can largely be dispensed with.

[0018] However, it has been found that the energy requirement for purely mechanochemical activation can be higher than for thermal activation. Therefore, the process according to the invention initially appears to be disadvantageous compared to conventional purely thermal activation. However, it has been shown that the process according to the invention, despite the comparatively potentially high energy requirement, is particularly advantageous for the activation of clays. However, there is a difference in the finished product between mechanochemical activation and thermal activation, which is difficult to determine due to the very complex material and the very local modification during activation, but is expressed, for example, in certain differences in setting behavior.It can therefore be assumed that the two different activation processes either activate different centers or activate them in different ways. The combination thus makes it possible to obtain a new binder. Therefore, according to the invention, both activation processes are combined. It is important that the mechanochemical activation in step b) is not just a grinding process to reduce the particle size, but actually activates the material. It is also important that when combining mechanochemical with thermal activation, the thermal activation step can take place at significantly lower temperatures than is the case with pure thermal activation.

[0019] In a further embodiment of the invention, thermal activation is carried out at a temperature of less than 600 °C, preferably less than 500 °C. For purely thermal activation, temperatures of 850 °C or more are common. This allows energy to be saved, at least partially eliminating the energy required for the mechanochemical activation. Furthermore, reducing the maximum temperature also has other positive effects, such as reducing the thermal formation of nitrogen oxides or preventing unwanted product changes, such as color changes due to the oxidation of color-imparting components.

[0020] In a further embodiment of the invention, the mechanochemical activation of the mineral material in step b) results in an increase in the R3 value (7d) according to ASTM C1897-20 by at least 150 J / g, preferably by at least 250 J / g. The activation is thus sufficiently high to allow the activated materials to be used as cement substitutes (supplementary cementitious materials, SCMs). The ASTM C1897-20 standard is the standard commonly used in the cement industry for investigating reactivity and setting behavior.

[0021] In a further embodiment of the invention, 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 25%, preferably at least 33%, of the total activation of steps b) and c). This means that at least 1 / 4, preferably at least 1 / 3 of the total activation (increased reactivity) is attributable to the mechanochemical activation. For example, if the total increase in activity via mechanochemical and thermal activation were 400 J / g and the proportion attributable to the mechanochemical activation were 200 J / g, the proportion would be 50%. This value can be easily determined by recording a first measured value of the R3 value between steps b) and c) (regardless of the order) and a second measured value of the R3 value after steps b) and c) (i.e., after complete activation).

[0022] In a further embodiment of the invention, thermal activation is carried out first in step c) and then mechano-chemical activation is carried out in step b). This enables color optimization to be carried out during the mechano-chemical activation in step b) in order to counteract unwanted discoloration caused by the thermal activation in step c). For this purpose, grinding and mechano-chemical activation in step b) are carried out in such a way that the mineral material is ground together with a reducing agent in the first high-energy mill. As the reducing agent, for example, a metal with an electronegativity of less than 1.8, preferably less than 1.7, can be selected. Alternatively, a hydrocarbon, preferably a gaseous hydrocarbon, very preferably propane, can also be selected as the reducing agent.In a further embodiment of the invention, the mechano-chemical activation in step b) is carried out with an energy input per grinding chamber volume of at least 100 kW / m. 3 , preferably at least 200 kW / m 3 A typical value for a ball mill, as an example of a fine mill, is usually around 20 kW / m 3 and thus significantly lower (and more energy-efficient). The grinding chamber volume is understood to be the volume available inside the first high-energy mill, i.e., the free volume when there is no material and, for example, no balls in the first high-energy mill. Components belonging to the mill, such as a shaft that is arranged to move inside, are therefore not included in the grinding chamber volume, since this volume cannot be occupied by material.

[0023] In a first embodiment of the invention, the mechanochemical activation in step b) takes place before the thermal activation in step c). The advantage here is that the mechanochemical activation, which goes beyond simple grinding and thus a reduction in particle size, already achieves activation and thus a change at the local level of the material. This, in turn, significantly simplifies subsequent thermal activation. For example, it can be assumed that "predetermined breaking points" are created in the material during the mechanochemical activation, so that the thermal activation can be carried out with significantly less effort, especially at a significantly lower temperature.

[0024] In a second embodiment of the invention, the mechanochemical activation in step b) takes place after the thermal activation in step c). The advantage here is that the preceding thermal activation and in particular the resulting gaseous products produce a more easily millable material, which in turn can then be more easily transferred to the second stage (activation during the milling process), so that the residence time and thus the energy input per quantity of product is shorter. At the same time, this product's binder properties correspond more closely to the purely mechanochemically activated binder, since no further changes occur after the mechanochemical activation. In a further embodiment of the invention, the first high-energy mill is operated continuously.This means that mineral material is continuously fed into the first high-energy mill, while activated mineral material is continuously removed. Therefore, the first high-energy mill is preferably operated as a continuous flow mill with an inlet and an outlet.

[0025] In a further embodiment of the invention, the first high-energy mill is selected from the group comprising vibratory mills, planetary ball mills, and agitated ball mills. Preferably, the first high-energy mill is selected from the group comprising planetary ball mills and agitated ball mills. These mill types have proven particularly suitable for mechanochemical activation, as particularly high energy densities can be achieved with these mill types. A dry-operated agitated ball mill is particularly preferred as the first high-energy mill.

[0026] In a further embodiment of the invention, a stirred ball mill with a length-to-diameter ratio of 2.5 to 5 is selected.

[0027] In a further embodiment of the invention, the first high-energy mill is filled with grinding media to a filling level of 50 vol.% to 95 vol.%, preferably 60 vol.% to 70 vol.%. The bulk volume of the grinding media is related to the volume of the first high-energy mill. Since the filling level is around 64% for a simple bed and around 74% for a densest sphere packing, even a theoretical grinding media filling level of 100% results in a corresponding free space, which can be occupied, for example, by the mineral material to be activated. However, since the filling level of a grinding media bed depends heavily on the shape and uniformity of the grinding media, it is practically easier to relate the grinding media filling level to the bulk volume and not to the actual (filled) volume.In a further embodiment of the invention, grinding media are selected from iron or an iron alloy, or from aluminum or an aluminum alloy. Preferably, grinding media are selected from iron or an iron alloy. In particular, grinding media are selected from steel.

[0028] In a further embodiment of the invention, ceramic grinding media are selected.

[0029] In a further embodiment of the invention, grinding media with a diameter of 1 mm to 10 mm are selected.

[0030] In a further embodiment of the invention, the agitator ball 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.

[0031] In a further embodiment of the invention, the agitator ball mill is operated with a gas volume flow and a material flow. The ratio of gas volume flow to material flow is adjusted such that the ratio of gas volume flow to material flow is between 0.0001 m 3 / kg and 5 m 3 / kg, preferably between 0.1 m 3 / kg and 2 m 3 / kg.

[0032] In a further embodiment of the invention, the drying and comminution in step a) is carried out to a residual moisture content of less than 1 wt.% and a grain size of less than 2 mm.

[0033] In a further embodiment of the invention, the mineral material is selected from the group comprising clay, ash, in particular fly ash, belitz cement clinker, old concrete fines, slag, phyllosilicates, and tectosilicates. Particularly preferred as the mineral material is clay or a mixture of clay and one or more other materials selected from the group comprising ash, in particular fly ash, belitz cement clinker, old concrete fines, slag, phyllosilicates, and tectosilicates. In a further embodiment of the invention, the mineral material is mechanochemically activated together with 0.1-50 wt.% quartz or corundum.

[0034] In a further embodiment of the invention, after the activated mineral material has been removed, the activated material is examined to determine its activation. This can be done either after only one activation step (mechanochemical or thermal) or after both activation steps. Preferably, it is performed at both points so that the activation can be determined in both consecutive steps. This enables optimization of both activation steps. For the examination, one or more methods are selected from the group comprising IR spectroscopy, RAMAN spectroscopy, X-ray diffraction analysis, heat flow calorimetry, thermogravimetry, scanning electron microscopy, particle size and / or particle shape analysis, and NMR spectroscopy.Particularly preferred for the investigation is one or more methods selected from the group comprising IR spectroscopy, RAMAN spectroscopy, X-ray diffraction analysis, heat flow calorimetry.

[0035] In a further embodiment of the invention, a gas is selected and used as the gas flow through the first high-energy mill, which gas is one or more gases selected from the group comprising nitrogen, argon, carbon dioxide, water vapor, carbon monoxide, hydrogen, hydrocarbons, in particular methane, ethane, propane, and butane. Particularly preferably, the gas comprises predominantly (more than 50 vol%) nitrogen, carbon dioxide, or water vapor. Particularly preferably, the gas comprises less than 1 vol%, preferably less than 0.1 vol%, oxygen.

[0036] In a further embodiment of the invention, the mineral material in step b) 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, a liquid hydrocarbon can be used as a liquid reducing agent. The addition serves, for example, to prevent oxidation, for example of iron. At the same time, this can be used to achieve a desired neutral gray tone in the finished product. In a further embodiment of the invention, the grinding in step b) takes place at a material temperature of 100 °C to 250 °C. This elevated temperature is advantageous in order to avoid condensation of water and, if necessary, to be able to remove additional water.In particular, if the thermal activation in step c) occurs before the mechanochemical activation in step b), this can already be achieved by the temperature at which the material is introduced.

[0037] 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, with the first fraction being recycled for further mechanochemical activation in step b). The second fraction is removed as a product (if the thermal activation in step c) was carried out before the mechanochemical activation in step b)) or 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).

[0038] In a further embodiment of the invention, the thermal activation in step c) is carried out in an entrained-flow reactor or a rotary kiln. An entrained-flow reactor is preferably used.

[0039] In a further aspect, the invention relates to a binder which is produced by the process according to the invention.

[0040] The method according to the invention is explained in more detail below with reference to embodiments shown in the drawings.

[0041] Fig. 1 first exemplary flowchart

[0042] Fig. 2 second exemplary flow chart

[0043] Fig. 1 shows a highly schematic representation of a first process using a first exemplary flow diagram. For example, a clay is introduced into the hammer mill 10, crushed there, and conveyed via a riser dryer 20 into a feedstock silo 30. The thus pre-crushed and dried clay is transferred to a first high-energy mill 40 (a dry-operated agitator ball mill with a grinding media filling ratio of 65%, using steel balls with a diameter of 4 mm as the grinding media). The energy input is 350 kW / m 3 The agitator ball mill has a length-to-diameter ratio of 4 and operates at a peripheral speed of 4 m / s. The ratio of gas flow to material flow is 0.01 m 3 / kg. The material removed from the first high-energy mill 40 is separated in a classifier 50. The fine material is transported back to the inlet of the first high-energy mill 40, and the coarse activated material is transferred to a thermal treatment device 90, preferably an entrained-flow reactor, where it is thermally activated at, for example, 450°C. The finished product can then be removed from the thermal treatment device 90 and transferred to a product silo 60.

[0044] Fig. 2 shows an alternative second process using a first exemplary flow diagram. The difference from the first process shown in Fig. 1 is that the thermal activation occurs before the mechanochemical activation. For example, a clay is introduced into the hammer mill 10, crushed there, and conveyed via a riser dryer 20 into a reactant silo 30. The thus pre-crushed and dried clay is transferred to a thermal treatment device 90, preferably an entrained-flow reactor, and thermally activated, for example, at 450 °C. The partially activated clay is then transferred to a first high-energy mill 40 (a dry-operated agitator ball mill with a grinding media filling ratio of 65%, using steel balls with a diameter of 4 mm as the grinding media). The energy input is 350 kW / m 3The agitator ball mill has a length-to-diameter ratio of 4 and operates at a peripheral speed of 4 m / s. The ratio of gas flow to material flow is 0.01 m 3 / kg. The material removed from the first high-energy mill 40 is separated in a sifter 50. The fine material is transported back to the inlet of the first high-energy mill 40, and the coarse activated material is transferred to a product silo 60. Reference symbol

[0045] 10 Hammer Mill

[0046] 20 riser dryers 30 reactant silo

[0047] 40 first high-energy mill

[0048] 50 sifters

[0049] 60 product silos

[0050] 90 thermal treatment device

Claims

Patent claims 1. A process for the combined thermal and mechano-chemical activation of mineral material, the process comprising the following steps: a) drying and coarse comminution of the mineral material, b) dry grinding and mechano-chemical activation in a first high-energy mill (40), c) thermal activation in a thermal treatment device (90), wherein step b) is carried out before step c) or step c) is carried out before step b).

2. Process according to claim 1, characterized in that the thermal activation is carried out at a temperature of less than 600 °C, preferably less than 500 °C.

3. Process according to one of the preceding claims, characterized in that the mechano-chemical activation of the mineral material in step b) causes an increase in the R3 value (7d) according to ASTM C1897-20 by at least 150 J / g, preferably by at least 250 J / g.

4. Method according to one of the preceding claims, characterized in that the mechano-chemical activation of the mineral material in step b) causes an increase in the R3 value (7d) according to ASTM C1897-20 by at least 25%, preferably at least 33%, of the total activation of steps b) and c).

5. Process according to one of the preceding claims, characterized in that the mechano-chemical activation in step b) is carried out with an energy input per mill volume of at least 100 kW / m 3 , preferably at least 200 kW / m 3 , is carried out.

6. Method according to one of the preceding claims, characterized in that the first high-energy mill (40) is operated continuously.

7. Method according to one of the preceding claims, characterized in that the first high-energy mill (40) is selected from the group comprising vibrating mill, planetary ball mill and agitator ball mill.

8. Method according to one of the preceding claims, characterized in that the first high-energy mill (40) is a dry-operated agitator ball mill.

9. Process according to one of the preceding claims, characterized in that an agitator ball mill with a length-to-diameter ratio of 2.5 to 5 is selected.

10. Method according to one of the preceding claims, characterized in that the first high-energy mill (40) is filled with a grinding media filling level of 50 vol.% to 95 vol.%, preferably of 60 vol.% to 70 vol.%, wherein the bulk volume of the grinding media is related to the volume of the first high-energy mill (40).

11. Method according to one of the preceding claims, characterized in that the agitator ball mill is operated at a peripheral speed of 2 m / s to 6 m / s, preferably of 3 m / s to 5 m / s, particularly preferably of 3.5 m / s to 4.5 m / s.

12. Method according to one of the preceding claims, characterized in that the agitator ball mill is operated with a gas volume flow and a material flow, wherein the ratio of gas volume flow to material flow is adjusted such that the ratio of gas volume flow to material flow is between 0.0001 m 3 / kg and 5 m 3 / kg, preferably between 0.1 m 3 / kg and 2 m 3 / kg.

13. Process according to one of the preceding claims, characterized in that the drying and comminution in step a) is carried out to a residual moisture content of less than 1 wt.% and a grain size of less than 2 mm.

14. Method according to one of the preceding claims, characterized in that the mineral material is selected from the group comprising clay, ash, in particular fly ash, belitz cement clinker, old concrete fines, slag, phyllosilicates and framework silicates.

15. Process according to one of the preceding claims, characterized in that after the mechano-chemical activation in step b), a separation of the activated mineral material into a first fraction and a second fraction, wherein the first fraction is returned for further mechano-chemical activation in step b), and wherein the second fraction is removed as a product or fed to the thermal activation in step c).

16. Process according to one of the preceding claims, characterized in that the thermal activation in step c) is carried out in an entrained flow reactor or a rotary kiln.

17. Binder prepared by the process according to any one of the preceding claims.

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