Mechanochemical activation of clays

Abstract

The present invention relates to a method for the mechanochemical activation of mineral material, the method comprising the following steps: a) drying and crushing the mineral material, b) transferring the mineral material into a first high-energy mill (40), c) grinding and mechanochemically activating the mineral material in the first high-energy mill (40), and d) removing the mineral material from the first high-energy mill (40), the grinding in step c) taking place with an energy input per mill volume of at least 100 kW m3.

Description

[0001] Mechano-chemical activation of clays

[0002] The invention relates to a process for the mechano-chemical activation of clays.

[0003] Activated clays have established themselves as additives, particularly in the cement industry. The current method is drying and calcining the clays, i.e., thermal activation. This requires a two-step process:

[0004] 1 ) Amorphization of the clay minerals by thermal activation (calcination) including pre-drying and

[0005] 2) Enlargement of the surface area of ​​the amorphous clay minerals by grinding.

[0006] The goal of thermal activation is to destroy the crystalline structure of the clay minerals and transform them into an amorphous structure so that the individual chemical components, such as aluminum oxide and silica, can react chemically with the ground clinker during cement hydration. The goal of the second step is further mechanical activation through grinding to increase the surface area of ​​the thermally activated clays and ultimately increase the kinetics of the cement hydration reaction.

[0007] The new mechano-chemical activation process combines the two activation steps – amorphization and mechanical activation – in a single-step process with a high-energy-density mill that uses only mechanical energy.

[0008] Thermal activation requires energy for heating, and the high temperature can also cause further material changes that may be undesirable. 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.

[0009] WO 2017 / 008863 A1 discloses a method and a plant arrangement for processing and activating a raw material. EP 3 909 682 A1 discloses a method and a roller mill for thermomechanically activating a clay mixture.

[0010] DE 10 2015 106 109 A1 discloses a process for the tribochemical activation of binders and additives.

[0011] A grinding process is known from US 8 783 589 B2.

[0012] A process for producing sludge powders is known from RU 2 209 824 C2.

[0013] A process for producing activated clay is known from CN 109 954 485 A.

[0014] Because clays are a complex system (especially compared to the burning of limestone), different activation processes lead to different products (activated clays) with different properties. While kaolinite, in particular, can be easily activated by thermal activation, other clay minerals such as muscovite cannot be thermally activated, or can only be insufficiently activated, even at high temperatures. Likewise, the diversity of the clays available means that not every process is suitable for every clay.

[0015] 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.

[0016] 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 drawing. The method according to the invention serves for the mechano-chemical activation of mineral material, in particular clay. In contrast to conventional thermal activation, a thermal treatment step after comminution is thus omitted. The method according to the invention comprises the following steps: a) drying and coarse comminution of the mineral material, b) transferring the mineral material to a first high-energy mill, c) dry grinding and mechano-chemical activation of the mineral material in the first high-energy mill, d) removing the activated mineral material from the first high-energy mill.

[0017] 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.

[0018] The first key point is that the activated mineral material is taken directly from the first high-energy mill and thus does not require a thermal activation step. The activation therefore already takes place entirely in the first high-energy mill. The amorphization and mechanochemical activation therefore take place in step c) and thus during the grinding process. The second key point is that, according to the invention, the amorphization by mechanochemical activation of mineral materials, in particular clay minerals, requires increased energy expenditure beyond the usual fine grinding, which requires a mill with high energy density, and in step c) the grinding and mechanochemical activation with an energy input per grinding chamber volume of at least 100 kW / m 3This process involves grinding without the addition of water, i.e., not wet or in a slurry, but rather, similar to the drying process in step a), as dry grinding without the addition of moisture, which distinguishes it from traditional wet grinding processes. A typical value for a ball mill, as an example of a micron mill, is usually closer to 20 kW / m 3 and thus significantly lower. 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 grinding media 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.

[0019] Mechanochemical activation consists of three phases or stages: In the first stage, the particle size decreases (more or less linearly) with the energy input (Rittinger zone). 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. From this point on, a second stage follows, in which the particle size cannot be further changed with further energy input (activation and aggregation zone). In this stage, the crystallographic structures are destroyed by the breaking of atomic bonds; individual atoms or entire groups of atoms are replaced by other atoms or groups of other atoms. Particularly on the particle surfaces, the initial crystal structure, as well as the bond type and oxidation states of atoms, are altered due to high energy transfer and subsequent chemical reactions.For economic reasons, the transition from the first stage to the second stage, which is necessary for mechanochemical activation, is avoided during normal grinding, where only the creation of surfaces is expected. If the energy input is increased even further, a third stage can be reached, in which an increase in particle size can be observed again due to the agglomeration of nanoparticles (agglomeration zone), which has a positive effect on the workability of activated clay-cement concrete. This zone is therefore much more likely to be avoided during grinding, as a better result in terms of particle size distribution can be achieved with less effort.

[0020] 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 be dispensed with.

[0021] 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 thermal activation. However, it has been shown that the process according to the invention, despite the comparatively high energy requirement, in particular electrical energy, is advantageous, particularly for the activation of clays that are difficult to activate thermally. Especially with complex starting materials such as clays, thermal activation regularly results in several negative effects. Firstly, it is known that, for example, substances can escape in gaseous form from clays at elevated temperatures, which require more complex exhaust gas purification. This can be avoided by avoiding higher temperatures.Secondly, at elevated thermal activation temperatures, color-providing components, such as iron compounds, are often oxidized, which, in the case of clays with a high iron content, leads to an undesirable red coloration of the product. To avoid this, either a protective gas atmosphere or subsequent reduction is necessary, both of which are technically complex. Thus, although the energy requirement for the actual activation step of the process according to the invention is increased, exhaust gas treatment is simplified and subsequent reduction can be avoided. Furthermore, carbon dioxide is still released during the thermal activation process. This carbon dioxide originates from fossil fuels or waste fuels, but also from the deacidification of carbonate minerals during calcination, which ultimately requires a carbon capture process.The process according to the invention requires only electrical energy, and it has been shown that the carbonate minerals are not decomposed during the mechanochemical activation process, but remain as amorphous and reactive material in the activated clay product. This allows the entire activation process to be efficiently simplified and decarbonized to produce a marketable binder. Furthermore, different clay minerals exhibit different optimal activation temperatures. For example, minerals from the kaolin and chlorite groups are activated at significantly lower temperatures than minerals from the mica group (muscovite, illite, and others). If the optimal activation temperature of kaolinite is chosen for thermal activation of clays containing minerals from these groups, minerals such as muscovite and illite will not be activated.However, if the significantly higher activation temperature of muscovite and illite is chosen for thermal activation, the formation of new mineral phases, particularly spinels, leads to overburning of the kaolinite, resulting in deactivation. This differentiation of clay minerals regarding the optimal activation temperature, however, is eliminated in mechanochemical activation.

[0022] According to the invention, the first high-energy mill is a dry-operated agitator ball mill. The dry-operated agitator ball mill is operated at a peripheral speed of 2 m / s to 8 m / s.

[0023] In a further embodiment of the invention, in step c) the grinding and mechano-chemical activation is carried out with an energy input per grinding chamber volume of at least 200 kW / m 3 carried out.

[0024] 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 according to step b), while activated mineral material is continuously removed according to step d). Therefore, the first high-energy mill is preferably operated as a continuous mill with an inlet side and an outlet side.

[0025] Alternatively, the first high-energy mill could be selected from the group comprising vibratory mills and planetary ball mills. In this alternative, the first high-energy mill is preferably a planetary ball mill. These mill types have proven particularly suitable for mechanochemical activation, as they allow particularly high energy densities to be introduced into the material.

[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 50 vol.% to 80 vol.%, particularly preferably 60 vol.% to 70 vol.%. The bulk volume of the grinding media is related to the grinding chamber volume of the first high-energy mill. Since the filling level is around 64% for a simple bed and only 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 extremely 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.

[0028] 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.

[0029] In a further embodiment of the invention, ceramic grinding media are selected. 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.

[0034] In a further embodiment of the invention, the mineral material is mechano-chemically activated together with 0.1-50 wt.% quartz or corundum.

[0035] In a further embodiment of the invention, after the activated mineral material has been removed in step d), the removed material is examined to determine its activation. 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 examination is one or more methods selected from the group comprising IR spectroscopy, RAMAN spectroscopy, X-ray diffraction analysis, and heat flow calorimetry.

[0036] 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.

[0037] In a further embodiment of the invention, the mineral material in step c) 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, it can be used to achieve a desired neutral gray tone in the finished product.

[0038] In a further embodiment of the invention, the grinding in step c) takes place at a material temperature of 100 °C to 250 °C. This elevated temperature is advantageous to prevent condensation of water and, if necessary, to be able to remove additional water.

[0039] In a further embodiment of the invention, after step d), in a step e), the activated mineral material is separated into a first fraction and a second fraction, with the first fraction being recycled to step b), and the second fraction being removed as product. For example, the separation is carried out using a classifier. Here, the finer first fraction is recycled, since activation is associated with an increase in particle size. This differs fundamentally from the normal separation and recycling in a mill, in which the coarse fraction is normally recycled. In a further aspect, the invention relates to a binder produced by the process according to the invention.

[0040] The method according to the invention is explained in more detail below using an embodiment shown in the drawing.

[0041] Fig. 1 Flowchart

[0042] The process is shown highly schematically in Fig. 1. 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, namely an agitated 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 sifter 50, 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.

[0043] Reference symbol

[0044] 10 Hammer Mill

[0045] 20 riser dryers

[0046] 30 reactant silo

[0047] 40 first high-energy mill

[0048] 50 sifters

[0049] 60 product silos

Claims

Patent claims 1. A method for the mechano-chemical activation of mineral material, the method comprising the following steps: a) drying and coarse comminution of the mineral material, b) transferring the mineral material to a first high-energy mill (40), c) dry grinding and mechano-chemical activation of the mineral material in the first high-energy mill (40), d) removing the activated mineral material from the first high-energy mill (40), wherein in step c) the grinding is carried out with an energy input per mill volume of at least 100 kW / m 3 is carried out, wherein the first high-energy mill (40) is a stirred ball mill, wherein the stirred ball mill is operated at a peripheral speed of 2 m / s to 8 m / s.

2. Process according to claim 1, characterized in that in step c) the grinding and mechano-chemical activation with an energy input per mill volume of at least 200 kW / m 3 is carried out.

3. 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.

4. Method according to one of the preceding claims, characterized in that the first high-energy mill (40) is filled with a grinding body filling level of 50 vol.% to 95 vol.%, preferably from 50 vol.% to 80 vol.%, particularly preferably from 60 vol.% to 70 vol.%, wherein the bulk volume of the grinding bodies is related to the grinding chamber volume of the first high-energy mill (40).

5. Method according to one of the preceding claims, characterized in that grinding bodies are selected from iron or an iron alloy or from aluminum or an aluminum alloy or from ceramic.

6. Method according to one of the preceding claims, characterized in that grinding bodies with a diameter of 1 mm to 10 mm are selected.

7. 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.

8. 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.

9. 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.

10. Method according to one of the preceding claims, characterized in that after the removal of the activated mineral material in step d), the removed material is examined to determine the activation, wherein one or more methods are selected for the examination 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, NMR spectroscopy.

11. The method according to claim 10, characterized in that after the removal of the activated mineral material in step d), the removed material is examined to determine the activation, wherein one or more methods are selected for the examination from the group comprising IR spectroscopy, RAMAN spectroscopy, X-ray diffraction analysis, heat flow calorimetry.

12. Method according to one of the preceding claims, characterized in that a gas is selected and used as the gas which is one or more gases selected from the group comprising nitrogen, argon, carbon dioxide, water vapor, carbon monoxide, hydrogen, hydrocarbon, in particular methane, ethane, propane and butane.

13. Process according to one of the preceding claims, characterized in that the mineral material in step c) is ground with a liquid or solid reducing agent and mechano-chemically activated.

14. Process according to one of the preceding claims, characterized in that the grinding and mechano-chemical activation in step c) takes place at 100 °C to 200 °C.

15. Process according to one of the preceding claims, characterized in that after step d), in a step e), the activated mineral material is separated into a first fraction and a second fraction, the first fraction being recycled to step b), the second fraction being removed as product.

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