Mechano-chemical activation of mineral materials

Abstract

The present invention relates to the selection of the size of a grinding mill for the economically reasonable mechano-chemical activation in particular of clays, for example in the cement industry.

Description

[0001] Mechano-chemical activation of mineral materials

[0002] The invention relates to the selection of the size of a mill for the economically viable mechano-chemical activation, in particular of clays, for example in the cement industry.

[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 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] Therefore, the so-called mechano-chemical activation by intensive grinding is increasingly being discussed.

[0005] From the subsequently published DE 10 2023 106 210 a process for grinding and pozzolanic activation in a stirred ball mill is known.

[0006] From the subsequently published DE 10 2023 106 217, a process for grinding and pozzolanic activation in two separate stages of a stirred ball mill is known.

[0007] From the subsequently published DE 10 2023 106 221, the combination of mechanochemical and thermal activation in at least one agitator ball mill is known.

[0008] The subsequently published DE 10 2023 106 222 describes color optimization through the mechanochemical activation of clays. The subsequently published DE 10 2023 123 525 describes a cement additive made from old concrete.

[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] Mechanochemical activation differs fundamentally from thermal activation in terms of understanding the processes involved. While thermal activation is primarily determined by temperature and time, mechanochemical activation in a mill appears to be considerably more complex and dependent on significantly more parameters. Furthermore, a large portion of the input grinding energy is converted into heat, so there is certainly potential for optimization here.

[0011] A wet mill for the industrial processing of concrete admixtures is known from CN 106 345 576 A.

[0012] A vertical ball mill is known from AU 2019 338 944 A1.

[0013] The object of the invention is to optimize the mechano-chemical activation in a mill in such a way that the activation (reactivity of the product) per amount of energy used for the mill is highest.

[0014] This object is achieved by a device for mechanochemical activation having the features specified in claim 1, the use of a mill having the features specified in claim 7, and by the method having the features specified in claim 10. Advantageous further developments emerge from the subclaims, the following description, and the drawings. The device according to the invention is suitable for mechanochemical activation. Clays, for example, but also old concrete or other materials can be activated thermally, but also mechanochemically, and then exhibit suitable setting behavior and other properties, allowing them to be used, for example, as a clinker substitute or additive. Such devices are known, for example, from DE 10 2023 106 210, DE 10 2023 106 217, DE 10 2023 106 221, DE 10 2023 106 222 or DE 10 2023 123 525. The device comprises a mill.This mill is operated for mechano-chemical activation in an area where significantly more grinding energy is introduced than is required for comminution and where a growth in size can already be observed during grinding.

[0015] 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 (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 changed any further with further energy input (aggregation zone). For economic reasons, the transition from the first to the second stage is avoided during grinding, as there is no further comminution effect for the additional effort. If the energy input is increased even further, a third stage can be reached, in which a further increase in particle size can be observed (agglomeration zone).This area 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.

[0016] However, it has been shown that high energy inputs, i.e., in the third stage, lead to changes in the material itself. In clays, for example, just like thermal activation, this leads to activation—that is, to a reactivity that enables its use as a binder (and thus as a clinker substitute). This third stage is therefore mechanochemical activation and differs from the grinding, which is carried out in the first stage. Thus, according to the state of the art, grinding is not mechanochemical activation.

[0017] It has surprisingly been found that a mill suitable for mechanochemical activation can provide a sufficiently high energy input, which has an internal volume of at least 1 m 3 can be used particularly efficiently and therefore particularly economically for activation. This difference in efficiency means that mills with an internal volume of less than 100 l are completely inefficient and only with an internal volume of more than 1 m 3exhibit economically viable efficiency. Surprisingly, pilot plant experiments have shown that the ratio between achieved activation and input energy depends to a large extent on the size of the machine, thus defining a minimum machine size for economical operation. This means that, regardless of the desired throughput, a comparatively large mill must be selected. Although large mills are familiar to those skilled in the art, they are usually only suitable for pure comminution and therefore cannot be used for mechanochemical activation.

[0018] In a further embodiment of the invention, the mill is a stirred ball mill.

[0019] In a further embodiment of the invention, the mill has an energy density of at least 200 kW / m 3 on.

[0020] In a further embodiment of the invention, the mill has a length of at least 2 m, preferably at least 2.5 m.

[0021] In a further embodiment of the invention, the mill has a cross-sectional area perpendicular to the longitudinal axis of at least 0.71 m 2 , preferably at least 0.75 m 2 In a further embodiment of the invention, the mill has a length-to-diameter ratio of at least 3, preferably at least 3.5.

[0022] In a further aspect, the invention relates to the use of a mill having an internal volume of at least 1 m 3 for mechano-chemical activation.

[0023] In a further embodiment of the invention, the mill used is a stirred ball mill.

[0024] In a further embodiment of the invention, the mill used has an energy density of at least 200 kW / m 3 on.

[0025] In a further aspect, the invention relates to a process for the mechano-chemical activation of clays, for example, for use in the cement industry. For the mechano-chemical activation, a mill with an internal volume of at least 1 m 3 selected.

[0026] In a further embodiment of the invention, a stirred ball mill is selected as the mill.

[0027] In a further embodiment of the invention, the mill is provided with an energy density of at least 200 kW / m 3 operated.

[0028] In a further embodiment of the invention, the mill is operated with a residence time of the material to be ground in the mill of at least 5 minutes, preferably at least 10 minutes, particularly preferably at least 20 minutes.

[0029] In a further embodiment of the invention, phyllosilicates are activated. Phyllosilicates have proven particularly suitable, and the positive effect of a large mill is even more noticeable with them. 1:1 clay minerals, especially kaolin, and 2:1 clay minerals, especially muscovite and illite, have proven particularly suitable. The relationship between the size of the interior chamber and the activation efficiency is shown below.

[0030] Fig. 1 Measurement data of two exemplary mills

[0031] Fig. 2 Dependence of the specific energy input on the internal volume

[0032] Fig. 1 shows two exemplary mills that differ only in the size of their interior. The interior of B is 10 times larger than that of A. The abscissa represents the energy input in kWh / t, and the ordinate represents the achieved degree of activation, with 100% representing the maximum achievable activation.

[0033] It is clearly visible that the curves for mill A and mill B are parallel, but in the larger mill a significantly higher activation is achieved with the same energy input or, in other words, the same activation with a significantly lower energy input per ton of product.

[0034] In Fig. 2, the internal volume of the mill in liters I is plotted against the applied energy density in kW / l. It can be clearly seen that the energy density below a mill volume of 1000 l or 1 m 3depends significantly on the volume; the slope of the determined curve is strongly negative. Only at a volume of 1000 l or more does the curve become significantly flatter. From this point on, economic efficiency is achieved.

Claims

Patent claims 1. Device for mechano-chemical activation, the device comprising a mill, characterized in that the mill has an internal volume of at least 1 m 3 has.

2. Device according to claim 1, characterized in that the mill is a stirred ball mill.

3. Device according to one of the preceding claims, characterized in that the mill has an energy density of at least 200 kW / m 3 has.

4. Device according to one of the preceding claims, characterized in that the mill has a length of at least 2 m, preferably of at least 2.5 m.

5. Device according to one of the preceding claims, characterized in that the mill has a cross-sectional area perpendicular to the longitudinal axis of at least 0.71 m 2 , preferably at least 0.75 m 2 , has.

6. Device according to one of the preceding claims, characterized in that the mill has a length to diameter ratio of at least 3, preferably of at least 3.

5.

7. Use of a mill with an internal volume of at least 1 m 3 for mechano-chemical activation.

8. Use according to claim 7, characterized in that the mill is a stirred ball mill.

9. Use according to one of claims 7 to 8, characterized in that the mill has an energy density of at least 200 kW / m 3 has.

10. A process for mechano-chemical activation, wherein a mill with an internal volume of at least 1 m 3 11. The method according to claim 10, characterized in that the mill is a Agitator ball mill is selected.

12. Method according to one of claims 10 to 11, characterized in that the mill is operated with an energy density of at least 200 kW / m 3 is operated.

13. The method according to any one of claims 10 to 12, characterized in that the residence time of the material to be ground in the mill is at least 5 minutes, preferably at least 10 minutes, particularly preferably at least 20 minutes.

14. The method according to any one of claims 10 to 13, characterized in that Phyllosilicates are activated.

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