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] 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.

[0002] Activated clays have become established as additives, particularly in the cement industry. The current standard method involves drying and calcining the clays, i.e., thermal activation. This process requires energy for heating, and the high temperature can also cause further material changes, which may be undesirable. Furthermore, the thermal process necessitates flue gas cleaning to remove the resulting nitrogen oxide and sulfur oxide emissions. In the future, the thermal process will also require the use of methods for capturing and, if necessary, purifying the carbon dioxide produced or released.

[0003] Therefore, the so-called mechano-chemical activation through intensive grinding is increasingly being discussed.

[0004] From the subsequently published DE 10 2023 106 210 a process for grinding and pozzolanic activation in a stirred ball mill is known.

[0005] 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.

[0006] The combination of mechanochemical and thermal activation in at least one stirred ball mill is known from the subsequently published DE 10 2023 106 221.

[0007] The color optimization in the mechano-chemical activation of clays is known from the subsequently published DE 10 2023 106 222.

[0008] A cement additive made from recycled concrete is known from the subsequently published DE 10 2023 123 525.

[0009] Because clays are a complex system (especially compared to limestone firing), different activation methods result in different products (activated clays) with varying properties. Similarly, the diversity of usable clays means that not every method is suitable for every type of clay.

[0010] Mechanochemical activation differs fundamentally from thermal activation in terms of the underlying processes. While thermal activation is primarily determined by temperature and time, mechanochemical activation in a mill appears to be significantly more complex and dependent on considerably more parameters. Furthermore, a large portion of the milling energy input is converted into heat, indicating potential for optimization.

[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) is highest per unit of energy expended on the mill.

[0014] This problem is solved by a device for mechano-chemical activation with the features specified in claim 1, the use of a mill with the features specified in claim 7, and by the method with the features specified in claim 10. Advantageous embodiments are described in the dependent claims, the following description, and the drawings.

[0015] The device according to the invention is suitable for mechanochemical activation. For example, clays, but also old concrete or other materials can be activated thermally or mechanochemically and then exhibit suitable setting behavior and other properties, enabling them to be used, for example, as clinker substitutes or additives. 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 includes a mill. This mill is operated for mechanochemical activation in a range where significantly more grinding energy is applied than is required for comminution and where size growth can already be observed during grinding.

[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 increasing 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 is almost impossible to reduce further. Beyond this point, a second stage begins, in which the particle size cannot be changed further with additional energy input (aggregation zone). For economic reasons, the transition from the first to the second stage is avoided during grinding, as the increased energy input does not result in any further reduction in size. If the energy input is increased even further, a third stage can be reached, in which an increase in particle size is again 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.

[0017] However, it has been found that at high energy inputs, i.e., in the third stage, changes occur in the material itself. In the case of clays, for example, this leads to activation, i.e., reactivity, similar to thermal activation, which enables their use as binders (and thus as clinker substitutes). This third stage is therefore mechano-chemical activation and differs from the grinding carried out in the first stage. Thus, according to the state of the art, grinding is not mechano-chemical activation.

[0018] It has surprisingly been found that a mill suitable for mechanochemical activation, meaning one capable of providing a sufficiently high energy input and possessing an internal volume of at least 1 m³, can be used for activation with particular efficiency and thus with high economic efficiency. This difference in efficiency means that mills with an internal volume of less than 100 liters are completely inefficient and only achieve economically viable efficiency with an internal volume of more than 1 m³. Surprisingly, pilot plant trials have shown that the ratio between the achieved activation and the energy input is highly dependent on the machine's size, thus establishing a minimum machine size for economical operation. This means that, regardless of the required throughput, a comparatively large mill must be selected.Although large mills are known to experts, they are usually only suitable for pure comminution and therefore cannot be used for mechano-chemical activation.

[0019] In another embodiment of the invention, the mill is a stirred ball mill.

[0020] In a further embodiment of the invention, the mill has an energy density of at least 200 kW / m³.

[0021] In a further embodiment of the invention, the mill has a length of at least 2 m, preferably at least 2.5 m.

[0022] In a further embodiment of the invention, the mill has a cross-sectional area perpendicular to the longitudinal axis of at least 0.71 m², preferably of at least 0.75 m².

[0023] In a further embodiment of the invention, the mill has a length-to-diameter ratio of at least 3, preferably at least 3.5.

[0024] In another aspect, the invention relates to the use of a mill with an internal volume of at least 1 m³ for mechano-chemical activation.

[0025] In another embodiment of the invention, the mill used is a stirred ball mill.

[0026] In a further embodiment of the invention, the mill used has an energy density of at least 200 kW / m³.

[0027] In another aspect, the invention relates to a method for the mechano-chemical activation, for example of clays for use in the cement industry. For the mechano-chemical activation, a mill with an internal volume of at least 1 m³ is selected.

[0028] In a further embodiment of the invention, a stirred ball mill is selected as the mill.

[0029] In a further embodiment of the invention, the mill is operated with an energy density of at least 200 kW / m³.

[0030] 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 min, preferably at least 10 min, particularly preferably at least 20 min.

[0031] In a further embodiment of the invention, layered silicates are activated. Layered silicates have proven to be particularly suitable, and the positive effect of a large mill is even more pronounced with these. 1:1 clay minerals, especially kaolin, and 2:1 clay minerals, especially muscovite and illite, have proven to be particularly suitable.

[0032] The relationship between the size of the interior space and the activation efficiency is shown below. Fig. 1 Measurement data of two exemplary mills Fig. 2 Dependence of the specific energy input on the internal volume

[0033] In Fig. 1 Two exemplary mills are shown, differing only in the size of their interior. The interior of mill B is 10 times larger than that of mill A. The abscissa represents the energy input in kWh / t, and the ordinate the achieved degree of activation, where 100% represents the maximum achievable activation.

[0034] It is clearly evident that the curves for mill A and mill B run 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.

[0035] In Fig. 2The internal volume of the mill in liters (L) is plotted against the energy density in kW / L. It is clearly evident that below a mill volume of 1000 L or 1 m³, the energy density depends significantly on the volume; the slope of the calculated curve is strongly negative. Only at volumes above 1000 L does the curve become significantly flatter. Economic efficiency is achieved from this point onward.

Claims

1. Device for mechanochemical activation, wherein the device has a mill, characterized in that the mill has an internal volume of at least 1 m3.

2. Device according to claim 1, characterized in that the mill is an attritor.

3. Device according to one of the preceding claims, characterized in that the mill has an energy density of at least 200 kW / m3.

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 m2, preferably of at least 0.75 m2.

6. Device according to one of the preceding claims, characterized in that the mill has a ratio of length to diameter of at least 3, preferably of at least 3.5.

7. Use of a mill with an internal volume of at least 1 m3 for mechanochemical activation.

8. Use according to claim 7, characterized in that the mill is an attritor.

9. Use according to one of claims 7 to 8, characterized in that the mill has an energy density of at least 200 kW / m3.

10. Method for mechanochemical activation, wherein a mill with an internal volume of at least 1 m3 is selected for the mechanochemical activation.

11. Method according to claim 10, characterized in that an attritor is selected as the mill.

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 / m3.

13. Method according to one of claims 10 to 12, characterized in that the dwell time of the ground material in the mill is at least 5 min, preferably at least 10 min, particularly preferably at least 20 min.

14. Method according to one of claims 10 to 13, characterized in that phyllosilicates are activated.

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