Method and preparation system for preparing rocks

Abstract

The invention relates to a method for preparing rock containing magnetisable valuable minerals, wherein the rock to be prepared is fed as feed material with a grain size of less than 200 mm in diameter to a mill-sifter combination for comminution. Here, the mill-sifter combination is realised by a vertical roller mill with a corresponding sifter. The mill-sifter combination is set up and operated in such a way that feed material comminuted at least once by the grinding rollers of the mill is fed to the sifter of the mill-sifter combination by means of a process air flow and sifted there into a fine fraction and a coarse fraction. The fine fraction is removed from the preparation process as a valuable fraction and fed to a process for further sorting. Furthermore, it is provided that at least a proportion of 50% to 250% per unit time, in relation to the fed feed material per unit of time, of the coarse material rejected by the sifter is supplied to a dry magnetic separation process, wherein a non-magnetisable or poorly magnetisable fraction is discharged from the preparation process as discharge material and a magnetisable fraction is supplied to the mill of the mill-sifter combination for further comminution. The invention additionally relates to a preparation system for carrying out the method according to the invention.

Description

[0001] PROCESS AND PROCESSING PLANT FOR PROCESSING ROCKS

[0002] The invention relates to a method for processing rocks which contain magnetisable valuable minerals as the material to be extracted. The ratio between rock and pure material to be extracted in the rock is 0.2 mass% to 50 mass%, preferably 0.5 mass% to 40 mass%, even more advantageously 5 mass% to 30 mass%. The pure materials to be extracted can be, for example, iron, nickel or copper, in the above ratio in particular in elemental form. In the case of iron, the proportion of pure material to be extracted in the rock can be between 10 mass% to 50 mass%, preferably between 12.5 mass% to 40 mass%, and in the case of copper, between 0.2 mass% to 7 mass%, preferably between 0.3 mass% to 2.0 mass%. The valuable minerals contain the iron and copper proportions largely in the form of oxides or other compounds, which are largely intergrown with the other components of the rock.Among copper minerals, chalcopyrite is the most important valuable mineral; these are compounds with sulfur, known as sulfide copper minerals. Furthermore, the invention also relates to a processing plant for carrying out the process according to the invention.

[0003] Depending on the deposits in the rock, the proportion of valuable materials present in the rock varies. The part of the rock that contains no valuable materials is referred to as gangue or waste rock. For reasons of efficiency, deposits with a high percentage of valuable minerals as extractable material in the mined rock are primarily exploited. However, those of these deposits that are more easily accessible have now been exhausted, so that deposits with a less favorable ratio between rock and extractable pure material are increasingly being exploited, for example, for iron in the range of 12.5 to 35 mass% and for copper in the range of 0.3 to 2.0 mass%. The exploitation of these low-value deposits is naturally significantly more cost-intensive.

[0004] Traditionally, such processing methods, particularly the sorting and separation of rock into valuable minerals and gangue or tailings, are often carried out using very fine comminution, which separates the valuable minerals and gangue, followed by sorting. For iron ores, this is done by magnetic separation followed by wet flotation, and for copper or nickel ores, by wet flotation, as well as corresponding upstream and downstream processes. However, the disadvantages are the high energy requirements for the very fine comminution, the high water consumption for wet flotation, and the energy required to subsequently dry the processed material.

[0005] The invention is therefore based on the object of specifying a method and a processing plant that can be carried out and operated efficiently.

[0006] The object is achieved according to the invention by a method having the features of claim 1 and a processing plant having the features of claim 13.

[0007] Advantageous embodiments of the invention are explained in more detail in the subclaims, in the description and with reference to the figures.

[0008] According to the method according to the invention, the rock to be processed is fed as feed material with a grain size of less than 200 mm, preferably less than 150 mm, to a mill-classifier combination for comminution. The mill-classifier combination comprises a vertical roller mill, in particular of the Loesche type, as the mill. The initial grain size can be achieved, for example, using crushers. The mill-classifier combination is set up and operated to feed the feed material, which has been crushed at least once by the mill's grinding rollers, to the classifier of the mill-classifier combination by means of a process air stream, where it is classified into a fine and a coarse fraction. The mill is therefore operated in air stream mode.

[0009] The fine fraction separated by the separator is discharged from the processing process according to the method of the invention as a valuable fraction and fed into a further sorting process. This involves sorting into valuable materials as material to be extracted and gangue.

[0010] Furthermore, a proportion of 50% to 250% of the coarse material rejected by the classifier, based on the feed material, is fed to a dry magnetic separation system in a magnetic separator per unit of time. This coarse material is also referred to as grit. During magnetic separation, a non-magnetizable or poorly magnetizable fraction is discharged from the processing process as flux, and a magnetizable fraction is returned to the mill of the mill-classifier combination for further comminution. This can be done together with the feed material or separately. Feeding can preferably be done in the middle, the center, or the middle section of the grinding table.

[0011] A fundamental idea of ​​the process according to the invention can be seen in the fact that it makes it possible to enrich the fine material, particularly in percentage terms, with magnetizable valuable materials compared to the feed material. This is achieved by means of magnetic separation, which allows the removal of gangue from the overall material flow as part of the grinding and processing process. This no longer needs to be further crushed, which in turn saves energy. The removal of the coarse material rejected by the sifter to a magnetic separation, which is preferably located outside the mill-sifter combination, can be achieved, for example, by means of a semolina screw, which at least partially removes the coarse material, also referred to as semolina, from the sifter. The semolina can also be removed from the mill using gravity, for example, via a chute or downpipe.Due to the enrichment of valuable minerals in the fines that are further processed, the subsequent sorting into valuable minerals and gangue can be carried out more efficiently and with lower energy consumption, as the amount of rock to be sorted is reduced by the separated non- or poorly magnetizable fraction. For example, if 80% of the valuable minerals in the material fed to this sorting process are extracted using a downstream sorting process, a significantly higher proportion of valuable minerals can be extracted with the same effort if the input material already contains a higher proportion of valuable materials.

[0012] By means of the method according to the invention, for example, the proportion of pure element to be obtained can be increased from 20 mass% to 35 mass%, particularly depending on the initial proportion and degree of intergrowth.

[0013] As explained, the proportion of coarse material removed per unit of time ranges between 50% and 250% of the feed material fed per unit of time. The corresponding mass flows are explained in more detail later in relation to Figure 2.

[0014] During operation of the mill-sifter combination, the material to be crushed is circulated, also known as internal circulation, until the desired fineness is achieved. For example, with a conventional mill-sifter combination, if 10 tons of feed material per hour are fed into the mill, 10 tons of fine material per hour are removed from the sifter only after a run-in period, once the internal circulation has stabilized. This process can take up to three hours.

[0015] The reason for this is that the process air flow, the resulting turbulence, and the movement of the grinding rollers rolling onto a rotating grinding table result in a large amount of partially crushed but also insufficiently crushed feed material within the housing of the mill-classifier combination. This is difficult to quantify. The technical literature generally assumes that the internal circulation is 3 to 10 times greater per unit of time, depending on the grindability of the feed material and the desired target product fineness. In other words, this means that between 300% and 1,000% of the feed material is contained within the mill per unit of time. For this reason, it is also possible to remove the previously described 50% to 250% of the mass of the feed material as coarse material from the processing process.

[0016] Preferably, the magnetic separator is adjusted and operated so that the non- or poorly magnetizable fraction comprises less than 5 mass% of the pure material to be extracted, particularly in its elemental form. The proportion of pure material depends largely on the degree of intergrowth of the valuable mineral with the other components of the rock.

[0017] To prevent excessive amounts of valuable material from being removed from the process through magnetic separation, the magnetic separator is configured and operated in such a way that a maximum of 5% by mass of the pure material to be extracted in the flow material is removed at this point. Ideally, this percentage is even lower. However, if too little flow material is removed, the efficiency of the process decreases. The adjustment parameters for the magnetic separator can be the strength of the magnetic field, the conveyor speed, or the geometry of the magnetic separator, either alone or in any combination.

[0018] It is advantageous if the mill-classifier combination, in particular the classifier, which can be a dynamic classifier, is adjusted and operated so that the fines fraction has a diameter of Dso = 30 pm to 150 pm, preferably Dso = 30 pm to 100 pm. The fines are then subjected to further sorting as described above. For this reason, it is advantageous if the fines fraction has a sufficiently high fineness so that sorting can be carried out as effectively as possible. For this purpose, the rock is crushed in such a way that a separation or exposure occurs between waste rock and valuable minerals. In other words, intergrowths are broken up by this fine grinding.

[0019] The designation Dso = 30 pm defines a fineness at which 80% of the ground material has a diameter of less than or equal to 30 pm. This can be analyzed, for example, using a sieve sample. Such values ​​are significantly more suitable for comminution and / or classifying processes than absolute values, since the dynamic processes during the grinding and classifying processes result in a particle size distribution that does not have sharp cutoffs. The mill-classifier combination, in particular the classifier, which, as already described, can be a dynamic classifier, is advantageously adjusted and operated so that the coarse material rejected by the classifier has a diameter of Dso = 200 pm to 1,500 pm, in particular Dso = 250 pm to 800 pm.It has been shown that coarse material with this grain size distribution already exhibits a good degree of extraction of valuable minerals, so that dry magnetic separation can achieve a good separation between gangue and valuable material. A significant portion can also be removed, allowing the process to be operated efficiently and with less energy consumption.

[0020] The desired fineness of both the fines and the coarse material, for example, in dynamic classifiers, can be influenced by the precise geometry of the classifier. The speed of the classifier rotor can also influence the fineness. For example, a higher speed shifts the cutoff point toward the finer grain. Other factors that influence the fineness, but especially the amount of material fed into the classifier, are the volume or speed of the process air flow through the mill-classifier combination and the working pressure of the grinding rollers.

[0021] In principle, even higher finenesses for the fines and coarse material would lead to even better results, but this would entail significantly higher energy requirements for grinding. According to the invention, the values ​​given here are to be viewed as a compromise between a high degree of extraction and thus a high purity of the fines, especially the valuable minerals in the fines, and the energy requirements required for this.

[0022] As already explained, the mill-classifier combination is operated in particular in airflow mode, in which an air flow flows around the grinding table towards the classifier arranged above the mill.

[0023] Additionally, the mill-classifier combination can also be configured and operated with a grinding table overflow. This means that the material falling from the grinding table during the grinding process is so large that it cannot be transported toward the classifier by the process airflow, but instead falls over the grinding table and down against the process airflow.

[0024] This material falling over the edge of the grinding table is referred to as grinding table overflow. This material can also be fed to further dry magnetic sorting, for example in a magnetic separator. This can involve either an additional magnetic separator or the magnetic separator already used for the coarse material. In the magnetic separator, a non-magnetizable or poorly magnetizable fraction can be discharged from the processing process as additional flux, and a magnetizable fraction can be fed to the mill-classifier combination for further comminution. This additional magnetic separation allows additional flux to be removed from the processing process, thus reducing the energy required to comminute flux and resulting in an even higher purity of the fine material.Purity in the sense of the invention can be understood as meaning that the proportion of valuable minerals to be extracted in the material under consideration is as high as possible.

[0025] In principle, the method according to the invention is suitable for any valuable materials that are magnetizable. It is particularly advantageous for iron materials, especially magnetite or hematite, as these exhibit good magnetizability. However, it can also be applied to copper-containing or nickel-containing valuable minerals. The invention is also applicable to rocks that contain rare earth elements as valuable minerals.

[0026] As explained, the fines fraction discharged from the processing process is subjected to further sorting. Various sorting methods can be used for this. Examples include dry or wet sorting. Wet sorting can, in particular, involve wet magnetic separation, sometimes followed by flotation. An example of dry sorting can be further air separation, provided there are significant mass or density differences between the gangue and the valuable mineral.

[0027] It is preferred, if the mill-classifier combination and the magnetic separator(s) are adjusted and operated accordingly, that the fraction discharged as gangue amounts to between 10% and 70% by mass of the feed material. A higher percentage is preferred here, since any feed material discharged as gangue no longer needs to be subjected to further sorting of the fine fraction. Likewise, this can reduce the grinding effort and wear costs, since discharged gangue is not further crushed. Parameters for adjusting this value include, for example, the sorting limit of the magnetic separator(s) used and, in this context, the fineness of the coarse material fed to the magnetic separation.

[0028] The mill-classifier combination is advantageously operated with a process air flow of 0.8 kg to 5 kg of process gas per unit of time per kg of discharged fine fraction per unit of time. This type of process air flow has been shown to be particularly suitable for achieving the previously discussed fineness and enabling even more energy-efficient operation. The process gas can be ambient air or other gases.

[0029] The preferred unit is kg of air per unit of time per kg of discharged fine fraction per unit of time, as this is independent of the exact volumetric and geometric design of the mill-classifier housing and the density of the process gas. When specifying by volume, the geometry, especially the volume of the mill-classifier, plays a decisive role, such as at bottlenecks where a higher flow velocity exists.

[0030] According to the invention, it is preferred if the mill-classifier combination is arranged in a common housing, and the classifier is located, in particular, above the mill with the grinding rollers. These grinding rollers can, in particular, be designed to be stationary, with themselves being rotatably mounted so that they can be set into rotation about their axis by a rotation of the grinding table over the fed material to be ground. In principle, an additional drive for the grinding rollers themselves is also possible.

[0031] It is advantageous if the mill is operated with a working pressure of the grinding rollers between 600 kN per m 2 and 2,400 kN per m 2 , preferably 900 kN per m 2 and 2,200 kN per m 2, based on the vertically projected area of ​​the average roller diameter. The working pressure of the grinding rollers can be generated by their own weight. Alternatively, a hydraulic system can be present, which can exert additional pressure on the grinding bed via the grinding roller suspension. The higher the pressure, the finer the material is crushed. However, it should be noted that this may in turn result in increased energy requirements. The most efficient grinding pressure can also vary from material to material, since crushing through shear forces is also possible in addition to pure pressure crushing.

[0032] As shown, the mill-classifier combination can also be operated in a combined airflow and overflow mode. Generally, but also specifically in this context, it is possible to provide a dam at the edge of the grinding table. The height of this dam can influence the height of the grinding bed and thus also the comminution of the material on the grinding bed. The height of the dam of the grinding table is preferably between 0.8% and 5.0%, in particular up to 3.5%, of the diameter of the mill's grinding table. This dimensioning of the dam ensures sufficiently fine comminution of the feed material and also takes into account the optimization of the energy consumption required for this.

[0033] Furthermore, the invention relates to a processing plant for processing rock containing magnetizable valuable minerals as the material to be extracted, in particular according to the method according to the invention. The ratio between rock and pure material to be extracted is 0.2% to 50% by mass. The processing plant comprises a mill-classifier combination that uses a vertical roller mill as the mill and can be designed and operated for comminuting rock to be processed as feed material with a grain size of less than 200 mm in diameter.

[0034] The mill-classifier combination is adjustable and operable with a process gas blower, which is responsible for generating the process gas or process air flow through the mill from the mill toward the classifier. This blower is designed to feed the feed material, which has been ground at least once by the mill's grinding rollers, to the classifier of the mill-classifier combination by means of a process air flow, where it is classified into a fine and a coarse fraction. The process gas blower is preferably arranged downstream of the classifier, ideally downstream of a filter for the fines, and creates a negative pressure in the mill-classifier combination. In this case, it is also referred to as negative pressure operation.

[0035] Furthermore, a discharge device for the fine fraction from the processing process is provided as a valuable fraction, in order to add the valuable fraction to a process for further sorting. The discharge device can be, for example, an airtight flap, rotary valve, a sandwich lock, or the like. It is advantageous if the discharge device is designed in such a way that no pressure drop can occur within the mill-sifter combination during discharge. If the mill-sifter combination is operated in negative pressure mode, an inadequate seal of the discharge device would lead to a pressure increase in the mill-safe combination or to the ingress of false air.

[0036] In addition, a semolina discharge and a magnetic separator are provided and configured to feed at least 50% to 250% of the semolina rejected by the classifier of the mill-classifier combination, based on the feed material, to the magnetic separator for dry magnetic separation per unit of time. The semolina discharge can, for example, be a semolina screw designed in the form of a conveyor screw and located below the semolina outlet of the classifier, thus removing semolina that would otherwise fall back onto the grinding table. The amount of semolina can be influenced depending on the rotation speed of the screw. The semolina that is not removed overflows the semolina discharge and falls back onto the grinding table. The semolina can also be removed from the mill via a chute or a downpipe using gravity.In these cases, the mass flow into the chute or downpipe can be adjustable by geometrically varying the feed.

[0037] A non- or poorly magnetizable fraction can be discharged from the system after the magnetic separator, while a magnetizable fraction can be returned to the mill-classifier combination for further comminution. This can be achieved with appropriate material guides. The invention is explained in more detail below using a schematic embodiment with reference to the figures. Herein:

[0038] Fig. 1 is a highly schematic view of a processing plant according to the invention; and

[0039] Fig. 2 is a flow chart illustrating the material flows.

[0040] Fig. 1 shows a highly simplified representation of the processing plant 1 according to the invention in the form of a flowsheet.

[0041] The central element of the processing plant 1 is a mill-classifier combination 10, which consists of a vertical roller mill 12, in particular of the Loesche type, and a classifier 14. The classifier 14 can preferably be arranged directly above the mill 12, so that the mill-classifier combination 10 is provided in a single, common housing. In principle, however, it is also possible to provide the classifier 14 remote from the mill 12 and to implement the mill-classifier combination 10 using appropriate connecting lines. Material crushed by the mill 12 is transported to the classifier 14 via these connections.

[0042] In the embodiment shown here, the separator 14 has two outlets: one for fines 62 and one for coarse material 63. The fines 62 are conveyed by a process air stream downstream of the separator 14 to a filter or dust separator 16, where they are filtered out of the process air stream. This can be, for example, a bag filter or one or more cyclones. In other words, the process air stream is dedusted, i.e., freed of fines, in the filter 16.

[0043] The fine material 62 separated in the filter 16 can be fed to a further sorting device 40. Additionally, a process air blower can be provided directly downstream of the filter 16, which is configured to generate the process air flow and draws process gases such as air through the mill-classifier combination 10.

[0044] The second outlet of the classifier 14 serves to discharge the coarse material 63, also referred to as grit. This is fed to a dry magnetic separator 20. Here, it is sorted into magnetic and non- or only poorly magnetizable components. The non- or poorly magnetizable components, or the corresponding fraction 72, can be discharged from the processing process, whereas the magnetizable fraction 71 is returned to the mill 12 for further comminution.

[0045] In the embodiment shown here, a second magnetic separator circuit is also shown, which can be optionally provided. This circuit is supplied with material via the overflow 65 of the mill 12. The material that falls above the grinding table of the mill 12 and is not carried by the air flow to the classifier 14 falls below the grinding table. From there, it is fed to a dry magnetic separator 21. Here, too, the magnetizable fraction 75 is returned to the mill 12 for further comminution, and the non-magnetizable or only poorly magnetizable fraction 76 is discharged from the processing process.

[0046] In the sense of the invention, “discharging” can be understood in particular to mean that the material is no longer processed further in this process.

[0047] In the following, the sequence of the method according to the invention with the processing plant 1 according to the invention will be discussed in more detail.

[0048] Raw rock containing magnetizable valuable minerals is fed to mill 12 via a feed stream 61. At mill 12, stationary grinding rollers roll on a rotating grinding table and crush the fed material. A large portion of the material, which has been crushed at least once, is conveyed to the separator 14 by means of the process air stream. Another portion falls over the grinding table and is further processed as overflow 65. This overflow can be fed back into the mill or, as shown here, to the magnetic separator 21.

[0049] In the classifier 14, the materials are sorted according to size or mass, distinguishing between a fine fraction 62 and a coarse fraction 63. The coarse fraction 63, also referred to as the classified grit, is fed to the magnetic separator 20. It is not absolutely necessary for the entire coarse fraction to be fed to the magnetic separator 2020. However, it is generally advantageous to feed as large a portion of the grit as possible to the magnetic separator 20 for further sorting. In the magnetic separator 20, sorting according to magnetic susceptibility is carried out, whereby a distinction is made between non-magnetizable or only poorly magnetizable materials 72 and a corresponding fraction of, at least better, magnetizable materials 71.

[0050] The non- or poorly magnetizable fraction 72 contains no or only a very small proportion of magnetizable valuable materials. Therefore, it can be removed from the processing process at this point, resulting in a higher proportion of valuable materials in the fine grain 62 discharged from the separator for further processing.

[0051] In a similar manner, the overflow 65 can also be fed to the magnetic separator 21. Here, too, sorting according to magnetizability takes place, whereby a fraction 76 that is non-magnetizable or only slightly magnetizable can again be removed from the processing process. This fraction 76 also contains very little or no valuable minerals, which leads to a percentage enrichment of the valuable minerals in the fine product 62 after further comminution.

[0052] The fine product 62 itself, as previously explained, is separated from the process air stream in the filter 16 and subjected to further sorting and processing. This may, for example, involve dry or wet sorting, such as magnetic separation.

[0053] The fine grain 62 can have a diameter between D80 = 30 pm and 150 pm, and the coarse grain 63 a diameter of D80 = 200 pm and 1,500 pm. The corresponding diameters can be adjusted using the geometry and rotation speed of a dynamic classifier. Likewise, the separation limit of the classifier can be influenced by the process air flow. This also ensures that material is present as overflow or the amount of overflow material, since this material is not carried by the process air flow to the separator 14.

[0054] The following describes the existing material flows in more detail with reference to Fig. 2. This is done in particular to explain that an internal circulation system exists within the mill-classifier combination in which the ground material accumulates. The material flows indicated in Fig. 2 refer to t per hour. In the embodiment shown in Fig. 2, the second magnetic separation of the overflow is omitted. This is done for reasons of clarity.

[0055] 750 t of feed material are fed into the mill-classifier combination 10. This material is crushed in the mill-classifier combination 10, as already described. During operation of the plant arrangement 1 according to the invention, more material accumulates in the internal circuit. It should be noted that the product quantities shown here only occur during ongoing operation and not during the start-up phase.

[0056] In the embodiment shown here, 75 t are returned to the grinding circuit as overflow 65. On the other hand, a total of 1,125 t are discharged from the grinding circuit as coarse material 63 and fed to the magnetic separator 20. In this separator, 75 t of non- or hard-to-magnetize material 72 are removed from the processing process, and the remaining material, in the form of magnetizable material 71, is returned to the mill-classifier combination 10 in a quantity of 1,050 t. This means that a total of 1,875 t is fed into the internal circuit of the mill-classifier combination 10.

[0057] As can be seen from this illustration, it is possible to remove a proportion of more than 100% of the feed material as coarse material 63 from the grinding circuit and feed it to the dry magnetic separation in the magnetic separator 20. In the example shown here, 150% of the feed material is used.

[0058] Using the method and plant configuration according to the invention, it is thus possible to process rock containing magnetizable valuable minerals efficiently and without significant water consumption. This method is particularly suitable for materials with a low content of valuable minerals.

Claims

PATENT CLAIMS 1 Method for processing rock containing magnetizable valuable minerals as the material to be extracted, wherein the ratio between rock and pure element to be extracted in the material to be extracted is 0.2 mass% to 50 mass%, • wherein the rock to be processed is fed as feed material with a grain size of less than 200 mm in diameter to a mill-classifier combination (10) for comminution, • wherein the mill-classifier combination (10) comprises a vertical roller mill as mill (12), • wherein the mill-classifier combination (10) is set and operated to feed feed material (61) comminuted at least once by the grinding rollers of the mill (12) to the classifier (14) of the mill-classifier combination (10) by means of a process air stream and to classify it there into a fine and a coarse fraction, • whereby the fine fraction is discharged from the processing process as a valuable fraction and is fed to a process for further sorting (40), • wherein at least per unit of time a proportion of 50% to 250%, based on the feed material (61) per unit of time, of the coarse material rejected by the classifier (14) is fed to a dry magnetic separation in a magnetic separator (20), • wherein a non- or hardly magnetizable fraction (72) is discharged from the processing process as gangue and a magnetizable fraction (71) is fed back to the mill of the mill-classifier combination (10) for further comminution.

2. Method according to claim 1, characterized in that the magnetic separator (20) is adjusted and operated in such a way that the non- or hardly magnetizable fraction (72) has less than 5 mass% of pure element to be recovered.

3. Method according to one of claims 1 or 2, characterized in that the mill-classifier combination (10), in particular the classifier (14), is adjusted and operated such that the fine material fraction has a diameter of Dso = 30 pm to 150 pm.

4. Method according to one of claims 1 to 3, characterized in that the mill-classifier combination (10), in particular the classifier (14), is adjusted and operated such that the coarse material rejected by the classifier (14) has a diameter of Dso = 200 pm to 1,500 pm.

5. Method according to one of claims 1 to 4, characterized in that the mill-classifier combination (10) is adjusted and operated in such a way that a grinding table overflow (65) is present.

6. The method according to claim 5, characterized in that the grinding table overflow (65) is fed to a dry magnetic sorting in a further magnetic separator (21), wherein a non- or hardly magnetizable fraction (76) is discharged from the processing process as further gangue, and a magnetizable fraction (75) of the mill (12) of the mill-classifier combination (10) is fed for further comminution.

7. Method according to one of claims 1 to 6, characterized in that the magnetizable valuable minerals are iron minerals, in particular magnetite or hematite.

8. Method according to one of claims 1 to 7, characterized in that the process for further sorting (40), to which the fine fraction discharged from the processing process is fed, is a dry or wet sorting, in particular flotation.

9. Method according to one of claims 1 to 8, characterized in that the mill-classifier combination (10) and the magnetic separator(s) (20) are adjusted and operated in such a way that the fraction discharged as gangue amounts to between 10 mass% and 70 mass% of the feed material (61).

10. Method according to one of claims 1 to 9, characterized in that the mill (12) is provided with a working pressure of the grinding rollers between 600 kN / m 2 and 2400 kN / m 2 , based on the vertically projected area of ​​the mean roll diameter.

11. Method according to one of claims 1 to 10, characterized in that the mill-classifier combination (10) is operated with a process air flow of 0.8 kg to 5 kg of air per unit of time per kg of discharged fine fraction per unit of time.

12. Method according to one of claims 1 to 11, characterized in that the mill (12) is provided with a dam edge with a height which is 0.8% to 5.0% of the diameter of the grinding table of the mill (12).

3. Processing plant for processing rock comprising magnetizable valuable minerals as material to be extracted, wherein the ratio between rock and pure element to be extracted is 0.2 mass% to 50 mass%, with a mill-classifier combination (10) which has a vertical roller mill as mill (12) for comminuting rock to be processed as feed material with a grain size having a diameter of less than 200 mm, wherein the mill-classifier combination (10) and a process blower are adjustable and operable to feed feed material which has been crushed at least once by the grinding rollers of the mill (12) to the classifier (14) of the mill-classifier combination (10) by means of a process air flow and to classify it there into a fine and a coarse fraction, wherein a discharge device for the fine fraction from the processing process is provided as a valuable fraction in order to feed the valuable fraction to a process for further sorting (40)wherein a grit take-off and a magnetic separator (20) are provided and arranged to feed at least per unit of time a proportion of 50% to 250%, based on the feed material (61) fed in per unit of time, of the grit (63) rejected by the classifier (14) of the mill-classifier combination (10) to the magnetic separator (20) for dry magnetic separation, wherein a non- or hardly magnetizable fraction (72) can be discharged from the processing plant after the magnetic separator (20) and a magnetizable fraction (71) can be fed back to the mill (12) of the mill-classifier combination (10) for further comminution.

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