OA22237A - Method and preparation system for preparing rocks - Google Patents

Abstract

The invention relates to a method for processing rock containing magnetisable valuable minerals, wherein the rock to be processed is fed as feed material with a grain with a diameter of less than 200 mm to a mill-sifter combination for comminution. Here, the mill-sifter combination is implemented 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 by means of a process air stream to the sifter of the mill-sifter combination and is separated there into a fine fraction and a coarse fraction. The fine fraction is discharged from the processing process as a valuable fraction and fed to a process for further sorting. Furthermore, it is provided that at least per unit of time, a proportion of 50% to 250%, relative to the feed material fed per unit of time of the coarse material rejected by the sifter is fed to a dry magnetic separation, wherein a non-magnetisable or difficult-to-magnetise fraction is discharged from the processing process as gangue and a magnetisable fraction is fed to the mill of the millsifter combination for further comminution. The invention also relates to a processing plant for carrying out the method according to the invention.

Description

METHOD AND PREPARATION SYSTEM FOR PREPAR1NO ROCKS

The invention relates to a method for processing rocks containing magnétisable valuable minerais as material to be extracted. The ratio between the rock and the pure material to be extracted in the rock is between 0.2 mass % and 50 mass %, preferably between 0.5 mass % and 40 mass %, and even more advantageously between 5 mass % and 30 mass %. The pure materials to be extracted may be, for example, iron, nickel or copper, in the above ratio, particularly in elemental form. In the case of iron, the proportion of pure material to be extracted in the rock may be between 10 mass % and 50 mass %, preferably between 12.5 mass % and 40 mass %, and for copper between 0.2 mass % and 7 mass %, preferably between 0.3 mass % and 2.0 mass %. The valuable minerais contain most of the iron and copper in the form of oxides or other compounds, which are largely intergrown with the other components of the rock. In copper minerais, copper pyrite is the most important valuable minerai, which are compounds with sulphur known as sulphidic copper minerais. The invention also relates to a processing plant for carrying out the method according to the invention.

Depending on the rock deposits, the rock contains varying proportions of valuable materials. The part of the rock that does not contain any valuable materials is referred to as gangue or waste rock.

For reasons of efficiency, deposits with a high percentage of valuable minerais as to mine material in the mined rock are primarily exploited. However, those deposits that are more easily accessible hâve now been exhausted, so that deposits with a less favourable ratio of rock to recoverable pure material are increasingly being exploited, for example in the case of iron in the range of 12.5 mass % to 35 mass % and copper in the range of 0.3 mass % to 2.0 mass %. The exploitation of these deposits low in valuable materials is naturally much more costintensive.

Conventionally, such processing methods, in particular the sorting and séparation of the rock into valuable minerais and gangue or waste material, are often carried out by means of very fine comminution, which séparâtes the valuable minerais from the gangue, followed by sorting, in the case of iron ores by means of magnetic séparation and subséquent wet flotation, in the case of copper or nickel ores by means of wet flotation and corresponding upstream and downstream

-2processes. However, the high energy requirement for the very fine comminution, the high water consumption for wet flotation and the energy required to subsequently dry the processed material are disadvantages.

The invention therefore addresses the obj ect of providing a process and a processing plant that can be efficiently carried out and operated.

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

Advantageous embodiments of the invention are explained in more detail in the dépendent claims, in the description and with reference to the figures.

According to the method of the invention, it is intended that the rock to be processed is fed as feed material with a grain diameter of less than 200 mm, preferably less than 150 mm, to a mil 1sifter combination for comminution. Here, the mill-sifter combination has a vertical roller mill, especially of the Loesche type, as the mill. The initial grain size can be produced, for example, by means of crushers.

The mill-sifter combination is set up and operated so that feed material comminuted at least once by grinding rollers of the mill is fed by means of a process air stream to the sifter of the mill-sifter combination, where it is separated into a fine fraction and a coarse fraction. The mill is therefore operated in air stream mode.

The fine fraction screened by the sifter is discharged from the processing process as a valuable fraction in accordance with the method of the invention and fed to a further sorting process for sorting. Here, the material is sorted into valuable materials as recoverable material and gangue.

Furthermore, per unit of time, a proportion of 50% to 250% of the coarse material rejected by the sifter, relative to the feed material per unit of time, is fed into a magnetic separator for dry magnetic séparation. The coarse material is also referred to as grit. During magnetic séparation, a non-magnetic or difficult-to-magnetise fraction from the processing process is discharged as gangue and a magnétisable fraction is fed back to the mill of the mill-sifter combination for further comminution. This can be done together with the feed material or separately. Feeding can preferably take place in the middle, in the centre or in the middle area of the grinding dise.

-3A basic idea of the method according to the invention can be seen in the fact that it enables magnétisable valuable materials in the fine material to be enriched in comparison to the feed material, in particular in percentage terms. This is achieved by removing gangue from the total material flow by means of magnetic séparation during the grinding and processing process. This no longer needs to be further comminuted, which in tum saves energy. The coarse material rejected by the sifter can be removed for magnetic séparation, which is located preferably outside the mill-sifter combination, by means of a grit screw, for example, which removes at least a part of the coarse material, also known as grit, from the sifter. However, the grit can also be removed from the mill by gravity, for example via a chute or a downpipe.

Due to the enrichment of valuable minerais in the fine material, which is further processed, the subséquent sorting into valuable minerais 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-magnetic or difficult-to-magnetise fraction. If, for example, 80% of the valuable minerais in the material fed into this sorting process are recovered by means of downstream sorting, a significantly higher proportion of valuable minerais can be recovered with the same effort if the material fed in already contains a higher proportion of valuable materials.

Using the method according to the invention, the proportion of pure element to be recovered can thus be increased from 20 mass % to 35 mass % for example, depending, in particular on the initial proportion and degree of intermingling.

As explained, the proportion of coarse material extracted per unit of time is between 50% and 250% related to the feed material per unit of time. The corresponding mass tlows are explained in more detail later with référencé to Figure 2.

When the mill-sifter combination is in operation, the material to be comminuted circulâtes, also known as internai circulation, until the desired fineness is achieved. This means, for example, that in a classic mill-sifter combination, if 10 tonnes per hour are fed into the mill, only after a run-in period will 10 tonnes of fine material per hour be removed from the sifter once the internai circulation has stabilised in terms of quantity. This process can take up to 3 hours.

The background to this is that the process air flow, the resulting turbulence and the movements of the grinding rollers, which roll onto a rotating grinding plate, cause a large quantity of feed

-4material, some of which has already been comminuted but also not yet sufficiently comminuted, to remain inside the housing of the mill-sifter combination. This is difficult to measure in ternis of quantity. In general, technical literature assumes that the internai circulation is 3 to 10 times of the feed material per unit of time, depending on the grindability as well as the desired target product fineness. In other words, this means that quantitatively between 300% and 1,000% of the feed material per unit of time is inside the mill.

For this reason, it is also possible to remove the 50% to 250% of mass of the feed material described above as coarse material from the processing process.

The magnetic separator is preferably set up and operated so that the non-magnetic or difficultto-magnetise fraction accounts for less than 5 mass % of the pure material to be recovered, particularly in relation to the elemental form. The proportion of pure material to be recovered dépends largely on the degree of intergrowth of the valuable minerai with the other components of the rock.

In order to avoid removing too much valuable material from the process by means of magnetic séparation, it is provided that the magnetic separator is to be set up and operated in such a way that a maximum of 5 mass % of the pure material to be recovered is discharged in the gangue at this point. Ideally, the proportion should be even lower. However, if too little gangue is discharged, the effïciency of the process is reduced. The adjustment variables for the magnetic separator can be the strength of the magnetic field, the conveying speed or the geometry of the magnetic separator, either individually or in any combination with each other.

It is advantageous if the mill-sifter combination, in particular the sifter, which may be a dynamic sifter, is set up and operated in such a way that the fine material fraction has a diameter of Dso= 30 pm to 150 pm, preferably Dso⁼ 30 pm to 100 pm. The fine material is fed to further sorting as described above. For this reason, it is advantageous if the fine material fraction has a sufficiently high fineness so that the sorting can be carried out as well as possible. For this purpose, the rock is comminuted in such a way that a séparation or respectively a breakdown between waste rock and valuable minerais is achieved. In other words, intergrowths or agglomérations are broken up by this fine grinding.

-5The désignation Dso= 30 pm defines a fineness at which 80% of the ground material has a diameter less than or equal to 30 pm. This can be analysed using a sieve sample, for example. Such values are much more suitable for comminution and/or screening processes than absolute values, as the dynamic processes during the grinding and screening process resuit in a particle size distribution that does not hâve any sharp séparation limits.

The mill-sifter combination, in particular the sifter, which, as already described. can be a dynamic sifter, is advantageously set up and operated so that the coarse material rejected by the sifter 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 has a good degree of libération of the valuable minerais, so that dry magnetic séparation can be used to achieve good séparation between gangue and valuable material. This also allows a signif'icant proportion to be removed, making the process efficient and less energy-intensive.

The desired fineness of both the fine material and the coarse material can be influenced, for example in dynamic sifters, by the exact geometry of the sifter on the one hand. On the other hand. the rotational speed of the sifter rotor can also influence the fineness. A higher rotational speed so results in shifting the séparation limit towards the fine grain. Other variables that influence the fineness, but above ail the amount of material being fed to the sifter, are the quantity or speed of the process air flow through the mill-sifter combination or the working pressure of the grinding rollers.

In principle, even higher finenesses for the fine and coarse material would lead to even better results, but this would entail significantly higher energy requirements during grinding. In accordance with the invention, the values given here are to be seen as a compromise between a high degree of pulvérisation and thus a high purity of the fine material, in particular the valuable minerais in the fine material, and the energy required for this.

As already explained, the mill-sifter combination is operated, in particular in air flow mode, in which an air flow streams around the grinding dise in the direction of the sifter arranged above the mill.

In addition, the mill-sifter combination can also be set up and operated in such a way that there is a grinding dise overflow. This means that during the grinding process, material falling from

-6the grinding dise is of such a size that it cannot be transported by the process air flow towards the sifter but falls downwards over the grinding dise against the process air flow.

This material falling over the edge of the grinding dise is referred to as grinding dise overflow. This material can also be fed to further dry magnetic sorting, for example in a magnetic separator. However, another magnetic separator or the magnetic separator already used for the coarse material can also be used for this purpose. In the magnetic separator, a non-magnetic or difficult-to-magnetise fraction from the processing process can be discharged as further gangue and a magnétisable fraction can be fed to the mill-sifter combination for further comminution. This additional magnetic séparation allows further gangue to be removed from the processing process, so that less energy is required for the comminution of gangue, on the one hand and the fine material has an still higher purity, on the other hand. Purity in the sense of the invention can be understood to mean that the proportion of valuable minerais to be recovered from the material under considération is as high as possible.

In principle, the method according to the invention is suitable for any valuable materials that are magnétisable. It is particularly advantageous for iron materials, especially magnetite or hématite, as these hâve good magnetisability. However, it can also be used on valuable minerais containing copper or nickel. The invention is also applicable to rocks that contain valuable minerais from the rare earth element class.

As explained, the fine material fraction separated out during the processing process is subjected to further sorting. Various sorting methods can be used for this purpose. Examples for this are dry or wet sorting. Wet sorting may involve wet magnetic séparation, sometimes followed by Rotation. An example of dry sorting can be a further air classification, provided that there are présent significant différences in mass or density between the gangue and the valuable minerai.

It is préférable if the mill-sifter combination and the magnetic separator(s) are set up and operated in an according way that the fraction discharged as gangue accounts for between 10 mass % and 70 mass % of the feed material. A higher percentage is preferred here, as any feed material discharged as gangue no longer needs to be subjected to further sorting of the fine fraction. This also reduces the grinding effort and wear costs, as the discharged gangue is not further comminuted. Parameters for setting this size include, for example, the sorting limït of

-7 the magnetic separator used and, in this context, also the fineness of the coarse material being fed to the magnetic sifter.

Advantageously, the mill-sifter combination is operated with a process air flow that amount to 0.8 kg to 5 kg of process gas per unit of time per kg of fine fraction discharged per unit of time. It has been shown that such a process air flow is particularly suitable for producing the finenesses described above and enabling a still more energy-efficient operation. The process gas can be ambient air or also other gases.

The unit kg of air per unit of time per kg of fine fraction discharged per unit of time is preferred because it is independent of the exact volume and géométrie design of the housing of the millsifter combination and the density of the process gas. When specifying by volume, the geometry, in particular the volume of the mill-sifter combination, such as narrow points where there is présent a higher flow velocity, plays a décisive rôle.

According to the invention, it is preferred that the mill-sifter combination is arranged in a common housing and that the sifter is located in particular above the mill with the grinding rollers. These grinding rollers can be designed, in particular stationary, wherein they are mounted so that they can rotate, so that they can be set in rotation about their axis by rotation of the grinding plate over the feed material to be ground. In principle, additional drive of the grinding rollers themselves is also possible.

It is advantageous if the mill is operated with a working pressure of the grinding rollers between 600 kN per m² and 2,400 kN per m², preferably 900 kN per m² and 2,200 kN per m², based on the vertical projected area of the average roller diameter. The working pressure of the grinding rollers can, on the one hand, be generated by their own weight. On the other hand, a hydraulic System can be used to apply additional pressure to the grinding bed via the grinding rollers and via the grinding roller suspension. The higher the pressure is, the finer the material is comminuted, although it shouid be noted that this may resuit in increased energy consumption. The most efficient choice of the grinding pressure may also vary from material to material, as in addition to pure pressure-based comminuted, shear forces are also at work for comminuting.

As shown, the mill-sifter combination can also be operated in a combined air flow and overflow mode. In general, but also specifically in this context, it is possible to provide a rétention rim at

-8the edge of the grinding dise. Its height can be used to influence the height of the grinding bed and thus also the comminution of the material to be ground located on the grinding bed. The height of the rétention rim or retaining edge of the grinding dise is preferably between 0.8% and 5.0%, in particular up to 3.5% of the diameter of the grinding dise of the mill. This dimensioning of the retaining edge ensures sufficiently fine comminution of the feed material and also takes into account optimisation of the energy requirement necessary for this.

Furthermore, the invention relates to a processing plant for processing rock containing magnétisable valuable minerais as the material to be extracted, in particular according to the method of the invention. Here, the ratio between rock and pure material to be extracted is 0.2 mass % to 50 mass %. The processing plant has a mill-sifter combination, which has a vertical roller mill as a 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.

The mill-sifter combination is adjustable and opérable with a provided process gas blower, which is responsible for generating the process gas or respectively process air flow through the mill from the mill towards the sifter, in order to feed the feed material comminuted at least once by the grinding rollers of the mill to the sifter of the mill-sifter combination by means of a process air flow and to classify it there into a fine and a coarse fraction.

The process gas blower is preferably arranged after the sifter, ideally after a filter for the fine grains, and generates a négative pressure in the mill-sifter combination. In this case, it is also referred to négative pressure operation.

Furthermore, a discharge device is provided for the fine fraction from the processing process as a valuable fraction in order to feed the valuable fraction to a process for further sorting. The discharge device can be, for example, an airtight flap, rotary valves, a sandwich valve 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 under négative pressure, insufficient sealing of the discharge device would lead to a pressure increase in the mill-sifter combination or respectively to a false air ingress.

In addition, a grit extractor and a magnetic separator are provided and set up to feed at least 50% to 250% of the grits per unit of time, relative to the feed material per unit of time rejected

-9by the sifter of the mill-sifter combination, to the magnetic separator for dry magnetic séparation. The grit extractor may, for example, be a grit screw, which is designed in the form of a screw conveyor and is arranged below the grit outlet of the sifter and so can extract grit that would otherwise fall back onto the grinding dise. The amount of grit can be influenced by the rotational speed of the screw. The grits that are not extracted flows over the grit extractor and falls back onto the grinding dise. The grit can also be extracted from the mill by gravity via a chute or a downpipe. In these cases, the mass flow into the chute or respectively downpipe can be designed adjustable by varying the geometry of the feed.

A non-magnetisable or difficult-to-magnetise fraction can be discharged from the System after the magnetic separator, wherein a magnétisable fraction can be fed again to the mill-sifter combination for further comminution. This can be achîeved with appropriate material guides.

The invention is explained in more detail below with référencé to a schematic exemplary embodiment with référencé to the figures. Here show:

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

Fig. 2 a flow diagram for illustrating the material flows.

Fig. 1 shows a highly simplified représentation of the processing plant 1 according to the invention in the form of a flow sheet.

A mill-sifter combination 10 is provided as the central element of the processing plant 1 and consists of a vertical roller mill 12, in particular ofthe Loesche type, and a sifter 14. The sifter 14 can preferably be arranged directly above the mill 12, so that the mill-sifter combination 10 is provided in a single common housing. In principle, however, it is also possible to provide the sifter 14 remote from the mill 12 and to réalisé the mill-sifter combination 10 by means of appropriate connecting lines. The material comminuted by the mill 12 is conveyed from the mill 12 to the sifter 14 via these connections.

In the embodiment shown here, the sifter 14 has two outlets. One for fine material 62 and one for coarse material 63. The fine material 62 is conveyed with a process air stream after the sifter 14 to a filter or dust separator 16, where it is filtered out of the process air stream. This may be,

- 10for example, a bag filter or one or more cyclones. In other words, the process air stream is dedusted in the filter 16, i.e. freed from fine material.

The fine material 62 separated in the filter 16 can be fed to a further sorting process 40. In addition, a process air blower may be provided directly after the filter 16, which is designed to generate the process air stream and suck process gases such as air through the mill-sifter combination 10.

The second outlet of the sifter 14 is used to discharge the coarse material 63, which is also referred to as sifter grit. This is fed to a dry magnetic separator 20. Here, the material is sorted according to magnetic and non-magnetic or only difficult-to-magnetise components. The nonmagnetic or difficult-to-magnetise components, or respectively the corresponding fraction 72, can be discharged from the processing procedure, whereas the magnetic fraction 71 is retumed to the mill 12 and subjected to further coinminution.

In the embodiment shown here, a second magnetic separator circuit is also shown, which can be provided as an option. This is supplied with material by means ofthe overflow 65 ofthe mill 12. The material that falls beyond the grinding dise of the mill 12 and is not carried by the air stream to the sifter 14 falls below the grinding dise. From there, it is fed to a dry magnetic separator 21. Here too, the magnétisable fraction 75 is retumed to the mill 12 again for further comminution and the non-magnetisable or only difficult-to-magnetise fraction 76 is discharged from the processing process.

The term discharged within the meaning of the invention, it is understood in particular to mean that the material is no longer further processed in this process.

The following section describes the sequence of the method according to the invention using the processing plant 1 according to the invention in more detail.

Raw rock containing magnétisable valuable minerais is fed into the mill 12 with a feed stream 61. In the mill 12, stationary grinding rollers roll on a rotatîng grinding plate and comminute the feed material to be ground. The process air flow conveys most of the ground material, which has been comminuted at least once, to the sifter 14. Another part falls over the grinding plate

- 11 and is further processed as overflow 65. This can be fed back again to the mill or, as shown here, to the magnetic separator 21.

In the sîfter 14, the material is classified according to size or respectively mass, wherein a fine fraction 62 and a coarse fraction 63 are separated. The coarse fraction 63, also known as sifter grit, is fed to the magnetic separator 20. In this connection, it is not absolutely necessary for the entire coarse fraction to be fed to the magnetic separator 20. However, it is generally advantageous to feed as much of the grit as possible to the magnetic separator 20 for a further sorting process. In the magnetic separator 20, sorting is carried out according to magnetic susceptibility, whereby a distinction is made between non-magnetic or only difficult-tomagnetise materials 72 and respectively a corresponding fraction of at least more easily-tomagnetise materials 71.

The non-magnetic or only diffïcult-to-magnetise fraction 72 contains no or only a very small proportion of magnetic valuable materials. It can therefore already be removed from the processing process at this point, which means that the fine grain 62 that is discharged from the sifter and fed into further processing has a higher proportion of valuable materials.

In analogue way, the overflow 65 can also be fed to the magnetic separator 21. Here, too, sorting according to magnetisability takes place, wherein a fraction 76 that is non-magnetisable or only difficult-to-magnetise can again be discharged from the processing procedure. This fraction 76 also has a very low or no proportion of valuable minerais again, which leads to a percentage increase in the valuable minerais in the fine product 62 after further comminution.

As explained above, the fine product 62 itself is separated from the process air stream in the filter 16 and fed to further sorting and processing. This may involve, for example, dry or wet sorting, such as magnetic séparation.

The fine grain 62 can hâve a diameter between D80 = 30 pm and 150 pm, while the coarse material 63 can hâve a diameter of D80 = 200 pm to 1,500 pm. The corresponding diameters can be set using the geometry and the rotational speed in a dynamic sifter. The séparation limit of the sifter can also be influenced by the process air flow. This also ensures that material is available as overflow or respectively the quantity of overflow material, as this material is not carried by the process air flow to the sifter 14.

-12The following section refers to Fig. 2 and discusses the existing material flows in more detail. This is done, in particular to explain that there is an internai circulation within the mill-sifter combination in which the ground material accumulâtes.

The material flows shown in Fig. 2 refer to t per hour. In the design shown in Fig. 2, the second magnetic séparation of the overflow is omitted. This is done for reasons of clarity.

750 tonnes of feed material are fed into the mill-sifter combination 10. This is comminuted in the mill-sifter combination 10 as already described. During operation of the plant arrangement 1 according to the invention, more material accumulâtes in the internai circuit. Here, it should be noted that the product quantities shown here only occur during operation and not in the startup phase.

In the embodiment shown here, 75 t are fed again 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, 75 tonnes of non-magnetic or difficult-to-magnetise material 72 are discharged from the préparation process and the remaining material in the form of magnétisable material 71 in a quantity of 1,050 tonnes is fed back again into the mill-sifter combination 10. This means that a total of 1,875 tonnes are fed into the internai circuit of the mill-sifter combination 10.

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

Using the method and respectively the plant arrangement according to the invention, it is thus possible to process rock containing magnétisable valuable minerais efficiently and without significant use of water. This method is particularly suitable for materials with a low proportion of valuable minerais.

Claims (12)

1. l. Method for processing rock containing magnétisable valuable minerais as the material to be extracted, wherein the ratio between rock and the 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 with a diameter of less than 200 mm to a mill-sifter combination (10) for comminution, • wherein the mill-sifter combination (10) comprises a vertical roller mill as the mill (12), • wherein the mill-sifter combination (10) is set up and operated so as to supply feed material (61) comminuted at least once by the grinding rollers of the mill (12) by means of a process air stream to the sifter (14) of the mill-sifter combination (10) and to sift it there into a fine fraction and a coarse fraction, • wherein the fine fraction is discharged from the processing process as a valuable fraction and 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) fed per unit of time, of the coarse material rejected by the sifter (14) is fed to a dry magnetic séparation in a magnetic separator (20), • wherein a non-magnetisable or difficult-to-magnetise fraction (72) is discharged from the processing process as gangue and a magnétisable fraction (71) is fed again to the mill of the mill-sifter combination (10) for further comminution, and • wherein the mill ( 12) can be operated with a working pressure of the grinding rollers between 600 kN/m² and 2,400 kN/m², based on the vertical projected area of the average roller diameter.
2. 2. Method according to claim 1, characterised in that the magnetic separator (20) is set up and operated in such a way that the non-magnetisable or difficult-to-magnetise fraction (72) comprises less than 5 mass % of the pure element to be recovered.
3. 3. Method according to any one of daims 1 or 2, characterised in that the mill-sifter combination (10), in particular the sifter (14), is set up and operated in such a way that the fine material fraction has a diameter of Dso ⁼ 30 pm to 150 pm.
4. 4. Method according to any one of daims 1 to 3, characterised in that the mill-sifter combination (10), in particular the sifter (14), is set up and operated such that the coarse material rejected by the sifter (14) has a diameter of Dso = 200 pm to 1,500 pm.
5. 5. Method according to any one of daims 1 to 4, characterised in that the mill-sifter combination (10) is set up and operated in such a way that a grinding dise overflow (65) is provided.
6. 6. Method according to daim 5, characterised in that the mill plate overflow (65) is fed to a dry magnetic sorting in a further magnetic separator (21 ) for, wherein a non-magnetisable or difficult-to-magnetise fraction (76) is discharged from the processing process as further gangue, and a magnétisable fraction (75) is fed to the mill (12) of the mill-sifter combination (10) for further comminution.
7. 7. Method according to any one of daims 1 to 6,

   -15characterised in that the magnétisable valuable minerais are iron minerais, in particular magnetite or hématite.
8. 8. Method according to any one of daims 1 to 7, characterised in that the process for further sorting (40), to which the fine fraction discharged from the processing process is fed, is dry or wet sorting process, in particular flotation.
9. 9. Method according to any one of daims 1 to 8, characterised in that the mill-sifter combination (10) and the magnetic sifter(s) (20) are set up and operated in such a way that the fraction discharged as gangue comprises between 10 mass % and 70 mass % of the feed material (61).
10. 10. Method according to any one of daims 1 to 9, characterised in that the mill-sifter 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 fine fraction discharged per unit of time.
11. 11. Method according to any one of daims 1 to 10, characterised in that the mill (12) is provided with a retaining edge with a height of 0.8% to 5.0% of the diameter of the grinding dise of the mill (12).
12. 12. Processing plant for processing rock containing magnétisable valuable minerais as material to be extracted, wherein the ratio between rock and pure element to be extracted is 0.2 mass % to 50 mass %,

    - 16with a mill-sifter combination (10) comprising a vertical roller mill as the mill (12) for comminuting rock to be processed as feed material with a grain with a diameter of less than 200 mm, wherein the mill-sifter combination (10) and a process blower are adjustable and opérable to feed the feed material comminuted at least once by the grinding rollers of the mill ( 12) by means of a process air flow to the sifter (14) of the mill-sifter combination (10) and to classify it there into a fine fraction and a coarse fraction, wherein an ejector device is provided for the fine fraction from the processing process as a valuable fraction in order to feed the valuable fraction to a process for further sorting (40), wherein a grit removal device and a magnetic separator (20) are provided and configured to feed, at least per unit of time, a proportion of 50% to 250%, based on the feed material (61 ) fed per unit of time, of the grit (63) rejected by the sifter (14) of the mill-sifter combination (10) to the magnetic separator (20) for dry magnetic séparation, wherein a non-magnetisable or difficult-to-magnetise fraction (72) can be discharged from the processing plant after the magnetic separator (20) and a magnétisable fraction (71) can be fed again to the mill (12) of the mill-sifter combination (10) for further comminution, and wherein the mill (12) can be operated with a working pressure of the grinding rollers between 600 kN/m² and 2,400 kN/m², based on the vertical projected area of the average roller diameter.