Magnetic matrix, high intensity magnetic separator and method of adjusting the magnetic field generated within such separator

Abstract

Disclosed is a magnetic matrix (6) for a high-intensity magnetic separator (1), com- prising a series of magnetizable material plates (21) provided with longitudinal grooves in at least one of its two faces, the grooved plates (21) being housed lined up and with a spacing distance (18) between them within a housing, and further com- prising at least a magnetic shim (14) disposed within the housing, lined up with the grooved plates (21), these matrices (6) being used in a magnetic separator (1) comprising at least one pair of magnetic poles (3) and at least one rotor (4) to which are connected a plurality of these magnetic matrices (6) within which flows an ore pulp fed to said magnetic separator (1), wherein the magnetizable material plate (21) and the mag- netic shim (14) are magnetized by the poles (3) as the rotor (4) rotates.

Description

1 Specification of the Patent of Invention for "MAGNETIC MATRIX, HIGH INTENSITY MAGNETIC SEPARATOR AND METHOD OF ADJUSTING THE MAGNETIC FIELD GENERATED WITHIN SUCH SEPARATOR".

[001] The invention relates to a magnetic matrix for a magnetic high- intensity separator used in recovering ore particles from tailings generated in the mining process, avoiding environmental damage due to their storage in dams. This magnetic matrix has a structure such that it allows for a very high magnetic field of about 18,000 Gauss, being generated by the magnetic sep- arator in the magnetic matrix, substantially increasing its ability to extract ore particles from the tailings. Description of the Prior Art

[002] In the mining process the ore, in the way it is extracted from mines, is mixed with impurities, clay and / or sand. This ore should be purified in order to increase the iron ore content and raise its added value. Prior to being purified, the ore is sieved with water and is transformed into a pulp, which then is fed to the separator magnetic matrices.

[003] Already known from the prior art are magnetic separators used in the magnetic concentration process for separating magnetic particles mixed in the pulp, thus obtaining a good quality product. These separators combine effectiveness and practicality, being used in the separation of magnetic min- eral fines and non-magnetic minerals. Examples of magnetic separators are described in documents US 3830367 and CA 717830.

[004] Within these magnetic separators are arranged magnetic matri- ces comprised of magnetizable metal plates, provided with longitudinal grooves over its entire surface, on both faces. Each matrix has several plates arranged vertically and parallel to each other, face to face, forming channels between the grooves of neighboring plates, which are traversed by the ore pulp. The grooves have the shape of triangles in which external vertexes concentrate the lines of force and generate the high magnetic field. The grooved plates are spaced apart by spacers which keep the vertices of the triangles of the opposing plate grooves at a defined distance. This spacing between the opposite vertices defining the matrix opening, in mm, through which the ore pulp to be separated and in technical language used in high intensity magnetic separation is called "Gap".

[005] The Gap or spacing between the grooved plates defines the air gap by which the lines of force of the magnetic field must pass and is, there- fore, a key factor to be defined to carry out the magnetic separation process, because it depends on the magnetic field strength which can be generated. The Gap also defines the maximum size of the mineral particles that can pass through the matrix. Typically Gaps are available in some typical dimen- sions, for example, 1.5; 2.0; 2.5; 3.0; 3.2; 3.8, reaching sometimes up to 5.0 mm.

[006] These matrices are magnetized by induction through the magnet- ic poles of the separators. Due to the magnetic field induced by the poles of the magnetizable particles of the ore pulp poured onto the magnetic matrices are stuck together on the plates of in these matrices, while the tailings con- taining non-magnetic particles pass through the channels formed between the grooves and are diverted to a tailings outlet.

[007] Nowadays, technologies of wet high intensity magnetic field sep- aration (WHIMS) require the separation to be made in very narrow channels or openings as a condition to be able to produce high magnetic fields and high magnetic gradients. The depletion of mineral resources and the reuse of tailings are increasing the demand for processing increasingly fine minerals and requiring increasingly high magnetic fields and gradients, thus causing even more, the reduction of the openings of magnetic matrices where parti- cles must pass to be separated.

[800] In the known magnetic separators, the maximum magnetic field strength has a practical limit of about 15,000 Gauss obtained by using the Gap of 1.5 mm. However, this intensity limitation of the field prevents the magnetic separation of some ore particles contained in the pulp that only generate products in magnetic fields in excess of 15,000 Gauss, because of ultrafine particle size and its low magnetic susceptibility by as a result of its prior processing in various field strengths. Consequently, these magnetic par- ticles that have commercial value end up getting stored in tailings dams, causing damage to the environment.

[009] A solution for obtaining fields higher than 15,000 Gauss in the existing equipment would be to decrease the spacing of the magnetic matri- ces using dimensions smaller than 1.5 mm, since the decrease in the spac- ing reduces the air gap of the matrix, thus facilitating the passage of magnet- ic lines of force. However, the solution to reduce the spacing less than 1.5 mm would have serious consequence of increasing the possibility of clogging of channels between the grooved plates, preventing the passage of the ore and discontinuing the production. The clogging of the matrices causes fre- quent interruptions of the plant and requires a complex equipment mainte- nance.

[0010] To date, are unknown in the prior art resources to increase the magnetic field strength within the matrix of the high intensity field magnetic separators without reducing the passageway of the ore pulp, preventing clogging of these matrices. Objects of the Invention

[0011] The object of the invention is to provide magnetic separators that achieve magnetic fields with higher strength, about 18,000 Gauss, and which do not result in reducing the spacing between the plates of the matrices. Preferably, the minimum spacing between the matrices must be kept at a minimum of about 1.5 mm.

[0012] The present invention also aims to improve the performance of magnetic separators, increasing the amount and variety of magnetic particles which are extracted and recovered from the ore pulp, allowing the extraction of particles with smaller grain size and lower magnetic susceptibility. Accord- ingly, the present invention also aims to reduce the amount of waste and 4 mineral tailings stored in dams and reducing water loss in the mining pro- cess.

[0013] Another object of the invention is to maximize the amount of ma- terial with commercial value extracted from the iron ore, thus raising the val- ue of this raw material. Brief Description of the Invention

[0014] The objects of the invention are achieved by a magnetic matrix for a high-intensity magnetic separator, comprising a series of magnetizable material plates provided with longitudinal grooves in at least one of its two faces, the grooved plates being housed lined up and with a spacing distance between them within a housing, the matrix further comprising at least a mag- netic shim disposed within the housing, lined up with the grooved plates.

[0015] The magnetic shim is preferably a steel sheet with permeability higher than or equal to 500, and has the same width and height as the grooved plates.

[0016] At least a magnetic shim may be disposed at any position in lin- ing up direction of the grooved plate adjacent to one face free from grooves of at least one of the grooved plates, or at least a magnetic shim may be dis- posed at each end of the housing, in the lineup direction of the grooved plates. Alternatively, a plurality of magnetic shims is disposed between the grooved plates in different positions in the lineup direction of the grooved plates. The magnetic shims may occupy 10 to 40%, preferably 30 to 35% of the width of the magnetic matrix in the lineup direction of the grooved plates. The matrix may comprise protection elements mounted to the top of the magnetic shims, the protection elements being made of abrasion-resistant material plates.

[0017] The objects of the invention can be also achieved by a high in- tensity magnetic separator comprising at least one pair of magnetic poles, and at least one rotor to which are connected a plurality of magnetic matrices of the type previously described, within which flows an ore pulp fed to said magnetic separator, wherein the rotor performs a rotational movement in the inner region of the magnetic poles, wherein the plates of magnetizable mate- rial and at least one magnetic shim of the magnetic matrices are magnetized by the poles as the rotor rotates. The magnetic field induced within the mag- netic matrices is able to reach at least 18,000 Gauss.

[0018] The objects of the invention are also achieved by a method of adjusting the magnetic field generated within a high intensity magnetic sepa- rator of the type described herein, the method comprising the steps of:

[0019] calculating a target magnetic field to be generated by the mag- netic separator (1) according to the ore pulp to be fed to the separator, and

[0020] filling the housing of the magnetic matrix with a number of grooved plates and magnetic shims needed to generate the target magnetic field calculated.

[0021] The method preferably comprises, after the step of calculating the target magnetic field, a step of sizing the width values of the magnetic matrix to be occupied by the grooved plates and the width of the magnetic matrix to be occupied by the magnetic shims. Brief Description of the Drawings

[0022] The present invention will be further described in more details based on one example of realization represented in the drawings. The figures show:

[0023] Figure 1 - is a view of a high intensity magnetic separator to which the magnetic matrices are applied according to the present invention;

[0024] Figure 2 - is a cross-section view of the separator of Figure 1, showing the magnetic field circulating inside it.

[0025] Figure 3 - is an enlarged cross-section view of the magnetic ma- trices arranged in the separator, illustrating the movement of the magnetic field at the interface of the matrices with the structure of the magnetic separa- tor;

[0026] Figure 4 - is a schematic perspective view of a magnetic separator matrix, showing also an enlarged top view of a detail of the matrix and the magnetic flux circulation through the grooved plates;

[0027] Figure 5 - is a cross-section view of the unitary magnetic circuit formed between a pole, the magnetic matrix usually used in magnetic separa- tors and the separator rotor, showing the lines of force that run between these elements;

[0028] Figure 6 - is a cross-section view of the unitary magnetic circuit shown in Figure 1, by employing a magnetic matrix according to a first embod- iment of the invention, with a magnetic shim at each end of the matrix;

[0029] Figure 7 - is a cross-section view of the unitary magnetic circuit shown in Figure 1, by employing a magnetic matrix according to a second em- bodiment of the invention, with two magnetic shims at a same end of the ma- trix;

[0030] Figure 8a - is a graph showing the variation of the maximum mag- netic field generated by the magnetic separator due to the width of the mag- netic matrix occupied by magnetic plates; and

[0031] Figure 8b - is a graph showing the same variation of the maximum magnetic field generated by the magnetic separator due to the width of the magnetic matrix occupied by magnetic plates, but in percent values. Detailed Description of the Figures

[0032] Figures 1 and 2 illustrate high intensity magnetic separators 1, to which are applied the magnetic matrices 6 according to the present invention, and are used for the separation of ore particles and reduction of tailings result- ing from the mining process.

[0033] Magnetic separators 1 have one or more pairs of magnetic poles 3, each pole being surrounded by a coil 2 which generates its respective mag- netic field. As can be seen in Figures 1 and 2, the separator is con-figured with 2 pairs of poles that are aligned vertically, with the poles of a same pair being disposed diametrically opposed in the horizontal direction. The separator according to the invention can also be configured with 8 poles, arranged in two stacked crosses, or how many pairs of poles are intended. The vertically aligned poles are opposed, and the horizontally aligned poles are also opposed, as shown in Figure 2. The vertically aligned poles are con- nected to each other, for example by means of metal plates, and the horizon- tally aligned poles are connected among themselves through the separator structure. By means of this arrangement, a closed circuit is formed in which the magnetic flux flows as shown by arrows shown in figure 2, to obtain higher magnetic permeability, and reduce the leakage flux, aiming at higher energy efficiency.

[0034] In this embodiment of separator 1 with two stacked pairs of poles two rotors 4 are used and are supported by a central shaft 5 which drives these two rotors simultaneously. The set of rotors 4 with the central shaft 5 is ar- ranged between the pairs of magnetic poles, each one is being disposed in the same horizontal plane of one of the pairs of poles. Each rotor has mounted to its periphery several magnetic matrices 6 that are traversed by the pulp ore, and where the ore particles separated from that pulp are retained. These ma- trices have a number of magnetizable material plates 21 provided with longi- tudinal grooves (grooved plates) which are best seen in figure 4. These grooved plates 21 are arranged within a housing, where they are lined up ver- tically with a spacing distance between them, also called "gap". By means of this arrangement of the grooved plates 21, the grooves generally with a "V" profile of neighboring plates are with their vertices and their valleys respec- tively aligned to form vertical channels which are traversed by the flow of ore pulp poured over the magnetic matrices. The channels between the grooved plates 21 can be better seen in the enlarged detail shown in Figure 4. The spacing or gap 18 formed between the plates is the distance between the ver- tices of the grooves of adjacent plates, which corresponds to the shortest dis- tance between them.

[0035] The housing is where are disposed the grooved plates 21 of the matrix delimited by two bronze wedges 8 (non-magnetic) on the sides, by the rotor edge on the bottom end, and by a closing plate 7 at the front end, as can be seen in figure 3 which corresponds to the detail 9 of figure 2. These magnetic matrices are disposed around the entire circumference of the rotors, as can be seen in figures 1 and 2. The wedges 8 disposed between each lined up set of plates help to form the circular arrangement of the matrices 6 around the rotor and secure the closing plate 7 to the rotor 4. This rotor rotates in the inner region of the poles, so that when passing in front of the magnetic poles 3, the magnetic matrices 6 are subjected to the north and south magnetic fields and are magnetized by induction.

[0036] The ore pulp is poured onto the magnetic matrices 6 of the sepa- rator at a position close to the start of each of the poles 3 of the separator, in the direction of the rotor rotation. Due to the magnetic field induced by poles 3 the magnetizable particles of the ore pulp poured onto the magnetic matrices are stuck together on the plates on matrices 6, while the tailings containing non-magnetic particles pass through the channels of these matrices and are diverted to a tailings outlet. As the matrices move between the poles due to rotational movement, the magnetic particles of ore stuck on the plates pass through a zero field region between two adjacent poles, and then come off the plates and are diverted towards a purified ore outlet of the separator.

[0037] The spacing 18 between the grooved plates 21 of the matrices 6 and the opening dimensions of the channels formed between them are im- portant requirements for the operation of the magnetic separator and its per- formance in terms of the amount of ore particles to be extracted from the pulp. The vertices of the grooves concentrate the lines of force 12 shown in figure 4, and generates high magnetic field within the magnetic matrices 6. The spac- ing between the vertices 18 of the grooved plates 21 corresponds to the air gap through which the lines of force 12 of the magnetic field and, therefore, the size of that spacing interferes with the magnetic field strength that can be generated. At the same time, the dimension of spacing 18 limits the maximum size of the mineral particles that can pass through the matrix.

[0038] Reducing this spacing increases the magnetic flux strength within the matrix, which helps in the separation of very fine particles with low mag- netic susceptibility, since the air permeability is lower than that of the grooved plates. However, a greatly reduced spacing prevents the passage of particles of larger particle size, or causes frequent clogging of the matrices, which re- quires interruption of the magnetic separation process for cleaning the grooved plates. The spacings between the grooved matrices typically used are 1.5; 2.0; 2.5; 3.0; 3.2; 3.8 mm, sometimes reaching up to 5.0 mm. The maximum mag- netic field strength, in turn, has a practical limit of about 15,000 Gauss obtained by using the spacing of 1.5 mm in the prior art separators. A spacing 18 lower than 1.5 mm excessively limits the particle size of the magnetic particles and are highly susceptible to clogging.

[0039] In order to increase the strength of the magnetic field generated by the separator, the magnetic matrices 6 according to the invention have one or more magnetic shims 14 disposed within the housing, lined up with the grooved plates, as shown in Figures 6 and 7. The magnetic shims are steel sheets with magnetic permeability greater than or equal to 500, for example, ABNT 1006 steel type. The inclusion of the shims 14 reduces the overall width of the magnetic matrix occupied by the grooved plates in the lineup direction of the grooved plates 21, and consequently the amount of spacings 18 be- tween the grooved plates is also reduced within the matrices 6. Since the shims 14 are made of high magnetic permeability materials, at least about 500 times greater than the magnetic permeability of air, reducing the air path through which the lines of force 12 must circulate, increases the magnetic field intensity. The lines of force and the magnetic field become intensified by the magnetic shims 14, without the need increase the power of the coils 2 at the poles.

[0040] Preferably, the magnetic shims 14 have the same dimensions in width and height as he grooved plates; however, the thickness of these shims may be different from the grooved plates. In the same magnetic matrix, the magnetic shims 14 with different thicknesses and in different positions can be mounted between the grooved plates 21. In the embodiment shown in Figure 6, two magnetic shims are mounted on the sides of the matrix, one at the side of the rotor 4, and the other at the front end, facing the pole 3 and coils 2. The grooved plate 21 is centered within the matrix 6. In the embodi- ment shown in figure 7, the two shims 14 are mounted side by side on the surface of the rotor 4, so that the grooved plates are closer to the poles than in the embodiment of figure 6. In both embodiments of figures 6 and 7, the two shims 14 have the same thickness; however, shims of various thickness- es can be used.

[0041] The magnetic shims 14 have two flat faces. The grooved plates 21 that are disposed neighboring these shims preferably have one of their faces groove-free, on the side facing the respective shim for better accom- modation within the magnetic matrix and to reduce the amount of air within the matrix. In the embodiments of the invention shown in Figures 6 and 7, as the shims 14 are arranged at the ends of the housings of the magnetic matri- ces, only the grooved plates 21 disposed on these ends have a flat surface. However, the magnetic shims can be mounted within the magnetic matrix in any position on the lineup direction of the grooved plates. In such cases, the grooved plates 21 adjacent to them within the matrix must have a face free from grooves on the side facing the shims 14.

[0042] Preferably, protection elements 15 made up of abrasion-resistant material plates are mounted on the top of the magnetic shims 14 to avoid occurrence of wear on the magnetic shims and extend their useful life.

[0043] To adjust the magnetic field within the matrices, there may be used several magnetic shims 14 of different thicknesses, arranged side by side, allowing great ease of assembly and sizing of these matrices by simply disengaging some grooved plates 21 within the matrices and replacing them with magnetic shims occupying the space opened by them in the magnetic matrix 6.

[0044] The graphs of Figures 8a and 8b show the variation of the maxi- mum magnetic field generated by the magnetic separator within the matrices 6, as a function of the width of the magnetic matrix. In the Figure 8a, the hori- zontal axis shows the width, in millimeters, of the magnetic matrix 6 occupied by grooved plates, in the lineup direction of the grooved plates. This width reduces from left to right on the graph, making it clear that the reduction is due to the corresponding replacement of grooved plates by magnetic shims. The axis of ordinates shows the variation of the magnetic field in Gauss with- in the matrices, according to the width of the magnetic matrix occupied by the magnetic plates. Figure 8b shows this same relationship, but in percent. Both graphs were generated from experimental data obtained on magnetic matri- ces with spacings between the grooved plates of about 1.5 mm. It is noted that a reduction of 85 mm (or 33.3%) of the width of the matrix causes an increase of 4,900 Gauss (or 37.1%) of the magnetic field in the matrices.

[0045] The magnetic separators using the magnetic matrices according to the invention are able to achieve magnetic fields around 15,000 to 18,000 Gauss or even higher. The value of 18,000 Gauss is sufficient to permit the separation of particles with low magnetic susceptibility and, optionally, low particle size, which normally remained in the ore pulp and were sent to the dams in the form of tailings.

[0046] Depending on the magnetic field values to be obtained, the mag- netic shims may occupy about 10 to 40% of the width of the magnetic matrix 6, in the lineup direction of the grooved plate, and preferably these magnetic shims occupy about 30 to 35% of the width of the magnetic matrix 6, to achieve sufficiently effective magnetic field values to separate magnetic par- ticles of ultrafine particle size and low susceptibility present in the ore pulp.

[0047] The present invention also relates to a method for adjusting the magnetic field generated in a high intensity magnetic separator of the type described herein, which comprises a first step of calculating a target magnet- ic field that must be generated by the magnetic separator to obtain the de- sired performance of magnetic separation, depending on the ore pulp to be fed to the separator.

[0048] Next, it is necessary to size which portion of the width of the magnetic matrix must be occupied by the grooved plates 21, and which por- tion of the width of the magnetic matrix has to be occupied by the magnetic shims 14. This sizing will also depend on the spacing 18 that will be applied to the grooved plates 21, among other parameters. After calculating these values, the housing of the magnetic matrices of the separator is filled up with an amount of grooved plates 21 and magnetic shims 14 corresponding to the result of said calculation, which will be capable of generating the target mag- netic field calculated.

[0049] Filling out of the share of matrices designed to the magnetic shims 14 can be done with one or more shims of varied thicknessses, being housed in several locations between the grooved plates, or at the ends of the housing where these plates are arranged in the lineup direction.

[0050] The consequence of replacing the space of air, which presents high magnetic reluctance, with high permeability steel shims results in in- creasing the overall permeability of the magnetic circuit, thus facilitating and letting through more lines of force. After one example of a preferred embodiment has been described, it should be understood that the scope of the present invention encompasses other possible embodiments and is limited only by the content of the appended claims, which include their possible equivalents.

Claims

1. A magnetic matrix for a high intensity magnetic separator comprising: a series of grooved plates of magnetizable material, the grooved plates having two faces and being provided with longitudinal grooves on at least one of the two faces thereof, the grooved plates be- ing housed lined up vertically and with a spacing distance between ad- jacent grooved plates within a housing, wherein the housing is delimited by two non-magnetic wedges on the sides, by a closing plate at a front end, and by a rotor edge of the high intensity magnetic separator at a bottom end; and at least one magnetic shim disposed within the housing, lined up with the grooved plates, wherein the at least one magnetic shim is a steel sheet with permeability higher than or equal to 500, and wherein the at least one magnetic shim occupies 10% to 40% of a width of the magnetic matrix, in a lineup direction of the grooved plates.

2. The magnetic matrix according to claim 1, characterized in that the at least one magnetic shim has a same width and height as the grooved plates.

3. The magnetic matrix according to claim 1 or 2, character- ized in that the at least one magnetic shim is disposed at any position in the lineup direction of the grooved plates, adjacent to one face free from the grooves of at least one of the grooved plates.

4. The magnetic matrix according to any one of claims 1 to 3, characterized in that at least one of the at least one magnetic shim is disposed at each end of the housing, in the lineup direction of the grooved plates.

5. The magnetic matrix according to any one of claims 1 to 4, characterized in that the at least one magnetic shim comprises a plurality of magnetic shims disposed between the grooved plates in different po- sitions in the lineup direction of the grooved plates.

6. The magnetic matrix according to any one of claims 1 to 5, characterized in that the at least one magnetic shim occupies 30% to 35% of the width of the housing of the magnetic matrix, in the lineup direction of the grooved plates.

7. The magnetic matrix according to any one of claims 1 to 6, further comprising protection elements mounted to a top of the at least one magnetic shim, the protection elements being made of abrasion- resistant material plates.

8. A high intensity magnetic separator comprising: at least one pair of magnetic poles aligned vertically with poles of a same pair of magnetic poles being disposed diametrically op- posed in a horizontal direction, and at least one rotor to which a plurality of magnetic matrices are connected within which flows an ore pulp fed to said magnetic separator, wherein the at least one rotor performs a rotational movement in an inner region of the magnetic poles, wherein the magnetic matrices are matrices as defined in any one of claims 1 to 7, and wherein the grooved plates of magnetizable material form vertical channels which are traversed by a flow of the ore pulp poured over the magnetic matrices and the grooved plates of magnetizable ma- terial and the at least one magnetic shim of the magnetic matrices are magnetized by the at least one pair of magnetic poles during the rota- tional movement of the at least one rotor.

9. The magnetic separator according to claim 8, character- ized in that the at least one magnetic shim is disposed within the housing at an end of the magnetic matrix facing the at least one rotor.

10. The magnetic separator according to claim 8 or 9, char- acterized in that the at least one magnetic shim is disposed within the housing at the end of the magnetic matrix facing the at least one pair of magnetic poles.

11. The magnetic separator according to any one of claims 8 to 10, characterized in that the at least one magnetic shim is disposed between the grooved plates at any position in the lineup direction of the grooved plates, adjacent to one face free from the grooves of at least one of the grooved plates.

12. A method of adjusting a magnetic field generated within the high intensity magnetic separator as defined in any one of claims 8 to 11, the method comprising the steps of: calculating a target magnetic field strength to be generated by the magnetic separator according to the ore pulp to be fed to the sep- arator, and filling the housing of the magnetic matrix with a number of the grooved plates and the at least one magnetic shim needed to generate the target magnetic field strength calculated.

13. The method of adjusting the magnetic field according to claim 12, comprising, after a step of calculating the target magnetic field strength, a step of sizing the width values of the magnetic matrix to be occupied by the grooved plates and a width of the magnetic matrix to be occupied by the at least one magnetic shim.