OA18678A - System and process for dry recovery of iron oxide fines from iron-bearing compacted and semi-compacted rocks - Google Patents

Abstract

The present invention relates to a system and a process for dry recovery of iron oxide fines from iron bearing compact and semicompact rocks that comprise primary (5), secondary (6) and ter-tiary (7, 7') crushing means for preliminarily reducing the granulometry of ores containing the iron oxide fines in compact and semicompact rocks; means for finely grinding (10, 10', 21) iron oxide minerais reduced through primary (5), secondary (6) and tertiary (7, 7') crushing, provided with a dynamic air classifier (3.5, 4.6, 5.4); means of static air classification (11, 12, 13) arranged in sériés for intermediate granulometric cuts and bag filters (14) for retaining fine frac-tion; and means of magnetic séparation (15, 16, 17), through magnetic rolls (71, 72, 73) arranged in cascade at a variable leaning angle, and formed by high and/or low magnetic intensity magnets.

Description

SYSTEM AND PROCESS FOR DRY RECOVERY OF IRON OXIDE FINES FROM IRON BEARING COMPACTED AND SEMICOMPACTED ROCKS

The invention in question relates to a process for dry recovery of iron oxide fines (Fe2O3 and Z or Fe3O4 = FeO.Fe2O3) présent in compact and semicompact rocks of the following type: compact itabirite iron ore, jaspelite iron oxide ore, taconite iron oxide ore and magnetite iron oxide ore. To effect the recovery of said iron oxides (Fe2O3 and / or Fe3O4), grinding must be performed till the iron oxide minerais are liberated from the canga. The libération degree is spécifie for each type of ore. Grinding granulometry is usually lower than 150 microns and may reach 25-45 microns.

In the context of the present invention, fines are the iron oxide minerais below 150 microns. In the current processes, fines are recovered in the presence of water by conjugating a magnetic séparation system with a flotation system (reverse flotation, floating silica and depressing iron ore or direct flotation of iron oxide). In the present invention, said process is performed through dry recovery.

Thus, the invention in question aims at innovating and simplifying the process for recovery of iron oxide fines (Fe2O3 and / or Fe3O4) present in said compact and semicompact iron oxide ores, particularly the ones of the following types: compact itabirite iron oxide ores, jaspelite iron oxide ore, taconite iron oxide ore and magnetite iron oxide ore, duly ground during libération granulometry, so as to provide high métallurgie and mass recovery.

In conséquence of the present invention a commercially superior iron oxide concentrate can be obtained by means of a totally-dry process, more precisely recovered from compact itabirite iron oxide ore, jaspelite iron oxide ore, magnetite iron oxide ore which content is above 63% Fe, that, by means of a single adjustment, the final content of the iron concentrate can reach up to 67% Fe.

In fact, a significant advancement in terms of environment protection can also be achieved, mainly because beneficiation (dressing) does not require water, which results in considérable economy of a substance that is becoming increasingly rare. Another relevant conséquence of said invention lies in the absence of tailings dams. In respect of that, one just hâve to bear in mind the shameful history of iron mining dam bursts occurred in Brazil as well as around the world, that caused terrible environmental catastrophes.

Therefore, amongst the innovative features of said process route, besides the above-mentioned benefits, the processing of compact iron ores has a low moisture content, thanks to the fact that compact and semicompact rocks (such as compact itabirite iron oxide ore, jaspelite iron oxide ore, taconite iron oxide ore and magnetite iron oxide) hâve a densely closed crystalline structure and, consequently, they prevent their inner portion from absorbing humidity. Such a feature éliminâtes one of the steps of the process that is the drying, when compared to the process of . 2 recovery of iron fines and superfines contained in tailings dams and/or moist process of recovery of compact iron oxide ore fines and superfines, like, for instance, the ones utilized in active mines in the U.S., that exploit taconite iron oxide ore. Thus, the 2-3% residual moisture can be eliminated during the fine grinding process, carried out according to the type of compact iron oxide ore in question.

DESCRIPTION OF THE PRIOR ART

In the conventional routes of compact iron oxide ore dressing, comminution (where the material is fragmented into small particles, normally below 150 micrometers) and concentration are entirely carried out in the presence of water. The initial steps of the process, both in the moist and dry routes, are conducted in the presence of natural humidity. Said steps correspond to primary, secondary and tertiary crushing, according to the type of ore and the beneficiation route as established. Following that, in the moist route, grinding rs performed by bail mills and vertical mills comprised of steel balls, always in the presence of water.

in the moist process route, iron balls are utilized as grinding agents in bail mills. Both in bail mills and vertical mills (e.g., Vertimill), granulométrie classification, i.e., grinding granulometry control, is performed through classification by hydrocyclones, wherein the vortex and apex parameters are adjusted to a granulométrie eut defined in the hydrocycloning process. Thus, the over flow corresponds to a fine fraction ground according to the libération granulometry, and the under flow corresponds to the thicker fraction, out of the libération granulométrie range, which re-feeds the mill.

Discharge from the bail mill feeds a slurry pump which, in turn, feeds a set of hydrocyclones. Occasionally, depending on the granulométrie eut, one or two more reprocessing steps are required both for under flow and over flow. Subsequently, for each of said Processing steps, one more slurry pump and one more set of hydrocyclones are required, which results in more water being added, which can render the project even more complex, with a greater volume of use of water.

Besides, over flow has a low content of solids, which has to be thickened in order to increase the solid content. Such a process is usually carried out by a thickener. Then, the thickened slurry must be subjected to other processing steps, which can be high intensity magnetic séparation and/or low intensity magnetic séparation followed by the high intensity one, the magnetic fraction (iron oxide concentrate) further being sent to reverse or direct flotation steps (cleaner step). By reverse flotation we mean having the contaminating eîement (silica, for example) float. By direct flotation we mean having the iron oxide minerais float. In reprocessing the over flow, a typical 20 pm or 10 pm fraction is disposed, which can be sent to the thickener and then to the tailings dam.

Patent BR 102014025420-0 discloses a process and a System for the dry recovery of iron oxide ore fines and superfines from iron mining tailings dam. However, it was noticed that the solution revealed by said invention does not apply to the dry recovery of iron oxide fines in compact and semicompact iron oxide bearing rocks in compact itabirite iron oxide ore, jaspelite iron oxide ore, taconite iron oxide ore and magnetite iron oxide ore.

OBJECTIVES AND ADVANTAGES OF THE INVENTION in view of the above-mentioned situation, the invention in question aims at providing a System and a process for dry recovery of iron oxide fines in compact and semicompact iron oxide bearing rocks in compact itabirite iron oxide ore, jaspelite iron oxide ore, taconite iron oxide ore and magnetite iron oxide ore, duly ground during libération granulometry.

The invention also aims at providing a magnetic séparation unit exhibiting satisfactory efficacy when it cornes to materials that are traditîonally non-processable by magnetic separators by means of permanent high intensity, rare earth magnet rolls (like iron-boron-neodymium) and low intensity ferrite magnets (like iron-boron).

Said objectives are achieved in an absolutely effective way by eliminating the environmental risks during the implémentation of the system, by promoting a conscious use of the natural resources, by producing an iron oxide concentrate product, reutilizing mining waste in the civil construction industry, thus saving a lot of water, for the technique in accordance with the invention in question does not require water.

In fîmes of growing environmental demands, the présent invention represents a definitive answer to the challenge of generating environmentally sustainable économie results, mainly characterized by:

• Non-use of water in the process of recovery of iron oxide, thereby sparing headwaters and aquifers;

• A more efficient séparation to produce a cleaner mining waste;

• Total reutilization of the mining waste by the civil construction industry;

• Improved mass and métal recovery of iron oxide;

• Recovery of iron oxide ore fines in fractions < 100 mesh (<0.15 mm) without losses caused by the arrastra;

• Absence of combustion residues;

• Non-existence of atmospheric effluents;

• Logistic optimization with localized treatment;

• Elimination of risks of accidents involving dams;

• Réduction of the physical space where the system is intended to be implemented;

• Low power consumption;

• System modularity and flexibility;

• Increase in the mines' useful life; and • Functional Independence of mines aiready in operation.

In the case of the instant invention, the absence of combustion residues and the non-existence of atmospheric effluents are due to the fact that in the compact iron oxide ore dressing, drying is not necessary, and in the combustion process fine powder is not produced either.

In the dry process according to the invention in question, grinding is performed by vertical mills, or pendulum (track) mills, or bail mills, ail of them provîded with an air-classification system. The presence of a dynamic air classifier aims at performing the granulométrie eut in the grid according to the diameter established by the libération degree, in which diameter can change depending on each type of iron oxide bearing ore.

It will be noticed that low moisture content compact iron oxide ores need to be dried because of their low moisture content, so that the friction between the minerais and grinders during grinding tends to generate the heat required to promote the residual drying of the moisture présent in the material.

DETAILED DESCRIPTION OF THE FIRST STEP - CRUSHING

Before starting the description of the invention, it should be noted that the magnitudes set forth herein are mere examples and should not be understood as limiting the scope of protection of the présent invention. One skilled in the art, faced with the concept disclosed herein, will know how to détermine the appropriate magnitudes to the case, in order to achieve the objectives of the présent invention. There are presented at least three arrangements and options of primary , secondary and tertiary crushing; the combinations are made between the secondary and tertiary crushing, and the equipment combined is:

• Jaw re-crusher as secondary crushing x HPGR (High Pressure Grinding Roll) as tertiary crushing, shown in figure 1 • Jaw re-crusher as secondary crushing x cône crusher as tertiary crusher, shown in figure 2.

Said unitary steps of size réduction by crushing are common to ail mining processes.

Option 1 for Crushing (Figure 1) in Figure 1, the unitary steps of the primary crushing process for iron ore oxide dry beneficiation are presented with primary crushing in the jaw crusher and the secondary crushing in the jaw re-crusher and tertiary crushing in high pressure grinding rolls (HPGR or similar).

In the extraction of compact ore 1, due to its high résistance as it is a compact rock, break up is made by fire (for example, by means of explosives). Next, the compact ore is removed from mining, for example, by means of a an excavator 2 and placed in the bucket of a truck 3. The bucket truck 3 feeds a silo or hopper 4 with the ore which is then taken to a primary jaw crusher 5, and may be combined with a re-crusher 6 which then feeds a further particle size réduction step in equipment known as HPGR Ί reducing the material to a particle size less than % (6,4 mm),

The crusher 5 and the re-crusher 6 provide an initial breaking of the ores into a particle size of +/- 75mm. After jaw crusher 5 and if a re-crusher is included, the final particle size is +/- 30 mm. Next, after Processing in HPGR 7, the particle size is reduced to +/- % (6.4 mm) and the material is transferred to a buffet silo. The need or absence of a buffer silo, as well as its capacity is a matter to be decided in the project design.

Option 2 for Crushing (Figure 2)

In Figure 2, the unitary steps of the primary crushing process for iron ore oxide dry beneficiation are presented with primary crushing in the jaw crusher and the secondary crushing in the jaw re-crusher and tertiary crushing in a cône crusher.

In the extraction of compact ore 1, due to its high résistance as it is a compact rock, break up is made by fire (for example, by means of explosives). Then, it is removed from mining, for example, by means of a an excavator 2 and placed in the bucket of a truck 3. The truck 3 feeds a silo or hopper 4 with the ore, then the ore is conducted to a primary jaw crusher 5 and then to a secondary re-crusher 6 and the material processed therein goes to another size réduction step, a cône crusher 7' reducing the material to a particle size less than !4 (6.4 mm), which can be deposited on a buffer pile 8.

Therefore, the first step of the présent invention consists of unitary processes of size réduction, by means of a crusher 5, a re-crusher and HPGR or cône crusher, which are known in the art. The unitary steps following the crushing process are described below, which are grinding, air classification in different particle size ranges and high intensity magnetic séparation in each of particle size ranges which, combined with the steps above, provide the effects desired by the présent invention.

DETAILED DESCRIPTION OF THE PROCESS FO THE PRESENT INVENTION

The inventive process is further based on the following unitary steps:

The unitary step of fine grinding in the degree of libération of iron ore x canga, with particle size eut effected by dynamic air classifier.

Static air classification unitary step in which cyclones are arranged in sériés, in which granulométrie cuts are made according to the degree of libération versus milling, which can be divided into three different particle size ranges. There may be one or two cuts and the decision on the number of granulométrie cuts will dépend on the degree of libération, and the super fine fraction of less than 10 or 5 micron may be retained in the bag filters.

Magnetic Séparation Sequence, which may be of low-intensity and of high-intensity and/or highintensity and of high magnetic intensity in each particle size ranges classified by the cyclone process of the static air classification type.

In the unitary step of milling, several types of equipment may be used, according to the présent invention, such as:

• Vertical mill;

• Pendulum mill;

• bail mill, duly transformed for dry Processing.

Unitary step of milling in a vertical mill (Figure 3)

Currently this type of equipment is widely used in the cernent industry for clinker grinding to a particle size of less than 45 micrometers. This equipment has shown a superior performance to other existing mills in the cernent industry and currently most cernent industries adopts this type of mill replacing the previous models. One of the innovations of the présent invention is to provide a process route that is the field of cernent industry for the primary mining beneficiation of iron oxide from compact and semi-compact rocks in a dry process.

In the dry process according to the présent invention, figures 10 and/or 11, from the buffer pile 8, the materiaî goes to the vertical mill 10 where grinding occurs. The vertical mill 10 introduced into the System and the process of the présent invention is shown in detail in figure 3.

Description of the main constituents of the Vertical Mill Figure 3.

• 3.1 Ore feed point;

• 3.2 Mobile track: it is driven by an electric motor and the power is calculated according to production capacity;

• 3.3 Grinding roll: the vertical mill can be equipped with two or more grinding rollers according to the size and productive capacity; The rolls exert a pressure on the grinding track and the whole ore présent in the grinding roller and the grinding track tends to crumble by compression;

• 3.4 Discharge of coarse fraction: the materiaî was not properly reduced falls by the side of the movable track, which in turn is directed to the discharge point. Then, the materiaî is collected and redirected to the feed point, closing the milling cycle • 3.5 The dynamic air classifier comprises a rotor having multiple blades. The larger the number of blades, the finer the granulométrie eut, and this is adjusted according to the degree of libération of each type of compact ore. The air classifier créâtes a dépression inside the mill which is responsible for removal of finely ground particles and discarding the coarse particles repelled by the rotor blades;

• 3.6 Return of unclassified materiaî: materiaî with coarser particle size rejected by the dynamic air classifier is collected by a cône directing materiaî back to the center of the movable track, joining it to the original materiaî;

• 3.7 Output of classified materiaî: ail the materiaî below the degree of libération col- lected by the air classifier is directed to the static classifiers, known as cyclones.

Unitary step of milling in a bail mill

Currently this type of equipment is widely used in the industry of industrial raw materials such as limestone, feldspar, silica and other industrial minerais, which can be reduced to a particle size that may range from 100 micrometers to 45 micrometers and may reach 20 micrometers. One of the technological innovations of the présent invention was to provide this process route in a primary mining process for beneficiation of iron oxide from compact and semi-compact rocks in a dry process.

In the dry process according to the présent invention, as shown in figures 14 and 15, from the buffer pile 8 the material goes to the bail mill 10’ where grinding occurs. The bail mill 10' introduced into the System and the process of the présent invention is shown in detail in figure 4.

Description of the main constituents of the Bail Mill (Figure 4):

• 4.1 Ore feed point;

• 4.2 Mill body with steel balls, properly scaled to the input particle size x the particle size at the end milling;

• 4.3 Openings in the mill body, to promote the discharge of pre-ground material, a coarser particle size of 4 mm to 0 mm. Fine grains are dragged by the dépréssion created by the dynamic air classifier 4.6 and coarser grains are collected and discharged by a worm thread 4.8;

• 4.4 The discharge end of the mill is composed of a chapel with two discharge points for coarse and fine fraction. For a coarse fraction, the material, which was not properly reduced, falls from the bottom of the chapel and is collected by the worm thread 4.8. The fine fraction is channeled through the top of the chapel, which is dragged by the dépression created by the dynamic aid classifier 4.6;

• 4.6. The dynamic air classifier consists of a rotor with several blades; the larger the number of blades, the finer the granulométrie eut, and this is adjusted according to the degree of libération of each type of compact ore. The air classifier créâtes an inner dépression in the mill that is responsible for removal of finely ground particles;

• 4.7 Return of not classified material. The coarser particle size material, rejected by the dynamic air classifier, is collected by a worm thread driving the material back to the feed point, joining it to the original material;

• 4.8 Output of classified material. Ali the material below the degree of libération collected by the air classifier is directed to the static classifiers, known as cyclones.

Unitary step of milling in a pendulum mill (Figure 5)

It relates to an equipment with lower production capacity than the vertical mill 10 and bail mill 10', which is also widely used in the industry of industrial raw materials such as limestone, feldspar, silica and other industrial minerais, which can be reduced to a particle size that may range from 100 micrometers to 45 micrometers and may reach 20 micrometers. One of the innovations of the présent invention is to combine this process route with the primary mining beneficiation of iron oxide from compact rocks in a dry process.

In the dry process according to the present invention, shown in figures 14 and 15, from the buffer pile 8 the material goes to the pendulum mill 21 where grinding occurs. The pendulum mill 21 introduced into the System and the process of the présent invention is shown in detail in figure 5, and has the following parts:

Description of the main constituées of the Pendulum Mill Figure 5 • 5.1 Ore Feed Point;

• 5.2 Fixed track for distribution of the material fed between the pendulums;

• 5.3 Rotating pendulums which promote the comminution of the feed material in the fixed track;

• 5.4 Air classifier that aspirâtes the comminuted material;

• 5.5 Returning coarse material, rejected by the air classifier, to the fixed track, along with the original material from the feed point;

• 5.6 Output of classified material: ail the material below the degree of libération collected by the air classifier is directed to the static classifiers, known as cyclones.

According to the présent invention, by means of cyclones, intermediate granulométrie cuts are made up to 10 to 5 mîcrometers and a fine fraction below this eut is retained in the bag filters. The dynamic air classifier 4.6 of figure 6 may be coupled to the bail mill 10' output , and may correspond to the dynamic air classifier 3.5 in the vertical mill 10, or to the dynamic air classifier 5.4 in the pendulum mill 21. It créâtes a dépréssion which drags ail particles of different sizes into the rotor 6.1 comprising a sériés of blades, which aims to disperse the particles to the side of the air classifier. The particles are subjected to three forces: centrifugal force (Fc) driven by the rotor, the air stream produced by the rotor dépression (Fd) and gravity (Fg). The resulting (R) refers to when Fc + Fg is smaller than the force of dépréssion (Fd) and corresponds to the fine particles that are dragged into the rotor and the resulting (G) refers to when Fc + Fg is greater than the force of dépression (Fd), and corresponds to the coarse particles that are directed downward. As an example, the action of these forces within the dynamic air classifier can be seen in Figure 6, which shows the Detail of the Dépression Forces (Fd), Centrifugal Force (Fc) and Gravity Force (Fg) in which:

R (0 fine) = Fd > Fg + Fc and G (0 coarse) = Fd < Fg + Fc

Thus, after the milling step and air classification, only the fraction with smaller particle size than that of the degree of libération, consisting of fine particles, i.e., when R (0 fine) = Fd> Fg + Fc, continues to the other steps of the process.

Comparing the process for granulométrie control of dry grinding carried out by an air classifier and the wet grinding process which is carried out by a set of hydrocyclones, the dynamic air classifier is a much simpler unit having lower capex and opex values compared to the process of granulométrie and hydrocyclone classification, as indicated in the section describing the prior art. Such air classification promotes the removal of the material ground in degree of libération, with rejection of the coarse material in the same equipment, which is subjected to one more step of grinding, closing the circuit of grinding and classification of particles by size.

Also in terms of energy consumption, the operation performed by the dry route with air classifiera proves advantageous considering that in a hydrocycloning particle size classification it is necessary to operate with a large amount of water, with a ratio of at least two parts water to one part of ore. In addition, for a good grinding granulometry classification, it is required at least more than one or two additional hydrocycloning steps, which corresponds to reprocessing the fraction under, so that most fine grains are removed and/or a further hydrocycloning step in the fraction over, with the purpose of ensuring the granulométrie eut. Therefore, considering these additional steps of reprocessing, up to additional parts of water to one part ore are necessary, while in the dry process only the material moves.

Unitary step of static air classification Figure 7

In the step after grinding and classification by the dynamic air classifier, the fraction smaller than the libération degree, predetermined in the physical/chemical characterization study, shall undergo more three particle size classification steps. The first step having a particle cut-off size at +/-45 pm, the second cut-off at +/- 22 pm, which may range between 35 to 18 pm and a third having a particle cut-off size of +/- 10 pm, which may range between 15 to 5 pm, that are performed by a set of three static cyclones connected in sériés with each other (Figure 7). These cut-off values in micrometera are a mere référencé and may vary according to the settings of the exhaustion System.

In Figure 6, the grinded fraction of the dynamic air classifier is directed to the first static cyclone 11. Said cyclone retains particles that are smaller than the libération degree, for example, 45 micrometera, which are discharged by the under 11 of the first cyclone. The 30-micrometer fraction cornes out by the over 11’ of the firat cyclone and feeds the second static cyclone 12. The second cyclone retains particles smaller than 30 micrometera and larger than 20 micrometers, which are discharged by the under 12 of the second cyclone. The 20-micrometer fraction cornes out by the over 12’ of the second cyclone and feeds the third static cyclone 13. The third cyclone retains particles smaller than 20 micrometera and larger than 10 micrometera, which are discharged by the under 13 of the third cyclone. The 10-micrometer fraction cornes out by the over 13’ of the third cyclone and feeds the set of bag filters 14, which must collect ali fraction under 10 pm. The particle size cut-off values refer to orders of magnitude that may vary either up or down according to the exhaust fan 19 speed settings.

The products collected in each of the cyclones 11, 12 and 13 arranged in sériés can be optionally allocated to the respective cooling columns (not shown), whose purpose is to reduce the température which is between 70 °C to 100 °C to a température around 40 °C. Said cooling is necessary to preserve the magnetic intensity of rare earth magnets (iron-boron-neodymium).

The materials collected in each cyclone (cyclone's under) and that pass though the cooling columns, feed the low and high intensity or high and high intensity magnetic separators with inclined rolls, properly adjusted for each particle size.

A unitary step of magnetic séparation, as that described in the claim process of patent BR102014025420-0 (incorporated here for reference) processes ail fractions that are smaller than the predetermined particle cut-off size derived from the libération degree and larger than 10 pm through magnetic séparation units.

Based on the possibility of performing tertiary crushing by two means, through HPGR (high pressure grinding rolls) or by means of a cône crusher and final grinding by three different apparatuses, it is possible to establish six different process routes.

The first type of dry process route of the présent invention is shown in Figure 10 and comprises primary crushing using a jaw crusher 5, secondary crushing using a jaw re-crusher 6, tertiary crushing having HPGR 7 (high pressure rolls) and grinding in vertical mill 10.

Thus, the compact ore 1, due to its high résistance for being a rock, is broken up by fire (explosive) and then is removed from the mining, for example, by means of an excavator 2 and laid on the bucket of a truck 3. The truck 3 feeds a silo or hopper 4 and then the material is conveyed to a primary jaw crusher 5 and from there is re-fed to a secondary jaw crusher 6 and the material processed therein goes to a further size réduction step in a HPGR-type roll mill (high pressure rolls) 7, thus reducing the material to a particle size smaller than % (6.4 mm). The fraction smaller than Va feeds magnetic roll separator 50 (235 mm diameter) of high intensity and high yield, thus generating a magnetic product that may or may not be stored in a buffer pile 8; the non-magnetic fraction, substantially free of iron oxide, is intended for use in the construction industry as a filler for concrète and/or for manufacturing cernent aggregate, such as blocks and pavers. The material deposited in the pile feeds the vertical mill 10, the grinding occurs through the movement of the mobile track 3.2, compressing the material under the rolls 3.3. The grinding occurs by shearing and because of the conical shape of the rolls it is possible to obtain different grinding levels. The material having the coarsest particle size is removed from the vertical mill and directed again to the feed point 3.1, thus closing the grinding cycle. The ground material is collected by the dynamic air classifier 3.5 located on top of the vertical mill 10. The ground material which has not yet reached the libération degree returns to the center of the movable track 3.2 to again be ground, and the ground material that has already reached the libération degree is discharged by the vertical mill 10 and collected by the exhaust System.

The exhaust System comprises three cyclones arranged in sériés 11, 12 and 13 shown in Figure 7, wherein the first cyclone 11 collects ail material discharged by the vertical mill and classifies them in a particle size of approximately 30 micrometers; the fraction larger than 30 micrometers, named under, is collected in the lower base 11” of the cyclone. The over 11’ fraction of the first cyclone 11 feeds the second cyclone 12, duly sized to capture any fraction larger than 20 micrometers and the fraction smaller than 20 micrometers of the second cyclone 12 feeds the third cyclone 13, sized to capture any fraction larger than 10 micrometers, rejecting the fraction smaller than 10 micrometers for the set of bag filters 14. The bag filters 14 hâve the pur pose of retaining ail particles which hâve not been classified or retained in the sets of cyclones. The particle cut-off size values are not spécifie values and may vary according to each project. It is important to note that said classification in three different particle size diameters is essentiaî for optimum magnetic séparation performance for fines.

The first type of dry process route of the présent invention is shown in Figure 11 and comprises primary crushing using a jaw crusher 5, secondary crushing using a jaw re-crusher 6, tertiary crushing having HPGR 7’ (high pressure rolls) and grinding in vertical mill 10.

Thus, the compact ore 1, due to its high résistance for being a rock, is broken up by fire (explosive) and then is removed from the mining, for example, by means of an excavator 2 and laid on the bucket of a truck 3. The truck 3 feeds a silo or hopper 4 and then the material is conveyed to a primary jaw crusher 5 and from there is re-fed to a secondary jaw crusher 6 and the material processed therein goes to a further size réduction step in a cône crusher 7’, thus reducing the material to a particle size smaller than % (6.4 mm). The material deposited in the pile feeds the vertical mill 10, the grinding occurs through the movement of the mobile track 3.2, compressing the material under the rolls 3.3. The grinding occurs by shearing and because of the conical shape of the rolls it is possible to obtain different grinding levels. The material The non-magnetic fraction, practically free of iron oxide, is intended for use in the construction industry as a filler for concrète and/or for manufacturing cernent aggregate, such as blocks and pavers. The magnetic fraction is re-directed to the feed point 3.1, thus closing the grinding cycle. The ground material is collected by the dynamic air classifier 3.5 located on top of the vertical mill 10. The ground material which has not yet reached the libération degree returns to the center of the movable track 3.2 to again be grounded, and the ground material that has already reached the libération degree is discharged by the vertical mill 10 and collected by the exhaust System. The ground material that has already reached the libération degree is discharged by the vertical mill 10 and collected by the exhaust System.

The exhaust System comprises three cyclones arranged rn sériés 11, 12 and 13 shown in Figure 7, wherein the first cyclone 11 collects ail material discharged by the vertical mill and classifies them in a particle size of approximately 30 micrometers; the fraction larger than 30 micrometers, named under, is collected in the lower base 11” of the cyclone. The fraction larger than 30 micrometers, named under, is collected in the lower base 11” of the cyclone. The over 11’ fraction of the first cyclone 11 feeds the second cyclone 12, duly sized to capture any fraction larger than 20 micrometers and the fractions smaller than 20 micrometers of the second cyclone 12 feeds the third cyclone 13, optimized to capture any fraction larger than 10 micrometers and reject the fraction smaller than 10 micrometers to the set of bag filters 14. The bag filters 14 hâve the purpose of retaining ail particles which hâve not been classified or retained in the sets of cyclones. The particle cut-off size values are not spécifie values and may vary according to each project. It is important to note that said classification in three different particle size diameters is essential for optimum magnetic séparation performance for fines.

The first type of dry process route of the présent invention is shown in Figure 12 and comprises primary crushing using a jaw crusher 5, secondary crushing using a jaw re-crusher 6, tertiary crushing having HPGR 7 (high pressure rolls) and grinding in vertical mill 10’.

Thus, the compact ore 1, due to its high résistance for being a rock, is broken up by fire (explosive) and then is extracted/removed from the mining, for example, by means of an excavator 2 and laid on the bucket of a truck 3. The truck 3 feeds a silo or hopper 4 and from there the material is conveyed to a primary jaw crusher 5 and then re-fed to a secondary jaw crusher 6 and the material processed therein goes to a further size réduction step in a HPGR-type (High Pressure Grinding Rolls) roll crusher 7, thus reducing the material to a particle size smaller than (6.4 mm). The fraction smaller than % feeds magnetic roll separator 50 (235 mm diameter) of high intensity and high yield, thus generating a magnetic product that may or may not be stored in a buffer pile 8. The material deposited on the pile feeds the bail mill 10’. Grinding occurs through the movement of the mill body 4.2, loaded with a load of steel balls that may vary from 35 to 40% of the internai volume. The Steel balls form a ripple effect: The particles are subjected to the impact of the balls and the friction with the balls promûtes the réduction of the particles. On the upper part of the mill, connected to the discharge hood, an air classifier 4.6 promûtes a dépréssion inside the bail mill, dragging the larger and smaller particles out of the mill. The larger particles fall, by gravity, into the lower part 4.4 of the hood. Those, in turn, collected by a worm thread 4.8, feed a magnetic roll separator 60 (diameter 235 mm) of high intensity and high yield, generating a magnetic product that may or may not be stored in a buffer pile and redirected to the bail mill feed 4.1. The non-magnetic fraction, practically free of iron oxide, is intended for use in the construction industry as a filler for concrète and/or for manufacturing cernent aggregate, such as blocks and pavers. On the upper part of the discharge hood, fines are dragged to the rotor of the dynamic air classifier 4.6, which in turn classifies the material ground in the libération degree. The material larger than the libération degree is directed out of the dynamic air classifier 4.6 and collected by a worm thread 4.7, which re-directs it to the feed point 4.1. The material ground smaller than the libération degree is thrown out of the air-classifying mill 4.6 and captured by the exhaust System.

The exhaust System consists of three cÿclones arranged in sériés 11,12 and 13 shown in Figure 7, wherein the first cyclone 11 collects ail material discharged by the bail mill 10’ and classifies them in a particle size of approximately 30 micrometers. The fraction larger than 30 micrometers, named under, is collected in the lower base 11” of the cyclone. The fraction over 11’ of the first cyclone 11 feeds the second cyclone 12, duly sized to capture any fraction larger than 20 micrometers, and the fraction smaller than 20 micrometers of the second cyclone 12 feeds the third cyclone 13, sized to capture any fraction larger than 10 micrometers and reject ing the fraction smaller than 10 micrometers to the set of bag filters 14. The bag filters 14 hâve the purpose of retaining ail particles which hâve not been classified or retained in the sets of cyclones. The particle cut-off size values are not spécifie values and may vary according to each project. It is important to note that said classification in three different particle size diameters is essential for optimum magnetic séparation performance for fines.

The fourth type of dry process route of the présent invention, shown in Figure 13, comprises primary crushing using a jaw crusher 5, secondary crushing using a jaw re-crusher 6 and tertiary crushing using a cône crusher 7', and grinding in a bail mill 10’.

The compact ore 1, due to its high résistance for being a rock, is broken up by fire (explosive). Subsequently, it is extracted/removed from the mining, for example, by means of an excavator 2 and laid on the bucket of a truck 3. The truck 3 feeds a silo or hopper 4 and from there the material is conveyed to a primary jaw crusher 5 and then is re-fed to a secondary jaw crusher 6 and the material processed therein goes to a further size réduction step in a cône crusher T, thus reducing the material to a particle size smaller than % (6.4 mm). The material deposited in the buffer pile 8 feeds the bail mill 10’. The grinding occurs through the movement of the mill body 4.2, loaded with a load of steel balls that may vary from 35 to 40% of the internai volume. The Steel balls form a ripple effect: the particles are impacted by the falling balls and the ball-onball friction promotes the réduction of the particles. On the upper part of the mill, connected to the discharge hood of the mill, an air classifier 4.6 promotes a dépréssion inside the bail mill, dragging the larger and smaller particles out of the mill, the [arger particles falling, by gravity, into the lower part 4.4 of the hood, and being in turn collected by a worm thread 4.8, that feeds a magnetic roll separator 60 (235 mm diameter) of high intensity and high yield, and are redirected to the feed 4.1 of the bail mill 10’. The non-magnetic fraction, practically free of iron oxide, is intended for use in the civil construction industry as a filler for concrète and/or for manufacturing cernent aggregates, such as blocks and pavers. On the upper part of the discharge hood, the fines are dragged to the rotor of the dynamic air classifier 4.6, which in turn classifies the materials ground in the libération degree. The material larger than the libération degree is directed out of the dynamic air classifier, collected by a worm thread 4.7 and re-directed to the feed point 4.1. The material ground smaller than the libération degree is thrown out of the air classifier 4.6 and collected by the exhaust System.

The exhaust System consists of three cyclones in sériés 11, 12 and 13 shown in Figure 7, wherein the first cyclone 11 captures ail the material released by the bail mill 10’ and classifies into a grain size of approximately 30 micrometers. The fraction greater than 30 micrometers called under is collected at the bottom base 1 T’ of the cyclone. The over fraction 1T of the first cyclone 11 feeds the second cyclone 12, properly sized to capture any fraction greater than 20 micrometers and the fraction below 20 micrometers of the second cyclone 12 feeds the third cyclone 13, sized to capture ali the fraction larger than 10 micrometers rejecting the fraction smaller than 10 micrometers for ail of sleeve fïlters 14. The sleeve filters 14 are intended to retain ail particles which were not classified or retained in the cyclone assemblies. The values of granulométrie cuts are not spécifie values and may vary according to each project. It is important to stress that this classification into three different particle size diameters is essential for optimum performance of magnetic séparation for the fines.

The fifth embodiment of the dry process route according to the présent invention, shown in Figure 14 is formed by primary crushing performed by means of jaw crusher 5, secondary crushing by jaw re-crusher 6, and tertiary crushing with HPGR 7 (High Pressure Grinding Roller) and grinding in a pendulum mill 21.

Compact ore 1, due to its high résistance for being a rock, is dismantled by means of fire (blasting). It is then extracted/removed from the mining, for example by means of an excavator 2 and arranged in the back of a truck 3. The truck 3 feeds a silo or a hopper 4 and is then taken to a primary jaw crusher 5 and this, then, feeds a secondary re-crusher jaw 6 and material processed therein moves to a further size réduction step, in a HPGR-type roll crusher 7 (high pressure rollers) 7, thus reducing the material to a particle size of %” (6.4 mm). The fraction lower than %” feeds a high intensity and high productivity magnetic separator roller 50 (diameter of 235 mm), generating a magnetic product that may or may not be deposited in a buffer pile 8. The non-magnetic fraction, practically free from oxide iron, is intended for application in the construction industry, as a filler for concrète and/or cernent aggregate production, as for example, blocks and pavers. The material deposited on the stack feeds the pendulum mill 21. Grinding is performed by moving pendulums 5.3 with the fixed track 5.2, grinding being performed, therefore, by shearing. The ground material is captured by the dynamic air classifier 5.4 arranged at the upper portion of pendulum mill 21. The ground material that has not yet reached the libération degree returns to the grinding zone in order to be ground again. The ground material that has aiready reached the libération degree is thrown out of the pendulum mill and picked up by the exhaust System.

The exhaust System consists of three cyclones in sériés 11, 12 and 13 shown in Figure 7, wherein the first cyclone 11 captures ali the material released by the vertical mill and classifies into a grain size of approximately 30 micrometers. The fraction greater than 30 micrometers called under is collected at the bottom base 11” of the cyclone. The over fraction 11’ of the first cyclone 11 feeds the second cyclone 12, properly sized to capture any fraction greater than 20 micrometers and the fraction below 20 micrometers of the second cyclone 12 feeds the third cyclone 13, sized to capture ali the fraction larger than 10 micrometers rejecting the fraction smaller than 10 micrometers for ail of sleeve filters 14. The sleeve filters 14 are intended to retain ail particles which were not classified or retained in the cyclone assemblies. The values of granulométrie cuts are not spécifie values and may vary according to each project. It is im portant to stress that this classification into three different particle size diameters is essential for optimum performance of magnetic séparation for the fines.

The sixth embodiment of the dry process route according to the présent invention, shown in Figure 15 is formed by primary crushing performed by means of jaw crusher 5, secondary crushing by jaw re-crusher 6, and tertiary crushing with cône crusher 7’ and grinding in a penduIummill21.

Compact ore 1, due to its high résistance for being a rock, is dismantled by means of fire (blasting). It is then extracted/removed from the extraction site, for example by means of an excavator 2 and arranged in the back of a truck 3. The truck 3 feeds a silo or a hopper 4 and is then taken to a primary jaw crusher 5 and this, then, feeds a secondary re-crusher jaw 6 and material processed therein moves to a further size réduction step in a cône crusher 7’, thus reducing the material to a particle size lower than %” (6.4 mm). The material deposited on the stack feeds the pendulum mill 21. Grinding is performed by moving pendulums 5.3 with the fixed track 5.2, grinding being performed, therefore, by shearing. Because of the rounded shape of pendulums 5.3, it is possible to obtain different grinding levels. The ground material is captured by the dynamic air classifier 5.4 arranged at the upper portion of pendulum mill 21. The ground material that has not reached the libération degree yet returns to the grinding zone in order to be ground again. The ground material that has already reached the libération degree is thrown out of the pendulum mill and picked up by the exhaust System.

The exhaust System consists of three cyclones in sériés 11, 12 and 13 shown in Figure 7, wherein the first cyclone 11 captures ail the material released by the vertical mill and classifies into a grain size of approximately 30 micrometers. The fraction greater than 30 micrometers called under is collected at the bottom base 11” of the cyclone. The over fraction 11’ of the first cyclone 11 feeds the second cyclone 12, properly sized to capture any fraction greater than 20 micrometers, and the fraction below 20 micrometers of the second cyclone 12 feeds the third cyclone 13, sized to capture ail the fraction larger than 10 micrometers rejecting the fraction smaller than 10 micrometers for ali of sleeve filters 14. The sleeve filters 14 are intended to retain ail particles which were not classified or retained in the cyclone assemblies. The values of granulométrie cuts are not spécifie values and may vary according to each project. It is important to stress that this classification into three different particle size diameters is essential for optimum performance of séparation.

Provided in the magnetic séparation unit shown in Figure 8 are magnetic séparation means provided with two to four magnetic rollers arranged in cascade development, formed by low intensity (iron-boron) and/or high magnetic intensity (Rare earths) magnets, wherein the magnetic rollers are arranged in a variable tilt angle between 5° and 55°.

Figure 09 shows the magnetic séparation scheme with three rollers in cascade development. In the first magnetic séparation unit 15, the material from the first cyclone 11 feeds a first magnetic roller 71, which can be low or high intensity, generating a first non-magnetic fraction, which will be immediately discarded; a first magnetic fraction consisting of a final product with a content above 64% of Fe(T), and a first mixed fraction which feeds a second high intensity magnetic roller. In the same sequence, the second magnetic roller 72 generates a second non-magnetic fraction, which also is discarded, and a second magnetic fraction with a content above 64% of Fe(T), besides a second mixed fraction which feeds the third magnetic roller. In turn, the third magnetic roller 73 generates a third non-magnetic fraction which is also discarded, a third magnetic fraction with a content above 64% of Fe(T) and a third mixed fraction which is discarded along with the third non-magnetic fraction.

Thus, successively, the product of the second cyclone 12 will feed a cooling column and, then, the second magnetic séparation unit 16, in the same sequence, as in the first magnetic séparation unit, feeds the first magnetic roller, which can be of low or high intensity, generating a first non-magnetic fraction, which must be immediately discarded; a first magnetic fraction consisting of a final product with a content above 64% of Fe(T), and a first mixed fraction which feeds a second high intensity magnetic roller. In the same sequence, the second magnetic roller generates a second non-magnetic fraction, which is also discarded, and a second magnetic fraction with a content above 64% of Fe(T), besides a second mixed fraction which will feed the third magnetic roller. In turn, the third magnetic roller generates a third non-magnetic fraction which is also discarded, a third magnetic fraction with a content above 64% of Fe(T) and a third mixed fraction which is discarded along with the third non-magnetic fraction. The same will occur in the third magnetic séparation unit 17.

Figure 09 also shows the magnetic séparation scheme with three rollers in cascade development, wherein the first magnetic roller 71 can be of low intensity or high intensity. Depending on the characteristics of the material to be separated, the use of a low intensity magnetic roller may be preferred in view of the fact that the permanent magnets are made from iron-boron, with variable magnetic intensity between 500 and 3000 Gauss, and is, therefore, intended for séparation of high magnetic susceptibility minerais (e.g. magnetite - FeOFe2O3). In turn, in the case of the high-intensity magnetic rollers, the permanent magnets are made of iron-boron-neodymium, with magnetic intensities ranging between 7,500 and 13,000 G, for séparation of low magnetic susceptibility minerais (such as hématite and iron-limonite hydroxides).

Figure 9, which consists of a représentation of a side section of the magnetic séparation unit, illustrâtes in detail ail the éléments of the magnetic séparation unit in cascade development, which in the case illustrated, has three rollers, one superimposed on the other. As already seen, each of the cyclones, with their properly classified particle sizes, feeds a respective set of magnetic separators. According to Figure 9, the set consists of a receiver silo 74, wherein the power to the set can alternatively be controlled by the intensity of vibration by means of a pneumatic vibrator 75. However, preferably, silo 74 configured with tilt angles which provide a better flowability of the material to the set of magnetic separators.

Then, the material is discharged to a PU-coated polyester belt 76; the belt is tensioned by a first low intensity ferrite magnet (iron-boron) magnetic roller 71 and by a support roller 77.

The magnetic séparation is controlled by the variation of the magnetic roller speed and by the positioning of the splits. To contain the dissipation of dust and direct the material to the magnetic roller 71 an acrylrc plate 78 is positioned adjacent to belt 76. A split 79 séparâtes the nonmagnetic fraction from the mixed fraction and a split 80 séparâtes the mixed fraction from the magnetic fraction. The first non-magnetic fraction is collected by chute 81, the first mixed fraction is collected by chute 82 and the first magnetic fraction is collected by chute 83. The first mixed fraction chute 82 feeds silo 84 of the second high intensity rare earth magnet (neodymium-iron-boron) magnetic roller 72. The second high intensity rare earth magnet (iron-boronneodymium) magnetic roller 72, after the magnetic séparation, créâtes a second non-magnetic fraction, which is discarded through chute 85, the second magnetic fraction is discarded in chute 86 and a second mixed fraction is directed to chute 87 which feeds the third high intensity rare earth magnet (neodymium-iron-boron) magnetic roller 73 through silo 88. third high intensity rare earth magnet (neodymium-iron-boron) magnetic roller 73, after the magnetic séparation, generates a third non-magnetic fraction which will be discarded through chute 89, a third magnetic fraction which will be discarded into chute 90 and a 3rd mixed fraction, which through chute 91, is discharged along with the other non-magnetic fractions. Item 77 in the three magnetic séparation units comprise support rollers for the PU-coated polyester belt 76.

The low and high intensity magnetic rollers are tîlted, wherein the tilt angle may range from 5° to 55°, with an idéal work range of 15° to 25°, wherein the tilt is defined in terms of particle size release of the oxide iron. This tilt, according to the tests already carried out, increases the séparation efficiency of the magnetic fraction from the non-magnetic fraction.

Although the présent invention has been described with respect to its particular characteristics, it is clear that numerous other forms and modifications of the invention will be obvious to those skilled in the art.

Obviously, the intention is not limited to the embodiments shown in the figures and disclosed in the above description, so that it may be modified within the scope of the appended claims.

Claims (8)

1. System for dry recovery of iron oxide fines from iron bearing compact and semicompact rocks that comprises:

(a) primary (5), secondary (6) and tertiary (7, 7’) crushing means for preliminarily reducing the granulometry of ores containing the iron oxide fines in compact and semicompact rocks;

characterized by (b) means for finely grinding (10, 10’, 21) iron oxide minerais reduced through primary (5), secondary (6) and tertiary (7, 7’) crushing, provided with a dynamic air classifier (3.5, 4.6, 5.4);

(c) means of static air classification (11, 12, 13) arranged in sériés for intermediate granulométrie cuts and bag filters (14) for retaining fine fraction;

(d) means of magnetic séparation (15, 16, 17) of low and high magnetic intensity in each of the granulométrie ranges classified by means of static air classification (11, 12, 13); wherein the means of magnetic séparation are provided with two to four magnetic rolls (71, 72, 73) arranged in cascade, and formed by low and/or high magnetic intensity rare earth magnets, wherein the magnet rolls are arranged at a variable leaning angle that ranges between 5° and 55°;

(e) means of disposai of a non-magnetic fraction in each means of magnetic séparation, its collection as final product; and (f) means for driving a discharged, mixed fraction in each means of magnetic séparation for Processing in following means of magnetic séparation.

2. System, according to claim 1, characterized in that each of the means of static air classification (11, 12, 13) is connected with the iniet of a respective column cooling unit, which outlet is connected with the means of magnetic séparation (15, 16, 17).

3. System, according to claim 1 or 2, characterized in that the means of primary crushing consists of a jaw crusher (5); the means of secondary crushing consists of a jaw recrusher (6); and means of tertiary crushing is selected from HPGR-type rolls (7) or cône crusher (7’).

4. System, according to any of daims 1 to 3, characterized in that the means of fine grinding is selected from vertical mill (10), bail mill (10’) and pendulum mil! (21).

5. System, according to any of daims 1 to 4, characterized in that the dynamic air classifiers (3.5, 4.6, 5.4) are arranged at the upper part of the grinding means (10, 10’, 21) and are provided with means of creating an inner dépréssion in said grinding means for removal of the finely ground particles.

6. System, according to any of daims 1 to 5, characterized in that the means of static air classification comprises static cyclones (11, 12, 13).

7. Process for dry recovery of iron oxide fines from iron bearing compact and semicompact rocks that comprises:

(a) primary, secondary and tertiary crushing for preliminarily reducing the granulometry of ores containing the iron oxide fines in compact and semicompact rocks;

characterized by the steps of:

(b) fine grinding of the iron oxide minerais reduced in the primary, secondary and tertiary crush5 ing step;

(c) static air classification of intermediate granulométrie cuts and rétention of fine fraction;

(d) magnetic séparation of high magnetic intensity in each of the granulométrie ranges classified in the static air classification step into sets of magnetic rails arranged in cascade with low and/or high magnetic intensity rare earth magnets, at a leaning angle ranging between 5° and 55°;

10 (e) disposai of a non-magnetic fraction in each magnetic séparation step, its collection as final product; and (f) driving of a discharged, mixed fraction in each magnetic séparation sub-step for Processing in following means of magnetic séparation.

8. Method, according to claim 7, characterized in that after the static air classifi-

15 cation step and before the magnetic séparation step, a column cooling step is provided.