OA17102A - A process and system for dry recovery of iron-ore fines and superfines and a magnetic separation unit. - Google Patents

Abstract

The present invention refers to a system and method for the totally dry treatment of iron-ore wastes from previous mining operations, suitable for both the processing of ore wastes deposited in barrages and wastes stored in piles. The present invention solves the problems of magnetic separation processes that employ the wet and waste- dewatering way, eliminating the risks which throwing solid wastes into retention barrages bring by a system and method wherein the moisture degree of the ore is reduced by means of a mechanical stir dryer (using natural gas to prevent contamination), which is then sorted into various fractions and finally separated magnetically, with the important difference of being an entirely dry process.

Description

The présent invention refers to a process and a System for dry recovery of fine and superfine-gralned oxidized Iron ore from iron-minlng waste basins (also known as taiiings). The invention further deals with a magnetic séparation unit to separate the fine-grained oxidized iron ore (generally In the form of hématite) using a dry process.

In this regard, the présent invention aîms to improve the recovery of iron ore still contained in mining dumps, often considered as waste, which ls provide with high metallurgîcal and mass recoveries. Thus, it is possible to obtain a commercially acceptable product, more predsely an oxidized Iran ore concentrate with Fe-contents higher than 63%. Such resuit represents a significant advance from the environmental point of view, If one considéra the risk that is historically represented by wastes of the mining industry In Brazil and in the rest of the worid.

The innovatory characteristics of the dry process In the présent Invention advantageously meet the economical, environmental and strategie requlrements of the mining industry, enabling the Improved recovery of the ore wastes that constitute a risk of high environmental Impact, changlng them Into commercially accepted products in a technlcally and economlcally feaslble manner. In this dry process no water ls used, and the final residue will be a stack of waste, without the need to further waste barrage.

Description of the Prior Art

At the beginnlng of the mining activities on an industrial scale, little was known about the techniques for waste disposai. The low Interest In this area was still due to the fact that the amount of generated waste was reasonably small and the environmental problems were not yet part of the operational concems of the Industry.

In this regard, the waste was usualiy thrown at random into streams. However, with the expansion of the mining sector, the growing social concems about the environmental issues, as well as the record of a few accidents Involving waste rétention barrages since the 1970's in various parts of the worid, including Brazil, the challenge of guaranteeing the operation of the Industrial units was Imposed on the mining companîes with a view to mlnimize the environmental impacts and to reduce the risks of accidents, through more secure and optimized projects.

In general, three techniques are used for dîsposlng mining wastes, namely:

• by wet way in barrages, • by dry way In waste stacks, or • by using the paste-fi II technology.

The différence between the wet-way disposai and the dry-way disposa! Is that, In the barrage wet way, there Is also rétention of liquids In conjunction with the solid material discarded.

The paste-fill disposa! is an alternative to conventional practices, with advantages like greater recovery and recirculation of water, larger rest angles and reduced environmental impact. However, this process is carried out at high Implantation and operation costs.

For Instance, the Brazilian Patent Application BR P! 0803327-7 discloses a magnetic concentration process with low consumption of water and low génération of waste slurry. The wet magnetic séparation and disposa! of the magnetic waste may decrease the accumulation of large volumes of solid waste Into décantation barrages. However, this process does not dea! with the waste recovery. So, there is no effective decrease in the environmental risk inhérent of the mining actîvity.

Another document, the patent application BR PI0103652-1 describes a process of recovering resldues from Iran oxide. These residues may be obtained directly by recovering fines from metallurgy réduction processes, as well as the déviation of retum of fines from companles that supply Iron ore to Iran and steel companles. The material Is loaded onto a feed silo and follows through chutes and conveyor belts Into a rotary drying oven. The dry material is unloaded for stock without passing through any sorting/concentration process or else it is led directly to the réduction fumaces by a conveyor-belt System.

With regard to the step of drylng/disaggregating the waste for subséquent séparation, the prior art employs traditionally a rotary drum dryer. By this technique, the presence of fines in the dryer results In formation of an expressive amount (30 to 50%) of pellets inside the dryer (which obviously is contrary to the objective of recovering fines), leadïng to a low efficiency rate of the equipment for coarse particles and even greater inefficiency for fine particles.

Fiuid-bed dry ers are recommended for coarse particles that enable the formation of fluid beds, but it is Impossible to form a fluid bed for fine particles.

Spray Dry is widely used today In the ceramic Industries especially in preparing masses for the process of manufacturing porceiaîn floors. However, in the Spray Dry, it Is necessary to form a pulp with 50% solids for promoting the spraying of particles to be injected against a current of hot air. Feeding 500 ton/h of feedstock requires more than 300 m³ of water, which makes the operational cost unfeasible.

As to the magnetic séparation process usually employed In the prior art, one usually employs a magnetic roll piece of equipment, or a hlgh-lntensity permanent magnet drummer, the efficiency of which is satisfactory for separating materials dimensionally higher than 100 pm.

For materials with dimensions lower than 100 pm, the high-lntenslty magnetic roîl separator, as It has been employed, has proved to be Inefficient This Inefficlency results from the fact that, at the moment when th the particles are expelled from the conveyor belt, the particle séparation takes place proportionally between the magnetic and centrifugal forces to which the particles are subjected.

Thus, for particles with dimension lower than 100 pm, in most cases the magnetic force is higher than the centrifugal force, which also leads to the conduction of non-magnetic particles to the zone intended for receiving magnetic particles.

In view of the average granulométrie distribution of the material in waste basins with d50 of 27 microns, which means that 50% of the passlng material Is at 27 microns, and a d80 of 51 microns, which means that 80% of the passing material Is at 51 microns, it is possible to notice an extremely fine material, difficult to dry by conventional methods.

Prior art reference US 3,754,713, published on August 28, 2013 is directed to the séparation of metailic iron obtained from the réduction of ilmenite with carbon, provided with a rotating magnetic drum which does not hâve the required magnetic intensity to separate fines and superfines as almed by the présent invention.

Document US 4,317,717, published on March 02, 1982 discloses an equipment for recycling urban waste, and recyclable materials such as aluminum cans, wherein the magnets used therein are ferrite magnets (iron-boron) whereby the maximum intensity of 1,500 Gauss is not sufficient to separate the oxldized iron minerais, such as hématite (FeîOa).

A further prior document, US 3,021,951, refers to an inner drum magnetic separator with several magnet devices aitemating north and south, which in the bottom of the drum coilects the magnetic minerais of high magnetic susceptibility, such as metailic iron in the recycling of Industrial and househoid waste, made of ferrite magnets (iron-boron), with a maximum Intensity of 1,750 Gauss, thus with a magnetic field that is also insufficient to separate the oxidized iron minerais such as hématite.

US 4,016,071 discloses a magnetic drum, developed for séparation of metailic iron in metailic waste, similar to US 4,317,717, built with ferrite magnets (iron-boron) and which, likewise, does not allow the attraction of iron minerais of low magnetic susceptibility that is the case of oxidized iron ores in general with particle size less than 150 microns.

Fînally, prior art document US 5,394,991 consiste of an apparatus for generating eddy current, wherein the magnet rotor rotâtes at high rpm (+/- 3500 rpm) and generales eddy current. This machine was designed for the recycling of non-magnetîc conductive metais and magnetic metals wherein non-magnetic conductive metais include aluminum cans, brass, stainless steel and copper and non-conductive and magnetic metals, which consists of metallic iron with a high magnetic susceptibility. Its manufacturing cost is extremely high which prevents it from being applied in the iron mining industry. In addition, the magnets that form the magnet rotor, are made of solid bars of ferrite magnet, therefore, of low intensity that lacks sufficient force to attract the oxidized iron minerais (e.g., hématite), which characteristically présent low magnetic susceptibility.

Objectives and Advantages of the Invention

According to the scénario set forth above, the présent invention has the objective of providing a system and a process for dry recovery of fines and superfines of oxidized iron ore, which are highly efficient and do not hâve the environment drawbacks of processes and Systems in use at présent, which further hâve implantation and operation costs that are perfectly admissible to the industry.

In the same way, the présent invention further aims at providing a magnetic séparation unit that is efficient for materials that traditionaliy cannot be processed by conventionally employed magnetic roll separators.

Such objectives are achieved in an absolutely effective manner, reducing the potential risk for the environment in implanting the system, promoting a rational use of the naturel resources, recovering the wastes that may represent environmental risk in case of accidents at the barrages and in stacks, and with a friendiy interaction with the surroundings.

In terms of growing environmental demands, the présent invention constitues a definitive reply to the challenge of generating économie results in an environmentally sustainable manner, characterized chiefly by:

• greater mass and metaliurgical recovery of iron;

• recovery of fines from iron ore in fractions < 100 mesh (about 150 microns) without loss by hauling;

• clean combustion, without residues;

• non-existence of residues to the atmosphère;

• more efficient séparation of iron with génération of cieaner waste having lower iron contents;

• logistic optimization with localized treatment;

• préservation of streams and aquifers;

• minimization of the risk of accidents with barrages;

• decrease in the physical space intended for implantation;

• low energy consumption;

• modularity and flexibility of the system;

• increase in the lifetime of the mines.

As said before, the singularity of the solution of the present invention lies on adopting of an entirely dry minerai processing route, which requires the introduction of a drying unit prior to the feedlng of the finest fractions into the magnetic separator.

The route that constitutes the mainstay of the present invention can be summarized as follows: the moisture degree of the ore is reduced by means of a mechanical stir dryer (using naturel gas to prevent contamination or buming of biomass), which is then sorted into various fractions and finaliy separated magneticaily, with the important différence of being an entirely dry process.

Brief Description of the Drawings

Figure 1 shows a schematic diagram:

Figure 2 shows an operational flowchart of the process;

Figure 3 shows a rapid dryer with mechanical stir/mechanical stir system used in the process and in the system of the present invention;

Figure 4 shows an arrangement of the set of cyclones;

Figure 5 shows a diagram of distribution of the forces actuating on the magnetic roll of a magnetic séparation unit;

Figure 6 shows a diagram of the magnetic field lines existing around a permanent magnet employed on the magnetic roll of a magnetic séparation unit;

Figure 7 is an illustrative diagram of the ratio of the field lines with the thicknesses of the magnets and the gap;

Figure 8 is a scheme of the magnetic séparation unit according to the present invention.

Detalled Description of the invention

Before initiating the description of the invention, it should be polnted out that the magnitudes set forth herein are given merely by way of example, so that they should not be taken as limitation of the scope of the present invention. A person skiiled In the art, In the face of the presently disclosed concept, will know how to détermine the magnitudes suitable to the concrète case, so as to achieve the objectives of the present Invention.

tn figure 1, the reference numbers 1 to 7 represent steps and components just as they are traditionally employed In the prior art, so that they do not incorporate the innovations brought by the present invention.

In this regard, there is a volume of material to be processed (1), which is extracted by an excavator (2) and placed in a truck bucket (3). The truck (3) feeds a silo or hopper (4), which is then led by a shaking conveyor (5) to a sieve (6) intended for carrying out the preliminary séparation.

The sieve (6) may consist of a shaking sieve for removal of contaminating material. In this way, the material Is led to a lung stack (7).

The capadty of said lung stack (7) can reach 2,000 tons of material, for instance.

Additionally, a mist curtain involving the hopper may be provided to prevent dust from falling on the extemal part of the hopper. In this regard, the belt conveyor may be completely enclosed, thus preventing possible loss of material and the conséquent émission of dusts Into the atmosphère.

Below the lung stack (7), there may be a duct comprising a shaking feeder (not shown), which wiil transfer the ore to the belt conveyor.

From the belt feeder of the lung stack (7), the material is then led to the first one of the so-called three unitary operations that constitute the présent invention. The first unitary operation is the particle drying/disaggregation process.

Hence, in order to solve the already mentioned problem of drying/disaggregation of fine particles, and to obtain particles 100% individualized to achleve maximum efficiency In the magnetic séparation process, It Is proposed the use of a rapid dryer (9) with mechanical stirring/mechanical stirring System, as shown in figure 3.

The dryer (9) Is composed by a heatlng chamber (87), which generates hot air (maximum température around 1,100°C) introduced in the main body, Inside which two axles (9.1) with propellers (9.2) are provided, which cause the movement of the particulates both vertically and horizontally. These gases go through a labyrinth System (9.5), which forces the heated air to corne into contact with the material. The moving of particles vertically, besldes promoting contact of particles with hot air to increase the efficiency of the dryfng process, further facilitâtes the removal of fines by the System of fine collection due to the négative pressure exerted by the exhauster. There Is also an efficient disaggregation step of the so-called “fine-waste barrage. In this way, particles are moved horizontally, so that the dry material moves along the main body as far as the discharge point.

The dryer may be sized, for instance, for a capacity of 200 t/h, based on the characteristics of the material to be dried; the dryer may hâve, for instance, capability for drying, disaggregating and, at the same time, removing the fines. Its operationai capabilities can hâve high performance whenever up to 98% of the total volume of the fed material to the dryer is iower than 100 mesh (about 150 microns).

The main characteristics of the dryer employed ln the tests carried out are listed hereinafter:

• two rapîd dryers, each being equipped with two 150 hp motors; the assembly has two pendulum double siuice valves with reducing motor, each having power of 7.5 HP X 2 = 15 HP, one being intended for feeding the product to the dryer and the other for dlscharging the fraction > 100 mesh of the dried product. These valves prevent the entry of air in the System, as well as the exït of hot gas, thus keeping the performance at the température of the hot gases, that Is, the thermal balance Is excellent;

• two hot gas generators with ducts that interconnect the generator to the dryer, coated with refractory material. There are still inlet valves for cold air to keep the balance of the températures measured In thermopairs. These températures may be Indicated and controlled on the panel;

• a duct for Interconnection of the cyclones to the sleeve fîlters 22, plus worm thread for letting out the products, exhauster and chimney;

• an electric panel for the System, plus automation and measuring and controlling Instruments.

The dryer further has a complété dust aspiration System, wherein the dusts are coliected at different cycloning stages, thus preventing the particulates from escaping Into the environment. As already said, in order to generate heat one uses natural gas, which together with the adéquate control of the air flow, in a correct air/fuel ratio, provides clean and complété combustion, with the gases being discharged after passing through press fîlters.

The process of removlng the gases containing water vapor and fines is carried out by a high-capadty exhauster arranged at the end of the circuit. Associated to the exhaustlon System circuit, there is the component that intégrâtes the so-called second unitary operation of the process of the présent invention, which consists In alr-sorting of 89% of fines fed. Such a component consists of at least one set of cyclones 10,12,14,16, 18 and 20 connected in sériés, as shown in figure 4.

The cyclones collect the fines with different grain sizes. These cyclones will perform a sélective and decreasing rétention depending on the grain size of the material fed. Therefore, the first cyclone may be configured, for instance, to hâve coarser particles, such as 44 pm, ln the second and ln the third, the grain size of the retained material would be about 37 pm, and gradually at each cyclone as far as the last cyclone with rétention of finer particles up to 10 pm. The airsorting takes place at the cyclones as a function of the loss of speed by each cyclone.

The grain distribution achieved with the exemplified arrangement In question ls shown In Table 1 below.

Table 1 - Graln-SIze Distribution - Exhaustlon System - Cyclones

Grain Distribution - Exhaustlon System - Cyclones	welght%	t/h
1 st cyclone (fraction -100 and + 325 mesh)	15.26	76.30
2nd cyclone (fraction -325 and + 400 mesh)	11.05	55.25
3rd cyclone (fraction -325 and +400 mesh)	11.05	55.25
4th cyclone (fraction -400 and +500 mesh)	15.24	76.20
5th cyclone (fraction -500 and +600 mesh)	12.73	63.65
6th cyclone (fraction -600 and +10 microns)	16.26	81.28
7th Sleeve filters (fraction -10 microns)	16.26	81.30
Totals	97.85	489.23

Finaliy, with regard to the superfine particles, below 10 pm, they are sucked and removed In a set of sleeve filters (22). The products coliected at the different cyclones are Intended for magnetic séparation, to recover a magnetic product of high iron contents In the pellet sorting (fraction -100 mesh or 0.15 mm at zéro mm).

The coarser fraction lower than 2 mm and higher than 0.15 mm is released at the dryer discharge. In order to prevent heat loss, the discharge is then controlled by two double-stage valves, the dried material is coliected and transported by a conveyor belt to a magnetic separator.

With regard to the séparation step, more specificaliy the magnetic séparation, it consiste of the third unitary operation of the process of the présent Invention.

The Installed capacity of the magnetic séparation unit ls of up to 15 ton/h for each drying unit (without being limited to this value), comprising relier magnetic separator. At this stage, each fraction has a different treatment, as exemplified hereinafter • the coarser fractions (fractions lower than 40 mm and higher than 6.35 mm and in the fraction lower than 6.35 mm and higher than 2 mm) are separated by the first and second magnetic high-intensity separators with roller diameter of 230 mm, equipment with magnetic intensity sufficient to retain particles of up to 40 mm on the surface of the magnetic rail;

• the intermediate fractions, lower than 2 mm and higher than 0.15 mm, wili be separated by the third medium-intensity drum magnetic separator (6.500 gauss);

• finally, finer fraction, lower than 0.15 mm (about 150 microns), has their magnetic dry séparation considered as a great operational difficulty, due to the dragging of non-magnetic fines to the magnetic fraction, caused by the magnetic fîeld lines. The fîeld lines, when moved at a high speed, generate currents (Eddy Current).

This process is used to separate conducting metals, for example, in recyclable aluminum cans, representing an invisible and actuating force for the fine-grained particles.

Hence, the présent invention further provides a high-intensity magnetic-roll-separation piece of equipment, exclusively for separating iron oxide fines at grain sizes of 0.15 mm to zéro. At this magnetic séparation, it is possible to obtain a product with high Fe (T) contents. For instance, in the test of ore sample, the recovered iron content was of 68.72. Each of the products is collected at different bails for better utilization and blending with the products obtained.

With regard to the functioning of said magnetic séparation, this operation consists of a process in which two or more materiaîs of different magnetic susceptibllity are separated from each other. The main driving power is magnetic force (Fm/Mf). In addition to this force, other forces also actuate on the particles, such as the centrifugal force (Fc/Cf) and the gravity force, as shown in figure 5.

Thus, a particle is considered to be MAGNETIC when Fm > Fc + Fg and is considered to be NON-MAGNETIC when Fm < Fc + Fg. For coarser particles, higher than 15 pm, at the same speed, a centrifugal force is greater than one at a 40-pm particle.

In the face of this scene, the magnetic séparation of fine particles is usually considered a great difficulty or even impossible. Fine-grained particles exhibit low centrifugal force, as demonstrated In the formula below.

Fc = m . v² /r wherein:

Fc = centrifugal force m = mass v = velocity r = radius.

As will be recognized by those skilled in the art, fine particles, besides exhibiting lower centrifugal force, further undergo the influence of the magnetic field, so that the smaller their diameter the greater this Influence. When this magnetic field Is subjected to rotation, a conducting field is generated, which Is known as Eddy Current, which tend to draw the fine particles to the magnetic fraction. The magnetic field lines created by a permanent magnet are shown In figure 6.

The magnetic rails used in the présent Invention are made by conjugating magnets having the same polarity (North) with a gap, thus creating magnetic field lines that alter throughout the magnetic rail. The ratio between the magnetic thickness and the gap thickness is responsible for the depth of the magnetic field known as gradient, as demonstrated In figure 7.

Thus, bearing In mind the fact that fine particles exhibit low centrifugal force and the drawing of the non-magnetic fraction to the magnetic fraction caused by the magnetic field fines, the présent Invention proposes a fine-separation scheme that has the objective of overcoming the limitations reported above. The scheme comprises inclining the magnetic rail, as shown in figure 8, to raise the particle velocity, decreasing the contact area of the magnetic field and, as a resuit, contributing to the increase of the resuit of the centrifugal force and gravity force.

Besides, In order to increase the particle velocity so as to overcome the draw of the non-magnetic fraction, it was necessary to Increase the magnetic field depth, as a ratio of 3:1 (magnetic thickness: gap thickness).

In this regard, the inclination angle may undergo a variation depending of the grain fineness, so that for finer particles the inclination angle may be greater. The variation of this angle will be easily determined by a person skilied in the art, as long as he is aware of the inventive concept disclosed In this patent.

The permanent-magnet used in the magnetic separators exhibit the following characteristics, which Impart selectivity to the magnetic séparation process:

• low gradient;

• high magnetic intensity, maximum up to 13,000 gauss, the magnetic intensity may be higher or lower depending on the arrangement, the magnet thickness and the gap thickness;

• ratio of magnet of larger thickness versus gaps of smaller thickness provide higher magnetic intensity;

• Rare-Earth permanent magnet having In their composition 52% of neodymium, besides Iran and boron. The magnetic saturation level is directly proportïonal to the amount of neodymium.

Other characteristics of this equipment are presented hereînafter.

• the magnetic roi! Is of the permanent type of high Intensity, high gradient, built with superpotent neodymium, résistant to températures of up to 80 °C and steel dise of high magnetic permeability;

• the actuation of the magnetic roll is effected by means of a complété, variable-velocity 2.0 HP AC motor with three-phase frequency Inverter for 220 VGA (VAC) 60 Hz, (it may be run on 220 / 380 / 440 VGA (VAC) • the belt tensioning and aligning system may solve the problem related to the short distance between small-diameter rolls of thin belt. It is possible to replace the belt In a few minutes, without the need for spécial tools. The three guide Systems used enable one to tension and align the belt, thus prolonging Its lifetime;

• a séparation belt of the type of polyester fabric coated with a PU (Polyuréthane) layer, with 0.6 -1.00 mm thickness;

• roller-type feed system with a 2.0 HP, 220 VAC, three-phase driving motor with frequency inverter, for regulating the feed velocity. It includes storage silo; this type of feeder enabies a more controlled and uniform feed, especially for particles having different densities or formats, and is not sensitive to variations in the level of materiai in the silo. This Is the main technicai advantage over shaklng feeders;

• support structure built with carbon steel profiles, with respective paint finish, maklng the assembly a compact and easy-to-install unit. Entîrely dust-proof control panel, including measuring instruments, velocity controllers, frequency Inverters, feed voltage: 220 VAC, 60 Hz, three-phase.

However, ail the above conditions and characteristics enable an improvement Induced In the unit, according to which the permanent-magnet roll magnetic separator is arranged with a determined angling with respect to the horizontal, so as to provide an additional force that sums to the centrifugal force and thus manages to retain non-magnetic materials satisfactorily.

Such an arrangement may be vlewed on the magnetic separators Illustrated In figure 1 under reference numbers 11,13,15,17 and 21.

The equally mentioned iow gradient results from the magnetic depth resulting from the arrangement of the magnets and gaps.

Example 1

Analysis of waste sample

With a view to make a physicochemical characterization of a known pile of wastes, to attest the efficiency of the technology of the plant of the présent invention in its dry processing, and with the highest recovery possible of the iron oxide contained therein, one has collected samples of said pile for analysis by a specialized laboratory, using a circuit mounted at the laboratory itself, simulating the same operational route adopted by the plant of the invention.

The ore sample of the waste pile exhibited an extremely simple mineralogy, constituted essentially by iron-bearing minerais and by a non-magnetic fraction, wherein the iron5 bearing materials are: magnetite, martite, hématite and by iron oxides and hydroxides, as shown hereinafter (Table 2). The non-magnetic fraction is composed essentially by silica. The percentage of these minerais is shown in Table 2 below.

Table 2

Minerais	Chemical formula	Weight%
Magnetite	Fe2’Fe2”O4 or Fe3O4	18
Martite	Fe3O4 => Fe2O3	15
Hématite	Fe2O3	47
Silica	SiO2	15
Iron Oxide and hydroxide	Fe(OH)2	5

In the first test, a metaliurgical recovery of 70.17% of total iron was obtained, which is quite high for the industry, the resuit of which can be seen in Table 3 below:

Table 3 - First test of sample of waste

Chemical analysis
Head contents	Fe(T) = 42.09%

Granulometry
Fraction	Weight	Weight%	% Fe	Fe count	Dist.Fe%
> 5mm	180.0	4.85	44.52	2.16	5.06
> 3mm	120.0	3.23	55.25	1.79	4.19
> 1mm	220.02	5.93	59.77	3.54	8.30
> 325#	2.170.0	58.59	37.14	21.72	50.50
> 325#	1,020.0	27.49	48.98	13.47	31.55
TOTAL	3,710.0	100.00		42.68	100.00

Magnetic Séparation - Hlgh-Intenslty Roll Magnetic Separator
Fraction -1mm and +325 mesh
Product	Weight	Weîght%	% Fe	Fe cont	Dist.fe%
MAGNETIC	986.05	26.88	66.60	17.90	41.94
MIXED	32.44	0.88	50.24	0.44	1.04
NON- MAGNETIC	1127.31	30.73	10.99	3.38	7.91
TOTALS	2145.80	56.49		21.72	50.89
The fraction -1mm and +325 mesh contains 21.72% Iran; a recovery of 41.94% relative to the sample was achieved;

Magnetic Séparation - Hlgh-Intenslty Roll Magnetic Separator
Fraction -325 mesh
Intensity	Weight	Weight%	% Fe	Fe cont	Dist. Fe%
1,000 gauss	10.06	0.27	67.26	0.18	0.43
2,000 gauss	28,42	0,77	68,09	0,52	1,22
4,000 gauss	82,55	2,22	68,38	1.52	3,56
8,000 gauss	331.10	8.92	68.40	6.10	14.30
16,000 gauss	206.73	5.57	66.76	3.72	8.71
nonmagnetic	361.14	9.73	14.56	1.42	3.32
total	1,020,00	27.49		13.47	31.55
The fraction -325 mesh contains 31,55 % of Iran; a recovery of 28.23% was achieved in this fraction.
RECOVERY % (fraction -1 mm +325 and -325 mesh) 70.17
The fraction +1mm further containing 17.55% of the Iran contained, which may be recovered in a hlgh-lntensity magnetic separator with différéntiated gradient, Is still

to be processed.

The maximum recovery can reach 70.17% + 17.55% = 87.72%.

ln order to prove the efficiency of the process, a new sample of larger volume was collected and processed.

After the processing, the foliowing résulte were obtained:

• Fraction higher than 6.35 mm achieved a recovery of 19.86% by weight, with Fe(T) contents of 63.75%, which corresponds to a metallurgical recovery of 26.33% of the Iran contained;

• Fraction lower than 6.35 mm and higher than 2 mm achieved a recovery of 11.85% by weight, with Fe(T) contents of 62.63%, which corresponds to a recovery of 15.44% of the iron contained;

• Fraction lower than 2 mm and higher than 100 mesh with recovery 14.87% by weight and Fe(T) contents of 62.03%, which corresponds to a metallurgical recovery of 19,18% of contained iron;

• Fraction lower than 100 mesh with recovery of 13.86% by mass and Fe(T) average contents of 68.72%, which corresponds to a metallurgical recovery of 19.80% of the iron contained.

Thus, in the second test, carried out according to the established flowchart, and a route simulating the invention, one achieved a recovery of 60.45% by weight with average Fe(T) contents of 64.23% and a metallurgical recovery of 80.75% of the Iran contained, still higher than that obtained in the first test.

The results of the tests developed in laboratory attest the efficacy of the technological route of dry magnetic recovery of the présent invention, in the processing of the dump from said pile of wastes. The results or the second test are shown in tables 4 (chemical grain analysis) and 4 (recovery table) below.

Table 4 - Second test of waste sample

Unit	3.20%
Chemical analysis
Head contents	Fe(T) = 48.08%
GRANULOMETRY

Fraction	Weight	Weight%	Fe%	Fe cont	Dist. Fe%
+1/4’	7,700.0	26.75	60.42	16.16	33.60
-1/4 and+2mm	3,700.0	12.85	59.73	7.68	1596
-2mm and +100 mesh	5,230.0	18.17	53.16	9.66	20.08
-100 mesh	12.160.0	42.24	34.57	14.60	30.36
TOTAL	28,790.0	100,00		48.09	100.00
Magnetic Séparation - Hlg	i-lntenslty Roil Magnetic Séparation
Fraction +1/4”
Product	Weight	Weight%	Fe%	Fe cont	Dlst. Fe%
Magnetic	5,719.,80	19.87	63.75	12.67	26.33
Mixed	1,461.30	5.08	59.47	3.02	6.28
Nonmagnetic	518.90	1.80	26.43	0.48	0.99
Totals	7,700.00	26.75		16.16	33.60
Metallurglcal recovery of Fe(T) In fraction -100 mesh of the Magnetic fraction = 16.33%
Fraction -1/4 and +2mm
Product	Weight	Weight%	Fe%	Fe cont	Dlst.Fe%
Magnetic	3,413.50	11.85	62.36	7.42	15.44
Mixed	114.60	0.40	40.35	0.16	0,33
Nonmagnetic	171.90	0.60	15.11	0.09	0.19
Totals	3,700.00	12.85		7.68	15.96
Metailurglcai recovery of the Fe(T) In fraction -100 mesh of t fraction = 15.44%	he Magnetic

Fraction -2mm and *100 mesh
Product	Weight	Weight%	Fe%	Fecont	Dlst.fe%
Magnetic	4.279.60	14.87	62.03	9.22	19.18
Mixed	132.10	0.46	25.22	0.12	0.24
Nonmagnetic	818.30	2.84	11.27	.032	0.67
Totals	5.230.00	18.17		9.66	20.08
Magnetic recovery of Fe (T) in fraction -2mm and +100 mesh of Magnetic fraction 19.18%
Magnetic Séparation - Hlgh-intensity Roi) Magnetic Separators
Fraction -100 mesh
Product	Weight	Weight%	Fe%	Fe Cont	Dist. Fe%
Magnetic	3,990.00	13.86	68.72	9.52	19.80
Mixed	1,090.00	3.79	43.57	1.65	3.43
Nonmagnetic	7,080.00	24.59	13.94	3.43	7.13
Totals	12.160.00	42.24		14.60	30.36
Metallurgical recovery of Fe(T) of Magnetic Fraction = 19.80% with Iron contents = 68.72%
Metallurgical recovery of Fe(T) of Magnetic Fraction + Mixed = 22.23% with Fe contents = 63.32%
	Weight%	Dist Fe(T)%
Total Iron Recovery ln the Sample	60.45%	80.75%

Table 5

Summary - Recovery Table

Product	Weight	Weîght%	Fe%	Fe cont	Dîst. Fe%
Magnetic +1/4	5,719.80	19.87	63.75	12.67	26.33
Magnetic - 1/4 and +2mm	3,413.50	11.85	62.63	7.42	15.44
Magnetic 2mm and +100mesh	4,279.60	14.87	62.03	9.22	19.18
Magnetic - 100 mesh	3,990.00	13.86	68.72	9.52	19.80
Totals	17.402.90	60.45	64.23	38.83	80.75

Moreover, during the tests camed out, one further determined the granulometry profile of the collected material, as shown in Table 6 below.

Table 6

Granulometry of the feed ofthe plant

Feed	250
		Weight	Weight%	Ton/solids
	Fraction +40mm	6.38	2.93	7
	Fraction+ 1/4	42.87	19.72	49
	Fraction +2mm	46.71	21.48	54
	Fraction +100 mesh	46.23	21.26	53
	Fraction +200 mesh	15.45	7.10	18
	Fraction +325	35.21	16.19	40
	Fraction +400 mesh	23.48	10.80	27
	Fraction +500	1.11	0.51	1

	mesh
	Fraction -500 mesh	32.58	14.99	37
	Totals	217.41	100.00	250

Although the present Invention has been described with respect to its particular characteristics, it is dear that many other forms and modifications of the Invention will be obvious to those skilled in the art.

The accompanying claims were worked out so as that they can cover such obvious 5 forms and modifications, which will be within the scope of the present invention.

Claims (11)

1. A System for dry recovery of fines and superfines particles of oxidized Iron ore (1), characterized ln that the recovery Is carried out ln a totaliy dry metallurgical route, provided with a dryîng means (9) with mechanical stirring, at least one set of cyclones (10,12,14,16, 18, 20) for air-sorting of fed material at different granulométrie ranges; and magnetic dfyer séparation (11,13,15, 17, 21) using a permanent high intensity Rare Earth roli separators arranged at an Inclination so as to Increase the resulting force between the centrifugal and the gravitational forces that are acting on the non-magnetic fine-grained particles of oxidized iron-ore (mostly ln the form of hématite), to avoid their dragging with the magnetic fraction and contamination of the oxidized Iron ore concentrate.

2. A system according to claim 1, characterized in that the metallurgical route further comprises a complementary Systems for material feed, preliminary réduction of ores, transport, storage, sieve sorting, sleeve filters.

3. A system according to claim 1, characterized ln that a mist curtain is provided to prevent dust from falling on the outside of the hopper.

4. A system for treating oxidized iron ore wastes according to claim 1, characterized ln that a conveyor belt Is enclosed in such a way that it prevents loss of material and émission of dust Into the atmosphère.

5. A system for treating oxidized iron ore wastes according to claim 1, characterized in that the iron-ore wastes are deposited in barrages.

6. A system for treating oxidized iron ore wastes according to claim 1, characterized in that the Iron-ore wastes are stocked ln piles.

7. A process for dry recovery of fines and superfines of oxidized iron ore , characterized by comprising the steps of:

(a) drying and disaggregating the ore by mechanical stirring;

(b) sélective air-sorting on the basis of the granulometry of the material in cyclonlng operation; and (c) magnetic séparation by means of permanent high intensity Rare Earth roli separators arranged at an inclination so as to increase the résultant of the centrifugal force and gravity force that actuates on the non magnetic fine ores to avoid their dragging with the magnetic fraction and contamination of the iron oxide ore concentrate.

8. A process according to claim 7, characterized by further comprising a step of transferring the ore to a storage area for the drying or disaggregation system by the a conveyor belt through a duct provided with a shaking feeder.

9. A process according to claim 7 or 8, characterized in that the separator opérâtes with magnetic intensity that can reach up to 13,000 gauss.

10. Magnetic séparation unit (11, 13, 15, 17, 21) for the séparation of determined fractions corresponding to ore wastes, characterized by comprising a permanent high intensity Rare

5 Earth roll separators arranged at an inclination so as to Increase the resulting forces between the centrifugal and the gravitational forces that are acting on the on the nonmagnetic fine-grained particles of oxidized iron-ore to avoid their dragging with the magnetic fraction and contamination of the iron oxide ore concentrate.

11. Magnetic séparation unit according to claim 11, characterized in that the permanent-

10 magnet roll comprises magnets of the same polarity (North) with a gab gap In the middle, followed by magnets of the same polarity (South) with a gap in the middle, with a magnetthickness: gap-thickness ratio of 3:1.