Patent Application
20150076037
The present invention refers to a process and a system for dry recovery of iron-ore fines and superfines from iron-mining waste basins. The invention further deals with a magnetic separation unit for separating the iron-ore fines by dry process.
In this regard, the present invention aims at improving the recovery of iron ores still contained in said wastes, providing high metallurgical and mass recoveries. Thus, it is possible to obtain a commercially superior product, more precisely an iron-ore concentrate with contents higher than 63% Fe. Such a result represents a significant advance from the environmental point of view, if one considers the risk that is historically represented by wastes of the mining industry in Brazil and in the rest of the world.
The innovatory characteristics of the dry process of the present invention meet advantageously the economical, environmental and strategic requirements of the mining industry, enabling the improved recovery of the ore wastes that constitute a risk of high environmental impact, changing them into commercial products in a technically and economically feasible manner. In this dry process no water is used, and the final residue will be a stack of waste, without the need to further waste barrage.
At the beginning of the mining activities on an industrial scale, little was known about the techniques for disposing waste. The low interest in this area was still due to the fact that the amount of wastes produced was reasonable small and the environmental problems were not part of the operational worries of the industry yet.
In this regard, the waste was usually thrown at random into streams. However, with the growth of the mining sector, the growing social concern about the environmental issue, as well as the appearance of a few accidents with waste retention barrages since the seventies in various parts of the world, including Brazil, the challenge of guaranteeing the operation of the industrial units was imposed on the mining companies with a view to minimize the environmental impacts and reduce the risks of accidents, through more secure and optimized projects.
In general, three techniques are used for disposing mining wastes, namely:
by wet way in barrages,
by dry way in waste stacks, or
by using the paste fill technology.
The difference between the wet-way disposal and the dry-way disposal is that, by the barrage wet way, there is also retention of liquids in conjunction with the solid material discarded. The high-intensity magnetic separation is traditionally adopted for continuous flows of material, like WHIMS—Wet High Intensity Magnetic Separation.
With regard to the paste-fill disposal, this is an alternative to conventional practices, which has advantages like greater recovery and recirculation of water, larger rest angels and smaller impact on the environment. However, this process is carried out at high implantation and operation costs.
For instance, Brazilian Patent Application BR PI 0803327-7 discloses a magnetic concentration process with low consumption of water and low generation of waste slurry. The wet magnetic separation and disposal of the magnetic waste may decrease the throwing of much of the solid waste into decantation barrages. However, said process does not deal with the recovery of the waste. So, there is no effective decrease in the environmental risk inherent in the activity.
Another document, patent application BR PI0103652-1 describes a process of recovering residues from iron oxide. These residues may be obtained directly by recovering fines from metallurgy reduction processes, as well as the deviation of return of fines from companies that supply iron ore to iron and steel companies. 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 reduction furnaces by a conveyor-belt system.
With regard to the step of drying/desegregating the waste for subsequent separation, 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), leading to a low efficiency rate of the equipment for coarse particles and even greater inefficiency for fine particles.
Fluid-bed dryers are recommended for coarse particles that enable the formation of fluid beds, and it is impossible to form a fluid bed for fine particles.
Spray Dry, which is widely used today in the ceramic industries in preparing masses for the process of manufacturing porcelanato floors. However, in order to dry 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 separation process usually employed in the prior art, one usually employs a magnetic roll piece of equipment, or a high-intensity permanent magnet drummer, the efficiency of which is satisfactory for separating materials dimensionally higher than 100 μm.
For materials having a lower dimension than this one (100 μm), the high-intensity magnetic roll separator, as it has been employed, has proved to be inefficient. This inefficiency results from the fact that, at the moment of expelling the particles from the conveyer belt, the particle separation takes place in the face of the proportion between the magnetic and centrifugal forces to which the particles are subjected.
Thus, for particles with dimension lower than 100 μm, 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 grain distribution of the material in medium waste basins with d50 of 27 microns, that is, 50% of the passing material at 27 microns and a d80 of 51 microns, that is, 80% of the passing material at 51 microns, it is possible to consider an extremely fine material, difficult to dry by conventional methods.
In the face of the situation set forth above, the present invention has the objective of providing a system and a process for dry recovery of fines and superfines of iron ore, which are highly efficient and do not have the environment drawbacks of processes and systems in use at present, which further have implantation and operation costs that are perfectly admissible to the industry.
In the same way, the present invention further aims at providing a magnetic separation unit that is efficient for materials that traditionally can be processed by conventionally employed roller magnetic 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 natural resources, recovering the wastes that may represent environmental risk in case of accidents at the barrages and in stacks, and with a friendly interaction with the surroundings.
In terms of growing environmental demands, the present invention constitutes a definitive reply to the challenge of generating economic results in an environmentally sustainable manner, characterized chiefly by:
greater mass and metallurgical recovery of iron;
recovery of fines from iron ore in fractions <100 mesh without loss by hauling;
clean combustion, without residues;
non-existence of residues to the atmosphere;
more efficient separation of iron with generation cleaner waste having lower iron contents;
logistic optimization with localized treatment;
preservation 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 useful life of the mines.
As said before, the singularity of the solution of the present invention lies on adopting an entirely dry mineral processing route, which requires the introduction of a drying unit prior to the feeding of the finest fractions to a 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 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.
Before initiating the description of the invention, it should be pointed 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 skilled in the art, in the face of the presently disclosed concept, will know how to determine the magnitudes suitable to the concrete case, so as to achieve the objectives of the present invention.
In
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 separation.
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 capacity of said lung stack 7 can reach 2,000 tons of material, for instance.
Additionally, a mist curtain involving the hopper may be provided, so as to prevent dust from falling on the external part of the hopper. In this regard, the belt conveyor may be completely enclosed, thus preventing possible loss of material and the consequent emission of dusts into the atmosphere.
Below the lung stack 7, there may be a duct comprising a shaking feeder (not shown), which provides transfer of 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 present invention. The first unitary operation is the particle drying/disaggregation operation.
Thus, in order to solve the already mentioned problem of drying/disaggregation of fine particles, and to obtain particles 100% individualized to achieve maximum efficiency in the magnetic separation process, one proposes the use of a rapid dryer 9 with mechanical stirring/mechanical stirring system, as shown in
The dryer 9 is composed by a heating chamber 87, which generates hot air (maximum temperature 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 force the heated air to come into contact with the material. The moving of particles vertically, besides promoting contact of particles with hot air to increase the efficiency of the drying process, further facilitates the removal of fines by the system of fine collection promoted by the negative 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 a capacity of, for instance, 200 t/h, on the basis of the characteristics of the material to be dried; the dryer may have, for instance, capability for drying, desegregating and, at the same time, removing the fines, wherein the material to be fed to the dryer being lower than 100 mesh may reach about 98%, based on the total.
The main characteristics of the dryer employed in the tests carried out are listed hereinafter:
two rapid dryers, each being equipped with two 150 hp motors; the assembly has two pendulum double sluice valves with reducing motor, each having power of 7.5 HP×2=15 HP, one being intended for feeding the product to the dryer and the other for discharging the fraction >100 mesh of the dried product. These valves prevent the entry of air in the system, as well as the exit of hot gas, thus keeping the performance at the temperature 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 temperatures measured in thermopairs. These temperatures may be indicated and controlled on the panel;
a duct for interconnection of the cyclones to the sleeve filters 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 complete dust aspiration system, wherein the dusts are collected 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 adequate control of the air flow, in a correct air/fuel ratio, provides clean and complete combustion, with the gases being discharged after passing through press filters.
The process of removing the gases containing water vapor and fines is carried out by a high-capacity exhauster arranged at the end of the circuit. Associated to the exhaustion system circuit, there is the component that integrates the so-called second unitary operation of the process of the present invention, which consists in air-sorting said 89% of fines fed. Such a component consists of at least one set of cyclones 10, 12, 14, 16, 18 and 20 connected in series, as shown in
The cyclones collect the fines with different grain sizes. These cyclones will perform a selective and decreasing retention depending on the grain size of the material fed. Thus, the first cyclone may be configured, for instance, to have coarser particles, such as 44 μm, in the second and in the third, the grain size of the retained material would be about 37 μm, and gradually at each cyclone as far as the last cyclone with retention of finer particles of up to 10 μm. the air-sorting 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 is shown in Table 1 below.
Finally, with regard to the superfine particles, below 10 μm, they are sucked and removed in a set of sleeve filters 22. The products collected at the different cyclones are intended for magnetic separation, to recover a magnetic product of high iron contents in the pellet sorting (fraction −100 mesh or 0.15 mm at zero 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 being collected and transported by a conveyor belt as far as the magnetic separator.
With regard to the separation step, more specifically the magnetic separation, it consists of the third unitary operation of the process of the present invention.
The installed capacity of the magnetic separation unit is of up to 15 ton/h for each drying unit (without being limited to this value), comprising roller magnetic separator. At this stage, each fraction has a differentiated 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 roll;
the intermediate fractions, lower than 2 mm and higher than 0.15 mm, will be separated by the third medium-intensity drum magnetic separator (6.500 gauss);
finally, finer fraction, lower than 0.15 mm, has their magnetic dry separation considered as a great operational difficulty, due to the hauling of non-magnetic fines to the magnetic fraction, caused by the magnetic field lines. The field lines, when moved at a high speed, generate currents (Eddy Current).
This process is used in separating conducting metals, for example, in recycling aluminum cans, representing an invisible and actuating force for the fine particles.
Therefore, the present invention further provides a high-intensity magnetic-separation roller piece of equipment, exclusively for separating iron fines at grain sizes of 0.15 mm to zero. At this magnetic separation, 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 differentiated bails for better utilization and blending with the products obtained.
With regard to the functioning of said magnetic separation, this operation consists of a process in which two or more materials of different magnetic susceptibility 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
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 μm, at the same speed, a centrifugal force is greater than the with respect to a 40-μm particle.
In the face of this scene, the magnetic separation of fine particles is usually considered a great difficulty or even impossible. Fine-grain 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
The magnetic rolls used in the present invention are made by conjugating magnets having the same polarity (North) with a gap, thus creating magnetic field lines that alter throughout the magnetic roll. 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
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 lines, the present invention proposes a fine-separation scheme that has the objective of overcoming the limitations reported above. The scheme comprises inclining the magnetic roll, as shown in
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 ration 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 skilled in the art, as long as he is aware of the inventive concept disclosed in this patent.
The permanent-magnet magnetic separators exhibit the following characteristics, which impart selectivity to the magnetic separation 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 iron and boron. The magnetic saturation level is directly proportional to the amount of neodymium.
Other characteristics of this equipment are presented hereinafter:
the magnetic roll is of the permanent type of high intensity, high gradient, built with superpotent neodymium, resistant to temperatures of up to 80° C. and steel disc of high magnetic permeability;
the actuation of the magnetic roll is effected by means of a complete, variable-velocity 2.0 HP AC motor with three-phase frequency inverter for 220 VCA (VAC) 60 Hz, (it may be run on 220/380/440 VCA (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 special tools. The threes guide systems used enable one to tension and align the belt, thus prolonging its useful life;
t separation belt of the type of polyester fabric coated with a PU (Polyurethane) 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 enables amore controlled and uniform feed, especially for particles having different densities or formats, and is not sensitive to variations in the level of material in the silo. This is the main technical advantage over shaking feeders;
support structure built with carbon steel profiles, with respective paint finish, making the assembly a compact and easy-to-install unit. Entirely dust-proof control panel, including measuring instruments, velocity controllers, frequency inverters, feed voltage: 220 VAC, 60 Hz, three-phase.
However, all 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 additional an force that sums to the centrifugal force and thus manages to retain non-magnetic materials satisfactorily.
Such an arrangement may be viewed on the magnetic separators illustrated in
The equally mentioned low gradient results from the magnetic depth resulting from the arrangement of the magnets and gaps.
With a view to make a physicochemical characterization of a known pile of wastes and to attest the efficiency of the technology of the plant of the present invention in its dry processing, and with the highest recovery possible of the iron 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 sample of ore of the pile of wastes exhibited an extremely simple mineralogy, constituted essentially by iron-bearing minerals and by a non-magnetic fraction, wherein the iron-bearing materials are: magnetite, matte, hematite and by iron oxides and hydroxides, as shown hereinafter. The non-magnetic fraction is composed essentially by silica. The percentage of these minerals is shown in Table 2 below.
In the first test, a metallurgical recovery of 70.17% of total iron was obtained, which is quite high for the industry, the result of which can be seen in Table 3 below:
The maximum recovery can reach 70.17%+17.55%=87.72%.
In order to prove the efficiency of the process, a new sample of larger volume was collected and processed.
After the processing, the following results 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 iron 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 iron 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 present 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.
Moreover, during the tests carried out, one further determined the granulometric profile of the collected material, as shown in Table 6 below.
Although the present invention has been described with respect to its particular characteristics, it is clear 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 forms and modifications, which will be within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| BR102012008340-0 | Mar 2012 | BR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/BR2013/000075 | 3/13/2013 | WO | 00 |
