U.S. patent application number 15/143871 was filed with the patent office on 2016-11-03 for process and system for dry recovery of fine-and superfine-grained particles of oxidized iron ore and a magnetic separation unit.
This patent application is currently assigned to New Steel Solucoes Sustentaveis S.A.. The applicant listed for this patent is New Steel Solucoes Sustentaveis S.A.. Invention is credited to Mauro Fumyo Yamamoto.
Application Number | 20160318037 15/143871 |
Document ID | / |
Family ID | 49221728 |
Filed Date | 2016-11-03 |
United States Patent
Application |
20160318037 |
Kind Code |
A1 |
Yamamoto; Mauro Fumyo |
November 3, 2016 |
PROCESS AND SYSTEM FOR DRY RECOVERY OF FINE-AND SUPERFINE-GRAINED
PARTICLES OF OXIDIZED IRON ORE AND A MAGNETIC SEPARATION UNIT
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.
Inventors: |
Yamamoto; Mauro Fumyo; (Rio
de Janeiro, BR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
New Steel Solucoes Sustentaveis S.A. |
Rio de Janeiro |
|
BR |
|
|
Assignee: |
New Steel Solucoes Sustentaveis
S.A.
|
Family ID: |
49221728 |
Appl. No.: |
15/143871 |
Filed: |
May 2, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14386574 |
Sep 19, 2014 |
9327292 |
|
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PCT/BR2013/000075 |
Mar 13, 2013 |
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15143871 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21B 2200/00 20130101;
B03C 1/30 20130101; B03C 1/12 20130101; B03B 9/00 20130101; B03C
2201/22 20130101; B03C 2201/20 20130101; B03C 1/10 20130101; B04C
9/00 20130101; B04C 2009/002 20130101; B03C 1/247 20130101; C22B
7/005 20130101 |
International
Class: |
B03C 1/247 20060101
B03C001/247; C22B 7/00 20060101 C22B007/00; B03C 1/30 20060101
B03C001/30; B03B 9/00 20060101 B03B009/00; B03C 1/12 20060101
B03C001/12; B04C 9/00 20060101 B04C009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2012 |
BR |
102012008340-0 |
Claims
1. A magnetic separation unit suitable for the separation of
determined fractions corresponding to fine and superfine particles
of oxidized iron ore, the magnetic separation unit comprising: a
permanent high intensity rare earth roll magnetic separator
operating with magnetic intensity that can reach up to 13,000 gauss
and arranged at an inclination that actuates over an inertial
reference of non-magnetic fines of oxidized iron ore and prevents
their dragging with a magnetic fraction and contamination of an
iron oxide ore concentrate.
2. The magnetic separation unit according to claim 1, wherein the
permanent high intensity rare earth roll magnetic separator
comprises magnets of north polarity with an intermediate gap,
followed by magnets of south polarity with an intermediate gap,
with a magnet-thickness: gap-thickness ratio where the
magnet-thickness is greater than the gap-thickness.
3. The magnetic separation unit according to claim 2, wherein the
magnet-thickness: gap-thickness ratio is 3:1.
4. The magnetic separation unit according to claim 2, wherein the
magnets of north polarity include at least two adjacent magnets of
north polarity with the intermediate gap thereof disposed between
the two adjacent magnets of north polarity, and the magnets of
south polarity include at least two adjacent magnets of south
polarity with the intermediate gap thereof disposed between the two
adjacent magnets of south polarity.
5. The magnetic separation unit according to claim 1, wherein the
permanent high intensity rare earth roll magnetic separator
comprises conjugated magnets having the same polarity with a gap
therebetween that create magnetic field lines that alternate
throughout the permanent high intensity rare earth roll magnetic
separator.
6. A system for dry recovery of fine and superfine particles of
oxidized iron ore, wherein the recovery is carried out in a totally
dry metallurgical route, the system comprising a plurality of
permanent high intensity rare earth roll separators capable of
reaching up to 13,000 gauss arranged at a conveyor belt with an
inclination that actuates over the inertial reference of
non-magnetic fine-grained particles of oxidized iron-ore and
prevents their dragging with a magnetic fraction and contamination
of a oxidized iron ore concentrate.
7. The system according to claim 6, wherein the permanent high
intensity rare earth roll magnetic separators each comprise magnets
of north polarity with an intermediate gap, followed by magnets of
south polarity with an intermediate gap, with a magnet-thickness:
gap-thickness ratio where the magnet-thickness is greater than the
gap-thickness.
8. The system according to claim 7, wherein the magnet-thickness:
gap-thickness ratio is 3:1.
9. The system according to claim 7, wherein the magnets of north
polarity include at least two adjacent magnets of north polarity
with the intermediate gap thereof disposed between the two adjacent
magnets of north polarity, and the magnets of south polarity
include at least two adjacent magnets of south polarity with the
intermediate gap thereof disposed between the two adjacent magnets
of south polarity.
10. The system according to claim 6, wherein each of the permanent
high intensity rare earth roll magnetic separators comprise
conjugated magnets having the same polarity with a gap therebetween
that create magnetic field lines that alternate throughout the
permanent high intensity rare earth roll magnetic separator.
11. A process for dry recovery of fines and superfines of oxidized
iron ore, comprising the step of: magnetically separating by means
of permanent high intensity rare earth roll separators operating
with a magnetic intensity that can reach up to 13,000 gauss and
arranged at a conveyor belt with an inclination that actuates over
an inertial reference of non-magnetic fines of oxidized iron ore
and prevents their dragging with a magnetic fraction and
contamination of the oxidized iron ore concentrate.
12. The process according to claim 11, wherein the permanent high
intensity rare earth roll magnetic separators each comprise magnets
of north polarity with an intermediate gap, followed by magnets of
south polarity with an intermediate gap, with a magnet-thickness:
gap-thickness ratio where the magnet-thickness is greater than the
gap-thickness.
13. The process according to claim 12, wherein the
magnet-thickness: gap-thickness ratio is 3:1.
14. The process according to claim 12, wherein the magnets of north
polarity include at least two adjacent magnets of north polarity
with the intermediate gap thereof disposed between the two adjacent
magnets of north polarity, and the magnets of south polarity
include at least two adjacent magnets of south polarity with the
intermediate gap thereof disposed between the two adjacent magnets
of south polarity.
15. The process according to claim 11, wherein each of the
permanent high intensity rare earth roll magnetic separators
comprise conjugated magnets having the same polarity with a gap
therebetween that create magnetic field lines that alternate
throughout the permanent high intensity rare earth roll magnetic
separator.
Description
RELATED APPLICATIONS
[0001] The present patent application is a Continuation of
application Ser. No. 14/386,574 filed on Sep. 19, 2014, which is a
371 of PCT/BR2013/000075 filed on Mar. 13, 2013, which claims
priority to Brazil Application No. 102012008340-0 filed on Mar. 19,
2012, the entire contents of which are hereby incorporated by
reference.
[0002] The present invention refers to a process and a system for
dry recovery of fine and superfine-grained oxidized iron ore from
iron-mining waste basins (also known as tailings). The invention
further deals with a magnetic separation unit to separate the
fine-grained oxidized iron ore (generally in the form of hematite)
using a dry process.
[0003] In this regard, the present invention aims to improve the
recovery of iron ore still contained in mining dumps, often
considered as waste, by providing high metallurgical and mass
recoveries. Thus, it is possible to obtain a commercially superior
product, more precisely an oxidized iron ore concentrate with
Fe-contents higher than 63%. Such 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.
[0004] The innovatory characteristics of the dry process in the
present invention advantageous and simultaneously meet the
economical, environmental and strategic requirements of the mining
industry, enabling the improved recovery of the ore wastes that
constitute a risk of high environ-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 tailings.
DESCRIPTION OF THE PRIOR ART
[0005] At the beginning of the mining activities on an industrial
scale, little was known about the techniques for waste disposal.
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
concerns of the industry.
[0006] In this regard, the waste was usually thrown at into water
streams in a random manner. However, with the expansion of the
mining sector, the growing social concern about the environmental
issues, as well as the occurrence of a few accidents involving
waste retention tailings since the 1970's 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 to
reduce the risks of accidents, through more secure and optimized
projects.
[0007] In general, three techniques are used for disposing mining
wastes, namely: [0008] by wet way in tailings, [0009] by dry way in
waste stacks, or [0010] by using the paste-fill technology.
[0011] The difference between the wet-way disposal and the dry-way
disposal is that, in the wet way at tailings, there is also
retention of liquids along with the solid material discarded. High
intensity magnetic separation is traditionally adopted for
continuous flow of material, operating normally wet, a process
known internationally as WHIMS-Wet High Intensity Magnetic
Separation.
[0012] The paste-fill disposal is an alternative to conventional
practices, with advantages like greater recovery and recirculation
of water, larger resting angles and reduced environmental impact.
However, this process is carried out at high implantation and
operation costs.
[0013] For instance, the 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 release of large volumes of solid waste into decantation
tailings. However, this process does not deal with the waste
recovery. So, there is no effective decrease in the environmental
risk inherent of the mining activity.
[0014] Another document, the 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 it is led directly to the
reduction furnaces by a conveyor-belt system.
[0015] With regard to the step of drying/disaggregating the waste
for subsequent separation, the prior art usually employs 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.
[0016] Fluid-bed dryers are recommended for coarse particles that
enable the formation of fluid beds, but it is impossible to form a
fluid bed for fine particles.
[0017] Spray Dry is widely used today in the ceramic industries
especially in preparing masses for the process of manufacturing
porcelain 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 500 m.sup.3 of water, which makes the
operational cost unfeasible.
[0018] As to the magnetic separation process usually employed in
the prior art, one usually employs a magnetic roll equipment, or a
high-intensity permanent magnet drum, the efficiency of which is
satisfactory for separating materials dimensionally higher than 100
.mu.m.
[0019] For materials with dimensions lower than 100 .mu.m, 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 when the particles are expelled from the
conveyor belt, the particle separation takes place to the
proportion between the magnetic and centrifugal forces to which the
particles are subjected.
[0020] Thus, for particles with dimension lower than 100 .mu.m, in
most cases the magnetic force is higher than the centrifugal force,
which also leads to the conduction also of non-magnetic particles
to the zone intended for receiving magnetic particles.
[0021] In view of the average granulometric distribution of the
material in waste basins with d50 of 27 microns, which means that
50% of the passing 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 consider an extremely fine material,
difficult to dry by conventional methods.
[0022] Prior art reference U.S. Pat. No. 3,754,713, published on
Aug. 28, 1973 is directed to the separation of metallic iron
obtained from the reduction of ilmenite with carbon, provided with
a rotating magnetic drum which does not have the required magnetic
intensity to separate fines and superfines as aimed by the present
invention.
[0023] Document U.S. Pat. No. 4,317,717, published on Mar. 2, 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 oxidized iron
minerals, such as hematite (Fe.sub.2O.sub.3).
[0024] A further prior document, U.S. Pat. No. 3,021,951, refers to
an inner drum magnetic separator with several magnet devices
alternating north and south, which in the bottom of the drum
collects the magnetic minerals of high magnetic susceptibility,
such as metallic iron in the recycling of industrial and household
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 minerals such as
hematite.
[0025] U.S. Pat. No. 4,016,071 discloses a magnetic drum, developed
for separation of metallic iron in metallic waste, similar to U.S.
Pat. No. 4,317,717, built with ferrite magnets (iron-boron) and
which, likewise, does not allow the attraction of iron minerals of
low magnetic susceptibility that is the case of oxidized iron ores
in general with particle size less than 150 microns.
[0026] Finally, prior art document U.S. Pat. No. 5,394,991 consists
of an apparatus for generating eddy current, wherein the magnet
rotor rotates at high rpm (+1- 3500 rpm) and generates eddy
current. This machine was designed for the recycling of
non-magnetic conductive metals and magnetic metals wherein
non-magnetic conductive metals 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 minerals (e.g.,
hematite), which characteristically present low magnetic
susceptibility.
OBJECTIVES AND ADVANTAGES OF THE INVENTION
[0027] According to the scenario set forth above, the present
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 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.
[0028] In the same way, the present invention further aims at
providing a magnetic separation unit that is efficient for
materials that traditionally cannot be processed by conventionally
employed magnetic roll separators.
[0029] 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 tailings and in stacks, and with a
friendly interaction with the surrounding environment.
[0030] 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: [0031] greater mass and
metallurgical recovery of iron; [0032] recovery of fines from iron
ore in fractions<100 mesh (about 150 microns) without loss by
hauling; [0033] clean combustion, without residues; [0034]
non-existence of residues to the atmosphere; [0035] more efficient
separation of iron with generation of cleaner waste having lower
iron contents; [0036] logistic optimization with localized
treatment; [0037] preservation of water streams and aquifers;
[0038] minimization of the risk of accidents with tailings; [0039]
decrease in the physical space intended for implantation; [0040]
low energy consumption; [0041] modularity and flexibility of the
system; [0042] increase in the lifetime of the mines.
[0043] As said before, the singularity of the solution of the
present invention lies on adopting of an entirely dry mineral
processing route, which requires the introduction of a drying unit
prior to the feeding of the finest fractions into the magnetic
separator.
[0044] 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 or burning of biomass), which is then
sorted into various fractions and finally separated magnetically,
with the important difference of being an entirely dry process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 shows a schematic diagram:
[0046] FIG. 2 shows an operational flowchart of the process;
[0047] FIG. 3 shows a rapid dryer with mechanical stir/mechanical
stir system used in the process and in the system of the present
invention;
[0048] FIG. 4 shows an arrangement of the set of cyclones;
[0049] FIG. 5 shows a diagram of distribution of the forces
actuating on the magnetic roll of a magnetic separation unit;
[0050] FIG. 6 shows a diagram of the magnetic field lines existing
around a permanent magnet employed on the magnetic roll of a
magnetic separation unit;
[0051] FIG. 7 is an illustrative diagram of the ratio of the field
lines with the thicknesses of the magnets and the air gap;
[0052] FIG. 8 is a scheme of the magnetic separation unit according
to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0053] 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
limitative of the scope of protection 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.
[0054] In FIG. 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.
[0055] 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.
[0056] The sieve (6) may consist of a shaking sieve for removal of
contaminating material. In this way, the material is led to a
stockpile (7).
[0057] The capacity of said stockpile (7) can reach 2,000 tons of
material, for instance.
[0058] Additionally, a mist curtain involving the hopper may be
provided 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.
[0059] Below the stockpile (7), there may be a duct comprising a
shaking feeder (not shown), which transfers the ore to the belt
conveyor.
[0060] From the belt feeder of the stockpile (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 process.
[0061] Hence, 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, it is proposed the use of a rapid dryer (9)
with mechanical stirring/mechanical stirring system, as shown in
FIG. 3.
[0062] The dryer (9) is composed by a heating chamber (8), which
generates hot air (maximum temperature around 1,100.degree. C.)
introduced in the main body, inside which two axles 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 come into
contact with the material. The vertical movement of particles,
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 due to the negative
pressure exerted by the exhauster (24). 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 to the discharge point (9.3).
[0063] 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 have, for instance, capability for drying, disaggregating
and, at the same time, removing the fines. The volume of the
material fed to the dryer that is lower than 100 mesh (about 150
microns) can reach up to 98% of the total.
[0064] The main characteristics of the dryer employed in the tests
carried out are listed hereinafter: [0065] two rapid dryers, each
dryer 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.times.2=15 HP, one being intended for feeding the
product to the dryer and the other for discharging the
friction>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; [0066] two safety valves to
each dryer, in case of the occurrence of explosion; [0067] two hot
gas generators with ducts that interconnect the generator to the
dryer, coated with refractory material. There are also inlet valves
for cold air to keep the balance of the temperatures measured by
thermocouples. These temperatures may be indicated and controlled
in the panel; [0068] a set of cyclones and interconnecting ducts
for output for gases and products, as well as helical threads with
rotating valves. There is provided the support structure for the
cyclones. [0069] a duct for interconnection of the cyclones to the
sleeve filters 22, and threads for exit of the products, exhauster
and chimney; [0070] an electric panel for the system, automation
measuring and controlling instruments.
[0071] The dryer further has a complete powder aspiration system,
wherein the powder is collected at different cycloning stages, thus
preventing the particulates from escaping into the environment. As
already said, in order to generate heat, natural gas is used, 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.
[0072] The process of removing the gases containing water steam 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 provided the component that integrates the so-called
second unitary operation of the process of the present invention,
which consists in air-sorting of 98% 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 FIG. 4.
[0073] 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. Therefore, the
first cyclone may be configured, for example, to have coarser
particles, such as 44 .mu.m, in the second and in the third, the
grain size of the retained material would be about 37 .mu.m, and
gradually at each cyclone until the last cyclone with retention of
finer particles up to 10 .mu.m. The air-sorting takes place at the
cyclones as a function of the loss of speed by each cyclone.
[0074] The grain distribution achieved with the exemplified
arrangement in question is shown in Table 1 below.
TABLE-US-00001 TABLE 1 Grain-Size Distribution - Exhaustion System
- Cyclones Grain Distribution - Exhaustion System - Cyclones weight
% t/h 1st 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
[0075] Finally, with regard to the superfine particles, below 10
.mu.m, they are aspirated 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).
[0076] The coarser fraction lower than 2 mm and higher than 0.15 mm
is released at the dryer discharge. In order to prevent heat
losses, the discharge is then controlled by two double-stage
valves, the dried material is collected and transported by a
conveyor belt to the magnetic separator.
[0077] 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.
[0078] The installed capacity of the magnetic separation unit is of
up to 150 ton/h for each drying unit (without being limited to this
value), comprising roller magnetic separator. At this stage, each
fraction has a different treatment, as exemplified hereinafter:
[0079] 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; [0080] 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);
[0081] finally, finer fraction, lower than 0.15 mm (about 150
microns), has their magnetic dry separation considered as a great
operational difficulty, due to the dragging of non-magnetic fines
along with the magnetic fraction, caused by the magnetic field
lines. The field lines, when moved at a high speed, generate
currents (Eddy Current).
[0082] This process is used to separate conducting metals, for
example, in recyclable aluminum cans, representing an invisible and
actuating force for the fine particles.
[0083] Hence, the present invention further provides a
high-intensity magnetic roll separation equipment, exclusively for
separating iron oxide 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 different containers for better utilization and
blending with the products obtained.
[0084] 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). In addition to this
force, other forces also actuate on the particles, such as the
centrifugal force (Fc) and the gravity force (Fg), as shown in FIG.
5.
[0085] 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 .mu.m, at the same speed, a
centrifugal force is greater than that at a particle of 40
.mu.m.
[0086] In this scenario, the magnetic separation 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=mv.sup.2/r
wherein: [0087] Fc=centrifugal force [0088] m=mass [0089]
v=velocity [0090] r=radius.
[0091] As will be recognized by those skilled in the art, fine
particles, besides exhibiting lower centrifugal force, also 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 non-magnetic metallic
fine particles to the magnetic fraction. The lines of magnetic
field created by a permanent magnet are shown in FIG. 6.
[0092] The magnetic rolls used in the present invention are made by
conjugating magnets having the same polarity (North) with a gap
therebetween, thus creating magnetic field lines that alternate
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 FIG. 7.
[0093] Thus, bearing in mind the fact that fine particles exhibit
low centrifugal force as well as 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 FIG. 8,
to raise the particle speed, decreasing the contact area of the
magnetic field and, as a result, contributing to the increase of
the result of the centrifugal force and gravity force.
[0094] 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).
[0095] 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.
[0096] The permanent-magnet roll separators exhibit the following
characteristics, which provide selectivity to the magnetic
separation process: [0097] low gradient; [0098] 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; [0099] ratio of magnet of larger
thickness versus gaps of smaller thickness provide higher magnetic
intensity; [0100] 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.
[0101] Other characteristics of this equipment are presented
hereinafter: [0102] the magnetic roll is of the permanent type of
high intensity, high gradient, built with superpotent neodymium
magnets, resistant to temperatures of up to 80.degree. C. and steel
disc of high magnetic permeability; [0103] the actuation of the
magnetic roll is effected by means of a complete, three-phase,
variable-velocity 2.0 HP AC motor with frequency inverter for 220
VCA (VAC) 60 Hz, (it may be run on 220/380/440 VAC) [0104] 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 employed three guide systems enable the
tensioning and alignment of the belt, thus extending its lifetime;
[0105] a separation belt of the type of polyester fabric coated
with PU (Polyurethane) layer, with 0.6-1.00 mm thickness; [0106]
roller-type feed system with a 2.0 HP, 220 VAC, three-phase driving
motor with frequency inverter, for regulating the feed speed. It
includes storage silo; this type of feeder enables more controlled
and uniform feeding, 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; [0107] support structure built with carbon
steel profiles, with respective paint finish, making the assembly a
compact and easy-to-install unit. Entirely powder-proof control
panel, including measuring instruments, speed controllers,
frequency inverters, feed voltage: 220 VAC, 60 Hz, three-phase.
[0108] However, all the above conditions and characteristics enable
an improvement introduced in the unit, according to which the
permanent-magnet roll magnetic separator is arranged with a
determined angle with respect to the horizontal direction, so as to
provide an additional force that sums to the centrifugal force and
thus manages to retain non-magnetic materials in a satisfactory
manner.
[0109] Such an arrangement may be viewed on the magnetic separators
illustrated in FIG. 1 with reference numbers 11, 13, 15, 17, 19, 21
and 23.
[0110] The mentioned low gradient results from the magnetic depth
resulting due to the arrangement of the magnets and gaps.
EXAMPLE 1
Analysis of Waste Sample
[0111] With a view to make a physicochemical characterization of a
known stack of wastes, 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 oxide contained
therein, samples of said stack were collected for analysis by a
specialized laboratory, using a circuit mounted therein, simulating
the same operational route adopted by the plant of the
invention.
[0112] The ore sample of the waste pile exhibited an extremely
simple mineralogy, constituted essentially by iron-bearing minerals
and by a non-magnetic fraction, wherein the iron-bearing materials
are: magnetite, martite, 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.
TABLE-US-00002 TABLE 2 Minerals Chemical formula Weight % Magnetite
Fe.sup.2+Fe.sub.2.sup.3+O.sub.4 or Fe.sub.3O.sub.4 18 Martite
Fe.sub.3O.sub.4 => Fe.sub.2O.sub.3 15 Hematite Fe.sub.2O.sub.3
47 Silica SiO.sub.2 15 Iron Oxide and hydroxide Fe(OH).sub.2 5
[0113] 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:
TABLE-US-00003 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 % >5 mm 180.0 4.85 44.52 2.16
5.06 >3 mm 120.0 3.23 55.25 1.79 4.19 >1 mm 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
Separation - High-Intensity Roll Magnetic Separator Fraction -1 mm
and +325 mesh Product Weight Weight % % 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 -1 mm and +325 mesh contains 21.72%
iron; a recovery of 41.94% relative to the sample was achieved;
Magnetic Separation - High-Intensity 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 non-magnetic 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 Iron; a
recovery of 28.23% was achieved in this fraction. Recovery %
(fraction -1 mm +325 and -325 mesh) 70.17 The fraction +1 mm
further containing 17.55% of the iron contained, which may be
recovered in a high-intensity magnetic separator with
differentiated gradient, is still to be processed.
[0114] The maximum recovery can reach 70.17%+17.55%=87.72%.
[0115] In order to prove the efficiency of the process, a new
sample of larger volume was collected and processed.
[0116] After the processing, the following results were obtained:
[0117] 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; [0118]
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; [0119]
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; [0120]
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.
[0121] Thus, in the second test, carried out according to the
established flowchart, and a route simulating the invention, a
recovery was achieved 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.
[0122] 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 5 (recovery table) below.
TABLE-US-00004 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 +2 mm 3,700.0 12.85 59.73 7.68
1596 -2 mm and +100 5,230.0 18.17 53.16 9.66 20.08 mesh -100 mesh
12,160.0 42.24 34.57 14.60 30.36 TOTAL 28,790.0 100.00 48.09 100.00
Magnetic Separation - High-Intensity Roll Magnetic Separation
Fraction +1/4'' Product Weight Weight % Fe % Fe cont Dist. 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 Non-magnetic 518.90 1.80 26.43 0.48 0.99 Totals
7,700.00 26.75 16.16 33.60 Metallurgical recovery of Fe(T) in
fraction -100 mesh of the Magnetic fraction = 16.33% Fraction
-1/4'' and +2 mm Product Weight Weight % Fe % Fe cont Dist. Fe %
Magnetic 3,413.50 11.85 62.36 7.42 15.44 Mixed 114.60 0.40 40.35
0.16 0.33 Non-magnetic 171.90 0.60 15.11 0.09 0.19 Totals 3,700.00
12.85 7.68 15.96 Metallurgical recovery of the Fe(T) in fraction
-100 mesh of the Magnetic fraction = 15.44% Fraction -2 mm and +100
mesh Product Weight Weight % Fe % Fecont Dist. fe % Magnetic
4.279.60 14.87 62.03 9.22 19.18 Mixed 132.10 0.46 25.22 0.12 0.24
Non-magnetic 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 -2 mm and +100 mesh of
Magnetic fraction = 19.18% Magnetic Separation - High-Intensity
Roll 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 Non-magnetic 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 in the Sample 60.45% 80.75%
TABLE-US-00005 TABLE 5 Summary - Recovery Table Product Weight
Weight % Fe % Fe cont Dist. Fe % Magnetic +1/4'' 5,719.80 19.87
63.75 12.67 26.33 Magnetic -1/4'' 3,413.50 11.85 62.63 7.42 15.44
and +2 mm Magnetic -2 mm 4,279.60 14.87 62.03 9.22 19.18 and +100
mesh Magnetic -100 3,990.00 13.86 68.72 9.52 19.80 mesh Totals
17,402.90 60.45 64.23 38.83 80.75
[0123] Moreover, during the tests carried out, the granulometry
profile of the collected material was also determined, as shown in
Table 6 below.
TABLE-US-00006 TABLE 6 Granulometry of the feed of the plant Feed
250 Sieve Weight Weight % Ton/solids Fraction +40 mm 6.38 2.93 7
Fraction +1/4 42.87 19.72 49 Fraction +2 mm 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
mesh 1.11 0.51 1 Fraction -500 mesh 32.58 14.99 37 Totals 217.41
100.00 250
[0124] 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.
[0125] The accompanying claims were drafted so as that they can
cover such obvious forms and modifications, which will be within
the scope of the present invention.
* * * * *