Note: Descriptions are shown in the official language in which they were submitted.
CA 02963990 2017-04-07
1
"PROCESS AND SYSTEM FOR TOTALLY DRY ORE-DRESSING THROUGH A
MAGNETIC SEPARATION UNIT"
BACKGROUND OF THE INVENTION
The present invention relates to a process and a system for
totally dry dressing of iron ore of fine to superfine granulometry lower than
150 microns, in a totally dry pathway. Iron ores of fine and superfine
granulometry are found at waste barrages and in dump ores from existing
plants.
At the present cold ore-dressing plants, which exist at large
mining companies, the original projects used to envisage the processing of
ores having high iron contents, for example, iron contents higher than 54%
Fe, so that the whole material lower than this percentage is considered
dump, which has been restricting more and more the dressing process due to
the lack of ore with iron contents higher than 54%.
However, in the terms of the present invention said dump is
considered useful for feeding a process and a system for totally dry dressing
of iron-oxide ore through a magnetic separation unit.
In this regard, the present invention aims at simplifying the
process of recovering the iron ores that are still contained in said dump,
bringing about high metallurgical and mass recoveries. Thus, it is possible to
obtain a commercially superior product, more precisely an iron-oxide ore
concentrate with contents higher than 63% Fe, and with a simple adjustment
to increase the final content of the concentrate, which may reach up to 67%
Fe(T). Such a result represents a significant advance from the environmental
point of view, if one considers the risk historically represented by the dump
basins of the mining industry in Brazil and around the world.
The innovatory characteristics of the dry process of the present
invention meet advantageously and simultaneously meets the demands of
economic, environmental and strategic nature of the mining industry, since
they enable improved recovery of dump that constitutes a high risk of
environmental impact and transformation thereof into marketable products in
CA 02963990 2017-04-07
2
,
'
a technically and economically feasible manner, as well as the possibility of
making use of the low-content iron ores that are dumped by the existing
plants at present.
In this dry process, no water is used, and the final residue is
formed by a pile of waste, entirely dispensing with the need for a waste
barrage. Besides, by means of the dry process of the present invention, the
waste generated becomes now by-products for the pavers-and-blocks
industries of building construction and also in the cement industry.
Said pavers and blocks are manufactured from sand and
cement. In a number of states in Brazil, the source of sand consists in
obtaining this raw material from dismounting altered-granite hills. However,
in
this process the altered granite is removed by mechanical dismounting or
with water-jet, undergoing a degradation process, by sieving and
hydrocycloning, wherein the sand fractioning is separated from the clay
fraction. In order to deposit this clay and recover water, it is necessary to
build a waste barrage. Another way to obtain this raw material consists in
removing the sand fraction from dug places by the draining process and the
sand fraction is separated from the clay fraction by a hydrocycloning process
in which the clay returns to the dug place. At the end of this process, due to
the removal of a large part of the substrate constituent, there will be
formation of large lakes, usually without economical utilization for these
liabilities. For instance, this is the case of the region of city of
Seropedica ¨
RJ ¨ Brazil, with great liabilities consisting of the presence of large
saturated
lakes of mineral sediments, due to the extraction of sand, without condition
of
sustaining any form of life or of economical utilization.
DESCRIPTION OF THE PRIOR ART
In the beginning of the mining activities on an industrial scale,
little was known about the techniques for disposal of dump. The low interest
in this area was still due to the fact that the amount of waste produced was
reasonably small and the environmental problems still were not part of the
operational concerns of the industry.
In this regard, the dump was usually thrown into streams at
CA 02963990 2017-04-07
3
random. However, with the growth of the mining sector, the growing social
concern about the environmental issue, as well as the occurrence of
accidents with dump retention barrages ever since the Seventies in various
parts of the world, including Brazil, the mining companies faced the challenge
of guaranteeing operation of the industrial units with minimization of
environmental impacts and reduction of accident risks through more careful
and optimized projects.
In general, three techniques are used for disposal of mining
dump, namely:
- by wet pathway in barrages;
- by dry pathway in dump piles, or
- by using past-fill technology.
The difference between the disposal by dry pathway and by wet
pathway is that by wet pathway in barrages there is retention of liquids in
conjunction with the solid material discarded. The high-density magnetic
separation is traditionally adopted for continuous flows of material, usually
by
wet operation, a process that is internationally known as WHIMS ¨ Wet High
Intensity Magnetic Separation).
With regard to the disposal in the form of paste, this is an
alternative to the conventional practices, which has advantages such as
greater recovery and circulation of water, greater rest angles and smaller
impact on the environment. However, this process is carried out at high costs
for implantation and operation.
For instance, Brazilian patent application BR PI0803327-7
discloses a magnetic concentration process with low consumption of water
and little generation of dump mud. The wet magnetic separation and the
pouring of the magnetic waste may decrease the throwing of a large part of
the magnetic waste into settling barrages. However, this process does not
deal with the recovery of this dump. So there no effective decrease in the
environmental risk inherent in the activity.
Another document, BR PI0103652-1, describes a process for
recovering iron-oxide dump. This dump can be obtained directly from the
CA 02963990 2017-04-07
4
recovery of fines from reduction processes of metallurgy, as well as from the
deviation of return of fines from companies that supply iron ore to iron-and-
steel companies. The material is charged into a feed silo and follows through
chutes and conveyor belts to a rotary drying furnace. The dried material is
discharged for stock without undergoing any sorting/concentration process,
or is then led directly to the reduction furnaces by a conveyor-belt system.
Document BR 102012008340-0, also belonging to the same
applicant, discloses a system and a process equally intended for the
separation of fines and superfines, but which are capable of processing ores
that are considered dump. Besides, the separation unit disclosed in this
document is operationally inadequate for processing minerals with high
magnetic susceptibility (such as magnetite ¨ Fe0Fe203). In addition, the feed
control at the silos of the separation unites of this system is made by
varying
the vibration intensity of the vibrating motor installed there, which not
always
results in an adequate flowability of the material in the separator. Finally,
the
system and the process disclosed in this document do not enable immediate
disposal of the non-magnetic fraction separated.
With regard to the step of drying the dump is for subsequent
separation, the prior art traditionally employs a rotary drum dryer. By this
technique, the presence of fines in the drier results in the formation of an
expressive amount (30 to 50%) of pellets inside the dryer (which obviously
runs counter to the objective of recovering fines), leading to low efficiency
of
the equipment for coarse particles and even greater inefficiency for fine
particles, since the particles are not released, thus preventing the
separation
between the iron-oxide minerals and the impurities.
Fluid-bed dryers are recommended for coarse particles that
enable one to form fluid beds, and it is impossible to form fluid bed for fine
particles.
Spray Dry, widely used at present in the ceramic industries in
preparing masses for the manufacture of porcelain floor tiles. However, for
drying on a Spray Dry it is necessary to form a pulp with 50% solids to
promote spraying of particles to be injected against a current of hot air. In
CA 02963990 2017-04-07
order to feed 500 ton/h, it is necessary to add a magnetic separation unit
that
exhibits satisfactory efficiency for materials that are traditionally
unfeasible to
process by magnetic separators by means of permanent-magnet rollers of
high rare-earth intensity (such as iron-boron-neodymium) and of low ferrite-
5 magnet intensity (such as iron-boron).
Such objectives are achieved in an absolutely effective manner
by reducing the potentiality of environmental risk in implanting the system,
by
promoting the rational use of natural resources, by recovering the dump that
may present environmental risk in the event of an accident at the barrages or
at piles, and by friendly interaction with the surrounding.
In times of increasing environmental demands, the present
invention constitutes a definitive response to the challenge of generating
economical results in an environmentally friendly manner, chiefly
characterized by:
- greater mass and metallurgic recovery of the iron;
- recovery of iron-ore fines in fractions < 100 mesh (about 150
microns)
without losses by due to drag in the during the wet magnetic
separation;
- clean combustion without residues;
- non-existence of residues to the atmosphere;
- more efficient separation of the iron with generation of cleaner
dump
with lower iron contents;
- logistic optimization with localized treatment;
- preservation of springs and aquifers;
- elimination of the risk of accidents with dump barrages;
- decrease in the physical space intended for the implantation;
- low consumption of energy;
- modularity and flexibility of the system;
- increase in the useful life of the mines, by virtue of the
possibility of
treating iron-oxide ores with much lower contents.
As already said, the singularity of the solution provided by the
present invention lies in adopting a totally-dry pathway for processing
CA 02963990 2017-04-07
6
minerals, which requires the introduction of a drying and disaggregating unit
before feeding the finer fractions to a magnetic separator.
The pathway that constitutes the pillar of the present invention
can be summarized as follows: the ore moisture is reduced by means of a
dryer with mechanical stirring (by using natural gas to prevent contamination
or burning biomass), the ore being sorted into various fractions by different
clycloning stages and then separated magnetically into each of the sorted
ranges, with the important differential of being a process developed in a
totally dry manner.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram showing the dressing of fines
from dump barrage and/or of the dump;
Figure 2 is an operational flowchart of the process for fines from
dump barrage;
Figure 3 is an operational flowchart of the process for utilization
of the dump by the wet plants in operation at present;
Figure 4 shows a rapid dryer with mechanical stirring/mechanical
stirring system used in the process and system of the present invention;
Figure 5 shows an arrangement of the set of cyclones;
Figure 6 is a scheme of the magnetic separation unit according
to the present invention;
Figure 7 is a representation of a side section of the magnetic
separation unit according to the present invention.
Figure 8 to 12 are graphs representing the granulometric
distribution of the different samples obtained in the example described in the
text, according to an exemplifying embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Before beginning to describe the invention, it is well to point out
that the magnitudes set forth herein are given by way of example, so that
they should not be taken as being !imitative of the protection 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
CA 02963990 2017-04-07
7
concrete case, so as to achieve the objectives of the present invention.
In figure 1, reference numbers 1 to 8 represent steps and
components such 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, for dump basins, the removal of fines and
superfines from iron oxide is started by extraction with a dredge 2 and
pumping as far as the bank to let off the excess water and form a pile for
charging the material. A number of piles are formed along the dump bank for
the purpose of separating as much water as possible from the dump. Once
the percentage of moisture of about 6 to 8% has been reached, the dump is
collected by an excavator 3, and carried on a dump-truck 4, for transport to
the silo or chute hopper 5.
For the dump, the process is started by extraction with an
excavator 3, which feeds directly a dump-truck 4 for transport as far as the
silo or chute hopper 5.
The discharge from the silo or chute hopper 5 is equipped with a
belt-feeder, which feeds a screen 7 intended for carrying out preliminary
separation.
The screen 7 may consist, for instance, of a shaking screen for
removal of contaminating material. Thus, the material is led to a lung-pile 8.
The capacity of said lung-pile 8 can be defined according to the
operational capacity of the plant.
Additionally, one may provide a mist curtain around the chute
hopper, so as to prevent dust from escaping out of the chute hopper. In this
regard, the belt-feeder may be completely enclosed, thus preventing possible
losses of material and the consequent emission of dust to the atmosphere.
Below the lung-pile 8, one may provide a duct comprising a
shaking feeder (not shown), which provides transfer of the ore to the belt-
feeder.
From the belt-feeder of the lung-pile 8, the material is then led to
the first of the three unitary operations that constitutes the present
invention,
relating to the process and to the system for dry recovery of iron-oxide fines
CA 02963990 2017-04-07
8
and superfines.
The first unitary operation consists of the dry
operation/disaggregation of fine particles. The process of drying fine and
superfine particles is usually considered a technically complex operation,
since the presence of other contaminating minerals, such as clay minerals
and iron hydroxide, in the rotary-drum drying process, tends to form pellets,
which is an aggregate of different minerals, thus preventing the possibility
of
carrying out the magnetic separation process.
Thus, in order to solve the already-mentioned problem of
drying/disaggregating fine particles, and to obtain particles 100%
individualized for achieving maximum efficiency of the magnetic separation
process, one proposes the use of a dryer 9 with mechanical stirring, as
shown in figure 4.
The dryer 9 is composed by a heating chamber 10, which
generates hot air (temperature around 850 C) introduced into the main body,
within which two axles 9.1 are provided with a plurality of blades 9.2 that
move the particulates both vertically and horizontally. These gases go
through a labyrinth system 9.5, forcing the heated air to come into contact
with the material. The vertical movement of particles, besides providing
contact of particles with the hot air to increase the efficiency of the drying
process, still facilitates the removal of fines by the system of capturing
fines
provided by the negative pressure exerted by the exhaust fan.
In the dryer 9, a further efficient step of disaggregating iron-oxide
ore fines and of the non-magnetic fraction takes place, through movement of
particles vertically, so that the dry material moves along the main body as
far
as the discharge point 9.3.
The dryer may be sized for a capacity of up to 600 t/h. For larger
capacities suffice it to add drying modules. Based on the characteristics of
the material to be dried, the dryer may have, for instance, capacity to dry,
disaggregate and, at the same time, remove the fines in which the material to
be fed to the lower dryer at 100 mesh (about 150 microns) can reach about
98% of the total.
CA 02963990 2017-04-07
9
The main characteristics of the dryer employed in the tests
carried out are listed hereinafter.
- It is equipped with two shafts driven by a duly sized electric motor. The
shafts are equipped with a plurality of blades for different positions,
namely: inclined in the direction of discharge, which causes the
material to move forward, straight blades to impel the material upward
and blades inclined in the feeding direction, which tend to retard or
control the velocity of the material inside the dryer;
- discharge of the fraction > 100 mesh of the dry product;
- sluice valves at both the feed and the discharge of the fraction > 100
mesh, these sluice valves tend to prevent the entry of cold air into the
system, as well as the exit of hot gas, keeping the performance at the
temperature of the hot gases, that is to say, providing optimization of
the thermal balance;
- there are two safety valves for each dryer, for the event of an
explosion taking place;
- a hot air generator with ducts that interconnect the generator to the
dryer coated with refractory materials;
- valves
for entry of cold air to make the balance of the temperatures
measured with thermocouple and pyrometers; these temperatures can
be indicated and controlled on a control panel;
- a set of cyclones and interconnection ducts for exit of gases plus
the
product and endless screws with rotary valves; a support structure is
provided for the cyclones;
- a duct interconnecting the cyclones to sleeve filters 22, besides
screws for exit of the products, exhaust fan and chimney;
- an electric board for the system, capable of providing automation and
measurement and control instruments;
- in the
drying process, the dryer 9 needs to operate with a depression
for removal of water vapor obtained in the drying process. Therefore,
the dryer should be coupled to an exhaustion system. In this process
of removing water vapor, the fines smaller than 150 microns are also
CA 02963990 2017-04-07
dragged by the exhaust system. For this reason, the exhaust system
is composed by different cycloning stages and a final collection
system close to the sleeve filters 22, so as to prevent any emission of
particulates to the atmosphere. For generation of heat, as already
5 said, one uses natural gas and/or biomass, which together with the
adequate control of the flow of air, in a correct air/fuel ratio provides
clean and complete combustion, having as discharge the gases after
passage through the sleeve filters 22.
The process of removing the gases, water vapor and fines is
10 carried out by a high-capacity exhaust fan arranged at the end of the
circuit.
Associated to the circuit of the exhaust system there is a component that
integrates the dryer to the so-called unitary operation of the process of the
present invention. In other words, it consists of a set of cyclones in series,
duly sized with losses of adequate load to make the separation by different
granulometry ranges.
Therefore, the second unitary step of this inventive process
consists in providing a set of cyclones arranged in series, each of the
cyclones being sized to separate a granulometry range, the granulometry
ranges being defined according to the release granulometry of the iron-oxide
ore with its associated interfering minerals. However, the number of cyclones
may be determined as from one to six units, according to the granulometry
range to be processed. The cyclones are usually pieces of equipment used
for collecting fines with granulometry bigger than 10 microns, exactly to
diminish the charge of fines in the sleeve filters 22. However, in order to
collect particles at different granulometry ranges, it is necessary to re-size
the
cyclone to capture in accordance with the desired granulometries. In this
regard, the cyclones can collect efficiently 100% of the particles bitter than
10
microns.
According to the embodiment given by way of example in figure
5, the sizing of the number of cyclones, arranged in series and according to
the intended granulometric cuts, three cyclones are provided in series, which
collect the following granulometry ranges: in the first cyclone 11, the
CA 02963990 2017-04-07
11
=
granulometric range collected is smaller than 150 microns and bigger than 45
microns; in the second cyclone 14, the granulometry range collected is
smaller than 45 microns and bigger than 22 microns; and in the third cyclone
17, the granulometry range collected is smaller than 22 microns and bigger
than 10 microns.
Finally, as to the superfines particles smaller than 10 microns,
they are sucked and withdrawn in a set of sleeve filters 22.
The products collected in each of the cyclones 11, 14 and 17
arranged in series are then sent to respective cooling columns 12, 15 and 18,
which have the function of lowering the temperature that is between 70 C
and 100 C to a temperature of about 40 C. This cooling is necessary to
preserve the magnetic intensity of the rare earth magnets (iron-boron-
neodymium).
The material collected in the first cyclone 11, which corresponds
to the fraction smaller than 150 microns and bigger than 45 microns, is sent
to the first cooling column 12 and then fed to the first magnetic separation
unit 13. The material collected in the second cyclone 14, which corresponds
to the fraction smaller than 45 microns and bigger than 22 microns, is sent to
the second cooling column 15 and then fed to the second magnetic
separation unit 16. The material collected in the third cyclone 17, which
corresponds to the fraction smaller than 22 microns and bigger than 10
microns, is sent to the third cooling column 18 and then fed to the third
magnetic separation unit 19.
Indeed, the magnetic separation comprises the next unitary step
of the present invention.
In the magnetic separation step, the products of each cyclone 1,
14 and 17, which feed successively the cooling columns 12, 15 and 18,
classified in different granulometry ranges, are sent to respective sets of
magnetic separators 13, 16 and 19, arranged in cascade, and by be from two
magnetic rollers to four magnetic rollers or more rollers according to the
need. However, this configuration depends chiefly on the separability
charactristics of the iron-oxide minerals present.
CA 02963990 2017-04-07
12
For each of the granulometric ranges separated in the different
cyclones positioned in series, the respective separators of high-intensity
rare-
earth (iron-boron, neodymium) rollers are fed with the due adjustments of
velocity, as well as the positioning of splits, which will be discussed later.
Figure 6 shows the magnetic separation scheme with three
rollers in cascade. In the first magnetic separation unit 13, the material
from
the first cyclone 11 and from the first cooling column 12 feed a first
magnetic
roller, which may be of low and/or high intensity, generating a first non-
magnetic fraction that should be discarded immediately, a first magnetic
fraction, which consists of a final product with contents higher than 64% Fe
(T), and a first mixed fraction that feeds a second high-intensity magnetic
roller. In the same sequence, the second magnetic roller 16 generates a
second non-magnetic fraction, which is also discarded, and a second
magnetic fraction with contents higher than 64% Fe (T), besides a second
mixed fraction, which will feed the third magnetic roller. The third magnetic
roller 10, in turn, generates a third non-magnetic fraction that is equally
discarded, a third magnetic fraction with contents higher than 64% Fe (T) and
a third mixed fraction, which is discarded together with the third non-
magnetic
fraction.
And so on, the products from the second cyclone will feed a
cooling column and, then, the second magnetic separation unit 16, in the
same sequence, just as in the first magnetic separation unit, feeds the first
magnetic roller, which may be of low and/or high intensity, generating a first
non-magnetic fraction that should be discarded immediately, a first magnetic
fraction, which consists of a final product with contents higher than 64% Fe
(T), and a first mixed fraction, which feeds a second high-intensity magnetic
roller. In the same sequence, the second magnetic roller generates a second
non-magnetic fraction that will also be discarded, and a second magnetic
fraction with contents higher than 64% Fe (T), besides a second mixed
fraction that will feed the third magnetic roller. The third magnetic roller,
in
turn, generates a third non-magnetic fraction that is equally discarded, a
third
magnetic fraction with contents higher than 64% Fe (T) and a third mixed
CA 02963990 2017-04-07
13
fraction that is discarded together with the non-magnetic fraction. The same
thing will happen in the third magnetic separation unit 19.
Further in figure 6, one shows the magnetic separation scheme
with three rollers in cascade, the first magnetic roller may be of low
intensity
or high intensity. Depending on the characteristics of the material to be
separated, the use of the low-intensity magnetic roller may be preferred,
considering the fact that the permanent magnets are made from iron-boron,
with magnetic intensity ranging from 500 to 3000 Gauss, being intended for
the separation of high magnetic susceptibility (such as magnetite ¨
Fe0Fe203). On the other hand, in the case of high-intensity magnetic rollers,
the permanent magnets are made from iron-boron-neodymium with magnetic
intensities ranging from 7,500 to 13,000 G, indented for the separation of
minerals having low magnetic susceptibility (such as hematite and iron-
limonite hydroxides.
In figure 7, which is a representation of a side section of the
magnetic separation unit, one illustrates in detail all the elements of the
magnetic separation unit in cascade, which in the exemplified case has three
rollers overlapping each other. As already seen, each of the cyclones, with
granulometries duly classified, feeds a respective set of magnetic separators
13, 16, and 19. According to figure 7, the set is composed by a receiving silo
30, wherein the feed to one set may be alternatively controlled by the
vibration intensity of a reducing motor (not shown, as will be discussed
later).
However, preferably the silo 30 configured with inclination angles that
provide
better flowability of the material to the magnetic separator assembly.
Then, the material is discharged onto a polyester belt 34 coated
with PU, the belt is tensioned by a first low-intensity magnetic roller of
ferrite
(iron-boron) magnets 32 and by a support roller 33.
The control of the magnetic separation is made by varying the
velocity of the magnetic roller and by positioning the splits. In order to
contain
the dissipation of powder and lead to the magnetic roller 32, one positions an
acrylic plate. The split 36 separates the non-magnetic fraction from the mixed
fraction, and the split 37 separates the mixed fraction from the magnetic
CA 02963990 2017-04-07
14
fraction. The first non-magnetic fraction is collected by the chute 38, the
first
mixed fraction is collected by the chute 39 and the first magnetic fraction is
collected by the chute 40. The chute of the first mixed fraction feeds the
silo
41 of the second high-intensity magnetic roller of rare earths (iron-boron-
neodymium) 42. The second high-intensity magnetic roller of rare earths
(iron-boron-neodymium) magnets 42, after the magnetic separation,
generates a second non-magnetic fraction, which will be discarded through
the chute 43, the second magnetic fraction is discarded in the chute 45 and a
second mixed fraction in the chute 44, which feeds the third high-intensity
magnetic roller 47 of rare earth (iron-boron-neodymium) magnets through the
chute 44 by means of the silo 46. The third high-intensity magnetic roller 47
of rare earths (iron-boron-neodymium) 46, after the magnetic separation,
generates a third non-magnetic fraction, which will be discarded through the
chute 48, a third magnetic fraction which will be discarded in the chute 50
and a third mixed fraction through the chute 49 is discharged together with
the other non-magnetic fractions. Item 51 in the three magnetic separation
units comprises support rollers for the polyester belt coated with PU 34.
The low-intensity and high-intensity magnetic rollers are inclined,
and the inclination may range from 5 to 55 degrees, with an ideal working
range of 15 ¨ 25 degrees, the inclination being defined as a function of the
release granulometry of the iron oxide. This inclination, by the tests already
carried out, increases the efficiency of separating the magnetic fraction from
the non-magnetic fraction.
Other characteristics of this equipment are presented hereinafter:
- the high-intensity magnetic roller of high-gradient permanent magnets
is preferably made with superponent neodymium magnets, which are
resistant to a temperature of up to 60 C and a steel disc of high
magnetic permeability;
- the
actuation of the magnetic roller may be made by means of an AC
2.0 CV motor, with variable velocity and frequency inverter (not
shown);
- a system
for tensioning and aligning the belt 50 is provided, 50 as to
CA 02963990 2017-04-07
prevent the occurrence of problems due the short distance between
rollers of small diameters of think belt. Thus, it is possible to replace
the belt in a few minutes, without need for special tools. The guide
systems used on each of the magnetic rollers enables tensioning and
5 aligning the respective belts, thereby increasing their useful life;
- a separation belt 34 of the type with polyester fabric coated with a
PU
(polyurethane) layer, with thickness ranging from 0.6 to 1.00 mm;
- the silo-type alignment systems 30, 41 and 46 operate by a discharge
system by gravity, wherein the inclination angle is duly designed so as
10 to enable a homogeneous discharge throughout the silo, for which
reason one can even dispense with the use of a vibration system;
- alternatively, if one adopts a feeding system by silo with a
vibration
drive motor, the latter may exhibit a configuration of 2.0 hp, 220 VCA,
three-phase and frequency inverter, for regulation of the feeding
15 speed. It includes a storage silo; this type of feeder enables
controlled
and uniform feed;
- a support structure constructed in carbon-steel profiles with
respective
finish painting, so as to provide an assembly characterized by a
compact and easy-to-install unit. One may also provide an entirely
dust-proof control panel (not shown), including measurement
instruments, velocity controllers, frequency inverters, power voltage:
220 VCA, 60 Hz, three-phase.
Such an arrangement can be viewed in the magnetic separators
illustrated schematically in figure 1 under reference number 13, 16 and 19.
EXAMPLE 1
ANALYSIS OF DUMP SAMPLE
With a view to test the efficiency of the totally dry process and
system for dressing iron-oxide ore through a magnetic separation unit, a
sample collected in the dump basin was subjected to a characterization study
and was processed in the pilot unit, simulating the same operation pathway
adopted by the plant of the process of the present invention.
The sample of ore from the dump pile exhibited an extremely
CA 02963990 2017-04-07
16
simple mineralogy, constituted essentially by minerals bearing iron and by a
non-magnetic fraction. The iron-bearing minerals of the sample collected
were constituted by hematite and iron oxides and hydroxides, as shown
below. The non-magnetic fraction is composes essentially by silica and a
small amount of clay in the form of kaolinite. The percentage of these
minerals is shown in Table 1 below.
TABLE 1 ¨ MINERALOGY OF THE SAMPLE OF DUMP
Minerals Chemical formula % by weight
Hematite Fe203 46
Silica Si02 52
Iron oxide and Fe(OH)2 2
hydroxide
The sample of dump, after being subjected to the
characterization assays, exhibits iron contents of 33.62% Fe(T), the result of
which can be seen in Table 2 below.
TABLE 2 ¨ CHEMICAL ANALYSIS OF HEAD CONTENTS
Chemical analysis
Head contents Fe (T) = 33.62%
The sample of dump was subjected to a granulometric analysis
and exhibits the following granulometry shown in Table 3 below.
_
17
TABLE 3 - GFtANULOMETRIC DISTRIBUTION SAMPLE OF DUMP
Log
Mesh Log Retained Passing
Passing
(ASTM) Aperture (pm) Mass (g) Retained (%)
Passing
Aperture Accumulated (%)
Accumulated (%) Accum Cal (%)
Accum
>100# 149 2.17 0.12 0.12 0.12 99.88
99.58 0.829
> 200# 74 1.87 11.26 10.98 11.09 88.91
79.01 0.342
> 325# 44 1.64 18.69 18.22 29.31 70.69
45.93 0.089
P
> 400# 37 1.57 9.36 9.12 38.44 61.56
36.29 -0.019
r.,
g
0
0
> 500# 25 1.40 17.20 16.77 55.21 44.79
20.01 -0.226
0
N,
0
>600# 22 1.34 10.24 9.98 65.19 34.81
16.27 -0.369 ...]
,
0
0
,
0
1.00 16.79 16.37 81.56 18.44 4.23 -
0.691 ...]
5 0.70 9.61 9.37 90.92 9.08
1.24 -1.022
1 0.00 6.74 6.57 97.49 2.51
0.07
100.01 97.49
0.10001 coef.ang.= 1.24
d80 (mm) = 54
coef.line.= -1.95
dso (mm) = 28
coef.corr.= 1.00
d20 (mm) = 11
CA 02963990 2017-04-07
18
The sample of the second cyclone exhibits the following
distribution: 80% (d80) of the mass is smaller than 55 microns, with a median
(d50) of 29 microns and 20% (d20) of the weight is smaller than 12 microns.
These values can be viewed in the graph in figure 8.
The sample of dump was subjected to the air classification step
at a pilot plant, the system being composed by three cyclones arranged in
series, sleeve filters and centrifugal exhaust fan. During the operation, one
collected samples from each of the three cyclones and fro the sleeve filters
and subjected them to a granulometric analysis, in which they exhibited the
following results.
The granulometric distribution of the first cyclone is shown in
Table 4.
..
19
_
TABLE 4 - GRANULOMETRIC DISTRIBUTION OF THE FIRST CYCLONE
Log Retained Passing
Passing Log Passing
Mesh (ASTM) Aperture (pm) Mass (g) Retained (%)
Aperture Accumulated (%)
Acccumulated (%) Acum Cal (%) Acum
>100# 149 2.17 0.23 0.22 0.22 99.78
99.58 0.785
> 200# 74 1.87 21.82 21.27 21.50 78.50
79.01 0.187
> 325# 44 1.64 34.35 33.49 54.98 45.02
45.93 -0.223
. .
> 400# 37 1.57 9.91 9.66 64.64 35.36
36.29 -0.360 P
.
N,
u,
..,
> 500# 25 1.40 16.07 15.67 80.31 19.69
20.01 -0.659 ,..
u,
u,
0
N,
> 600# 22 1.34 3.47 3.38 83.69 16.31
16.27 -0.749 0
1-
...]
,
0
10 1.00 13.35 13.01 96.71 3.29 4.23
-1.475 1
0
...]
5 0.70 1.77 1.73 98.43 1.57 1.24
-1.801
1 0.00 1.61 1.57 100.00 0.00
0.07
_
102.58 100.00
0.10258 coef.ang.= 1,79
d80 (mm) = 75
coef.line.= -3,16
c150 (mm) = 47
coef.corr.= 1,00
d20 (mm) = 25
CA 02963990 2017-04-07
= .
The sample of the first cyclone exhibited the following
distribution: 80% (d80) of mass smaller than 75 microns, with a median (d50)
of 47 microns and 20% (d20) of the weight smaller than 25 microns. These
values can be viewed in the graph in figure 9.
5 The
granulometric distribution of the second cyclone is presented
in Table 5 below.
_
21
TABLE 5 - GRANULOMETRIC DISTRIBUTION OF THE SECOND CYCLONE
Passing Passing
Mesh (ASTM)Aperture (pm)Log Aperture Mess (g)Retained (%) Retained Accumulated
(%) Log Passing Accum
Accumulated (%) Accum Cal (%)
>100# 149 2.17 0.00 0.00 0.00 100.00
100.00 1.207
> 200# 74 1.87 0.03 0.03 0.03 99.97 99.54
0.916
> 325# 44 1.64 4.63 4.07 4.09 95.91 87.05
0.505
> 400# 37 1.57 20.05 17.61 21.71 78.29
77.27 0.184 P
N,
u,
..,
> 500# 25 1.40 35.48 31.17 52.88 47.12
51.08 -0.196 0
0
0
0
i.,
> 600# 22 1.34 29.16 25.62 78.49 21.51
43.10 -0.616 0
1-
...i
i
0
0
l
1.00 11.72 10.30 88.79 11.21 12.21
-0.925 0
...i
5 0.70 7.11 6.25 95.04 4.96 3.53 -1.293
1 0.00 5.65 4.96 100.00 0.00 0.18
113.83 100.00
0.11383 coef.ang.= 1.86 d80 (mm) =
39
coef.line.= -2.74 ids() (mm)
= 25
coef.corr.= 0.98 d20 (mm) =
13
CA 02963990 2017-04-07
22
The sample of the second cyclone exhibited the following
distribution: 80% (d80) of mass smaller than 39 microns, with a median (d50)
of 25 microns and 20% (d20) of the weight smaller than 13 microns. These
values can be viewed in the graph in figure 10.
The granulometric distribution of the third cyclone is presented in
Table 6 below.
_
23
_
TABLE 6 - GRANULOMETRIC DISTRIBUTION OF THE THIRD CYCLONE
Retained
Mesh (ASTM) Aperture (pm) Log Aperture Mass (g) Retained (%) Passing
Accumulated (%) Pasing Accum Cal (%) Log Passing Accum
Accumulated (%)
>100# 149 2.17 0.00 0.00 0.00 100.00
100.00 1.207
_
> 200# 74 1.87 0.45 0.43 0.43 99.57
99.95 0.736
> 325# 44 1.64 0,83 0.80 1.24 98.76
96.53 0.643
>400# 37 1.57 1.81 1.75 2.98 97.02
92.30 0.546 P
0
N,
0
0
>500# 25 1.40 11,50 11.10 14.08 85.92
75.13 0.292 0
0
0
0
N,
> 600# 22 1.,34 16,42 15.84 29.92 70.08
68.02 0.082
1-
...]
,
0
0
'
1.00 36,64 35.36 65.28 34.72 28.35 -
0.370 0
...]
5 0.70 29.53 28.50 93.78 6.22
10.70 -1.192
. .
1 0.00 6.45 6.22 100.00 0.00
0,92
103.63 100.00
0,10363 coef.ang.= 1.56
d80 (mm) = 27
coef.line.= -2.04
d50 (mm) = 16
coef.corr.= 0.98
d20 (mm) = 8
CA 02963990 2017-04-07
24
The sample of the third cyclone exhibited the following
distribution: 80% (d80) of mass smaller than 27 microns, with a median (d50)
of 26 microns and 20% (d20) of the weight smaller than 8 microns. These
values can be viewed in the graph in figure 11.
The granulometric distribution of the fines collected sleeve filters
is presented in Table 7 below.
_
...
TABLE 7 - GRANULOMETRIC DISTRIBUTION OF THE SLEEVE FILTERS
Mesh (ASTM) Aperture (pm) Log Aperture Mass (g) Retained (%) Retained
Accumulated (%) Passing Accumulated (%) Passing Accum Cal (%) Log Passing
Accum
>100# 149 2.17 0.00 0.00 0.00 100.00
100.00 1.207
> 200# 74 1.87 0.55 0.62 0.62 99.38
99.90 0.707
> 325# 44 1.64 1.32 1.48 2.10 97.90
98.86 0.587
> 400# 37 1.57 0.41 0.46 2.56 97.44
97.92 0.564 P
N,
u,
..,
> 500# 25 1.40 1.68 1.88 4.44 95.56
93.83 0.493
u,
.
N,
>600# 22 1.34 1.13 1.27 5.70 94.30
91.81 0.457 .
1-
...]
,
.
,
10 1.00 19.30 21.63 27.33 72.67
72.51 0.113 .
...]
5 0.70 26.89 30.14 57.47 42.53
51.41
_
1 0.00 37.95 42.53 100.00 0.00
17.06
89.23 100.00
0.08923 coef.ang.= 0.84
d80 (mm) = 13
coef.line.= -0.73
d50 (mm) = 5
coef.corr.= 0.97
d20 (mm) = 1
CA 02963990 2017-04-07
26
The sample of the sleeve filters exhibited the following
distribution: 80% (d80) of mass smaller than 13 microns, with a median (d50)
of 5 microns and 20% (d20) of the weight smaller than 1 microns. These
values can be viewed in the graph in figure 12.
The chemical analysis of the products obtained in the three
cyclones positioned in series plus the product from the sleeve filters
exhibited
the following results, shown in Table 8 below:
TABLE 8 ¨ CHEMICAL ANALYSIS
Cyclone product Weight % % Fe Fe cont % Dist Fe
1st cyclone 52.3 34.67 18.13 53.93
2nd cyclone 22.6 33.23 7.51 22.34
3rd cyclone 16.2 31.64 5.13 15.25
Sleeve filters 8.9 32.05 2.85 8.48
Totals 100 33.62 100.00
As can be seen, the first cyclone exhibits retention of 52.3% by
weight, with contents of 34.67% Fe (T) and exhibits 53.96% of the iron
contained. The second cyclone with 22.6% by weight, with contents of
33.23% Fe (T), which corresponds to 22.35% the iron contained. The third
cyclone exhibits retention of 16.2% by mass, with contents of 31.64% iron,
which represents 15.25% the iron contained. The sleeve filters had 8.9% by
weight, with contents of 32.05% Fe (T), which represents 8.53% of non-
recoverable iron.
All the products collected in each of the cyclones 11, 14 and 17
were classified in different granulometry ranges, according to the above-cited
granulometric distributions. Each of the fractions was processed in a
magnetic separation unit, which in this case corresponds to the magnetic
separation units 13, 16, 19 of the pilot plant, being composed by two
magnetic rollers overlapping each other. All the magnetic rollers are high-
CA 02963990 2017-04-07
27
intensity rollers of rare-earth (iron-boron-neodymium) magnets.
Each of the products obtained in the cyclones 11, 14, and 17
respectively for each of the magnetic separation units 13, 16 and 19, as
shown in figure 7, was inserted into the first silo 30 of the first high-
intensity
magnetic roller 32,0 generating the first non-magnetic fraction, which is
discarded from the magnetic separation unit through the chute 37. In this
separation, one guarantees the first magnetic fraction, which is also removed
through the chute 38 and further generates a mixed fraction that will feed the
second magnetic roller, the material will be collected and led to the second
silo 39 through the collecting chute 43. The silo of the second magnetic
roller
39 feeds the second high-intensity magnetic roller of rare-earth magnets 40,
which in turn generates a second non-magnetic fraction that will be collected
and removed fro the magnetic separation unit through the collecting chute
41, and a second magnetic fraction is also generated, which will be collected
through the chute 42, besides a second mixed fraction, which is collected
through the chute 44, which in incorporated in conjunction with the second
non-magnetic fraction.
All the non-magnetic products from the first roller and from the
second roller of high intensity and, therefore, derived from chutes 37, 41,
besides the mixed fraction derived from the chute 44, are collected on a
conveyor belt called non-magnetic.
All the magnetic products from the first roller and from the
second roller of high intensity and, therefore, derived from the chutes 38 and
42, are collected on a conveyor belt called non-magnetic.
For each of the magnetic separation units, after processing on
the first magnetic roller, all the first magnetic products, first non-magnetic
products and first mixed products from the first roller were collected and
subjected to the calculation of mass balance and chemical analysis.
For each of the magnetic separation units, the mixed fraction
from the first magnetic roller fed the second high-intensity magnetic roller,
wherein the products generated were collected as second magnetic products
CA 02963990 2017-04-07
28
and second non-magnetic products, besides second mixed products and also
subjected to the calculation of mass balance and chemical analysis.
The result of the mass balance and the chemical analysis of the
first high-intensity magnetic rollers is shown in Table 9.
TABLE 9 ¨ RESULTS, RECOVERY OF THE FIRST HIGH-INTENSITY
MAGNETIC ROLLERS
1st Magnetic roller of the three magnetic separation units
Fraction Weight%
Fe Fe cont % dist Fe
-150 and +10 microns 1st magnetic 28.28 65.41 18.50 55.02
Fracao -150 and +10 microns 1st mixed 32.90 35.10 11.55 34.35
Fraction -150 and +10 microns 1st non-
29.92 2.42 0.72 2.15
magnetic
91.10 91.52
In the three cyclones 11, 14 and 17, arranged in series, which
correspond to the magnetic fraction -150 and +10 microns, one achieved a
recovery of 28.28% by mass, with contents of 65.41% Fe(T) and a
metallurgical recovery of 55.02%. One achieved a generation of a non-
magnetic fraction -150 and +10 microns, 29.92% by weight, with contents of
2.42% Fe(T), which corresponds to a metallurgical loss of 2.15%. Besides, a
first mixed fraction -150 and +10 microns of 32.90% by mass, with contents
of 35.10% Fe(T) was generated, further with a presence of 34.35% contained
iron to be separated in the second high-intensity magnetic roller.
The result of mass balance and chemical analysis of the re-
processing of the mixed fractions from the second magnetic rollers is shown
in Table 10.
TABLE 10 ¨ RESULTS, RECOVERY OF THE SECOND HIGH-
INTENSITY MAGNETIC ROLLERS
CA 02963990 2017-04-07
29
2nd magnetic roller
Fraction Weight % % Fe DFe cont % dist Fe
Fraction -150 and +10 microns 2nd magnetic 14.90 64.20 9.57 28.46
Fraction -150 and +10 microns 2nd non-
18.00 11.79 1.98 5.90
magnetic
32.90 34.36
For the magnetic fraction -150 and +10 microns, from the
three rollers of the magnetic separation units, one observes a recovery
of 14.90% by mass, with contents of 64.20% Fe(T) and with a
metallurgical recovery of 28.46%. One further observes a generation of
a combined non-magnetic and mixed fraction -150 and +10 microns,
with 18.00% by weight with contents of 11.03% Fe(T), which
corresponds to a metallurgical loss of 5.90%.
The composition of the final metallurgical balance,
composing the magnetic fractions from the first rollers plus the
magnetic fractions from the second rollers, is shown ion Table 11
below.
TABLE 11 - RECOVERY (1st magnetic + 2nd magnetic)
Recovery (1st magnetic + 2nd magnetic)
Weight
Products % Fe Fe
cont % dist Fe
'u
Fraction -150 and +10 microns 1st
28.28 65.41 18.50 55.02
magnetic
Fraction -150 and +10 microns 2nd
14.90 64.20 9.57 28.46
magnetic
Totals 43.18 83,.8
Composing the magnetic products from the first magnetic
rollers with the products from the second magnetic rollers, one
observes a recovery in mass of 43.18% by weight, with contents of
64.99% Fe(T), which corresponds to a metallurgical recovery of
CA 02963990 2017-04-07
83.48% contained iron.
The composition of the final metallurgical balance,
composing the non-magnetic fractions from the first rollers plus the
non-magnetic fraction and of the mixed from the second rollers is
5 shown in Table 12 below.
TABLE 12 - DISPOSAL (1st NON-MAGNETIC + 2nd NON-
MAGNETIC + 2nd MIXED)
Disposal (1st Non-magnetic + 2nd Mixed + 2nd magnetic)
Weight
Product % Fe Fe
cont % dist Fe
Fraction -150 and +10 microns 1st non-
29.92 2.42 0.72 2.15
magnetic
Fraction -150 and +10 microns 2nd non-
18.00 11.03 1.98 5.90
magnetic
Totals 47.92 5.65
2.71 8.06
Therefore, 47.92% by masse is discarded, with contents of
10 5.65 Fe(T), which corresponds to 8.92% unrecovered iron.
In the sleeve filters, the granulometric fraction smaller than
10 microns, which in the process of the present invention does not
enable its magnetic recovery, exhibits 8.9% by weight, with contents of
32.05% Fe(T) and 8.48% non-recovered iron, as shown in Table 13
15 below.
TABLE 13 ¨ COLLECTION FROM THE SLEEVE FILTERS
Collection, sleeve filters
Products % Peso %
Fe Fe cont % dist Fe
Fraction -10 microns Sleeve filter 8.90 32.05 2.85 8.48
Other modifications within the spirit and concept of this
invention and evident to a person skilled in the art, after considering
this specification, will also be regarded as being within the scope of the
20 invention, as defined in the accompanying claims.
