Note: Descriptions are shown in the official language in which they were submitted.
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A LONG TERM-STABILIZED SUSPENSION FOR COVERING IRON MINERAL,
AND A PROCESS FOR ITS PRODUCTION
BACKGROUND OF THE INVENTION
A. FIELD OF THE INVENTION
This invention relates to a stabilized suspension and more particularly to a
long term-stabilized suspension, having a stability of at least three months
without substantially settling and without forming a hard solid substrate, for
covering briquettes, particles, pellets or powder of iron mineral and also of
several materials in order to avoid the adhesion between each other and thus
its
agglomeration when stored or submitted to a heat treatment and a process for
its
production and application.
B. DESCRIPTION OF RELATED ART
In the treatment of briquettes, particles or pellets made of materials such
as dolomite, magnesite, iron ore, etc., in which is necessary to sinter a
plurality of
briquettes, particles or pellets inside furnaces at high temperatures, there
is a
tendency of said materials to adhere to each other producing an agglomeration
or clustering of briquettes.
Some of these treatments comprise the direct reduction iron of mineral
iron pellets inside a furnace at high temperatures, and also the production of
steel in a Blast Furnace. When the sintering is complete, usually, some or all
of
the pellets are agglomerated in a solid mass, forming a cluster and making
necessary to submit the solid mass to a mechanic shock in order to separate
each pellet from the agglomerate.
In order to avoid the agglomeration of pellets during sintering, there were
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tested several compounds which must be applied over the pellet's surface
before
the sintering process. Among these compounds, there were tested slurries of
magnesium hydroxide, calcium hydroxide, bauxite and even cement, but none of
these compounds produced the expected results, and had some disadvantages
when used for the above referred purpose. Some of the disadvantages related to
the previously mentioned compounds comprise the necessity of continuously stir
the slurries in order to maintain a constant concentration, and that once the
compound was applied over the pellets, the compounds proved to have a very
bad adherence to the briquettes, particles or pellets, since the cover, once
it
dries, tends to separate from the particles only by the movement produced by
normal manipulation of the particles.
When it is necessary to transport the suspension to places far away from
the Production Plant, as well as for further processing, it is necessary to
store the
suspension for a long time in a storage container. Under such circumstances,
the
solid particles of the suspension normally tend to settle down producing a
hard
solid substrate as a hard cake in the bottom of the storage container, which
is
often very difficult to remove. Under such circumstances, the remaining
suspension results useless because it doesn't have the required concentration
and the particles in suspension do not have the required particle size and
therefore it has to be poured from the storage container and discarded in
order to
remove the hard solid cake from the bottom of the container, increasing costs
and high raw material loses.
Therefore, it would be highly desirable to have and produce a suspension
which may be used for covering briquettes, particles, pellets or powder iron
and
several kinds of materials in order to avoid the agglomeration of a plurality
of
particles when stored or submitted to a heat treatment on Direct Reduction
Furnace or Blast Furnace for example, having good adherence properties and
which may be stored for long terms without substantially settling and cake
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formation.
U.S. patent No. 4,743,396 disclose a magnesium hydroxide slurry, for very
specific purposes, having a concentration of 50% by weight or higher of
Mg(OH)2
and 0.1 to 5% of a sulfomethylated polyacrylamide which allow the slurry to be
pumped through pipelines.
Furthermore, U.S. patents No. 4,164,521 (involving the use of a
polyanionic polymer containing at least 50% mole of repetitive units derived
from
an acrylic acid and a polycathionic polymer); 4,412,844 (involving the use of
1.0
to 8.0% of a water dispersible, oil-soluble emulsifying agent); 4,155,741
(including an encapsulated material); and 3,957,674 (including at least 0.5%
of
sodium naphtalen-sulfonate), all of them disclose suspensions which, when
there
were stored for long periods of time, showed some settlement but when they are
agitated, they recover their concentration and physical properties, but all of
them
do not mention a long term stability of about three months.
Because of its nature, a stabilized suspension can be more easily pumped
than one which is not stabilized because the non-stabilized suspension tends
to
form thickened particles and solid substrates complicating or even impeding
their
pumping.
PCT published patent application No. PCT/AU95/00446 discloses an
example of a magnesium hydroxide suspension having both characteristics of
pumping and stability for about seven days without substantial agitation.
However, up to now, there is no suspension in the market having a long
term stability of about three months and which may be used for covering
briquettes, particles, pellets or iron powder.
Regarding processes for producing suspensions, U.S. patent No.
5,487,979 disclose a process for the production of magnesium hydroxide
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suspension, by pressure hydrating burnt natural magnesite in presence of
chlorine ions and a cationic polymer (polyamide).
U.S. Patents Nos. 5,143,965; 4,548,733; 4,430,248; 4,230,610; 4,166,040;
and 4,166,041 disclose representative processes for producing magnesium
hydroxide suspensions, by using ultrasonic mixing steps and some cationic
polymers such as the ammonium metacriloxiethyl-trimethyl-methasulfonate and
the polyacrylic acid, among others, showing more or less stability, but none
disclosing a stability near a range of about three months.
SUMMARY OF THE INVENTION
It is therefore highly desirable to provide a long term stabilized suspension
and a new process for producing a long term stabilized suspension, which
stabilized suspension may be used for covering briquettes, particles, pellets
or
powders of iron mineral and other several materials in order to avoid the
agglomeration of a plurality of briquettes, particles, pellets or powders when
stored or submitted to heat treatments on Direct Reduction Furnaces or Blast
Furnaces, and that additionally, may be stored for long terms without
substantially settling.
In accordance with the present invention, it is disclosed a suspension
having a content of from 50 to 70% in weight of an alkaline, alkaline-earth or
other metal hydroxide, carbonate or silicate, a solid content between about
52%
to 72%, a water content of 28% to 48%, a viscosity of about 1000 centipoises
(cp), a average particle size of about 2 microns, a pH value greater than
10.5, an
equivalent magnesium oxide content of 34% to 48%, a specific gravity of 1.40
to
1.60, and including one or more anionic polyelectrolytes, at a concentration
of at
least 25%, in an amount of about 0.5 to 2.5% in dry basis, and an adherent
compound applied to the suspension, at a concentration of at least 30% in an
amount of 0.5 to 5%, in dry basis, showing a stability of at least three
months
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without substantial agitation, and which may be used for covering briquettes,
particles, pellets or powders of iron mineral and several kinds of materials
in
order to avoid its agglomeration when treated at high temperatures .
Thanks to the average particle size (of about 2 microns) in combination
with the use of the anionic polyelectrolytes, the suspension may be stable
over a
number, for example, three, months. In fact this product may require only
somewhat (not vigorous) agitation once a day, in order to keep it fluid
without
experiencing particle thickening or substantial settlement.
Regarding the production of stabilized suspensions, these can be
produced by adding a soluble alkaline material to an aqueous salt of, for
example, magnesium at atmospheric pressure and at a temperature from near
ambient temperature to about 100°C.
A process for the production of the stabilized suspension, in accordance
with the present invention, may comprise producing a paste comprising an
alkaline, alkaline-earth or other metal hydroxide, carbonate or silicate,
washing
and repulping the paste in order to reduce the soluble salts; reducing the
particle
size until approximately 2 microns average; adding additives for improving the
fluidity and stability of the suspension, and adding an adherent compound in
order to obtain a long term stability to the suspension which has a stability
of at
least three months without substantial agitation, which does not settle down
forming a hard solid cemented cake, and which can be used for covering
briquettes, particles, pellets or powders of iron mineral and also several
kinds of
materials, in order to avoid its agglomeration when stored or submitted to
high
temperatures on Direct Reduction Furnaces or Blast Furnaces; said suspension
may be applied to the surface of the briquettes, particles, pellets or powders
by
averages of a plurality of spraying nozzles, which are passed under said
spraying
nozzles by averages of a conveyor belt.
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The suspension of the present invention has a high coverage area, of
5m2/g minimum, and it can be applied on the surface of the briquettes,
particles,
pellets or powders, as a diluted suspension having a concentration of from 4
to
50% in weight. Furthermore, the suspension of the present invention adheres
strongly to the briquettes, particles, pellets or powders so it does not
separate
from the surface of the briquettes, particles, pellets or powders during
transportation, manipulation and different treatment phases.
By covering the briquettes, particles, pellets or powders with the
suspension of the present invention there are obtained the following benefits:
~ Lesser maintenance costs of conveyor belts, rollers, sieving devices,
etc.
~ Easier product manipulation procedures, thanks to the liquid nature of
the suspension of the present invention.
~ Few emanations of hazardous and polluting elements to the
environment.
~ When the suspension of the present invention is used for covering iron
ore pellets to be treated at high temperatures in order to reduce the
iron ore, there are obtained high quality reduced iron pellets.
~ High productivity in Furnaces working at temperatures greater than
1,000 °C.
~ Improved slag fluidity, and easier removal of impurities inside pipes,
containers, etc.
Thus in accordance with a broad aspect of the present invention, there is
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provided a long term stabilized suspension, which can be used for covering
briquettes, particles, pellets or powder of several kinds of materials for
avoiding
adhesion between each other and thus the formation of agglomerates when
treated at high temperatures having:
a solid content of about 52% to 72%;
a water content of about 28% to 48%;
a viscosity of about 500 to 1,500 cp.;
an average particle size of about 1 to 3 microns;
an alkaline, alkaline-earth or other metal hydroxide, carbonate or silicate
content of about 50% to 70% in weight;
a pH value of over 10.5;
an equivalent alkaline, alkaline-earth or other metal hydroxide, carbonate
or silicate content of 34% to 48%;
a specific gravity of 1.4 to 1.6;
at least one anionic polyelectrolyte, at a concentration of at least 25%, in
an amount of about 0.5 to 2.5% in dry basis and
and an adherent compound that improves the adhesion of the suspension
to the pellets or briquettes during the process, at a concentration of at
least 30%
in an amount of 0.5 to 5% in dry basis;
wherein the long-term stabilized suspension can be stored for at least
three months without substantial agitation, and without experiencing
substantial
settlement and solid hard substrate formations.
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In some embodiments, the alkaline, alkaline-earth or other metal
hydroxide, carbonate or silicate may include magnesium hydroxide, magnesium
carbonate, magnesium silicate, calcium hydroxide, calcium carbonate, calcium
silicate, aluminum hydroxide, aluminum carbonate, aluminum silicate, sodium
hydroxide, sodium carbonate and/or sodium silicate.
In some embodiments, the anionic polyelectrolyte may be selected from
the group consisting of sodium polyacrylate and ammonium polystyrene/maleate.
In one embodiment, the adherent compound may be selected from
styrene acrylic emulsions.
In one embodiment, the long term stabilized suspension may have a
coverage area of 5 m2/g minimum.
The long term stabilized suspension may be applied on the surface of the
briquettes, particles, pellets or powders and may be in the form of a diluted
suspension having a concentration of from 4 to 50% in weight.
In accordance with another aspect of the present invention, there is
provided a process for the production of a long term stabilized suspension
using
as raw material an alkaline, alkaline-earth or other metal hydroxide,
carbonate or
silicate and the process may include:
a) washing the raw material solids;
b) filtering and repulping the raw material solids in order to obtain
agglomerated solid particles having less than 0.6% of chloride values;
c) adding at least one anionic polyelectrolyte, at a concentration of at
least 25%, in an amount of about 0.5 to 2.5% in dry basis.
d) dispersing the agglomerated solid particles in a dispersing equipment;
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e) grinding the dispersed product, to reduce the particle size so that at
least the 50% of the ground product have a particle size of about 2 microns;
f) adding an compound type styrene acrylic emulsion, at a concentration
of at least 30% in an amount of 0.5 to 5% in dry basis; and
g) dispersing the product of step f) in a dispersing equipment.
In one embodiment, the step d) may be carried out in a minimum 5
minutes.
In one embodiment, the step e) may be carried out in a sand mill using
high density balls, as milling media.
In an embodiment of the invention, the anionic polyelectrolyte may include
sodium polyacrylate or ammonium polystyrene/maleate.
It is therefore a main object of the present invention, to provide a long-term
stabilized suspension, for covering briquettes, particles, pellets or powders
of iron
or other several materials, for avoiding its agglomeration when treated at
high
temperatures on Direct Reduction Furnaces or Blast Furnaces for example,
having good adherence properties and a high coverage area.
It is another object of the present invention, to provide a long-term
stabilized suspension of the above disclosed nature, having a stability of at
least
three months without substantial agitation, and having a very low tendency to
settle down, forming a hard cemented cake.
It is still main object of the present invention, to provide a process for the
production of a long-term stabilized suspension, for covering briquettes,
particles,
pellets or powders of iron mineral and several kinds of materials, for
avoiding its
agglomeration when treated at high temperatures, having good adherence
properties and a high coverage area.
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These and other objects and advantages of the present invention will be
apparent to those persons having ordinary skill in the art, from the following
description of the invention, referring to specific examples of practice.
DETAILED DESCRIPTION OF THE INVENTION.
The invention will be described in the following by making reference to a
preferred embodiment and some specific examples of the process and materials
used to produce the a long-term stabilized suspension which can be used for
covering briquettes, particles, pellets or powder of iron mineral and other
several
materials, in order to avoid its agglomeration when treated at high
temperatures,
and having a stability of at least three months without substantial agitation,
and
which has a very low tendency to settle down forming a hard solid cemented
cake.
In a preferred embodiment, a raw material of magnesium hydroxide
Mg(OH)2 may be used, which may be produced by the following processes:
~ Production of magnesium hydroxide by reacting calcined dolomite or
limestone with sea water or magnesium chloride brines
~ Production of magnesium hydroxide by thermal decomposition of
magnesium chloride brines.
~ Production of magnesium hydroxide by burning natural magnesite
(magnesium carbonate) in order to obtain magnesium oxide which
afterwards is hydrated with water in order to obtain magnesium hydroxide.
~ Production of magnesium hydroxide by hydrating Magnesium Oxide
~ Production of magnesium hydroxide by reacting sodium hydroxide with
magnesium sulfate or Epsom salt.
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~ Production of magnesium hydroxide from sodium hydroxide and
magnesium chloride brines.
~ From ammonia or ammonium hydroxide with magnesium chloride brines.
In one embodiment, the process for producing a long-term stabilized
suspension may comprise:
washing the magnesium hydroxide;
filtering and repulping the magnesium hydroxide solids in order to obtain
chloride values of less than 0.6%;
dispersing the agglomerated solid particles in a dispersing equipment for a
minimum 5 minutes;
adding one or more anionic polyelectrolytes at a concentration of at least
25% in an amount of about 0.5 to 2.5% in dry basis;
conditioning and micronizing the magnesium hydroxide solids in order to
reduce the particle size until approximately 2 microns;
adding a styrene acrylic emulsion, at a concentration of at least 30% in an
amount of 0.5 to 5% in dry basis;
dispersing the product obtained by the above step; and
storing the obtained suspension in a storing tank wherein it can be stored
for at least three months without substantially agitation without
experimenting
tendency to settle down forming a hard solid cake in the bottom of the storage
tank, nor particle thickening of the solid particles of the suspension and
which
can be used to cover briquettes, particles, pellets or powders of iron mineral
and
different materials.
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By the above referred process it is obtained a long-term stabilized
suspension having a pH of over 10.5; solid content of about 52% to 72%; a
water
content of about 28% to 48%; a viscosity of about 500 to 1,500 cp; an average
particle size of about 1 to 3 microns; an Mg(OH)2 content of about 50% to 70%;
a
pH value of over 10.5; an equivalent magnesium oxide content of 34% to 48%; a
specific gravity of 1.4 to 1.6; at least one anionic polyelectrolyte, at a
concentration of at least 25%, in an amount of about 0.5 to 2.5% in dry basis;
and an adherent compound that improves the adhesion of the suspension to the
pellets or briquettes during the process, at a concentration of at least 30%
in an
amount of 0.5 to 5% in dry basis; which can be stored for at least three
months
without substantial agitation, and without experimenting substantial
settlement
and the formation of a solid hard substrate formation.
The anionic polyelectrolytes are macromolecules originated from
monomeric units with ionizable groups in comparison with a simple electrolyte
such as the sodium chloride in which the Na+ cation and the CI- anion are
relatively small and similar in size. A polyelectrolyte is characterized by
having a
macro ion which is the vertebral column (a large ion and similar number of
charged groups connected by bonds) and an equivalent number of independent
and opposite small charges. Because of their high molecular weight, these are
also known as dispersant resins.
Examples of anionic polyelectrolytes are: sodium polyacrylate, ammonium
poly(styrene/maleate) among others.
The suspension of the present invention may have a high coverage area
of, for example, 5 m2/g minimum, and it can be applied on the surface of the
briquettes, particles, pellets or powders, as a diluted suspension having a
concentration of from 4 to 50%.
Although it was described that the raw material may comprise magnesium
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hydroxide, it may comprise magnesium/ calcium/ aluminum/ sodium hydroxide/
carbonate/ silicate.
The following are examples of the specific process for obtaining the long-
term stabilized suspension in accordance with the present invention:
EXAMPLE 1
A sample of the long-term stabilized suspension was prepared and was
divided in three portions.
Each portion was diluted with good quality water in order to obtain
concentrations of 1, 2 and 5% in weight.
Adhesion tests were carried out for each sample by covering iron mineral
pellets with each portion. An additional adhesion test was carried out using a
sample of cement at a concentration of 15% in weight for comparison purposes,
as well as another adhesion test using a control sample having no adhesion
additives.
The 5 samples were placed inside a laboratory reactor in order to carry
out the iron mineral reduction (change of iron oxide to metallic iron) and the
following results were obtained:
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Sample % of clustering
Control, without additives 87
Cement suspension at 15 % 30
Stabilized suspension at 5 % 4
Stabilized suspension at 2 % 10
Stabilized suspension at 1 % 19
The best results were obtained with the suspension at 5%, by which a
lesser quantity of agglomerated pellets were produced at the reactor exit, and
even at a concentration of 1 % there were obtained better results compared to
the
results obtained with the cement suspension at 15%.
EXAMPLE 2
A sample of the long-term stabilized suspension was prepared and divided
in six portions.
Two portions were diluted with water in order to obtain a concentration of
2% in weight, another two portions were diluted at a 3% in weight and the last
two portions were diluted at a 5% in weight.
Each portion was used to cover iron mineral pellets. Three samples were
maintained with concentrations of 2%, 3% and 5%, and three samples were air
blew (i.e. dried) in order to eliminate water excess and to determine if the
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adherence to the pellets decreases.
The 6 samples were placed inside a laboratory reactor in order to carry
out the iron mineral reduction and the following results were obtained:
Sample % of clustering
Stabilized suspension at 2 % 15
Stabilized suspension at 2 % air blew 19
Stabilized suspension at 3 % 11
Stabilized suspension at 3 % air blew 14
Stabilized suspension at 5 % 6
Stabilized suspension at 5 % air blew 11
From the above referred results, It can be concluded that air blowing the
samples before placing them inside the reactor, produce a slight decrease of
the
stabilized suspension performance, but there was always obtained low
percentages of agglomerated pellets.
EXAMPLE 3
Four samples of the stabilized suspension were prepared, adding a
styrene acrylic compound to each sample, in amounts of from between about 2%
to 5% in weight.
The four samples were diluted with water until obtain a final concentration
of 5% in weight which were used to cover iron mineral pellets. Subsequently
the
pellets covered with the stabilized suspension samples were placed inside a
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reactor in order to carry out an iron reduction and the following results were
obtained. A control sample comprising a cement suspension at a concentration
of 15% in weight having no additives, was also evaluated. The following
results
were obtained:
Sample % of clustering
Stabilized suspension with a 2% of additive 14
Stabilized suspension with a 3% of additive 9
Stabilized suspension with a 4% of additive 8
Stabilized suspension with a 5% of additive 8
Cement suspension at 15% without additive 28
From the above experiment it can be concluded that the lesser percentage
of remnant agglomerates were obtained with additive amounts of 4% and 5% in
weight.
EXAMPLE 4
Three samples of the stabilized suspension were prepared, using as a raw
material natural magnesite (magnesium carbonate) which was burned at a
temperature of 900°C in order to obtain magnesium oxide.
After obtaining the magnesium oxide, water was added to the magnesium
oxide in order to obtain magnesium hydroxide and to adjust its concentration
at
55% in weight.
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The obtained suspension was divided in three portions, adding 1 %, 3%
and 5% in weight of a styrene acrylic compound to each portion respectively.
Finally there was added water in order to obtain a magnesium hydroxide
concentration of 5% in weight.
Each sample was used to cover different iron pellets which were placed
inside a laboratory reactor in order to carry out an iron reduction at a
temperature
of 950°C.
Other iron pellets were covered with a cement suspension at a
concentration of 15% in weight and placed inside the same reactor in order to
use them as control samples. The following results were obtained:
Sample % of clustering
Stabilized suspension with 1 % of additive 15
Stabilized suspension with 3% of additive 9
Stabilized suspension with 5% of additive 8
Cement suspension at 15% 26
The best results were obtained with the stabilized suspensions having
additive amounts of 3% and 5%. Also there was demonstrated that the stabilized
suspension of the present invention may be produced using other different raw
materials.
Finally it must be understood that the long term-stabilized suspension, for
covering briquettes, particles, pellets or powder iron and the process for its
production and application of the present invention, is not limited
exclusively to
the above described and illustrated embodiments and that the persons having
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ordinary skill in the art can, with the teaching provided by this invention,
make
modifications to the long term-stabilized suspension for covering iron mineral
and
the process for its production and application of the present invention, which
will
clearly be within the true inventive concept and scope of the invention which
is
claimed in the following claims.
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