[0001] Iron ore needs to be in the form of agglomerates of substantial size when it is charged
into a blast furnace. If the available ore is in the form of particles that are too
small for direct feed to the blast furnace it is necessary to convert them to a sinter
or to pellets. With the increasing use of lower grade ores it has become necessary
to grind the ore more finely and, for these fine particles, pelletisation is the only
satisfactory method of production of feedstock for the furnaces.
[0002] The pellets are made by adding binder to the fine particulate ore and stirring in
the presence of a small amount of water (generally moisture in the ore) to form a
moist mixture, and then pelletising the mixture, e.g., in a balling drum or disc pelletiser.
The green pellets are then fired in a kiln through a temperature range that extends
from an inlet temperature typically in the range 200-400°C up to a final temperature
of e.g., 1200°C.
[0003] Important properties of the pellets are the initial or wet strength, the dry strength
(after drying the green pellets in an oven at 105°C) and the tendency of the pellets
to spall (or burst) upon exposure to firing temperatures. The tendency for spalling
can be defined by determining the minimum temperature at which spalling occurs or
by observing the percentage of fines formed during a particular firing cycle. The
moisture content of the mixture and the porosity of the pellets must be chosen carefully.
A high "drop number" for the green pellets is desirable. For cost reasons the amount
of binder should be as low as possible and, to ensure uniform properties, its flow
properties must be such that it can easily be added uniformly in these low quantities.
[0004] Although many binders have been proposed in the literature, (e.g., bentonite and
other clays, ferrous sulphate, lignin sulphate, asphalt, starches, calcium and sodium
compounds, and certain polymers) in practice bentonite is the binder that is generally
used.
[0005] In GB 1,324,838 work was described that was conducted in or before 1970, more than
15 years ago. This used, as binder, a water soluble linear organic polymer having
a molecular weight of 1 million to 20 million. Suitable polymers were modified natural
polymers such as starch and sodium carboxymethyl cellulose and various non-ionic,
anionic or cationic synthetic polymers. The process involved forming a solution of
the polymer and spraying the solution on to the particulate iron ore. The patent noted
that the sprayed solution was viscous and that this could be a problem, but that the
viscosity could be reduced by including sodium chloride, sodium sulphate or potassium
chloride in the water used for making the solution.
[0006] Although direct comparisons of the polymers in GB 1,324,838 is difficult it appears
from the patent that various non-ionic, anionic and cationic polymers can be used
to give improved green strength and/or spalling properties compared to bentonite,
at very much lower dosages than bentonite. For instance a straight chain polyethylene
oxide was reported as giving improved strength and spalling values and a cationic
copolymer and a polymer formed from about 8% sodium methacrylate and 92% acrylamide
were reported as giving improved strength values.
[0007] A disadvantage of the process in GB 1,324,838 is that it is necessary to introduce
substantial amounts of water with the polymer and so the initial iron ore must be
very dry (involving the use of drying energy) or the final pellets will be very wet
(increasing the risk of spalling).
[0008] In Aus.I.M.M. Newcastle Pellets and Granules Symposium October 1974 pages 151 to
156 R.L.Smythe describes what appears to be the same work as is discussed in this
patent. It describes the problems that had been incurred with converting dry powder
polymer into the polymer solution that could be sprayed on to iron ore. The article
proposed the use of polymer supplied as a 35% solution (necessarily therefore involving
bulk handling problems) and the use of polymer supplied as a liquid suspension, that
presumably was converted to an aqueous solution before use. The article warned about
handling problems of the resultant pellets and the risk of blockage of chutes and
referred to the study of alternative polymers, namely "natural polymers and derivatives
of petroleum products".
[0009] Despite all this work in the early 1970's an authoritative review of iron ore pelletisation
by G.K.Jones in Industrial Minerals March 1979 pages 61 to 73 mentions, as binders,
only Portland cement, lime and bentonite, and emphasises the large amount of bentonite
that is used and predicts that it will continue to be used despite the shortages of
bentonite.
[0010] Despite the acceptance by Jones, and the whole industry, that bentonite would continue
to be the most widely used binder it has, for very many years, been recognised to
incur various problems. Thus some grades of bentonite give satisfactory pellet properties
but others are less satisfactory. A problem with all grades of bentonite is that the
bentonite is not combustible and so contributes to the gangue in the furnace, and
this gangue tends to be corrosive to the lining of the furnace. Another problem with
bentonite is that the optimum grades are becoming less available. Bentonite must be
present in the pellets in quite large amounts, thus reducing the iron content of the
pellet significantly and increasing the amount of gangue. Lime and some inorganic
salts have been proposed as alternatives to bentonite, but again they cause the formation
of unwanted gangue and can be less satisfactory than bentonite. The added gangue constituents
require increased energy consumption in the furnace.
[0011] A problem with bentonite and other binders is that the spalling temperature is low.
Typically the inlet temperature of the kiln has to be in the range 200 to 400°C to
prevent spalling. Higher inlet temperatures would be economically desirable if spalling
could still be avoided.
[0012] In Mining Engineering October 1984 pages 1437 to 1441 de Souza et al reported that
organic binders would have the inherent advantage, over inorganic binders, of being
eliminated during firing. Results were reported on the use of polymers based on cellulose,
in particular the material sold under the trade name Peridur and which is believed
to be carboxymethyl cellulose. The article reported adding Peridur powder to an aqueous
pulp of iron ore before filtration and also reported adding the powder manually to
the ore flow. The article noted the need for water soluble polymers to be hydrated
and dissolved during mixing and pelletising. Spalling at 250°C was reported, but this
is unsatisfactorily low.
[0013] A difficulty with powdered cellulosic binders such as carboxymethyl cellulose is
that the irregular particle shape and size distribution is such that the powder does
not flow freely. Instead the dry particles tend to clump together rather than flow
over one another. As a result it is difficult to achieve uniform supply of the low
dosages that are required. Another problem is that the amount of cellulosic binder
that has to be used for adequate strength tends to be too high to be cost effective.
Another problem with some cellulosic polymers is that they can reduce surface tension,
and this appears to be undesirable in pellet formation.
[0014] In practice the use of cellulosic binders has not been widely adopted, presumably
because of these or other problems. At present therefore there is very little use
of organic binders and bentonite is still very widely used, despite the long-recognised
disadvantages and decreasing availability of suitable grades of bentonite and despite
the long-established possibility of using organic binder.
[0015] In EP 0203855A2 (not published until after the priority date of this application)
it is proposed to use a water soluble high molecular weight polymer in the form of
a dry powder or, preferably, a water-in-oil emulsion that preferably contains both
water-in-oil and oil-in-water surfactants. Non-ionic, anionic and cationic polymers
are proposed. The use of the polymer in combination, with an inorganic salt, to increase
strength, is also proposed.
[0016] Spalling properties are not discussed in a manner that allows judgement as to whether
these polymers could give improved spalling properties compared to the spalling properties
of bentonite.
[0017] The only dry powders that are specifically proposed in EP 0203855A2 are Rhone Poulenc
AD10 which is said to be a non-ionic polyacrylamide having intrinsic viscosity (IV)
15.4dl/g and which we believe to be a coarse crushed gel product, and Percol 725 and
Percol 726, both of which are made by the assignees of the present application. Percol
725 is a crushed gel copolymer having IV about 18 of 80% acrylamide and 20% by weight
sodium acrylate and Percol 726 is a bead copolymer of about 65% acrylamide and 35%
by weight sodium acrylate and has IV about 17. In particular the bead form of Percol
726 is made by reverse phase polymerisation and a significant amount of the particles
have a dry size above 450µm and up to about 800µm, and the crushed gel of Percol 725
also has a particle size of up to about 800µm.
[0018] When considering possible binders that might be used there are several critical factors
that have to be recognised. The iron ore always has a very small particle size, and
therefore a huge surface area. The binder must be introduced with the absolute minimum
of water in order that the pellets can conveniently have a total moisture content
of not more than about 15%. The duration and energy of mixing the binder with the
iron ore particles must be as short as possible in order to maximise production and
minimise capital costs. The amount of binder must be as low as possible in order to
minimise cost and to avoid the risk of excess binder accentuating the stickiness problems
noted in the article by R.L.Smythe.
[0019] Bentonite has a very small particle size (typically below 10µm) and adequate admixture
of these very small particles with the particulate iron ore is achieved because the
bentonite is used in a relatively large amount (typically 1%). However it would be
expected that the use of a binder that is substantially coarser and/or present in
a substantially smaller amount would tend to give less satisfactory results, due to
non-uniform mixing of the binder with the relatively large volume of very fine particulate
iron ore.
[0020] The use of cellulosic binders or the powder or emulsion binders proposed in EP 0203855A2
is inconvenient from the point of view of application methods that give reasonable
results. Also the results are, at best, generally no better than those obtainable
with bentonite, and they are often worse. It has been our object to improve application
methods and/or obtain better results.
[0021] In the methods of the invention mineral ore pellets are made by adding binder comprising
organic polymer to particulate mineral ore having substantially all particles below
250µm and stirring in the presence of about 5 to about 15% by weight water (based
on total mixture) to form a substantially homogeneous moist mixture and pelletising
the moist mixture.
[0022] In Applicants EP-A-225171 (published 10 June 1987, after the priority date of this
application) there is claimed a process in which iron ore pellets are made by adding
binder comprising organic polymer to particulate iron ore having substantially all
particles below 250µm and stirring in the presence of 5 to 15% by weight (based on
total mix) to form a substantially homogeneous moist mixture and pelletising the moist
mixture, and the process is characterised in that the binder comprises up to 0.2%
by weight, based on the total mix, of a water soluble synthetic polymer that has intrinsic
viscosity 3 to 16dl/g and that is an anionic polymer of one or more water soluble
ethylenically unsaturated monomers comprising an anionic monomer and that is added
to the iron ore as a dry, free flowing, powder having substantially all particles
above 20µm and below 300µm. Table 5 mentions the use of a cationic polymer blend.
[0023] Although that process is very successful for pelletising conventional iron ores it
has been found that less satisfactory results are obtained with some unusual ores,
for instance one particular of haematite iron ore in Canada. It has been ascertained
that this particular ore as supplied is acidic, in that has a much lower pH than normal
pelleting ores.
[0024] In the invention pellets are made from mineral ore by adding binder comprising organic
polymer to acidic particulate mineral ore having substantially all particles below
250µm and stirring in the presence of 5 to 15% by weight water (based on total mix)
to form a substantially homogeneous moist mixture and pelletising the moist mixture,
and in this process the binder comprises about 0.002% to about 0.5% by weight, based
on total mix, of water soluble polymer that is cationic.
[0025] When a small amount, e.g., 2 to 10% by weight, of particulate ore is slurried with
water the pH of the resultant water may depend upon the amount of ore that is used
but at higher amounts of ore, typically 30 to 40% solids, the pH becomes substantially
independent of the amount of ore. It is this pH, that is substantially independent
of ore concentration, which is intended herein when reference is made to the ore giving
a specified pH. Normal ores give a pH of above 8.1, typically 8.2 to 8.4 or higher.
The invention is directed to the treatment of ores which are acidic and give a pH
in this test of up to 6.
[0026] By the invention it is possible to obtain very good pelletising results even at very
low pH values. This is in marked contrast to existing systems, and especially systems
using bentonite, where reasonable results are sometimes obtainable at pH values 7
to 8 but the results at lower pH values, for instance 6.5 to 4 or even down to 3,
are totally inadequate in most instances. Thus the invention permits, for the first
time, satisfactory pelletising of acidic, and often highly acidic, ore.
[0027] The mineral can be any acidic ore, e.g., a zinc ore, but is preferably an iron ore,
normally a haematite, magnetite or taconite. The ore may be naturally acidic or may
have been rendered acidic by some treatment prior to blending with the binder. For
instance the ore may have been washed with acid to remove acid soluble components,
typically to produce a pH of from 5 to 6 if manganese is being washed out of the ore.
[0028] The ore may have acquired an acidic pH during other processing treatments. For instance
the ore may be dried under conditions that result in the dry ore giving the specified
relatively low pH in water. This may be because, for instance, the drying is conducted
using hot gases that contain sulphur or other impurities that cause acidification
of the ore during drying or may be due to chemical changes in the surface properties
of the ore that are caused by dehydration.
[0029] As a result of the invention it is possible, for the first time, to use for pelletising
ores that hitherto would have been rejected, either because of their acidity or because
of their low grade. The reason why it is now possible to use low grade ores for pelletising
is because a preferred process of the invention comprises forming acidic particulate
ore from the mineral ore (that can be of low grade) by a process comprising washing
or leaching the mineral ore in acid, and thereafter using the resultant, enriched,
acidic particulate ore for pelletising. It has not previously been practicable to
use acid washed or acid leached ores for pelletising. The ore that is acid washed
or leached is normally an iron ore.
[0030] Numerous methods of purifying or enriching mineral ores by acid treatment are well
known, and can be used in the invention.
[0031] The soluble cationic polymer is formed by the polymerisation of cationic ethylenically
unsaturated monomer, optionally with other ethylenically unsaturated monomers. The
monomer or monomer blend will normally be water soluble. One suitable class of cationic
monomers are the dialkylaminoalkyl (meth) acrylates, especially dimethylaminoethyl
(meth) acrylate (DMAEA or DMAEMA). Another suitable class are the dialkylaminoalkyl
(meth) acrylamides. A suitable material is dimethylaminopropyl (meth) acrylamide.
All such monomers are generally present in the form of acid addition or quaternary
ammonium salts. For instance a suitable monomer is methacrylamido propyl trimethyl
ammonium chloride (MAPTAC). Other suitable cationic monomers include diallyl dialkyl
quaternary monomers, especially diallyl dimethyl ammonium chloride (DADMAC). Preferred
cationic polymers are polymers having recurring quaternary ammonium groups. Blends
of cationic polymers (e.g., a blend of synthetic cationic with natural or modified
natural cationic polymer) can be used.
[0032] The polymers can be copolymerised with non-ionic monomers, generally (meth) acrylamide
(ACM). Other suitable cationic polymers are polyethylene imines and epichlorhydrin
polyamine reaction products made in bead form. We find that homopolymers and other
polymers having a very high cationic content can be of relatively low molecular weight,
for instance having intrinsic viscosity below 5 dl/g, often in the range 0.4 to 2
dl/g. When such polymers are formed from ethylenically unsaturated monomers at least
70 weight percent, and preferably at least 90 weight percent, of the monomers should
be cationic, and preferably the polymer is substantially a homopolymer.
[0033] Other preferred polymers have medium to high molecular weight and medium cationic
content. For instance the IV may be from about 3 to about 20 dl/g or higher, generally
3 to 12 dl/g, preferably from 5 to 9 dl/g. Such polymers are best made by copolymerisation
of about 20 to about 75, preferably about 25 to about 60, weight percent cationic
monomer with a non-ionic monomer such as acrylamide. Best results are generally obtained
with about 35 to about 55 weight percent cationic monomer, with the balance non-ionic.
[0034] Although best results are achieved most easily when the cationic polymer is added
in the form of water soluble beads all below 300µm (microns) as discussed below, in
some instances the cationic polymer can be added in other forms. Thus it can be added
in the form of particles that are within the size ranges discussed above for beads
but which have been made by comminution of gel in air or, preferably, in an organic
liquid for instance as described in EP 169674. It may be necessary to sieve the particles
to give the desired particle range and to exclude oversize particles.
[0035] Instead of being a synthetic polymer, it can be a naturally occurring polymer (or
a modified natural polymer) such as Chitosan or cationic starch, but this usually
less satisfactory than the use of synthetic polymers.
[0036] When the ore is wholly dry, or is drier than is required in the moist pelleting mixture,
it is necessary to add water to the ore in order to form the moist mixture and it
is then possible to incorporate the polymer as a solution in this water. For this
purpose the polymer can initially be provided in any suitable physical form. When
the polymer is being added as a solution, the aqueous polymer solution may be sprayed
on to the ore prior to pelleting. The solution can be made from polymer in the form
of a concentrated solution, a polymer-in-oil dispersion or powder. Alternatively the
polymer-in-oil dispersion of the polymer can be added direct to the ore. The polymer
particles in any such dispersion can be dry or can be swollen gel particles.
[0037] Preferably however the polymer is added in the form of dry, free flowing powder having
substantially all particles below about 300µm, usually in the range about 20 to about
300µm. The particles can be comminuted gel, especially if the comminuted gel particles
had been formed or treated in known manner so as to promote their flow, but preferably
the particles are beads, for instance as made by reverse phase bead polymerisation.
[0038] Reverse phase bead polymerisation is a well known process. Thus an aqueous solution
of the chosen monomer or monomer blend is dispersed in water immiscible liquid, generally
in the absence of an emulsifying agent but often in the presence of an amphipathic
polymeric stabiliser, the polymerisation is induced in conventional manner to provide
a suspension of gel particles in the non-aqueous liquid, the suspension is then dried
by azeotropic distillation and the particles are separated from the non-aqueous liquid
in conventional manner. The desired particle size range is controlled in known manner,
for instance by the choice of stabiliser, emulsifying agent (if present) and, especially,
the degree of agitation during the formation, of the initial suspension of aqueous
monomer particles in the water immiscible liquid. The beads are substantially spherical.
[0039] Some reverse phase polymerisation methods involve the use of relatively large amounts
or emulsifiers or other materials that depress surface tension. It is particularly
desirable in the invention to make the polymer particles in the substantial absence
or any such material. In particular, it is desirable that the entire binder (and also
the polymer component of the binder) should have substantially no depressant effect
on surface tension. Thus if binder is dissolved with water at 20°C at 0.075% by weight
concentration the surface tension of the solution should be above 65, and preferably
above 70·10⁻⁵N(dynes)/cm. Thus it is preferred to avoid the use of amounts of surfactant
that would depress surface tension significantly and reliance should be placed instead
on agitation or stabiliser, in known manner, to control bead size.
[0040] Although it might have been expected to be desirable to use swellable but insoluble
particles (in an attempt at matching the properties of bentonite) in fact the use
of such polymer as the only polymer is unsatisfactory and soluble polymer must be
used.
[0041] The failure of the cross-linked polymers, and the article in Mining Engineering October
1984 page 1438, might have indicated that it is necessary for the polymer to go into
solution and/or to form a viscous phase during mixing, but results can be improved
(or the required polymer dose reduced) by the presence in the water of certain simple
compounds. Many of these are monomeric, usually inorganic, electrolyte that can be
shown experimentally to reduce the rate of solution and the viscosity when the polymer
is dissolved into bulk water. However it appears that some mechanism other than depression
of solubility or viscosity is involved. In practice the water is generally moisture
that is present in the ore, remaining from a previous filtration stage, and this water
is itself normally a solution of one or more inorganic electrolytes.
[0042] Although this contamination appears satisfactory results are improved further, and
often synergistically, if the powdered binder that is added to the ore includes additional
monomeric compound that is usually an inorganic or organic electrolyte but can be
a non-electrolyte.
[0043] The compound is normally water soluble and inorganic and so is preferably a water
soluble salt of an acid. However salts of strong acids (e.g., sodium chloride, sulphate
or nitrate) are less satisfactory than salts of weak organic acids or carbonic acid.
The strong acid salts may generate corrosive acids during smelting or firing. Accordingly
preferred compounds that are incorporated as part of the binder are organic molecules
such as urea, inorganic water soluble salts of carboxylic, dicarboxylic and tricarboxylic
acids such as sodium acetate, sodium citrate, sodium oxalate, sodium tartrate, sodium
benzoate and sodium stearate, other sodium salts of weak acids such as sodium bicarbonate
and sodium carbonate, other miscellaneous sodium salts such as sodium silicate or
phosphate, the corresponding ammonium, potassium, calcium or magnesium salts of the
preceding salts and calcium oxide. Sodium carbonate, bicarbonate or silicate are generally
preferred as they give the best anti-spalling and dry strength results.
[0044] An important advantage of the use of beads made by reverse phase bead polymerisation
is that they can readily be added in very uniform and very small amounts to the ore
that is to be pelleted, because of the substantially spherical shape of the beads.
If the binder is to be a blend of the polymer with other material such as any of the
compounds discussed above then this other material should also be added in a form
that is easily flowable on to the ore. Preferably the compound is incorporated in
the beads. For instance a salt of a weak acid can be present in the aqueous monomer
during polymerisation. Alternatively the compound can be added separately to the ore
or it can be preblended with the polymer beads, but in either instance the compound
itself is preferably put into a free flowable, generally bead, form, by known techniques.
[0045] The optimum amount of added salt or other compound can be found by experimentation.
For many purposes it is in the range 0 to about 60% by weight based on the binder
(below 0.1% and usually below 0.02% based on ore). In some instances amounts of from
about 10 to about 30% based on soluble polymer are the most cost effective but usually
greater amounts, for instance 30 to about 100% or even 150%, preferably 50 to 90%,
based on soluble polymer are preferred.
[0046] The soluble polymer (in bead or other form), optionally with the added salt or other
compound, can be used in combination with other binders. In particular, despite the
fact that cross linked polymers have proved, by themselves, to be unsatisfactory we
find valuable results are achieved if a cross linked, swellable, particulate organic
polymer is included with the soluble polymer. The cross linked polymer must have a
small particle size, below 100µm and often below 50µm. The size can be as small as
is commercially available, e.g., down to 10µm or 1µm. The particles are normally introduced
as dry powder and preferably this powder is in the form of bead fines separated during
the production of coarser particulate swellable polymer as produced by bead polymerisation.
The inclusion of the cross linked polymer particles can give surprisingly improved
dry strength and drop number values and so a blend of soluble particles and cross
linked particles can give an excellent combination of dry strength, wet strength and
spalling properties. Also the pellets tend to have improved surface appearance, such
as smoothness.
[0047] The cross linked polymer may be non-ionic (e.g., polyacrylamide), but when the soluble
polymer is ionic it is preferably of the same ionic type as the soluble polymer and
so may be formed from the same monomers as are discussed below for the preparation
of the soluble polymer. Preferably 20 to 100% by weight, most preferably 60 to 100%
by weight, are ionic. The use of homopolymer, e.g., cross linked sodium polyacrylate,
is very satisfactory. Cross linking may be by any of the conventional cross linking
agents used in the production of swellable or absorbent polymers. Thus it may be by
an ionic cross linking agent but is preferably covalent, e.g., methylene bis acrylamide
or other polyethylenically unsaturated monomer. The amount of cross linking agent
is generally in the range 20 to 1,000 ppm, preferably 50 to 500 ppm, and must be such
that the particles are insoluble but highly swellable in water, e.g., having a gel
capacity in water above 50, and preferably above 200, grams per gram.
[0048] The amount of cross linked polymer particles may be relatively low, e.g., 10 to 30%
based on soluble polymer, but generally greater amounts, e.g., up to 300% or even
600% based on soluble polymer are preferred. Amounts of 0 to 80% often 20 to 50%,
based on total binder are suitable. Particularly preferred binders consist essentially
of 1 part by weight soluble polymer, 0.3 to 1.5 parts by weight sodium carbonate or
other added salt or simple compound, and 0.3 to 5 parts by weight cross linked anionic
homopolymer or copolymer, with proportions of about 1:1:1 often being convenient.
[0049] Substantially all the particles of the soluble polymer (and of other binder particles)
must be below about 300µm for good results, presumably since otherwise the particle
size is too large to establish adequate contact with the very large number of very
small iron ore particles. Preferably substantially all the polymer particles are below
about 200 and preferably below about 150µm (microns). Although it might be expected
to be necessary to have exceedingly small polymer particle size, similar to bentonite,
this is unnecessary and it is satisfactory for most or all of the particles to be
above 20µm (microns). Best results are often achieved when substantially all the polymer
particles are in the range 20 to 100µm (microns) but a satisfactory fraction is 100%
below about 200µm and at least 50% below about 100µm.
[0050] Good results are achieved at very low soluble polymer additions. The amount, therefore,
is usually below about 0.2% and generally it is below about 0.1% (by weight based
on the total mix). It is often preferred for the amount to be below 0.05% by weight,
but amounts below 0.01% are usually inadequate except when the soluble polymer is
used with significant (e.g., at least 20% by weight) other binder components. the
amount of soluble polymer may then sometimes be reduced, e.g., to 0.005%.
[0051] The particle size of the ore is generally less than 250 microns, usually 90% or 80%
by weight of the particles being less than 50 microns. The ore is preferably an iron
ore such as magnetite, haemetite or taconite, but can be any other mineral ore that
needs to be put into the form of pellets, for instance a zinc ore. Satisfactory results
can be obtained even if the ore is contaminated with clay.
[0052] Before adding binder in the form of dry polymer, the ore usually already has the
desired final moisture content of 5 to 15%, preferably 8 to 10%, by weight based on
the weight of iron ore. This moisture content is the moisture as measured by heating
up to 105°C. However if the ore is too dry then water may be added to it, e.g., before
or after the addition of polymer binder (or the binder may be predissolved).
[0053] The binder can be blended with the ore in the same manner as bentonite is blended,
preferably by scattering the polymer particles on to the ore as it is carried towards
a mixer, for instance a paddle mixer provided with stators. It may be mixed for the
same duration as when bentonite is used, for instance 2 to 20, generally about 10,
minutes.
[0054] The damp blend of ore and polymer is converted to pellets in conventional manner,
for instance by balling in conventional manner. This may be effected using a rotating
tilting disc but generally is conducted in a balling drum. The size of the pellets
is generally from 5 to 16 mm, preferably 8 to 12 mm.
[0055] Before the resultant green pellets can be utilised for the production of metal they
need to be fired, generally at a temperature up to above 1000°C, for instance up to
1200°C. For this purpose they can be introduced into a kiln or other firing apparatus
and fired in conventional manner. It is desirable to be able to introduce them into
this furnace at the highest possible inlet temperature with the minimum risk of spalling.
The inlet temperature at which spalling becomes significant can be referred to as
the spalling temperature and a particular advantage of the invention is that it is
possible to make pellets having a spalling temperature higher than can conveniently
be obtained by the use of bentonite and other known binders.
[0056] Good results can be achieved while using easy application techniques and low amounts
of polymer. It is easy to make pellets which have satisfactorily high wet strength
and dry strength (measured after drying in an oven) and a satisfactorily high drop
number when wet (indicating the number of drops before they shatter). In particular
it is possible to obtain excellent spalling properties, often much better than are
obtainable with bentonite.
[0057] In examples 1 and 2 below the binders were each scattered on to acidic moist particulate
haematite iron ore at an appropriate dosage. The moisture content was 8.3%. The blend
was then converted to pellets in a balling drum, the pellets having a size typically
of about 5-16mm.
[0058] The following synthetic cationic polymeric binders were used. They were made by reverse
phase polymerisation to a bead size below 200µm and the beads were dried and separated.
- Polymer A :
- copolymer of 40% methyl chloride quaternised dimethylaminoethyl acrylate (MeCl.q DMAEA)
60% acrylamide (ACM)
IV ∼ 7-8 dlg⁻¹
- Polymer B :
- copolymer of 50% MAPTAC with 50% ACM
IV = 6.9 dlg⁻¹
- Polymer C :
- 100% PolyMAPTAC
IV = 1.3 dlg⁻¹
- Polymer D :
- copolymer of 60% MeCl q DMAEA with 40% ACM
IV ∼ 6-7 dlg⁻¹
- Polymer E :
- copolymer of 80% MeCl q DMAEA with 20% ACM
IV ∼ 8-9 dlg⁻¹
- Polymer F :
- 100% Poly-diallyldimethyl ammonium chloride solid grade
IV = 0.7 dlg⁻¹
Example 1
[0059] An ore from the Wabush mine was dried, giving a pH of 6.2, and was blended while
moist with the binder. The wet strength, dry strength, drop number and spalling temperatures
were recorded, as shown in Tables 1 and 2 below.
Table 1
|
Dose % w/w |
Wet Strength/kg |
Dry Strength/kg |
Drop Number |
% Moisture |
Blank |
- |
0.56 |
0.59 |
7.9 |
8.0 |
Bentonite |
0.7 |
1.17 |
8.20 |
18.5 |
10.0 |
Peridur |
0.04 |
0.56 |
0.14 |
9.2 |
8.7 |
Polymer A |
0.04 |
0.92 |
1.24 |
22.7 |
8.8 |
Polymer B |
0.04 |
0.72 |
1.82 |
19.2 |
9.4 |
Polymer C |
0.1 |
0.86 |
3.31 |
8.2 |
8.2 |
Table 2
|
% Spalled |
|
700°C |
850°C |
1000°C |
Blank |
0 |
70 |
100 |
Bentonite |
40 |
50 |
100 |
Peridur |
- |
100 |
- |
Polymer A |
- |
0 |
80 |
Polymer B |
- |
10 |
100 |
Polymer C |
0 |
0 |
70 |
Example 2
[0060] An acid leached iron ore having pH about 5 was used and the following results were
obtained.
Table 3
|
Dose % w/w |
Wet Strength/kg |
Dry Strength/kg |
Drop Number |
% Moisture |
Polymer A |
0.04 |
0.49 |
1.61 |
8.2 |
8.9 |
B |
0.04 |
0.50 |
2.15 |
16.9 |
9.1 |
D |
0.04 |
0.58 |
2.11 |
6.8 |
8.0 |
E |
0.04 |
0.51 |
1.94 |
5.4 |
7.8 |
F |
0.1 |
0.48 |
3.50 |
4.2 |
7.9 |
[0061] Spalling was tested for all binders at 850°C and for binders B, E and F at 1000°C.
No spalling occurred.
1. A process in which pellets are made from mineral ore by forming acidic particulate
ore having substantially all particles below 250µm and that gives a pH in water of
up to 6 by a process comprising washing or leaching the mineral ore in acid and blending
binder comprising organic polymer into the acidic particulate ore in the presence
of 5 to 15% by weight water (based on total mix) to form a substantially homogeneous
moist mixture and pelletising the moist mixture, and in which the binder comprises
about 0.002% to about 0.5% by weight, based on total mix, of a water soluble polymer
that is cationic.
2. A process according to claim 1 in which the polymer is synthetic and formed from ethylenically
unsaturated monomers comprising a cationic monomer.
3. A process according to claim 1 or claim 2 in which the mineral ore is iron ore which
has been acid washed or acid leached.
4. A process according to claim 3 in which the cationic polymer is selected from polymers
that have intrinsic viscosity 0.4 to 5dl/g and that are formed from monomers of which
at least 70% by weight are cationic, and polymers that have intrinsic viscosity of
3 to 20dl/g and that are formed by copolymerisation of 20 to 75 weight percent cationic
monomer with 80 to 25 weight percent non-ionic monomer.
5. A process according to claim 3 in which the cationic polymer is substantially a homopolymer
having intrinsic viscosity 0.4 to 2dl/g, the cationic monomer preferably being selected
from diallyl dimethyl ammonium chloride and quaternised dialkylaminoalkyl (meth) acrylates
and quaternised dialkylaminoalkyl (meth) acrylamides.
6. A process according to claim 3 in which the cationic polymer is a copolymer of 25
to 60 weight percent cationic monomer 75 to 40 weight percent acrylamide and has an
intrinsic viscosity in the range 3 to 12 dl/g.
7. A process according to claim 3 in which the cationic polymer is a copolymer of about
20 to about 60% acrylamide with about 80 to about 40% by weight of a quaternised monomer
selected from dialkylaminoalkyl (meth) acrylates and dialkylaminoalkyl (meth) acrylamides
and has intrinsic viscosity of from 3 to 12 dl/g.
8. A process according to any of claims 3 to 7 in which the polymer is added to the ore
as dry free flowing powder having substantially all particles above 20µm and below
300µm.
9. A process according to any of claims 3 to 8 in which the polymer is added in the form
of beads made by reverse phase suspension polymerisation.
10. A process according to any preceding claim in which the binder gives a surface tension
of above 70·10⁻⁵N/cm at a concentration in water at 20°C of 0.075% by weight.
11. A process according to any preceding claim in which the amount of polymer is from
0.01 to 0.05% by weight.
12. A process according to any preceding claim in which at least 70% by weight of the
acidic particulate ore has a particle size below 50µm.
1. Verfahren, in dem Pellets von Mineralerz hergestellt werden, indem säurehaltiges,
aus Teilchen bestehendes Erz mit im wesentlichen allen Teilchen kleiner als 250 µm
gebildet wird, und das einen pH-Wert in Wasser bis zu 6 hat, mittels eines Verfahrens,
das umfasst, das Mineralerz in Säure zu waschen oder auszulaugen, ihm ein Bindemittel
beizumengen, das organisches Polymer in dem säurehaltigen, aus Teilchen bestehenden
Erz in der Gegenwart von 5 bis 15 Gewichts% Wasser (beruhend auf der ganzen Mischung)
umfasst, um eine im wesentlichen homogene feuchte Mischung zu bilden und die feuchte
Mischung zu pelletieren, und in dem das Bindemittel ungefähr 0,002 bis ungefähr 0,5
Gewichts% eines wasserlöslichen Polymers, das kationisch ist, beruhend auf der ganzen
Mischung, umfasst.
2. Verfahren nach Anspruch 1, in dem das Polymer synthetisch ist und von ethylenisch
ungesättigten Monomeren gebildet ist, die ein kationisches Monomer umfassen.
3. Verfahren nach Anspruch 1 oder Anspruch 2, in dem das Mineralerz Eisenerz ist, das
mit Säure gewaschen oder ausgelaugt ist.
4. Verfahren nach Anspruch 3, in dem das kationische Polymer von Polymeren ausgewählt
wird, die eine Grenzviskosität von 0,4 bis 5 dl/g haben, und die von Monomeren gebildet
sind, von denen wenigstens 70 Gewichts% kationisch sind, und Polymeren, die eine Grenzviskosität
von 3 bis 20 dl/g haben, und die durch Copolymerisation von 20 bis 75 Gewichtsprozent
aus kationischem Monomer mit 80 bis 25 Gewichtsprozent aus nichtionischem Monomer
gebildet sind.
5. Verfahren nach Anspruch 3, in dem das kationische Polymer im wesentlichen ein Homopolymer
mit einer Grenzviskosität von 0,4 bis 2 dl/g ist, wobei das kationische Monomer vorzugsweise
von Diallyldimethylammoniumchlorid und quaternisierten Dialkylaminoalkyl(meth)acrylaten
und quaternisierten Dialkylaminoalkyl(meth)acrylamiden ausgewählt wird.
6. Verfahren nach Anspruch 3, in dem das kationische Polymer ein Copolymer von 25 bis
60 Gewichtsprozent aus kationischem Monomer 75 bis 40 Gewichtsprozxent Acrylamid ist,
und eine Grenzviskosität in einem Bereich von 3 bis 12 dl/g hat.
7. Verfahren nach Anspruch 3, in dem das kationische Polymer ein Copolymer von ungefähr
20 bis ungefähr 60 Gewichts% Acrylamid mit ungefähr 80 bis ungefähr 40 Gewichts% eines
quaternisierten Monomers ist, das von Dialkylaminoalkyl(meth)acrylaten und Dialkylaminoalkyl(meth)acrylamiden
ausgewählt wird und eine Grenzviskosität von 3 bis 12 dl/g hat.
8. Verfahren nach einem der Ansprüche 3 bis 7, in dem das Polymer dem Erz als trockenes,
frei fliessendes Pulver zugegeben wird, wobei im wesentlichen alle Teilchen grösser
als 20 µm und kleiner als 300 µm sind.
9. Verfahren nach einem der Ansprüche 3 bis 8, in dem das Polymer in Gestalt von Kügelchen
zugegeben wird, die durch Umkehrphase-Suspensionspolymerisation hergestellt sind.
10. Verfahren nach einem der vorhergehenden Ansprüche, in dem das Bindemittel eine Oberflächenspannung
von ungefähr 70 10⁻⁵N/cm bei einer Konzentration bei 20°C von 0,075 Gewichts% in Wasser
hat.
11. Verfahren nach einem der vorhergehenden Ansprüche, in dem die Menge des Polymers zwischen
0,01 und 0,05 Gewichts% liegt.
12. Verfahren nach einem der vorhergehenden Ansprüche, in dem wenigstens 70 Gewichts%
des säurehaltigen, aus Teilchen bestehenden Erzes eine Teilchengrösse hat, die kleiner
als 50 µm ist.
1. Procédé dans lequel des boulettes sont préparées à partir d'un minerai minéral par
formation d'un minerai particulaire acide dont sensiblement toutes les particules
sont inférieures à 250 µm et qui donne dans l'eau un pH atteignant 6 par un procédé
comprenant le lavage ou le lessivage du minerai minéral dans l'acide et le mélange
d'un liant comprenant un polymère organique avec le minerai particulaire acide en
présence de 5 à 15 % en poids d'eau (par rapport au mélange total) pour former un
mélange humide sensiblement homogène et le bouletage du mélange humide, et dans lequel
le liant comprend environ 0,002 % à environ 0,5 % en poids, par rapport au mélange
total, d'un polymère hydrosoluble qui est cationique.
2. Procédé selon la revendication 1, dans lequel le polymère est synthétique et est formé
de monomères éthyléniquement insaturés comprenant un monomère cationique.
3. Procédé selon la revendication 1 ou la revendication 2, dans lequel le minerai minéral
est du minerai de fer qui a été lavé à l'acide ou lessivé à l'acide.
4. Procédé selon la revendication 3, dans lequel le polymère cationique est choisi parmi
les polymères qui ont une viscosité intrinsèque de 0,4 à 5 dl/g et qui sont formés
à partir de monomères dont au moins 70 % en poids sont cationiques, et les polymères
qui ont une viscosité intrinsèque de 3 à 20 dl/g et qui sont formés par copolymérisation
de 20 à 75 % en poids de monomère cationique avec 80 à 25 % en poids de monomère non
ionique.
5. Procédé selon la revendication 3, dans lequel le polymère cationique est essentiellement
un homopolymère ayant une viscosité intrinsèque de 0,4 à 2 dl/g, le monomère cationique
étant choisi de préférence parmi le chlorure de diallyldiméthylammonium, les (méth)acrylates
de dialkylaminoalkyle quaternisés et les (méth)acrylamides de dialkylaminoalkyle quaternisés.
6. Procédé selon la revendication 3, dans lequel le polymère cationique est un copolymère
de 25 à 60 % en poids de monomère cationique et de 75 à 40 % en poids d'acrylamide
et a une viscosité intrinsèque située dans la plage de 3 à 12 dl/g.
7. Procédé selon la revendication 3, dans lequel le polymère cationique est un copolymère
d'environ 20 à environ 60 % d'acrylamide et d'environ 80 à environ 40 % en poids d'un
monomère quaternisé choisi parmi les (méth)acrylates de dialkylaminoalkyle et les
(méth)acrylamides de dialkylaminoalkyle et a une viscosité intrinsèque de 3 à 12 dl/g.
8. Procédé selon l'une quelconque des revendications 3 à 7, dans lequel le polymère est
ajouté au minerai sous forme d'une poudre sèche s'écoulant librement dont sensiblement
toutes les particules sont supérieures à 20 µm et inférieures à 300 µm.
9. Procédé selon l'une quelconque des revendications 3 à 8, dans lequel le polymère est
ajouté sous forme de billes obtenues par polymérisation en suspension en phase inverse.
10. Procédé selon l'une quelconque des revendications précédentes, dans lequel le liant
donne une tension superficielle supérieure à 70.10⁻⁵ N/cm à une concentration dans
l'eau à 20°C de 0,075 % en poids.
11. Procédé selon l'une quelconque des revendications précédentes, dans lequel la quantité
de polymère est de 0,01 à 0,05 % en poids.
12. Procédé selon l'une quelconque des revendications précédentes, dans lequel au moins
70 % en poids du minerai particulaire acide ont une taille de particules inférieure
à 50 µm.