Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~3:l9~
Allied Colloids I,imited 60/2669/02
Ore Pelletlsation
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.
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 pelletisPr. The green pellets
are then fired in a kiln through a temperature range that
extends from an inlet temperature typically in the range
200-400C up to a final temperature of e.g., 1~00C.
Important properties of the pellets are the initial
or wet strength, the dry strength (after drying the green
pellets in an oven at 105C) and the tendenc~ of ~he
pellets to spall (or burst) upon exposure to firing
temperatures. The tendency for spalling can be defined
~5 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 propertiPs must be such that
it can easily be added uniformly in these low quantities.
Although many binders have been proposed in the
literature, (e.g., bentonite and other clays, ferrous
13~9~6
sulphate, lignin sulphate, asphalt, starches, calcium and
sodium compounds, and certain polymers) in practice
, bentoni~e is the binder t~a~ is ge~rally used.
i~f n~blis ~d ~ J~ lql~
In GB 1,324,838~ work ~as desc~ibed that was
~5 conducted in or before 1970, more than 15 years ago.
Thls used, as binder, a water soluble linear organic
polymer having a molecular weight of 1 million to 20
milllon. Suitable polymers were modified natural
polymers such as starch and sodium carboxymethyl
cellulose and various non-ionic, anionlc or cationic
synthetic polymers. The process lnvolved forming a
solutlon of the polymer and spraying the solution on to
the particulate lron ore. The patent noted that the
sprayed solutlon was viscous and that this could b~ a
problem, but that the viscosity could be reduced by
lncluding sodium chlorlde, sodium sulphate or potassium
chloride in the water used for making the solution.
Although dlrect comparisons o~ the polymers in GB
1,324,838 lS di~icult it appears ~rom the patent that
various non-ionic, anionlc 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 spalllng values and a cationic copolymer and
a polymer formed ~rom about 8~ sodium methacrylate and
92~ acrylamide were reported as giving improved strength
values.
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).
3 ~3~90~
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 thls 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 (necessarlly 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 alternatlve polymers, namely "natural
polymers and derivatives of petroleum products".
Desplte 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 mentlons, as binders, only Portland cement, lime and
bentonlte, and emphasises the large amount of bentonite
that is used and predicts that it will continue to be
used despite the shortages o~ bentonite.
Despite the acceptance by Jones, and the whole
industry, that bentonite would continue to be the most
widely used blnder it has, for very many years, been
recognised to incur varlous problems~ Thus some grades
o~ bentonite give satls~actory pellet propertles but
others are less satisfactory. A prGblem with all grades
of bentonlte is that the bentonlte lS not combustible and
so contr1butes to the gangue ln the furnace, and thls
gangue tends to be corrosive to the lining o~ the
furnace. Another problem with bentonite is that the
optimum grades are becoming less avallable. Bentonite
must be present in the pellets in quite large amounts,
thus reducing the iron content of the pellet
~319~
significantly and increasing the amount of gangue. Lime
and some inorganic salts have been proposed as
alternatives to bentonite, but again they cause the
~ormation of unwanted gangue and can be less satlsfactory
than bentonite. The added gangue constituents require
increased energy consumptlon ln the furnace.
A problem with bentonite and other hindars lS that
the spalling temperature is low. Typlcally the inlet
temperature of the kiln has to be ln the range 200 to
400C to prevent spalling. Higher inlet temperatures
would be economically desixable if spalling could still
be avoided~
ln Mlning Engineering October 1984 pages 1437 to
1441 de Souza et al reported that organic binders would
have the inherent advantage, over inorganlc binders, of
being eliminated during ~lring. Results were reported
on the use of polymers based on cellulose, in partlcular
the material sold under the tracle ~ k Perldur and which
~``.1~
is believed to be carboxymethyl cellulose. The article
reported adding Peridur powder to an aqueous pulp of iron
ore before ~iltration and also reported adding the powder
manually to the ore flow. The article noted the need
~or water soluble polymers to be hydrated and dissolved
during mixing and pelletising. Spalling at 250C was
reported, but this is unsatis~actorily low.
A difficulty with powdered cellulosic blnders such
as carboxymethyl cellulose lS that the irregular partlcle
shape and size dlstribution is such that the powder does
not flow ~reely. Instead the dry particles tend to
clump together rather than flow over one another. As a
result it is difficult to achieve uniform supply o~ the
low dosages that are required. Another problem is that
the amount o~ cellulosic binder that has to be used for
adequate strength tends to be too high to be cost
e~ective. Another problem with some cellulosic
1319~
polymers is that they can reduce surface tension, and
this appears to be undesirable in pellet formation.
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.
In EP 0203855A2 published in 3 December 1986 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 cakionic polymers are proposed. The use of the
polymer in combination, with an inorganic salt, to increase
strength, is also proposed.
Spalling properties are not discussed in a manner that
allows judgement as to whether these polymers could give
impro~ed spalling properties compared to the spalling
properties of bentonite.
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 beliave 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 signi~icant amount of
* Trademark
13190~6
the particles have a dry sl~e above 450~m and up to about
800~m, and the crushed gel of Percol 725 also has a
particle size ot up to about 800~m.
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 lntroduced 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 mixin~ the binder with the iron
ore particles must be as short as possible in order to
maximise production and minimlse 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 stlckiness problems noted in the article
by R.L.Smythe.
Bentonite has a very small particle slze (typically
below lO~m) and adequate admixture of these very small
particles with the partlculate iron ore is acnieved
because the bentonite is used ln a relatively large
amount (typically 1~). However it would be expected
that the use of a blnder that is substantially coarser
and/or present in a substantlally smaller amount would
tend to give less satis~actory results, due to
non-uniform mixing o~ the binder with the relatively
large volume of very fine particulate iron ore.
The use of cellulosic binders or the powder or
emulsion binders proposed in EP 020385~A~ lS inconvenient
from the point of vie~ of application methods that give
reasonable results. ~lso 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.
7 13~9~
In the methods of the invent.ion mineral ore pel:lets
are made by adding binder comprisiny organic polymer to
particulate mineral ore having substantially all particles
below 250~m 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.
Canadian Patent Application No. 523996 claims a
process in which iron ore pellets are made by adding binder
comprising organic polymer to particulate iron ore having
substantially all particles below 250~m and stirring in the
pres~nce of 5 to 15% by weight (based on total mix) to form
a substantially homogeneous moist mixture and pelletising
the moist mi~ture, and the process is characterised in that
the binder comprises up to 0.2% by weight, based on 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 ~lowing, powder
having substantially all particlles above 20~m and below
300~m.
Although that process is very successful for
pelletising conYentional 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 as~ertained that this particular ore
as supplied is acidic, in that has a much lower pH than
normal pelleting ores.
In the invention pellets are made from mineral ore by
adding binder comprising organic polymer to acidic
particulate mineral ore having suhstantially all particles
below 250~m and stirring in the presence of 5 to 15% by
weight water (based on total mix) to form a
h~
8 ~31~0~ 6
substantially homogeneous moist mixture and pelletising
the moist mixture, and in this process the binder
comprises about 0.02~ to about 0.5~ by weight, based on
total mlx, of water soluble polymer that is cationic.
When a small amount, e.g., 2 to 10% by weight, of
partlculate 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 o~ the
amount o~ ore. It is this pH, that lS substantially
independent o~ ore concentration, whlch lS intended
herein when re~erence is made to the ore glving a
speci~led pH. Normal ores give a pH of above 8.1,
typically 8.2 to 8.4 or higher. The invention is of
part1cular value when the ore lS acidic and thus gives a
pH in this test o~ below 7, and often below 6.
By the lnvention it is possible to obtain very good
pelletlsing results even at very low pH values. Th1s lS
in marked contrast to existing systems, and especially
systems us-ing bentonlte, where reasonable results are
sometimes obtainable at p~ values 7 to 8 but the results
at lower pH values, for instance 6.~ to 4 or even down to
3, are totally 1nadequate in most instances. Thus the
lnvention permits, ~or the first time, satis~actory
pelletising of acidic, and often highly acidic, ores.
The mineral can be any acidic ore, e.g., a zinc ore,
but is preferably an iron ore, normally a haematite,
magnetite or tachonlte. The ore may be naturally acidic
or may have been rendered acidic by some treatment prior
to blending with the binder. For 1nstance the ore may
have been washed with acid to remove acid soluble
components, typlcally to produce a pH o~ ~rom 5 to 6 if
manganese is being washed out o~ the ore.
The ore may have acquired an acidic pH during other
processing treatments. For instance the ore may be
9 131~
dried under conditions that xesult in the dry ore ~iving
the speclfied 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.
As a result of the invention it is possible, for the
first tlme, 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 lt lS now
possible to use low grade ores for pelletising is because
a preferred process of the invention comprlses forming
acidlc particulate ore from the mineral ore (that can be
of low grade) by a process comprising washing or leach`ng
the mineral ore ln acid, and thereafter using the
resultant, enrlched, acidic partlculat~ ore for
pelletisln~. It has not previously been practicable to
use acld washed or acid leached ores for pelletising.
The ore that is acid washed or leached is normally an
iron ore.
Numerous methods of purifylng or enriching mineral
ores by acid treatment are well known, and can be used in
the inven~i~n.
The soluble cationic polymer is forme~ by the
polymerisation of cationlc ethylenically unsaturated
monomer, optionally with other ethylenically unsaturated
monomers. The monomer or monomer blend will normally be
water soluble. One sultable 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
(meth3 acrylamide. All such monomers are generally
present in the ~orm of acid addition or quaternary
~,3:L~a~
ammonium salts. For instance a suitable monomer is
methacrylamido propyl trlmethyl ammonium chloride
~MAPTAC). Other sultable cationic monomers lnclude
diallyl dialkyl quaternary monomers, especially diallyl
dlmethyl ammonium chloride (DADMAC). Preferred cationic
polymers are polymers having recurring quaternary
ammonium groups. Blends of cationic polymers (e.g., a
blend of svnthetic catlonlc with natural or modl~ied
natural cationic polymer) can be used.
The polymers can be copolymerised with non-ionic
monomers, generally (meth) acrylamide (ACM). Other
suitable catlonic polymers are polyethylene imines and
epichlorhydrin polyamine reactlon products made in bead
torm. We find that homopolymers and other polvmers
having a very high catlonic content can be of relatively
low molecular weight, for instance having intrinsic
ViSCOSlty below 5 dl/g, often ln the range 0.4 to 2 dl/g.
When such polymers are ~ormed from ethylenically
unsaturated monomers at least 70 weight percent, and
preferably at least 90 weight percen~, o~ the monomers
should be cationic, and preferably the polymer is
substantially a homopolymer.
Other preferred polymers have medium to high
molecular weight and medium cationic content. For
in~tance the IV may be from about 3 to about 20 dl/g or
higher, generally 3 to 12 dl/g, preterably from 5 to 9
dl/g. Such polymers are best made by copolymerisation
ot about 20 to about 75, pre~erably about 25 to about 60,
we1ght percent cationic monomer with a non-ionic monomer
such as acrylamide. Best results are generally obtained
with about 35 to about 55 welght percent cationic
monomer, with the balance non-ionic.
Although best results are achieved most easily wheri
the cationic polymer is added in the f~rm of water
soluble beads all below 300 microns, as discussed below,
11 13~9~6
in some instances the cationic polymer can be added in
other ~orms. Thus it can be added ln ~he form of
particles that are within the size ranges discussed above
~or beads but which have been made by comminution o~ gel
in air or, preferab1y, in an organic liquid ~or lnstance
as described in EP 169674. It may be necessary to sieve
the particles to give the desired particle range and to
exclude oversize particles.
Instead of beiny a synthetic polymer, it can be a
naturally occurring polymer (or a modlfied natural
polymer) such as Chitosan or catlonlc starch~ but this
usually less satisfactory than the use of synthetlc
polymers.
When the ore is wholly dry, or is drier than is
required in the molst pelleting mixture, it is n~cessary
to add water to the ore in order to ~orm the moist
mixture and it lS then possible to incorporate the
polymer as a solution in thls 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 pelletingO The solution can be made
from polymer in the form o~ a concentrated solution, a
polymer-in-oil dlspersion or powder. A1ternatively the
polymer-in-oil disperslon of the polymer can be added
dlrect to the ore. The polymer particles in any such
disperslon can be dry or can be swollen gel particles.
Preferablv however the polymer is added ln the form
of dry, free flowing powder having substantially all
partlc1es below about 300~m, usually in the range about
20 to about 300~m. The particles can be comminuted gel,
especially l~ the comminuted gel partlcles had been
~ormed or treated in known manner so as to promote their
~low, but preferably the particles are beads, ~or
instance as made by reverse phase bead polymerisati~n.
~ ~3 ~ ~3 0 :~ ~
Reverse phase bead polymerisation is a well known
process. Thus an aqueous solution of the chosen monomer
or monomer blend is dispersed in water immisci~le llquid,
generally ln the absence of an emulsl~ying agent but
often in the presence of an amph1path1c polymeric
stablllser, the polymerlsatlon is induced in convent1onal
manner to provide a suspension of gel part1cles in the
non-aqueous llqu1d, the suspension lS then dried by
azeotropLc distillation and the particles are separated
from the non-aqueous liquid in conventional manner. The
desired part1cle size range is controlled in known
manner, for instance by the choice of stablliser,
emulsi~ying agent ~if present) and, especially, the
degree o~ agitation during the ~ormation of the initial
suspension of aqueous monomer partlcles in the water
immiscible liquld. The beads a;e substantially
spherical.
Some reverse phase polymerisation methods lnvolve
the use of relat1vely large amounts o~ emulsifiers or
other materials that depress sur~ace tension. It is
particularly desirable 1n the invention to make the
polymer particles in the substantial absence o~ any such
material. In particular, it is deslrable that the
entire blnder (and also the polymer component of the
binder) should have substantially no depressant ef~ect on
surface tension. Thus if binder is dissolved with water
a~ 20C at 0.075% ~y weight concentration the surface
tension of the solution should be above 65, and
preferably above 70 dynes/cm. Thus it is pre~erred to
avoid the use of amounts o~ surfactant that would depress
surface tension significantly and reliance should be
placed lnstead on agitation or stabiliser, in known
manner, to control bead slze.
Although it might have been expected to be deslrable
to use swellable but insoluble particles (in an attempt
13 1 3 1 ~
at matching the properties of hentonite) in fact the use
of such polymer as ~he only polymer 1s unsatisfactor~ and
soluble polymer must be used.
The failure of the cross-linked polymers, and the
artlcle in Mining Engineering October 1984 page 1438,
might have indicated that it is necessary ~or the polymer
to go into solution and/or to form a viscous phase during
mlxing, but results can be 1mproved (or the requ1red
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 dlssolved into bulk water.
However it appears that some mechanism other than
depression of solubllity or viscosity is involved. In
practice the water is generally moisture that is present
in the ore, remalning from a previous ~lltration stage,
and thls water is itself normally a solution of one or
more lnorganic electrolytes.
Although this contamlnation appears satls$actory
results are improve~ ~urther, and often synergistically,
i~ the powdered binder that lS added to the ore includes
addltlonal monomeric compound that is usually an
inorganic or organic electrolyte but can be a
non-electrolyte.
The compound is normally water soluble and inorgan1c
and so lS prefera~ly a water solubLe salt o~ an acid.
However salts o~ strong acids (e.g., sodium chloride,
sulphate or nitrateJ are less satisfactory than salts of
wea~ organic acids or carbonic acid. The strong acid
salts may generate corrosive aclds during smelting or
firing. Accordingly preferred compounds that are
ncorporated as part o~ the binder are orgarlic molecules
such as urea, inorganlc water soluble salts o~
carboxyllc, dlcarboxylic and trlcarboxylic acids such as
14 ~31~16
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.
An important advantage of the use of beads made by
reverse phase bead polymerisation ls that they can
readlly be added in very unl~orm and very small amounts
to the ore that is to be pelleted, because of the
substantially spherical shape o~ the beads. If the
binder is to be a blend of the polymer with other
material such as any of the compounds dlscussed above
then this other material should also be added in a form
that is easily flowable on to the ore. Preferahly the
compound is incorporated 1n the beads. For instance a
salt of a weak acid can be present in the aqueous monomer
during polymerisation. Alternatlvely the compound can
~e added separately to the ore or it can be preblended
with the polymer beads, but in either instance the
compound itsel~ is preferably put lnto a free flowable,
~generally bead, form, by known techniques.
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
blnder (~elow 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, ~or instance 30 to about 100% or
even 150~, preferably 50 ~o 90%, based on soluble polymer
are pre~erred.
:~3i~0~ ~
The soluble polymer ~in bead or other form),
optionally wi.th the added salt or other compound, can be
used in combination with other binders. In particular,
desplte the fact that cross lin~ed polymers have proved,
by themselves, to be unsatisfactory we ~lnd valuable
results are achieved if a cross linked, swellable,
particulate organic polymer lS included with the soluble
polymer. The cross linked polymer must have a small
particle size, below lOO~m and often below 50~m. The
size can be as small as lS commercially available, e.g.,
down to lO~m or l~m. The particles are normally
introduced as dry powder and preferably this powder is in
the form of bead tines separated during the production of
coarser particulate swellable polymer as produced by bead
polymerisation. The inclusion of the cross lin~ed
polymer partlcles can give surprisingly improved dry
strength and drop number values and so a blend of so~uble
particles and cross lin~ed particles can give an
excellent combination of dry strength, wet strength and
spalling properties. Also the pellets tend to have
improved sur~ace appearance, such as smoothness.
The cross linke~ polymer may be non-ionlc (e.g.,
polyacrylamide), but when the soluble polymer is ionic lt
is pre~erably of the same ionlc type as the soluble
polymer and 50 may be ~ormed from the same monomers as
are discussed below $or the preparation o~ the soluble
polymer. Preferably 20 to loo~ by weight, most
preferably 60 to 100% by weight, are ionic. The use of
homopolymer, e.g., cross llnked sodium polyacrylate, is
very satis~actory. Cross linking may be by any of the
conventlonal cross linking agents used in the production
o~ swellable or absorbent polymers. Thus it may be by
an ionic cross linking agent but is preferably covalent,
e.g., methylene bis acrylamlde or other polyethylenically
unsaturated monomer. The amount of cross lln~lng agent
16 13~9~16
is generalL~ in the range 20 to 1,000 ppm, preferably 50
to 500 ppm, and must be such that the particles are
lnsoluble but highly swellable in water, e.g., having a
gel capacity in water above 50, and pre~erably above 200,
grams per gram.
The amount of cross linked polymer partlcles 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 pre~erred. Amounts of
0 to 80% often 20 to 50%, based on total binder are
suitable. Part1cularly preferred binders consist
essentlally of 1 part by welght 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
lin~ed anionic homopolymer or copolymer, with proportions
of about 1:1:1 often belng convenient.
Substantially all the particles of the soluble
polymer (and of other binder particles) must be below
about 300~m ~or good results, presuma~ly since otherwise
the partlcle size is too large to establis~ adequate
contact with the very large ~umber of very small lron ore
particles. Preferably substantially all the polymer
particles are below about 200 a~d preferably below about
150 microns. Although it might be expected to be
necessary to have exceedingly small polymer partlcle
size, similar to bentonite, this is unnecessary and it is
satisfactory for most or all of the par~icles to be above
microns. Best results are o~ten achieved when
substantially all the polymer particles are in the range
20 to 100 microns bUt a satisfactory fractlon is 100
below about 200~m and at least 50% below about lOO~m.
Good results are achieved at very low soluble
polymer additions. The amount, therefore, lS usually
below about 0.2% and generally it is below about 0.1~ (by
weight based on the total mix). It lS often prefexLed
17 ~3~
for the amount to be below 0.05% by welght, 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~.
The particle size of the ore is generally less than
250 micron.s, usually 90% or 80~ by weight of the
particles being less than 50 microns. The ore is
preferably an iron ore such as magnetlte, haemetite or
taconite, but can be any other mineral ore that needs to
be put lnto the form of pellets, ~or instance a zinc ore.
Satisfactory results can be obtained even 1~ the ore is
contaminated with clay.
Before adding binder in the form o~ 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 105C. However if
the ore is too dry then water may be added to it, e.g.,
be~ore or after the addition of polymer binder (or the
binder may be predissolved).
The binder can be blended with the ore in the same
manner as bentonlte lS blended, prefera~ly ~y scattering
the polymer particles on to the ore as it is carried
towards a mixer, for instance a paddle mixer provlded
with stators. It may be mixed for the same duration as
when bentonite lS used, for instance 2 to 20, generally
about 10, minutes.
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 condueted in a
balling drum. The size of the pellets is generally from
35 5 to 16 mm, preferabLy 8 to 12 mm.
18 ~3~901~
Be~ore the resultant green pellets can be ukilised
for the production of metal they need to be fired,
generally at a temperature up to above 1000C, for
instance up to 1200C. For this purpose they can be
introduced into a kiln or other firing apparatus and
fired in conventlonal manner. It is deslrable to be
able to lntroduce them into thls ~urnace at the highest
possible inlet temperature with the minimum risk o~
spalling. The inlet temperature at which spalling
becomes signl~lcant can be referred to as the spalling
temperature and a particular advantage of the inventlon
is that it lS possible to make pellets having a spalling
temperature higher than can conveniently be obtained by
the use of bentonite and other known binders.
Good results can be achieved while using easy
application techniques and low amounts o~ polymer. It
lS easy to make pellets which have satisfactorlly high
wet strength and dry strength (measured after drying in
an oven) and a satisfactorily high drop number when wet
(lndlcating the number o~ drops before they shatter).
In particular it lS possible to obtain excellent spalling
properties, often much better than are obtalnable with
bentonite.
In a second aspect of the invention, a modification
lS provided in the process described in EP2~5171 for the
treatment of conventlonal ores, especially lron ores,
e.g., those giving a pH above 8. Although optimum
results are more easily obtained, with or without added
sodium carbonate or other inorganic salt, when using a
soluble anionic polymer having intrinsic viscosity of
about 3 to about 16, as in that U.S. patent, it has now
been found that it is possible to obtain useful
pelletising with other anionic pol~mers under particular
clrcumstances.
19 ~319~g
In particular, the inventlon also includes a process
in which organic polymer lS added to conventional
particulate iron or other ore having substantially all
particles below 250~m 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, the process being characterised in
that the binder comprlses up to 0.2% by weight, based on
total mix, of water soluble synthetic polymer that has
intrinslc VlSCoSity above about 17dl/g and -that is an
anionic polymer of one or more water soluble
ethylenically unsaturated monomers comprlsing an anionic
monomer and the binder also comprises about lO to about
lSO~, based on total binder, o~ added salt or other
monomeric compound as discussed above. Although the
high IV anionic monomers cannot be used alone, adequate
results are obtainable when blended with such salt or
other monomerlc compound, for instance ln proportions by
weight 2:1 to 1:2. The very high molecular weight
polymer is introduced ln the form of fine powder which
can be beads or crushed gel. The particle sizes and
other characterisitcs of the anionlc polymer, suitable
inorganic matexials and cross linked polymes and other
additives may all be as described above for the cationic
binders.
In a third aspect of the invention, that is
applicable to all types of ores, the b1nder comprises
about 0.005~ to 0.5~ by weight, based on total mix, of a
water soluble synthetlc polymer that is added to the ore
as dry, free flowing, beads that are substantlally all
above 20~m and below 300~m and that are made by reverse
phase bead polymerisation from water soluble
ethylenically unsaturated monomer or monomer blend.
The polymer of the beads pre~erably is not anionic
polymer of intrinsic viscosity 3 to 16. Thus it may be
20 ~319~6
anionic below 3 and preferably below 2, anionic above 16
and preferably above 17, nonionic or cationic. The bead
polymer may be mixed with othex polymer particles and/or
add salts, for instance as described above.
In examples 1 and 2 below the binders were each
scattered on to acidic moist partlculate haematite iron
ore at an appropriate dosage. The molsture content was
8.3~. The blend was then converted to pellets ln a
balling drum, the pellets having a size typically of
about 5-16mm.
The following synthetic cationic polymeric binders
were used. They were made by reverse phase
polymerisation to a bead size below 200~m and the beads
were dried and separated.
Polymer A : copolymer o~ 40% methyl chloride quaternised
dimethylaminoethyl acrylate (MeCl.q DMAEA)
60% acrylamide (ACM)
IV ~ 7-B dlg 1
Polymer B : copolymer of 50~ MAPTAC with 50~ ACM
IV =-6.9 dlg 1
Polymer C : 100% PolyMAPTAC
IV = 1.3 dlg
Polymer D : copolymer o~ 60~ MeCl q DMAEA with
40% ACM
IV ~ 6-7 dlg
Polymer E : copoLymer of 80~ MeCl q DMAEA with
20% ACM
IV ~ 8-9 dlg
Polymer F : 100% Poly-diallyldimethyl ammonium chloride
solid grade
IV = 0.7 dlg 1
Example 1
An ore ~rom the Wabush mine was dried, giving a pH
o~ ~.2, and was blended whlle moist with the blnder.
The wet strength, dry strength, drop number and spalling
21 ~31~
temperatures were recorded, as shown in Tables 1 and 2
below.
Table 1
Dose Wet Dry Drop
5% w/w Stren~th/k~ Strength/k~ Nm~er Mbisture
Blank - 0.56 0.59 7.9 8.0
Bentonite 0.7 1.17 8.20 18.5 10.0
Peridur0.04 0.56 0.14 9.2 8.7
Polymer A 0.04 0.92 1.24 22.7 8.8
10 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 850C 1000C
Blank 0 70 100
Bentonite 40 50 100
Peridur - 100
Polymer A - 0 80
20 Polymer B - 10 100
Polymer C 0 0 70
Example 2
An acid leached iron ore having pH about 5 was used
and the following results were obtained.
Table 3
Dose Wet Dry Drop %
% w~w Strength/kg Strength/k~ Number oisture
Polymer A 0.04 0.49 1.61 8.2 8.9
B0.04 0.50 2.15 16.9 9.1
D0.04 0.58 2.11 6.8 8.0
E0.04 0.51 1.94 5.4 7.8
F0.1 0.48 3.50 4.2 7.9
22 1 31 9 ~1 ~
Spalling was tested for all binders a-t 850C and for
binders B, E and F at 1000C. No spalling occurred.
Example 3
A gel polymer o$ 60% acrylamide 40% sodium acrylate
having intrinslc viscosity 23.9dl/g was dried and
comminuted in conventional manner to a particle size of
around lOO~m and is blended with an equal amount by
weight of sodium carbonate particles. Thls binder was
blended with iron ore glving a conventional alkaline pH,
at a dosage of 0.04%. The spalling properties o$ the
anionic synthetic polymer binder system at 1,000C were
excellent relative to the other systems and the other
properties were satls$actory, although the molsture
content was slightly hlgner than with the other systems.
