PROCEDE DE BOULETAGE DE MINERAI

ORE PELLETISATION

Abrégé anglais

In an iron ore pelletisation process in which particulate ore is mixed with
particulate polymeric binder in the presence of
moisture and the mixture is pelletised, the particulate binder is a blend of
ionic synthetic water soluble polymer, such as a
copolymer of acrylamide and sodium acrylate having intrinsic viscosity 2 to 16
dl/g, with a larger amount of a soluble natural
polymer, especially guar gum.

Revendications

7
CLAIMS:
1. An ore pelletisation process comprising mixing particulate
ore with particulate polymeric binder in the presence of
moisture and pelletising the mixture. wherein the particulate
polymeric binder is a dry powdered particulate composition and
is a blend of one part by weight ionic synthetic water soluble
polymer with 2 to 30 parts by weight of soluble natural polymer
which is guar gum.
2. A process according to claim 1 in which the synthetic
polymer is an anionic polymer.
3. A process according to claim 1 or 2 in which the amount of
synthetic polymer is 0.005 to 0.1% and the amount of the guar
gum is from 0.05% to 0.2%, by weight of the total mixture.
4. A process according to any one of claims 1 to 3 in which
the amount of the guar gum is 3 to 10 parts by weight per part
by weight synthetic polymer.
5. A process according to any one of claims 1 to 4 in which
the synthetic polymer is formed of a blend of 10 to 90%
acrylamide and 90 to 10% sodium acrylate and has intrinsic
viscosity 2 to 16dl/g.
6. A process according to any one of claims 1 to 5 in which
the synthetic polymer is formed of a blend of 60 to 90% by
weight acrylamide and 40 to 10% by weight sodium acrylate and
has intrinsic viscosity 5 to 9dl/g.

8
7. A process according to any one of claims 1 to 6 in which
the ore is iron ore in the form of particles of which a
majority are below 250µm.

Description

WO 93/0389
~ ~ ~'~ ~
~ ~ PCT/G6392/01432
Ore Pelletisation
. This in ention relates to ore pelletisation processes
which comprise forming an intimate mixture of particulate
ore and particulate binder in the presence of moisture,
forming green pellets by agitation of the mixture (for
instance by rolling or tumbling) and firing the green
pellets to produce ore pellets.
Bentonite has been a widely used particulate binder
but numerous proposals have been made to use synthetic or
natural organic polymers.
One class of natural polymers that has been used are
various soluble starches. Another class are soluble
cellulose derivatives which are usually esters (especially
carboxymethyl cellulose) or ethers (especially hydroxyethyl
15~ cellulose). Another class are soluble gums such as
xanthan gum or guar gum. It has been proposed to use
mixtures of binder clay (bentonite) with the polymers. For
instance Clum et al in Mining Engineers 178 (NY) 30(1),
page 53 show the results obtained using binders comprising
guar hum, hydroxyethyl cellulose, polyoxyethylene oxide,
and also bentonite.
There have been numerous proposals to use various
soluble particulate synthetic polymers. Thus the
particulate binder may comprise synthetic polymer particles
often having a size up to 300um formed by polymerisation of
water soluble, ionic, ethylenically unsaturated monomer or
monomer blend to form water soluble polymer particles: The
monomer blend is free of cross linking agent, so as to
avoid cross linking ~~ith the consequentia l risk of
insolubility.
For example cr.Je describe in EP-A-225171 the use, as
particulate binder, of water soluble synthetic polymer that
has intrinsic viscosity 3 to l6dl/g and that is an anionic
polymer and we describe in EP 0288150 the use of cationic
polymers.
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W() 93/03189 ~ PC'f/(~~92/~1432
The use as pelletisation binder of soluble anionic
synthetic polymer has several advantages over the use of
bentonite, but it can suffer from one disadvantage in that
it is difficult to achieve adequate dry strength in the ore
pellets at economic dosages. Even if the dosage is
increased in order to improve dry strength, there may then
be other disadvantages, such as stickiness and aggregation
of pellets in the drum and instability during the
palletising process.
l0 Similarly, the use of natural polymers alone has not
proved entirely satisfactory since they may not lead to the
optimum combination of green strength, dry strength and
drop number.
~, In an ore pelletisaticn process according to the
invention, particulate ore is mixed with particulate binder
in the presence o~ moisture and the mixture is pelletised~,
and the particulate bindezw comprises a blend of 1 part
ionic synthetic water soluble polymer with from 2 to 30
parts of a soluble natural polymer selected from soluble
gums, soluble starches and soluble cellulose derivatives.
Throughout this specification, party are parts by weight.
The natural polymer can be, for instance, a cellulose
ether such as hydraxyethyl cellulose, a cellulose ester
such as carboxymethyl cellulose, a soluble starch, or
xanthan gum, but ~.t is preferably soluble guar gum. The
gum may have been heated in known manner to increase its
solubility, for instance it may be a phosphated guar gum'.
~'he amount of synthetic polymer is generally at least
0.005a and usually at least O.Olo (by weight of the total
mix) but the amount is generally not more than O.lo and is
frequently less, for instance below 0.060 . amounts of
0.01 to 0.04% are often suitable.
The total amount of water soluble synthetic and water
soluble natural polymer used in the invention is usually at
least 0.030 and often at least 0.050. It is generally
undesirable for it to be more than 0.3% and it is usually

wo =»003 so ~~ri~ ~9zio ~ 43z
belaw 0.2%. Amounts of 0.05 to 0.1 or 0.15% are often
suitable.
The amount of the natural polymer is usually at least
0.020 and generally at least 0.04%. Although the amount
can be, for instance, 0.2% or even more it is preferably
below 0.15% and generally below 0.1%. Tt is very
surprising that these low amounts of natural polymer give
a beneficial effect, since it is usually necessary to use
relatively large amounts, typically 0.4% or more, to obtain
beneficial binding results when using natural polymer.
The amount of the natural polymer is generally (per
part by weight of the soluble synthetic polymera at least
3 parts and frequently at least 5 or 6 parts. Tt is
normally below 15 parts, and is generally blow l0 parts.
The binder preferably also includes sodium carbonate
or other water soluble monomeric additive of the type
described in EP 2251'71. The amount of this is generally
from 0.2 to 2 parts, often around 0.7 to 1. ~ parts, per
part by weight of the synthetic polymer.
Preferred binders compa.-ise ~. part by weight soluble
synthetic polymer; 0.7 to 1.3 parts by weight sodium
carbonate and 2 to l2 parts by weight guar gum.
The components of the binder may be premixed or they
may be supplied to the pe3letising procbss separately but
preferably substantially simultaneously.
The total amount of binder (water soluble synthetic
polymer plus natural polymer plus sodium carbonate or other
salt) is typically in the range 0.03 to 0.3%; often around
Ov05 to 0.2%.
The polymer can be cationic, for instance as described
in EP 0283f50, but is generally anionic as in EP 2251"71.
The amount by weight of sodium acrylate or other anionic
monomer is generally in the range 5 to 90% by weight, with
the balance preferably being acrylamide. It is normally
preferred for the polymer to be a copolymer of acrylamide
with 10 to 400, often 15 to 300, sodium acrylate.
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WC~ 93/03189 ~.~ ~ 1~~~~ fC'f/G4392/01432
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However it can be desirable to use larger amounts of
sodium acrylate, e.g., 50 to 80a, typcially around 70~.
Intrinsic viscosity can be in the range 2 or 3 to 16d1/g,
often in the range 5 to 12d1/g, but in some instances can
be higher, for instance up to 25d1/g.
It is generally desired that the soluble synthetic
polymer should be wholly linear in which event it will
normally have been polymerised in the absence of any added
cross linking agent. However it can be advantageous for
the synthetic polymer to be a water soluble, partly cross
linked polymer. The amount of cross linking agent should
be selected so that it is insufficient to render the
polymer particles predominantly water insoluble but
sufficient to give a useful benefit, particularly an
~15 increase in the dry strength of the ore pellets, provided
that the amount is such that the particles still behave
predominantly as water soluble polymer particles, for
instance as regards their film-forming and Theological
characteristics. The amount of cross linking agent
typically is 5 to 50ppm, pz-eferably 7 to 2oppm when the zV
is 2 to 7dl/g and 2 to 3oppm, Preferably 5 to l5ppm, when
IV is 7 to l6dl/g. These 7:V's pre measured on the polymer
in the absence of cross linking agent and the amounts of
cross linking agent are calculated as methylene bis
acrylamide. Different, generally larger, amounts will be
required to obtain the same Theology and solubility
characteristics using other cross linkers. Generally the
amount of cross linking agent is below l8ppm, measured as
methylene bis acrylamide.
In this specification, IV values are determined by
' cohventional single point IV measurement in d1/g at 20°C.
Some or all of the components of the particulate
binder used in the invention can be supplied as a
dispersion of particles in oil, but it is generally
preferred for them to be supplied as a dry powdered
particulate composition. The particles may be aggregates,
for instance as described in ~P 0326382. The size of the
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W() 93/03189 ~ ~ ~ ~ _I~ ~ ~l P~ TlG 1392/() 1 ~b32
binder particles is normally below 300,~m, generally below
200~,m and preferably below 150~,m, but is generally above
20~am.
The particulate ore is preferably an iron ore but can
5 be any other mineral
ore that is capable
of being
pelletised, for instance
a zinc ore. The materials
and
process conditions can be broadly as described in EP
2251'71, except that the binder must include the defined
large amount of guar gum. Bentonite can be used as part
of the binder.
In Examples 1 and 2 belaw, pelletisation processes
were conducted as in the examples of EP 225171 using
various combinations of guar gum and anionic polymer formed
as in EP 225171. The
results were as follows.
Example 1
Product A - a 20o anionic polyacrylamide blended
50/50 with sodium carbonate
Product B - a guar gum
Product C - a 2/7 active polymer blend of A and
B
2 Green Dry Drot~
0
Stren~thLKq Strength/Kct Number Moisture
0.090 C 1.00 2.80 29.3 10.3
O.lOo B 2.31 2.26 37.0 9.7
Example 2
Product D - a 1/5 active polymer blend of A and B
Green D~ DrOta
StrenqthlKq Strenqth/Kct Number Moisture
0.12% D 1.18 8.15 21.3 10.5
0.12p B 1.30 6,08 45.0 10.0
3p A combination of an anionic polyacrylamide blend with
sodium carbonate and guar gum gives acceptable green
properties whilst increasing the dry strength over that
obtained with guar gum on its own.
In the two examples described, the dry strength has
been increased by 24.0 and 34.0% respectively as a result
of blending the guar gum with the synthetic polymer.
Thus, even though dry strength tends to be a problem with
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W~ 93/03189 ~ PCT/~B9~/01432
~~~ v~
6
binders based an synthetic polymer, the addition of the
synthetic polymer to the guar gum increases the dry
strength attainable using a similar amount of the natural
polymer in the absence of the synthetic polymer.