AU613351B2 - Ore pelletisation with water soluble polymers - Google Patents

Description

If 0M MON WE AL T H OF PATENT ACT 1952 A US13351LI COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE CLASS INT. CLASS Application Number: Lodged: 4e 4 *4 4 .4 4

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*4 4 4 Complete Specification Lodged: Accepted: Published: Priority: Related Art-: NAME OF APPLICAN~T: ALLIED COLLOIDS LIMITED ADDRESS OF APPLICAN~T: P.O. Box .3 8, Low Moor, Bradford, West Yorkshire, BD12 OJZ, 4* 41England.

NAME(S) OF INVENTOR(S) Anthony ALLEN ADDRESS FOR SERVICE: DAVIES COILISON, Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED.: ORE PELLETISATION WITH WATER SOLUBLE POLYMERS' The following statement is a full description of this invention, including the best method of performing it known to us 1A Allied Colloids Limited 60/2669/02 ORE PELLETISATION WITH WATER SOLUBLE POLYMERS Iron ore needs to be in the form of agglomerates of substantial size when it is charead 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 10 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 *t particulate ore and stirring in the presence of a small amount of water (generally moisture in the ore) to form a 15 moist mixture, and then pelletising the mixture, 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 0 C up to a final temperature of 1200°C.

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 S"S" 25 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.

Although many binders have been proposed in the literature, bentonite and other clays, ferrous 2'M' 111 _1_ i '*2 sulphate, lignin sulphate, asphalt, starches, calcium and sodium compounds, and certain polymers) in practice bentonite is the binder that is generally used.

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 million. Suitable polymers were modified natural polymers such as starch and sodium carboxymethyl o, 10 cellulose and various non-ionic, anionic or cationic o..o synthetic polymers. The process involved forming a solution of the polymer and spraying the solution on to I the particulate iron ore. The patent noted that the o °sprayed solution was viscous and that this could be a o 15 problem, but that the viscosity could be reduced by including sodium chloride, sodium sulphate or potassium 00 chloride in the water used for making the solution.

o 0 Although direct comparisons ot the polymers in GB f0 f 1,324,838 is ditticult it appears from the patent that 20 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 25 strength and spalling values and a cationic copolymer and a polymer formed trom about 8% sodium methacrylate and 92% acrylamide were reported as giving improved strength values.

SA 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).

i 3 SIn 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 o000 °ooo° article warned about handling problems of the resultant 0 o pellets and the risk of blockage of chutes and referred feito the study of alternative polymers, nately "natural o a a o.o 15 polymers and derivatives of petroleum products".

Despite all this work in the early 1970's an authoritative review of iron ore pelletisation by o° G.K.Jones in Industrial Minerals March 1979 pages 61 to o. 73 mentions, as binders, only Portland cement, lime and U0 O bentonite, and emphasises the large amount of bentonite Sthat is used and predicts that it will continue to be used despite the shortages ot bentonite.

Despite the acceptance by Jones, and the whole a.3 industry, that bentonite would continue to be the most 25 widely used binder it has, for very many years, been recognised to incur various problems. Thus some grades of bentonite give satistactory pellet properties but 1 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 ot 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 tormation of unwanted gangue and can be less satisfactory than bentonite. The added gangue constituents require increased energy consumption in the furnace.

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 o0 10 4000C to prevent spalling. Higher inlet temperatures would be economically desirable if spalling could still be avoided.

a In Mining Engineering October 1984 pages 1437 to 1441 de Souza et al reported that organic binders would 15 have the inherent advantage, over inorganic binders, of being eliminated during tiring. Results were reported on the use of polymers based on cellulose, in particular oo> the material sold under the trade name Peridur and which o O is believed to be carboxymethyl cellulose. The article reported adding.Peridur powder to an aqueous pulp of iron S" ore before tiltration and also reported adding the powder manually to the ore flow. The article noted the need tor water soluble polymers to be hydrated and dissolved 0o0 during mixing and pelletising. Spalling at 250°C was 25 reported, but this is unsatistactorily low.

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 treely. Instead the dry particles tend to clump together rather than flow over one another. As a result it is difficult to achieve uniform supply ot the low dosages that are required. Another problem is that the amount ot cellulosic binder that has to be used for adequate strength tends to be too high to be cost ettective. Another problem with some cellulosic 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 ot 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 ot suitable grades of bentonite and despite the long-established possibility of using 10 organic binder.

rr In EP 0203855A2 (not published until after the t priority date ot 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 be 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 o r in combination, with an inorganic salt, to increase ;O strength, is also proposed.

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.

44o* The only dry powders that are specitically proposed 4 o 25 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 ot 80% acrylamide and 20% by weight sodium ac:rylate 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 g0 me 4p r f n ThVnydypwesta r pctclypooe b the particles have a dry size above 4504m and up to about 800m, and the crushed gel of Percol 725 also has a particle size ot up to about 800m.

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 0o 10 total moisture content of not more than about 15%. The oeo 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 09) 00 o amount of binder must be as low as possible in order to 15 minimise cost and to avoid the risk of excess binder accentuating the stickiness problems noted in the article by R.L.Smythe.

o Bentonite has a very small particle size (typically o below lO.±m) 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 However it would be expected that the use of a binder that is substantially coarser 0400 and/or present in a substantially smaller amount would oo 25 tend to give less satistactory results, due to non-uniform mixing ot 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 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.

U

7 In the methods ot the invention mineral ore pellets are made by adding binder comprising organic polymer to particulate mineral ore having substantially all particles below 250.m and stirring in the presence ot about 5 to about Ib% by weight water (based on total mixture) to torm a substantially homogeneous moist mixture and pelletising the moist mixture.

In EP225171 (not published at the priority date of this application) there is claimed a process in which o. 10 iron ore pellets are made by adding binder comprising 0 organic polymer to particulate iron ore having oo. substantially all particles below 2504m and stirring in the presence ot 5 to 15% by weight (based on total mix) °0 to form a substantially homogeneous muist mixture and pelletising the moist mixture, 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 °o polymer that has intrinsic viscosity 3 to 16dl/g and that 0 is an anionic polymer ot one or more water soluble ethylenically unsaturated monomers comprising an anionic o monomer and that is added to the iron ore as a dry, free flowing, powder having substantially all particles above 204m and below 300pm.

Although that process is very successtul tor S 25 pelletising conventional iron ores it has been found that less satistactory results are obtained with some unusual ores, tor instance one particular ot haematite iron ore i 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.

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 250im and stirring in the presence of to 15% by weight water (based on total mix) to form a I IIC- 8 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 mix, of water soluble polymer that is cationic.

When a small amount, 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 solids, the pH becomes substantially independent ot the S 1 0 amount ot ore. It is this pH, that is substantially independent ot ore concentration, which is intended 9'4 herein when reterence is made to the ore giving a specitied pH. Normal ores give a pH of above 8.1, S" o typically 8.2 to 8.4 or higher. The invention is of 15 particular value when the ore is acidic and thus gives a pH in this test ot below 7, and often below 6.

By the invention it is possible to obtain very good 0o 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 o sometimes obtainable at pH values 7 to 8 but the results at lower pH values, for instance 6.b to 4 or even down to 3, are totally inadequate in most instances. Thus the invention permits, tor the first time, satisfactory «9 o 9: 25 pelletising of acidic, and often highly acidic, ores.

The mineral can be any acidic ore, a zinc ore, but is preferably an iron ore, normally a haematite, magnetite or taheni~te. 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 ot trom 5 to 6 if manganese is being washed out ot the ore.

The ore may have acquired an acidic pH during other processing treatments. For instance the ore may be I l 9 I 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.

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 a o possible to use low grade ores for pelletising is because s a preferred process of the invention comprises forming acidic particulate ore from the mineral ore (that can be 15 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 S iron ore.

Numerous methods of purifying or enriching mineral ores by acid.treatment are well known, and can be used in .o the invention.

25 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 torm of acid addition or quaternary 4) ammonium salts. For instance a suitable monomer is methacrylamido propyl trlmethyl ammoniumi 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 a blend of synthetic cationic with natural or moditied natural cationic polymer) can be used.

The polymers can be copolymerised with non-ionic 000 monomers, generally (meth) acrylamide (ACM). Other goo.

suitable cationic polymers are polyethylene imines and epichlorhydrin polyamine reaction products made in bead form. We find that homopolymers and other polymers 15 having a very high cationic content can be of relatively 0ooooo 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 tormed from ethylenically 0or unsaturated monomers at least 70 weight percent, and preferably at least 90 weight percent, ot the monomers O° should be cationic, and preferably the polymer is substantially a homopolymer.

Other preferred polymers have medium to high "I'0 molecular weight and medium cationic content. For oo 25 instance 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, preterably about 25 to about 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.

Although best results are achieved most easily whei the cationic polymer is added in the furm of water soluble beads all below 300 microns, as discussed below, 11 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 tor beads but which have been made by comminution of gel in air or, preferably, in an organic liquid tor 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.

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 Spolymers.

When the ore is wholly dry, or is drier than is 15 required in the moist pelleting mixture, it is necessary to add water to the ore in order to torm the moist mixture and it is then possible to incorporate the ooO 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 ot a concentrated solution, a S polymer-in-oil dispersion or powder. Alternatively the 25 polymer-in-oil dispersion of the polymer can be added direct to the ore. The polymer particles in any such dispersion -an be dry or can be swollen gel particles.

Preferably however the polymer is added in the form of dry, free flowing powder having substantially all particles below about 300gm, usually in the range about to about 300pm. The particles can be comminuted gel, especially 2t the comminuted gel particles had been tormed or treated in known manner so as to promote their flow, but preferably the particles are beads, tor instance as made by reverse phase bead polymerisatiun.

12 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 emulsitying 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 *t f desired particle size range is controlled in known manner, for instance by the choice of stabiliser, emulsitying agent (if present) and, especially, the t degree ot agitation during the formation of the initial 4 1 S 15 suspension of aqueous monomer particles in the water immiscible liquid. The beads are substantially spherical.

t Some reverse phase polymerisation methods involve o* the use of relatively large amounts ot emulsifiers or other materials that depress surtace tension. It is particularly desirable in the invention to make the polymer particles in the substantial absence ot any such material. In particular, it is desirable that the *:44 entire binder (and also the polymer component of the 25 binder) should have substantially no depressant eftect on surface tension. Thus if binder is dissolved with water at 20 0 C at 0.075% by weight concentration the surface tension of the solution should be above 65, and preferably above 70 dynes/cm. Thus it is preferred to avoid the use of amounts ot surfactant that would depress surface tension significantly and reliance should be placed instead on agitation or stabiliser, in known manner, to control bead size.

Although it might have been expected to be desirable to use swellable but insoluble particles (in an attempt Ej 13 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.

The failure of the cross-linked polymers, and the article in Mining Engineering October 1984 page 1438, might have indicated that it is necessary tor 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 0404 experimentally to reduce the rate of solution and the oviscosity when the polymer is dissolved into bulk water.

However it appears that some mechanism other than 9 15 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, 0o and this water is itself normally a solution of one or 0 more inorganic electrolytes.

Although this contamination appears satistactory results are improved turther, and often synergistically, it 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 25 non-electrolyte.

The compound is normally water soluble and inorganic and so is preferably a water soluble salt of an acid.

However salts ot strong acids 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 ot the binder are organic imolecules such as urea, inorganic water soluble salts ot carboxylic, dicarboxylic and tricarboxylic acids such as t 14, 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 is that they can Sooo readily be added in very uniform and very small amounts o O.o, to the ore that is to be pelleted, because of the substantially spherical shape ot the bead,. If the 15 binder is to be a blend of the polymer with other 0 material such as any of the compounds discussed above then this other material should also be added in a form o00 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 itselt is preferably put into a free flowable, 25 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 binder (below 0.1% and usually below 0.02% based on ore).

In some instances amounts of from about 10 to about based on soluble polymer are the most cost effective but usually greater amounts, tor instance 30 to about 100% or even 150%, preferably 50 to 90%, based on soluble polymer are preferred.

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 tind 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 100m and often below 50m. The size can be as small as is commercially available, e.g., down to 10lm or lum. The particles are normally o* introduced as dry powder and preferably this powder is in the form of bead tines separated during the production of °.o°Pt 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 *0 particles and cross linked particles can give an 'e excellent combination of dry strength, wet strength and spalling properties. Also the pellets tend to have Simproved surface appearance, such as smoothness.

The cross linked polymer may be non-ionic polyacrylamide), but when the soluble polymer is ionic it ais preterably of the same ionic type as the soluble S 25 polymer and so may be tormed from the same monomers as are discussed below tor the preparation ot the soluble polymer. Preferably 20 to 100% by weight, most preferably 60 to 100% by weight, are ionic. The use of homopolymer, cross linked sodium polyacrylate, is very satistactory. 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, methylene bis acrylamide or other polyethylenically unsaturated monomer. The amount of cross linking agent

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16 is generally in the range 20 to 1,000 ppm, preferably to 500 ppm, and must be such that the particles are Insoluble but highly swellable in water, having a gel capacity in water abolre 50, and preterably above 200, grams per gram.

The amount of cross linked polymer particles may be relatively low, 10 to 30% based on so'uble polymer, but generally greater amounts, up to 300% or even 600% based on soluble polymer are preterred. Amounts of S 10 0 to 80% often 20 to 50%, based on total binder are soo suitable. Particularly preferred binders consist 0 00 essentially of 1 part by weight soluble polymer, 0.3 to o 1.5 parts by weight sodium carbonate or other added salt o b oor simple compound, and 0.3 to 5 parts by weight cross S15 linked anionic homopolymer or copolymer, with proportions 0 0 of about 1:1:1 often being convenient.

Substantially all the particles of the soluble o polymer (and of other binder particles) must be below 00 0 about 300m tor good results, presumably since otherwise the particle size is too large to establish adequate o au 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 0 150 microns. Although it might be expected to be I 25 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 microns. Best results are often achieved when substantially all the polymer particles are in the range 20 to 100 microns but a satisfactory fraction is 100% below about 200 m and at least 50% below about I00c m.

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 l 4 ont ct wi h t e er l rge nube of vey mal i on or 17 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 at least by weight) other binder components. the amount of soluble polymer may then sometimes be reduced, to 0.005%.

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 Itaconite, but can be any other mineral ore that needs to 'Ilt o. be put into the form of pellets, tor instance a zinc ore.

Satisfactory results can be obtained even it the ore is contaminated with clay.

r Before adding binder in the form ot dry polymer, the ore usually already has the desired final moisture content of 5 to 15%, preferably 8 to 10%, by weight based o on the weight of iron ore. This moisture content is the o omoisture as measured by heating up to 105 0 C. However if the. ore is too dry then water may be added to it, e.g., betore 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 bentonite is blended, preferably by scattering S, 25 the po.lymer 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.

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.

I_ '1 9 9 18 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 0 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 turnace at the highest possible inlet tempe::ature with the minimum risk ot spalling. The inlet temperature at which spalling becomes significant can be referred to as the spalling o temperature and a particular advantage of the invention is that it is possible to make pellets having a spalling oo temperature higher than can conveniently be obtained by the use of bentonite and other known binders.

15 Good results can be achieved while using easy application techniques and low amounts ot polymer. It is easy to make pellets which have satisfactorily high o° wet strength and dry strength (measured after drying in 9 90 an oven) and a satisfactorily high drop number when wet (indicating the number of drops before they shatter).

o In particular it is possible to obtain excellent spalling properties, often much better than are obtainable with bentonite.

990 In a second aspect of the invention, a modification ,0 25 is provided in the process described in EP225171 for the treatment of conventional ores, especially iron ores, 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 polymers under particular circumstances.

1 1 1 1 19o o O 0 000O 0 e o o oo 0 o 1 e 0 0 o 4 4 0 0 In particular, the invention also includes a process in which organic polymer is added to conventional particulate iron or other ore having substantially all particles below 250pm and stirring in the presence of 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 comprises up to 0.2% by weight, based on total mix, of water soluble synthetic polymer that has intrinsic viscosity above about 17dl/g and that is an anionic polymer of one or more water soluble ethylenically unsaturated monomers comprising an anionic monomer and the binder also comprises about 10 to about 150%, based on total binder, of added salt or other 15 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 monomeric compound, for instance in proportions by weight 2:1 to 1:2. The very high molecular weight 20 polymer is introduced in the form of fine powder which can be beads or crushed gel. The soluble anionic polymer is added as a dry, free flowing, powder having substantially all particles above 20pm and below 300pm.

The other characteristics of the anionic polymer, suitable inorganic materials and cross linked polymers 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 binder comprises about 0.005% to 0.5% by weight, based on total mix, of a water soluble synthetic polymer that is added to the ore as dry, free flowing, beads that are substantially all above 20pm and below 300pm and that are made by reverse phase bead polymerisation from water soluble ethylenically unsaturated monomer or monomer blend, the polymer of the beads being non-ionic or cationic, or

M

910517,PHH5..S.oO15,137588spe.19 t~iv a anionic with an IV below 3 (preferably below 2) or above 16 (preferably above 17). The bead polymer may be mixed with other polymer particles and/or added salts, for instance as described above.

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 The blend was then converted to pellets in 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 200m and the beads were dried and separated.

o gi oQ a o 9 99 o0 0I 9 0 949 9 9 9 9 49 Polymer A Polymer B Polymer C Polymer D Polymer E Polymer F Example 1 An ore copolymer ot 40% methyl chloride quaternised dimethylaminoethyl acrylate (MeCl.q DMAEA) 60% acrylamide (ACM) IV 7-8 dlg-l copolymer of 50% MAPTAC with 50% ACM IV 6.9 dig' 100% PolyMAPTAC IV 1.3 dig-1 copolymer of 60% MeCl q DMAEA with

ACM

IV s 6-7 dlg- 1 copolymer of 80% MeCl q DMAEA with

ACM

IV N 8-9 dlg 1 100% Poly-diallyldimethyl ammonium chloride solid grade IV 0.7 dlg-1 trom the Wabush mine was dried, giving a pH ot 6.2, and was blended while moist with the binder.

The wet strength, dry strength, drop number and spalling temperatures were be low.

recorded, as shown in Tables 1 and 2 Table 1 Blank Bentonite Peridur Polmr A Polymer B Polymer C Dose w/w 0.7 0.04 0.04 0.04 0.1 Wet Strength/kg 0.56 1.17 0.56 0.92 0.72 0.86 Dry Strength/kg 0.59 8.20 0.14 1.24 1.82 3.31 Drop Number 7.9 18.5 9.2 22.7 19.2 8.2 Mo~isture 10.0 8.7 8.8 9.4 8.2 0 0 a 0 0 0 0 090 09 00 0 00 0 Table 2 15 Blank Bentonite Peridur Polymer A Polymer B Polymer C 7000 C 0 40 Spalled 85 0 0C 70 50 100 10000 C 100 100 100 00550 90 0 9 00 0 00 Example 2 An acid leached iron ore having pH 25 and the following results were obtained.

Table 3 about 5 was used Polynmr A

B

D

E

F

Dose W/w 0.04 0.04 0.04 0.04 0.1 Wet Dry Strength/kg Strength/kg 0.49 1.61 0.50 2.15 0.58 2. 11 0.51 1.94 0.48 3.50 Drop Number 8.2 16.9 6.8 5.4 4.2 Mo~isture 8.9 9.1 7.8 7.9 -22- Spalling was tested for all binders at 850*C and for binders B, E and F at 1000°C. No sialling occurred.

Example 3 A gel polymer of 60% acrylamide 40% sodium acrylate having intrinsic viscosity 23.9dl/g was dried and comminuted in conventional manner to a particle size of around 100pm and is blended with an equal amount by weight of sodium carbonate particles. This binder was blended with iron ore giving a conventional alkaline pH, at a dosage of 0.04%. The spalling properties of the anionic synthetic polymer binder system at 1,000*C were ,"excellent relative to the other systems and the other properties were satisfactory, although the moisture content was slightly higher than with the other systems.

S' 15 The names Percol and Peridur used herein are Registered Trade Marks.

The units of intrinsic viscosity (IV) given herein are dl/g.

I

910517,PHHSPE.015,13705-8.spe,22

Claims (16)

1. A process in which pellets are made from mineral ore by forming acidic particulate ore having substantially all particles below 2504m and that gives a pH in water of below 7 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 ot 5 to 15% by weight water (based on total mix) to torm a substantially homogeneous moist mixture and pelletising the moist mixture, and in which the binder comprises abct- 0.002% to -abe4t-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 tormed from ethylenically unsaturated monomers comprising a cationic monomer.

3. A process according to claim 1 in which the mineral ore is iron ore and the polymer is synthetic and is formed from ethylenically unsaturated monomer comprising cationic monomer.

4. A process according to claim 3 in which the cationic P polymer is selected from polymers that have intrinsic viscosity 0.4 to 5dl/g and that are tormed from monomers of which at least 70% by weight are cat'ionic, and list polymers that have intrinsic viscosity of 3 to 20dl/g and 25 that are tormed by copolymerisation of 20 to 75 weight percent cationic monomer with 80 to 25 weight percent non-ionic monomer. A process according to claim 3 in which the cationic L polymer is substantially a homopolymer having intrinsic viscosity 0.4 to 2dl/g.

6. A process according to claim 3 in which the cationic polymer is a copolymer of 25 to 60 weight percent cationic monomer with 75 to 40 weight percent acrylamide and has IV 3 to 12. ,24

7. A process according to claim 3 in which the cationic polymer is a substantial homopolymer of monomers selected from diallyl dimethyl ammonium chloride and quaternised dialkylaminoalkyl (meth) acrylates and quaternised dialkylaminoalkyl (meth) acrylamides and has intrinsic viscosity 0.4 to 2dl/g.

8. A process according to claim 3 in which the cationic polymer is a copolymer of abou-t- 20 to about- acrylamide with abeut- 80 to -a4bu-t- 40% by weight of a S 8 10 quaternised monomer selected trom dialkylaminoalkyl 8 o (meth) acrylates and dialkylaminoalkyl (meth) acrylamides and has intrinsic viscosity of from 3 to 12dl/g. 8 V 9. A process according to claim 3 in which the ore is iron ore which gives a pH in water of below 6. ooooo 15 10. A process according to claim 3 in which the polymer is added to the ore as dry tree flowing powder having substantially all particles above 204m and below 300gm.

11. A process according to claim 3 in which the polymer 00 is added in the form of beads made by reverse phase suspension polymerisation and that are substantially all 0 8 above 204m and below 300im.

12. A process according to claim 3 in which the binder gives a surface tension of above 70 dynes/cm at a concentration in water at 20 0 C of 0.075% by weight. *B 25 13. A process according to claim 3 in which the amount of polymer is from 0.01 to 0.05% by weight.

14. A process according to claim 3 in which at least by weight of the acidic particulate ore has a particle 1size below 504m.

15. A process according to claim 3 in which substantially all the polymer particles are below 150im.

16. A process according to claim 3 in which substantially 100% of the polymer particles are below 200gm and at least 50% are below 1004m. 04h y ^c

17. A process in which pellets are made from mineral ore by adding binder comprising organic polymer to acidic particulate iron ore having substantially all particles below 250pm 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 which the binder comprises 0.002% to by weight, based on total mix, of a water soluble polymer that is cationic and the ore gives a pH in water of below 7. .4 18. A process in which iron ore pellets are made by adding binder comprising organic polymer to particulate iron ore having substantially all particles below 250pm and stirring in the presence of 5 to 15% by weight water So (based on total mix) to form a substantially homogeneous Smoist mixture and pelletising the moist mixture, 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 above 17dl/g and 9e a that is an anionic polymer of one or more water soluble S ethylenically unsaturated monomers comprising anionic monomer, and the binder also comprises 10 to 150%, by a weight binder, of a compound selected from urea, sodium acetate, sodium citrate, sodium oxalate, sodium tartrate, sodium benzoate, sodium stearate, sodium bicarbonate, a sodium carbonate, sodium silicate, sodium phosphate and •the corresponding ammonium, potassium, calcium and magnesium salts of the preceding salts, and calcium oxide, the soluble anionic polymer being added as a dry, free flowing, powder having substantially all particles above 20pm and below 300pu.i.

19. A process according to claim 18 in which the binder contains sodium carbonate, sodium bicarbonate or sodium silicate in an amount of 50 to 150% based on soluble polymer A process in which pellets are made from mineral 910517,PHHSPEO15,13705-8.spe,25 4. 4 S-26- particulate ore having substantially all particles below 250pm by adding binder in the presence of 5 to 15% by weight water (based on total mix) to form a substantially homogeneous moisture mixture and pelletising the moist mixture, and in which the binder comprises 0.002% to by weight, based on total mix, of a water soluble polymer that is added in the form of dry, free flowing, beads that are substantially all above 20pm and below 300pm and that are made by reverse phase bead polymerisation from water soluble ethylenically unsaturated monomer or S, monomer blend, the polymer of the beads being nonionic or to, cationic, or anionic with an IV below 3 or above 16 dl/g.

21. A process according to claim 20 in which an anionic bead polymer has an IV below 2 or above 17 dl/g. S22. An ore pelletising process substantially as hereinbefore described with reference to the Examples.

23. Ore pellets whenever made by the process of any one of the preceding claims. DATED this 17th day of May, 1991. 4o84 a 0 ALLIED COLLOIDS LIMITED By its Patent Attorneys DAVIES COLLISON iarbo: 4 0