|Title of Invention||
A PROCESS OF PELLETISING A METAL ORE
|Abstract||A process is provided for pelletising a metal ore comprising forming an intimate mixture of particulate ore and a binder in the presence of moisture, forming green pellets by agitation of the mixture and firing the green pellets to produce ore pellets. In the process the binder comprises a hydroxamate polymer made from water- soluble ethylenically unsaturated monomer or monomer blend and which has pendant groupS of the formula This provides advantages in wet strength, drystrength and drop number of pellets, especiallY at low moisture content of the pellets.|
This invention relates to the pelletisation of metal ores .
The standard method of pel. letising an ore comprises form i nq an i nt i mate mixture of the ore in particulate form and a 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 pel lets.
Bentonite has been a widely used particulate binder but its use has some undesirable consequences. Also, there is decreasing availability of suitable grades of bentonite. There have been numerous proposals to use synthetic or natural organic polymers to replace part or all of the bentonite,
In GB 1,324,838 solutions are used of water soluble polymers which can be non-ionic, anionic or cationic. In FP-A-203,854 various polymers are proposed as binders and include water-in-oil emulsion polymers and powder polymers formed of acrylamide and sodium acrylate. In EP-A-225,171 particular powdered polymers of acrylamide and, for instance, sodium acrylate are proposed. In EP-B-2 8 8,150 certain cationic polymers are proposed as binders for acidic ores, such as haematite. The polymer can be added as a soluti on or can be added as a polymer-in-oi 1 di sporsion or as a powder, optionally with additional moisture to promote pelletisation. The use of polymers made with a small amount of cross linker is described in WO91/03190.
It is well established to use binders which consist of a blend of natural or synthetic polymer, such as any of those d i scussed above, with certain inorganic components such as sodium carbonate or calcium oxide (both of wh i rli are mentioned in EP-B-288,150). The inclusion of 1ime as a flux during pelletisation is well known, but lime can i nteract undes i rabiy with some organic binders.
The pellets that, ar^ obtained are judged by various physical' tests that are intended to be indicative of actual performance in use. These tests include measurement of the wet st renqth, the dry .strength and the drop number. The measured va1ues may be i nf1uenced significantly by the moisture content of the pellet and so the relevant values are those which are obtained at moisture contents which are conveniently available for the particular ore and the part i cu1ar pel 1eti sat i on process that is bei ng used.
In general it is desirable to increase the wet st r enqt h , i increase the dry strength and increase the drop miiiiht'i . I ;•; i s t i ng b i nder syst ems tend to give adequate wet and dry st rength at convert i ent moisture contents for a range of ores but may give a rather low drop number, espec i a 1ly at low moisture contents.
Other relevant properties are the amounts of moisture and meta 1 oxide on the surface of the pellets. For instance these can be estimated by contacting the pellets with a filter paper. In general, it is desirable for these vn]ues to be as low as possible.
A wide range of metal ores may be pelletised, including for instance zinc ores and various iron ores, including haematite, magnetite and taconite. Existing binders, such as those described in EP-A-225,171, are very satisfactory for many ores and in many pelletisation processes, but may be less satisfactory if the moisture content is not held at the optimum for that particular ore or il the optimum for that ore is rather low for that part i en l ar [riant. For i nstanco satisfactory opera ti on at many plants genera 11y requi res the moisture content to be at least 8.5% or 9% but some ores are pel let i sed more effectively at moisture contents below this. This problem of needing to pelletise at a low moisture content occurs with various types of over,, but especially with some haemat i te ores.
ft would be desirable to be able to achieve sa t i s f actory pe11et isat i on , and in particuLar to obtai n
i mpr fivod df op number wh i 1 st ma i nta ining adequate wet and In the invention, we pelletise a metal ore by a process compri s ing
forming an i nt i mate mixture of particulate ore and a binder in the presence of moisture,
f orm i nq green pe1]ets by ag i tation of the mixture and
f irinq the green pellets to produce ore pellets,
who rei n f im b i ndor compri ses
a po1ymer made f rom water soluble ethylenicaily unsaturated monomer or monomer blend and which has pendent
The pendent groups are hydroxamic derivatives of (moth) acrylamide groups and so it is convenient to refer to the polymer as a hydroxnmated (meth) acrylamide polymer.
The process of the i nvention can result in improved pelletisat ion properties as manifested especially by drop number, and also surface properties, even though the moisture content may be unusually low, and lime may be present.
The polymer can be made by polymerisation of the hydroxamic der i vati ve of (meth) acrylamide but preferably i t. i s made by hydroxama t i ng previous ly formed (meth) aery 1 amide polymer.
The polymer consists of recurring units of which at 1 east 20 mo ] ° are hydroxamatod (meth) acrylamide units. The amount is preferably at least 50 mol% and usually it is at least 7r> mol°$. It can be 90 or 100 moll.
The amount of (met})) acrylamide units can be as much as Rf) mol % but is usua 1 ly be] ow 5 0 mol% and is pre f era hi y
I^lnw 20 moll. Often it is 0 to 5 mol* . It is generally prof o?Tod f or the amount of non-hydroxamated (moth) a cry ] am i do un i ts to bo as .1 ow as possi ble and the amount of hydroxama tod units to hn a s h i qh as poss i bl e .
The pendent groups are preferably hydroxamatod aery I ami do groups rather than hydroxamated methacry 1 ami do groups.
The polymer may include other recurring units, usually units of water soluble monomer, for instance anionic unj ts such as aery 1ic acid or other ethylenica1ly unsaturated earboxylic acid. The anionic units are generally in the form of the sodium or other alkali metal or ammonium salt.
['referred polymers are formed by essentially complete hydroxamation of copolymers of 0 to 50 moll, preferably 1 to 20 (for instance 2 to 10) mol% sodium acrylate with the ha lance acrylamide.
The polymers can be essentially linear in that they am made without the do 1 i borate addition of any cross 1 i nki ng agent. however good results can be obtained when the polymers fMe branched or even crosslinked, for instance as a result of polymerisation in the presence of a small amount oI po1yethy1 en i ca1ly unsaturated or other cross 1 i nk i ng agent . 7'he amount of cross linking agent must not be too high and so is generally below 500ppm, usually in the range 10 to 3OOppm.
The polymer typically has intrinsic viscosity above 4d1/g, often in the range 5 to 13dl/g. In this spec i f i eat i on, i ntri ns i e vi scos ity is measured by a suspended level viscometer in a IN sodium chloride solution at ;>l),,c: buf to red to pM7 .
The po1ymer can be added to the pel 1et isat i on m i xturo in the form, for example, of an aqueous solution or a reverse phase emu Is ion (i.e., polymer, or aqueous polymer, fl i spersod in oil).
The hydroxamatod polymer is preferably made by providing the aerylamido polymer having an appropriate TV and de'ji oe oi 1 i near i t y or cross 1 i nk i ng and then
sub I'M't i ng this polymor to hydroxamat ion, for instance using techniques as described in EP-A-347,424. The process i s preferably conducted wh i .1 e the aery 1 amide polymer is in the f orm of a solution or an emulsion in oil of aqueous po1ymer. The process genera 1ly comprises mixing the polymer solution or emulsion with a suitable source of hydroxylamine such as hydroxyfamine hydrochloride, allowing the mixture to stand (with sti rring) for a suitable period of time generally of up to about an hour, adding alkal i to provide an alkaline pH which is generally above about pH 12, allowing the mixture to stand again with stirring for typical ly up to about an hour and then leaving it to stand, opt ionally with occasional stirring, for sufficient time to allow reaction to occur, for instance for more than half a day, typically 74 hours. The resultant product can then be used d i root 1y as the binder in the invention, without any i nt ermed i ate treatment stages.
11 i s part i cu1ar1y pref erred for the polymer to be a \ rv^rr.p phase d i spers i on. This can be made by reverse phase emu 15; i on pel ymer i sat i on of aery lam ide , optiona 1 ly with other monomer, under conditions which give the desired pait iole size. The reverse phase emulsion can have a typical [(article size in tire range 90% by weight of the part i c 1 PS bet ween 0 - '* nnd 1/tm but often the particle size i s sma1 1 or, f or \nstance 90% by weight between 0.05 and n. rc//m, often about 0.1 to 5/im. In particular it is prof erably of a size such that it may be referred to as a in i eroomu 1 s i on .
The emu 1sion, a ftor the conversion with hydroxy 1 am ine hydrochloride, typically has a polymer content of 10 to 30 weight percent, a water content of 20 to 40 wt% and an oil eont pfit of 2 5 to 5 5 wt % and surfactant content of 10 to
2 0 wt°;.
The oil phase can be any suitable oil phase that is
convent i t >na] tor use in reverse emulsions and can i nclude
conventi ona 1 emu 1s i f i or and/or polymeric amphi path i c
stabi 1 isei . The storage stability of the hydroxamated
'■mi i I :■ i on will depend on rno components m un^ i-nm i ;- > wi.. So 1 f M -t ion of a surf actant ( or surfactant blend) hav i nq HT.B in the range 8 to 10, preferably about 8.7 to 9.4, can be benef i ci a 1 in t h i s respect.
The ore that i s to be pe 1 1 et ised can bo any oonven i ent met a 1 ore such as v. i nc ore or iron ores whi ch can be t neon i to, magnet ite or, preferably, haematite.
The ore is normally provided to a particle size which is convent i ona1 for pel 1eti sati on, usually 90% be i nq be 1ow 25n microns and preferably 90% by weight being below 75 m i crons.
The amniint. of polymer that is added, based on the amount of ore, is generally 0.01 to 0.2%, often 0.02 to (». 1° and preferably 0.025 to 0.075% based on the dry weight of poIymor.
'I'he tot a 1 moi sture content of the mixture that is to be pelletised is generally in the range 5 to 11% by weight of the ore. The amount is often in the range 6 to 8 - 5 or 9% frequently 6.5 to 8.3%. The amount is usually at least 1% below, and often 2 to 4% below, the amount that is opt i mum when us i ng powdered hinders such as aery1amide-sod ium acrylate copolymer. If the polymer is added as a solution or reverse phase aqueous emulsion then it will provide some or all of the water that is required for pel 1etisation. Often, however, at least some of the moisture is present as moisture in the ore, and extra water may be added if regu i red at the pelletisation stage to provide the desired moi sture content.
The invention is of particular value when an inorganic component is included ns part of the binder. The inorganic et >mponcnt . flri be any of the mater ia 1 s 1 i sted i n, for instance, EP-A-288, 150 and may be included in a dry weight, ratio of pol ymer : add i t i ve of from 3:1 to 1:3. Preferably, however, the binder i ncludes calcium oxide or ca1c i urn hydroxide. Preferably it is provided as hydrated lime but crushed 1imestone can be used in the invention. hi me may be added in the form oi slurry. Lime or other inorganic
b i nd'M may be addfMi s i imi 1 t anoous 1 y with the pol ymer or sequent ■ i a I 1. y in e i t her order. The amount of lime is typically in the range 0.5 to 5%, often 1 to 2.5%, by we i ght of the mi x to bo pe11et ised.
I -"or t (ipr- i nor gap i c components , for instance salts such in' r "f "\ i urn cat bona to, may a 1 so be added in a dry weight tario fit p I ymer: sa 1 t of from 1:1 to 1:3. Preferably such sa I t s are m i xod with the polymer prior to pel let i sat ion.
The process of the i n vent ion not only has the advantage of g i vi ng good drop number despite low moisture content and despite the presence of lime in the mix that is be i ng pe 1 1 et i sed , but a 1 r^o g i ves pel lets having desirable surf
A haemat i t.e ore conta ining 2.9% moisture as supplied was mixed with tap water to produce a 7 . 0% moisture content and then bagged up and allowed to stand overnight. Prior to pel let i sat ion 1.8% (based on weight of ore) lime + appropriate binder was premixed where possible and added or added separately at the same time over 1 minute with a further The f ol lowing bi nders were used in this example. Hinders A and H are according to the invention. A Ki.9° sol ids mirroomu1sion of a fully hydroxamated
copolymer of 0^ wt°s aery 1 amide/5 wt% sodium aery 1 ate
t he i nt r i ns i c v i scosi ty (IV) of the hydroxamated
1OOppm methy1 one bi s acrylamide (MBA) and the TV of
the hydroxamated polymer was 5.5 dl/g. c fiiiar gum. 0 Non-ionic corn starch (Chemstar 1908G).
[ Powdered copol ymrr of 5 0 wtl AMPS/5 0 wt% aery 1 ami do ,
IV r> . 0 d 1 / q . F As E, but IV 8.6 d .1/q.
The wot and dry strength and drop number values wore recorded. The resu1ts are q i ven in the fol1ow i ng Tablo 1 .
'i h Testinq was carried out as in Example 1 with the exception that the haematite ore was mixed with tap water-to produce a 7.^% mo i sture content.
The f o 1 lowi nq b i nders were used i n t.h i s exampl e . Binder B is the same as Binder B used in Example 1 and is accord ing to the invention.
G 50% active dispersion of high molecular weight (IV 16.0 dl/g) copolymer of 35 wt% sodium acrylate/65 wt% aerylamide.
H Modi fi ed starch National B3 8 .
I Powdered medium molecular weight (IV G.3 dl/g) sodium aery I ate homopolymer.
.7 Powdered copolymer of 3 0 wt% dimethylaminoethy 1 aery 1 ate quaternised with NaCl/70 wt% aery1amide, IV 7.3 dl/g. K Dextran flakes.
The wet and dry strength and drop number vaIues were recorded. The resu.l ts are g i ven in the following Table 2 .
The (ci 1 lowinq hinders were used in this example. Hinders O and P are according to the invention. Binder G is- the same as Binder G used in Example 2.
I. Powdered copolymer of 20 wt% sodium acrylate/80 wt% acrylamide, TV 6.0 dl/g; contains 50 wt% sodium carbonate. M As L but without sodium carbonate and with a small amount of MBA cross-1i nk i nq.
N A o°n act i ve sol ut ion of 80 wt% AMPS/20 wt% sodium aery 1 ate, low molocular weights
0 17.7% solids microemulsion of a fully hydroxamated copolymer of 9 5 wt% acrylamide/5 wt% sodium acrylate, the IV of the hydroxamated copolymer being 8.6 dl/q. P As 0 but the acrylamide copolymer was cross-linked with 100 ppm methylene bis acrylamide (MBA) and the IV of the hydroxamated polymer was 6.6 dl/g.
The wet and dry strength and drop number values were recorded. The results are given in the following Table 3.
These resu 1 t:r> aqa i n show that the Bi ndors O and P of: t ho invontion give a significant improvement .in drop niipihor, even in comparison with other binders in which the pellets have a greater moisture content. In pai t iniiar improvements are shown over the standard commorc i a J products I, and M . Example, 4
Tests were carried out as in Example 3.
The following binders were used in this example. Binders C, G and L, to P are the same as the binders with the same letters in previous examples. Q As L, with small amount of MBA cross-1 inking.
The wet find dry strength and drop number values were recorded. The results are given in the following Table 4 .
Again these results show that the Polymers O and P of the invention give significantly improved drop number even at relatively low moisture contents. In particular they give improvements over the standard commercial products L, M and Q.
In all of these examples, the moisture contents obtained are at the low end of the range which is typically seen. For pellets having these moisture contents drop numbers tend generally to be low, so any significant improvements are particularly advantageous.
1. A process of pelletising a metal ore comprising
forming an intimate mixture of particulate ore and a
binder in the presence of moisture,
forming green pellets by agitation of the mixture and
firing the green pellets to produce ore pellets,
wherein the binder comprises
a polymer made from water soluble ethylenically unsaturated monomer or monomer blend and which has pendent groups of the formula
2. A process according to claim 1 in which the polymer consists of recurring units which are 20 to 100 mol% hydroxamated (meth) acrylamide units, 0 to 80 mol% (meth) aery 1amide units and 0 to 50 mol% other units derived from water soluble ethylenically unsaturated monomer.
3. A process according to claim 1 in which the polymer is a copolymer of 50 to 100 mol% hydroxamated acrylamide units, 0 to 20 mol% sodium acrylate units and 0 to 50 mol% acrylamide units.
4. A process according to any preceding claim in which the polymer has intrinsic viscosity above 4dl/g.
5. A process according to any preceding claim in which the polymer is cross linked.
6. A process according to any preceding claim in which the polymer is supplled as an emulsion of the polymer in an oil phase and th is emulsion is mixed with the
part iculate ore.
7. A process according to any preceding claim in which the mixture of binder and ore includes lime.
8. A process according to any preceding claim in which the amount of moisture in the mixture of ore and binder is below 9%, preferably 6 to 8.3%, based on weight of ore .
9. A process of pelletising a metal ore substantially as herein described and exempli f ied.
|Indian Patent Application Number||2517/MAS/1998|
|PG Journal Number||50/2007|
|Date of Filing||06-Nov-1998|
|Name of Patentee||ALLIED COLLOIDS LIMITED|
|Applicant Address||P O BOX 38, LOW MOOR, BRADFORD, WEST YORKSHIRE BD12 OJZ,|
|PCT International Classification Number||C22 H 1/244|
|PCT International Application Number||N/A|
|PCT International Filing date|