Specialized metallurgical processes – compositions for use therei – Processes – Consolidating metalliferous material by agglomerating,...
Patent
1994-02-02
1995-07-25
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Consolidating metalliferous material by agglomerating,...
75321, C22B 1244
Patent
active
054358345
DESCRIPTION:
BRIEF SUMMARY
This invention 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.
In Canadian patent 890,342 it is proposed to include a water swellable polymer preferably having a gel capacity of at least 100, where the gel capacity is defined as the number of grams of water absorbed by one gram of polymer, the free water having been drained away by gravity. The inclusion of the particles is said to increase water tolerance and to give improved green strength, and an important advantage is said to arise when the initial ore is too wet. The polymers are described as lightly cross linked swellable polymers, with amounts of cross linking agent being from 50 to 10,000, preferably 500 to 7,000, ppm. Bentonite is used with the polymer as binder.
More usually, polymers used as binder for pelletisation processes are wholly water soluble. Thus the particulate binder may comprise synthetic polymer particles often having a size up to 300 .mu.m 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 with the consequential risk of insolubility.
For example we describe in EP-A-225171 the use, as particulate binder, of water soluble synthetic polymer that has intrinsic viscosity 3 to 16 dl/g and that is an anionic polymer and we describe in EP 0288150 the use of cationic polymers. All the monomers described for use in the production of the soluble polymers are monoethylenically unsaturated and so the polymers are linear and are free of significant cross linking.
we mention in EP-A-225171 that the soluble polymer can be used in combination with a cross linked polymer that is cross linked with an amount of cross linking agent that is in the range 20 to 1000 ppm and that must be such that the particles are insoluble and have a gel capacity often above 50 g/g.
The amount of cross linking agent required to insolubilise a polymer will depend on the molecular weight of the polymer in the absence of the cross linking agent. Thus a very high molecular weight polymer may be totally insolubilised by the use of a very low amount of cross linking agent, but a relatively low molecular weight polymer may remain soluble even when a substantial amount of cross linking agent is used. Accordingly, in order to achieve the required insolubility at 20 ppm, as suggested in EP 225171, the polymerisation conditions must be such that, in the absence of the cross linking agent, a very high molecular weight polymer would be obtained.
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 pelletising process.
We now include, as particulate binder, synthetic polymer particles that comprise particles of a water soluble, partly cross linked polymer. As a result of using a partly cross linked polymer, in contrast to a polymer that is otherwise substantially identical but is substantially free of the deliberate partial cross linking, it is possible to achieve a significant increase in the dry strength of the ore pellets. However the benefit is only obtained over a relatively narrow range of partial cross linking and so the advantages of the invention are obtained when we select an amount of cross linking that is sufficient to increase the dry strength
Allied Colloids Limited
Andrews Melvyn
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