Specialized metallurgical processes – compositions for use therei – Processes – Consolidating metalliferous material by agglomerating,...
Patent
1992-10-08
1994-04-12
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Consolidating metalliferous material by agglomerating,...
75320, C22B 124, C22B 1242
Patent
active
053021860
DESCRIPTION:
BRIEF SUMMARY
This invention relates to surface treatment of mineral ore pellets.
Pelletisation of mineral ores and other water insoluble particulate material is well known and provides a convenient way of converting fine particulates into a more easily handleable form.
Pelletisation of the particulate material involves the use of a binder and moisture. The binder can be an inorganic binder such as a clay type material, for example bentonite, or it can be an organic polymeric material for example, carboxymethyl cellulose or water soluble synthetic polymer.
The amount of moisture in such pellets is critical and this has been studied and the theory described by Newitt and Conway-Jones in Trans Instn Chem. Engrs., pages 422 to 442, 36 1958. They describe three states occuring in water-particle systems in the pelletisation process. Firstly, the Pendular state in which water is present at the point of grain contact only and the surface tension holds the particles together. Secondly, the Funicular state where some of the internal voids of the pellet are fully occupied by water. Thirdly the capillary state where all of the internal voids of the pellet are filled but the surface is not covered by a coherent film.
In practice the capillary state is the commercial optimum and this corresponds to a moisture content overall in the pellets generally of from 7 to 15%. However, it can be difficult to produce the pellets in the capillary state with high internal moisture, but without having too much surface moisture. If the water content is too high then not only are the voids of the pellets filled with water but there is also a significant amount of water on the outside of the pellets. There are several adverse side effects of this, including a reduction in the green strength of the pellet, attraction of fines which lead to subsequent higher dust levels, and low permeability of a bed of the pellets during subsequent treatment.
In the present invention it is intended to provide a way of keeping the moisture levels within the pellet high enough to produce substantially the optimum capillary state with the high green strength which that produces, while avoiding or reducing surface moisture problems.
In the process of the present invention, pellets of water insoluble particulate material are made from a mixture of the particulate material, moisture and pelletising binder by forming moist green pellets and then drying the green pellets characterised in that at least one water displacing additive is applied to the surface of the moist green pellets after they are substantially wholly formed and before they are dried.
The particulate material can be coal or other particulate water insoluble material, but preferably a mineral ore, for example zinc ore or preferably an iron ore, normally a haematite, magnetite or taconite. The particle size of the particulate material is generally substantially all below 300 .mu.m and preferably below 200 .mu.m and most preferably below 100 .mu.m.
The binder may be an inorganic binder such as bentonite or other clays, lignosulphonates, ferrous sulphate, asphalt, or organic material which may be natural or modified natural materials for example polymers of starch, sodium carboxymethyl cellulose and various non-ionic, anionic or cationic synthetic polymers. As examples of synthetic polymers, water soluble acrylic polymer and other polymers as defined in EP 225171, EP 288150 and EP 203855 are suitable. Mixtures of for example synthetic polymer and bentonite are also suitable binders.
Preferred binders are water-soluble polymers of 5-30% acrylic acid with 95-70% acrylamide having an intrinsic viscosity of about 3 to 15 dl/g, introduced as fine powder, for example as described in EP 225171. Often the binder includes sodium carbonate or other additive, for example in EP 225171.
Moisture is present in the particulate mixture before addition of the binder and more water can be added after or during addition of the binder. If the moisture content of the particulate mixture is already sufficiently high then no further w
REFERENCES:
patent: 3660073 (1972-05-01), Youngs
patent: 3966427 (1976-06-01), Herment
patent: 4659374 (1987-04-01), Alanko
Allen Anthony P.
Field John R.
Allied Colloids Limited
Rosenberg Peter D.
LandOfFree
Pelletisation process does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pelletisation process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pelletisation process will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2095597