Specialized metallurgical processes – compositions for use therei – Compositions – Solid treating composition for liquid metal or charge
Patent
1992-05-19
1994-04-26
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Compositions
Solid treating composition for liquid metal or charge
75303, 75321, 75772, C22B 108
Patent
active
053063279
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to modified native starch base binders for pelletizing particulate mineral materials and to mineral ore concentrates and mineral ore pellets containing the novel binders. Methods of using the novel binder are also disclosed.
BACKGROUND OF THE INVENTION
In order to reduce impure deposits of iron ore to commercially usable grades of iron, impure deposits of iron ore are generally concentrated and pelletized prior to reduction processing in blast furnaces. Pelletizing impure mineral deposits has grown into a very large industry since the end of World War II. Mineral ores of various kinds are pelletized for ore production but the process is most commonly with impure iron ores, such as taconite. Approximately 40 million tons of iron ore pellets are produced annually in the United States and another 30 million tons are produced in Canada. Other significant pellet production facilities exist in several other countries including Brazil, Australia, Turkey, India, Norway and Japan.
High grade iron ore deposits in the United States were severely depleted by the war effort during World War II. In order to continue to produce steel in blast furnace operations in the U.S., alternate sources of iron were needed to feed the blast furnaces. The University of Minnesota and a number of steel companies concentrated their efforts on developing technology to upgrade low grade magnetic ores, commonly called taconite, into an acceptable iron ore feed for these blast furnaces. Taconite, which is abundant in Minnesota's Iron Range, typically contains about 25% magnetic iron as compared to the roughly 50-70% iron content of some higher grade iron ores. In order to use taconite in place of the higher grade ores in commercial reduction processes, the iron content of the taconite needed to be concentrated.
The process for concentrating the iron in taconite evolved to include blasting the taconite and crushing it into particles small enough to liberate most of the grains of magnetite. The pulverized ore is then upgraded to an iron content in excess of preferably about 67% iron in a series of concentrating steps. The resulting mineral material is typically an aqueous slurry which is filtered or otherwise reduced to a moisture content of between about 9-10% by weight.
This material cannot be added directly to a blast furnace because the average particle size is so small, typically in a range of about 10-40 microns in diameter. Small particles such as these can plug a blast furnace. In addition, they are often lost as air entrained dust when fed directly into a blast furnace. It was believed, however, that this problem could be overcome by agglomerating the resulting mineral material. The need for some method of agglomerating this material subsequently led to the development of the iron ore pelletizing industry.
The commercial pelletizing or agglomeration process is generally a continuous process in which filtered mineral material is conveyed into balling drums or "disks" to form pellets. The rotating drum or disk causes the concentrated mineral material to roll into balls, typically called "green" or undried balls or pellets.
Green ball growth is somewhat similar to the growth of a snowball when it is rolled in wet snow. As the ball is rolled, successive layers are added as the ball grows to form a large ball. Seed pellets are initially formed from the mineral material by the rolling action of the drum. During commercial operation, pellets are typically screened at the drum discharge and the undersized pellets are recycled back into the drum as seed pellets until they have grown to form a ball having a diameter of about 1/2 inch (about 1.25 cm).
These green pellets are typically screened to remove pellet fines, dried at increasingly higher temperatures, and "fired" at a temperature of about 2400.degree. F. (1315.degree. C). When the pellets are fired, the iron grains grow together to form somewhat porous iron matrices which provide strength to enable the pellets to survive significa
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Dingeman David L.
Skagerberg William E.
Oriox Technologies, Inc.
Rosenberg Peter D.
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