Iron ore, its beneficiation and agglomeration - as required for iron and steel industry:

Iron ore, its beneficiation and agglomeration - as required for iron and steel industry:

A. Iron Ore: A naturally occurring mineral from which iron (Fe) metal is extracted in various forms viz Hot metal/ DRI etc.

B. Types of Ore: Two major varieties used for iron making are Haematite Ore( containing Ferric Oxide - Fe2O3) and Magnetite Ore (containing Ferro-Ferric Oxide – Fe3O4). When chemically pure, Haematite contains apprx 70% and Magnetite 72.4% iron . But usually iron content of ores ranges between 50-65/67% (rich ores) and 30-35% (lean ores); the remains being impurities known as Gangue (such as Alumina, silica etc.) and Moisture.

C. Grades of Ore: Iron ore is typically classified as High grade (+65% Fe), Medium grade (+62 – 65% Fe) and Low grade (-62% Fe). Typically, the Integrated Steel Plants(ISPs) use medium/High grade Iron Ore whereas the Sponge Iron plants require only High Grade iron ore, preferably, with +67% Fe.

(i) Lumpy/Fine Ore: Iron Ore is traded in lumps (i.e. sized ore) or in fines. Production/availability of lumps is limited by virtue of the natural occurrence and also because of generation of lot of fines during crushing of large lumps present in the run-of –mines (ROM).

(ii) Natural pellet: It is a term coined by producers in some Asian counties, to designate sized iron ore used directly in Sponge Iron production.

(iii) Blue Dust: Blue Dust is the name given to naturally occurring, extremely friable, high grade Haematite Iron Ore powder.

D. Beneficiation of Ore: Very low grade Iron ore cannot be used in metallurgical plants and needs to be upgraded to increase the iron content and reduce the Gauge content. A process adopted to upgrade ore is called Beneficiation.

Asian, specially of Indian origin of ore, is generally rich in iron (Fe) content but theAlumina content is very high which call for special adjustments/techniques for production of iron/steel at the cost of productivity and quality and hence money. Some of the mines have set up a Beneficiation plant to beneficiate Magnetite ore with approximately 35% Fe to high grade Iron Ore Concentrates.

E. Agglomeration of Iron Ore: Iron Ore Fines/blue dust cannot be charged in the blast furnace directly since they block the passage for ascending gas inside the fee. So, they are agglomerated (by igniting at lower temperature causing only interfacial fusion) into larger lumpy pieces with/without addition of additives like limestone, dolomite etc. Two types of agglomerated products are commonly produced/used in the industry namely Sinter and Pellet. Accordingly the processes are known as Sintering and Pelletising respectively:

(a) Sinter : Sinter is a clinker like aggregate which is normally produced from relatively coarser fine iron ore (normally –3mm) mixed with coke breeze (-3mm), limestone dolomite fines (-3mm) and other metallurgical return wastes from the plant. Sinter is a much preferred input/raw material in blast furnaces. It improves BF operation and productivity and reduces coke consumption in blast furnace. Presently, more than 70% hot metal in the world (in India 50%) is produced through the sinter.

(b) Pellet: Pellets are normally produced in the form of Globules from very fine iron ore (normally –100 mesh) and mostly used for production of Sponge Iron in gas based plants, though they are also used in blast furnaces in some countries in place of sized iron ore.