Iron Ore - Mine To Metal

1. The fragile nature of sizeable Indian iron ore (hematite) deposits produces lumps & fines in the ratio of 2:3. Thus, large chunks of fines are not utilized. Partially, a meagre of these fines are utilized after agglomeration (sintering & pelletization) at present.

2.  Size specification of hematite iron ore for iron making through (i) Blast furnace: Lumps (-30+6 mm); Sinter (-6+0.15 mm) & pellet fines (-0.15 mm/100 mesh ground to -325 mesh size for pellet making); (ii) Sponge iron Lumps (-18+6 mm) & pellets.

3.  BIF (Banded Iron Formation) is distributed in five broad belts: (i) Singhbhum (Jharkhand) & Cuttack (Odisha); (ii) Dantewara-Durg (Chattisgarh) & Chandrapur- Gadchirolli (MS); (iii) Bellary-Hospet Belt (Karnataka); (iv) Goa, Ratnagiri (MS) & North Karnataka; and (v) Metamorphosed BIF (magnetite) along the West coast in Karnataka & Kerala. No magnetite mining is done as on day.

4.  Kudremukh (Kr.) mine in western ghat has been closed due to environment consideration by Supreme Court.

5.  Hematite (Fe2O3) 70% Fe; Sp. Gr. 4.9-5.3; Goethite (Fe2O3.H2O) 62.9% Fe, Sp. Gr. 3.4-4.2, Limonite (2Fe2O3.H2O) 60% Fe, Sp. Gr. 3.4-4.2; Magnetite (Fe3O4) 72.4% Fe, Sp. Gr. 5.17.

6.   Mode of occurrence of hematite ore generalization in B

Threshold value (mining cut-off) for hematite ore 45% Fe; Siliceous Goa Ore 40% Fe for both lumpy ore as well as fines.

8.     Reserves (As per NMI 2010): Existing reserves of hematite merely accounts for around 28% of the total iron resource of the country (28.52 billion tons). In India, hematite reserves and resources are mostly confined in the states of Orissa (42% & 34%), Jharkhand (29% & 26%) Chhattisgarh (11% & 19%), Karnataka (11% & 12%) and Goa (6% & 5%). Balance (1% reserves 4% resources) is spread across Maharashtra, Andhra Pradesh, Uttar Pradesh, Rajasthan etc.

9. The overall grade of the hematite reserve in the country is +62% Fe (NMI 1.4.2010). A close look at the grade wise share of hematite reserves in the country will reveal that a cut-off grade of 60% Fe has only been taken for exploration program as against present threshold of 45% Fe

Important Mines: Bailadila (CG), Donimalai (Kr) of NMDC; Dalli Rajhara (BSP), Raoghat (CG); Noamundi & Joda (TATA)

 10. Iron ore Processing (Beneficiation)

(i)   Dry Processing: Multistage crushing & screening to obtain calibrated lumps i.e., -30+6 mm (for BF); -18+6 mm (for sponge iron) & fines (=10/6 mm).

(ii)   Dry-cum-wet Processing: similar to dry processing and only fines -10/6+0.15 mm subject to wet processing i.e., mechanical classifier, hydro-cyclone etc.

(iii)   Wet Processing: Generally practiced for low/medium-grade (60-62% Fe) hematite ore. The process consists of multi-stage crushing followed by different stages of washing in the form of scrubbing and or wet screening, classification etc.

Need for Processing: Removal of deleterious impurities like silica, alumina, Sulphur & Phosphorus.

11. About 2.5 tons of r.o.m. or 1.7-2.0 tons of processed iron ore (63-65% Fe) is required for per ton of steel production.

12. Present Indian steel production is accounted for by two major routes:

(a)   The blast furnace (BF) and basic oxygen furnace (BOF/LD) route of steel making followed in Integrated Steel Plants (ISP). These plants are large in capacity ranging from 1 to 5 million tons per year and covering a fairly large area of 4 to 8 sq.km.

(b)   Scrap/DRI or sponge iron and electric arc furnace (EAF) and induction furnace (IF) route of steel making as adopted in Mini Steel Plants (MSP). These are small in capacity ranging from 0.5 to 1 million tons and in some cases, up to 2 million tons per year, covering an area up to 2 sq.km.

13. Pig iron and sponge iron form the feed stock for steel making. Integrated steel plants (ISP) require large capital investment, longer gestation period and depend on metallurgical coke which is not available everywhere. DRI units on the other hand require limited capital investment, shorter conception period and the reductant can be non-coking coal or natural gas. Consequently, the DRI process became popular among developing countries. Such units in large number are spread across the country and India is the largest producer of sponge iron (mostly coal based) in the world.

14. Blast furnace route of iron making would continue to dominate the iron production in India followed by sponge iron (DRI). Lumpy iron ore (-30+10 mm) and agglomerates like sinter & pellets form the feed for the production of pig iron in blast furnace; whereas, steel scrap, lumpy iron ore (-18+6 mm) or pellets are the feed for sponge iron production.

15. Agglomeration of iron ore fines basically involves two main methods, they are, sintering and pelletization.

16. Sintering is the agglomeration technique of iron ore fine in the size range of -10+0.15 mm (100 mesh) to produce clusters by incipient fusion at high temperature.

17. The pelletization is the other mode of agglomeration applicable for fines below 325 mesh size at high temperature by incipient fusion.

18. Sponge Iron Making Processes (Solid Iron/ DRI)

Iron produced as a solid by the reduction of iron oxide is known as sponge iron. It is also referred to as direct reduced iron (DRI). It is often compacted to reduce the porosity; to convert into hot briquetted iron (HBI) for storage or sale. Direct reduction (DR) includes a family of processes in which iron ore (in the form of lumps or pellets) is reduced to the solid-state either by solid or gaseous reducing agent. Reformed natural gas or non-coking coal is generally employed as the reductant as well as the primary source of energy. The final product from all DR processes is a solid, which has to be melted during steel making in a manner similar to scrap. For coal-based DR, rotary kilns, rotary hearth furnaces and multi-hearth furnaces are employed, while for gas-based processes, the reactors used are shaft furnaces, fluidized beds, or retorts. Globally the natural gas is a preferred reductant for producing sponge iron. In India, however, coal based rotary kiln processes are more popular because of restricted and localized availability of natural gas. 

Disclaimer: The above publication content is the excerpts of Iron & Steel Industry Interactions & Statistical Sources are from IMYB 2015-16