IRON ORE

The important iron minerals are magnetite (Fe3O4) Hematite (Fe2O3), limonite (hydrated oxide), goethite (hydrated ferric oxide), siderite (FeCO3), pyrite (FeS2) and laterite (hydrated oxide of aluminum or iron). Out of these hematite and magnetite are the ores from which iron is extracted.

Iron ores are almost entirely used in the manufacture of pig iron and steel. Non – metallurgical uses are very few. Spathic iron ore, also known as siderite, is used for the production use of the hydrogen by the steam iron content proceeds. Micaceous iron ore, which is a variety of hematite, is used as a coating material in the preparation of welding rods (electrodes). Pig iron ore (Fe3OH6) is used as a purifying and de – sulphurizing material of producer and municipal gases. Magnetite is used for the preparation of heavy media in coal washing plants. Iron fines are also used in pipe coating.

Metallurgical uses:

Most important use of iron is in the blast furnace for the production of pig iron. It is used in the furnace in the form of sinters and pellets as also lumpy ore. It is also consumed in the open health furnaces.

The specification of ores for the production of sinters and pellets ore given below. The specification of used in the blast and OH furnace are also discussed below:

1.      Iron Ore Sinters:

Sinters are produced from iron ore fines for uses in the blast furnace. The Bhilai Steel Plant uses the sizes + 10 mm less than 5% minus 8 mm 65%. Minus 1 mm 40%. The Fe content should be 61.5% ±0.5%. The Bokaro Steel Limited used fines of the sizes minus 3 mm 55%, + 10 mm 5% (max.). Fe content should be 62% ±1%, A12O3 3.3% (max.), SiO2 2% (max.). The Rourkela Steel Plant used fines of the sizes 10 mm (max.), minus 1 mm 30% (max.). Fe content should be 61% ±1%, A12O3 4 –5% ±1% Silica 3.00% ±0.5%. Durgapur Steel Plant uses unwashed fines of the sine’s + 10 mm 5% (max.) With iron content 63% Alumina 3.5% and silica 2.5%. They also use washed fines of the sizes + 10 mm 5% (max.) with iron 63%, alumina 3% and silica 1.5%.

2.      Iron Ore Pellets:

High-grade iron ore fines are used for the preparation of pellets. Iron content in the ore has got to be very high and gangue low to confirm to the quality of pellets. The content generally is 66% Fe, SiO2 + A12O3 – 3%, Sulfur and Phosphorus 0.05% each. The sizes of the fines should be minus 100 mesh 95% minus 325 mesh 60 – 75%.

3.      Blast furnace:

These days all blast furnaces require tailored ores such as sinters, pellets and calibrated lumps as furnace fee, mainly to effects economics in fuel consumption and to increase productivity.

Fe Content: Iron of as high-grade as possible is required because an increased of 1% Fe in the burden increased the productivity by 2% and decreased the coke rate by 3%. In the Indian plants, the range of the Fe content in iron ore lumps is 60.52% to 66.5%.

Silica: 1.5% decreased of silica causes reduction in the slag volume of 65kg per ton of pig iron. Increase of 100-kg slag per tonne of pig iron raised fuel consumption by 40 kg of coke per tonne of pig iron. In the Indian Plants, the range of silica in iron ore lumps varies from 1.6% (max.) to 2.5% (max.).

Alumina: If the ore is high in alumina, the fluidity of slag is affected. It should not also be too low. In the Indian Plants, alumina content in the ore varies from 3% to 4.5% Generally, the alumina – silica ration should be 1:1to 1: 1.5 Phosphorus should not exceed 0.15% sized. In the Indian Plants sizes of iron ore lumps varies from + 10 mm to + 75 mm.

OH Furnace: In the Bhilai Steel Plants, the sizes of lumps ore used in OH Furnace are minus 50 mm less than 5%, 100 mm less than 5%. The Fe content should be 68% ± 1%, silica 3% (max.) and phosphorus 0.1% (max.). In the Rourkela Steel Plant, the ore sized should be + 50 mm 64% ±1%, A12O3 3% ±1%, SiO2 2% ±0.5%. In Durgapur Steel Plant, the size of ore should be 50 – 125 mm, Fe 67%, and silica 2.3%. In Tata Iron should be 50 - 125 mm, of ore are minus 100 to + 50 mm. Fe content varies from 65 to 67% and A12O3 1.5 to 2% (max.).

In – red, E1 – red and Plasma smelts process: Fines and super fines ores can be directly used in these processes.

Utilization of Quartz – magnetite rocks: The only project of this kind is Kudramukh deposits where material containing + 38% Fe from the oxidized zone is mined and treated to produce magnetite concentrates and pellets. These concentrates contain + 67% Fe.

Non – Metallurgical Uses:           

Pipe Contain:    Especially calibrated iron fines have been found to be useful as a high-density aggregate for pipe coating. Such coated pipes are essential for the transport of crude oil from offshore wells.

Utilization of magnetite in coal washery: Magnetite is also used in the      coal washery. It is used in granulated form. The magnetite content in the ore should be + 95%.

Other non-metallurgical uses are of minor significance.

Future trends:            The steel industries required beneficiated and agglomerated high quality furnace charge. The limitation on input of alkalies is being increasingly enforced. In iron ores 0.15% Na2O is the maximum limit. Besides, reducibility is another factor to judge the suitability of ore for the steel industry.

Hematite deposits are broadly classified into high, medium and low-grade containing + 65% Fe, 62 – 65 % Fe and – 65% Fe respectively. This classification is linked with the marketability of iron ore, but it is obvious that the classification is based on single through principle chemical constituent i. e., iron. The other constituents such as silica, alumina, phosphorus and sulfur that have a bearing on the economics of utilization have not at all been considered. The Physical Characteristics such as sizes, such as lumps and fines have also not been considered. In the absence of such information, it is not possible to classify the reserves according to the industrial uses like its use in blast furnace, steel smelting shops, sintering plant, Pelletization plants, etc. Efforts have been made by the Indian Bureau of Mines to give lumps and fines ratio of various hematite deposits based on the information available in the adjoining general Physical characteristics of ores.

So far as, magnetite ores are concerned, the broad data on the degree of weathering and average iron content of a number of deposits have enabled Indian Bureau of Mines to segregate part of the reserves as of metallurgical grade, guided mainly by the experience of the Kudramukh mine. In case of the reserves of the deposits from which the ore is known to be fed to coal washers the same has been classified as coal washery grade reserves.

Summarizing the reserve classification is as follows:

1.      Hematite:

(a)        High-grade                   :           > 65% Fe

(b)        Medium-grade :                       62 – 65% Fe

(c)        Low-grade                   :           < 62% Fe

2.      Magnetite:

(a) Metallurgical: >38% Fe oxidized / weathered ore

(b) Conditional: <38% Fe un-oxidized ore, resources unclassified oxidized/un-oxidized ore

(c) Coal washery: > 70% magnetite content

The group of the vies that iron undergo preparation by way of crushing, secreting, washing, etc., before it is fir-enough for sintering, palletizing, blast furnace operations, etc. therefore, it may be possible for the field geologist to categories reserves precisely according to the end use. Even a comparatively lower grade deposit can yield high quality furnace charge after benefaction and agglomerates. And yet it is also a fact that we have grade deposits. Considering all these factors from a field geologist point of view the following grades are suggested for the purpose of classification of reserves.

(1) Hematite:

(a)

High-grade (lump)

Fe 65 % (min.)
Sio2 3% (max.)
Al2O3 3% (max.)
P 0.10% (max.)
Na2O + K2O 0.15% (max.)
Size + 10mm

(b)

High-grade (Fines)

Fe 65 % (min.)
Sio2 + Al2O3 (max.)
Al2O3 4.5% (max.)
P 0.10% (max.)
Na2O + K2O 0.15% (max.)
Size 10mm to 100mm

(c)

Medium-grade (lump)

Fe 62 - 65% (min.)
Sio2 2.5% (max.)
Al2O3 4.5% (max.)
P 0.10% (max.)
Na2O + K2O 0.15% (max.)
Size 10mm to 100mm

(d)

Medium-grade (Fines)

Fe 62 - 65% (min.)
Sio2 4% (max.)
Al2O3 4.5% (max.)
P 0.10% (max.)
Na2O + K2O 0.15% (max.)
Size (-) 10mm

(e)

Low-grade (lump)

Fe (-) 62% (+) 56%
Sio2 + Al2O3 = 8 – 10%
P 0.10% (max.)
Na2O + K2O 0.15% (max.)
Size 10mm to 100mm

(f)

Low-grade (Fines)

Fe (-) 62%
Sio2 + Al2O3 = 8 – 10%
P 0.10% (max.)
Na2O + K2O 0.15% (max.)
Size (-) 10mm

(2) Magnetite:

a.       Metallurgical >38% Fe Oxidized / weathered ore.

b.      Coal washery >95% magnetite

c.       Conditional resources <38% Fe Un oxidized ore.

The BIS (IS: 5442 – 1982) has classified hematite ore depending upon its chemical composition:

Grade

Chemical Analysis Percent

Fe

Al2O3

S

P

TiO2

Total of all other metals
Except Mg & Ca max.

68 and +  &nb