Type of iron ores in India

• Classification of ore

• black ore = magnetite
• red or reddish black ore = hematite
• brown ore  = limonite
• gray or whitish ore = carbonates

•   Nature of ores
  1. siliceous  = predominantly silica
  2. aluminous = largely alumina
  3. argillaceous = chiefly clayer matter.
  4. calcarious = predominantly lime
  5. bituminous = large amount of coal matters
  6. titaniferous = large amount of ilmenite ( FeO.TiO2)

If the ore contains elements like Phosporous, Sulphur, Arsenic, Znic, Lead, Nickel etc  is called impurities in the ore. If it is present in considerable amount then it creats difficulties in iron making process and its quality.

Iron ore generally classified  according to there geological  origin as,

• Sedimentary  ;    this is the largest and important group of ores present in four forms
  • B.H.Q.( blended hematite quartzite)  –   Iron oxide and silica are in alternate  bands .It is porous,fragile and less pure but where secondary depositions of iron oxide has taken place it is dense, massive and more pure.
  • Minnette ores: –  These are precipitate ores from sallow water around granules, often of foreign matters.
  •  Iron stone – These types of iron stones are found in U.K.
  • Blue dust – It is in the form of a powder (purity often more then 60%).
• Igneous  :    It is derived from igneous materials of volcanic  origin and occure mainly as magnetite.
•  Laterite :     It is formed in tropical conditions of alternating dry and wet seasons resulting in leaching away of silica and alkalies from the mother igneous rock, leaving behind mainly iron and alumina oxides.

The constitute minerals of iron ore are not necessarily distributed at random throughout the ore body.They frequently follow a patten which has been determined by the geological, metamorphic and geochemical influences which the ore body undergone. The following  things are taken into consideration.

•  Oolitic ore :  concentric layers or as radiating crystals and iron may be present in these or in matrix rock.
• Lateritic ores : They are formed by surface  action at the expansion of underlaying rocks rich in iron and consists of intermingled mass of iron hydroxides,aluminium hydroxides and other minerals.
• Blended ores:  These are characterized by alternate bands usually a few mm thick but sometimes upto several cms. In these predominance of iron as well as silicates or quartz present.these ores are easy for benification.
• Hard massive ores :  The constituents are intergrown into a hemogenous mass showing no preferential direction or pattern except occassionaly very slight banding.It is fine grained material and offer high resistance to crushing and abrasion.These materials are very difficult to reduce even in blast furnace.
• Soft ore : These can be massive but the crystals are loosely knit to eachother.These are more porous and can be fines while crushing.
• Powdery ores :  It must be agglomerared before charging for reduction

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In order to obtain good reduced iron  the ore should have following properties;

• Physical;
  • A closed size range with minimum of fines.
  • An ability to withstand the physical stresses incurred on being transported to the kiln, charged to hoppers etc.
  • Non – decrepitating nature.
  • An ability to withstand mildly reducing conditions at lower temperature without breaking.
  • A good bulk  reducibility so as to obtain closely equilibrium conditions between solid and gas phase in the stack.
  • Low swelling tendency during reduction.
  • A high softening temperature with a narrow temperature range of fusion.
• Chemical :
• A high percentage of iron and low percentage of gangue materials.
• A low percentage of silica and alumina etc and a low alumina/silica ratio.
• Proper overall chemistry of the budern to ensure proper reduction.