1. Ore Crushing:
Ore comes from mines in lumps up to 1 m. across. The lumps are reduced in size in several stages:
Primary crushing: – Here they break down to 100-200 mm.
Secondary crushing: – Here they break down to10- 50 mm.
Fine crushing :- :- Here they break down to, to 2- 20 mm or , and finally
Grinding :- (if necessary), down to 0.05 mm.
Every size of crushing follows by screening of the comminuted material size fractions on a series of screens. The simplest of them is the Bar Screen. Its grate, made of parallel steel bars spaced to pass the undesired size, makes an angle of 35- 450 with the horizontal. As the rock feed slides down the screen by gravity the fines fall through the openings.
3. Ore Dressing:
In order to increase the iron content of an ore, it undergoes dressing to remove some of the waste component, called tailing. The efficiency of a dressing is assessed either by a concentrate (remaining valuable portion) yield, or by the degree of iron extraction.
The concentrate yield is
= (O- T)/ (C-T) * 100%
Some the usual methods of dressing are:
Ore and concentrate blending.
4. Agglomeration of iron ores:
Dressing produces a fine grained iron-ore concentrate which can’t be used in the blast furnace. The fine powder should be converted to a lumpy material. The most popular agglomeration process is sintering. Sintering process consists of:
A. Preparatory Stage.
5. Pellet Production:
The product of palletizing process goes both to the blast furnaces and direct iron making by reducing pellets with gas. This method came into existence as sintering of finely comminuted concentrates would not be economically feasible as the sintering machines would drop their output and the quality of sinter would be poor.