Extraction Of Ferrochrome
Ferro chrome is the ferro alloy of iron and chromium. It is extracted from chromite. The chromite ore is crushed and cleaned properly.
It is beneficiated and gangue minerals are separated. The ore concentrate is put in a submerged electric arc furnace. Coke and limestone is added to the ore. The current is switched on
and heating of ore concentrate is started. The coke is heated to produce carbon monoxide. Carbon monoxide reacts with the chromite ore concentrate and reduces the ore. Oxygen is separated and converted into carbon dioxide. Carbon dioxide and carbon monoxide goes into the air. In some cases, it may be cleaned and may be reused as reduction gas. Due to the increase of heat, melting of chromite concentrate takes place. Oxygen is supplied to the molten bath for refining of the ferrochrome. The presence of limestone as flux helps in development of slag with silicon and other impurities. After the formation of the slag, the slag is removed through an opening. The remaining molten ferroalloy is checked for the presence of carbon. If high carbon ferrochrome is required, some amount of powdered coke is injected into it. Thus, carbon goes into ferroalloy. After completion of the melting and refining, the ferrochrome is separated and poured into castings. In case of removal of excess carbon, oxygen supply is increased and the composition of molten ferro chrome is adjusted accordingly.
The grade of ferro chrome is fixed according to the variation of carbon unit.
GRADES OF FERROCHROME
| High Carbon | |
|---|
| Carbon | 7% maximum |
| Silicon | 3% maximum |
| Chromium | 58%-65% |
| Low Carbon | | | |
|---|
| Category1 | Category2 | Category3 | |
| Carbon | up to 0.75% maximum | up to 0.5% | 0.01 to 0.02% |
| Silicon | 2% maximum | 5% maximum | 5% maximum |
| Chromium | 67%-73% | 64%-68% | 64%-68% |
Chromite ore is also grouped into three groups as high chromium, high iron and high aluminium ore.
| High chromium | Cr2O3 |
| High iron | Cr2O3 |
| High aluminium | Cr2O3 |
| Al2O3 |