Selection of Raw Materials in High Carbon Ferrochrome

The raw materials for smelting high carbon ferrochrome are chrome ore, coke and silica. Among them coke and silica are used as reducing agents.

I.Chrome ore:

Principle of beneficiation: Chromium is the most widely used metal and ranks first among the “strategic metals”. Today many countries are stepping up the study of chrome ore beneficiation, the normal selection methods are as follows:

Re-selection: such as jigging, shaking table, spiral chute, heavy media cyclone, and so on.

Magnetic-election: including high-intensity field magnetic separation, high voltage election

Flotation and flocculation flotation.

Combined selection: such as re-selection – magnetic selection

Chemical beneficiation: processing of very fine-grained poor chrome ore difficult to be selected.

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In the above chrome ore beneficiation methods, the production of the main re-election method, often uses shaking table and jig separation. Sometimes re-election concentrates with weak nuisance election or strong magnetic re-election, to further improve the grade of chrome ore concentrate and chromium-iron ratio.

Principle of chrome ore matching: in the actual production of high-carbon ferrochrome often needs to choose the right type of ore matching and matching ratio. The main principles of chrome ore matching are.

The appropriate chromium-iron ratio (Cr2O3/∑FeO). Generally speaking, smelting chromium content greater than 50% of the alloy required to enter the furnace integrated ore Cr2o3 / ∑ FeO ratio greater than 2.0; and smelting chromium content greater than 60% of the alloy requires that this ratio is greater than 2.6.

The appropriate MgO/Al2O3 ratio. It not only affects the conductivity of the slag and reducing properties but also affects the alloy’s carbon disk. In actual production, the use of MgO/Al2O3, the ratio of low chrome ore needs to be matched with a sufficient amount of coke to increase the thickness of the coke layer, on the one hand, to ensure that the bottom of the furnace is not easy to damage, on the other hand, it is also to increase the unreduced ore nuclei in the coke layer of the retention time. Reduce the chromium running in the slag.

Suitable block size matching. When using powdered ore alone, it is easy to cause powdered ore sintering, which makes the material surface less permeable and seriously damages the smelting atmosphere; the use of chrome ore with a large block size is easy to increases the thickness of the refining layer, resulting in a low carbon content of the alloy.

Suitable melting performance. Simply using fusible chrome ore will cause slag too early, so that the melting speed is faster than the reduction speed, easily causing the slag to run high chromium phenomenon; Simply using refractory chrome ore will thicken the refining layer, a large number of unreduced nuclei and the alloy carbon content is low and other phenomena, the normal smelting has brought great difficulties. Reasonable matching of chrome ore so that the slag has a reasonable melting point, it is very important to improve the economic indicators.

 Reducing agent:

In alloy production, the most common and the cheapest reducing agent – metallurgical coke ‘broken pieces’ (blast furnace coke after screening under the sieve coke). Due to the quality of the coal used for coking and the different conditions of coke plant coke production, the quality of crushed coke varies. But they have a common disadvantage of low resistance, poor reactivity, high ash and sulfur and phosphorus content, as well as high moisture content, and also unstable.

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Sulfur contained in coke is mainly organic Ryukyu and a large number of sulfides, a small amount of sulfate, and a very small amount of elemental sulfur that exists in the state of solid solution in carbon. The phosphorus content of coke also varies. Coke block has spongy organization, and a large number of cracks, its porosity fluctuates in the range of 35% -55%, and the apparent density of coke is 0.8-1t/m3.

The resistance of coke briquettes with a block size of 25-40 mm is 10-15% lower than that of coke grains (10-25 mm). It is very important that the amount of powder produced in the crushing of coke for the production of ferroalloys should be as small as possible, and that the ash composition should be as favorable as possible to the variety of ferroalloys to be refined.

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