Chromite is magnetic, its density is between 4.1~4.7g/cm3, its Mohs hardness is between 5.5~6.5, and its color varies from black to dark brown. Its main gangue minerals are talc, olivine, serpentine and pyroxene.
Chromite is insoluble in weak acids such as acetic acid, boric acid, and also in 1:1 HCl, 1:1 HNO3, 1:1 H2SO4, aqua regia and HF acid. But it is soluble in 1:1 mixed acid of phosphorus and sulfur.
When calcined at low temperature, the dehydration of chromite changes from dark brown to blue-black. At high temperatures, chromite reacts with soda ash or sodium peroxide to convert Cr3+ to Cr6+.
The general chromite mining process consists of two parts:
Chromium lump ore has to be pulverized and ground into powder due to its medium and fine dispersion.
Chromium lump ore to chromite fines
And chromite placer does not need these two steps. For example, most of the chromite in the Philippines and Vietnam is chromite sand. After desilting with water, the grade of ferrochrome sand will be greatly improved, and the use of jig and vibrating table will further improve.
The main method of chromite beneficiation is gravity separation. However, in view of the slightly different properties of chromite in the world, magnetic separation, flotation, chemical beneficiation, combined beneficiation and other methods can also be used flexibly.
Chromium Ore Gravity
The specific gravity of chromite is 4.1~4.7g/cm3, and the specific gravity of associated gangue and iron silicate minerals is generally 2.7~3.2g/cm3. Therefore, we can use the difference in specific gravity between minerals to recover chromite through gravity separation equipment such as shakers, spiral chutes, and jigs. Shakers are more popular due to their high separation accuracy.
In the chrome ore concentrator, the jig is suitable for medium and fine-grained chromite, and the vibrating table is suitable for fine chromite. In chromite gravity separation plants, the combination of clamps and shakers is more common for optimal recovery.
Two problems should be paid attention to in the treatment of low-grade chromite by gravity separation:
(1) Chromium lump ore is fragile and will produce a large amount of fine-grained chromite that is difficult to recover by gravity separation. Therefore, flotation equipment is required.
(2) Due to the huge difference in particle size of chromite, we will use multiple separators, that is, different combinations of jig, vibrating table and spiral chute, to form a chromium treatment process to achieve better recovery effect.
Magnetic separation of chromium ore
Chromium ore is weakly magnetic. Therefore, magnetic separation would be a good separation method.
Low-intensity magnetic separation: This method is used to remove magnetite, improve the Cr/Fe ratio, and select qualified chromium concentrates. This method is significant for off-spec chromium concentrate after gravity separation, as it contains a small amount of magnetite.
High-intensity magnetic separation: In high-intensity magnetic fields, chromite can be extracted from gangue material as a magnetic product. It is mainly suitable for fine-grained chromite powder that cannot be effectively recovered by gravity separation.
However, magnetic separation is rarely used alone, and is widely used in combination with re-selection.
Chromium ore flotation
Often, flotation provides an alternative technology to beneficiate fine and ultrafine chromite rocks and fine chromite tailings, which require fine grinding to release, when gravity and magnetic separation fail. But grinding produces a lot of sludge.
If a cationic collector is used to extract the chromite in the alkaline slurry, it needs to be deslimed in advance, but the fine mud removed will take away a large amount of chromite.
The use of anionic collectors in alkaline slurries can eliminate the need for pre-desliming.
Customize targeted beneficiation methods to obtain ideal beneficiation indicators
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