Understanding Chrome Ore Beneficiation Basics

Chrome is an important element of stainless steel and an indispensable raw material for industrial production. Chrome ore beneficiation technology is closely related to the physical and chemical properties of chromium ore. This article will introduce you the types of chrome ore, its resource distribution, beneficiation process and equipments, and industrial use. Let's dive right in now!

01Common types of chrome ore

1. Magnesium chromite (Cr2O3 50%-65%)

2. Aluminum chromite (Cr2O3 35%-55%)

3. Chromium-rich spinel (Cr2O3 35%-50%)

4. Chromite (Cr2O3 47%-60%)

The selectivity of chromite ore mainly depends on the grade, purity, disseminated particle size, composition and quantity of symbiotic gangue minerals of chromite ore. Chromite has high density and weak magnetic properties.

The platinum group, cobalt, titanium, vanadium, nickel and other elements are often associated with chromium deposits. When the platinum content is greater than 0.2-0.4g/t, the cobalt content is greater than 0.02%, and the nickel content is greater than 0.2%, comprehensive recovery should be considered. The associated platinum group elements in chromite ore, such as sulfide, arsenide or sulfur arsenide, can be recovered by flotation method.

The olivine and serpentine in the ore can be comprehensively recycled for use in the production of refractory materials, calcium magnesium phosphate fertilizer or diabase cast stone. Amorphous magnesite is sometimes found in the shallow part of the ultrabasic rock mass, which is also a good raw material for refractory materials.

02Distribution of chrome ore resources

The world is rich in chromium ore resources, with proven reserves of approximately 510 million tons. The world's chromium ore resources exceed 12 billion tons of shipping grade, enough to meet the demands of centuries. The distribution of chromium ore in the world is extremely uneven, with a high geographical concentration in Kazakhstan and South Africa.

South Africa is the country with the richest chromium ore resources in the world. The identified chromium ore resources amount to 8.6 billion tons, accounting for 74.8% of the total global resources. The Bushveld Complex in northeastern South Africa is the world’s largest source of chromium ore. Chrome ore resources are shallowly buried and of good quality.

Global chromium ore reserves in 2020 is 570.000 kilotons, Kazakhstan has 230.000 kilotons (40.35%), South Africa has 200.000 kilotons (35.09%), India has 100.000 kilotons (17.54%), Turkey has 26.000 kilotons (4.56%), Finland has 13.000 kilotons Tons (2.28%). Global chrome ore production in 2020 is 40.000 kilotons, Kazakhstan has 6.700 kilotons (16.75%), South Africa has 16.000 kilotons (40%), India has 4.000 kilotons (10%), Turkey has 6.300 kilotons (15.75%), Finland has 2.400 kilotons (6%).

Chromium is an important element of stainless steel, and stainless steel generally contains 10%-30% of chromium. Chrome ore is usually processed into ferrochrome, and more than 90% is used in the production of stainless steel. China has a huge demand for chrome ore. However, China's chromium ore resources are scarce and almost entirely dependent on import. China is a major chromium consumer and also a leading producer of stainless steel and ferrochrome.

03Benefication process and equipments

Chrome ore beneficiation generally has three processing methods: gravity separation, magnetic separation and flotation.

1. Gravity separation

The advantage of gravity separation lies in its wide range of ore particle sizes. It can separate coarse and large ore that cannot be processed by other methods. Generally speaking, gravity separation equipment is relatively simple in structure, easy to manufacture, does not require chemicals in production, and has little environmental pollution.

Equipments:

(1) Jig machine

It belongs to deep trough sorting, the processing particle size range is generally 35-0.1mm, the equipment has large processing capacity, simple operation and wide application. It is suitable for processing coarse-grained minerals with uneven inlays, and the final product can be obtained in a single separation.

(2) Spiral chute

It belongs to the slant flow sorting, the processing particle size range is generally 2-0.03mm, with large processing capacity, simple operation, wide application. The slurry is in a long spiral chute, and the inertial centrifugal force generated by the slurry in the rotary motion is used to promote the zoning of light and heavy minerals on the chute. The light minerals are thrown to the outside and the heavy minerals are on the inside, then continuously producing and discharging minerals. It is generally used as rough separation because of low concentration ratio, and the final concentrate product is obtained by combining with shaking table.

(3) Shaking table

Shaking table is used for separating fine-grained ore, and the processing particle size range is generally 3-0.019mm. The separating is realized by the combined action of the longitudinal and lateral water flow on the bed surface.

It is generally used as a beneficiation equipment with a high enrichment ratio to directly obtain the final concentrate. But shaking table has a small processing capacity and low efficiency, which requires a large number of unit and area.

In actual application, in order to improve the separation effeciency, the materials are generally divided into several different sizes for separating.

2. Magnetic separation

Weak, mediu, and strong magnetic separation are all used in chromite.

Weak magnetic separation can remove magnetite, increase the chromium-iron ratio of the concentrate, and further enrich qualified chromite concentrate products. It is of great significance especially for the unqualified chromite concentrate containing a small amount of magnetite after gravity separation.

Chromite has weak magnetic properties, which can use strong magnetic separation. In the beneficiation of chromite ore, a medium magnetic machine is used to remove magnetite first, and then a strong magnetic machine is used to recover chromite and separate gangue minerals, which especially suitable for fine-grained minerals.

Equipments:

(1) Permanent magnet drum type magnetic separator

Permanent magnet drum type magnetic separator can be used for pre-selection, rough selection, beneficiation, etc. The selected particle size range is 2~10mm. Permanent magnet drum type magnetic separators can be divided into three types: downstream type, counter-current type and semi-counter-current type according to the structure of the bottom of the box. It is mainly different from the direction of slurry feeding and cylinder turning.

(2) High gradient strong magnetic separator

High gradient magnetic separator equipment is suitable for the separation of weak magnetic minerals and the iron removal and enrichment of non-metallic minerals. The high-gradient magnetic separator adopts the rotating ring vertical rotation, recoil concentrate, and is equipped with a high-frequency vibration mechanism, which fundamentally solves the problem that the magnetic medium of the flat-ring high-gradient magnetic separator is easy to block.

3. Flotation separation

The flotation process is mainly used to process micro fine-grained chromite, which requires the use of flotation cell and the addition of flotation reagents. The process is complicated, the power consumption and the reagents cost are high. Generally, it is considered when the reselection and strong magnetic separation treatment are not performed well.

Equipments:

(1) Agitation tank

The agitation tank is mainly used for agitating the slurry before the flotation operation, forcing the slurry to circulate up and down in the tank, so that the reagent and the slurry are fully mixed.

(2) Flotation cell

In the flotation machine, the slurry treated by adding reagents，then was agitated and aerated, so that some of the mineral particles are selectively fixed on the bubbles; it floats to the surface of the slurry and is scraped out to form a foam product, and the rest is retained in the slurry. In this way, we can get the minerals we want to separate. There are three main types of flotation machines：air inflation agitation flotation cell, mechanical agitation flotation cell and air inflation  flotation machine.

04Industrial uses of chrome ore

In metallurgical industry

Chromite is mainly used to produce ferrochrome and metallic chromium. Ferrochrome are used as steel additives to produce a variety of special steels with high strength, corrosion resistance, wear resistance, high temperature resistance and oxidation resistance. Metal chromium is mainly used to smelt special alloys with cobalt, nickel, tungsten and other elements. These special steels and special alloys are widely used in aviation, aerospace, automobiles, shipbuilding, and the defense industry to produce guns, missiles, rockets, and ships.

In refractory materials

Chromite is used to make chrome bricks, chrome magnesia bricks and other special refractory materials.

In chemical industry

It is mainly used to produce sodium dichromate, and then to produce other chromium compounds, which are used in industries such as pigments, textiles, electroplating, and leather making, as well as catalysts and activator.

As the main raw material of stainless steel, the price of ferrochrome is closely related to the price of stainless steel, and the two have basically been synchronized since 2011. Relevant data shows that the global economic recovery in 2021 will effectively promote the recovery of stainless steel and chromium salt consumption, and the growth in demand for chromium can be expected, which will eventually be transmitted to upstream mines and drive the price of chromium ore to gradually increase.

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