Solutions

The main component of bauxite is Al₂O₃, containing a small amount of Fe₂O₃, SiO₂, and other impurities. The main objective of bauxite beneficiation is to lower the concentration of reactive silica, and also to increase the alumina content. In addition, bauxite beneficiation can also be used for iron extraction or iron removal.
Silicon is a harmful substance in the alumina production process.If the content of silicon in bauxite is too high, a large amount of red mud will be formed. The accumulation of red mud will not only cause environmental pollution but also damage the bauxite processing machines. What's more, in the process of producing alumina by the Bayer process, silica will waste extra alkaline solution, which increases production costs.

Bauxite beneficiation technology

Ore washing for bauxite

Generally, the gibbsite type and diaspore type bauxite with more mud and lower grade are washed to obtain the raw material for alumina production.
At present, for easy-washing bauxite ore, the two-stage ore washing process using cylinder washing machine (also referred to as drum washer) and trough washing machine is applied. For difficult-to-wash ore, a three-stage ore washing process using cylinder washing machine, trough washing machine and linear vibrating screen is adopted.
Ore washing is the simplest and most effective method to improve the bauxite aluminum-silicon ratio. Generally, the aluminum-silicon ratio of bauxite can be doubled through ore-washing, which is more effective for the sorting of loose-textured ore.

Flotation for bauxite

The bauxite deposits in different regions are slightly different.Kaolinite in the Bayer Process is known as reactive silica. Data shows that it increases the consumption of NaOH and energy in the digestion stage without resulting in alumina formation. So the bauxite must be pre-desiliconized.

Magnetic separation for bauxite

Beneficiation by magnetic elimination of iron is practiced on a limited scale, primarily on ore consumed in abrasive and refractory industries. The bauxite is usually dried or calcined before magnetic separation because the heating converts siderite (FeCO₃) to magnetite (Fe₃O₄), leaves pyrite (FeS₂) as a magnetic residue, and makes hematite (Fe₂O₃) and other magnetic minerals strongly magnetic. Then use a magnetic separator to separate the magnetic material.
The magnetic roasting method uses reducing gas or coal as a reducing agent to reduce the iron minerals in bauxite to strong magnetic magnetite. Then the magnetite is separated to obtain iron concentrate and high-grade aluminum concentrate.

Chemical beneficiation for bauxite

At present, the production of alumina from bauxite mainly adopts chemical beneficiation technology, and there are three methods: alkali method, acid method and electrothermal method.
The acid method and the electrothermal method are still seldom used in industry, and the alkaline method is currently the main method for producing alumina. Alkali method can be divided into Bayer process, lime sinter process and combined Bayer Process and bauxite calcination method.
In general, the beneficiation methods of bauxite are complicated, and the corresponding beneficiation process should be selected according to the type and characteristics of the ore during the beneficiation process.