Optimizing Iron Ore Processing: The Key Role of Flotation Techniques

In the vast system of the iron and steel industry, iron ore, as a key raw material, directly affects the performance and quality of steel products. In nature, there are a wide variety of iron ores with different characteristics, and the flotation process has become a powerful means to achieve efficient separation.

Magnetite, with the main component of Fe₃O₄, has an inverse spinel crystal structure. Due to its structural characteristics, it has strong magnetism and often coexists with hematite and other minerals, resulting in a complex ore structure. For magnetite, common flotation methods include reverse flotation and magnetic - flotation combined processes. In reverse flotation, cationic collectors (such as amines) are used to make gangue minerals (such as quartz) hydrophobic on the surface and float, while magnetite remains in the pulp to achieve separation. The magnetic - flotation combined process first enriches magnetite by magnetic separation to obtain magnetic concentrate and tailings. The magnetic concentrate is reground to improve the degree of monomer dissociation, and then flotation is used to remove the remaining gangue. If there are residual iron minerals in the tailings, appropriate flotation methods can also be selected for re - separation according to their characteristics to improve the iron recovery rate. This process is suitable for magnetite ores with uneven dissemination particle size and diverse gangue minerals.

Hematite, with the main component of Fe₂O₃, has various crystal structures, and the common corundum - type structure belongs to weakly magnetic minerals. Its aggregate forms are rich, and the embedding relationship with gangue minerals is complex, making flotation separation difficult. Positive flotation and reverse flotation are commonly used. In positive flotation, regulators are added to adjust the pH value of the pulp, which is conducive to the flotation of hematite. The collector chemically adsorbs with the iron ions on the surface of hematite to make it hydrophobic. With the help of a foaming agent, bubbles are generated, and hematite adheres to the bubbles and floats to form iron concentrate, while the gangue remains in the pulp. However, this process is sensitive to impurities such as calcium and magnesium ions in the pulp and requires pretreatment. In reverse flotation, an anionic collector (such as sodium dodecyl sulfate) is used. Under appropriate pH conditions, the collector adsorbs on the gangue minerals to make them hydrophobic and float, while hematite remains. However, it has strict requirements for the selectivity and dosage of the collector and the particle size composition of the pulp.

Limonite is a mixture of hydrated iron oxides. Its chemical composition can be expressed as mFe₂O₃·nH₂O. It has poor crystallization, a colloidal structure, no or weak magnetism, contains many clay minerals and impurities, and is prone to slime during grinding, affecting flotation. Its iron grade fluctuates greatly, and it is difficult to separate from gangue. The commonly used methods are dispersion flotation and magnetization roasting - flotation. In dispersion flotation, a dispersant (such as sodium hexametaphosphate) is added to reduce the interference of slime, and then regulators and collectors are added to achieve separation from gangue. This process has high requirements for flotation equipment. Magnetization roasting - flotation is to roast limonite into magnetite or martite with strong magnetism. Magnetic separation is used for preliminary enrichment, and then the magnetic concentrate is further purified by flotation. This process has high energy consumption, high requirements for equipment and process control, and environmental protection issues need to be paid attention to.

Siderite, with the main component of FeCO₃, has a trigonal crystal system and a stable structure. It has almost no magnetism and is easily decomposed into limonite under oxidation, often coexisting with it. Its iron grade is low, and its surface properties are similar to those of gangue minerals during flotation, making separation difficult. Activation flotation and combined flotation are commonly used. In activation flotation, activators such as copper sulfate are added to change the surface properties of siderite, which is conducive to the adsorption of collectors. Then collectors and foaming agents are added to achieve separation. For combined flotation, in view of the fact that siderite often coexists with limonite and the complex nature of the ore, a variety of flotation methods are combined. For example, dispersion flotation is first used to remove slime, then activation flotation is used to recover siderite, and finally the tailings are re - separated.