In the production, the methods used for the extraction of iron from hematite are not single, mainly include the froth flotation method, magnetic separation method, gravity separation method and roasting magnetic separation method.
The froth flotation method is mainly used for the extraction of hematite with fine and micro-fine weak magnetic ore, including positive flotation method (positive flotation of anionic collector) and reverse flotation method (negative flotation of cationic collector).
• Positive flotation method
Hematite positive flotation method is a method used for the extraction of iron from hematite, which uses anionic collectors to float iron ore from raw ore. It can achieve discarding tailings under the coarse particles without desliming.
Hematite positive flotation method is featured with a simple dosage, low processing cost, which is especially suitable for the extraction of iron from single hematite. However, the qualified hematite concentrate can only be obtained after many times of cleaning, and the foam is easy to be sticky, so the product is not easy to be concentrated and filtered.
• Reverse flotation method
Hematite reverse flotation method is a method used for the extraction of iron from hematite, which uses ionic or cationic collectors to float gangue minerals from raw ore.
The anionic collector reverse flotation method is mostly used when the pH value is 8-9. It is used to treat quartz-containing gangue minerals. After activated by calcium ions, collector of fatty acid is used to reverse flotation for obtaining hematite concentrate.
The cationic collector reverse flotation method usually adopts a mine collector as the flotation reagent, which is suitable for the flotation of quartz gangue. Ether amine is the first choice as the amine collector, followed by the fatty amine. The inhibitor of iron ore uses the sodium silicate, tannin and sodium lignosulfonate, and their inhibitory effect is the best when the pH value is 8-9.
In terms of the ore properties of hematite ore, the reverse flotation method is more advantageous as the method used for the extraction of iron from hematite than the positive flotation method. Because the collecting object of the reverse flotation method is gangue, while the collecting object of the positive flotation method is iron ore. Therefore, it is difficult to obtain high-quality hematite concentrate for gangue minerals with serious inclusions.
Hematite magnetic separation method mostly adopts a weak-strong magnetic separation method, which is used for the extraction of iron from hematite-magnetite mixed ore. Tailings of low-intensity magnetic separation are sent to strong magnetic roughing and scavenging after thickening, and the strong magnetic roughing concentrate is concentrated and selected by the strong magnetic separator after the thickening. The amount of strong magnetic minerals is easy to lead to the blockage of strong magnetic separation. So when the strong magnetic separation method is adopted, the weak magnetic separation operation is usually added before the strong magnetic separation operation to remove or separate the strong magnetic minerals in the ore.
In addition, the magnetic separation method can also adopt the strong magnetic-flotation method for the extraction of iron from hematite. The monomer quartz and clay chlorite and other gangue minerals in the ore are discharged under the rough grinding condition by strong magnetic separation, and the rough magnetic separation concentrate is sent to the flotation method after the fine grinding for producing the qualified hematite concentrate.
Hematite gravity separation method mainly includes coarse grain gravity separation method and fine grain gravity separation method:
• Coarse grain gravity separation method is used to treat the deposit with high geological grade (about 50%), but the ore body with thin or multiple layers. For this kind of ore, only crushing without grinding can be adopted. In the case of coarser grain size, adopting the gravity separation method to discard the coarse tailings to restore the geological grade.
• Fine-grain gravity separation method is mostly used to treat hematite with fine grain size and high magnetic content. After crushing and grinding, the mineral is in monomer separation, and then fine and high-grade concentrate can be obtained by the gravity separation method.
For most of the weak magnetic iron ore, the grade of strong magnetic concentrate is not high, and the unit processing capacity of gravity separation method is low, so the combined process of strong magnetic separation-heavy separation is often used for the extraction of iron from haematite, that is, firstly adopting the strong magnetic separation method to discard a large number of unqualified tailings, and then using the gravity separation method to treat the strong magnetic concentrate, which can improve the concentrate grade.
When the mineral composition is complex and adopting other mineral processing methods are difficult to obtain a good separation index, the roasting magnetic separation method is often used for the extraction of iron from hematite.
Roasting magnetic separation method means to carry on magnetizing roasting, so that the hematite or pseudomorphic hematite are transferred to magnetite, and then adopting the weak magnetic separator for the extraction of iron from hematite.
In order to further improve the grade of hematite concentrate, fine screen used for regrinding and re-separation (which can improve the concentrate grade to more than 65%)- regrinding and reverse flotation method (which can improve the concentrate grade to 66%) is often adopted to treat the hematite concentrate separated by magnetic separation method.
The above mentioned are the common methods used for the extraction of iron from hematite. It is recommended that the most suitable mineral processing method shall be adopted through the mineral processing test.
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