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In the processing of steel smelting, the main harmful elements are phosphorus and sulfur. The phosphorus and sulfur in ores enter sinter and pig iron in sintering and blast furnace smelting process, which influences the quality of pig iron product. If the content of phosphorus and sulfur is over a certain amount, the mechanical behavior of pig product would be influenced. Therefore, phosphorus and sulfur need to be removed in iron ore processing stage.
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The grinding fineness has a large influence on pyrite-bearing iron ore benefication. Different grinding fineness inflluences the dissociation degree of mineral monomer and washability. When the inlaid granularity of iron is fine, fine grinding is needed to reach the dissociation degree of iron monomer. Therefore, fine inlay single iron ore with fine particle size and sulfur-containing type, such as iron pyrite and pyrrhotite, usually applies stage grinding – stage processing technology to reach the aim of reducing sulfur content.
At present, there are a large amount of pyrrhotite and iron pyrite in selected magnetite. Magnetic agglomeration easily happens during processing, which causes serious negative impact. Single magnetic process is hard to obtain high grade concentrates. If the magnetic separation and verse flotation are combined to separate iron minerals, complementary advantages in the process of magnetite ore separation is achieved. It is also advantage for improving concentrate grade. Besides, weak magnetic separation – verse flotation – weak magnetic sepration combined process is also under consideration. In this process, iron pyrite and gangue minerals are first removed. Then pyrrihotite are separated by verse flotation. Finally, magnetic separation guarantees the grade of iron concentrates and removes sulfur as much as possible.
This processing technology is mainly suitable for limonite, siderite and other iron ore with high burning loss. For weak magnetic iron ore with low theory grade and various types of sulfur, roasting – magnetic separation – flotation combined technology can obtain iron concentrates with low impurity content. At present, the domestic iron ore reduction roasting and magnetic separation process has high cost, and the obtained iron ore concentrate is of low grade, which has not been widely used.
Verse flotation is the main iron ore phosphorus reduction processing at present. The raw ores are grinded to 85% -44µm. Magnetic separation - verse flotation – magnetic separation can acquire high-quality iron concentrates. Because of the fine inlaid granularity of phosphorus minerals in iron ore, fine grinding must be carried out to realize full monomer dissociation, which increases the cost of ball mill. It also has the problems in product settlement and concentrating. Part of phosphorus element exists as cellophane. It is hard to reach ideal processing indexes. Phosphorus minerals and iron minerals have the same floatability, and the recovery rate of iron is reduced during the process of phosphorus removal.
Acid leaching is also to reduce phosphorus. Preconcentration is usually used to improve iron grade, reduce phosphorus content and acid consumption. The acid leaching process includes direct acid leaching, degumming acid leaching, roasting-acid leaching, and chlorinating roasting-acid leaching. The method used depends on the nature of the mineral. Hydrochloric acid, nitric acid, and sulfuric acid leaching can obtain iron concentrates with qualified phosphorus content, but the price of nitric acid is relatively high, so hydrochloric acid and sulfuric acid are often used as leaching agents.
Compared with verse flotation, this technology has a better effort in reducing phosphorus and less iron loss in leaching. Although fine grinding is unnecessary in this technology, part of iron minerals dissolve, reducing iron recovery rate. The MgO and CaO content reduces after leaching in iron concentrates, which reduces the alkalinity of concentrates. As a result, the self-fusion of concentrate products is destroyed, which increases the cost of smelting.At the same time, a large amount of acid needs to be added during the leaching process, which causes great environmental pollution.
The above are the common iron desulfurization and phosphorus reduction process. In actual production, the specific processing technology flow is depending on various factors such as the nature of its own ore, processing plant conditions, investment budget, etc. We suggest to choose iron ore processing flow and customize iron ore processing equipment according to mineral processing experiment.