The current international situation makes more and more people focus on iron ore. The common iron ores include magnetite, hematite, limonite and siderite. Among them, as typical refractory iron ore, limonite has the characteristics of easy-to-sliming, poor separation index, etc, but it still is a favorable backing to solve the shortage of iron mineral resources due to its abundant reserves. The common process used in the extraction of iron from limonite mainly includes a single separation process and joint separation process.
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The common single separation processes used in the extraction of iron from limonite mainly include the gravity separation process, magnetic separation process and flotation process (positive flotation process and reverse flotation process).
The gravity separation is to extract the iron from limonite based on gravity. As the main process used in the extraction of iron from limonite, the gravity separation process is often used to deal with coarse grain ore in most cases.
In order to further improve the concentrate quality, most limonite concentrators usually use the washing-gravity separation process for the extraction of iron from limonite. That is, use the cylindrical screen washer, groove ore washer and scrubbing machine to wash the ore, then use the dense media separator, jigging and other gravity separators, which is mostly used for extraction of iron from limonite and pseudohematite. The process has the advantages of simple gravity separator, low cost and less power consumption, while it also the disadvantages of low recovery rate and high tailings grade, which is not conducive to the comprehensive recovery of resources.
Limonite stone containing the iron, so they are magnetic. The different iron content in the limonite also makes their magnetism different. Therefore, we can make use of the magnetic differences to the extraction of iron from limonite. Generally, the strong magnetic separation process is often used for the extraction of iron from limonite, but the recovery rate of this process is poor for the fine-grained limonite (-20 um).
The single flotation process has a good recovery effect for fine iron ore, but the flotation effect is seriously affected because limonite is easy to be sliming. So, it is very important to consider desliming or strengthening dispersed slime before flotation. Because the fine particle size is difficult to adhere to the bubble surface, a separate mineralized foam layer emerges, and easy to adhere to the coarse surface. When gangue mud was attached to the surface of coarse limonite, its selectivity and floatability decreased significantly. Slime than the surface and surface energy (activity) are large, one is adsorption (consumption) a large number of flotation agents, resulting in slurry oil drugs, viscous, reduce the selectivity and flotability of floating ore; The second is the strong hydration ability, once the slime adheres to the bubble, the hydration film on the bubble surface is not easy to remove, thus bringing serious difficulties to the concentration and filtration of the concentrate, resulting in the decrease of recovery rate.
The flotation process used in the extraction of iron from limonite can adopt positive flotation or reverse flotation process. Research and practice show that the reverse flotation is more suitable for the removal of quality and impurity of limonite. In addition, the limonite has the loose crystal particle and large specific surface area, which can absorb and consume a lot of flotation reagents, so the flotation process used in the extraction of iron from limonite need to adopt multistage dosing and multistage separation flow.
General, the extraction of iron from limonite can adopt gravity separation-strong magnetic separation process to obtain the good effect, that is, the limonite is sent to washing after the fine crushing or rod mill, then sent to screening, classifying and desliming process, the coarse grain is processed by gravity separation process to obtain concentrate, the intermediate grade adopts roller-type magnetic separator to obtain concentrate, the fine grain and slime adopt the high gradient magnetic separator to obtain concentrate.
In order to improve the recovery rate of iron metal, regrinding and reprocessing can be considered during the gravity separation process, which can obviously improve the iron grade of the concentrate, and obtain the high recovery rate because the iron ore in the fine grain and sludge is also recovered.
When the grinding fineness reaches a certain value, adding the sodium carbonate and sodium silicate in the grinding process, making the pulp achieve the good dispersion, so adopting the selective flocculation process can make the limonite flocculate selectively. But sometimes a single flocculation process is still difficult to improve the grade of limonite concentrate because a large number of coarse-grain of gangue minerals are failed to remove. Therefore, the selective flocculation-flotation process can obtain a better mineral processing index.
For low-grade and fine-grain embedded limonite, only the fine grinding can obtain the high-grade iron concentrate, but sliming phenomenon also occurs at the same time, resulting in a low recovery rate. In this case, adopting the flocculation-strong magnetic separation process can deal with the low-grade and fine-grain embedded limonite.
It is shown that the flocculation-strong magnetic separation process improves the iron recovery by 10.97-15.73% compared with the direct magnetic separation process under a similar grade of iron concentrate. The fine iron ore that lost in the strong magnetic separation process is recovered by selective flocculation because its apparent size is increased. Therefore, the flocculation-strong magnetic separation process can be used for fine-grade limonite, but it is important to control the slurry dispersion, selective flocculation process and separation conditions of the strong magnetic separator (mainly the feeding way and the volume of flushing water).
The limonite has the special output structure, and it is easy to produce mud in the grinding process, which leads to the difficulty in the extraction of iron from limonite, and the gangue mineral composition of limonite varies greatly. In view of the particularity of limonite, the composition types of main iron ore and gangue minerals in limonite shall be determined through ore dressing test, and the suitable processes used in the extraction of iron from limonite shall be formulated accordingly.