Iron ore beneficiation is a multi-stage process in which pig iron ore is purified prior to the smelting process, which involves melting the ore to remove the metal content. The iron ore beneficiation process has two complementary objectives that define the methods used to refine it. The iron content in the ore needs to be increased, and the gangue, which is a mineral of lower value as a natural rock and ore itself, must be separated. Methods such as screening, crushing and grinding of iron ore are commonly used in various ways to purify iron ore, as well as several stages of magnetic separation.
The iron ore industry classifies materials based on the concentration of metals present after iron ore beneficiation is completed. High-grade iron ore must have an iron concentration of 65% or higher, and medium-grade iron ore must have an iron concentration of 62% to 65%. Low-grade iron ores include all mixtures with an iron concentration below 62% and are not considered a type of ore useful in metallurgy.
Several different types of natural iron ore exist, but the two most common types used in metal refining are hematite, FeO, which is typically 70% iron, and magnetite, FeO, which is 72 % of iron. Low-grade iron ores also exist, such as limonite, which is hematite bound to water molecules and has an iron content of 50 to 66%, and siderite FeCO 3, which has an iron content of 48%.
One of the methods of iron ore beneficiation first involves basic screening or filtering of the ore and then crushing it using equipment such as jaw crushers, which break the rock from its natural state into individual pieces with length or height dimensions. These rocks are then further crushed in intermediate and fine cone crushers or fine jaw crushers, and then enter the flotation process for separation. Separation involves using low-power magnetic fields to separate metal-rich ores from lower-grade metal particles. The low-grade ore at this time is recycled back to the rough flotation stage for further refining.
The final product produced from the crushing and magnetic separation equipment is then ground in a ball mill to a powdery consistency. The material is then further refined through iron ore beneficiation by removing the water using dewatering tanks and by applying a high-intensity magnetic field generated by a disc magnetic separator. At this stage, low-grade ore that still contains metal value is put back at the beginning of the cycle, while tailings, or even lower-grade residues, are removed as waste.
