Ball mills play a crucial role in grinding small iron ore chunks into fine particles, with the typical requirement for the particle size of ground ore being 60% to 95% at -200 mesh. The selection of ball mill types varies significantly based on different product granularities. This article analyzes the selection of iron ore ball mills for four different types of ores: hematite, magnetite, limonite, and siderite.
Hematite is an iron oxide with an iron content of around 70%. It generally has a hardness of 5 to 6 and appears in red to light gray, sometimes black or streaked with dark red. For this type of iron ore, a grid-type ball mill is commonly chosen as the first-stage grinding mill, followed by an overflow ball mill as the second-stage grinding mill in the beneficiation process.
Magnetite is also an iron oxide ore with an iron content of around 72%. It has a black-gray appearance with metallic luster and black streaks, commonly known as "magnetic ore." Magnetite is generally hard. In beneficiation plants, depending on the nature of magnetite ore and the processing scale, an energy-saving grid ball mill is usually used for the first-stage grinding to achieve a fineness of -200 mesh accounting for 67%. This is complemented by a spiral classifier to form a grinding and classification system. The second-stage grinding employs a cone overflow ball mill, combined with a hydrocyclone, to constitute a grinding and classification system. Fine screening is employed to strictly control the classification granularity.
Limonite is a hydrated iron oxide, and it collectively refers to two different structured ores: goethite and lepidocrocite. Its iron content ranges from 37% to 55%, and some limonite ores contain high phosphorus, making separation challenging. For such ores, a three-stage grinding process is often employed. The first stage uses a grid ball mill with a grinding fineness of -200 mesh accounting for 60%, while the second and third stages use overflow ball mills with grinding granularities of 87% at 200 mesh and 95% at 325 mesh, respectively.
Siderite's main component is ferrous carbonate, with an iron content generally around 48.2%. Its color is usually gray-white or yellow-white and can turn brown or brown-black after weathering. It is a hard and dense siderite. This type of iron ore often adopts a stage grinding and stage magnetic separation process. The first stage uses a grid ball mill, the second stage uses an energy-saving overflow ball mill, and the third stage can use either an overflow ball mill or a cone overflow ball mill, depending on the nature of the siderite ore and the grinding granularity requirements.
Regardless of the type of iron ore, careful consideration of the specifications and models of ball mills is crucial. Choosing the appropriate mill type can enhance the efficiency of iron ore beneficiation plants, promoting improvements in ore recovery rates and concentrate grades.
