A gas–solid fluidized bed using magnetite particles is an effective methodology for coal beneficiation in the field of dry coal cleaning. Broadening the size range of magnetite used in the bed decreases medium preparation cost.
The dense medium separation process used in most coal washing and magnetic separation plants requires a suspension of finely milled magnetite in water. Magnetite for coal washing must be of overall high purity and be devoid of contaminants, such as hematite, sulphides or other minerals.
Abstract Although most of the magnetite used in dense-medium coal beneficiation can be recovered by magnetic separation, there are small but significant losses. The magnetite losses can be attributed to removal in the wash wastes or uptake into fractures of the coal particles.
According to Mikhail and Osborne (1990), the following is the standard particle-size distribution of magnetite used in coal preparation: maximum 5% by mass coarser than 45 μm, and 30% by mass finer than 10 μm. View chapter Purchase book
Density separation processes employed in coal preparation are typically performed in a medium suspension of fine ground (− 45 μm) magnetite (Fe 3 O 4) dispersed in water. Magnetite is added to the suspension to maintain the desired medium density.
Magnetite for coal washing must be of overall high purity and be devoid of contaminants, such as hematite, sulphides or other minerals. Magnetite is reasonably durable (and therefore does not readily break down), and is chemically stable during coal washing and magnetic separation.
Magnetite could be lost in multiple stages of the coal beneficiation process. The drain-and-rinse screens, for example, are trying to wash as much magnetite off the clean coal as possible. If they do not have enough water, however, the magnetite could be lost to the clean coal stream.