densemedium

Dense medium refers to a separation technique used in mineral processing and coal preparation in which a suspension with a tunable density is used as the separating medium. In dense medium separation (DMS), particles are divided by density: minerals denser than the medium sink, while lighter ones float. The medium is typically a slurry of dense solids, most commonly magnetite or ferrosilicon in water, whose concentration is adjusted to achieve the desired specific gravity.

Common dense media are magnetite-based slurries or ferrosilicon suspensions. The specific gravity of the medium can be set to suit the target separation, often in the range of about 1.5 to 3.0, depending on the material and the size of the particles. The medium is circulated, and both the product and waste streams are separated by density. The medium is recovered and recycled, with magnetic separation often used to reclaim magnetite from tailings.

Applications include coal cleaning to reduce ash content, iron ore and other metal ores to separate valuable minerals from gangue, and the processing of heavy mineral sands and diamonds. Dense medium separation is valued for its chemical-free nature and suitability for a variety of particle sizes; it can be more energy-efficient for certain separations compared with alternative processes.

Limitations include sensitivity to particle size and distribution, the need for careful density control, and the costs associated with medium preparation, handling, and recovery. Environmental and operational considerations include medium loss, wear, and the need for water treatment and recycling systems. Equipment commonly used comprises dense medium separators, dense medium cyclones, and magnetic separators to recover the medium.