4. Dry ultrafine comminution

The definition of fineness of grind varies with the use of the ground product. For some industries, a d ₈₀ of 20 µm is considered finely ground, for others it is considered ultra-fine. For high-tech applications, a d ₈₀ of 4 µm is required (mineral filler industry, ceramics, cosmetics, pharmaceuticals, etc.). In all these cases, energy expenditure is extremely high: to grind minerals to finenesses where the d ₉₈ is less than 3 µm, 2,000 to 3,000 kWh/t must be consumed. Ultra-fine grinding is generally carried out dry, either because the materials being processed fear water, or because liquid-solid separation is virtually impossible. These grinding techniques require the grinding unit to be coupled to a pneumatic selector, to extract sufficiently fine...