size

To size material is to separate it into fractions based on particle diameter, using mechanical sieving or screening. In mining and ore processing, this is one of the most fundamental operations, performed after crushing or grinding and before concentration or smelting. A load of run-of-mine ore or crushed rock goes across a vibrating screen deck or into a set of nested sieves; finer particles fall through, coarser ones travel across and over the edge. The result is sorted material: oversize (rejection or recycling), target-size (feed to the next process), and undersize (often slimes or waste to tailings).

Sizing is distinct from other separation methods because it depends only on physical size, not density, magnetism, or flotation behavior. A vibrating screen with 25 mm apertures will separate everything above and below that cut point, regardless of whether the ore is iron, copper, or gold. Industrial screens use wedge-wire decks, woven cloth, or polyurethane panels; aperture sizes range from 100 mm down to 75 micrometers for fine sizing. Multiple decks stacked vertically, each with progressively finer apertures, can produce three, four, or more size fractions in one pass.

The term "size" as a verb comes from the noun, which originally meant the regulated dimensions of finished goods; here it means bringing material into a defined size range. In older mining parlance, sizing work was called "jigging" or "buddling" when done by hand or in water; modern industrial sizing almost always means mechanical screening, typically vibrating at 1,200 to 1,800 strokes per minute to prevent blinding (apertures clogging with sticky fine material).

Common problems include blinding with damp or clay-laden material, uneven feed distribution leading to poor separation efficiency, and rapid wear of the screen surface from abrasive ore. The efficiency of a screen is measured as the percentage of material finer than the aperture that actually passes through; poor efficiency means valuable fines are lost to the oversize stream. Moisture content and particle shape both affect recovery; flaky or needle-shaped particles pass through screens less readily than equant grains of the same nominal size.

Sizing sits early in the flowsheet, right after primary or secondary crushing and before concentration. Many operations perform more than one sizing stage: coarse screening to separate out waste rock before transport, then finer sizing at the mill to prepare feed for flotation, gravity separation, or magnetic separation. The size fractions generated are often recirculated: oversize may return to a ball mill or cone crusher, while undersize might be pumped to a thickener or sent directly to tailings depending on mineral content.