jigging

Jigging is a mineral processing method in which ore particles are separated by density using vertical oscillation in water. A jig consists of a bed of material (often coal, magnetite, or garnet) held in a vessel with a perforated bottom. Water is pulsed upward and downward through this bed, typically 100 to 300 times per minute, creating cycles of expansion and compression. Heavier particles settle faster and lodge in the lower layers; lighter waste materials are carried away in overflow during the upstroke.

The vessel itself is called a jigging cell or jigger. Modern industrial units are steel-framed boxes ranging from 2 to 4 meters wide, holding 10 to 30 tons of ore per cycle. The motion comes from a plunger (a moving floor) or diaphragm (a flexible membrane) driven hydraulically or pneumatically. Multiple jigs are arranged in series to achieve finer separation, with the heaviest material settling in the first cell and progressively lighter fractions in subsequent ones.

Conditions and variables

The pulsation frequency, stroke length, and water-to-ore ratio are the critical operating parameters. Higher frequency favors smaller particles; longer strokes aid stratification of coarser material. The density difference between ore and gangue must exceed roughly 0.5 tons per cubic meter for effective separation. Jigging works best on particles between 0.5 and 50 millimeters; finer material tends to float with waste, and coarser material settles too quickly to separate properly.

Jigging is a wet process and generates significant slurry. The water must be recycled to control costs and tailings volume. Suspended clay and slime coating particles can prevent proper settling, so preliminary scrubbing or desliming stages are often necessary. Jigs are also sensitive to variations in feed rate and ore characteristics; inconsistent mineral density or grain size in the incoming ore reduces separation efficiency.

The term originated in textile manufacture, where jigs were racks that held cloth in motion for dyeing. The mining application retained the name because the vertical bobbing motion resembles a jig dance. Although jigging has been largely displaced by dense-media separation and flotation in large-scale operations, it remains common in artisanal mining and in processing of specific ores where the density spread between ore and waste is favorable. It requires less chemical input than flotation and is simpler to operate than dense-media circuits, making it valuable where infrastructure is basic.