keeve

A keeve is a large, typically cylindrical or rectangular vat, usually made of wood or lined concrete, where crushed ore is agitated in water to separate valuable minerals from waste rock. The ore slurry settles by density; heavier minerals sink while lighter gangue material stays suspended or overflows. The process is called keeve classification or keeve washing, and it remains one of the oldest mechanical methods of ore dressing.

Keves range from 2 to 6 meters in diameter and are equipped with a slow-turning rake or spiral mechanism along the bottom that moves settled ore toward a discharge point while allowing water and fine particles to exit through overflow lips or weirs. The mechanism operates at speeds between 1 and 3 revolutions per minute, gentle enough not to break the ore fragments but vigorous enough to maintain suspension and promote settling. Some keves use compressed air injection from below to aid stratification.

Variants and application context

The keeve was essential in gravity separation circuits before flotation became dominant in the 20th century. It is still used in alluvial mining, tin dressing, and iron ore beneficiation where simple density separation is cost-effective. Operators monitor discharge density, overflow clarity, and rake torque as indicators of proper settling. Common problems include bridging, where fine material clogs the discharge, and sanding, where the underflow becomes too thick to move.

The name comes from Dutch or Afrikaans (cf. kuif, meaning tub), suggesting Cornish and South African mining heritage. Unlike a thickener, which aims to produce a clear supernatant, a keeve prioritizes classification by gravity and particle size. It occupies a middle ground between simple settling ponds and more complex jigs or hydrocyclones in the hierarchy of ore preparation equipment.