pulsator

A pulsator is a gravity separation device that uses reciprocating vertical motion to stratify and classify diamond-bearing ore. Water or air pulses drive a bed of heavy media or dense mineral particles up and down within a chamber, causing diamonds to settle selectively while lighter gangue material is flushed away. The machine exploits density differences: diamonds at 3.5 g/cm³ sink and concentrate while waste rock disperses and overflows.

The pulsator became standard equipment in South African alluvial and near-surface diamond mining during the mid-20th century, particularly in operations processing kimberlite and weathered deposits. A typical unit consists of a cylindrical or rectangular vessel with a perforated screen deck, fed from above with ore slurry and make-up water. A mechanical or pneumatic pulsing mechanism creates 60 to 120 strokes per minute, with amplitude usually between 25 and 100 mm depending on ore type and feed rate.

Variants include wet pulsators using water cycles and dry pulsators using air pulses. Feed density, stroke frequency, and media composition must be matched to ore characteristics. Too rapid pulsing causes loss of fine diamonds; too slow allows misclassification. Operators monitor wash-water flow, feed rate, and underflow density to maintain recovery of both large stones and smaller industrial diamonds that might otherwise escape.

Limitations and Decline

The pulsator performs well on coarse, alluvial material but struggles with fine diamonds, clay-bound ore, and very heavy concentrates. Modern operations have partially replaced pulsators with dense-medium cyclones and X-ray fluorescence sorters, which offer better precision and automation. However, pulsators remain in use where water is abundant and ore is relatively clean, as the equipment is robust, low-cost to operate, and requires minimal training.

Wear on the screen deck and seals is inevitable; media attrition adds to operational cost. Despite these drawbacks, the pulsator's simplicity and proven track record in alluvial diamond recovery ensure it remains a reference technology in mining engineering and still appears in small to medium-scale operations in southern Africa.