Latest design improvements increase spiral concentrator efficiency

Spiral concentrators have, over numerous years, found many varied applications in mineral processing. Until relatively recently, all spirals were very similar, based upon the original Humphreys design, which is now obsolete. However, in recent years there have been considerable developments in spiral technology, and a wide range of devices is now available. The main areas of development have been in the introduction of spirals with only one concentrate take-off, at the bottom of the spiral, and the use of spirals without added wash water.

Spirals are now made with slopes of varying steepness, the angle affecting the specific gravity of separation, but having little effect on concentrate grade and recovery. Although a simple device, the separation mechanisms are complex, stratification being due to the combined effect of the differential settling rates of the particles, the effect of interstitial trickling through the flowing bed and the mild centrifugal force, often being likened to the stratification of particles in a river as it flows around a bend.

Southern and Northern
Hemisphere Spirals

A small team of workers at the Bodmin Institute in Cornwall has shown that this centrifugal force can be enhanced by that produced by the spin of the earth. Under the leadership of research director Dr. Corrie Hayles, they have shown that the orientation of the spiral pitch has an effect on performance, an anti-clockwise flow performing better in the UK than a spiral with a clockwise flow. Dr Hayles calls these spirals northern hemisphere and southern hemisphere devices respectively. He is now keen to develop collaboration with workers in the southern hemisphere to assess performance of the two devices, and he would be interested to hear from anyone who has any thoughts on this.