Advanced grease belt for diamond recovery

Most diamonds are recovered in the final stages of the process plant by x-ray sorting machines, because x-rays cause them to luminesce. However, type 2 diamonds, i.e., flawless (higher value) diamonds, do not luminesce. These escape with the x-ray tails, which are usually passed over a grease table to recover these diamonds, because diamonds are attracted to grease (oleophilic). But grease tables require human intervention to change the grease every five minutes, making them insecure and inefficient.

Johannesburg, South Africa-based Oblique Engineering has developed a secure, continuous, energy-efficient grease belt system for recovering diamonds.

Oblique’s GB400 grease belt or the larger GB2.4 two-belt system uses a special recipe based on beeswax, which is spread onto a moving belt, kept at a constant 25-35C. Diamonds are caught in the grease and move up the belt as the non-oleophilic minerals are washed down the belt by water. A blade scrapes the diamond-bearing grease off the belt and into an 85C melting tank. The diamonds drop out of the melted grease and are recovered, the grease is cleaned and reused, and the water is recirculated. The machine achieves a remarkable 99% recovery rate on grease-recoverable diamonds.

On a test run in southern Africa, a GB400 processed 860 kg of tailings in 30 minutes, recovering 35,000 diamonds (weighing about 8,000 ct with an average value of US$30/ct).

The compact machine has proven to be popular in African and Australian mines and is now being marketed in Canada. For more information visit www.oblique.co.za.