Technology provider to the De Beers group DebTech has developed a range of wet diamond magnetic roll separa- tor equipment, which achieves diamond recoveries of more than 99% on size fractions from 1 mm to 8 mm.

DebTech marketing manager Nico van Zyl tells Mining Weekly that tests conducted on samples from several potential clients have shown that material feed rates equal or better to those typical of dry MagRolls and with similar mass splits between the magnetic and nonmagnetic products can be achieved with wet MagRolls.

The dry MagRoll is constructed of large-diameter, high-strength permanent magnets, which are assembled in a proprietary configuration to provide an exceptionally strong and optimally shaped magnetic field. It can separate a wide size range of material at high throughputs and with enhanced separation efficiencies. The company reports that the wet MagRoll is expected to deliver even better results.

Van Zyl says that dry diamond-recovery plant flowsheets need to dry large quantities of concentrate from the wet dense-media separation plants prior to processing. This necessitates the use of large-scale dryers, which incur high capital and operating costs. The use of entirely wet processes in the recovery circuit eliminates the need for large-scale drying and requires only a small quantity of X-ray machine concentrate to be dried prior to final sorting.

“The economic advantage has steered the industry towards wet processing and prompted DebTech to develop its latest CWX118CD wet X-ray machine, as well as to embark on the development of a wet version of the dry MagRoll,” he asserts. The wet MagRoll magnetic separator will be commercially available later this year.

The separation of wet gravel on conventional magnetic separators poses the challenge of agglomeration, whereby the surface tension of the water layer coating each gravel particle tends to bind adjoining particles. This can lead to the misplacement of particles into either the magnetic or nonmagnetic product streams during magnetic separation. Non- magnetic particles, like diamonds, may then agglomerate with magnetic particles and get carried into the magnetic stream, which may be discarded as waste.

DebTech technical expert serving on the development team Mohammed Fofana has developed a pair of prototype wet machines to overcome this challenge and complement the CDX118CD wet X-ray machine. The machines have been integrated into a test plant at DebTech’s premises.

Fofana explains that at the test plant, a test batch of gravel, spiked with diamonds, is passed over the first wet MagRoll, which is fitted with a low-strength magnetic roll to remove any strong magnetic material. The nonmagnetic product from this machine is then passed over the second wet MagRoll, which is fitted with a DebTech-designed SuperRoll magnetic head pulley. The diamond recovery through this process is tracked by feeding the nonmagnetic and magnetic pro- ducts from both machines through the wet X-ray machine, which retrieves the diamonds for accounting purposes and subsequent reuse.

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