WILUNA, Western Australia Protecting equipment, cutting power consumption and reducing recurring maintenance costs were prime factors leading to NEWMONT JUNDEE's decision to integrate new trommel magnet separation technology as part of their Nimary gold plant's new scats crushing circuit installation. The trommel magnet technology had promise of superior waste iron removal along with lower operating cost.
Plant management, along with engineering consultants AUSENCO, had initially considered installing a pair of self-cleaning, suspended electromagnets to remove the waste iron exiting the mill to minimize the damage to downstream pebble crushers. But the use of electromagnets is not inexpensive. Their operation requires a significant amount of power, and the ongoing maintenance of self-cleaning belts can be considerable.
The new trommel magnet from ERIEZ, by comparison, uses permanent magnets that require no power to operate, and their maintenance needs are no more expensive than that of a self-cleaning magnet. The magnet mounts to the mill's discharge trunnion and consists of an arc of permanent magnets partially surrounding a blind trunnion. As the mill rotates, the powerful magnet attracts and holds the worn steel balls and chips to the inner surface of the trunnion extension. The ball fragments are carried to the top, where the magnetic arc terminates, and fragments fall into a discharge chute.
After careful consideration, the plant team opted to equip the mill with the new high-efficiency trommel magnet and a simple manually-cleaned suspension magnet positioned downstream. The trommel magnet does the bulk of the work, and the secondary suspended magnet provides the safety of a backup. A suspended magnet placed just ahead of the crusher removes any iron tools or steel that might have dropped onto the conveyed ore after the mill.
After months of operation, the trommel magnet installation has been a success. It removes the majority of the waste iron at the mill discharge, with only the odd piece of iron being collected by the downstream suspended magnet. This magnet, being a permanent magnet, generally requires cleaning only on a weekly basis.
Plant management sited a number of factors that contributed to the effectiveness of the Eriez trommel magnet. First, as the iron is tumbled, it must pass close to the face of the magnet where the field intensity is highest. Second, gravity aids separation rather than working against a suspended magnet. And, the trommel magnet uses in-motion, induced lifters together with the stationary permanent magnet.
(This item was submitted for consideration on behalf of Eriez by Altman-Hall Associates.)