SEPARATION & CLASSIFICATION has a significant impact on the overall recovery of magnetite . When testing samples of magnetite ( 100 % -31.5 mm ) from Mauritania the results indicated an overall recovery of magnetite of over 99 %. Similar rougher LIMS ( Low Intensity Magnetic Separators ) tests with finer material and lower capacity showed only 72 to 80 % recovery .”
But he adds that development of stronger magnetic elements for dry magnetic separators can be a double-edged sword . As higher energy and stable magnetic material becomes commercially available , the magnetic fields generated by the circuits can drastically intensify which in turn creates a problem when Eddy currents begin to damage the stainless steel shells . These Eddy currents intensify as the speed of the drums increases . “ That energy is transferred into heat and can damage the magnetic material as a result of excessive temperature . Composite shells are now a perfectly viable replacement for stainless steel shells . Composite shells are structurally sound and can be lined with polyurethane to prevent wear and tear on the shell itself . The liner applied on composite shell has different coloration , so operators know exactly when to reline the shells . These shells are limited in shelf life but are perfectly acceptable alternatives for high-speed drums for iron ore concentration .”
Marin says that the key to obtaining highgrade magnetite concentrate in dry concentration is to strategically control the dust inside the magnetic separators . “ Cleaner and finisher drums process material that contains a very high percentage of fines . Strategically eliminating the dust that is generated as soon as the feed enters the separating zone of the drum separator will have a significant impact on the final results . Testing of various samples of magnetite showed that proper dust control can increase the total iron from approximately 62 to 64 %. Prior to discovering that dust control played an important factor on these drums , the best results ever obtained were 62 % total Fe . The nature of dry milling generates a significant amount of fines and a simple change in existing dry magnetic concentrators can make a big difference when considering dry over wet concentration .”
Other forms of iron can easily be concentrated in a dry process like the case of specular haematite . A former Cliffs property in Canada replaced electrostatic separators ( used to remove silica from specularite ) with Medium Intensity Rare Earth Magnetic separators . By replacing the electrostatic separators with Rare Earth drum separators , the company increased the life of the mine by at least 20 years because of one added benefit : the MIMS could reduce the overall manganese level in the final concentrate as well . Cliffs eventually sold the property , but the new
owners continued to use this technology and were able to increase the capacity of the plant .
Marin concludes : “ These are examples that underscore how dry magnetic concentration can make a difference at mining companies . Both major and minor technological advances in magnetic separation are helping them benefit from dry processes especially when wet processing is not an option .”
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The continuous operation of a grinding circuit is integral to maintaining productivity and profitability . SmartCyclone™ is a new monitoring and automation solution from FLSmidth that combines roping sensor technology , wear detection technology , wireless controller system and ECS / ProcessExpert ® process control
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MAY 2023 | International Mining 17