The primary cyclone circuit incorporates acluster of eight Minerals cyclones. The feed density to the cluster is controlled to ensure the correct cut point isobtained while the number of cyclones operatingcan be altered to match the feed flow volume.The cyclone overflow product is 20% solidswith a P80 of 53 µm containing mostly liberatedmagnetite . The underflow is mostlyunliberated magnetite and low-SG gangue andreports to the existing flotation tailings sump. Inthe size classification circuit, 47% of themagnetite is recovered from the cyclone feed.“The effective classification of the magnetiteis paramount to the success of the separationprocess.
This is complicated by the bimodaldensity properties of the high-SG magnetite andthe low-SG gangue. This was evident throughoutthe metallurgical test work campaigns and was approached to model the suitabilityof cyclones as a classification .”A regrind circuit treats the cyclone underflowand recovers the unliberated magnetite.
The additional magnetite captured passesthrough a set of regrind magnetic separators.The concentrate produced is directed onto thecleaner magnetic separator circuit, mixing oncemore with the liberated magnetite from theprimary cyclone cluster, while the tailings arediscarded as final tails.
The cleaner magnetic separator circuit worksin the same way as the rougher and regrindmagnetic separator circuits, using drums andmagnets to further separate the magnetite fromthe non-magnetic material but at a differentmagnetic strength. The slurry is introduced intothe cleaner separator first, which is a permanentlow intensity magnet and operates with amagnetic strength of 750 Gauss. The cleanerseparator produces a concentrate which flowsinto the feed launder of the following finisherdrum separator which also operates at 750Gauss. The last finisher drum separator isoperated at 550+ Gauss and serves as apolishing separator for magnetite and nonmagneticgangue materials. At the end of thisstage, 99.8% of the magnetite is recovered fromthe feed and a clean concentrate containing upto 98% iron oxides is produced, which issuitable for sale.
The concentrate is directed to the dewateringcircuit while the tailings are recycledback to the rougher and cyclone feedsumps to be re-used as dilution water inthese earlier stages of processing,minimising raw water usage in theprocess.
The concentrate is dewatered using two ceramic disc filters to create a product ofsuitable density for transportation. Asthe discs rotate through the slurry,capillary action causes the liquid to drawthrough the discs while the solids buildup on the external surface of the discs toform magnetite cake. The cake (finalmagnetite concentrate) contains around8-10% moisture. It is removed from thediscs with a scraper and discharged intothe concentrate stockpile for storageuntil it is time for transportation. Thefinal product is a premium grade iron oreconcentrate containing around 90-98%magnetite.