SEPARATION
extremely high level of purity . High level of purity in this case means a very low level of metallic impurities . “ The lithium industry is one of the industries that benefits from the power of the matrix type separator which uses not only a strong background magnetic field , but the magnification of the field within the matrix to capture very fine magnetic particulates that no other piece of equipment can capture . Some of the contamination of lithium compounds is in a form single digit micron ferrous particles or weakly magnetic materials , such as wear and tear of 304 Stainless Steel . These are easily collected in the matrix while the lithium compounds flow through the matrix .”
Marin adds : “ Consider that producers of lithium carbonate 10 years ago would seek contamination levels of 200 ppm of metal or less . Current market demand is for lithium carbonate with less than 50 ppb . There are no pieces of equipment that can purify this ultra-fine powder more effectively than the DVMF .” The 5000 , gauss DVMF consists of a solenoid clad type of electromagnet where there is a vibrating canister through the open bore . The coils are driven quite hard and generate a substantial amount of heat that requires dissipation through the surface of the electromagnet and force cooling . The sensor based cooling system available on the Eriez unit allows an operator to monitor all the operating parameters of the unit , delivering information that can be transmitted to the central control system . Operators know the exact water and oil flows and their corresponding temperatures . Additionally , electromagnet operating data is transmitted , as well as the vibration displacement of the canister .
Looking at wider mining magnetics applications , trunnion magnet systems are magnetic separators that are installed at the discharge of a ball mill . “ These magnets ’ main objective is to remove ball chips and worn out balls from the milling circuit . It is a simple concept that requires a short stainless steel barrel and a permanent magnet around it covering an arc length of about 200 degrees on unidirectional mills . There is also a longer arc option for bidirectional ball mills . The magnetic arc induces a magnetic field into specially designed cleats inside the barrel which attract the ferromagnetic worn balls and chips as the slurry discharges from the mill . As the barrel rotates with the mill , the magnetic material is carried up to the end of the magnetic element . At this point , gravity takes over and the magnetic fraction is collected on a chute and diverted away from the mill discharge . Trunnion magnets can be used on most ore , with the exception of ferromagnetic ores such us magnetite or monoclinic pyrrhotite .”
Why is a trunnion magnet so important to a milling circuit ? Marin says that unless worn out balls and chips ( scats ) are magnetically removed , those hard pieces of metal remain in the circuit until they are milled into a fine metallic powder and eventually make it to the concentrators ( flotation , gravity or magnetic ). “ Knowing this , the real question becomes : Why spend so much energy milling the milling media ? Ball mills are designed to mill ore and can do that very effectively when trunnion magnets are utilised . While ball mill manufacturers are already incorporating trunnion magnet systems into new ball mills , these can also be retrofitted in existing ball mills . The most important thing to remember when considering a retrofit is that the ball mill is full of chips . The mill will undergo a massive evacuation of chips during the first two to three weeks of operation which causes a reduction in power draw . This can be adjusted by adding a higher load of fresh ore to bring the system back to normal .”
Eriez states that the trunnion magnet has undergone a series of improvements in recent years , including : n New wash water manifold to better wash the ore off the chips n The barrel has been fitted with a 6 in extension at the end which helps properly seal the discharge of the mill n Top section of the magnetic arc can now pivot open which effectively reduces disassembly time during barrel maintenance Lastly , Marin discussed Wet Drums ( Low Intensity Magnetic Separators / Medium Intensity Magnetic Separators ) with Hybrid Magnetic Element . “ Wet drums are extensively used in mining . Whether it is iron ore concentration or recovery of magnetite in heavy media circuits , there are countless applications that require a solid design for
Eriez states that the trunnion magnet has undergone a series of improvements in recent years metallurgical and mechanical performance . Even though significant improvements on wet drums took place during the 90s and early 2000s , we continue to see further improvement in reliability and features on this product category .”
Eriez developed a hybrid magnetic element with one objective in mind : improve iron recovery in the rougher stage of magnetite concentration . Comparative tests performed at an iron ore plant proved iron recovery performance . “ A comparison was performed on self-levelling CDA wet drums that were 48 in diameter by 125 in wide with a 1,000 gauss interpole magnetic element versus the hybrid element . It should be noted the hybrid element develops peaks of 3,500 to 4,000 gauss , as opposed to 2,100 gauss on the 1,000 gauss interpole element . In addition to the hybrid element , a number of other magnetic elements exist . Selection of elements depends on the application , minerals , and their magnetic susceptibility , such as transitional magnetite which is known for lower magnetic susceptibility of magnetite .”
This ore can easily be separated and concentrated using the Salient Pole RE wet drum . Not all gold processing plants have a gravity circuit in their flowsheet , but those that do Marin says know the benefit of wet drums to remove magnetite and fine ferrous prior to the gravity concentrator . This allows the concentrator to operate continuously without having to deal with the nuisance of magnetite or fine steel in the bed of the concentrator .
Last but not least he covered next generation RE Roll Separators ( High Intensity Magnetic Separators ). Rare earth roll separators effectively replaced the induced magnetic roll separators ( IMR ) because of the equipment ’ s simple and compact design and low power consumption . Its performance was as good as or better than that of the IMR . “ The early models were manufactured with samarium cobalt Rare Earth magnets and the maximum roll width at the time was the 40 in ( 1 m ) wide . Those units evolved into the 60 in ( 1.5 m ) and Eriez is now pleased to announce the development of an 80 in ( 2 m ) wide RE Roll is near . The 80 in wide RE Roll is completely re-designed to bring the RE rolls to current engineering design standards . The housing has been simplified by making it ‘ bolt-on ’ construction as compared to the conventional welded construction . The cantilever assembly has been re-designed with fewer components and a more rugged design . Bearing replacement has been simplified so operators do not struggle with the weight of a magnetic roll that will stick to any metallic part on the machine and nearby area . The belt tracking mechanism has
46 International Mining | APRIL 2021