Driving Improvements and Efficiency in all Mining Processes.
Edited by Mark S. Kuhar
Demand for higher purity industrial minerals continuous to grow as new applications are released throughout the world. What does this mean to the producers of industrial minerals that proudly produce their products, but find out that the production run from yesterday will no longer cut it?
This is exactly what drives technological advances so that plants can produce with state-of-the-art equipment, which helped improve a few percentage points of increased recovery or the product purity has gone up a few notches which, in return, opens the doors to applications that a producer never thought could produce a product for the ever-changing market.
Magnetic separation is one of those technologies that can help make significant improvements in products and minerals. Magnetic separation technology is no different than other technologies, it is constantly searching for improvements and efficiency gains in all possible processes.
The following discussion identifies current trends and lists recent technological improvements on the magnetic separators manufactured by Eriez Magnetics.
Trunnion Magnet systems are magnetic separators that are installed at the discharge of a ball mill with the main purpose of removing 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 ferro magnetic 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 where 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 any ore except ferromagnetic such us magnetite or Monoclinic pyrrhotite.
Why is a trunnion magnet so important to a milling circuit? 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).
Thus, the question is why spend so much energy milling the milling media? Ball mills are designed to mill ore and they can do that very effectively when trunnion magnets are utilised.
Ball mill manufacturers are already incorporating trunnion magnet systems in new ball mills, however, these can also be retrofitted in existing ball mills. The most important thing to remember about a retrofit, is the fact 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 causing a reduction in power draw. This can be adjusted by adding a higher load of fresh ore to bring the system back to normal.
The trunnion magnet has undergone a series of improvements in recent years. These are the most significant ones:
- New wash water manifold to better wash the ore off the chips.
- The barrel has been fitted with a 6-in. extension at the end that helps properly seal the discharge of the mill.
- Top section of the magnetic arc can now pivot open, which effectively reduced disassembly time during barrel maintenance.
WET DRUMS (LIMS AND MIMS)
Wet drums are extensively used in mining. Whether it is iron ore concentration or recovery of magnetite in heavy media circuits, there are countless other applications that require a solid design for metallurgical and mechanical performance. Even though significant improvements on wet drums took place during the 1990s and early 2000s, Eriez continues to further improve reliability and features on this product.
Eriez developed the “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 as illustrated in the graph below. The comparison was performed on self-leveling CDA wet drums 48-in. diameter by 125-in. wide with a 1000 Gauss Interpole Magnetic Element vs. the Hybrid element. It should be noted the hybrid element develops peaks of ~3500 to 4000 gauss as opposed to 2100 gauss on the 1000 gauss interpole element.
In addition to the hybrid element, Eriez offers a number of magnetic elements depending on the application, minerals and their magnetic susceptibility such as transitional magnetite which is know for the 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, know the benefit of wet drums to remove magnetite and fine ferrous prior to the Falcon 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.
DRY VIBRATING MAGNETIC FILTER (DVMF
The dry vibrating magnetic filter is a unique piece of equipment for processing dry very fine industrial minerals and materials requiring extremely high level of purity. High level of purity in this case means very low level of metallic impurities.
The lithium industry is one of the industries that benefits from the power of the matrix type separator that 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 the form of 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. For example, 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 and there are no pieces of equipment that can purify this ultra-fine powder than the DVMF.
The 5000 gauss DVMG consist 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 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 monitor all the operating parameters of the unit and this information can be transmitted to the central control system. Operators know the exact water and oil flows and their corresponding temperatures. Not only that but operating data of the electromagnet is also transmitted as well as the vibration displacement of the canister.
RE ROLL SEPARATOR (HIMS)
The Rare Earth Roll separators effectively replaced the Induced Magnetic Roll separators (IMR) because of its simple and compact design as well as low power consumption. Its performance was as good as or better than IMRs. 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 the 80-in. (2-m) wide RE Roll.
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 redesigned 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 wants to stick to any metallic part on the machine and nearby area. The belt tracking mechanism has been simplified to make the belt replacement procedure even faster than the previous models but the Kevlar belts are still the longest lasting belts for that unit. Belts with diagonal splices as well finger splices are also available.
Information for this article courtesy Eriez Magnetics.