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December 8, 2023
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Trends in Magnetic Separation and Flotation in the Mining Industry By Jose Marin, Eriez® Director—Minerals and Materials Processing

The demand for higher purity industrial minerals continues to grow as new applications are released
throughout the world, including Africa. Companies that do not want to get left behind must drive
technological advances to produce newer, more state-of-the art equipment. Equipment advancements
give companies the keys to unlock doors to new applications in changing markets.
Magnetic separation and flotation engineering are important technologies that can help make
significant improvements in products and minerals by delivering increased recovery. The following
discussion identifies current trends and lists recent improvements in magnetic separators and flotation
applications and technology.

Trunnion Magnets for New and Retrofit 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. Trunnion magnets can be used on most ore, except
for ferromagnetic ores 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).
The trunnion magnet has undergone a series of improvements in recent years. Below is a list of

  • New wash water manifold to better wash the ore off the chips
  • The barrel has been fitted with a six-inch extension at the end which helps properly seal the
    discharge of the mill
  • Top section of the magnetic arc can now pivot open which effectively reduces disassembly time
    during barrel maintenance
Trunnion magnets remove ball chips and worn-out balls from the milling circuit.


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 metallurgical and
mechanical performance. Even though significant improvements on wet drums took place during the
90s and early 2000s, we continue to see additional improvement in reliability and more advanced
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. The comparison was conducted on self-leveling CDA wet drums that are 48-inch
diameter by 125 inches wide with a 1000 gauss interpole magnetic element versus the hybrid element.

Dry Vibrating Magnetic Filter (DVMF) Perfect for Lithium Carbonate
The dry vibrating magnetic filter is a unique piece of equipment for processing very dry fine industrial
minerals and materials requiring an 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. 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.

Next Generation RE Roll Separator (High Intensity Magnetic Separator)
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 inches (1 m) wide. Those units evolved into
the 60 inch (1.5 m) and Eriez is now pleased to announce the development of an 80 inch (2 m) wide RE
Roll is nearby.
The 80-inch wide RE Roll is completely re-designed to bring the RE rolls to current engineering design
standards. The housing has been simplified with “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.

Newly designed Model RE 80-3 Roll Separator, non-magnetic repass configuration


Advances and Applications in Flotation Technology

Applications for flotation equipment and systems include, but are not limited to, metallic and non-
metallic minerals, bitumen recovery, fine coal recovery, organic recovery (solvent extraction and
electrowinning) and gold/silver cyanidation. The product line offered by Eriez Flotation encompasses
flotation cells, gas spargers, slurry distributors and flotation test equipment.
Eriez Flotation has designed, supplied and commissioned more than 1,000 flotation column systems
worldwide for cleaning, roughing and scavenging applications. The company has made significant
advances in fine coal recovery with flotation systems to recover classified and unclassified coal fines.
For example, Eriez Flotation completed shipments to two major minerals processing projects in Brazil.
More than twenty flotation columns were delivered, including some of the largest in the world with six-
meter diameter size.
In another instance, Eriez Flotation suppled four HydroFloat® Separators to Newcrest Mining for
utilization in Stage 2 of its Cadia Valley Operations expansion project in New South Wales, Australia.
That project followed the commission and ramp-up of four Eriez CrossFlow Separators and two
HydoFloats. Newcrest Mining is the first mining company to commercialize HydroFloat coarse particle
flotation in sulfides and the first in a tail scavenging application.

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