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Magnetic Separation (EDS and Automatic Sorting). Lecture 11 – MINE 292. Main Applications. Tramp Metal Removal To protect crushers (electromagnets as well as metal detectors) Magnetite Recovery Primary iron ore processing (taconite ores) Pyrrhotite Recovery or Removal Nickel recovery

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main applications
Main Applications
  • Tramp Metal Removal
      • To protect crushers (electromagnets as well as metal detectors)
  • Magnetite Recovery
      • Primary iron ore processing (taconite ores)
  • Pyrrhotite Recovery or Removal
      • Nickel recovery
      • Gangue removal (zinc ores, gold ores, nickel ores)
  • Magnetic minerals removal
      • Scheelite, talc, quartz, kaolinite,, industrial minerals
  • DMS Magnetite Recovery
      • Media recovery and upgrading (purification)
  • Cleaning hematite concentrates (high-intensity)
      • Final stage upgrading
types of materials
Types of Materials
  • Diamagnetic
    • Repulsion by magnetic forces
  • Paramagnetic
    • Attraction to magnetic forces
    • Rutile, ilmenite, chromite
  • Ferro-Magnetic
    • Very-highly attracted to magnetic forces
    • 1,000,000 times effect of paramagnetism
    • Effect disappears above Curie temperature (~620 °C)
    • Iron, nickel, magnetite, pyrrhotite
field strength and flux density
Field Strength and Flux Density
  • Magnetic Induction (flux) = B in Tesla
  • Field Intensity induced through particle = H (A/m)
  • Permeability = µo (T·m/A)
  • Magnetization Intensity = M (4π x 10-7 T) - ignored

B = µo (H + M)

B = µoH

  • For ferromagnetic materials, must consider magnetic susceptibility (S = M/H)

B = µoH (1 + S)

magnetization vs field intensity
Magnetization vs. Field Intensity
  • Slope = S (magnetic susceptibility)
magnetization vs field intensity for fe 3 o 4
Magnetization vs. Field Intensity for Fe3O4
  • Slope = S (magnetic susceptibility)
  • For H = 1 T, S = 0.35
  • Full saturation at 1.5 T
  • Iron saturates at ~ 2.3 T
magnetic field gradient
Magnetic Field Gradient
  • Capacity depends on field gradient as well as field intensity
  • Rate at which intensity increases as surface of magnet is approached
  • F is proportional to

H x dH/dl

  • Introduction of magnetic particles has the same effect but agglomeration of particles will block the separator
methods
Methods
  • Low-intensity (LIMS)
      • 600 – 700 gauss (0.6-0.7 Tesla)
  • High-intensity (HIMS)
      • WHIMS (wet)
      • 10,000 gauss (10 T)
  • High-gradient (HGMS)
      • Fine magnetic matrix
      • 15,000 gauss (15 T)
  • Permanent Rare-Earth Magnetic Separators (PREMS)
      • 500-1,000 gauss (0.5-1.0 T)
  • Super-Conducting Magnetic Separation (SCMS)
      • 50,000 gauss (50 T)
  • Eddy-Current Magnetic Separation (ECMS)
      • Application of current to mixture of substances
      • Separation of metals in electronic waste
cbm cross belt magnetic separator
CBM (cross-belt magnetic separator)
  • Magnets (5-6) located above belt
  • Operating variables
    • Field strength (up to 15 T)
    • Pole gap typically 2 mm
    • Belt speed (fixed)
    • Splitter position (manually adjusted)
    • Feed rate ~1.5 tph
irm induced roll magnetic separator
IRM (induced roll magnetic separator)
  • Operating variables
    • Field strength (up to 15 T)
    • Pole gap typically 2 mm
    • Roll speed (fixed)
    • Splitter position (manually adjusted)
    • Feed rate ~2.5 tph
lims units
LIMS Units
  • Applied to coarse sized particles that are strongly magnetic
  • Drum-type separators
  • Dry for sizes > 0.5 cm
  • Wet for sizes < 0.5 cm
  • Called Cobbing
  • Applied to DMS media recovery and upgrading
  • Typical field strength = 0.6-0.7 T
  • Gap for Magnetite = 50-75 mm
  • Gap for pyrrhotite = 10-15 mm down to 2 mm
  • uses permanent ceramic or rare-earth magnets
lims units1
LIMS Units

Drum Cylinder Rotation Capacity Feed Power

Diameter Length Speed Top Size

(mm) (mm) (rpm) (tph) (mm) (kW)

600 1200-1800 35 10-30 2 1.5-2.2

900 1800-2400 28-35 40-70 3 3.0-4.0

1200 1800-3000 18 80-180 3 5.5-7.5

1500 3000 16 150-260 3 11.0

high intensity magnetic separation
High-Intensity Magnetic Separation
  • Dry High Gradient Magnetic Separator
whims
WHIMS
  • Must remove highly-magnetic material to prevent blocking
  • Feed size > 1mm
  • Constant supply of clean, high-pressure water
  • Steady feed rate and density
  • Generally applied for fine particle removal
  • Final stage cleaning or upgrading
  • Field Strength up to 15 T (electromagnetic)
  • Feed rate = 25-30 tph for 16-pole unit
  • Gap typically 2 mm
  • Splitter position varied to control process
eddy current magnetic separation
Eddy-Current Magnetic Separation
  • Applied in recycling industry
  • Diamagnetic materials can be separated
  • Spinning magnets cause an eddy-current in Aluminum such that a magnetic field is created that repels Al particles
automatic sorting
Automatic Sorting
  • Sensors
      • Cameras & Video cameras
      • X-ray tubes
      • lasers
  • Types
      • Photometric - colour/reflectance optical properties
      • Radiometric - gamma radiation - Uranium
      • UV - scheelite
      • Conductivity - sulfides
      • Magnetic - iron minerals
      • X-rays luminescence- diamonds
      • microwave attenuation
      • hyper-spectral
      • neutron absorption - boron
  • Throughput
      • 25 tph for -25 + 5 mm (1 in to 0.2 in)
      • 300 tph for -300+80 mm (12 in to 32 in)
  • > 1-2 inches in size with all fines scalped
  • Reject a portion of feed to reduce comminution costs and possibly produce a very high-grade product.
  • Talc, magnesite, limestone, phosphates, diamonds, kaolinite, unranium, Pb/Zn, gold ores, glass sands, industrial minerals,