Magnetic Separation (EDS and Automatic Sorting) Lecture 11 – MINE 292
Dec 15, 2015
Main Applications1. Tramp Metal Removal
To protect crushers (electromagnets as well as metal detectors)
2. Magnetite Recovery Primary iron ore processing (taconite ores)
3. Pyrrhotite Recovery or Removal Nickel recovery Gangue removal (zinc ores, gold ores, nickel ores)
4. Magnetic minerals removal Scheelite, talc, quartz, kaolinite,, industrial minerals
5. DMS Magnetite Recovery Media recovery and upgrading (purification)
6. Cleaning hematite concentrates (high-intensity) Final stage upgrading
Types of MaterialsDiamagnetic
Repulsion by magnetic forces
ParamagneticAttraction to magnetic forcesRutile, ilmenite, chromite
Ferro-MagneticVery-highly attracted to magnetic forces1,000,000 times effect of paramagnetismEffect disappears above Curie temperature (~620 °C)Iron, nickel, magnetite, pyrrhotite
Field Strength and Flux DensityMagnetic Induction (flux) = B in TeslaField 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 = µo H
For ferromagnetic materials, must consider magnetic susceptibility (S = M/H)
B = µo H (1 + S)
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 GradientCapacity 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
MethodsLow-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)Magnets (5-6) located above beltOperating variables
Field strength (up to 15 T)Pole gap typically 2 mmBelt speed (fixed)Splitter position (manually adjusted)Feed rate ~1.5 tph
IRM (induced roll magnetic separator)Operating variables
Field strength (up to 15 T)Pole gap typically 2 mmRoll speed (fixed)Splitter position (manually adjusted)Feed rate ~2.5 tph
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 UnitsDrum Cylinder Rotation Capacity Feed PowerDiameter 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 3.0-4.01200 1800-3000 18 80-180 3 5.5-7.51500 3000 16 150-260 3 11.0
WHIMSMust remove highly-magnetic material to prevent blockingFeed size > 1mmConstant supply of clean, high-pressure waterSteady feed rate and densityGenerally applied for fine particle removalFinal stage cleaning or upgradingField Strength up to 15 T (electromagnetic)Feed rate = 25-30 tph for 16-pole unitGap typically 2 mmSplitter position varied to control process
Eddy-Current Magnetic SeparationApplied 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 SortingSensors
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,