Magnetic separation
In mineral processing plant, By creating an environment comprimising a magnetic force (Fm), a gravitional force (Fg) and a drag force (Fd) magnetic
particles can be separated from nonmagnetic particles
by Magnetic
Separation.
Competing forces
• Gravitational force (Fg) determined by particle size and particle
density.
• Hydraulic force (Fd) for wet magnetic separators, determined
by particle diameter, shape, liquid viscosity and velocity (see wet LIMS and
wet HGMS below.)
• Centrifugal force (Fc) for rotating dry magnetic separators,
determined by particle size, density and drum speed. (see dry LIMS below.)
• Air drag force (Fa) for dry magnetic separators, determined
by particle size, density and air velocity. (see dry HGMS below).
Separator Types
Wet LIMS = Low Intensity Magnetic Separator
• Wet
separation of ferromagnetic particles
•
Magnetic field in separation zone * = 1-3 kGauss
* approx. 50 mm
(2 inches) from drum surface
Wet HGMS = High Gradient Magnetic Separators
• Wet
separation of paramagnetic particles
•
Magnetic field in separation zone* = 2-20 kGauss
* on matrix
surface
Dry LIMS = Low Intensity Magnetic Separators
• Dry
separation of ferromagnetic particles
•
Magnetic field gradient in* separation zone = 1-3 kGauss
* approx. 50 mm
(2 inches) from drum surface
Dry HGMS = High Gradient Magnetic Separators
• Dry
separation of paramagnetic particles
•
Magnetic field in separation zone* = 2-20 kGauss
* on matrix
surface
Wet LIMS - Concurrent (CC)
•
Short pickup zone
• Coarse
particle tolerant up to 6 mm - 0.2 inch (up to 20 mm - 0.8 inch with special
tank)
•
High capacities for low grade feeds
CC is normally
used as primary separation (cobber), "working horse" for large
capacities and
coarse feeds, mainly in iron ore industry.
Wet LIMS - Countercurrent (CTC)
•
Long pickup zone = improved recovery
•
Many pole passages = improved grade
•
Self adjusting level control
•
Coarse particle intolerant max 0.8 mm, due to sedimentation risk.
CTC used as:
Rougher and finisher for multistage concentration of magnetic iron ore.
Wet LIMS - Counter Rotation (CR)
•
Very long pickup zone
•
Good separation with high recoveries
• For
both low and high grade feeds
•
Unsensitive for sedimentation, particles up to 3 mm can be separated
•
Self adjusting level control
CR used as: same
as CTC above when sedimentation is at risk, mainly in the iron ore industry.
Wet LIMS - Dense Media Recovery (DM)
•
Very long pickup zone
• For
extremely high recoveries of very fine particles
• HG (high gradient) version available for high recovery from very dilute
pulp
Dry LIMS – Drum Separator (DS)
•
Alternating polarity with different pole pitches giving good recovery and grade
•
Variation of drum speed 1-8 m/s (3 – 26 ft/s) gives metallurgical flexibility
• Not
sensitive to particle size 0.01 - 20 mm (150 mesh - 3/4")
DS can be used
for separation of all types of dry ferromagnetic separation processes:
•
Iron and steel slag treatment
•
Reduced pyrite ash separation
•
Calcined ilmenite production
•
Iron metal powder production
•
Magnetite or supergrade magnetite production
Dry LIMS – Belt Separator (BSA)
• For
coarse particles minus 200 mm
•
Alternating polarity with different pole pitches giving good selectivity
•
Rubber belt for protection of separator drum and even distribution of the feed
•
Variable speed for optimal separation
BSA and BSS
mainly used for separation of coarse ferromagnetic ores and slags
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