Gravity concentration
- the separation of minerals based upon the difference in density.
- density-based separation methods
- main concentrating methods for iron and tungsten ores and are used extensively
for treating tin ores, coal, gold, beach sands, and many industrial minerals.
- The efficiency of gravity processes therefore increases with particle size, and the
particles should be sufficiently coarse to move in accordance with Newton’s law
- Gravity separators are sensitive to the presence of slimes (ultrafine particles),
which increase the viscosity of the slurry and hence reduce the sharpness of
separation, and obscure visual cut points for operators.
- 10 μm from the feed are removed, put into tailings, can cause loss.
NOTE:
- The feed to jigs and spirals should, if possible, be screened before separation
takes place.
- Control of pulp density within the circuit can be made by the use of settling cones
Nucleonic density gauges - Automatic density control.
JIGS
- separation of minerals of different specific gravity is accomplished in a particle bed,
which is fluidized by a pulsating current of water, producing stratification based
upon density.
- They have a relatively high unit capacity on classified feed and can achieve good
recovery of values down to 150μm and acceptable recoveries often down to 75
μm.
- Less dense minerals are discharged from the tailing port
- Has 3 slots used for collection, the middle collects the heavy minerals, while both
edge collects the light minerals.
- jig is normally used to concentrate relatively coarse material and, if the feed is fairly
close-sized (e.g., 3 10mm),
- Essentially, the jig is an open tank filled with water, with a horizontal jig screen at
the top supporting the jig bed, and provided with a spigot in the bottom, or hutch
compartment, for “heavies” removal
NOTE:
fine sand and slime should be controlled to provide optimum bed conditions.
• USED IN:
o Many large jig circuits are still operated in coal, tungsten, gold, and iron
ore concentrators.
• Ragging
o bed may be a specific mineral added to and retained in the jig.
o composed of a certain density and shape through which the dense
particles penetrate and the light particles pass over the top.
TYPES OF JIGS
Harz Jig
- which the plunger moves up and down vertically in a separate compartment.
- four successive compartments are placed in series in the hutch.
• 1st compartment – high-grade, heavy product
Denver mineral jig
- Rectangular tank
- Screen perforated plate, for coarse particles,installed in grinding circuits, coarse
particle
- Diaphragm for pulsation, expantion and compaction of bed
- Spigot for conventrate discharge
- removing heavy minerals from closed grinding circuits, thus preventing over-
grinding.
- Recover gold,cassiterite, hematite, ect
- rotary water valve can be adjusted, to open at any desired part of the jig cycle,
- synchronization between the valve and the plungers being achieved by a rubber
timing belt.
Conventional Mineral Jigs
- Square or rectangular tanks
- 2,3,or 4 cells in series to compensate for the increase in cross-flow velocity over jig
bed
- trapezoidal-shaped jigs were developed, circular, or radial, jig.
