### Gravity Separation

```Lecture 10 – MINE 292 – 2013
Free Settling Ratio
For fine particles that follow Stoke’s Law (< 50 microns)
(  h   f ) 
0 .5
F .S .R .  

(  l   f ) 
If F.S.R is greater than 2.5, then effective separation can be achieved
If F.S.R is less than 1.5, then effective separation cannot be achieved
Free Settling Ratio
For coarse particles that follow Newton’s Law
( h  f )
F .S .R . 
( l  f )
If F.S.R is greater than 2.5, then effective separation can be achieved
If F.S.R is less than 1.5, then effective separation cannot be achieved
Free Settling Ratio
1. Consider a mixture of fine galena and fine quartz particles in water
F.S.R. = [(7.5 – 1)/(2.65 – 1)]0.5 = 1.99
So a fine galena particle will settle at the same rate as a
quartz particle that is about twice as large in diameter
2. Consider coarse galena and coarse quartz particles in water
F.S.R. = (7.5 – 1)/(2.65 – 1) = 3.94
So a coarse galena particle will settle at the same rate as a
quartz particle that is about four times as large in diameter
Always aim to achieve separation at as coarse a size as possible
If significant fines content, then separate and process separately
Free Settling Ratio
General Guideline:
If F.S.R. = 3.0, one can assume an efficiency of about 100%
If F.S.R. = 2.5, one can assume an efficiency of about 80%
If F.S.R. = 1.5, one can assume an efficiency of about 20%
If F.S.R. = 1.0, one can assume the efficiency will be 0%
where efficiency of separation = f (conc. grade, %recovery)
Gravity Separation Devices
 Sedimentation Dependent:
 Jigs
 Heavy media (or Dense media – DMS or HMS)
 Flowing Film Methods:
 Sluices
 Reichert cones (pinched sluice)
 Tables
 Spirals
 Centrifugal concentrators
Sluices
Sluices
Sluices
Sluices
Sluices
Sluices
Sluices
Sluices
Mean Size
(microns)
10,000
2,600
1,200
800
500
200
120
90
%Recovery
100
100
100
67
56
37
13
12
Jigs
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Primary stage to recover coarse liberated minerals > 2mm
Feed slurry enters hutch beneath lip into slurry
Moving slurry “bed” located above a screen
Hutch fluid is subjected to a pulsating motion
Upward hutch water creates dilation and compaction
Pulses caused by a diaphragm or vibration of screen
Separation assisted by “ragging “ (galena, lead, magnetite, FeSi)
High S.G. particles pass through ragging and screen
Low SG particles discharge over hutch lip
Feed size ( 1 inch to 100 mesh)
Jigs
 Floats can be tailings or concentrate depending on
application (coal floats > concentrate / gold floats > tailing)
Jigs
Jigs
 Idealized jigging particle distribution over time
Jigs
 Idealized water flow velocities
Jigs
 Idealized water flow velocities
Jigs
 Idealized water flow velocities
Jigs
 Particle separation - conventional
Jigs
 Particle separation – saw-tooth pulse
Jigs
 Baum Jig (coal)
 Air used to create pulsation
Jigs
 Batac Jig (coal)
 Air used to create pulsation (note multiple chambers)
Jigs
 Operating variables:
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Hutch water flow
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Pulsation frequency
Pulsation stroke length
Ragging SG, size and shape
Bed depth
Screen aperture size
Feed rate and density ( 20 tph / hutch at 40% solids)
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Jigs
 Applications:
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Gold recovery in primary grinding
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Coal separation from ash
Tin recovery (cassiterite)
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Reichert Cone
 Can recover iron minerals down to 400 mesh (in theory)
Reichert Cone
 Can recover iron minerals down to 400 mesh (in theory)
Reichert Cone
 Can recover iron minerals down to 400 mesh (in theory)
Dense Media Separation
 Coal – DMS Partition Curve
Free Settling Ratio - DMS
1. Consider a mixture of fine galena and fine quartz particles in water
F.S.R. = [(7.5 – 1)/(2.65 – 1)]0.5 = 1.99
So a fine galena particle will settle at the same rate as a
quartz particle that is about twice as large in diameter
2. Consider coarse galena and quartz particles in a liquid with S.G. = 1.5
F.S.R. = (7.5 – 1.5)/(2.65 – 1.5) = 5.22
Note that the use of a fluid with higher density produces a
much higher F.S.R. meaning separation efficiency is enhanced
In the lab, we can use liquids;
in the plant we use fine slurry of a heavy mineral (magnetite)
Dense Media Separation
Procedure for Laboratory DMS Liquid Separation
Dense Media Separation
Heavy Liquids
a. Tetrabromo-ethane (TBE) - S.G. 2.96
- diluted with mineral spirits or carbon tetrachloride (S.G. 1.58)
b. Bromoform - S.G. 2.89
- diluted with carbon tetrachloride to yield fluids from 1.58-2.89
c. Diiodomethane - S.G. 3.30
- diluted with triethylorthophosphate
d. Solutions of sodium polytungstate - S.G. 3.10
- non-volatile/less toxic/lower viscosity)
e. Clerici solution (thallium formate – thallium malonite)
- S.G. up to 4.20 @ 20 °C or 5.00 @ 90 °C (very poisonous)
Dense Media Separation
 Heavy Liquid Analysis (tin ore)
S.G.
Fraction
- 2.55
+ 2.55 - 2.60
+ 2.60 - 2.65
+ 2.65 - 2.70
+ 2.70 - 2.75
+ 2.75 - 2.80
+ 2.80 - 2.85
+ 2.85 - 2.90
+ 2.90
Total
Weight%
1.57
9.22
26.11
19.67
11.91
10.92
7.87
2.55
10.18
100.00
Cum.
Weight%
1.57
10.79
36.90
56.57
68.48
79.40
87.27
89.82
100.00
-
Assay
%Sn
0.003
0.04
0.04
0.04
0.17
0.34
0.37
1.30
9.60
1.12
Distribution
%
Cum. %
0.004
0.004
0.33
0.334
0.93
1.27
0.70
1.97
1.81
3.78
3.32
7.10
2.60
9.70
2.96
12.66
87.34
100.00
100.00
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Dense Media Separation
 Heavy Liquid Separation (coal sink/float)
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S.G.
Fraction
- 1.30
+ 1.30 - 1.32
+ 1.32 - 1.34
+ 1.34 - 1.36
+ 1.36 - 1.38
+ 1.38 - 1.40
+ 1.40 - 1.42
+ 1.42 - 1.44
+ 1.44 - 1.46
+ 1.46 - 1.48
+ 1.48 - 1.50
+ 1.50
Total
Weight%
0.77
0.73
1.26
4.01
8.92
10.33
9.28
9.00
8.58
7.79
6.42
32.91
100.00
Ash
%
4.4
5.6
6.5
7.2
9.2
11.0
12.1
14.1
16.0
17.9
21.5
40.2
22.2
Cum. Floats (Clean Coal) Cum. Sinks (Residue)
Wt%
%Ash
Wt% %Ash
0.77
4.4
99.23
22.3
1.50
5.0
98.50
22.4
2.76
5.7
97.24
22.6
6.77
6.6
93.24
23.3
15.69
8.1
84.31
24.8
26.02
9.2
73.98
26.7
35.30
10.0
64.70
28.8
44.30
10.8
55.70
31.2
52.88
11.7
47.12
34.0
60.67
12.5
39.33
37.1
67.09
13.3
32.91
40.2
100.00
22.2
0.00
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Dense Media Separation
 Rotating Drum DMS (50 – 200 mm)
Dense Media Separation
 Rotating Drum DMS (50 – 200 mm)
Dense Media Separation
 Drum DMS Raw Coal Capacities
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1.22 m ( 4-ft) diameter drum = 45 tonnes/hr (50 tons/hr)
1.83 m ( 6-ft) diameter drum = 91 tonnes/hr (100 tons/hr)
2.44 m ( 8-ft) diameter drum = 159 tonnes/hr (175 tons/hr)
3.05 m (10-ft) diameter drum = 249 tonnes/hr (275 tons/hr)
3.66 m (12-ft) diameter drum = 363 tonnes/hr (400 tons/hr)
Dense Media Separation
 DMS Cyclone (1 – 150 mm)
Dense Media Separation
 DMS Cyclone (1 – 150 mm)
Dense Media Separation
 Magnetite Slurry Particle Size (media S.G. = 1.4)
Size
(microns)
Cum. Wt%
Passing
-300
-150
- 75
- 38
- 15
99.6
97.5
94.5
86.9
43.0
Magnetite Consumption = 1.2 kg/t
Dense Media Separation
 DMS Mass Balance Example
Wt%
Assays
Distribution
%Solids
Solids %Fe3O4 %Coal %Fe2O4 %Coal
O/F
31.0
28.03
30.15 69.85 11.75 71.34
U/F
67.2
71.97
89.07 10.93 88.35 28.66
DMS Feed 50.2 100.00
72.55 27.45 100.00 100.00
Dense Media Separation
 DMS Separator Performance
Ash in feed
Ash in clean coal
Ash in refuse
Yield of clean coal
Combustible recovery
Ash rejection
33.1%
15.6%
72.0%
69.0%
87.0%
67.5%
Tables
Tables
 Particle action in a flowing film
Tables
Tabling
 Shaking Table
Tabling
 Shaking Table Flowsheet (note feed is classified)
Tabling
 Stacked Shaking Tables (to minimize floor space)
Tabling
 Operating variables include:
 Tilt angle
 Splitter positions
 Stroke length
 Feed rate
Spiral Separator
 Spirals
Spiral Separator
 Double Start Humphrey Spirals
Spiral Separator
 Spiral Concentrator Circuit at Quebec Cartier Mining
Spiral Separator
 Spiral Concentrator Recovery by Size at QCM
Spiral Separator
 Operating variables include:
 Feed rate (1 to 6 tph/spiral start depending on ore)
 Feed density (25 - 50 %solids depending on duty)
 Splitter positions
Centrifugal concentrators
 Falcon (Sepro)
 Knelson (FD Schmidt)
Centrifugal concentrators
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Falcon C and Knelson CVD – continuous units
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Initial units were SB types (semi batch)
Extensive use in the gold industry
Falcon U/F is a batch machine spinning at extremely high speeds (up to 600G)
All units exploit centrifugal force generated by spin to enhance gravity separation
Apply to fine gold particles (down to 400 mesh)
Slurry enters centrally and is distributed outwards at the base of the cone by centrifugal force
Slurry /flows up inclined surface of bowl with high SG particles on the outside closest to the bowl surface
and low SG particles on the inside which discharge over the lip at the top of the bowl.
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Falcon C spins generates a G force up to 200
Features a positioning valve for continuous concentrate discharge
Knelson CVD operates at lower G force (up to 150G)
Uses an injection water system to fluidize the bed and collect gold particles in rings
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Operating variables include:
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Spin
Concentrate valve pulsing frequency and duration (Knelson)
Injection water flow (Knelson)
Concentrate valve position (Falcon C)
Centrifugal concentrators
 Falcon C and Knelson CVD – continuous units
 Applications
 Cyclone underflow in primary grinding circuit
 Flotation feed
 Tailings recovery
 Placer gold fines
Centrifugal concentrators
 Cyclone Partition Curves (GRG = Gravity Recoverable Gold)
Centrifugal concentrators
 Knelson lab unit
Centrifugal concentrators
 Knelson SB unit
 Knelson CVD unit
Centrifugal concentrators
 Falcon “SB”unit
 Falcon “C”unit
End of Lecture
Magnetic Separation
 Dry High Gradient Magnetic Separator
Electronic Sorting
Filtration
 Filter Plate Press
```