1. Gravity Separation
Lecture 10 – MINE 292 – 2013

2. Free Settling Ratio
For fine particles that follow Stoke’s Law (< 50 microns)
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

3. Free Settling Ratio For coarse particles that follow Newton’s Law
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

4. 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

5. 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)

6. 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

7. Sluices

8. Sluices

9. Sluices

10. Sluices

11. Sluices

12. Sluices

13. Sluices

14. Sluices Mean Size %Recovery (microns) 10,000 100 2,600 100 1,200 100
10, 2, 1,

15. Jigs 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)

16. Jigs
Floats can be tailings or concentrate depending on application (coal floats > concentrate / gold floats > tailing)

17. Jigs

18. Jigs
Idealized jigging particle distribution over time

19. Jigs
Idealized water flow velocities

20. Jigs
Idealized water flow velocities

21. Jigs
Idealized water flow velocities

22. Jigs
Particle separation - conventional

23. Jigs
Particle separation – saw-tooth pulse

24. Jigs
Baum Jig (coal)
Air used to create pulsation

25. Jigs
Batac Jig (coal)
Air used to create pulsation (note multiple chambers)

26. Jigs Operating variables: Hutch water flow 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)

27. Jigs Applications: Gold recovery in primary grinding
Coal separation from ash
Tin recovery (cassiterite)

28. Reichert Cone
Can recover iron minerals down to 400 mesh (in theory)

29. Reichert Cone
Can recover iron minerals down to 400 mesh (in theory)

30. Reichert Cone
Can recover iron minerals down to 400 mesh (in theory)

31. Dense Media Separation
Coal – DMS Partition Curve

32. 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)

33. Dense Media Separation
Procedure for Laboratory DMS Liquid Separation

34. Dense Media Separation
Heavy Liquids
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
Diiodomethane - S.G. 3.30
- diluted with triethylorthophosphate
Solutions of sodium polytungstate - S.G. 3.10
- non-volatile/less toxic/lower viscosity)
Clerici solution (thallium formate – thallium malonite)
- S.G. up to 20 °C or 90 °C (very poisonous)

35. Dense Media Separation
Heavy Liquid Analysis (tin ore)
S.G. Weight% Cum. Assay Distribution
Fraction Weight% %Sn % Cum. %
Total

36. Dense Media Separation
Heavy Liquid Separation (coal sink/float)
S.G. Weight% Ash Cum. Floats (Clean Coal) Cum. Sinks (Residue)
Fraction % Wt% %Ash Wt% %Ash
Total

37. Dense Media Separation
Rotating Drum DMS (50 – 200 mm)

38. Dense Media Separation
Rotating Drum DMS (50 – 200 mm)

39. Dense Media Separation
Drum DMS Raw Coal Capacities
1.22 m ( 4-ft) diameter drum = tonnes/hr (50 tons/hr)
1.83 m ( 6-ft) diameter drum = tonnes/hr (100 tons/hr)
2.44 m ( 8-ft) diameter drum = tonnes/hr (175 tons/hr)
3.05 m (10-ft) diameter drum = tonnes/hr (275 tons/hr)
3.66 m (12-ft) diameter drum = tonnes/hr (400 tons/hr)

40. Dense Media Separation
DMS Cyclone (1 – 150 mm)

41. Dense Media Separation
DMS Cyclone (1 – 150 mm)

42. Dense Media Separation
Magnetite Slurry Particle Size (media S.G. = 1.4)
Size Cum. Wt%
(microns) Passing
Magnetite Consumption = 1.2 kg/t

43. Dense Media Separation
DMS Mass Balance Example
Wt% Assays Distribution
%Solids Solids %Fe3O4 %Coal %Fe2O4 %Coal
O/F
U/F
DMS Feed

44. Dense Media Separation
DMS Separator Performance
Ash in feed 33.1%
Ash in clean coal 15.6%
Ash in refuse 72.0%
Yield of clean coal 69.0%
Combustible recovery 87.0%
Ash rejection 67.5%

45. Tables

46. Tables
Particle action in a flowing film

47. Tables

48. Tabling
Shaking Table

49. Tabling
Shaking Table Flowsheet (note feed is classified)

50. Tabling
Stacked Shaking Tables (to minimize floor space)

51. Tabling Operating variables include: Tilt angle Splitter positions
Stroke length
Feed rate

52. Spiral Separator
Spirals

53. Spiral Separator
Double Start Humphrey Spirals

54. Spiral Separator
Spiral Concentrator Circuit at Quebec Cartier Mining

55. Spiral Separator
Spiral Concentrator Recovery by Size at QCM

56. Spiral Separator Operating variables include:
Feed rate (1 to 6 tph/spiral start depending on ore)
Feed density ( %solids depending on duty)
Splitter positions

57. Centrifugal concentrators
Falcon (Sepro)
Knelson (FD Schmidt)

58. Centrifugal concentrators
Falcon C and Knelson CVD – continuous units
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.
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
Operating variables include:
Spin
Concentrate valve pulsing frequency and duration (Knelson)
Injection water flow (Knelson)
Concentrate valve position (Falcon C)

59. Centrifugal concentrators
Falcon C and Knelson CVD – continuous units
Applications
Cyclone underflow in primary grinding circuit
Flotation feed
Tailings recovery
Placer gold fines

60. Centrifugal concentrators
Cyclone Partition Curves (GRG = Gravity Recoverable Gold)

61. Centrifugal concentrators
Knelson lab unit

62. Centrifugal concentrators
Knelson SB unit
Knelson CVD unit

63. Centrifugal concentrators
Falcon “C”unit
Falcon “SB”unit

64. End of Lecture

65. Magnetic Separation
Dry High Gradient Magnetic Separator

66. Electronic Sorting

67. Filtration
Filter Plate Press