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### Gravity Separation

Lecture 14 – MINE 292

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

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

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:
- Sluices
- Jigs
- Reichert cones (pinched sluice)
- Heavy media (or Dense media – DMS or HMS)
- Flowing Film Methods:
- Tables
- Spirals
- Centrifugal concentrators

Sluices

Mean Size %Recovery

(microns)

10,000 100

2,600 100

1,200 100

800 67

500 56

200 37

120 13

90 12

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)

Jigs

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

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:
- 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)

Jigs

- Applications:
- Gold recovery in primary grinding
- Coal separation from ash
- Tin recovery (cassiterite)

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
- 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
- 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 4.20 @ 20 °C or 5.00 @ 90 °C (very poisonous)

Dense Media Separation

- Heavy Liquid Analysis (tin ore)

S.G. Weight% Cum. Assay Distribution

Fraction Weight% %Sn % Cum. %

- 2.55 1.57 1.57 0.003 0.004 0.004

+ 2.55 - 2.60 9.22 10.79 0.04 0.33 0.334

+ 2.60 - 2.65 26.11 36.90 0.04 0.93 1.27

+ 2.65 - 2.70 19.67 56.57 0.04 0.70 1.97

+ 2.70 - 2.75 11.91 68.48 0.17 1.81 3.78

+ 2.75 - 2.80 10.92 79.40 0.34 3.32 7.10

+ 2.80 - 2.85 7.87 87.27 0.37 2.60 9.70

+ 2.85 - 2.90 2.55 89.82 1.30 2.96 12.66

+ 2.90 10.18 100.00 9.60 87.34 100.00

Total 100.00 - 1.12 100.00 -

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
- - 1.30 0.77 4.4 0.77 4.4 99.23 22.3
- + 1.30 - 1.32 0.73 5.6 1.50 5.0 98.50 22.4
- + 1.32 - 1.34 1.26 6.5 2.76 5.7 97.24 22.6
- + 1.34 - 1.36 4.01 7.2 6.77 6.6 93.24 23.3
- + 1.36 - 1.38 8.92 9.2 15.69 8.1 84.31 24.8
- + 1.38 - 1.40 10.33 11.0 26.02 9.2 73.98 26.7
- + 1.40 - 1.42 9.28 12.1 35.30 10.0 64.70 28.8
- + 1.42 - 1.44 9.00 14.1 44.30 10.8 55.70 31.2
- + 1.44 - 1.46 8.58 16.0 52.88 11.7 47.12 34.0
- + 1.46 - 1.48 7.79 17.9 60.67 12.5 39.33 37.1
- + 1.48 - 1.50 6.42 21.5 67.09 13.3 32.91 40.2
- + 1.50 32.91 40.2 100.00 22.2 0.00 -
- Total 100.00 22.2 - - -

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
- 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 Cum. Wt%

(microns) Passing

-300 99.6

-150 97.5

- 75 94.5

- 38 86.9

- 15 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 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%

Tables

- Particle action in a flowing film

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

- 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)

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

Magnetic Separation

- Dry High Gradient Magnetic Separator

Filtration

- Filter Plate Press

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