Gravity Separation

Lecture 10 – MINE 292 – 2013

Free Settling Ratio

5.0

fl

fh

)()(

.R.S.F

If F.S.R is greater than 2.5, then effective separation can be achievedIf F.S.R is less than 1.5, then effective separation cannot be achieved

For fine particles that follow Stoke’s Law (< 50 microns)

Free Settling Ratio

)()(

.R.S.Ffl

fh

If F.S.R is greater than 2.5, then effective separation can be achievedIf F.S.R is less than 1.5, then effective separation cannot be achieved

For coarse particles that follow Newton’s Law

Free Settling Ratio

Always aim to achieve separation at as coarse a size as possibleIf significant fines content, then separate and process separately

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) = 3.94So a coarse galena particle will settle at the same rate as a quartz particle that is about four times as large in diameter

Free Settling RatioGeneral 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 DevicesSedimentation Dependent:

Jigs Heavy media (or Dense media – DMS or HMS)

Flowing Film Methods: Sluices Reichert cones (pinched sluice) Tables SpiralsCentrifugal concentrators

Sluices

Sluices

Sluices

Sluices

Sluices

Sluices

Sluices

SluicesMean Size %Recovery (microns) 10,000 100 2,600 100 1,200 100 800 67 500 56 200 37 120 13 90 12

JigsPrimary stage to recover coarse liberated minerals > 2mm Feed slurry enters hutch beneath lip into slurryMoving slurry “bed” located above a screenHutch fluid is subjected to a pulsating motionUpward hutch water creates dilation and compactionPulses caused by a diaphragm or vibration of screenSeparation assisted by “ragging “ (galena, lead, magnetite, FeSi)High S.G. particles pass through ragging and screenLow SG particles discharge over hutch lipFeed size ( 1 inch to 100 mesh)

JigsFloats can be tailings or concentrate depending on

application (coal floats > concentrate / gold floats > tailing)

Jigs

JigsIdealized jigging particle distribution over time

JigsIdealized water flow velocities

JigsIdealized water flow velocities

JigsIdealized water flow velocities

JigsParticle separation - conventional

JigsParticle separation – saw-tooth pulse

JigsBaum Jig (coal)Air used to create pulsation

JigsBatac Jig (coal)Air used to create pulsation (note multiple chambers)

JigsOperating variables:

Hutch water flowPulsation frequencyPulsation stroke lengthRagging SG, size and shapeBed depthScreen aperture sizeFeed rate and density ( 20 tph / hutch at 40% solids)

JigsApplications:

Gold recovery in primary grindingCoal separation from ashTin recovery (cassiterite)

Reichert ConeCan recover iron minerals down to 400 mesh (in theory)

Reichert ConeCan recover iron minerals down to 400 mesh (in theory)

Reichert ConeCan recover iron minerals down to 400 mesh (in theory)

Dense Media SeparationCoal – DMS Partition Curve

Free Settling Ratio - DMS

In the lab, we can use liquids; in the plant we use fine slurry of a heavy mineral (magnetite)

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) = 5.22Note that the use of a fluid with higher density produces a much higher F.S.R. meaning separation efficiency is enhanced

Dense Media Separation

Procedure for Laboratory DMS Liquid Separation

Dense Media SeparationHeavy 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 SeparationHeavy Liquid Analysis (tin ore)

S.G. Weight% Cum. Assay DistributionFraction Weight% %Sn % Cum. % - 2.55 1.57 1.57 0.003 0.004 0.004+ 2.55 - 2.60 9.22 10.790.04 0.33 0.334+ 2.60 - 2.65 26.11 36.900.04 0.93 1.27+ 2.65 - 2.70 19.67 56.570.04 0.70 1.97+ 2.70 - 2.75 11.91 68.480.17 1.81 3.78+ 2.75 - 2.80 10.92 79.400.34 3.32 7.10+ 2.80 - 2.85 7.87 87.270.37 2.60 9.70+ 2.85 - 2.90 2.55 89.821.30 2.96 12.66+ 2.90 10.18 100.00 9.60 87.34100.00Total 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 SeparationRotating Drum DMS (50 – 200 mm)

Dense Media SeparationRotating Drum DMS (50 – 200 mm)

Dense Media SeparationDrum 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 SeparationDMS Cyclone (1 – 150 mm)

Dense Media SeparationDMS Cyclone (1 – 150 mm)

Dense Media SeparationMagnetite 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 SeparationDMS 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 28.66DMS Feed 50.2 100.00 72.55 27.45 100.00 100.00

Dense Media SeparationDMS 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

TablesParticle action in a flowing film

Tables

TablingShaking Table

TablingShaking Table Flowsheet (note feed is classified)

TablingStacked Shaking Tables (to minimize floor space)

TablingOperating variables include:

Tilt angle

Splitter positions

Stroke length

Feed rate

Spiral SeparatorSpirals

Spiral SeparatorDouble Start Humphrey Spirals

Spiral SeparatorSpiral Concentrator Circuit at Quebec Cartier Mining

Spiral SeparatorSpiral Concentrator Recovery by Size at QCM

Spiral SeparatorOperating variables include:

Feed rate (1 to 6 tph/spiral start depending on ore)

Feed density (25 - 50 %solids depending on duty)

Splitter positions

Centrifugal concentratorsFalcon (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 concentratorsFalcon C and Knelson CVD – continuous units

Applications Cyclone underflow in primary grinding circuitFlotation feedTailings recoveryPlacer gold fines

Centrifugal concentratorsCyclone Partition Curves (GRG = Gravity Recoverable Gold)

Centrifugal concentratorsKnelson lab unit

Centrifugal concentratorsKnelson SB unit Knelson CVD unit

Centrifugal concentratorsFalcon “SB”unit Falcon “C”unit

End of Lecture

Magnetic SeparationDry High Gradient Magnetic Separator

Electronic Sorting

FiltrationFilter Plate Press