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Gravity Separation Lecture 10 – MINE 292 – 2013

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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

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**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

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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

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**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)

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**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

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Sluices

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Sluices

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Sluices

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Sluices

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Sluices

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Sluices

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Sluices

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

10, 2, 1,

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**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)

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

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Jigs

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Jigs Idealized jigging particle distribution over time

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Jigs Idealized water flow velocities

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Jigs Idealized water flow velocities

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Jigs Idealized water flow velocities

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Jigs Particle separation - conventional

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Jigs Particle separation – saw-tooth pulse

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Jigs Baum Jig (coal) Air used to create pulsation

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

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**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)

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**Jigs Applications: Gold recovery in primary grinding**

Coal separation from ash Tin recovery (cassiterite)

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

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

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

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**Dense Media Separation**

Coal – DMS Partition Curve

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**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)

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**Dense Media Separation**

Procedure for Laboratory DMS Liquid Separation

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**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)

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**Dense Media Separation**

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

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**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

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**Dense Media Separation**

Rotating Drum DMS (50 – 200 mm)

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**Dense Media Separation**

Rotating Drum DMS (50 – 200 mm)

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**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)

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**Dense Media Separation**

DMS Cyclone (1 – 150 mm)

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**Dense Media Separation**

DMS Cyclone (1 – 150 mm)

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**Dense Media Separation**

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

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**Dense Media Separation**

DMS Mass Balance Example Wt% Assays Distribution %Solids Solids %Fe3O4 %Coal %Fe2O4 %Coal O/F U/F DMS Feed

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**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%

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Tables

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Tables Particle action in a flowing film

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Tables

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Tabling Shaking Table

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Tabling Shaking Table Flowsheet (note feed is classified)

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Tabling Stacked Shaking Tables (to minimize floor space)

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**Tabling Operating variables include: Tilt angle Splitter positions**

Stroke length Feed rate

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Spiral Separator Spirals

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Spiral Separator Double Start Humphrey Spirals

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Spiral Separator Spiral Concentrator Circuit at Quebec Cartier Mining

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Spiral Separator Spiral Concentrator Recovery by Size at QCM

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**Spiral Separator Operating variables include:**

Feed rate (1 to 6 tph/spiral start depending on ore) Feed density ( %solids depending on duty) Splitter positions

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**Centrifugal concentrators**

Falcon (Sepro) Knelson (FD Schmidt)

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**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)

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**Centrifugal concentrators**

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

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**Centrifugal concentrators**

Cyclone Partition Curves (GRG = Gravity Recoverable Gold)

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**Centrifugal concentrators**

Knelson lab unit

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**Centrifugal concentrators**

Knelson SB unit Knelson CVD unit

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**Centrifugal concentrators**

Falcon “C”unit Falcon “SB”unit

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End of Lecture

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Magnetic Separation Dry High Gradient Magnetic Separator

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Electronic Sorting

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Filtration Filter Plate Press

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