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##### Gravity Separation

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**Gravity Separation**Lecture 10 – MINE 292 – 2013**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: • Jigs • Heavy media (or Dense media – DMS or HMS) • Flowing Film Methods: • Sluices • Reichert cones (pinched sluice) • 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)