heloise thiele, mintek
DESCRIPTION
TRANSCRIPT
Iron Ore Beneficiation Africa - Heavy Liquid Separation at High
Densities
Date: 17 March 2014 Author Heloise Thiele
Designation Specialist Consultant: Physical Separation
Presentation Outline
• Why is High Density HLS Required? • The MDS – Minerals Density Separator • Why could conventional HLS not be used? • Alternative powders • Evaluation method • Results • HLS versus MDS in practice • Conclusions
Why is High Density HLS Required? • Characterising Fe ores at densities >4.0g/cm3 • In the past techniques like:
– Batch Jigging/Mineral Density Separator(MDS)
– Stone-by-stone pycnometry was used • But these techniques had limitations like:
– MDS, inherent inefficiencies due to particle size effects etc. Modelling required
– Stone-by-stone pycnometry extremely time consuming and exposed to operator error
The MDS – Mineral Density Separator
The MDS – Mineral Density Separator
The MDS – Mineral Density Separator
The MDS – Results
The MDS – Modelled density distributions
The MDS – Modelled Washability results
Why could conventional HLS not be used? • Typical HLS separation makes use of mixtures of
fine atomised FeSi and TBE.
• At densities >3.8g/cm3, high viscosities prohibits efficient separation from taking place.
• The density of the FeSi used, required high mass% FeSi to be mixed with TBE (SG= 2.96g/cm3).
Alternative powders • Tungsten and Tungsten Carbide Powders were then
considered – Readily available – Fine particle size distribution – High densities
• W= 19.25g/cm3 • WC = 16.8g/cm3 compared to • FeSi = 6.8g/cm3
Evaluation method • Settling Velocities: To create a stable media for
separation to occur in, settling velocities should be low. Thus finer material will be required than with FeSi
• Viscosity: Separation efficiency is related to viscosity of the media
• Separation Efficiency: How do we measure if the separation was in fact efficient? – Density tracers – only up to 4.0g/cm3
– Classified stones
Method: Viscosity measurements
a) Physica Rheolab QC rheometer. b) Double-gap measuring system
Method: HLS
Method: HLS
Hematite Stones: Efficiency of separation
Results: Mixing Ratios
Mass [%] in TBE
SG FeSi WC W
3.2 10.7 9.3 9.0
3.6 31.4 21.9 20.9
3.8 39.1 27.2 25.7
4.0 46.1 32.0 30.5
4.2 52.5 36.4 34.8
4.4 40.3 38.6
4.6 44.0 42.1
4.8 47.2 45.2
Results: Settling Velocities • The terminal settling velocity was calculated using
the following formula: • V = kd2(Ds-Df) • k=g/18*η • Where: V= terminal velocity • k = ratio constant • g = gravitational acceleration (9.8g/m2) • η = viscosity of fluid (TBE = 0.1 P.sec) • d = diameter of the particle • Ds = density of solid • (FeSi = 6.8g/cm3, WC = 15.8g/cm3, W = 19.25g/cm3) • Df = density of fluid (TBE = 2.96g/cm3)
Results: Settling Velocities (cont)
Results: Viscosity
0.00 20.00 40.00 60.00 80.00
100.00 120.00 140.00 160.00 180.00 200.00 220.00 240.00
3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 5.75 6 6.25 6.5
Viscosity
(mPa.s)
Rela%ve density (g/cm3)
Viscosity as a func%on of medium density
WC
W
FeSi
Results: Efficiency of separation
0
10
20
30
40
50
60
70
80
90
100
3.60 3.70 3.80 3.90 4.00 4.10 4.20 4.30 4.40 4.50 4.60 4.70 4.80 4.90 5.00
Par%%on
Coe
fficien
t (%
)
Average Density (g/cm3)
Effeciency in Separa%on as func%on of density
4.29 g/cm3
4.79 g/cm3
4.55 g/cm3
D50=4.29g/cm3 Ep=0.016 D50=4.55g/cm3
Ep=0.053 D50=4.79g/cm3 Ep=0.016
HLS versus MDS in practice • High Density HLS results
HLS versus MDS in practice • HLS versus MDS (modelled HLS)
Predictive DMS modelling • Use an empirical Weibull function to represent
partition surface of gravity concentrators in terms of size-density attributes
• Y = 100[1-exp(-(ln(1/1-Yp))(ρ/ρp)(pd^q)] – Y Partition number, a function of particle size – and density – Yp Pivot partition number, representing fraction of by-pass in gravity concentrators – p that captures viscosity effects – q represents flow conditions of the separator
Predictive DMS modelling
Back to the Fe Ore example
Conclusions • The relationship between solid media density (FeSi,
W and WC) and viscosity was established • A sharp increase in media viscosity prevents FeSi in
the presence of TBE to obtain efficient separation at densities >4.0g/cm3.
• Since WC and W are at significantly higher particle densities than FeSi, finer particle size distributions, such as <12µm, should be considered for these powders.
• Fine WC (84% <25µm) in the presence of TBE is successful, in obtaining media densities as high as 6.0g/cm3, at low viscosities.
Conclusions • Very efficient separation could be measured at
densities as high as 4.79g/cm3 in WC and TBE media.
• Due to the low viscosities measured up to densities as high as 6.0g/cm3, it is expected that efficient separation could be achieved at these densities. Further testwork should be conducted to confirm this.
• The effect of particle size on the efficiency of separation should be evaluated.