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FeTech 2013
Effects of Dewatering Iron Ore Slurries
for Improved Tailings Disposal and
Water Recovery
Fiona Sofra
FeTech November 2013
• Why dewater?
• Effect of mineralogy, PSD, particle shape, pH, shear
processes on slurry flow (rheology) and dewatering
properties
• Optimising performance by understanding and/or
manipulating flow properties
• How to minimize testwork to maximize the information
gained
Outline
FeTech November 2013
• Reduced footprint – land availability and cost, environmental
and social impacts
• Safety – reduced water storage and high dams, creation of
stable landform less susceptible to liquefaction. Dam failures
average one per year (ICOLD).
• Expedite/progressive rehabilitation
• Increased water recovery/recycle and decreased consumption
– $ and environmental impacts of water consumption
– Water availability/quality
– Recovery of valuables in process water
Motivation for Dewatering
FeTech November 2013
Wet Disposal:
Storage Efficiency = X
Central Thickened
Tailings Deposition:
Storage Efficiency = 1.5X
Storage Efficiency = 2X - 3X
Dry Stacking:
1% 10-15%
+ paste backfill
Tailings storage options
Up to ~70% of total tailings
FeTech November 2013
Rheology?
…or how a fluid
(liquid, slurry, paste, emulsion)
responds to a force
FeTech November 2013
Where is rheology important?
Source: www.projectconnect.com.au/Project_Details.asp?PID=349
Filter press
Slurry
tank
Concentrate
launder
Slurry
pipeline
Concentrate
pump
Magnetite
thickener
Tailings dam Tailings
thickener
Regrind ball
mill
Classifying
screen
Finishing
magnetic
separator
Secondary
classifying
cyclone Rough
magnetic
separator
Primary
classifying
cyclone
Pebble
crusher
Autogenous
grinding mill
FeTech November 2013
Solids concentration increases…
• Greater particle interaction. Especially fines.
Dewatering becomes more difficult
• Compressive yield stress increases
• permeability decreases
Yield stress increases
Viscosity changes
What changes when slurry is dewatered?
Removal from thickener/filter
Pumping and pipeline transport
Deposition
FeTech November 2013
Rheology
• The flow behaviour, or rheology is a function
of all of the physical characteristics of the
slurry!
• Solids concentration
• Particle size distribution (PSD)
• Solids density (can vary with PSD)
• Particle morphology or shape
• Particle mineralogy/surface chemistry, liquid
chemistry
FeTech November 2013
• Yield stress, ty (Pa)
Concentration
Yie
ld S
tre
ss
Slurry flow behaviour a) will it flow?
Yielding in
compression
(thickening) is
analogous to
yielding in shear
~ order of
magnitude
difference
FeTech November 2013
• Viscosity, (Pa.s)
Shear Rate
Shear
Str
ess
Slurry flow behaviour b) how fast/easily?
Constant viscosity = Newtonian fluid
t
FeTech November 2013
• Viscosity, (Pa.s)
tShear Rate
Shea
r S
tres
s
True Yield Stress, ty
Bingham Fluid
Yield-pseudoplastic
Yield-dilatant
Extrapolated
Bingham
yield stress
Shear Rate
Shea
r S
tres
s
True Yield Stress, ty
Bingham Fluid
Yield-pseudoplastic
Yield-dilatant
Extrapolated
Bingham
yield stress
Shear Rate
Shear
Str
ess
Shear rate dependence
(shear thinning)
(shear thickening)
FeTech November 2013
Time
Shea
r S
tress
Thixotropic
Rheopectic
Fixed flow rate
Time (shear history) dependence
Thixotropy - reversible
Rheomalaxis – irreversible breakdown (flocs, agglomerates etc)
FeTech November 2013
• Related to: – mineralogy
– processing
– liquid characteristics
Particle Morphology or Shape
FeTech November 2013
It’s not what you do, it’s the way you do it.
FeTech November 2013
DV
H
Speed TorqueTorsionHead
Sample
Vane
DV
H
Speed TorqueTorsionHead
Sample
Vane
Vane
Cup and Bob
Slump
Capillary
R
L
TorqueSensor
Cup
Bob
Air Gap
Fluid
RR
L
TorqueSensor
Cup
Bob
Air Gap
Fluid
R
L
PGas
Patm
R2
R0
L
1
2
0
L
PGas
Patm
R2
R0
L
1
2
0
Pipeline
Slurry rheology measurement
FeTech November 2013
0
100
200
300
400
500
600
700
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Shear
yie
ld s
tress (
Pa)
Solids Concentration(mass fraction)
Coal Mine Clay Tailings
Clay Tailings
Sand Mine Clay Tailings 1
Sand Mine Clay Tailings 2
Manganese Mine Tailings
Nickel Mine Tailings 1
Red Mud Tailings 2
Copper Tailings
Paste Fill Sample
Uranium tailings
Copper tailings
Nickel Limonite
Fly Ash
Mineral Sands tailings
Lead zinc tailings
Neut zinc tailings
Red mud, Jamaica
Red mud, Australia
Fe Tails 1
Fe Tails 2
Fe Tails 3
Fe Tails 4
Yield Stress Profiles
FeTech November 2013
Yield Stress – Fe Tailings Mineralogy and PSD
0
50
100
150
200
250
300
350
400
0.50 0.52 0.54 0.56 0.58 0.60 0.62 0.64 0.66 0.68 0.70 0.72 0.74 0.76 0.78
Yie
ld S
tre
ss
(P
a)
Solids Mass Fraction (x)
Mean PSD:
40 – 65mm
Mean PSD:
115 – 334mm
100Pa: 61 to 73wt%
Both
materials to
be processed
in one plant
FeTech November 2013
Solids Mass Fraction (x)
Yie
ld S
tress (
Pa)
unsheared sheared
Thickener
rake
Pipeline
transport
Design point
Yield stress – flocculation and thickening
-Which curve to use for design?
FeTech November 2013
Oops…
FeTech November 2013
0
10
20
30
40
50
60
70
80
90
100
0.56 0.58 0.6 0.62 0.64 0.66 0.68 0.7
Sh
ear
Yie
ld S
tress
(P
a)
Solids Mass Fraction, x (-)
Unsheared
Sheared
Yield stress – shear thickening long distance pumping
Same material –
increased shearing
causes an increase
in yield stress
FeTech November 2013
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0.1 1 10 100 1000 10000
Dif
fere
nti
al
Vo
lum
e P
erc
en
t (%
)
Particle Diameter (mm)
Unsheared
Sheared
PSD changes causing yield stress increase
FeTech November 2013
Effect of solids concentration
- on flow curves
- implications for ‘non-settling’ slurries
0
20
40
60
80
100
120
0 100 200 300 400 500 600 700 800
Shear Rate (s-1
)
Sh
ear
Str
ess (
Pa)
Fe Tails 59.6wt%"
Fe Tails 58.7wt%"
Fe Tails 57.2wt%"
Fe Tails 55.7wt%"
tt BB
FeTech November 2013
0
50
100
150
200
250
300
0 100 200 300 400 500 600 700
Time of shear (sec)
Van
e y
ield
str
ess (
Pa)
37.22 wt%
42.09 wt%
45.18 wt%
1490s
4500s
1170s
Effect of shear history
– common, flocculated tailings…can be exploited in thickening and pipeline
transport
FeTech November 2013
0
100
200
300
400
500
600
700
800
0 50 100 150 200
Time (min)
Yie
ld S
tre
ss
(P
a)
Limonite 1
Saprolite 2
Effect of shear history
– extreme, same ore body
FeTech November 2013
Effect of shear history
– rare, shear induced aggregation (what implications does this
have on pumping?)
FeTech November 2013
0
20
40
60
80
100
120
140
160
0 200 400 600 800 1000 1200Shear Rate (s
-1)
Sh
ear
Str
ess (
Pa)
96 hrs
24 hrs
24 hrs
18 hrs
12 hrs
3 hrs
0 hrs
Effect of shear
– 62wt%
FeTech November 2013
Electrokinetics and Rheology – Ionic strength
Hematite IEP ~5-9
Magnetite IEP ~ 3-7 (highly variable)
dispersed
coagulated
Water quality effects
FeTech November 2013
Calcium ion concentration [CaCl2], M
0.0 0.001 0.002 0.003 0.005 0.01 0.02 0.03 0.04 0.05 0.1 0.2 0.5
Sediment solids concentration (wt%)
NA 11.9 23.1 24.8 25.1 25.2 25.6 27.3 28.5 32.0 35.2 41.5 45.8
weeks hours
Controlling clay dispersion – settling effects
FeTech November 2013
First Order:
• Mineralogy – variability
• PSD
• SG
• Yield stress profile
• Any shear history dependence?
Second order:
• Flow curves – effect of solids concentration
• Surface chemistry effects (Zeta potential, effect of ionic strength, additives)
• Quantification of shear history effects
• Quantification of PSD effects
• Clay analysis
Minimising rheology testwork
FeTech November 2013
• “…fail early and fail cheaply”
Gavin Diener, yesterday.
FeTech November 2013
Contact Details: Fiona Sofra Managing Director Rheological Consulting Services Pty Ltd The University of Melbourne, Vic 3010 Australia p: +61 (0)3 8344 6385 f: +61 (0)3 8344 3748 m: +61 (0)413 953 036 e: [email protected]