Dr Fiona Sofra

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


• 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


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


Rheology?

…or how a fluid

(liquid, slurry, paste, emulsion)

responds to a force


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


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


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


• 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


• Viscosity, (Pa.s)

Shear Rate

Shear

Str

ess

Slurry flow behaviour b) how fast/easily?

Constant viscosity = Newtonian fluid

t


• 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)


Time

Shea

r S

tress

Thixotropic

Rheopectic

Fixed flow rate

Time (shear history) dependence

Thixotropy - reversible

Rheomalaxis – irreversible breakdown (flocs, agglomerates etc)


• Related to: – mineralogy

– processing

– liquid characteristics

Particle Morphology or Shape


It’s not what you do, it’s the way you do it.


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


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


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


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?


Oops…


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


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


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


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


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


– extreme, same ore body



– rare, shear induced aggregation (what implications does this

have on pumping?)


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%


Electrokinetics and Rheology – Ionic strength

Hematite IEP ~5-9

Magnetite IEP ~ 3-7 (highly variable)

dispersed

coagulated

Water quality effects


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


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


• “…fail early and fail cheaply”

Gavin Diener, yesterday.


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]

Business

Dr Fiona Sofra