1. Marek S. Żbik1,2, David J. Williams1
1Geotechnical Engineering Centre, The University of Queensland, Brisbane
Qld Australia.
2Centre for Tropical Crops and Biocommodities
Faculty of Science & Technology
Qeensland University of Technology Brisbane Qld Australia
Clay suspension voluminous
structure, the possible cause of poor
settling and sludge dewatering

2. Clay-Rich Layers within Coal
Rock layer
Coal with clay layers

3. Tailings Management
3
Tailings slurry
(typically segregating)
Thickened tailings
(dewatered, ideally non-segregating
“Wet” filter cake
(near-saturated)
“Dry” filter cake
(85 to 70% saturated)
Simple water management
Efficient water recovery
Process chemical recovery
Minimal containment required
Negligible seepage losses
Progressive rehabilitation
possible
Stable tailings mass
High OpEx and CapEx,
but low rehabilitation cost
Complex water management
Inefficient water recovery
Containment required
Seepage likely
Rehabilitation difficult
Likely low OpEx and CapEx,
but high rehabilitation cost Paste tailings
(dewatered, ideally non-bleeding
CONTINUUM
Pumpable
Non-Pumpable
Clay-rich tailings
are stuck here!

4. Na-Bentonite – Effect of Initial %
Solids on Settling
CRICOS Provider No
00025B
Initial % Solids >5% will not settle!

5. Mechanisms of aggregate formation and
transformation
At critical concentration, clay particles form spanned network through entire
suspension living clear supernatant layer

6. SEM & AFM IMAGES OF SMECTITE
REVEALS FLEXIBLE SHEET

7. High resolution SEM and AFM images of kaolinite reveals
pseudo hexagonal crystals with visible molecular
arrangement on siloxane planes

8. TEM images show differences between
smectite and kaolinite samples
morphology patterns
Sample 2 Sample 6

9. Differences in structural ararngement within
flocked suspensions

10. CONTACTS BETWEN CLAY
PARTICLES WITHIN 3D NETWORK
Stairstep structure after O”Brien 1971

11. 0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 10 20 30 40 50 60 70 80
Time (min.)
D(50)mm
pure water (nat. pH 10.8)
0.05 M CaCl2 (nat pH ~8.9)
CaCl2
addition
conductivity (S/m)
Smectite aggregate forming by
Ca2+ cation introduction

12. 2-D & 3-D reconstruction of the montmorillonite gel
Na sorption complex (left), Ca sorption complex
(right), sample as seen within the aqueous solution

13. Force - separation curves for the interaction between Swy-
2 on silicon wafer on approach. The dashed line Na+
exchangeable cation form, solid line Ca2+ exchangeable
cation form
0.001
0.01
0.1
1
10
-15 185 385 585 785 985 1185
Separation (nm)
Force/2pR(mN/m)

14. SMECTITE AGGREGATES OF AUSTRALIAN
AMCOL BENTONITE WITHIN NaCl SALT 2.5
WT% SUSPENSION

15. Mutual arrangement of clay
minerals
a- house of cards b- pack of cards

16. CLAY STRUCTURE
A- CELLULAR B- FLOCCULENT
SEM TXM

17. The formed structure may correspond to the well
known Terzaghi “honeycomb” structure, described
for more rigid, platelet shaped minerals such as
kaolinite
• Repulsive forces between flakes basal surfaces
• Attractive forces between flakes edges and basal
surfaces
1 µm

18. C O N C L U S I O N
• Newly introduced methods of clay soil investigation like
TXM, Cryo-TEM/SEM and FIB/SEM gives new possibility
to study and engineering mutual particle orientation in 3-
dimensional aqueous clay suspension.
• Results show that clay particles of nano-meter in size
liberated smectite particles build spanned network in which
most mineral particles and water are arrested.
• This phenomenon may be blamed for poor tailing
dewatering and settling behaviour.
• In the inorganic cations treated smectite dense suspensions
display severe gelation and form the micelle-like texture of
fringe like strong superstructure.
• Future investigations would be focused on primary dense
aggregate building rather then flocculating loosely
coagulated particles which in effect create extremely
voluminous sludge.