Post on 09-Jan-2017
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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
Clay-Rich Layers within Coal
Rock layer
Coal with clay layers
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 tailingsare stuck here!
Na-Bentonite – Effect of Initial % Solids on Settling
CRICOS Provider No 00025B
Initial % Solids >5% will not settle!
Mechanisms of aggregate formation and transformation
At critical concentration, clay particles form spanned network through entire suspension living clear supernatant layer
SEM & AFM IMAGES OF SMECTITE REVEALS FLEXIBLE SHEET
High resolution SEM and AFM images of kaolinite reveals pseudo hexagonal crystals with visible molecular
arrangement on siloxane planes
TEM images show differences between smectite and kaolinite samples
morphology patternsSample 2 Sample 6
Differences in structural ararngement within flocked suspensions
CONTACTS BETWEN CLAY PARTICLES WITHIN 3D NETWORK
Stairstep structure after O”Brien 1971
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(5
0) m
m
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
2-D & 3-D reconstruction of the montmorillonite gel Na sorption complex (left), Ca sorption complex
(right), sample as seen within the aqueous solution
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)
Forc
e/2p
R (m
N/m
)
SMECTITE AGGREGATES OF AUSTRALIAN AMCOL BENTONITE WITHIN NaCl SALT 2.5 WT
% SUSPENSION
Mutual arrangement of clay minerals
a- house of cards b- pack of cards
CLAY STRUCTUREA- CELLULAR B- FLOCCULENT
SEM TXM
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
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.