Transcript CODISPOSAL - InfoMine - Mining Intelligence and Technology

CODISPOSAL
Presented by
Mike Gowan
Principal
DEFINITION
 In mining and mineral processing,
materials are separated according
to their particle size and
mineralogy
 The wastes produced fall into
Coarse-grained (waste/rejects); &
Fine-grained (tailings)
 Conventionally disposed of
separately
Co-disposal involves the
combining of these waste
streams
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MINE WASTES -1
 Tailings - rock flour resulting from
the crushing and or grinding of
mine ore - <1mm
 Rejects - washery waste resulting
from the processing of coal - >1 to
120 mm
 Spoil/Waste - rock separated in
the mining process and not
processed - 0 to >1 m
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CODISPOSAL WITH MINING PRODUCTS
 Tailings disposed as a slurry has
a high porosity (>40%), with
water-filled voids.
 Rejects/waste has a high
porosity (>30%), with largely airfilled voids.
Codisposal - some of the tailings
can be made to settle in the voids
in the coarse waste.
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POROSITIES
Tailings
Rejects
Waste
SG
1.8
2.2
2.7
Dry Density
0.9
1.2
1.8
Void Ratio
1.000
0.833
0.500
Porosity
50%
45%
33%
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TYPICAL WASTE
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CONCRETE - IDEAL CODISPOSAL
 Aggregate, sand, cement & water
mixed together
 No air voids
 Coarse aggregate suspended in
fines mixture
Sand/Cement
Aggregate
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CONCRETE - IDEAL CODISPOSAL MODEL
 Using concrete as the model:
 Products need to be:
Nearly dry
Well mixed before placement
Minimum water added
 Coarse:fine ratio not critical
 Low energy placement to reduce
risk of segregation
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IDEAL CODISPOSAL
 Tailings needs to be dewatered to
paste or cake
 Tailings and rejects need to be
mixed together
 Mixture then pumped, trucked or
conveyed to disposal
 Expensive operations, dictated by
circumstances
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MIXED CODISPOSAL
 Used successfully:
Wollongong by BHP
Westcliff coal mine
 Trialled at Dartbrook
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CODISPOSAL
 Co-mingling
 Co-placement
 Co-disposal
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CO-MINGLING
 The coarse and fine products are
transported separately and
allowed to mix together within the
disposal site after deposition.
An example of this the dumping of
rock and the deposition of tailings
at Kidston Gold Mine.
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CO-PLACEMENT
 The coarse and fine products are
transported separately and mixed
together just prior to or on
placement in the disposal site.
An example of this is the mixing of
slimes and tailings used at the
Argyle Diamond Mine.
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CO-DISPOSAL
 Coarse and fine waste products
are mixed together before they
are transported to the disposal
site.
An example of this is the pumped
codisposal practice carried out in
Australian coal mines.
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CO-MINGLING at KIDSTON
 AIM – to fill a pit and produce a stable
landform at closure
 Materials available tailings and waste
rock
 Reviewed many codisposal systems:
 Autogenous mixing
 Active mixing
 Winrowing
 Tailings cells
 Selected co-mingling
 Other systems too costly
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AUTOGENOUS MIXING
Tailings Discharge
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ACTIVE MIXING
Tailings Discharge
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WINROWING - 1
Tailings Deposition
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WINROWING - 2
Tailings filling between Windrows
Tailings Spigot Pipeline
Tailings/Waste Windrows
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TAILINGS CELLS - 1
Waste cells
Tailings deposition
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TAILINGS CELLS - 2
Tailings
Waste Cell
Waste cover/mixture
Mixed Tailings/Waste
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KIDSTON DETAILS
Thickened tailings
deposited into pit pond
Waste rock end-dumped
into pit
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VIEW OF KIDSTON PIT
Thickened tailings
Waste
Eventually Waste extended over
Tailings to produce a Closure Cover
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Tarong – Comingled Reject & Tailings
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CO-PLACEMENT-ARGYLE
 Problem – very fine slimes that
would not settle
 Solution – mix the two materials
 Slimes & Tailings mixed at
disposal area
Slimes pumped
Tailings conveyed
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NE USA
Mixing Rejects &
Dewatered Tailings
Placing and Spreading
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DEVELOPMENT OF CODISPOSAL
 Tried in
 The UK in 1960’s
South Africa in 1980’s
 Tailings slurry spread over layer of
rejects
 Penetration up to 300 mm
 Costly to operate
Thin layers of rejects
Moving tailings pipeline
Spreading tailings
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SOUTH AFRICA TRIALS
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AUSTRALIAN TRIALS
 Tested placing rejects over tailings
 Some penetration of rejects
 Problems:
Development of Bow-wave
Slow advancement rate
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REJECTS INTO & OVER TAILINGS
Bow-wave
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WASTE PLACEMENT OVER 10 m TAILINGS
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CODISPOSAL IN AUSTRALIA
 Confined to Coal Mines
 Idea developed at Jeepropilly
 Now used at:
Hail Creek
Kestrel
North Goonyella
Mooranbah
Coppabella
Moorevale
Stratford
Others???
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COAL CODISPOSAL - 1
 Tailings & Reject mixed at CHPP
 Pumped to disposal site
 Slurry solids 27 to 35%
 Flow velocities 2.7 to +4 m/sec
 Single point full pipe discharge
 Clean water recovery
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LIMITATIONS OF CODISPOSAL
 3 Stage pumping reaches ~2 km
 Steel pipe for high heads
 High pipe wear
 Limited tailings encapsulation
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2 STAGE PUMPING
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CERAMIC LINED STEEL PIPE
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TYPICAL CODISPOSAL BEACH
Rejects only
Beach
Well Mixed
Codisposal &
Encapsulated
Tailings
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COAL CODISPOSAL BEACH
Codisposal beach
Tailings beach
Decant Pond
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TOTAL
Coarse
Fine
500
357
143
SG
2.2
1.8
C:F Ratio
2.5
1
Split
71%
29%
1.4
0.8
Void Ratio
0.57
1.25
Porosity
36%
56%
Waste
tph
Slurry
solids
27%
Water
tph
1,352
Mean Density
t/cum
TAILINGS BEACH
Total
Total
Coarse
Fine
Beach
500
TOTAL
100%
Beach
86%
Tailings
Waste
Pond
48%
tph
357
143
431
69
500
Dry density
t/cum
1.40
0.80
1.69
0.80
1.47
Total Volume
cum
255
179
255
86
341
0.57
1.25
Void Ratio
Solids volume
cum
162
79
Void volume
cum
93
99
26%
69%
11.9%
69%
19.8%
93
99
52
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99
Moisture Content
Water contained
cum
1,352
Return water
cum
1,253
93%
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EFFECT OF C:F RATIO
100%
Fraction of Tailings Contained
in Coarse
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
1
2
3
4
5
Coarse:Fine Ratio - :1
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ADVANTAGES OF CODISPOSAL
 Pumping lower cost than trucking
 No transport fleet required
 Stable landform made by beach
 Tailings contained by beach
 High water return
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TRAFFICABLE BEACH
Generally cannot drive
easily over rejects, but
can over upper
codisposal beach
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STABLE CODISPOSAL – Despite Wall Failure
Stable
Codisposal
Wall
Clay starterwall failure
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BEARING CAPACITY LIMITATIONS
Codisposal
beach
Tailings
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WATER RETURN
Tails
143
SG
1.8
Slurry
35%
Water
551
cum/hr
Dry Density
0.8
t/cum
MC
69%
Retained
99
tph
cum/hr
Return water
82%
Rejects
8%
Retained
29
cum/hr
TOTAL
128
cum/hr
Codisposal
99
cum/hr
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SUMMARY
 Codisposal difficult but not
impossible in metalliferous mines
 Codisposal works for coal mines
 There is a tailings pond that
needs to be managed
 Water losses are no higher than
for separate reject:tailings
disposal systems
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ACKNOLEDGEMENTS
 The many mines mentioned
 Assoc. Prof. David Williams of
The U of Q
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THE END
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