1. Presented by Mike Gowan Principal
CODISPOSAL
Presented by
Mike Gowan
Principal

2. Co-disposal involves the combining of these waste streams
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

3. 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

4. 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 air-filled voids.
Codisposal - some of the tailings can be made to settle in the voids in the coarse waste.

5. POROSITIES Tailings Rejects Waste SG 1.8 2.2 2.7 Dry Density 0.9 1.2
Tailings
Rejects
Waste SG
1.8
2.2
2.7
Dry Density
0.9
1.2
Void Ratio
1.000
0.833
0.500
Porosity
50%
45%
33%

6. TYPICAL WASTE

7. CONCRETE - IDEAL CODISPOSAL
Aggregate, sand, cement & water mixed together
No air voids
Coarse aggregate suspended in fines mixture
Aggregate
Sand/Cement

8. 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

9. 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

10. MIXED CODISPOSAL Used successfully: Trialled at Dartbrook
Wollongong by BHP
Westcliff coal mine
Trialled at Dartbrook

11. CODISPOSAL
Co-mingling
Co-placement
Co-disposal

12. 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.

13. 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.

14. 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.

15. 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

16. AUTOGENOUS MIXING
Tailings Discharge

17. ACTIVE MIXING
Tailings Discharge

18. WINROWING - 1
Tailings Deposition

19. WINROWING - 2 Tailings filling between Windrows
Tailings Spigot Pipeline
Tailings/Waste Windrows

20. TAILINGS CELLS - 1
Waste cells
Tailings deposition

21. TAILINGS CELLS - 2 Waste Cell Tailings Waste cover/mixture
Mixed Tailings/Waste

22. deposited into pit pond
KIDSTON DETAILS
Thickened tailings
deposited into pit pond
Waste rock end-dumped
into pit

23. Eventually Waste extended over Tailings to produce a Closure Cover
VIEW OF KIDSTON PIT
Thickened tailings
Waste
Eventually Waste extended over Tailings to produce a Closure Cover

24. Tarong – Comingled Reject & Tailings

25. 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

26. NE USA
Mixing Rejects &
Dewatered Tailings
Placing and Spreading

27. 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

28. SOUTH AFRICA TRIALS

29. AUSTRALIAN TRIALS Tested placing rejects over tailings
Some penetration of rejects
Problems:
Development of Bow-wave
Slow advancement rate

30. REJECTS INTO & OVER TAILINGS
Bow-wave

31. WASTE PLACEMENT OVER 10 m TAILINGS

32. CODISPOSAL IN AUSTRALIA
Confined to Coal Mines
Idea developed at Jeepropilly
Now used at:
Hail Creek
Kestrel
North Goonyella
Mooranbah
Coppabella
Moorevale
Stratford
Others???

33. 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

34. LIMITATIONS OF CODISPOSAL
3 Stage pumping reaches ~2 km
Steel pipe for high heads
High pipe wear
Limited tailings encapsulation

35. 2 STAGE PUMPING

36. CERAMIC LINED STEEL PIPE

37. TYPICAL CODISPOSAL BEACH
Rejects only Beach
Well Mixed Codisposal &
Encapsulated Tailings

38. COAL CODISPOSAL BEACH
Codisposal beach
Tailings beach
Decant Pond

39. TAILINGS BEACH TOTAL Coarse Fine Waste tph 500 357 143 SG 2.2 1.8
TOTAL
Coarse
Fine
Waste
tph
500
357
143 SG
2.2
1.8
C:F Ratio
2.5 1
Split
71%
29%
Slurry
solids
27%
Water
1,352
Mean Density
t/cum
1.4
0.8
Void Ratio
0.57
1.25
Porosity
36%
56%
TAILINGS BEACH
Total
Coarse
Fine
Beach
Pond
TOTAL
500
100%
86%
Tailings
48%
Waste
tph
357
143
431 69
Dry density
t/cum
1.40
0.80
1.69
1.47
Total Volume
cum
255
179 86
341
Void Ratio
0.57
1.25
Solids volume
162 79
Void volume 93 99
Moisture Content
26%
69%
11.9%
19.8%
Water contained
1,352 52 48
Return water
1,253
93%

40. EFFECT OF C:F RATIO

41. ADVANTAGES OF CODISPOSAL
Pumping lower cost than trucking
No transport fleet required
Stable landform made by beach
Tailings contained by beach
High water return

42. TRAFFICABLE BEACH
Generally cannot drive easily over rejects, but can over upper codisposal beach

43. STABLE CODISPOSAL – Despite Wall Failure
Stable Codisposal Wall
Clay starter-
wall failure

44. BEARING CAPACITY LIMITATIONS
Codisposal beach
Tailings

45. WATER RETURN Tails 143 tph SG 1.8 Slurry 35% Water 551 cum/hr
Slurry
35%
Water
551
cum/hr
Dry Density
0.8
t/cum MC
69%
Retained 99
Return water
82%
Rejects 8% 29
TOTAL
128
Codisposal

46. 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

48. ACKNOLEDGEMENTS The many mines mentioned
Assoc. Prof. David Williams of The U of Q

49. THE END