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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)

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codisposal

CODISPOSAL

Presented by

Mike Gowan

Principal

definition
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

mine wastes 1
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
codisposal with mining products
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.

concrete ideal codisposal
CONCRETE - IDEAL CODISPOSAL
  • Aggregate, sand, cement & water mixed together
  • No air voids
  • Coarse aggregate suspended in fines mixture

Aggregate

Sand/Cement

concrete ideal codisposal model
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
ideal codisposal
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
mixed codisposal
MIXED CODISPOSAL
  • Used successfully:
    • Wollongong by BHP
    • Westcliff coal mine
  • Trialled at Dartbrook
codisposal11
CODISPOSAL
  • Co-mingling
  • Co-placement
  • Co-disposal
co mingling
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.
co placement
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.
co disposal
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.
co mingling at kidston
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
autogenous mixing
AUTOGENOUS MIXING

Tailings Discharge

active mixing
ACTIVE MIXING

Tailings Discharge

winrowing 1
WINROWING - 1

Tailings Deposition

winrowing 2
WINROWING - 2

Tailings filling between Windrows

Tailings Spigot Pipeline

Tailings/Waste Windrows

tailings cells 1
TAILINGS CELLS - 1

Waste cells

Tailings deposition

tailings cells 2
TAILINGS CELLS - 2

Waste Cell

Tailings

Waste cover/mixture

Mixed Tailings/Waste

kidston details
KIDSTON DETAILS

Thickened tailings

deposited into pit pond

Waste rock end-dumped

into pit

view of kidston pit
VIEW OF KIDSTON PIT

Thickened tailings

Waste

Eventually Waste extended over Tailings to produce a Closure Cover

co placement argyle
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
ne usa
NE USA

Mixing Rejects &

Dewatered Tailings

Placing and Spreading

development of codisposal
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
australian trials
AUSTRALIAN TRIALS
  • Tested placing rejects over tailings
  • Some penetration of rejects
  • Problems:
    • Development of Bow-wave
    • Slow advancement rate
codisposal in australia
CODISPOSAL IN AUSTRALIA
  • Confined to Coal Mines
  • Idea developed at Jeepropilly
  • Now used at:
    • Hail Creek
    • Kestrel
    • North Goonyella
    • Mooranbah
    • Coppabella
    • Moorevale
    • Stratford
    • Others???
coal codisposal 1
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
limitations of codisposal
LIMITATIONS OF CODISPOSAL
  • 3 Stage pumping reaches ~2 km
  • Steel pipe for high heads
  • High pipe wear
  • Limited tailings encapsulation
typical codisposal beach
TYPICAL CODISPOSAL BEACH

Rejects only Beach

Well Mixed Codisposal &

Encapsulated Tailings

coal codisposal beach
COAL CODISPOSAL BEACH

Codisposal beach

Tailings beach

Decant Pond

advantages of codisposal
ADVANTAGES OF CODISPOSAL
  • Pumping lower cost than trucking
  • No transport fleet required
  • Stable landform made by beach
  • Tailings contained by beach
  • High water return
trafficable beach
TRAFFICABLE BEACH

Generally cannot drive easily over rejects, but can over upper codisposal beach

stable codisposal despite wall failure
STABLE CODISPOSAL – Despite Wall Failure

Stable Codisposal Wall

Clay starter-

wall failure

bearing capacity limitations
BEARING CAPACITY LIMITATIONS

Codisposal beach

Tailings

summary
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
acknoledgements
ACKNOLEDGEMENTS
  • The many mines mentioned
  • Assoc. Prof. David Williams of The U of Q