Codisposal presented by

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

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

• 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.

POROSITIES

TYPICAL WASTE

CONCRETE - IDEAL CODISPOSAL

• Aggregate, sand, cement & water mixed together

• No air voids

• Coarse aggregate suspended in fines mixture

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

• 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

• Used successfully:

• Wollongong by BHP
• Westcliff coal mine

• Trialled at Dartbrook

CODISPOSAL

• Co-mingling

• Co-placement

• Co-disposal

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

• 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

• 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

• 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

ACTIVE MIXING

WINROWING - 1

WINROWING - 2

TAILINGS CELLS - 1

TAILINGS CELLS - 2

KIDSTON DETAILS

VIEW OF KIDSTON PIT

Tarong – Comingled Reject & Tailings

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

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

SOUTH AFRICA TRIALS

AUSTRALIAN TRIALS

• Tested placing rejects over tailings

• Some penetration of rejects

• Problems:

• Development of Bow-wave
• Slow advancement rate

REJECTS INTO & OVER TAILINGS

WASTE PLACEMENT OVER 10 m TAILINGS

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

• 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

• 3 Stage pumping reaches ~2 km

• Steel pipe for high heads

• High pipe wear

• Limited tailings encapsulation

2 STAGE PUMPING

CERAMIC LINED STEEL PIPE

TYPICAL CODISPOSAL BEACH

COAL CODISPOSAL BEACH

TAILINGS BEACH

EFFECT OF C:F RATIO

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

STABLE CODISPOSAL – Despite Wall Failure

BEARING CAPACITY LIMITATIONS

WATER RETURN

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

• The many mines mentioned

• Assoc. Prof. David Williams of The U of Q

THE END

• THE END