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CODISPOSAL

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

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  1. CODISPOSAL Presented by Mike Gowan Principal

  2. 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

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

  23. 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

  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

  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

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

  48. THE END

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