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Mining and environmental impact

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Mining and environmental impact

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Mining and environmental impact

  1. 1. Mining And its environmental impact
  2. 2. Outline  1. Types of Mining (and why we use them)  2. Beneficiation  3. Smelting  4. Environmental Concerns of 1 through 3
  3. 3. What determines the type of mining?  Underground v.s. Surface Mining v.s. Solution – Depth of below surface – Size of the ore body – Shape of the ore body – Grade – Type of Ore
  4. 4. Depth and Size
  5. 5. Shape of Ore Body
  6. 6. versus
  7. 7. Type of Ore  Is the ore mineral soluble in water?  Can the ore be melted?
  8. 8. What are the types of mining?  Surface – Strip – Open Pit – Placers--Dredging  Underground  Solution
  9. 9. When do you use Surface Mining?  Large tonnage  High rates of production  Overburden (including rock) is thin
  10. 10. Strip Mining of Coal Kansas Geological Survey
  11. 11. Open Pit Mining
  12. 12. Some photos and machinery used in open-pit mining
  13. 13. ?Dinky Toy?
  14. 14. Drilling in pit
  15. 15. Crushing in pit
  16. 16. Loading ore in pit
  17. 17. Underground Mining
  18. 18. When do we mine underground?  The ore deposit is deep  Ore body is steep  Grade is high enough to cover costs
  19. 19. Some types of underground mining  Room and Pillar  Cut and Fill  Long wall (coal)  Shrinkage Stoping  Block Caving
  20. 20. Room and Pillar
  21. 21. Cut and Fill
  22. 22. Long Wall
  23. 23. Shrinkage Stoping
  24. 24. Block Caving www.ivanhoe-mines.com/s/Mongolia_ImageGallery
  25. 25. Solution Mining
  26. 26. Beneficiation Means of separation of ore mineral from waste material (or gangue minerals) Also known as Liberation
  27. 27. What does it entail?  Crushing and Grinding – Ball mill or rod mill  Separation – Density (e.g. diamonds with a jig) – Magnetic properties – Electric properties – Surface properties
  28. 28. Refining the Ore Smelting removes the metal from the ore mineral by a variety of ways Heap Leaching removes metal from the ore by solution
  29. 29. Iron in review  Blast Furnace  3CO + Fe2O3 2 Fe + 3CO2 (gas)  4CO + Fe3O4 3Fe + 4CO2 (gas)
  30. 30. Sulphide Minerals  Are sometimes roasted – Heated in air without melting to transform sulphides to oxides – Gives off H2S and SO2 – Then oxides processed like Fe
  31. 31. Sulphides cont’d  Process of roasting and smelting together creates a matte – Sulfides are melted into a matte and air is blown through. S is converted to sulfur dioxide and Fe to iron oxide, and Cu and Ni stay in melt
  32. 32. Smelting
  33. 33. Result at Kidd Creek
  34. 34. Sulphides cont’d  Solvent extraction/electroplating – Used where rock contains Cu but in too little amounts to be recovered by classical methods
  35. 35. Heap Leaching  In this process, typically done for Au, the ore is not ground, but rather, crushed and piled on the surface.  Weak solutions of NaCN (0.05%) percolate through the material leaching out the desired metals.  The solutions are collected and the metals are precipitated
  36. 36. Potential Environmental Problems  A. Mining operation itself – Disposal of a large amount of rock and waste – Noise – Dust  Beneficiation  Smelting and refining
  37. 37. From Underground Mining  Subsidence – Block/caving – Room and pillar – Salt mining (Droitwich)
  38. 38. Subsidence in rancher’s field
  39. 39. Subsidence from Pb-Zn mining
  40. 40. From Underground  Acid Mine Drainage – FeS minerals in coal – Sulphide deposits – Acidic streams can pick up heavy elements and transport them
  41. 41. Rock that has acid forming material
  42. 42. Drainage
  43. 43. Acid and open pits Berkley Pit
  44. 44. Other problems with open pits  Very large holes  Pit slopes steep and not stable. Cannot be maintained  May fill with water  Strip coal mines –loss of top soil in past – Now smoothed out and top soil added
  45. 45. Disposal of Waste Rock  More problematic for open pit than underground  Waste rock piles have steep angle of repose and thus may not be stable  Bingham in its hay day produced 400,000 tons of waste rock per DAY!
  46. 46. Tailings ponds  From concentrating usually have high pH – At Bingham acid waters mixed with tailings water to neutralize  Different metals have different problems
  47. 47. Problems with Smelting/Roasting  Air: SO2 and CO2 and particulate matter  Noranda Quebec used to have the highest single point source of SO2 in the world. It may have been surpassed.  CN (Au); NaOH and F (Al); solvents (electrotwinning); heavy metals; oil and grease

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