Mining and environmental impact

1. Mining
And its environmental impact

2. Outline
 1. Types of Mining (and why we use
them)
 2. Beneficiation
 3. Smelting
 4. Environmental Concerns of 1 through 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. Depth and Size

5. Shape of Ore Body

6. versus

7. Type of Ore
 Is the ore mineral soluble in water?
 Can the ore be melted?

8. What are the types of mining?
 Surface
– Strip
– Open Pit
– Placers--Dredging
 Underground
 Solution

9. When do you use Surface Mining?
 Large tonnage
 High rates of production
 Overburden (including rock) is
thin

10. Strip Mining of Coal
Kansas Geological Survey

11. Open Pit Mining

14. Some photos and
machinery used in open-pit
mining

16. ?Dinky Toy?

17. Drilling in pit

18. Crushing in pit

19. Loading ore in pit

20. Underground Mining

21. When do we mine underground?
 The ore deposit is deep
 Ore body is steep
 Grade is high enough to cover costs

23. Some types of underground mining
 Room and Pillar
 Cut and Fill
 Long wall (coal)
 Shrinkage Stoping
 Block Caving

24. Room and Pillar

25. Cut and Fill

26. Long Wall

27. Shrinkage Stoping

28. Block Caving
www.ivanhoe-mines.com/s/Mongolia_ImageGallery

29. Solution Mining

30. Beneficiation
Means of separation of ore mineral from
waste material (or gangue minerals)
Also known as Liberation

31. 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

36. 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

37. Iron in review
 Blast Furnace
 3CO + Fe2O3 2 Fe + 3CO2 (gas)
 4CO + Fe3O4 3Fe + 4CO2 (gas)

38. 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

39. 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

40. Smelting

41. Result at Kidd Creek

42. Sulphides cont’d
 Solvent extraction/electroplating
– Used where rock contains Cu but in too little
amounts to be recovered by classical methods

44. 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

45. Potential Environmental Problems
 A. Mining operation itself
– Disposal of a large amount of rock and waste
– Noise
– Dust
 Beneficiation
 Smelting and refining

46. From Underground Mining
 Subsidence
– Block/caving
– Room and pillar
– Salt mining (Droitwich)

47. Subsidence in rancher’s field

48. Subsidence from Pb-Zn mining

49. From Underground
 Acid Mine Drainage
– FeS minerals in coal
– Sulphide deposits
– Acidic streams can pick up heavy elements
and transport them

50. Rock that has acid forming material

51. Drainage

52. Acid and open pits
Berkley Pit

54. 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

55. 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!

56. Tailings ponds
 From concentrating usually have high pH
– At Bingham acid waters mixed with tailings
water to neutralize
 Different metals have different problems

57. 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