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Revegetation of mine tailings
Elena I. Khozhina
Environmental ServicesMining DivisionWardrop Engineering Inc.Winnipeg, MBE-mail: [email protected]
Outline
Introduction
Rehabilitation of mine sites under the
Mines and Minerals Act Definitions
Revegetation of Base Metal Mine Tailings
Revegetation of Coal Mine Wastes
Introduction: Rehabilitation of mine sites under the Mines and Minerals Act
Closure plan
Environment protection Site rehabilitation
Mine Closure Regulation, 67/99
during the life of a project upon closing of a project
Closure plan - a program for environment protection during the life of a project and for project site rehabilitation upon closing of the project
Rehabilitation means:
(a) protecting the environment against adverse effects resulting from operations,
(b) minimizing the detrimental impact on adjoining lands of operations,
(c) minimizing hazards to public safety resulting from operations, and
(d) leaving the site or quarry in a state that is compatible with adjoining land uses
The Mines and Minerals Act M162
Introduction: Definitions
Introduction: Rehabilitation of mine sites under the Mines and Minerals Act (Cont.)
Site rehabilitation
The aim of rehabilitation is to restore the site to a satisfactory condition
Mine Closure Regulation, 67/99
A project proponent shall institute and carry out a program for rehabilitation
Introduction: Rehabilitation of mine sites under the Mines and Minerals Act (Cont.)
Site rehabilitation
Revegetation
Rehabilitation of contaminated soils
Building dismantling
Backfilling underground and open pit work
Restoration of mine dewatering
ponds
Rehabilitation of mine rock piles
Rehabilitation of tailings and sedimentation ponds
Collection of contaminated water
Mining Effluent Control
Removing sanitary Installations
Removing hazardous Waste
Mine Closure Regulation, 67/99
Introduction: Rehabilitation of mine sites under the Mines and Minerals Act (Cont.)
Requirements for revegetation:
• Vegetation characteristics should resemble that of the natural environment;
• The land must be properly prepared before revegetation;
• Vegetation must be self-sufficient six years after planting;
• Vegetation must require no fertilization or maintenance
Mine Closure Regulation, 67/99
Introduction: Rehabilitation of mine sites under the Mines and Minerals Act (Cont.)
Revegetation
Restoration of natural conditions
All affected areas must be revegetated
Building sites
Tailings ponds
Sedimentation ponds
Waste rock piles
Erosion control
Mine Closure Regulation, 67/99
Major Actors in Pyrite Oxidation
Mine tailings
Metal mine tailings
Coal mine wastes
INCO, Thompson , August 2005
Base Metal Mine Tailings
Norilsk Nickel http://www.platinum.matthey.com/media_room/1043401763.htm
Underground Mining Stope Smelter
Flotation cells
INCO, Thompson , August 2005
How much of ore material is usually disposed into tailings area after processing?
Natural Area Tailings Area
Ni-Cu Tailings, Thompson Operations, July 2004
Base Metal Mine Tailings
Oxidized TailingsReduced Tailings
S2- + H2O + 3.5 O2 (aq)
Pyrrh
otite
Pyrite
Salts Acids
2S042- + 2 H+
200 µm
Base Metal Mine Tailings
Ni-Cu Tailings, Thompson Operations, July 2004
Tailings characteristics: Dust storms
Evaporate salts formed in dry weather (Ni, Cu, and Fe sulphates)
Oxidized Tailings
Salts
Tailings characteristics: Evaporate salts
Ni-Cu Tailings, Thompson Operations, July 2004
Reduced tailings
Oxidized tailings
Plant roots
• Oxidised and reduced tailings alternate
Ni-Cu Tailings, INCO, Thompson, MB (Khozhina and Sherriff, 2007)
Tailings characteristics: Alternating layers
•Low organic matter;•Low moisture.
7.3 27
1.2
13.1
5.6
2.33.5
23
1.2
8.3
6.5
1.76.
7
48
3.8
0.4
30.2
0.1
1
10
100
pH H2O OM EC Sulphides CaCO3 eq% ppm
Reduced tailings
Oxidised tailings
Natural Soils
µS/cm%%
Ni-Cu Tailings, INCO, Thompson, MB (Khozhina and Sherriff, 2007)
Tailings characteristics: OM and moisture
Water sedge (Carex aquatilis Wahl.)
Plants naturally colonising tailings
• Poor species composition
• Low viability of seed
Ni-Cu Tailings, Thompson Operations, July 2004
•Dust storms;
•Acidic;
•Saline;
•Low organic matter;
•Low moisture.
Summary of tailings characteristics
In strongly acid soils(4 < pH < 5):• Macronutrients less available
(Ca, Mg, K, P, N, and S);
• Micronutrients more available (Fe, Mn, Zn, and Cu);
• Micronutrients toxic to microorganisms and higher plants.
Acidity and nutrient availability
Brady and Weil, 1999
Fungi
Bacteria and actinomycetes
N
K
S
Ca, Mg
P
Fe, Mn
Mo
Cu
Zn
B
Soil pH
Neutralisation of acidity
Liming materials
Carbonate forms Oxide/Hydroxide forms
Ground limestone(calcite plus dolomite)
Calcitic limestone(little/no dolomite)
Dolomitic limestone(Magnesium increases)
Calcium oxide (CaO)(Quicklime/Burned lime)
Calcium hydroxide (Ca(OH)2) (Hydrated lime)
Reaction of lime with ARD :
Ca(OH)2 (s) + Me2+/Me3+
(aq) + H2SO4
Me(OH)2/Me(OH)3 (S) + CaSO4 (S)
+ H2O
S2-
H 2O
, O2
Neutralisation of acidity (Cont.)
Active acidity
Acidity
Acid Base Accounting (ABA)
Neutralisation of acidity (Cont.)
Potential acidity
Lime requirement for acidity neutralisation
Neutralisation of acidity (Cont.)
NNP (kg CaCO3per ton) = NP -AP
NNP - Net Neutralization PotentialNP - Neutralization PotentialAP - Acid Production Potential (31.25 x pyritic sulfur, %)
Most common method of ABA computation:
mNP Software for NNP calculation
Limestone amendments: Large scale
• The most widespread method;
• Lime is applied to sod land and the ploughed under;
• Used to spread commercial fertilisers too.
Bulk application
Agricultural disk on steep slopes
Bomag rotary mixer
Limestone amendments: Large scale
• For deep lime incorporation
Practical implementation: Small scale
•Incorporation of organic matter
•Fertiliser application
•Native plant seeding
Salinity and plant growth
0
10
20
30
40
50
60
70
80
0 4 8 12 16 20EC, dS/m
strongly
very strongly
moderately
Strongly tolerant crops
Salinity
Ni-Cu Tailings, Thompson Operations, July 2004
Waste rocks
Limestone
Tailings
2-3 cm
20 cm Sewage sludge
Ni-Cu Tailings, Thompson Operations, July 2004
Salinity and revegetation: case study
20 cm
Slender wheatgrasCanada wildrye
Salinity and revegetation: case study
Ni-Cu Tailings, Thompson Operations, July 2004
After two growing seasons
Additional benefits from protective layer
• Prevents dust storms;
• Prevents erosion;
• Decreases tailings oxidation.
ANTHRACITEBITUMINOUSSUB-BITUMINOUSLIGNITE
CANADIAN COAL FIELDS
Major coal deposits are concentrated in the west
Coal deposits in Canada, 2003
THE HIGHER THE CARBON CONTENT, THE HIGHER THE RANK(North American coal classification)
Higher ranked coal produces more energy.
Most of Canada’s coal reserves are bituminous.
Coal deposits in Canada, 2003
Mining Techniques
Surface mining
Coal mining
Underground mining
Strip mines
Open-pit mines
Remote-controlled, continuous mining machine for underground coal mining
Coal deposits in Canada, 2003
Coal mining: Underground
The only operating underground coal mine in Canada is on Vancouver Island, British Columbia.
•For deep coal deposits;
•High operating cost.
Coal deposits in Canada, 2003
Coal mining: Open pit
• Conducted in foothills and mountains;
• Coal lies in dipping seams.
•For blanket-like coal deposits;•Coal is mined in rows or strips.
Coal deposits in Canada, 2003
Coal mining: Strip mining
1 Soil is stripped ahead of mining and is salvaged for use in subsequent reclamation. 2 A dragline removes the overburden to expose the coal seam. 3 Coal is loaded into large, off-road trucks for transport to the power plant. 4 “Spoil” piles left by the dragline are recontoured to produce suitable post-mining topography. 5 Soil, which was salvaged before mining, is replaced. 6 Revegetation is completed in increments roughly equal to the area mined each year
Environmental Concerns
Craig et al., 1996
0.2 - 7.0 % of sulphur is present in all coals
Organic macerals
Iron sulphides(pyrite, marcasite)
1/2 1/2
Coal
Wastes
Pyrite crystalsin coal
Daniels, 2003
Pyrite
Acid Rock Drainage (ARD)
Acid waters seeping from the base of a pile of waste rock left after coal mining, southwest Pennsylvania (Craig et al., 1996).
Environmental Concerns: ARD
Atmospheric oxygen
Environmental Concerns: Combustion
Reject coal materialSpontaneous combustion
Oxygen
The mechanism is not clear: coal reacts exothermically with atmospheric oxygen
T
Form layers (< 5 m)
Compact layers with a roller
Cover each layer by inert material (1 m)
Elimination of combustion
Minimisaion of oxygen infiltration
Reclamation into forest
Burger and Zipper, 2002; A Canadian Coal Photo Album, 2003
Returning to agricultural land uses