revegetation of mine tailings elena i. khozhina environmental services mining division wardrop...

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


A project proponent shall institute and carry out a program for rehabilitation


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



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



Revegetation

Restoration of natural conditions

All affected areas must be revegetated

Building sites

Tailings ponds

Sedimentation ponds

Waste rock piles

Erosion control


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


Oxidized TailingsReduced Tailings

S2- + H2O + 3.5 O2 (aq)

Pyrrh

otite

Pyrite

Salts Acids

2S042- + 2 H+

200 µm



Tailings characteristics: Dust storms

Evaporate salts formed in dry weather (Ni, Cu, and Fe sulphates)

Oxidized Tailings

Salts

Tailings characteristics: Evaporate salts


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


•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)


Potential acidity

Lime requirement for acidity neutralisation


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


Waste rocks

Limestone

Tailings

2-3 cm

20 cm Sewage sludge


Salinity and revegetation: case study

20 cm

Slender wheatgrasCanada wildrye

Salinity and revegetation: case study


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.


Mining Techniques

Surface mining

Coal mining

Underground mining

Strip mines

Open-pit mines

Remote-controlled, continuous mining machine for underground coal mining


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 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 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

revegetation of mine tailings elena i. khozhina environmental services mining division wardrop...

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