Should metal bioavailability be considered in the evaluation of

treatment and remediation methodologies for acid mine

drainage?Vigneault, B.*, Neculita, C.M.**, Zagury, G.J.**, Kwong, Y.T.J.* and Tisch, B.** CANMET-Mining and Mineral Sciences Laboratories** École Polytechnique de Montréal

5th World Congres of the Society of EnvironmentalChemistry and Toxicology, Sydney, Australia, August 2008

Introduction : Context

• Treatment efficiency is often assessed based on metal removal alone

• More jurisdictions are implementing effluent toxicity requirements and discharge objective or limits based on generic water quality criteria

Introduction : AMD Treatment• Acid Mine Drainage (AMD) is the most

significant environmental issue related to mining world-wide

• AMD treatment most often involves of neutralization with lime

• AMD prevention and / or passive treatment are more preferable

• Prevention and treatment options include:- Water covers- Soil covers- Passive bioreactors

The current presentation highlights the relevance of metal bioavailability in assessing alternative methods for AMD prevention and treatment:

I. Shallow water coverII. Papermill sludge coverIII. Passive bioreactor

Introduction : Objective

AMD Prevention : Water Cover• Subaqueous disposal of reactive sulphide

tailings is an effective way to prevent AMD

• Shallow water cover of ~ 30 cm is preferable for geotechnical considerations

• Formation of a biofilm has been found at the surface of the tailings

Materials and Methods: Water Cover

• Geochemical measurements were completed at the water/tailings interface to assess the impact of biofilm:- Micro-profiles of O2 and pH- Profiles of metals, major ions,

sulphides and DOC - Biotic Ligand Model

(Hydroqual) to estimate the effect of DOC

Vigneault et al. (2001) Wat. Res. 35(4): 1066-1076.

-6

-4

-2

0

2

4

[ ] (µg · L-1)

0.0 0.1 0.2 0.3 0.4-6

-4

-2

0

2

4

0 10 20 30 40

Dep

th (c

m)

-6

-4

-2

0

2

4

Copper

Zinc

Cadmium

Water Cover: Trace metal profiles

[ ] (mg · L-1)

10 15 20 25 30 35 40

Dep

th (c

m)

-6

-4

-2

0

2

4DOC

Water Cover: DOC Profiles

Water Cover: DOC Protective Effect

0

5

10

15

20

25

30

Copper Cadmium Zinc

DOC

Effe

ct R

atio

s

AMD Prevention : Paper Mill Biosolids

• Paper mill biosolids are used to reclaim mine tailings

• If possible, paper mill biosolid covers will be use to grow energy crops

• Besides suppressing metal mobilization, the utilization of paper mill biosolids may impact effluent composition

Materials and Methods: Biosolid Covers

• Pulp and paper sludge were obtained from two Canadian mills

• Biosolids leachates tested for:

- Direct toxicity- Copper complexation capacity- Effect on copper toxicity

Materials and Methods: Metal Speciation

• Ion selective electrode for the determination of copper complexationcapacity

• Effect of leachates on copper toxicity to C. dubia (7 day survival and reproduction) tested in laboratory water

Biosolid Covers: Cu Complexation

Domtar

[Cu]Total (µM)12.9 33.8 71.3

{Cu2+

} (µM

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Measured (ISE)Predicted (WHAM VI)

Biosolid Covers: Cu Toxicity

Survival Reproduction

Cu

LC50

/ IC

25 (µ

g · L

-1)

0

50

100

150

200

250

Control Domtar St. Marys

~

C. dubia

Biosolid Covers: DOC Protective Effect

0

2

4

6

8

10

12

Copper Cadmium Zinc

DOC

Effe

ct R

atio

s

AMD Treatment : Passive bioreactors

• Field passive bioreactors are effective to increase pH and remove metals

• Bioreactors require an organic amendment and can release DOC in the treated effluent

Materials and Methods: Passive Bioreactor

• Bioreactor with a hydraulic retention time up to 10 days used to treat artificial AMD

• Reactive mixture composed of 60% organic materials (10% maple wood chips, 20% sawdust, 10% poultry manure and 20% leaf compost) and 40% inorganic materials.

Materials and Methods: Metal Speciation

• Ultrafiltration used to determine truly dissolved metals

• Cadmium, nickel and zinc speciation estimated using WHAM VI (Tipping 1998)

Neculita, Vigneault and Zagury (2008) Env. Toxicol. Chem. 27(8): 1659-1667.

Passive Bioreactor: Metal Speciation

• Treated effluent had a pH of 6.2 and a DOC of 7 mg · L-1

• The majority of cadmium and zinc was < 1 Kda

• Predicted fraction of metal bound to dissolved and particulate organic matter was only 0.2% for nickel and 0.4% for zinc and cadmium

Passive bioreactor: DOC Protective Effect

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Copper Cadmium Zinc

DOC

Effe

ct R

atio

s

Conclusions• Shallow water cover: metal toxicity can

potentially be reduced by 4 x to 25 x

• Biosolid covers: copper toxicity in limed effluent could be reduced by ~ 10 x as supported by the copper toxicity tests and copper speciation measurements

• Passive bioreactor: metal toxicity is not expected to be largely affected by the released organic matter

Conclusions• Expected organic matter releases are

significant (~ 101 mg · L-1) for the 3 tested methods

• Data suggest that the released organic matter can significantly affect metal toxicity and should be considered when using water quality guidelines to establish discharge objectives

Acknowledgements

• Natural Resources Canada

• Vale Inco

• Teck Cominco

• INRS-ETE

Thank You !

Dissolved oxygen (µM)

0 100 200 300 400 500 600 700

Dep

th (m

m)

-20

-15

-10

-5

0

5

10

15

5700 Lux 18500 Lux >20000 Lux

Water Cover: Oxygen micro-profiles

Cu Zn Cd

Diff

usiv

e flu

x to

the

wat

er c

over

(m

ol ·

cm-2

· s-1

)

10-19

10-18

10-17

10-16

10-15

10-14

1998 2005

No flux

Water Cover: Trace metal fluxes

Materials and Methods: Toxicity Tests

• Canadian Metal Mining Effluent Regulations:- acute lethality to Daphnia magna

and rainbow trout

- sublethal toxicity to Pseudokirchneriellasubcapitata, Lemna minor, Ceriodaphnia dubia and Pimephalespromelas

Biosolid Covers: Leachate Toxicity

Rainbow trout D. magna

LC50

(mg

C ·

L-1)

0

50

100

150

200

Domtar St. Marys

>

>

>

~

P. prom

elas

C. dub

ia

L. mino

rP. s

ubca

pitata

IC25

(mg

C ·

L-1)

0

20

40

60

80

100

120

Domtar St. Marys >

>

Biosolid Covers: Leachate Toxicity

Biosolid Covers: Cu Complexation

St. Marys

[Cu]Total (µM)15.0 37.0 73.0

{Cu2+

} (µM

)

0.0

0.1

0.2

0.3

0.4

0.5

Measured (ISE)Predicted (WHAM VI)

Passive bioreactor: Truly Dissolved Metals

0.000

0.010

0.020

0.030

0.040

0.050

0.060

Cd Zn

[ ] u

g / L Total

DissolvedPermeable