centre of excellence for sustainable mine lakes considerations for remediation of acid mine lakes in...

Centre of Excellence for Sustainable Mine Lakes

Considerations for remediation of acid

mine lakes in South-West Australia

Lessons from old lakes

Clint McCullough & Mark Lund

smart mine lakes


Muja

180 m

~3 km ~1.5 km

Fill Time ~50 yrsFinal Volume >200 GL

Lake Kepwari


What models already exist?

Collie has a four old mine lakes (abandoned in early 1960s).

They feature a range of;– morphologies,– catchment features,– water chemistries,– ecologies

Fertile ground for understanding what influences mine lake development


Black Diamond

Ewington Stockton Blue Waters

Area (Ha) 6 1.1 16 12

Depth (m) 8 11 47 24

Conductivity (µS cm-1) 421 1073 468 1368

pH 5.4 4.4 5.5 4

Sulphate (mg L-1) 46 30 31 90

Ammonia (µg L-1) 52 22 23 19

NOx (µg L-1) 163 3 18 3

FRP (µg L-1) 2 2 2 2

Chlorophyll a (µg L-1) 0.3 0.6 0.4 0.5

Aluminium (mg L-1) 0.006 0.6 0.006 2

Calcium (mg L-1) 4.4 1.9 2.2 5.9

Magnesium (mg L-1) 10.5 10.9 7.5 14.3

Iron (mg L-1) 0.01 0.3 0.02 0.3

Poorer environmental quality


What happened over 45 years?

• Metals/sulphate have precipitated out to form– Goethite (FeO.OH), Gibbsite (AL[OH]3), with possibly small

amounts of Jarosite (KFe3[SO4]2[OH]6), Jurbanite (Al[SO4][OH]5H2O) & Ferrihydrite (Fe[OH]3),

– This often releases further H+ ions– No evidence of metal sulfides

• Despite this acidity has reduced from >150 mg CaCO3 L-

1 (Chicken Creek) to <20 mg CaCO3 L-1 (old lakes)


Trends of historical lakes


Influences on lake chemistry

• Abiotic1) Catchment surface water inflow

2) Groundwater through-flow

• Biotic3) Sulfate reduction

4) Primary production

Abiotic processes probablymore important


Surface water contributionsBlue Waters

Overburden in catchment, unstable banks with little

vegetation

Black DiamondLess spoil, better vegetated and more stable


Surface water inflow

Mean pH Mean acidity Mean alkalinity

Ewington (n=6)

5.5 5.6 5.8

Blue Waters (n=10)

4.7 19.0 2.7

Unstable catchments may have buried iron-bound phosphorus and secondary minerals effectively

removing them from these systems.

Ongoing catchment contributions of acidity may hinder lake water quality remediation.


Stratification


pH change in Blue Waters

2.5

3

3.5

4

4.5

5

5.5

605

/97

07/9

7

09/9

7

11/9

701

/98

03/9

8

05/9

807

/98

09/9

8

11/9

8

01/9

903

/99

05/9

9

07/9

9

09/9

9 Dates

pH Top

Bottom


Lake water chemistry changes during stratification

Black Diamond

Ewington Blue Waters

Max diff. surface – bottom Temperature

0.8oC 1.4oC 3.6oC

Δtemperature vs

ΔSulfate (r2)

-34%Groundwater sulfate,

sediment release?

57%Sulfate

reduction?

84%Sulfate

reduction?

Δtemperature vs bottom Total N* (r2)

-25%Chara uptake?

4%Benthic algae?

55%Ammonia -sediment

*Total N assumed to be conservative in anoxic hypolimnion (no 1o production), limited denitrification

Although a slow process, groundwater thru-flow perhaps more important than previously thought


P

Mulch + P

Mulch

20 µg L-1

Sulfate Reduction


pH change in mesocosms

3

3.5

4

4.5

5

5.5

6

Jun-

2003

Jul-2

003

Aug

-200

3

Sep

-200

3

Oct

-200

3

Nov

-200

3

Dec

-200

3

Jan-

2004

Feb

-200

4

Mar

-200

4

Apr

-200

4

May

-200

4

Jun-

2004

Dates

pH

Control

Mulch + P

Mulch

P


Trends of historical lakes


Sulfate Reducing Bacteria activity

Sulfate reduction is limited by availability of labile carbon.

Sulfate reduction is likely to be a relatively weak alkalinity process.


Light limitation of photosynthesis

Euphotic depth


Primary production

20µg/L phosphorus,

20µg/L & mulchMulch only

P Chlor a

Black Diamond

2.0 0.31

Blue Waters

1.8 0.50

Ewington 1.8 0.60

Stockton 2.0 0.37

Phosphorus, nitrogen, carbon and light may all limit phytoplankton production.


Blue Waters

Conceptual models of lakes

Surface waters

Summer groundwater

Winter groundwater

Primary production

Sulfate reduction

Black DiamondStocktonEwington


Conclusions

• Water quality is largely stable as abiotic processes are the major determinator of water chemistry in acid mine lakes

• Alkalinity-generating biotic processes can be made to dominate through additions of macro-nutrients

• However, biotic remediation processes are weaker than current abiotic processes e.g., acid inputs

For passive biological remediation strategies to be successful, they need assistance, and not

hindrance, from simultaneous abiotic factors.

centre of excellence for sustainable mine lakes considerations for remediation of acid mine lakes in...

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