Tailings Dam Failures, ARD,
and Reclamation Activities
John A Meech
Professor of Mining Engineering
The University of British Columbia
Email: cerm3dir@mining.ubc.ca
Outline
• Tailings Dam Construction Methods
• Tailings Dam Failures
• Reclamation of Dams, Waste Piles, and Sites
• Britannia Beach and the Millennium Plug Project
• Atmospheric Risks at the Sullivan Mine
• Acid Rock Drainage – what is it?
• ARD Control Methods
• Microbiology of ARD
Issues
Stability of dam structures
a. Use borrowed coarse material
b. Cyclone tailings to extract coarse fraction
c. Control pond water level so ground water does not
enter the structure (phreatic surface)
- Use barge/pump system
- Use a tunnel/overflow tower system
Water-Retention Type Dam
Steven G. Vick, 1983. Planning, Design, and Analysis of Tailings Dams, John Wiley
& Sons, New York, pp. 369, ISBN 0-471-89829-5
[The textbook on the subject! A reprint was published in 1990 by BiTech Publishers
Ltd., Richmond B.C., Canada (ISBN 0-921095-12-0)
Sequentially-built Tailings Dams
Each lift requires more material – 1,3,5,7, etc.)
Each lift requires more material – 1,2,3,4, etc.)
Sequentially-built Tailings Dams
Sequencing of Up-steam Tailing Dam Lifts
Phreatic Surface in Upstream Dams
kL = permeability at the edge of the pond water at the slimes zone
k0 = permeability at the spigot point (dam crest)
kF = permeability of foundation
kh / kv = anisotropy ratio (horizontal vs. vertical)
Ring Dike Construction - Kalgoorlie
Valley Deposit - HVC
Cross-Valley Plan View
CROSS VALLEY IMPOUNDMENT - SINGLE AND MULTIPLE
(Extracted from Vick, 1983. Planning, Design, and Analysis of Tailings Dams)
Side-Hill and Valley-Bottom Plan Views
SIDE-HILL and VALLEY-BOTTOM IMPOUNDMENT - SINGLE AND MULTIPLE
(Extracted from Vick, 1983. Planning, Design, and Analysis of Tailings Dams)
In-Pit Storage
Underground Storage
• Hydraulic sand
– Cycloned tailings sand (coarse fraction)
• Cemented fill
– Required to fill void space and create strength
• Paste backfill
– All tailings dewatered to 60-65% solids
• Dry rock fill
– With and without cement
Paste Backfill - Lisheen Mine, Ireland
• Backfill plant with deep cone thickener
Hazards for Tailings Dam Stability
Two Major Hazards:
• Excessive increase in level of pond water on impoundment
•
•
•
•
Operational error during filling
Natural events (thunderstorms and/or flood inflow)
Beach width between the water and dam crest becomes too small
Phreatic surface rises in the dam and leads to collapse
• Liquefaction during an earthquake
• Tailings may change physical properties under seismic stress
• Cyclic stresses can lead to liquefaction
• Highly susceptible due to low bulk density and high saturation
• Hazards are not theoretical
• Many tailings dam failures prove the theories over and over again.
• Recent example - Harmony gold mine tailings dam in
South Africa (Feb. 1994) after heavy rainstorm
- village completely buried
- 17 people killed
Water Balance in a Tailings Dam
Up-steam Tailing Dam Typical Failure
Up-steam Tailing Dam Piping Failure
Up-steam Tailing Dam Failure
too rapid rise - must be < 15 m/year
Up-steam Tailing Dam Failure
over-topping
Up-steam Tailing Dam Failure
liquifaction
Up-steam Tailing Dam Failure
slope stability
Comparison of Surface Impoundment Types
Water Retention
Mill Tailings
Requirements
Discharge
Requirements
Water Storage
Suitability
Upstream
40-60% sand in tailings.
Suitable for any Low feed pulp density
type of tailings
to enhance
size segregation
Peripheral discharge
Any discharge
and well-controlled
procedure suitable
beach necessary
Good
Not suitable for
significant water
storage
Downstream
Centerline
Suitable for any Sands or low-plasticity
type of tailings
slimes
Varies according
to design details
Good
Peripheral discharge
and nominal beach
necessary
Not so good for
permanent storage.
Temporary flood
storage adequate with
proper design
Comparison of Surface Impoundment Types
Water Retention
Seismic Resistance
Good
Raising Rate
Restrictions
Entire
embankment
constructed
initially
Embankment Fill
Requirements
Natural soil
borrow
Relative
Embankment Cost
High
Upstream
Poor
in high seismic areas
4.5 - 9 m/yr desirable.
> 15 m/yr
is hazardous.
Downstream
Centerline
Good
Acceptable
None
Height restrictions for
individual lifts may
apply
Sand tailings or
mine waste if
Natural soil, sand
production rates
tailings, or mine waste
are sufficient, or
Natural soil
Low
High
Sand tailings or mine
waste if production
rates are sufficient,
or Natural soil
Moderate
Tailings Dam Failures
• From 1968 to August 2009 - 149 documented failures worldwide
• 3,500 tailings dams exist around the world
25,000 to 48,000 large water storage dams exist around the world.
• Tailings dam failures closely match water storage dam failures
So, failure frequency is far higher (an order of magnitude).
• Since 2001, the failure rate is roughly one every 8 months.
• 85% of incidents were Active tailings dams / 15% Abandoned dams
• 76% of incidents were Upstream construction methods
• 56% of incidents were dams greater than 30 m in height
M. Rico, G. Benito, A.R. Salgueiro, A. Díez-Herrero, H.G. Pereira, 2010.
Reported tailings dam failures. A review of the European incidents in a worldwide context.
20th Century Tailings Dam Failures
Ten Causes of Failure
________________________________________________
Type of Failure
Number
%
________________________________________________
Unusual Rainfall
36
24.5
Seismic Liquefaction
21
14.3
Poor Management Operation
15
10.2
Structural Failure
13
8.8
Piping/Seepage
10
6.8
Foundation Failure
9
6.1
Overtopping
9
6.1
Slope Instability
7
4.8
Mine Subsidence
3
2.0
Snow melt
2
1.4
Unknown
22
15.0
_________________________________________________
TOTAL
147
100.0
_________________________________________________
Dam Failures due to Management Issues
• Poor beach management
• Faulty maintenance of drainage structures
• Inappropriate dam procedures
– rapid dam growth
• Heavy machinery on top of unstable dam
Real-Time Monitoring of Tailings Dams
•
•
•
•
•
Piezo-electric gauges
Pore pressures at depth
Both horizontal and vertical directions
Control of barge pumps
Controllable CCD cameras
– On top of dam structure
– Along all diversion ditches
• Water levels in all collection ditches/drains
Piezo-electric Gauges
Basis of piezoelectric effect:
-
crystals under compressive loading generate an
electric charge directly proportional to force applied.
Piezo-electric Gauges
Strain gauge transducer with bridge circuit
Charge is amplified into a proportional output voltage
Piezo-electric Gauges
• Piezoelectric sensors are
small in construction
• Their high natural frequency
is ideal for dynamic
measurements.
• Virtually no displacement,
as quartz gives mechatronic
component with an electrical
output signal.
• Sensitivity doesn't depend
on size of quartz crystal
Spigot Discharge
Other Methods
Submarine Tailings Disposal
• Alpine lake disposal
– High alpine regions (no fish)
• Riverine disposal
– Banned except in Indonesia
• Deep Ocean disposal
– Kitsault and Island Copper
Sub-aqueous
Tailings Disposal
Options
•
•
•
•
Impoundment
Covered Dam
Pit Filling
Submarine
Factors affecting Submarine Disposal
Island Copper Site Reclamation
After 20 years of operation, the Island Copper Mine began
reclaiming its waste dumps in 1996. Tailings were discharged
deep into the adjacent fjord known as Rupert Inlet.
Island Copper Pit Flooding
Pit was flooded with sea water to create
a Meromictic lake – 3 layers:
Top
– clean water;
Middle – a reactor for surface ARD;
Bottom – retain precipitated solids.
Island Copper Pit Flooding
Pit was flooded with sea water to create a 3-layer meromictic lake:
Top
– clean water;
Middle – a reactor for surface ARD;
Bottom – retain precipitated solids.
Deep Sea Disposal of Tailings
MillMill
EZD
– Euphotic depth
UWD – –
Upwelling
depth
EZD
Euphotic
depth
MLD – –
Mixed Layer
depth
UWD
Upwelling
depth
MLD – Mixed Layer depth
Thickened Discharge
• Water drainage management is key
http://technology.infomine.com/articles/1/1507/tailings.paste.thickened/paste.and.thickened.aspx
Dry Stack Tailings
• Anglo-American's La Coipa Mine in Chile
http://www.tailings.info/index.htm
Dry Stack Tailings
• Anglo-American's La Coipa Mine in Chile
Dry Stack Tailings
• Deposition by trucking
Dry Stack Tailings
• Anglo-American's La Coipa Mine in Chile
– Dewatering tailings to a filtered wet (saturated) or dry
(unsaturated) cake
– Must be transported by conveyor or truck
– Material is deposited, spread and compacted as
unsaturated tailings pile
– Produces a stable deposit requiring no retention dam
– Typical moisture content is below 20% - several percent
below saturation
– Combination of belt, drum, horizontal and vertical
pressure plates and vacuum filtration systems
Dry Stack Tailings
• Advantages
– Dewatering tailings to a filtered wet (saturated) or dry
(unsaturated) cake
– Must be transported by conveyor or truck
– Material is deposited, spread and compacted as
unsaturated tailings pile
– Produces a stable deposit requiring no retention dam
– Typical moisture content is below 20% - several percent
below saturation
– Combination of belt, drum, horizontal and vertical
pressure plates and vacuum filtration systems
Dry Stack Tailings
• Disadvantages
–
–
–
–
–
–
–
–
–
–
High capital and operating costs due to filtration
Limited to low throughput operations (~20,000 tpd)
Diversion systems to prevent inundation of stack
Surface contour management to handle surface water
Must prevent ponding and erosion of the stack
No option to store water within a dry stack facility
Sulfide oxidation creates high metal levels, low volumes
Dust generation is problematic in arid climates
Not suitable in high rainfall environment
Seasonal fluctuations are important considerations
Co-Disposal of Waste & Tailings
• Co-mingling
– Tailings and coarse waste rock material transported independently
– Mixed together mechanically in storage facility or slurry-pumped
– Mixing promotes voids filling (mingling) to maximise density
• Co-placement
–
–
–
–
Tailings and coarse waste rock material transported independently
Not mixed to form a single discharge stream
Waste rock end dumped into tailings facility
Waste rock used to create internal berms or retaining walls (sometimes)
• Co-deposition
– Similar to co-placement, but waste streams placed in layers
– Deposited tailings naturally enters voids in underlying rock
– End-dumping waste rock with tailings deposition down face prior to
further end dumping
Dam Remediation Efforts
By today's standards this dam is just too high for its design water flow and
material properties. Built over many decades, a second dam was required
to be built in the late 1990s to prevent water release (high As content).
Main dam of the Helmsdorf uranium mill tailings
deposit, Oberrothenbach (Saxony)
Reparation Work
Stava Fluorite Mine
Dam Failure,
Italy
1985
Before
After
Tailings dam consisted
of two basins built on a
slope. Failure started with
collapse of the up-slope
basin. Inflow of released
material caused overtopping and collapse of
the lower basin. The
resulting slurry wave
travelled to Stava at a
speed of 30 km/h; later
it reached 90 km/h.
Lives lost = 268
Damages = $133 x 106
Failure at Aznalcollar, Spain - 1998
Failure at Aznalcollar, Spain - 1998
1. Slab of soil beneath the dam
slid ~1m towards Río Agrio.
2. The dam cracked and broke;
the wall collapsed sweeping
out the separation dam.
3. Between 5 to 7 million m3
contaminated water and slurry
spilled through the gap.
4. The Río Agrio rose 3m, changing
its course and eroding bed rock.
Los Frailes tailing dam failure, 1998
Los Frailes tailing dam failure, 1998
Reclamation and Revegetation
Reclamation at Igarapé Bahia Mine
in the Carajás Region, Amazon, Brazil
20 cm of organic soil over leached material
Mines Operate in Sensitive Regions
Waste Dump Reclamation, Igarape Bahia Mine, Carajas, Brazilian Amazon
Mining Protects the Environment
Installing a Heap Leach Liner in Chile
Mining Repairs its Past Problems
Rio Algom's Reclamation Operation at the
Poirier Mine Tailing Dam in Northern Quebec
Mine Site Reclamation and Closure
BHP's Beenup
Titanium Minerals
mine at closure in
early 1999
- W. Australia
BHP's Beenup
Titanium Minerals
mine after final
revegetation and
reclamation
The Britannia Mine
Reclamation Project
UBC at Britannia Beach
Britannia
Mine
UBC at Britannia Beach
Britannia Beach
UBC-CERM3 has been involved at Britannia Beach since 2001 when we
installed a plug inside the 2200 Level tunnel to create a research facility.
This plug had the “spin-off” benefit of eliminating all pollution flowing into
Britannia Creek and the surface waters of Howe Sound.
Reclamation Issues in 2001
• Acid mine drainage from tunnels (620 m3/hr)
• About 800 kg of Cu & Zn discharged per day
• Over 10,000 tonnes of metal since closure
• Groundwater contamination on the Fan
• Potential impacts on aquatic life
• Waste dumps and stockpiles
• Tailings at bottom of Howe Sound
• Sealing abandoned adits, demolition of derelict
buildings (public safety issues)
Groundwater discharge
< 5% of the flow
2-3% of the copper
3-4% of the zinc
4100 Level effluent
50-80% of the flow
30-55% of the copper
60-75% of the zinc
2200 Level effluent
20-50% of the flow
45-70% of the copper
25-40% of the zinc
Plug the 2200 Adit
Build a
Treatment Plant
Reclaim pits
and waste dumps
Cutaway View of the Mine Workings
Cutaway View of the Mine Workings
Jane Creek after confluence of 2200 level effluent
Britannia Mine – October 2000
Millennium Plug Research Project
Pollution Plume – pre 2001
Millennium Plug Research Project
Pollution Plume – pre 2001
Outcome – September 2011
Return of Adult Pink Salmon to Britannia Creek
Numerous Media Reports
The Sullivan Mine Reclamation Failure
Reclamation Activities at Sullivan Mine
1998 - mine closed after 92 years
2000 – site reclamation on waste dumps
(Number 1 Shaft and North dumps)
2004 - ditch was partially covered when
the dump toe was extended 70m
2005 - 1m of glacial till was placed over
the dump surface and the ditch
• Reduce water percolation
• Restrict air infiltration
• Slow rate of oxidation
Monthly sampling to monitor flowrate and
contaminant levels
Sampling Shed
Sullivan Mine Accident – May 15-17, 2006
• Four people lost consciousness and died
after entering the sampling shed
Douglas Erickson, 48, a contractor
Robert Newcombe, 49, Teck employee
Kim Weitzel, 44, a paramedic
Shawn Currier, 21, a paramedic
• Reason: lack of oxygen
• Immediately after the accident,
O2 level in sump was ~2% & CO2 was ~7%
• Shed used regularly with no problem and
effluent flow was previously open channel
• Reasonable to conclude shed was not a
confined space at that time
• Shed was used 1 week before tragedy
• Oct. 2006, accident was identified as being
• Other mines were warned immediately by
B.C. Chief Inspector of Mines to treat all
sampling sheds as confined spaces
"unprecedented in the
history of mining"
Contributing Factors to the Accident
• During Summer of 2005
• Dump & drainage ditch were covered to limit air/water
•
•
infiltration and prevent human exposure to ARD
O2-depleted effluent now isolated from the atmosphere
Air in shed now directly connected to "bad" air in dump
• Prior use showed no problem (1 week before)
• False sense of security (9 years without any problem)
• Shed was safe before the ditch became a drain
• Design change created dangerous hazard
• Atmospheric conditions play a major role
• Temperature & pressure affect gas flowrate and direction
Contributing Factors to the Accident
• Before covering, ARD effluent was not O2-depleted
• O2-depleted out of dump, but contact with air restores O2 level
• After covering, ARD effluent was O2-depleted
• O2-depleted out of dump, and no contact with air until shed
• Possible mechanism
• O2 removal from static air in the shed by O2-depleted effluent
Before
O2 transfer
In ditch
After
O2 transfer
In shed
Breathing Waste Dump
• August 2006 - dump was instrumented
• Measure air velocity and gas composition in shed and pipe
• Temperatures below ~10°C- the dump "inhales“ (positive flow)
• Temperature above ~10°C- the dump "exhales“ (negative flow)
• May 13-17, 2006 - Increase in temperature / decrease in pressure
DANGEROUS
SAFE
DANGEROUS
Temperature during week of the accident
25
Temperature (oC)
20
15
10
5
0
5/1/2006
5/6/2006
5/11/2006
5/16/2006
5/21/2006
5/26/2006
Daily average air temperature at Cranbrook airport in May 2006.
Monitoring station was entered safely on May 8, 2006.
5/31/2006
Gas Velocity vs. Outside Temperature
Cyclical Changes in Risk
For a Confined Structure near dump toe
Seasonal Variations
•
•
•
•
•
Safe in winter / Dangerous in summer
In Summer, minimum night temperature may
lie above maximum dump temperature
Dump blows toxic gas all the time - deadly.
In Winter, maximum day temperature may lie
below maximum dump temperature
Dump will suck in air all the time - safe
Cyclical Changes in Risk
For a Confined Structure near dump toe
Diurnal Variations
•
•
•
•
•
Safe at night / Dangerous in day time
Outside temperature cycles from hot to cool
Dump may transition from blowing to sucking
if maximum dump temperature lies between
maximum day and minimum night temperature
In Spring – transition from Safe all the time to
Dangerous in day
In Fall – transition from Dangerous all the time
to Safe at night
Summer Conditions
Temperature
30
20
10
Daily Atmospheric
Temperatures
Maximum Internal
Dump Temperature
0
-10
-20
Time
of Day
Fall Conditions
Temperature
30
20
10
Daily Atmospheric
Temperatures
Maximum Internal
Dump Temperature
0
-10
-20
Time
of Day
Winter Conditions
Temperature
30
20
10
Daily Atmospheric
Temperatures
Maximum Internal
Dump Temperature
0
-10
-20
Time
of Day
Spring Conditions
Temperature
30
20
10
Daily Atmospheric
Temperatures
Maximum Internal
Dump Temperature
0
-10
-20
Time
of Day
Cyclical Changes in Risk
For a Confined Structure near dump toe
Decadal Variations
•
•
Safe(r) when maximum dump temperature has
reached its long-term maximum value
Dangerous when transitioning up or down
Conceptual Period Boundaries:
0 - 10 years
Initial period with rising danger
10 - 60 years
Maximum danger - extremely hazardous
60 - 80 years
Danger transitions from hazardous to problem
80 - 150 years
Constant reduced danger – dump temp > max. outside temp.
150 - 170 years
Rapid increase in risk - internal temp goes below max. outside temp.
170 - 180 years
Maximum danger returns - extremely hazardous
180 - 190 years
Danger transitions from hazardous to safe (pore gas O2 levels rise)
190 – onward
Site is now safe - no O2-depleted gas generated or emitted
Decadal Variation in Risk Assessment
Risk of a Confined
Space Accident
Estimated Maximum
Dump Temperature
Maximum Outside
Temperature
Summer Conditions – transition to safe
Dump reaches maximum temperature after 60-80 years
Perhaps sooner with highly reactive dumps
Temperature
30
20
10
Daily Atmospheric
Temperatures
Maximum Internal
Dump Temperature
0
Time of Day
-10
-20
Reference Dumps
1. White’s Dump at the Rum Jungle mine (U) in Australia
(Harries and Ritchie, 1980, 1983, 1986, 1987; Ritchie, 2003)
2. Sugar Shack South Dump at Questa Mine (Mo) in New Mexico
(Wels et al. 2003; Lefebvre et al., 2001a, 2001b & 2002; Shaw et al., 2002
Robertson GeoConsultants Inc., 2001)
3. South Waste Dump at the Doyon Mine (Au) in Quebec
(Wels et al. 2003)
4. Nordhalde Dump at the Ronnenburg Mine (U) in Germany
(Wels et al. 2003; Smolensky et al. 1999)
5. Aitik Mine dump (Cu) in Sweden
(Stromberg and Bawart, 1999; Stromberg & Bawart, 1994;
Ritchie, 2003; Takala et al., 2001)
6. Number One Shaft Waste Dump at the Sullivan mine (Pb/Zn)
(Lahmira et al., 2009)
Test Dumps
1. Main Waste Dump at Equity Silver Mine (Au/Cu/Ag) in British Columbia
(Aziz and Ferguson, 1997; Lin, 2010)
2. West Lyell Dump at Mt. Lyell Mine (Cu) in Tasmania
(Garvie et al. 1997)
3. North Dump at the Sullivan mine (Pb/Zn)
(Lahmira et al., 2009; Dawson et al., 2009)
Validation of the Model
Dump Site
Estimated
Internal Temperature
Reported
Internal Temperature
Nordhalde
10-15
14
Doyon
40
45
Sugar Shack South
> 40
40
Aitik Mine
2-6
3
White’s Dump (1 year after cover)
> 40
44
Number One Shaft
10 -15
12
Equity Silver Main
> 40
52
West Lyell
35-40
38 (Max)
Sullivan North
30-35
33
Nordhalde, Doyon, Sugar Shack S., Aitik, White’s, and
Number One Shaft dumps are reference input cases
North Dump, West Lyell, and Equity Silver Main are test cases
Note: confined structure on
top of the dump
Sampling Shed
ARD
Dealing with Reactive Tailings
• Two major types each creating a third issue
– Acid Rock Drainage (ARD)
– Cyanide
• ARD leads to dissolution of Heavy Metals
• Cyanide forms complex metallic ions
• Metallic pollution (Al, Cu, Cd, Co, Fe, Mn, Pb, Zn)
• Arsenic and/or selenium
What is ARD and how do we deal with it?
• Impact first reported in 1556 by Agricola in De Re Metallica
• Yet the term Acid Rock Drainage wasn’t coined until 1970
• Significant work by NRCan (MEND Program) and Canadian
companies developed innovative techniques to handle this
ubiquitous problem
• ARD requires sulphides, water, and air (and bacteria)
–
–
–
–
Minerals are the source of sulphur and iron
Air is the source of oxygen
Water is the transfer medium for oxygen from air to rock
Bacteria catalyze the reaction of Fe+2 to Fe+3
How long does ARD last?
ROCK
Generation of ARD from pyrite
• ARD from surface coal mine in
Missouri
• Iron hydroxide (yellow boy)
precipitates as pH rises from
downstream dilution
• Problem can last for decades
Photo Credit: D. Hardesty, USGS Columbia Environmental Research Center
The Colours of ARD
How long does ARD last?
- Forever!
Corta Atalaya, Rio Tinto, Spain
- abandoned pyritic open pit
Rio Tinto in Spain
– 2 millennium after mining
Is it only Mining that causes ARD?
Blood Falls at Taylor Glacier, Antarctica
Acid Rock Drainage – Metal Leaching
• ARD
– Formed by atmospheric oxidation (i.e., water, oxygen, and
carbon dioxide) of the common Fe-S minerals pyrite and
pyrrhotite in the presence of bacteria
Thiobacillus ferrooxidans, T. acidophilus, and T. thiooxidans
• ML
– Acid (H2SO4) leads to dissolution of metals and subsequent
pollution of aquatic environments
Basic Chemistry of ARD (from FeS2)
Basic Issues behind the Chemistry:
-
Equilibrium of Ferrous-Ferric Ions
Presence of Bacteria (Thiobacillus ferrooxidans)
Must have an initial source of oxygen (i.e., air)
Must have a way to transfer electrons (i.e., water)
ARD Reactions
Ferrous Sulphate formed by Abiotic Oxidation (slow):
2FeS2 + 2H2O + 7O2 = 2FeSO4 + 2H2SO4
Bacterial Oxidation of Ferrous Sulphate (T. ferrooxidans):
4FeSO4 + O2 + 2H2SO4 = 2Fe2(SO4) 3 + 2H2O
Ferric Sulphate is Reduced and Pyrite Oxidized by these reactions:
Fe2(SO4)3 + FeS2 = 3FeSO4 + 2S
2S + 6Fe2(SO4)3 + 8H2O = 12FeSO4 + 8H2SO4
Elemental Sulphur Oxidation (T. thiooxidans):
2S + 3O2 + 2H2O = 2H2SO4
Acid dissolves metals into solution meaning ARD is virtually always
accompanied by high metal levels discharged into the environment.
Bacteria are Essential
Thiobacilli from bacterial generator (no flagella)
Thiobacilli grown on ferrous iron (flagella)
- left
(x 5,000)
- centre (x 20,000)
- right (x 5,000)
Formation of Bio-films can lead to long delay in onset of ARD (7-10 years)
from Le Roux, N.W., et al., 1974. Bacterial Oxidation of Pyrite, Proc. 10th International Mineral Processing Congress,
Institution of Mining and Metallurgy, London, 1051-1066.)
Role of Bacteria
• T. ferrooxidans acts to oxidize ferrous to ferric iron
(Fe+2 to Fe+3)
• The ionic reaction is:
4Fe+2 + O2 + 4H+ = Fe+3 + 2H2O
• Fe+3 is a very powerful oxidizing agent
• With Fe+3:Fe+2 ratio of only 1:106, ORP (Eh) > +0.4v *
• General reaction of Fe+3 with base metal sulphides is:
MS + nFe+3 = M+n + S + nFe+2
• Base metal sulphides react slowly with H2SO4 alone
* ORP = Oxidation Reduction Potential (REDOX)
Metal Leaching – Influence of ORP
(Eh or REDOX) and Bacteria
Malouf, E.E. and Prater, J.D. (1961), Role of Bacteria in
the Alteration of Sulphide, J. Metals, NY, 13, p353-356.
Garrels, R.M. and Christ, C.L. (1965), Solutions, Minerals
and Equilibria, Harper & Row, New York, 216-222.
Stages in ARD Generation
(note the lag time)
Control of ARD
Removal of one essential component (sulfide, air, or water):
1. Waste Segregation and Blending
– Blend-in neutralizing potential (NP) rock to yield pH 7.0
2. Base additives
– Add limestone to buffer acid reactions
3. Liners, Covers, and Caps
– Water covers are the most effective
4. Soil, clay, and synthetic covers (geomembranes)
– minimize water and air infiltration
Control of ARD
5. Bactericides
– Chemicals that reduce/kill bacteria (T. ferrooxidans)
– Effective, but costly, and “bugs” mutate
6. Collection and treatment of contaminants
•
Active or Passive treatment
– Active treatment - high-density lime sludge
– Passive treatment in constructed wetlands
7. Bioremediation (micro-organisms)
– Remove metals directly
– Introduce viruses against the bacteria
Active Treatment
•
•
•
•
Most effective
Most expensive
All effluent processed in a treatment plant
May require processing for decades
High-Density Sludge Water Treatment Plant
WTP at Britannia Mine Site
Howe Sound, British Columbia
Capital Cost
Operating Costs
= ~ $12.0M
= ~ $ 1.5M/year
HDS Plant – Process Flow Diagram
Recycle Water
Flocculants
Lime Paste
Acidic Feed Water
Flocculants
Tanks
Lime
Tank
Lime Reactor
Sludge/Lime
Mix Tank
Sludge Recycle
Clarifier
Air
Effluent
Overflow
Sludge disposal
Sludge Disposal
• Sludge Disposal by truck – cost = ~$40/tonne
• Other options
– Manufacture bricks by blending sludge with clay or pumice
– Use low-temperature process with organic resins
– Use high-temperature process to harden into a ceramic
• Examine opportunities to recover Cu and Zn
– From the effluent prior to HDS
– From the sludge by leaching
So Reduction Process Schematic
Sulphur
Nutrients
Electron donor
BIOREACTOR
(So Reduction)
H2S
Soda Ash or Lime
Contaminated
Drainage
Cu
Precip
Zn
Precip
CuS
ZnS
Metals, SO4
BioteQ
After R.W. Lawrence, BioteQ
Treated
Water
Production Summary
Flow
Feed Water
Discharge Water
Cu Concentrate
14,880 m3/d – average over 12 months
[mg/L] 18.0 Cu, 20.0 Zn, 0.1 Cd
[mg/L] 0.05 Cu, 0.01 Zn, 0.01 Cd
187.0 tonnes per year contained copper
51.1% Cu, 2.1% Zn, 0.24% Fe, 33.1% S
Zn Concentrate
185.5 tonnes per year contained zinc
52.4% Zn, 1.5% Cu, 0.3% Cd, 0.8% Fe, 27.1% S
Additional Benefits
Lime Savings
Sludge Reduction
$64,000 per year (32%)
340-450 tonnes per year (15-20%)
Commercial Scale Plants
Pumice rock – extremely light
Brick Veneer Cladding - examples
NRC Process Evaluation - http://www.nrc-cnrc.gc.ca/eng/ibp/irc/ci/volume-4-n4-7.html
Canyon Stone - http://www.canyonstonecanada.com
Passive Treatment Technologies
Name
Description
Function
Shallow
wetlands
Fe and
Mn oxidation, Co-precipitation
• Limited Emergent
to
low
effluent
flowrates
vegetation
of Metals, Sorption on Biomass
Aerobic wetlands
Selected References
Eger and Wagner, 2003
USDA and EPA, 2000
Open limestone
channels
Acidic water flows over
limestone, or other alkali
Alkalinity addition
Al, Fe, Mn oxide precipitation
Ziemkewicz et al., 1997
Anoxic limestone
drains
Water flows through limestone
channel under anoxic
conditions
Alkali addition; Fe Precipitation;
Limestone Armouring Prevention
Watzlaf et al., 2000
Anaerobic wetlands
Subsurface wetland, isolated
from air by water or material
Alkali addition; Sulphate Reduction;
Precipitation of metal sulfides;
Sorption on Vegetation
Brenner, 2001
USDA and EPA, 2000
Successive Alkalinity
Producing Systems
Vertical flow systems drain
through limestone layers &
anaerobic organic matter
Alkalinity addition; Sulphate Reduction
Metal Precipitation
Kepler and McCleary,1994
Zipper and Jage, 2001
Sulfate-Reducing
Bioreactors
Collected water in anoxic
chamber containing organic
matter and SRBs
Alkalinity addition; Sulphate reduction;
Metal Precipitation
Gusek, 2002
Permeable Reactive
Barriers
Intercepted groundwater flows
through permeable barrier
containing reactive material
Alkalinity addition; Sulphate reduction;
Metal Precipitation and Sorption
Benner et al., 1997
US DOE, 1998
Amendments
Materials added to ARD
sources or holding areas
Alkalinity addition; Sulfate reduction;
Metal Precipitation; Sorption;
Chelation; Revegetation
Chaney et al., 2000
Covers
Liners, Covers, and Caps
•
•
•
•
•
•
Liners used to prevent seepage form the dam
Covers used to inhibit influx of water and air
Caps used to seal dam entirely
Expensive materials and installation
Must be installed with great care
Biggest issue – degradation over time
Factors affecting Soil Cover Performance
International Network for Acid Prevention, 2003. Evaluation of Long-term Performance of
Dry Cover Systems, Final Report. O’Kane Consultants Inc., (Eds.), Report No. 684-02.
Geomembranes
1.
2.
3.
4.
5.
6.
7.
8.
Plastics (polyethylene (PE)
High density poly. (HDPE)
Chlorinated poly. (CPE)
Chloro-sulphonated poly.
(DuPont HYPALON)
polyvinyl chloride (PVC)
Low-density poly. (LLDPE)
Geosynthetic clay liners (GCL)
Geomembranes impregnated
with bitumen
After Meer, S.R. and C.H. Benson, 2007. Hydraulic conductivity of geosynthetic clay liners exhumed from
landfill final covers. J. Geotech. and Geoenviron. Eng., 133(5):550-563.
Geo-Membranes: Benefits and Disadvantages
Benefits
Disadvantages
 Low permeability
 High cost
 Relatively easy to install
 Cost depends on distance from supplier to site
 Resistant to chemical and bacterial attack  Limited design life - 50 to 100 years
 Requires proper bedding and protective cover
 Geotechnical instability on steep slopes
 Vulnerabilities include:
- Sun light (UV breakdown)
- Puncture by surface traffic
- Cracking and creasing
- Seam difficulties
- Uplift pressure from fluid or gases
- Degradation by cation exchange with GCLs
- Settlement of underlaid materials
- Thermal expansion and contraction
After Meer, S.R. and C.H. Benson, 2007. Hydraulic conductivity of geosynthetic clay liners exhumed from
landfill final covers. J. Geotech. and Geoenviron. Eng., 133(5):550-563.
Field Monitoring of a Waste Pile Cover
MEND, 2004. Design, construction and performance monitoring of cover systems for waste rock and
tailings. Report 2.21.4, O’Kane Consultants Inc., (Eds.), Natural Resources Canada.
Sub-aqueous
Tailings Disposal
Options
•
•
•
•
Impoundment
Covered Dam
Pit Filling
Submarine
Factors affecting Submarine Disposal
Microbiology of ARD
Microbiological Aspects of ARD
• Bacteria form films on sulfide surfaces
• Reaction rate accelerates up to 108 times
• T. ferrooxidans/L. ferrooxidans considered
responsible for catalytic behaviour
• Microbial makeup is controlled by site environment
• Microbes not well-studied or understood
Microbiological Aspects of ARD
Thiobacillus ferrooxidans
Leptospirillum ferrooxidans
http://www.mines.edu/fs_home/jhoran/ch126/thiobaci.htm
http://microbewiki.kenyon.edu/index.php/Leptospirillum
Microbiological Aspects of ARD
• Key organisms (T. & L. ferrooxidans) >> global significance
• Physiological and genetic aspects well studied
• Microbial diversity specific to site environment
• Recent advances on structural dynamics of communities
• Biofilms on sulfide surfaces play a key role
• Bacteriophage impact negatively on bacterial populations
ARD Mitigation with Bacteriophage
• Novel approach to ARD control
• Isolate phage that infect ARD-generating “bugs”
• Create deadly mixture of viruses to control
microbial ARD communities with biology
• New and unexplored cross-disciplinary field
Microbiological Aspects of ARD
Structure of microbial communities
Microbiological Aspects of ARD
Biogeographic distribution of key microbes
Microbiological Aspects of ARD
Diversity revealed by molecular methods
Bacteriophage
• Viruses that infect bacterial cells
• Intracellular parasites – do not generate energy or
synthesize proteins by themselves
• Infection results in death, if phage is virulent
• Temperate phages kill only a small fraction of cells
and cause infected host to mutate
Bacteriophage – friend or foe
• Many shapes and sizes
• Phage are very small,
(20-200 nm in diameter)
• Some phage break down
biofilm matrix to infect
"protected" cells
Photo credits: ICTV Database www.ncbi.nlm.nih.gov/ICTVdb
Bacteriophage – friend or foe
T4 bacteriophage attacking an E. Coli bacterium
Bacteriophage – an ARD solution?
Like lunar landers,
bacteriophage attach to
the microbial cell wall and
inject their DNA for
replication
Cell Wall
Bacteriophage - an ARD Solution?
Photomicrographs of T4 bacteriophage for E. Coli
Bacteriophage - an ARD Solution?
The Lytic Cycle leads to the death of the host
The Lysogenic Cycle leads to mutation of the host
ARD Mitigation with Phage
• Inject phage into a dump/dam
• Coat surfaces with phage-containing biofilm
• Phage will control microbial population, not
eliminate it
• Phage for ARD-microbes do exist
– why do they become dormant at low pH?
Biofilms and Quorum Sensing
• Complex association of cells with an exopolysaccharide matrix
• Adhere strongly to sulfide surface or grow
deep within pores and cracks
• Play integral role in composition & stability
of microbial communities
Progression of Biofilms
Evolution from Planktonic Behaviour to a Biofilm
REVERSIBLE
ADSORPTION
OF BACTERIA
(seconds)
IRREVERSIBLE
ATTACHMENT
OF BACTERIA
(sec - min)
GROWTH &
DIVISION
OF BACTERIA
(hours - days)
EXOPOLYMER
PRODUCTION
& BIOFILM
FORMATION
(hours - days)
ATTACHMENT
OF OTHER
ORGANISMS TO
BIOFILM
(days - months)
Benefits of Biofilms for Microbes
Common Example of a Biofilm
Dental Plaque Stained with Gram's Iodine
Bio-Films and Quorum-Sensing
• Gene expression regulated by cell density changes
• Q-S bacteria release signal molecules (auto-inducers)
• Auto-inducer concentration increases with cell density
• At threshold concentration, gene expression changes
• Q-S communication regulates many physiologies:
- symbiosis
- competence
- antibiotic production
- sporulation
- virulence
- conjugation
- Programmed Cell Death (PCD)
- biofilm formation
Bio-Films and Quorum-Sensing
• Big Question?
Can we use Q-S knowledge to get microbes
in a bio-film to “commit suicide” without
creating new side-effect problems?
Conclusions
• Tailings Dam Construction must be done with care
and knowledge about the tailing material, about the
foundation material – both physical and chemical
factors are important
• Every 8 months, a tailings dam fails somewhere in
the world
• Downstream methods are safest
• Reactive Tailings require additional care and concern
for ARD and Metal Leaching
• Cyanide Tailings also generate metal pollution
• Confined Space issues may exist with ARD wastes
• Microbiology is a new approach receiving attention
Questions?