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Tailings Dam Failures, ARD, and Reclamation Activities John A Meech Professor of Mining Engineering The University of British Columbia

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Presentation on theme: "Tailings Dam Failures, ARD, and Reclamation Activities John A Meech Professor of Mining Engineering The University of British Columbia"— Presentation transcript:

1 Tailings Dam Failures, ARD, and Reclamation Activities John A Meech Professor of Mining Engineering The University of British Columbia

2 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

3 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

4 Water-Retention Type Dam Steven G. Vick, Planning, Design, and Analysis of Tailings Dams, John Wiley & Sons, New York, pp. 369, ISBN [The textbook on the subject! A reprint was published in 1990 by BiTech Publishers Ltd., Richmond B.C., Canada (ISBN )

5 Sequentially-built Tailings Dams Each lift requires more material – 1,3,5,7, etc.) Each lift requires more material – 1,2,3,4, etc.)

6 Sequentially-built Tailings Dams

7 Sequencing of Up-steam Tailing Dam Lifts

8 Phreatic Surface in Upstream Dams k L = permeability at the edge of the pond water at the slimes zone k 0 = permeability at the spigot point (dam crest) k F = permeability of foundation k h / k v = anisotropy ratio (horizontal vs. vertical)

9 Ring Dike Construction - Kalgoorlie

10 Valley Deposit - HVC

11 Cross-Valley Plan View CROSS VALLEY IMPOUNDMENT - SINGLE AND MULTIPLE (Extracted from Vick, Planning, Design, and Analysis of Tailings Dams)

12 Side-Hill and Valley-Bottom Plan Views SIDE-HILL and VALLEY-BOTTOM IMPOUNDMENT - SINGLE AND MULTIPLE (Extracted from Vick, Planning, Design, and Analysis of Tailings Dams)

13 In-Pit Storage

14 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

15 Paste Backfill - Lisheen Mine, Ireland Backfill plant with deep cone thickener

16 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

17 Water Balance in a Tailings Dam

18 Up-steam Tailing Dam Typical Failure

19 Up-steam Tailing Dam Piping Failure

20 Up-steam Tailing Dam Failure too rapid rise - must be < 15 m/year

21 Up-steam Tailing Dam Failure over-topping

22 Up-steam Tailing Dam Failure liquifaction

23 Up-steam Tailing Dam Failure slope stability

24 Comparison of Surface Impoundment Types Water RetentionUpstreamDownstreamCenterline Mill Tailings Requirements Suitable for any type of tailings 40-60% sand in tailings. Low feed pulp density to enhance size segregation Suitable for any type of tailings Sands or low-plasticity slimes Discharge Requirements Any discharge procedure suitable Peripheral discharge and well-controlled beach necessary Varies according to design details Peripheral discharge and nominal beach necessary Water Storage Suitability Good Not suitable for significant water storage Good Not so good for permanent storage. Temporary flood storage adequate with proper design

25 Comparison of Surface Impoundment Types Water RetentionUpstreamDownstreamCenterline Seismic ResistanceGood Poor in high seismic areas GoodAcceptable Raising Rate Restrictions Entire embankment constructed initially m/yr desirable. > 15 m/yr is hazardous. None Height restrictions for individual lifts may apply Embankment Fill Requirements Natural soil borrow Natural soil, sand tailings, or mine waste Sand tailings or mine waste if production rates are sufficient, or Natural soil Relative Embankment Cost HighLowHighModerate

26 Tailings Dam Failures From 1968 to August 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, Reported tailings dam failures. A review of the European incidents in a worldwide context.

27 20 th Century Tailings Dam Failures

28 Ten Causes of Failure ________________________________________________ Type of FailureNumber % ________________________________________________ Unusual Rainfall Seismic Liquefaction Poor Management Operation Structural Failure Piping/Seepage Foundation Failure Overtopping Slope Instability Mine Subsidence Snow melt Unknown _________________________________________________ TOTAL _________________________________________________

29 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

30 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

31 Piezo-electric Gauges Basis of piezoelectric effect: - crystals under compressive loading generate an electric charge directly proportional to force applied.

32 Piezo-electric Gauges Strain gauge transducer with bridge circuit Charge is amplified into a proportional output voltage

33 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

34 Spigot Discharge

35 Other Methods

36 Submarine Tailings Disposal Alpine lake disposal – High alpine regions (no fish) Riverine disposal – Banned except in Indonesia Deep Ocean disposal – Kitsault and Island Copper

37 Sub-aqueous Tailings Disposal Options Impoundment Covered Dam Pit Filling Submarine

38 Factors affecting Submarine Disposal

39 Island Copper Site Reclamation After 20 years of operation, the Island Copper Mine began reclaiming its waste dumps in Tailings were discharged deep into the adjacent fjord known as Rupert Inlet.

40 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.

41 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.

42 Deep Sea Disposal of Tailings EZD– Euphotic depth UWD– Upwelling depth MLD– Mixed Layer depth Mill EZD– Euphotic depth UWD– Upwelling depth MLD– Mixed Layer depth Mill

43 Thickened Discharge Water drainage management is key

44 Dry Stack Tailings Anglo-American's La Coipa Mine in Chile

45 Dry Stack Tailings Anglo-American's La Coipa Mine in Chile

46 Dry Stack Tailings Deposition by trucking

47 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

48 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

49 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

50 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

51 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). Dam Remediation Efforts

52 Main dam of the Helmsdorf uranium mill tailings deposit, Oberrothenbach (Saxony)

53 Reparation Work

54 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 over- topping 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 10 6

55 Failure at Aznalcollar, Spain

56 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.

57 Los Frailes tailing dam failure, 1998


59 Reclamation and Revegetation

60 Reclamation at Igarapé Bahia Mine in the Carajás Region, Amazon, Brazil 20 cm of organic soil over leached material

61 Waste Dump Reclamation, Igarape Bahia Mine, Carajas, Brazilian Amazon Mines Operate in Sensitive Regions

62 Installing a Heap Leach Liner in Chile Mining Protects the Environment

63 Rio Algom's Reclamation Operation at the Poirier Mine Tailing Dam in Northern Quebec Mining Repairs its Past Problems

64 BHP's Beenup Titanium Minerals mine at closure in early W. Australia BHP's Beenup Titanium Minerals mine after final revegetation and reclamation Mine Site Reclamation and Closure

65 The Britannia Mine Reclamation Project

66 UBC at Britannia Beach Britannia Mine

67 Britannia Beach UBC at 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.

68 Acid mine drainage from tunnels (620 m 3 /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) Reclamation Issues in 2001

69 2200 Level effluent 20-50% of the flow 45-70% of the copper 25-40% of the zinc 4100 Level effluent 50-80% of the flow 30-55% of the copper 60-75% of the zinc Groundwater discharge < 5% of the flow 2-3% of the copper 3-4% of the zinc Plug the 2200 Adit Build a Treatment Plant Reclaim pits and waste dumps

70 Cutaway View of the Mine Workings


72 Jane Creek after confluence of 2200 level effluent Britannia Mine – October 2000

73 Millennium Plug Research Project Pollution Plume – pre 2001

74 Millennium Plug Research Project Pollution Plume – pre 2001

75 Outcome – September 2011 Numerous Media Reports Return of Adult Pink Salmon to Britannia Creek

76 The Sullivan Mine Reclamation Failure

77 mine closed after 92 years 2000 – site reclamation on waste dumps (Number 1 Shaft and North dumps) ditch was partially covered when the dump toe was extended 70m m 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 Reclamation Activities at Sullivan Mine

78 Sampling Shed

79 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, O 2 level in sump was ~2% & CO 2 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"

80 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 O 2 -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

81 Contributing Factors to the Accident Before covering, ARD effluent was not O 2 -depleted O 2 -depleted out of dump, but contact with air restores O 2 level After covering, ARD effluent was O 2 -depleted O 2 -depleted out of dump, and no contact with air until shed Possible mechanism O 2 removal from static air in the shed by O 2 -depleted effluent Before O 2 transfer In ditch After O 2 transfer In shed

82 Breathing Waste Dump August 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, Increase in temperature / decrease in pressure DANGEROUS SAFE DANGEROUS

83 Temperature during week of the accident Daily average air temperature at Cranbrook airport in May Monitoring station was entered safely on May 8, /1/20065/6/20065/11/20065/16/20065/21/20065/26/20065/31/2006 Temperature (oC)

84 Gas Velocity vs. Outside Temperature

85 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

86 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

87 Summer Conditions Temperature Daily Atmospheric Temperatures Maximum Internal Dump Temperature Time of Day

88 Fall Conditions Temperature Daily Atmospheric Temperatures Maximum Internal Dump Temperature Time of Day

89 Winter Conditions Temperature Daily Atmospheric Temperatures Maximum Internal Dump Temperature Time of Day

90 Spring Conditions Temperature Daily Atmospheric Temperatures Maximum Internal Dump Temperature Time of Day

91 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 yearsInitial period with rising danger yearsMaximum danger - extremely hazardous yearsDanger transitions from hazardous to problem yearsConstant reduced danger – dump temp > max. outside temp yearsRapid increase in risk - internal temp goes below max. outside temp yearsMaximum danger returns - extremely hazardous yearsDanger transitions from hazardous to safe (pore gas O 2 levels rise) 190 – onwardSite is now safe - no O 2 -depleted gas generated or emitted Conceptual Period Boundaries:

92 Decadal Variation in Risk Assessment Estimated Maximum Dump Temperature Maximum Outside Temperature Risk of a Confined Space Accident

93 Summer Conditions – transition to safe Temperature Daily Atmospheric Temperatures Maximum Internal Dump Temperature Time of Day Dump reaches maximum temperature after years Perhaps sooner with highly reactive dumps

94 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)

95 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)

96 Validation of the Model Dump Site Estimated Internal Temperature Reported Internal Temperature Nordhalde Doyon4045 Sugar Shack South> 4040 Aitik Mine2-63 White’s Dump (1 year after cover)> 4044 Number One Shaft Equity Silver Main> 4052 West Lyell (Max) Sullivan North 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

97 Overall Results for all 9 dumps Dump Time of Year DoB in High Gas Velocity at dump toe Degree of Belief in High Risk Value Assessment Cover Value "high" reactivity Gas Generati on in Summer Gas Emission via pathway Gas Confinement Human Exposure Nordhalde Summer 88%60% Neg. Small100%63% Marginal Hazard JanuaryPos. Big66%18% L Problem DoyonSummer0%100%Pos. Big43% ML15% L Problem Sugar ShackSummer0%74%Pos. Big23% ML18% L Problem Aitik Summer 0%5% Neg. Big66% MH76% ML Significant JanuaryNeg. VS20% MH37% MH Significant White’sSummer0%100%Pos. VS100%27% ML Significant No. 1 Shaft Summer 89%69% Neg. VB100% Hazardous MayNeg. Big100%80% Marginal Hazard Main Equity Silver Summer 100%71% Pos. Big46% MH18% Problem JanuaryPos. VB35% MH18% Problem West LyellSummer0%94%Pos. Big21% M18% Problem NorthSummer89%100%Pos VS60%18% Significant * L = low ML = medium-low M = medium MH = medium-high A fuzzy term other than "high" was used because the related DoB in "high" = 0. Note:Risk Value for May at No. 1 Shaft dump calculated at 0.65, yet we know with full certainty the accident occurred. This poor correlation reflects fluctuations each day in May. A value of 0.65 causes AFRA to recommend caution.

98 Sampling Shed Note: confined structure on top of the dump

99 ARD

100 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

101 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

102 How long does ARD last? ROCK

103 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 Generation of ARD from pyrite

104 The Colours of ARD

105 How long does ARD last? Rio Tinto in Spain – 2 millennium after mining Corta Atalaya, Rio Tinto, Spain - abandoned pyritic open pit - Forever!

106 Is it only Mining that causes ARD? Blood Falls at Taylor Glacier, Antarctica

107 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 (H 2 SO 4 ) leads to dissolution of metals and subsequent pollution of aquatic environments

108 Basic Chemistry of ARD (from FeS 2 ) 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)

109 ARD Reactions Ferrous Sulphate formed by Abiotic Oxidation (slow): 2FeS 2 + 2H 2 O + 7O 2 = 2FeSO 4 + 2H 2 SO 4 Bacterial Oxidation of Ferrous Sulphate (T. ferrooxidans): 4FeSO 4 + O 2 + 2H 2 SO 4 = 2Fe 2 (SO 4 ) 3 + 2H 2 O Ferric Sulphate is Reduced and Pyrite Oxidized by these reactions: Fe 2 (SO 4 ) 3 + FeS 2 = 3FeSO 4 + 2S 2S + 6Fe 2 (SO 4 ) 3 + 8H 2 O = 12FeSO 4 + 8H 2 SO 4 Elemental Sulphur Oxidation (T. thiooxidans): 2S + 3O 2 + 2H 2 O = 2H 2 SO 4 Acid dissolves metals into solution meaning ARD is virtually always accompanied by high metal levels discharged into the environment.

110 Bacteria are Essential Thiobacilli from bacterial generator (no flagella)- left (x 5,000) - centre (x 20,000) Thiobacilli grown on ferrous iron (flagella) - 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., Bacterial Oxidation of Pyrite, Proc. 10th International Mineral Processing Congress, Institution of Mining and Metallurgy, London, )

111 Bacteria and Metal Leaching For substantial metal mobilization, the following conditions must be present: – Ferric iron for rapid sulphide oxidation – T. ferrooxidans and O 2 for Fe +2 to Fe +3 oxidation – pH compatible with T. ferrooxidans, typically pH

112 Role of Bacteria T. ferrooxidans acts to oxidize ferrous to ferric iron (Fe +2 to Fe +3 ) The ionic reaction is: 4Fe +2 + O 2 + 4H + = Fe H 2 O Fe +3 is a very powerful oxidizing agent With Fe +3 :Fe +2 ratio of only 1:10 6, 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 H 2 SO 4 alone * ORP = Oxidation Reduction Potential (REDOX)

113 Metal Leaching – Influence of ORP (Eh or REDOX) and Bacteria Garrels, R.M. and Christ, C.L. (1965), Solutions, Minerals and Equilibria, Harper & Row, New York, Malouf, E.E. and Prater, J.D. (1961), Role of Bacteria in the Alteration of Sulphide, J. Metals, NY, 13, p

114 Stages in ARD Generation (note the lag time)

115 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 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

116 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

117 Active Treatment Most effective Most expensive All effluent processed in a treatment plant May require processing for decades

118 High-Density Sludge Water Treatment Plant WTP at Britannia Mine Site Howe Sound, British Columbia Capital Cost= ~ $12.0M Operating Costs= ~ $ 1.5M/year

119 HDS Plant – Process Flow Diagram Sludge/Lime Mix Tank Lime Reactor Clarifier Effluent Overflow Sludge disposal Sludge Recycle Lime Tank Flocculants Tanks Recycle Water Flocculants Lime Paste Acidic Feed Water Air

120 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

121 S o Reduction Process Schematic BioteQ After R.W. Lawrence, BioteQ H2SH2S Nutrients BIOREACTOR (S o Reduction) Sulphur Electron donor Cu Precip Zn Precip CuSZnS Treated Water Contaminated Drainage Metals, SO 4 Soda Ash or Lime

122 SRB Plant – Major Equipment BioteQ After R.W. Lawrence, BioteQ Copper ProductZinc Product ARD Bioreactor S o e - donor Lamellar Clarifier Filter Press Gas-Liquid Contactor To Lime Plant or Discharge

123 SRB Plant Layout: ~100m 2 BioteQ After R.W. Lawrence, BioteQ GAS-LIQUID CONTACTOR BIOREACTOR 1.8 m LAMELLA CLARIFIER (projected settling area 150 m 2 ) 5.9 m 3.1 m LAMELLA CLARIFIER (projected settling area 150 m 2 ) GAS-LIQUID CONTACTOR 2.4 m FILTER-PRESSES 0.8 m x 3 m W x L REAGENT PREP AREA Cu -CONC STORAGE 8 m MCC REAGENT STORAGE TRUCK DOOR Zn -CONC STORAGE 7 m BLOWERS SCRUBBER

124 Production Summary Flow Cu Concentrate Zn Concentrate Feed Water Discharge Water [mg/L] 18.0 Cu, 20.0 Zn, 0.1 Cd [mg/L] 0.05 Cu, 0.01 Zn, 0.01 Cd tonnes per year contained copper tonnes per year contained zinc 51.1% Cu, 2.1% Zn, 0.24% Fe, 33.1% S 52.4% Zn, 1.5% Cu, 0.3% Cd, 0.8% Fe, 27.1% S 14,880 m 3 /d – average over 12 months Sludge Reduction tonnes per year (15-20%) Lime Savings $64,000 per year (32%) Additional Benefits

125 Commercial Scale Plants

126 Chemistry of SRB Process for Metal Recovery Sulphate reduced by organic compounds: SO 4 = + CH 3 COOH + 2 H + = HS HCO H + 1. Sulphide ions precipitate metal sulphides: HS - + M 2+ = MS↓ + H + 2. S = + M 2+ → MS↓3. Equilibrium of H 2 S H 2 S (g) = H 2 S (s) = HS - + H + = S = + 2H + 4.

127 Pumice rock – extremely light

128 Brick Veneer Cladding - examples NRC Process Evaluation - Canyon Stone -

129 Limited to low effluent flowrates Passive Treatment Technologies NameDescriptionFunctionSelected References Aerobic wetlands Shallow wetlands Emergent vegetation Fe and Mn oxidation, Co-precipitation of Metals, Sorption on Biomass 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

130 Covers

131 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

132 Factors affecting Soil Cover Performance International Network for Acid Prevention, Evaluation of Long-term Performance of Dry Cover Systems, Final Report. O’Kane Consultants Inc., (Eds.), Report No

133 Geomembranes 1.Plastics (polyethylene (PE) 2.High density poly. (HDPE) 3.Chlorinated poly. (CPE) 4.Chloro-sulphonated poly. (DuPont HYPALON) 5.polyvinyl chloride (PVC) 6.Low-density poly. (LLDPE) 7.Geosynthetic clay liners (GCL) 8.Geomembranes impregnated with bitumen After Meer, S.R. and C.H. Benson, Hydraulic conductivity of geosynthetic clay liners exhumed from landfill final covers. J. Geotech. and Geoenviron. Eng., 133(5):

134 Geo-Membranes: Benefits and Disadvantages BenefitsDisadvantages  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, Hydraulic conductivity of geosynthetic clay liners exhumed from landfill final covers. J. Geotech. and Geoenviron. Eng., 133(5):

135 Field Monitoring of a Waste Pile Cover MEND, Design, construction and performance monitoring of cover systems for waste rock and tailings. Report , O’Kane Consultants Inc., (Eds.), Natural Resources Canada.

136 Covers and Climate Types Wickland, B.E., Wilson, G.W., Wijewickreme, D., and B. Klein, Design and evaluation of mixtures of mine waste rock and tailings. Canadian Geotechnical Journal, 43:

137 Sub-aqueous Tailings Disposal Options Impoundment Covered Dam Pit Filling Submarine

138 Factors affecting Submarine Disposal

139 Microbiology of ARD

140 Microbiological Aspects of ARD Bacteria form films on sulfide surfaces Reaction rate accelerates up to 10 8 times T. ferrooxidans/L. ferrooxidans considered responsible for catalytic behaviour Microbial makeup is controlled by site environment Microbes not well-studied or understood

141 Microbiological Aspects of ARD Thiobacillus ferrooxidans Leptospirillum ferrooxidans

142 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

143 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

144 Microbiological Aspects of ARD Structure of microbial communities

145 Microbiological Aspects of ARD Biogeographic distribution of key microbes

146 Microbiological Aspects of ARD Diversity revealed by molecular methods

147 Microbiological Aspects of ARD Fluorescent micrographs (FISH) of active phage

148 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

149 Bacteriophage – friend or foe Many shapes and sizes Phage are very small, ( nm in diameter) Some phage break down biofilm matrix to infect "protected" cells Photo credits: ICTV Database

150 T4 bacteriophage attacking an E. Coli bacterium Bacteriophage – friend or foe

151 Bacteriophage – an ARD solution? Like lunar landers, bacteriophage attach to the microbial cell wall and inject their DNA for replication Cell Wall

152 Photomicrographs of T4 bacteriophage for E. Coli Bacteriophage - an ARD Solution?

153 The Lysogenic Cycle leads to mutation of the host The Lytic Cycle leads to the death of the host Bacteriophage - an ARD Solution?

154 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?

155 Biofilms and Quorum Sensing Complex association of cells with an exo- polysaccharide matrix Adhere strongly to sulfide surface or grow deep within pores and cracks Play integral role in composition & stability of microbial communities

156 Biofilms and Quorum-Sensing Biofilms - bacterial colonies living in a kind of social order Biofilms form on: 1. wet solid surfaces 2. soft tissue surfaces in living organisms 3. liquid-air and liquid/solid interfaces ARD-relevant locations: rock surfaces in marine or freshwater environments

157 Progression of Biofilms 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) Evolution from Planktonic Behaviour to a Biofilm

158 Benefits of Biofilms for Microbes

159 Common Example of a Biofilm Dental Plaque Stained with Gram's Iodine

160 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- virulence - competence- conjugation - antibiotic production- Programmed Cell Death (PCD) - sporulation- biofilm formation

161 Big Question? Can we use Q-S knowledge to get microbes in a bio-film to “commit suicide” without creating new side-effect problems? Bio-Films and Quorum-Sensing

162 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 Conclusions

163 Questions?

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