Presentation on theme: "Tailings Dam Failures, ARD, and Reclamation Activities"— Presentation transcript:
1 Tailings Dam Failures, ARD, and Reclamation Activities John A MeechProfessor of Mining EngineeringThe University of British Columbia
2 Outline Tailings Dam Construction Methods Tailings Dam Failures Reclamation of Dams, Waste Piles, and SitesBritannia Beach and the Millennium Plug ProjectAtmospheric Risks at the Sullivan MineAcid Rock Drainage – what is it?ARD Control MethodsMicrobiology of ARD
3 Issues Stability of dam structures Use borrowed coarse material Cyclone tailings to extract coarse fractionControl 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.)
8 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)
14 Underground Storage Hydraulic sand Cemented fill Paste backfill Cycloned tailings sand (coarse fraction)Cemented fillRequired to fill void space and create strengthPaste backfillAll tailings dewatered to 60-65% solidsDry rock fillWith 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 impoundmentOperational error during fillingNatural events (thunderstorms and/or flood inflow)Beach width between the water and dam crest becomes too smallPhreatic surface rises in the dam and leads to collapseLiquefaction during an earthquakeTailings may change physical properties under seismic stressCyclic stresses can lead to liquefactionHighly susceptible due to low bulk density and high saturationHazards are not theoreticalMany tailings dam failures prove the theories over and over again.Recent example - Harmony gold mine tailings dam inSouth Africa (Feb. 1994) after heavy rainstorm- village completely buried- 17 people killed
24 Comparison of Surface Impoundment Types Water RetentionUpstreamDownstreamCenterlineMill Tailings RequirementsSuitable for any type of tailings40-60% sand in tailings. Low feed pulp density to enhancesize segregationSands or low-plasticity slimesDischarge RequirementsAny discharge procedure suitablePeripheral discharge and well-controlled beach necessaryVaries according to design detailsPeripheral discharge and nominal beach necessaryWater Storage SuitabilityGoodNot suitable for significant water storageNot so good for permanent storage. Temporary flood storage adequate with proper design
25 Comparison of Surface Impoundment Types Water RetentionUpstreamDownstreamCenterlineSeismic ResistanceGoodPoorin high seismic areasAcceptableRaising Rate RestrictionsEntire embankment constructed initiallym/yr desirable.> 15 m/yris hazardous.NoneHeight restrictions for individual lifts may applyEmbankment Fill RequirementsNatural soil borrowNatural soil, sand tailings, or mine wasteSand tailings or mine waste if production rates are sufficient, or Natural soilSand tailings or mine waste if production rates are sufficient, or Natural soilRelative Embankment CostHighLowModerate
26 Tailings Dam FailuresFrom 1968 to August documented failures worldwide3,500 tailings dams exist around the world25,000 to 48,000 large water storage dams exist around the world.Tailings dam failures closely match water storage dam failuresSo, 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 dams76% of incidents were Upstream construction methods56% of incidents were dams greater than 30 m in heightM. 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.
28 Ten Causes of Failure________________________________________________ Type of Failure Number % 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 managementFaulty maintenance of drainage structuresInappropriate dam proceduresrapid dam growthHeavy machinery on top of unstable dam
30 Real-Time Monitoring of Tailings Dams Piezo-electric gaugesPore pressures at depthBoth horizontal and vertical directionsControl of barge pumpsControllable CCD camerasOn top of dam structureAlong all diversion ditchesWater 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 circuitCharge is amplified into a proportional output voltage
33 Piezo-electric Gauges Piezoelectric sensors are small in constructionTheir 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
47 Dry Stack Tailings Anglo-American's La Coipa Mine in Chile Dewatering tailings to a filtered wet (saturated) or dry (unsaturated) cakeMust be transported by conveyor or truckMaterial is deposited, spread and compacted as unsaturated tailings pileProduces a stable deposit requiring no retention damTypical moisture content is below 20% - several percent below saturationCombination 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) cakeMust be transported by conveyor or truckMaterial is deposited, spread and compacted as unsaturated tailings pileProduces a stable deposit requiring no retention damTypical moisture content is below 20% - several percent below saturationCombination of belt, drum, horizontal and vertical pressure plates and vacuum filtration systems
49 Dry Stack Tailings Disadvantages High capital and operating costs due to filtrationLimited to low throughput operations (~20,000 tpd)Diversion systems to prevent inundation of stackSurface contour management to handle surface waterMust prevent ponding and erosion of the stackNo option to store water within a dry stack facilitySulfide oxidation creates high metal levels, low volumesDust generation is problematic in arid climatesNot suitable in high rainfall environmentSeasonal fluctuations are important considerations
50 Co-Disposal of Waste & Tailings Co-minglingTailings and coarse waste rock material transported independentlyMixed together mechanically in storage facility or slurry-pumpedMixing promotes voids filling (mingling) to maximise densityCo-placementNot mixed to form a single discharge streamWaste rock end dumped into tailings facilityWaste rock used to create internal berms or retaining walls (sometimes)Co-depositionSimilar to co-placement, but waste streams placed in layersDeposited tailings naturally enters voids in underlying rockEnd-dumping waste rock with tailings deposition down face prior to further end dumping
51 Dam Remediation Efforts By today's standards this dam is just too high for its design water flow andmaterial properties. Built over many decades, a second dam was requiredto be built in the late 1990s to prevent water release (high As content).
52 Main dam of the Helmsdorf uranium mill tailings deposit, Oberrothenbach (Saxony)
54 Stava Fluorite Mine Dam Failure, Italy 1985 Before After Tailings dam consistedof two basins built on aslope. Failure started withcollapse of the up-slopebasin. Inflow of releasedmaterial caused over-topping and collapse ofthe lower basin. Theresulting slurry wavetravelled to Stava at aspeed of 30 km/h; laterit reached 90 km/h.Lives lost = 268Damages = $133 x 106
56 Failure at Aznalcollar, Spain - 1998 Slab of soil beneath the damslid ~1m towards Río Agrio.2. The dam cracked and broke;the wall collapsed sweepingout the separation dam.3. Between 5 to 7 million m3contaminated water and slurryspilled through the gap.4. The Río Agrio rose 3m, changingits course and eroding bed rock.
67 UBC at Britannia BeachBritannia BeachUBC-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 Reclamation Issues in 2001 Acid mine drainage from tunnels (620 m3/hr) About 800 kg of Cu & Zn discharged per dayOver 10,000 tonnes of metal since closureGroundwater contamination on the FanPotential impacts on aquatic lifeWaste dumps and stockpilesTailings at bottom of Howe SoundSealing abandoned adits, demolition of derelict buildings (public safety issues)
69 Groundwater discharge < 5% of the flow2-3% of the copper3-4% of the zinc4100 Level effluent50-80% of the flow30-55% of the copper60-75% of the zinc2200 Level effluent20-50% of the flow45-70% of the copper25-40% of the zincPlug the 2200 AditBuild aTreatment PlantReclaim pitsand waste dumps
77 Reclamation Activities at Sullivan Mine mine closed after 92 years2000 – site reclamation on waste dumps (Number 1 Shaft and North dumps)ditch was partially covered when the dump toe was extended 70mm of glacial till was placed over the dump surface and the ditchReduce water percolationRestrict air infiltrationSlow rate of oxidationMonthly sampling to monitor flowrate and contaminant levels
79 Sullivan Mine Accident – May 15-17, 2006 Four people lost consciousness and died after entering the sampling shedDouglas Erickson, 48, a contractorRobert Newcombe, 49, Teck employeeKim Weitzel, 44, a paramedicShawn Currier, 21, a paramedicReason: lack of oxygenImmediately after the accident, O2 level in sump was ~2% & CO2 was ~7%Shed used regularly with no problem and effluent flow was previously open channelReasonable to conclude shed was not a confined space at that timeShed was used 1 week before tragedyOct. 2006, accident was identified as beingOther mines were warned immediately by B.C. Chief Inspector of Mines to treat all sampling sheds as confined spaces"unprecedented in thehistory of mining"
80 Contributing Factors to the Accident During Summer of 2005Dump & drainage ditch were covered to limit air/water infiltration and prevent human exposure to ARDO2-depleted effluent now isolated from the atmosphereAir in shed now directly connected to "bad" air in dumpPrior use showed no problem (1 week before)False sense of security (9 years without any problem)Shed was safe before the ditch became a drainDesign change created dangerous hazardAtmospheric conditions play a major roleTemperature & pressure affect gas flowrate and direction
81 Contributing Factors to the Accident Before covering, ARD effluent was not O2-depletedO2-depleted out of dump, but contact with air restores O2 levelAfter covering, ARD effluent was O2-depletedO2-depleted out of dump, and no contact with air until shedPossible mechanismO2 removal from static air in the shed by O2-depleted effluentBeforeO2 transferIn ditchAfterO2 transferIn shed
82 Breathing Waste Dump August 2006 - dump was instrumented Measure air velocity and gas composition in shed and pipeTemperatures 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 pressureDANGEROUSSAFEDANGEROUS
83 Temperature during week of the accident 5101520255/1/20065/6/20065/11/20065/16/20065/21/20065/26/20065/31/2006Temperature (oC)Daily average air temperature at Cranbrook airport in May 2006.Monitoring station was entered safely on May 8, 2006.
85 Cyclical Changes in Risk For a Confined Structure near dump toeSeasonal VariationsSafe in winter / Dangerous in summerIn Summer, minimum night temperature may lie above maximum dump temperatureDump blows toxic gas all the time - deadly.In Winter, maximum day temperature may lie below maximum dump temperatureDump will suck in air all the time - safe
86 Cyclical Changes in Risk For a Confined Structure near dump toeDiurnal VariationsSafe at night / Dangerous in day timeOutside temperature cycles from hot to coolDump may transition from blowing to sucking if maximum dump temperature lies between maximum day and minimum night temperatureIn Spring – transition from Safe all the time to Dangerous in dayIn Fall – transition from Dangerous all the time to Safe at night
87 Summer Conditions Daily Atmospheric Temperatures Temperature 302010-10-20Daily AtmosphericTemperaturesMaximum InternalDump TemperatureTemperatureTimeof Day
88 Fall Conditions Daily Atmospheric Temperatures Temperature 302010-10-20Daily AtmosphericTemperaturesMaximum InternalDump TemperatureTemperatureTimeof Day
89 Winter Conditions Daily Atmospheric Temperatures Temperature 302010-10-20Daily AtmosphericTemperaturesMaximum InternalDump TemperatureTemperatureTimeof Day
90 Spring Conditions Daily Atmospheric Temperatures Temperature 302010-10-20Daily AtmosphericTemperaturesMaximum InternalDump TemperatureTemperatureTimeof Day
91 Cyclical Changes in Risk For a Confined Structure near dump toeDecadal VariationsSafe(r) when maximum dump temperature has reached its long-term maximum valueDangerous when transitioning up or downConceptual Period Boundaries:yearsInitial period with rising dangeryearsMaximum danger - extremely hazardousyearsDanger transitions from hazardous to problemyearsConstant reduced danger – dump temp > max. outside temp.yearsRapid increase in risk - internal temp goes below max. outside temp.yearsMaximum danger returns - extremely hazardousyearsDanger transitions from hazardous to safe (pore gas O2 levels rise)190 – onwardSite is now safe - no O2-depleted gas generated or emitted
92 Decadal Variation in Risk Assessment Estimated MaximumDump TemperatureMaximum OutsideTemperatureRisk of a ConfinedSpace Accident
93 Summer Conditions – transition to safe Dump reaches maximum temperature after yearsPerhaps sooner with highly reactive dumps302010-10-20Daily AtmosphericTemperaturesMaximum InternalDump TemperatureTemperatureTime of Day
94 Reference Dumps1. 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., 2002Robertson 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 Dumps1. 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 SiteEstimated Internal TemperatureReported Internal TemperatureNordhalde10-1514Doyon4045Sugar Shack South> 40Aitik Mine2-63White’s Dump (1 year after cover)44Number One Shaft10 -1512Equity Silver Main52West Lyell35-4038 (Max)Sullivan North30-3533Nordhalde, Doyon, Sugar Shack S., Aitik, White’s, andNumber One Shaft dumps are reference input casesNorth Dump, West Lyell, and Equity Silver Main are test cases
97 Overall Results for all 9 dumps Time of YearDoB in HighGas Velocity at dump toeDegree of Belief in HighRiskValueAssessmentCover Value"high" reactivityGas Generation in SummerGas Emission via pathwayGas ConfinementHuman ExposureNordhaldeSummer88%60%Neg. Small100%63%901000.53Marginal HazardJanuaryPos. Big66%18% L0.19ProblemDoyon0%Pos. Big43% ML15% L0.14Sugar Shack74%23% ML0.15Aitik5%Neg. Big66% MH76% ML0.38SignificantNeg. VS20% MH37% MH0.21White’sPos. VS27% ML0.33No. 1 Shaft89%69%Neg. VB0.90HazardousMay80%0.65Main Equity Silver71%46% MH18%0.16Pos. VB35% MHWest Lyell94%21% MNorthPos VS0.31* L = low ML = medium-low M = medium MH = medium-highA 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 Note: confined structure on top of the dumpSampling Shed
100 Dealing with Reactive Tailings Two major types each creating a third issueAcid Rock Drainage (ARD)CyanideARD leads to dissolution of Heavy MetalsCyanide forms complex metallic ionsMetallic 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 MetallicaYet the term Acid Rock Drainage wasn’t coined until 1970Significant work by NRCan (MEND Program) and Canadian companies developed innovative techniques to handle this ubiquitous problemARD requires sulphides, water, and air (and bacteria)Minerals are the source of sulphur and ironAir is the source of oxygenWater is the transfer medium for oxygen from air to rockBacteria catalyze the reaction of Fe+2 to Fe+3
103 Generation of ARD from pyrite ARD from surface coal mine in MissouriIron hydroxide (yellow boy) precipitates as pH rises from downstream dilutionProblem can last for decadesPhoto Credit: D. Hardesty, USGS Columbia Environmental Research Center
105 How long does ARD last? - Forever! Corta Atalaya, Rio Tinto, Spain - abandoned pyritic open pitRio Tinto in Spain– 2 millennium after mining
106 Is it only Mining that causes ARD? Blood Falls at Taylor Glacier, Antarctica
107 Acid Rock Drainage – Metal Leaching ARDFormed by atmospheric oxidation (i.e., water, oxygen, and carbon dioxide) of the common Fe-S minerals pyrite and pyrrhotite in the presence of bacteriaThiobacillus ferrooxidans, T. acidophilus, and T. thiooxidansMLAcid (H2SO4) leads to dissolution of metals and subsequent pollution of aquatic environments
108 Basic Chemistry of ARD (from FeS2) Basic Issues behind the Chemistry:Equilibrium of Ferrous-Ferric IonsPresence 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 H2O + 7O2 = 2FeSO H2SO4Bacterial Oxidation of Ferrous Sulphate (T. ferrooxidans):4FeSO4 + O H2SO4 = 2Fe2(SO4) H2OFerric Sulphate is Reduced and Pyrite Oxidized by these reactions:Fe2(SO4)3 + FeS2 = 3FeSO S2S + 6Fe2(SO4) H2O = 12FeSO H2SO4Elemental Sulphur Oxidation (T. thiooxidans):2S + 3O H2O = 2H2SO4Acid 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 oxidationT. ferrooxidans and O2 for Fe+2 to Fe+3 oxidationpH compatible with T. ferrooxidans, typically pH
112 * ORP = Oxidation Reduction Potential (REDOX) Role of BacteriaT. ferrooxidans acts to oxidize ferrous to ferric iron(Fe+2 to Fe+3)The ionic reaction is:4Fe+2 + O2 + 4H+ = Fe+3 + 2H2OFe+3 is a very powerful oxidizing agentWith 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+2Base metal sulphides react slowly with H2SO4 alone* ORP = Oxidation Reduction Potential (REDOX)
113 Metal Leaching – Influence of ORP (Eh or REDOX) and Bacteria Malouf, E.E. and Prater, J.D. (1961), Role of Bacteria inthe Alteration of Sulphide, J. Metals, NY, 13, pGarrels, R.M. and Christ, C.L. (1965), Solutions, Mineralsand Equilibria, Harper & Row, New York,
115 Control of ARDRemoval of one essential component (sulfide, air, or water):Waste Segregation and BlendingBlend-in neutralizing potential (NP) rock to yield pH 7.0Base additivesAdd limestone to buffer acid reactionsLiners, Covers, and CapsWater covers are the most effectiveSoil, clay, and synthetic covers (geomembranes)minimize water and air infiltration
116 Control of ARD Bactericides Collection and treatment of contaminants Chemicals that reduce/kill bacteria (T. ferrooxidans)Effective, but costly, and “bugs” mutateCollection and treatment of contaminantsActive or Passive treatmentActive treatment - high-density lime sludgePassive treatment in constructed wetlandsBioremediation (micro-organisms)Remove metals directlyIntroduce viruses against the bacteria
117 Active Treatment Most effective Most expensive All effluent processed in a treatment plantMay require processing for decades
118 High-Density Sludge Water Treatment Plant WTP at Britannia Mine SiteHowe Sound, British ColumbiaCapital Cost = ~ $12.0MOperating Costs = ~ $ 1.5M/year
119 HDS Plant – Process Flow Diagram Sludge/LimeMix TankLime ReactorClarifierEffluent OverflowSludge disposalSludge RecycleLimeTankFlocculantsTanksRecycle WaterLime PasteAcidic Feed WaterAirThis a simplified process flow diagram for the HDS process at Britannia Beach .Starting on the left, lime slurry is combined with recycled sludge in a small mix tanksThis lime/sludge mixture overflows to a rapid mix tank where it combines with the acidic feed. Lime dosage to the lime/sludge mix tank is controlled by pH at the rapid mix tank overflow.The rapid mix tank overflows to a lime reactor. Oxidation and precipitation reactions are carried out in this reactor. Iron and manganese are oxidized using air to assist the process by co-precipitating other elements as well such as arsenic.Flocculant is added to the lime reactor O/F prior to flocculation in the clarifier feed-well .The clarifier separates treated effluent from the sludge. The sludge is pumped back to the lime/sludge mix tank to complete the process.Clarifier overflows to a recycle water tank (not shown), which provides water for flocculant dilution, flushing and dilution of the recycle and sludge transfer systems.Excess sludge at a density of 20 to 25 wt% solids is sent for filtering to a cake that is about 35%solids (like toothpaste).119
120 Sludge Disposal Sludge Disposal by truck – cost = ~$40/tonne Other optionsManufacture bricks by blending sludge with clay or pumiceUse low-temperature process with organic resinsUse high-temperature process to harden into a ceramicExamine opportunities to recover Cu and ZnFrom the effluent prior to HDSFrom the sludge by leaching120
121 So Reduction Process Schematic H2SNutrientsBIOREACTOR(So Reduction)SulphurElectron donorCuPrecipZnCuSZnSTreatedWaterContaminatedDrainageMetals, SO4Soda Ash or LimeBioteQAfter R.W. Lawrence, BioteQ
123 (projected settling area SRB Plant Layout: ~100m2GAS-LIQUIDCONTACTORBIOREACTOR1.8 mLAMELLA CLARIFIER(projected settling area150 m2)5.9 m3.1 m2.4 mFILTER-PRESSES0.8 m x 3 m W x LREAGENTPREP AREACu -CONCSTORAGE8 mMCCDOORTRUCKZn -CONC7 mBLOWERSSCRUBBERBioteQAfter R.W. Lawrence, BioteQ
124 Production Summary Flow Feed Water Discharge Water Cu Concentrate 14,880 m3/d – average over 12 monthsFeed Water[mg/L] 18.0 Cu, 20.0 Zn, 0.1 CdDischarge Water[mg/L] 0.05 Cu, 0.01 Zn, 0.01 CdCu Concentrate187.0 tonnes per year contained copper51.1% Cu, 2.1% Zn, 0.24% Fe, 33.1% SZn Concentrate185.5 tonnes per year contained zinc52.4% Zn, 1.5% Cu, 0.3% Cd, 0.8% Fe, 27.1% SAdditional BenefitsLime Savings$64,000 per year (32%)Sludge Reductiontonnes per year (15-20%)
128 Brick Veneer Cladding - examples NRC Process Evaluation -Canyon Stone -
129 Passive Treatment Technologies NameDescriptionFunctionSelected ReferencesAerobic wetlandsShallow wetlandsEmergent vegetationFe and Mn oxidation, Co-precipitation of Metals, Sorption on BiomassEger and Wagner, 2003USDA and EPA, 2000Open limestonechannelsAcidic water flows overlimestone, or other alkaliAlkalinity additionAl, Fe, Mn oxide precipitationZiemkewicz et al., 1997Anoxic limestonedrainsWater flows through limestone channel under anoxic conditionsAlkali addition; Fe Precipitation; Limestone Armouring PreventionWatzlaf et al., 2000Anaerobic wetlandsSubsurface wetland, isolated from air by water or materialAlkali addition; Sulphate Reduction; Precipitation of metal sulfides; Sorption on VegetationBrenner, 2001Successive AlkalinityProducing SystemsVertical flow systems drain through limestone layers & anaerobic organic matterAlkalinity addition; Sulphate ReductionMetal PrecipitationKepler and McCleary,1994Zipper and Jage, 2001Sulfate-ReducingBioreactorsCollected water in anoxic chamber containing organic matter and SRBsAlkalinity addition; Sulphate reduction; Metal PrecipitationGusek, 2002Permeable ReactiveBarriersIntercepted groundwater flows through permeable barrier containing reactive materialAlkalinity addition; Sulphate reduction;Metal Precipitation and SorptionBenner et al., 1997US DOE, 1998AmendmentsMaterials added to ARD sources or holding areasAlkalinity addition; Sulfate reduction; Metal Precipitation; Sorption;Chelation; RevegetationChaney et al., 2000Limited to low effluent flowrates
131 Liners, Covers, and Caps Liners used to prevent seepage form the dam Covers used to inhibit influx of water and airCaps used to seal dam entirelyExpensive materials and installationMust be installed with great careBiggest 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 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 bitumenAfter 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 Low permeabilityHigh costRelatively easy to installCost depends on distance from supplier to siteResistant to chemical and bacterial attackLimited design life - 50 to 100 yearsRequires proper bedding and protective coverGeotechnical instability on steep slopesVulnerabilities 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 contractionAfter 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:
140 Microbiological Aspects of ARD Bacteria form films on sulfide surfacesReaction rate accelerates up to 108 timesT. ferrooxidans/L. ferrooxidans considered responsible for catalytic behaviourMicrobial makeup is controlled by site environmentMicrobes not well-studied or understood
141 Microbiological Aspects of ARD Thiobacillus ferrooxidansLeptospirillum ferrooxidans
142 Microbiological Aspects of ARD Key organisms (T. & L. ferrooxidans) >> global significancePhysiological and genetic aspects well studiedMicrobial diversity specific to site environmentRecent advances on structural dynamics of communitiesBiofilms on sulfide surfaces play a key roleBacteriophage impact negatively on bacterial populations
143 ARD Mitigation with Bacteriophage Novel approach to ARD controlIsolate phage that infect ARD-generating “bugs”Create deadly mixture of viruses to control microbial ARD communities with biologyNew 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 themselvesInfection results in death, if phage is virulentTemperate phages kill only a small fraction of cells and cause infected host to mutate
149 Bacteriophage – friend or foe Many shapes and sizesPhage are very small, ( nm in diameter)Some phage break down biofilm matrix to infect "protected" cellsPhoto credits: ICTV Database
150 Bacteriophage – friend or foe T4 bacteriophage attacking an E. Coli bacterium
151 Bacteriophage – an ARD solution? Like lunar landers,bacteriophage attach tothe microbial cell wall andinject their DNA forreplicationCell Wall
152 Bacteriophage - an ARD Solution? Photomicrographs of T4 bacteriophage for E. Coli
153 Bacteriophage - an ARD Solution? The Lytic Cycle leads to the death of the hostThe Lysogenic Cycle leads to mutation of the host
154 ARD Mitigation with Phage Inject phage into a dump/damCoat surfaces with phage-containing biofilmPhage will control microbial population, not eliminate itPhage 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 matrixAdhere strongly to sulfide surface or grow deep within pores and cracksPlay integral role in composition & stability of microbial communities
156 Biofilms and Quorum-Sensing Biofilms - bacterial colonies living in a kind of social orderBiofilms form on:1. wet solid surfaces2. soft tissue surfaces in living organisms3. liquid-air and liquid/solid interfacesARD-relevant locations:rock surfaces in marine or freshwater environments
157 Progression of Biofilms Evolution from Planktonic Behaviour to a BiofilmREVERSIBLEADSORPTIONOF BACTERIA(seconds)IRREVERSIBLEATTACHMENTOF BACTERIA(sec - min)GROWTH &DIVISIONOF BACTERIA(hours - days)EXOPOLYMERPRODUCTION& BIOFILMFORMATION(hours - days)ATTACHMENTOF OTHERORGANISMS TOBIOFILM(days - months)
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 changesQ-S bacteria release signal molecules (auto-inducers)Auto-inducer concentration increases with cell densityAt threshold concentration, gene expression changesQ-S communication regulates many physiologies:- symbiosis - virulence- competence - conjugation- antibiotic production - Programmed Cell Death (PCD)- sporulation - biofilm formation
161 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?
162 ConclusionsTailings Dam Construction must be done with care and knowledge about the tailing material, about the foundation material – both physical and chemical factors are importantEvery 8 months, a tailings dam fails somewhere in the worldDownstream methods are safestReactive Tailings require additional care and concern for ARD and Metal LeachingCyanide Tailings also generate metal pollutionConfined Space issues may exist with ARD wastesMicrobiology is a new approach receiving attention
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