Acid Mine Drainage 11.11.2015 H-ESD : Environmental and Sustainable Development Michael Staudt, GTK.
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Transcript of Acid Mine Drainage 11.11.2015 H-ESD : Environmental and Sustainable Development Michael Staudt, GTK.
![Page 1: Acid Mine Drainage 11.11.2015 H-ESD : Environmental and Sustainable Development Michael Staudt, GTK.](https://reader033.fdocuments.in/reader033/viewer/2022051517/5697bf941a28abf838c9023c/html5/thumbnails/1.jpg)
Acid Mine Drainage 11.11.2015
H-ESD : Environmental and Sustainable Development
Michael Staudt, GTK
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Table of contents
Acid Mine Drainage• Excercise• Steps of the excercise • Equations
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Managing Sulphidic Mine Wastes and
Acid Drainage
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Acid Drainage
Caused by the oxidation of sulphide minerals, especially iron sulphides, associated with mining
Oxidation produces sulphate ion which when dissolved in water forms sulphuric acid
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Acid Drainage
Some effects:Acid drainage affects water
quality downstreamRehabilitation becomes more
difficultMetal ions are released
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Acid Drainage
Acid drainage is one of the most significant environmental issues facing the mining industry.
Canadian liability estimated as C$ 2-5 billionAustralian liability estimated as A$
60M/yearin the USA 20,000 km of streams and rivers
adversely affected
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Longevity of the Problem
• Acid drainage may not develop immediately• Acid drainage can continue for tens to thousands of years
Rio Tinto region, Spain; for more than 2000 years Many examples more than 50 years with little reduction in rate of acidic drainage
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What is Acid Drainage?
• Oxidation of sulphidic minerals, especially in connection with mining– Exposure to air and water– Increase in surface area– Reactive minerals
• Pyrite (iron sulphide) most common sulphide mineral associated with mines
• Other iron and other metal sulphides• Drainage of acid away from its source
FeS2 + 3.75 O2 + 3.5 H2O = Fe(OH)3 + 2 SO42- + 4 H+
(Iron sulphide + Oxygen + Water = Ferric Hydroxide + Aqueous sulphuric acid)
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Factors Influencing Acid Drainage • Water (required for oxidation and transport)• Oxygen availability• Physical characteristics of the material• Temperature, pH• Ferric (Fe+3)/ferrous (Fe+2) ion equilibrium• Microbiological activity• Presence of neutralising minerals
– Carbonates are most effective– Silicates & aluminosilicates may contribute
• Chemistry of receiving waters
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Impacts of Acid Drainage
• Potential for reuse of water on mine is limited– corrosion problems for equipment
• Toxic effects to aquatic ecosystems– acidity and dissolved metals
• Toxic effects on downstream vegetation• Adverse impacts on ground water• Limits uses of downstream water
– Irrigation, stock watering, recreation, fishing
• Causes difficulties in revegetation and stabilising mine wastes
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Best Practice Approach
• During feasibility stages:– Characterise acid
generating potential of materials
– Characterise mobility of potential contaminants such as heavy metals
– Estimate the potential for oxidation products to migrate to the environment
– Estimate effects on host environment
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Identifying and Predicting Acid Drainage
• When characterising rock types at site important characteristics include:– Geological description– Mineralogy of both ore and waste– Fracturing
• Sampling and analysis:– Acid-base accounting– Simulated oxidation, usually with hydrogen peroxide – pH and conductivity tests of paste or slurry – Total and soluble metal analysis – Geochemical Kinetic Tests
• Humidity cells• Column Leach Tests
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Acid Drainage Control Strategies
• Control requires:– Data on physical and chemical properties of
materials– Risk assessment– Strategies to minimise oxidation
• Control strategies– Containment and isolation– Treatment of acid drainage
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Soil Covers
• Materials– Imported materials e.g. clay, soil– Low-sulphide waste rock, if compactable– Geotextile fabrics– Covers may require zones
• Base (main sealing) layer - high water retention, low permeability
• Middle layer - water reservoir (may have higher permeability)• Surface layer (barrier zone) - erosion protection and/or
substrate for plant growth
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15BEST PRACTICE ENVIRONMENTAL MANAGEMENT IN MINING
Isolation
Sulphidic waste
Top non-sulphidic waste layer
Basal layer
Revegetated and contoured cover material(surface capping and water storage medium)
Original ground surface
Freedumpednon-sulphidicwaste
Freedumpednon-sulphidicwaste
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Water Covers Blending
• Most readily used in high rainfall, low evaporation areas
• Creation of a permanent lake or swamp
• Use of an existing lake or the sea
• Flooding of underground tunnels and pits
• Mixing of acid and non-acid forming waste rock• Incorporation of alkaline materials
• Lime• Fly ash• Kiln dust
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Bacterial Inhibition
Bacteria can catalyse sulphide oxidationApplying bactericides can slow the processEffect may be short-term onlySome success claimed in USA coal industryUsed in establishing a vegetation cover before acid production starts
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Treatment Systems
• Collection of acid drainage followed by neutralisation– Passive Anoxic Limestone Drains (PALID)
• Drainage passed through a channel of coarse limestone gravel in the absence of oxygen
– Successive Alkalinity Producing Systems (SAPS)• Variation on PALID
– Wetland treatment systems
• Newer treatments, moving from experimental to operational– Bioreactors– KAD (kaolin amorphous derivative)– Bauxite derivatives– ‘Green rust’ precipitation
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19BEST PRACTICE ENVIRONMENTAL MANAGEMENT IN MINING
Passive Treatment Systems
Cross section through an anoxic limestone drain
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20BEST PRACTICE ENVIRONMENTAL MANAGEMENT IN MINING
Treatment Systems
Conceptual design of a wetland system for treating Acid Mine Drainage
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Monitoring
An essential component of sulphidic waste management• Classification of materials• Point source monitoring • Monitoring surface water and ground water in both up- and
down-stream gradients• Monitoring of effectiveness of control measures
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Monitoring
Waters:•pH, conductivity, SO4-2 •Other major ions (Ca+2, Mg+2, Al+3, Na+, K+)•Alkalinity•Metals/metalloids (Fe, Al, As, Cd, Cu, Zn, Mn, Pb)•Toxicity to organisms
Rock materials:•Static and kinetic geochemical tests•Water flux through stockpiles•Physical stability: cracking, erosion