csm

Information about csm

Published on December 18, 2007

Author: Burnell

Source: authorstream.com

Content

Contaminated Sites and the Mining Industry:  Contaminated Sites and the Mining Industry Content of the Presentation:  Content of the Presentation Introduction Environmental Problems in the mining industry Acid mine drainage Emissions in the metal-producing industry Aluminium Dross Closing the loop Underground waste disposal plant Introduction:  Introduction Mining and metallurgic industry → demonstrative examples for the term “ecological rucksack” - Impact´s on the Environment Waste intensive excavation´s Destruction of the natural habitat at the mine and the disposal site´s Pyrite Oxidation – acid mine drainage Mobilisation of heavy metals Soil Erosion Milling and metal extraction Energy consumption especially in the primary metal industry Arsenic-containing waste from Copper-smelting Cyanide- and nitride-containing salts from steel curing Mining – acid mine drainage:  Mining – acid mine drainage In mining sites with (long lasting) hard rock mining activities: (pyritiferous ores with sulfides of copper, zinc and lead):  Acid mine drainage caused by PYRITE OXIDATION is a severe long-term burden to environment. Acid Mine Drainage (AMD) is currently the main pollutant of surface water in the mid-Atlantic region. (EPA) Mining – acid mine drainage:  Mining – acid mine drainage Acid Mine Drainage observed at foot of abandoned tailing dam (Lorber 1999) water draining a sulfide-rich lignite seam in the Czech Republic (Murad 2003) Mining – acid mine drainage:  Mining – acid mine drainage Environmental impacts and economic concerns Contaminated drinking water Disrupted growth and reproduction of plants and animals Corroding effects of acid on parts of infrastructure such as buildings Reduction of biodiversity Negative impact on tourism Mining – acid mine drainage:  Mining – acid mine drainage Acid Mine Drainage is caused by sulfide oxidation (oxidation of Pyrite, Marcasite, Pyrrhotite) to sulphate. Under aerobic conditions and in presence of bacteria (like: Thiobacillus ferrooxidans, Thiobacillus thiooxidans) suphuric acid is formed together with characteristic bright red coloured Fe2O3 (respectively Fe(OH)3 or FeO(OH)). The chemical equation of the reaction may be summarised as follows: 4 FeS2 + 15 O2 + 14 H2O ↔ 4 Fe(OH3) + 8 SO42- + 16 H+ Mining – acid mine drainage:  Mining – acid mine drainage As shown above, the main oxidant for FeS2 is Fe(III), and the slowest step of the total reaction is equation b) which determinates the reaction velocity. This conversion of Fe(II) to Fe(III) is bio-catalysed by Thiobacillus ferrooxidans. (Bio-Leaching) Mining – Mitigation of the environmental impact:  Mining – Mitigation of the environmental impact Soil Covers with clay subsoil's → reducing of oxygen permeability and water percolation Water Covers by establishing a permanent wetland Underground “in pit” disposal of wastes Blending and Co-disposal of acid generating and consuming material (limestone, fly ash) Surface coating (microencapsulation) of waste rocks with iron phosphate Bacterial Inhibition with biodegradable bactericides (e.g. sodiumlaurylsulphate) Metal producing Industry – Al-Dross:  Metal producing Industry – Al-Dross Secondary Al → less energy- and water consumptions and emission than primary Al industry remelting of Al-Scrap layer of aluminum oxide formed protects the metal against further oxidation by Surface Passivation 2 Al + 3 O2  2 Al2O3 Metal producing Industry – Al-Dross:  Metal producing Industry – Al-Dross Al-Oxide = MELT LOSS → unwanted reaction in Al-Industry Complex Mixture of: Metallic Oxides Nitrides Carbides Sulfides Salts from Fluxing Process (NaCl, KCl, Na3AlF6, etc) Dirt Impurities Metallic Aluminum Metal producing Industry – Al-Dross:  Metal producing Industry – Al-Dross Strong Reactivity of DROSS with Moisture or Water → hazardous waste: Because of high Reactivity: Direct Landfilling of Dross not possible, Pretreatment is necessary! Metal producing Industry – Al-Dross:  Metal producing Industry – Al-Dross SOLIDIFICATION: Chemical – physical pretreatment of wastes with HYDRAULIC or LATENT HYDRAULIC binders (e.g. Portland cement, Puzzolane cement, Fly Ash with additives etc.) for FIXING of problematic components in a concrete like solid matrix during LANDFILLING. Concrete block Problem: NONE of the INVESTIGATED SAMPLES COULD MEET LIMIT VALUE of > 3 N/mm2 of COMPRESSIVE STRENGTH increased concentrations of CN-, F-, NH4+ and SO42- were measured in the collected LANDFILL-LEACHATE Metal producing Industry – Al-Dross:  Metal producing Industry – Al-Dross LANDFILL-LEACHATE Metal producing Industry – Al-Dross:  Metal producing Industry – Al-Dross Thermal Oxidation in Fluidized Bed In a PILOT-SCALE Trial, DROSS was crushed to a particle size < 3 mm and fed into a FLUIDIZED BED at 850°C. STATIONARY FLUIDIZED BED Turbulent BED MOVEMENT: Protective Al2O3 – surface skin is removed, total OXIDATION of reactive Al to Al2O3 is achieved. Remaining BED ASH / BOTTOM ASH is inert material, direct LANDFILLING is possible. underground waste disposal plant Herfa-Neurode:  underground waste disposal plant Herfa-Neurode Conditions for storage in the underground waste disposal plant:  Conditions for storage in the underground waste disposal plant The waste must (under storage conditions): not be explosive not be self-igniting not be flammable not reactive not be in liquid form not be radioactive not contain or produce pathogens or contagious diseases Types of waste stored:  Types of waste stored Examples of industries Incinerator plants Metallurgical works Metal-processing industry Chemical industry Pharmaceutical industry Electrical industry Glass-making industry Decontamination of polluted sites Waste disposal industry Examples of types of waste Incineration residues Electroplating residues Quenching salt residues Arsenic-containing waste Chemical distillation residues Mercury-containing wastes Capacitors/transformers containing PCBs Broken fluorescent tubes Filtration and filter bed residues Contaminated soil and construction/demolition waste reverse osmosis concentrate from landfill leachate after evaporation Packaging Criteria's:  Packaging Criteria's Criteria's for the packaging selection: Toxicity pH-Value of the waste residue moisture content Types of packaging Steel drum Big bag Steel container Security of deposited waste:  Security of deposited waste Waste is sealed in by a mulitbarrier system Natural barriers Gastight salt rock formation waste stored in salt deposit is thus enclosed safely and sealed off by the impermeable salt rock formation Clay layers important barriers isolating the stored waste Bunter sandstone Further sections with groundwater barrier Security of deposited waste:  Security of deposited waste Hand made barriers Packaging Waste packaging (Drum´s, Big bag´s, Container) Walling in After storage chamber has been filled, it is walled off by a brick wall Isolation of zones Plant zone is separated from adjacent pot ash mining fields by thick safety pillars Filling the shafts After closing the disposal operation the shafts will be filled with solid matter, so that the sealing is watertight Conclusion:  Conclusion

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