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Satellite Event - Mining and Environment: Old Problems and New Solutions


Convener: Dr. Carlos Ayora, IDAEA-CSIC, Spain.

Day after day regulations force the mining companies to ensure that mining areas are returned to conditions close to their original state. Large amounts of wastes produced from mine extraction and ore processing increase the potential for chemicals to contaminate ground and surface water. Thus, careful measurements of water and soil are carried out in well-regulated mines to exclude any type of water pollution. Furthermore, minimizing the amount of wastes and the concentration of ores in the wastes should be both an economic and environmental goal. This goal can be better achieved through the use of non-toxic extraction processes such as bioleaching. Finally, if the sites are nonetheless polluted and no mining is anymore active, mitigation techniques such as passive remediation systems should be implemented.


Workshop agenda

Date: 25 June 2013 (Half day) - Preliminary Program

Workshop Reception: 08:30 - 09:00.

Talk 1 (09:00 - 09:45): Dr. Kirk Nordstrom, US Geological Survey, Boulder, CO, USA.

Baseline and premining geochemical characterization: the issue of natural background.

A rational goal for environmental restoration of new, active, or inactive mine sites would be “natural background” or the environmental conditions that existed before any mining activities or other substantial anthropogenic activities. In a strictly technical sense, there is no such thing as natural background, hence the terms “baseline” and “premining” are preferred. Protocols for geochemically characterizing premining conditions are not well-documented but should be based on existing studies for new mines and analog studies for active or inactive mine sites. Examples will be described based on the Pebble mine in Alaska for new mines and the Questa mine for active or inactive mines.

Talk 2 (09:45 - 10:30): Dr. Jose Miguel Nieto, Department of Geology, University of Huelva, Spain.

The genesis of acid mine drainage: the case of the Iberian pyrite belt.

Mining operations often induce acid or neutral drainage with high metal concentrations that potentially could affect adversely the environment and human health. Generally mine rock drainage occurs through tailing dams, stock piles, waste rock piles and leach pads and in mine pits or tunnels. The extent and the effects of this phenomena depend heavily on specific mine site characteristics. It is therefore necessary to develop and implement a plan to prevent, control, mitigate and prepare for the mine rock drainage

Acid Mine Drainage (AMD) in the Iberian Pyrite Belt is probably the worst case in the world of surface water pollution associated with mining of sulphide mineral deposits. The Iberian Pyrite Belt is located in SW Iberian Peninsula and it has been mine during the last 4.500 years. The oxidative dissolution of the sulphides exposed by mining releases large amount of AMD. The central and eastern part of the Iberian Pyrite Belt is drained by the Tinto and Odiel rivers, which receive most of the acidic leachates. As a result, the main channel of the Tinto and Odiel rivers are very rich in metals and highly acidic until reaching the Atlantic Ocean.

Talk 3 (10:30 - 11:15): Dr. Bernhard Dold, Sustainable Mining Research & Consult. EIRL, Santiago de Chile.

Biometallurgical pre-mining characterization of ore deposits: a new approach to increase sustainability in the mining process.

Based on the knowledge obtained from acid mine drainage formation in mine waste environments (tailings impoundments and waste-rock dumps), a new methodology is applied to characterize new ore deposits before exploitation starts. This gives the opportunity to design optimized processes for metal recovery of the different mineral assemblages in an ore deposit and at the same time to minimize the environmental impact and costs downstream for mine waste management. Additionally, the whole economic potential is evaluated including rare earth elements (REE). The methodology integrates high-resolution geochemistry by sequential extractions and quantitative mineralogy by QEMSCAN® or MLA in combination with kinetic bioleach tests. The produced data set allows to define biogeometallurgical units in the ore deposit and to predict the behaviour of each element, economically or environmentally relevant, along the mining process.

Coffee-Break (11:15 - 11:45).

Talk 4 (11:45 - 12:30): Dr. David Arcos, Amphos 21 Consulting S.L., Barcelona, Spain.

Mine rock drainage: characterization and modeling for assessment of waste rock dumps.

The hydrogeochemical processes involved in MRD generation are complex. It is necessary to characterize the processes and parameters involved at different scales varying in orders of magnitude both in volumetric samples and representative times. Characterization of mineralogy and geo-chemical processes through laboratory scale tests provide accurate results of the composition of the drainage as a result of the interaction of sulfide minerals with water and oxygen and the potentially buffering minerals of the rock sample. This characterization phase however, needs to be combined with field scale in-situ pilot tests which characterize the hydrological as well as bio-geo-chemical processes occurring under site specific conditions. The plan must consider a phase to integrate all the information in a conceptual model that accounts for the entire previous characterization step.

The prediction of MRD generation and its impacts at basin scale are attained with numerical models. Reactive transport models of varying complexity are used to predict the impacts of the facilities in soils, aquifers and spring downstream. Numerical models should then be used to evaluate technically the effectiveness of different alternatives to prevent and/or mitigate MRD. A cost-benefit and/or multicriteria analysis of the different alternatives may then be developed in order to present the decision maker a tool to take informed decisions.

Talk 5 (12:30 - 13:15): Dr. Ricardo Amils, Department of Molecular Biology, UAM; Astrobiology Center, CSIC, Madrid, Spain.

Bioleaching, the future of mining.

Since the discovery that chemolithotrophic microorganisms were responsible of the generation of AMD in the forties, bioleaching has gone over a long way. The introduction of molecular ecology tools for the analysis of bioleaching operations has resulted in important advances in the field.

Lunch Break (13:15 - 15:00).

Talk 6 (15:00 - 15:45): Dr. Rafael Pérez-López, Department of Geology, University of Huelva, Spain.

Delaying sulfide oxidation: long-term treatment of acid-producing mine wastes using coal combustion fly ash.

Flotation processing of sulfide ores for obtaining base metals produces highly-reactive tailings that are stored in impoundments and, if not managed properly, exposed to weathering conditions. Exposure of residual sulfides to air and water leads to the release of extremely acidic leachates with high concentrations of sulfate and potentially toxic elements, known as Acid Mine Drainage. Consequently, the tailings impoundments are an almost inexhaustible source of contamination by sulfide oxidation. Hence, an effective treatment requires environmentally and economically sustainable solutions that can prevent the production of these acidic leachates over long time. To this aim, the addition of a cover of coal combustion fly ash on sulfide mine tailings seems to meet the necessary requirements, minimizing the release of chemical contaminants to the environment.

Talk 7 (15:45 - 16:30): Dr. Adam Jarvis, School of Civil Engineering & Geosciences, Newcastle University, UK.

The importance of chemical and biological processes in the passive remediation of iron-dominated coal mine waters compared to zinc-dominated metal mine waters.

In the UK the construction and operation of passive treatment systems for remediation of coal mine drainage has been ongoing for nearly 20 years, and there are now more than 50 full-scale systems in operation.  These systems primarily consist of aeration, settlement lagoons and aerobic wetland units, in which the primary remediation process is the abiotic oxidation of ferrous iron and precipitation of ferric iron.  The performance of these systems is discussed, and some of the limits of their application, and potential difficulties of long-term operation, are discussed.  In contrast, drainage from abandoned metal mines in the UK continues to discharge to streams and rivers largely unabated.   Measurements of the scale of pollution from these metal mines shows that they are a major source of freshwater pollution in the UK, and therefore in recent years there have been increased efforts to develop full-scale passive treatment systems for their remediation.  Much of this effort has been directed into compost-based bioreactors.  The performance of laboratory-scale and pilot-scale systems is discussed, highlighting both the performance of the systems and their potential limits, and illustrating the importance of biotic process such as bacterial sulphate reduction in such units.

Talk 8 (16:30 - 17:15): Dr. Tobias W. Rötting, Dpt. of Engineering and Geophysics, Catalonia Polytechnics, Barcelona, Spain.

Passive treatment of acid mine drainage: conventional treatment systems and new developments based on inorganic processes to remove high metal concentrations.

Acid mine drainage (AMD) and other heavy metal-polluted discharges from active or abandoned industrial sites are a major cause of water contamination world-wide. Conventional treatment plants are expensive to operate, and application at remote sites may be impractical. Passive treatment systems which once built only require naturally available energy sources and infrequent maintenance may be an economical option to decontaminate these waters. Nevertheless, they are prone to clogging and passivation (loss of permeability or reactivity, respectively) when used to treat water with high metal concentrations or high acidity loads. This talk will give an overview on existing passive treatment systems and explain new designs based on inorganic processes that were tested in the Iberian Pyrite Belt to remove high metal concentrations from AMD.

Workshop Closing: 17:15.