Abstract: Lime neutralization technology is widely used in Canada for the treatment of acid mine drainage and other acidic effluents. In many locations, improvements to the lime neutralization process are necessary to achieve a maximum level of sludge densification and stability. Conventional lime neutralization technology effectively removes dissolved metals to below regulated limits. However, the metal hydroxide and gypsum sludge generated is voluminous and often contains less than 5% solids. Despite recent improvements in the lime neutralization technology, each year, more than 6 700 000 m³ of sludge are generated by treatment facilities operated by the Canadian mining industry. Because lime neutralization is still seen as the best available approach for some sites, sludge production and stability are expected to remain as issues in the near future. Several treatment parameters significantly impact operating costs, effluent quality, sludge production and the geochemical stability of the sludge. Studies conducted both at CANMET and NTC have shown that through minor modifications to the treatment process, plant operators can experience a reduction in operating costs, volume of sludge generated, metal release to the environment and liability. This paper discusses how modifications in plant operation and design can reduce treatment costs and liability associated with lime treatment.

Abstract: The technical knowledge and practical experience accumulated by industry and others in abating acid mine drainage (AMD) is being proactively applied at every phase of the mine life cycle. This paper traces the mine life cycle from exploration to post closure monitoring and maintenance, and reviews AMD abatement measures that have become an integral component of exploration and mining activities. Attention is increasingly being given to evaluating AMD potential as part of exploration work, and studies related to project feasibility and design. Mining, mineral processing and waste management options are selected taking into consideration their suitability to inhibit AMD. These inhibition measures are typically committed to in closure plans submitted at the permitting stage. Mines are operated and decommissioned, often progressively, as planned and in accordance with environmental protection policies. Es wird über das Problem der Säurebildung aus sulfidischen Aufbereitungsbergen und taubem Gestein im Verlauf des Existenzzyklus eines Bergwerkes berichtet. In Kanada werden seit etwa 10 Jahren intensive Forschungen für Vorhersage, Kontrolle und Eindämmung von Saürebildungen im Bergbau betrieben. Schwerpunkt ist dabei die sulfidische Oxidation (2FeS2 + 7O2 = 2FeSO4 + 2H2SO4) unter Einwirkung verschiedener physikalischer, geochemischer und biologischer Faktoren. Diese Reaktion führt zu einem Komplex weiterer chemischer Reaktionen unter Bildung von zusätzlicher Säure und Lösung von Metallen. Daraus ergeben sich zwei Hauptmöglichkeiten diesen Prozeß zu steuern: 1. die Sulfidoxidation verhindern, 2. den Oxidationsprozeß verlangsamen. Mit dem heutigen Wissensstand ist es möglich, das Säurebildungspotential von Aufbereitungsbergen zu bestimmen, den Prozeß der Sulfidoxidation von Mineralen unter bestimmten physikalischen, geochemischen und biologischen Bedingungen zu modellieren und die Säurebildung von Aufbereitungsbergen und sulfidischen Gesteinen einzudämmen. Im einzelnen werden Maßnahmen zur Bewertung des Säurebildungspotentials und zur Kontrolle und Reduzierung dieses Prozesses während der Existenzstadien Exploration, Durchführbarkeitsstudie und Genehmigung, Gewinnung und Stillegung eines Bergwerkes erläutert. An Beispielen wird gezeigt, daß bei rechtzeitgem Erkennen des Säurebildungspotentials in der Phase der Exploration Verfahren und Maßnahmen bezüglich Aufbereitung, Umgang mit Aufbereitungsbergen ausgewählt werden können.

Abstract: Acid mine drainage (AMD) is one of the most significant environmental challenges facing the mining industry worldwide. It occurs as a result of natural oxidation of sulphide minerals contained in mining wastes at operating and closed/decommissioned mine sites. AMD may adversely impact the surface water and groundwater quality and land use due to its typical low pH, high acidity and elevated concentrations of metals and sulphate content. Once it develops at a mine, its control can be difficult and expensive. If generation of AMD cannot be prevented, it must be collected and treated. Treatment of AMD usually costs more than control of AMD and may be required for many years after mining activities have ceased. Therefore, application of appropriate control methods to the site at the early stage of the mining would be beneficial. Although prevention of AMD is the most desirable option, a cost-effective prevention method is not yet available. The most effective method of control is to minimize penetration of air and water through the waste pile using a cover, either wet (water) or dry (soil), which is placed over the waste pile. Despite their high cost, these covers cannot always completely stop the oxidation process and generation of AMD. Application of more than one option might be required. Early diagnosis of the problem, identification of appropriate prevention/control measures and implementation of these methods to the site would reduce the potential risk of AMD generation. AMD prevention/control measures broadly include use of covers, control of the source, migration of AMD, and treatment. This paper provides an overview of AMD prevention and control options applicable for developing, operating and decommissioned mines.