Kaisa Turunen (GTK), Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, FINLAND, kaisa.turunen(at)gtk.fi
Although minerals are mainly chemically stable under natural geological conditions, anthropogenic activities can affect their behaviour and form by changing the chemistry and oxidizing conditions of water and soil. This may result in contaminated mine waters as the metals and metalloids harmful to the environment may dissolve from the minerals. Therefore, elevated concentrations in solid wastes may pose a risk to human health and the environment in the form of contaminated drainage. In fact, water is by far the greatest pathway for mining related contaminants, and acid mine drainage (AMD) and other metalliferous waste waters derived from mine sites are the major cause of ground and surface water pollution. The major cause of acidic metal-rich mine drainage is accelerated oxidation of pyrite (FeS2) and other sulphide minerals due to ore excavation and mineral processing. Because mining related contamination can continue for decades and even centuries after the cessation of mining activities, the related processes must be realized so that the possible mine water derived risks and sources are identified, controlled and reduced by appropriate measures as well as by feasible, sustainable technological solutions. (e.g. Younger 2002, Johnson & Hallberg 2005, Wolkersdorfer 2008).
Due to the diversity of ore deposits, every mine site and its waters are unique in nature and there is an extensive group of variables which affect on the quantity and quality of mine water even within a single mine. Thus, there is no single solution for water treatment in mining and a sound understanding of the hydrogeology and hydrodynamics of each mine is crucial also for water treatment. In addition, since the contaminant sources and the water quality are usually very different from those of urban or industrial areas, the conventional waste water treatment systems are often unsuitable for mine waters. (Taylor et al. 2007, Wolkersdorfer 2008).
Since there are many different types of mine waters, there are also several different treatment techniques available. The treatment technique used at a mine depends on the water chemistry, the strength of the contamination, contaminants, flow rate, water volume and the objectives of the treatment (e.g. required water quality standards, use of water after treatment).
To ensure that mine water meets the environmental standards prior to being discharged, it is necessary to capture and control contaminants in surface water and monitor the surrounding surface and groundwater quality. Different combinations of control techniques and water management practices can be used to reduce the potential for water contamination and to minimize the volume of water requiring treatment. The excess water is relevant concern for mine water management and treatment in environments with high rates of precipitation as in Finland. Therefore, to prevent unnecessary contamination of clean waters, the off-site surface waters (rain and snowmelt runoff, streams and lakes) should be directed and intercepted to avoid entering the mine site. The water management techniques are presented in water management part of Closedure pages. The monitoring and sampling are presented in the monitoring part of these pages.
Figure 1. The water cycle at mine site. (Photo © GTK, 2014. Modified from Kauppila et al. 2013)
The pages below describe the general structure of this water treatment part. This part presents objectives of water treatment, evaluates specific active and passive water treatment technologies, goes through selected examples from actual mine sites and presents the results of research performed during the Closedure-project. Also, the ongoing research and development of mine water treatment is presented.
Johnson, D.B. & Hallberg, K.B. 2005. Acid mine drainage remediation options – a review. Science of the Total Environment. Volume 338. pp. 3–14.
Taylor, J., Pape, S. & Murphy, N. 2005. A Summary of Passive and Active Treatment Technologies for Acid and Metalliferous Drainage (AMD). Proceedings of the fifth Australian Workshop on acid drainage 29th-31stAugust 2005, Fremantle, Australia. p. 151-200.
Younger, P.L., Banwart, S.A. & Hedin, R.S. 2002. Mine water – Hydrology, Pollution, Remediation. Environmental pollution. Volume 5. Kluwer Academic Publisher, The Netherlands.464 p.
Wolkersdorfer, C. 2008. Water Management at Abandoned Flooded Underground Mines. Fundamentals, Tracer Tests, Modelling, Water Treatment. Springer. 465 p.