Closure technologies / Water treatment
Kaisa Turunen (GTK), Geological Survey of Finland, P.O. Box 1237 Kuopio, FI-70211 FINLAND, kaisa.turunen(at)gtk.fi
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).
Mine water treatment technologies are usually divided between active and passive methods. Active treatment technologies require the input of energy and chemicals, whereas passive treatment methods are based on natural chemical and biological reactions without or little nutrient and energy addition. In addition, passive technologies are self sustaining processes, they require usually only infrequent maintenance and function well without or little human interference when established. In contrast, active treatment technologies require usually frequent maintaining, regular labour inputs for continued operation. Due to the economical reasons, the water treatment should be designed passive, but the active treatment should be kept operational for the first few years of the closure to prevent high pollution peak caused by deteriorating water control structures and during the building and validating the effectiveness of the passive treatment. (Younger et al. 2002, Taylor et al. 2005, Wolkersdorfer 2008).
Active treatment technologies can be engineered to accommodate essentially any acidity and flow rates of mine waters and since the treatment system can be adjusted instantaneously in response to the changes in water quality and flow rates, the treatment process can be precisely controlled. However, due to high maintenance and operational costs and the requirement of frequent maintenance, active treatment methods are usually used at operating mines. In contrast, passive treatment technologies are most commonly used at closed mines to treat mine waters with low acidity and low flow rates and the process cannot be usually adjusted according to the changes in water quality and flow rates. (Younger et al. 2002, Taylor et al. 2005, Wolkersdorfer 2008). The suitability of passive and active water treatment systems is based on influent water characteristics. Acidity and pH ranges and flow rates for determining suitable treatment system is presented in table 1.
Table 1. Acidity and pH ranges and flow rates for passive and active treatment methods (modified from Taylor et al. 2005).
|Treatment system||Average acidity range ( mg CaCO3/l)||Average acidity load (kg CaCO3/day)||Average flow rate (l/s)||Average pH range||Max attainable pH|
|Active||1 – 10 000||1 – 50 000||No limit||No limit||14|
|Passive||1- 800||1 – 150||< 50||>2||7.5-8|
The third type of treatment techniques are other in-situ or at-source treatment methods in which the source of contamination is treated or the pollution is prevented at its origin. In-situ methods are commonly used at surface mines to prevent generation of acid rock drainage by alkalinisation (Wolkersdorfer 2008).
Figure 1. The flowchart for choosing active or passive mine water treatment method. (Modified after Hedin et al. 1994, Skousen et al. 2000 and Wolkersdorfer 2008)
More specific descriptions and evaluations of different treatment technologies can be found in the following Closedure pages:
In addition, new emerging technologies are presetented in article: Futures aspects of mine water treatment.
Hedin, R.S., Nairn, R.W. & Kleinmann, R.L.P. 1994. Passive treatment of coal mine drainage, US Bureau of Mines Information Circular 9389 (2nd Ed.). Pittsburg, 35 pp.
Skousen, J., Sextone, A. & Ziemkiewicz, P.F. 2000. Acid mine drainage control and treatment. In: Barnhisel, R.I., Darmody, R.G. & Daniels, W.L. (Eds.): Reclamation of drastically disturbed lands. Monograph Number 41. American Society of Agronomy, Madison. pp. 131-168
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.
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. pp. 151-200.