Ecological water treatment processes for underground uranium mine water: Progress after three years of operating a const
Sustainable treatment approaches are sought for U mine waste water u-tilizing constructed wetlands. In 1998 a pilot system was constructed to remove U, 226Ra, As, Fe and Mn from the effluents of the flooded workings of the Pöhla-Tellerhauser mine of Wismu
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Boojum Research Ltd. Toronto, Ontario, M5A 1T7 Canada Wismut GmbH, Jagdschänkenstrasse 29, Chenmitz, 09117, Saxony, Germany
Abstract. Sustainable treatment approaches are sought for U mine waste water utilizing constructed wetlands. In 1998 a pilotsystemwas constructed to remove U, 226Ra,
As, Fe and Mn from the effluents of the flooded workings of the Pöhla-
Tellerhäuser mine of Wismut in Germany. Gravel beds and their biofilms in the system concentrate
226Ra.
As is co-precipitated/adsorbed onto iron-oxyhydroxide
particles collecting in treatment cells. U occurs as uranyl carbonate at pH 7.3-8.0 and is not removed. An ecological system oxidizes iron, provides particulates for adsorption and organic matter to support bio-mineralization in anaerobic sediments.
lntroduction Metal and radionuclide-contaminated waters from underground mine workings, waste rock piles and tailings deposits represent long-term environmental and financialliabilities. Low cost, environmentally sustainable approaches to waste water treatment are sought by utilizing wetlands, sometimes constructed specifically for this purpose. W etlands as treatment systems are very effective in addressing organic water pollution (Hammer 1989; Moshiri 1993; Kadlec and Knight 1996). Similar passive treatment techniques have begun to show value to the mining industry with a number of successful applications over the past two decades. However, in many systems, metal adsorption onto organic/ inorganic material used in the construction of the wetland will ultimately cease, and so will the capacity of the wetland to generate sufficient new organic material (Fyson et al. 1995). These approaches have certainly assisted in advancing knowledge and awareness of the potential of natural systems, and contribute to the resolution of these industrial challenges. However, they fall short of providing a sustainable ecological solution
B. J. Merkel et al. (eds.), Uranium in the Aquatic Environment © Springer-Verlag Berlin Heidelberg 2002
588
Margarete Kalin et al.
to water treatment, as such systems are likely to have a limited functional life span. A long-term, sustainable wetland is composed of three integrated but critical parts; an oxidation pond, a biological section, and a settling pond. Metals must be reduced in an oxidation pond, before the waste stream is allowed to enter the biological section, to prevent them from coating the organics that would then cease to function as adsorption sites and serve as microbial carbon source. In the biological section, productivity must be high to produce organic matter at a rate equal to or higher than adsorption sites are needed to adsorb metals. Finally, settling ponds must provide anaerobic conditions in the sediments in which the metals can be bio-mineralized by reducing microbial consortia. When a pilot wetland test system was constructed in 1998 to treat passively underground water from the Pöhla-Tellerhäuser mine it was believed that U, 226Ra, Fe, As and Mn would be removed primarily by the actions of plants (Gerth
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