Strip diffusers support the remediation of contaminated uranium mining sites

When uranium mining in Saxony and Thuringia was abruptly discontinued at the turn of the century, it left behind profound damage to the environment. People and nature in many areas of the „Wismut region“ were equally affected. Wismut GmbH was founded in 1991 as a German federal company to secure the legacy and recultivate the affected areas. Water management has been one of the biggest challenges since the beginning of the remediation process. Huge water-filled mine workings, massive pools of radioactive sludge and extensive waste rock pile landscapes require comprehensive expertise in this area. The extent of the damage caused to groundwater and surface water bodies during 45 years of uranium production between Ronneburg and Königstein is the reason why active water treatment will remain necessary for a long time during and after remediation. „Wismut currently operates six water treatment plants for this purpose. We collect the water escaping from pits, dumps or tailings management facilities and treat it in technical plants,“ says Wismut spokesman Frank Wolf.

AEROSTRIP® strip diffusers from AQUACONSULT are used at the Seelingstädt site. This is where the industrial tailings management facilities of the former uranium ore mine are being cleaned up: „One of the biggest challenges, because this is where the residues from the processing of the uranium ore are stored,“ emphasises Wolf. In order to extract the uranium from the mined ore, it had to be chemically processed. To do this, the rock was taken to processing plants, ground and leached with sulphuric acid or alkaline. After uranium extraction, the finely ground radioactive residues (tailings) were pumped into a total of four settling plants. With a total area of 684 hectares and 154 million cubic metres, this resulted in the largest landfills of this type in the whole of Europe, which are also located in densely populated regions. 

Diffusers made of 100% plastic guarantee maximum corrosion resistance 

„There were no strategies and technologies for remediating the tailings management facilities like the ones we found in Seelingstädt anywhere in the world,“ says Wolf. Wismut GmbH had to create its own solutions, search for technologies and combine them in order to treat all the contaminated water produced. 

One of these technical solutions was found in the AEROSTRIP® Q series strip diffuser. Given the challenging composition of the wastewater, the only way to treat it efficiently was to use diffusers that are completely metal-free and therefore particularly resistant to corrosion. „We are one of the few suppliers on the market to offer such a special variant made of 100% plastic for the highly efficient aeration of wastewater,“ emphasises Rüdiger Vrabac, Branch Manager at AQUACONSULT Anlagenbau GmbH in Germany. Another special requirement was that the aeration technology had to be installed in existing elevated tanks. „Even the fastenings for the strip diffusers were custom-made from pure plastic especially for this project,“ says Vrabac. 

Strip diffusers crucial for the success of the wastewater treatment process

Since 2014, the corresponding leachate has been collected in a complex drainage system around the former sedimentation tanks and purified in water treatment plants. Treatment is based on the principle of modified lime precipitation. In the first step, the incoming water is acidified to a pH value of 3.5 and then dissolved carbon dioxide is blown out via a three-stage stripping process. This is the only way to achieve subsequent uranium precipitation by adding milk of lime. The water to be treated is therefore particularly salty, is also acidified and is subject to strong temperature fluctuations. In addition, some of the water is significantly contaminated with solids. „Stripping must be highly effective and reliable. If it is inadequate, this can no longer be compensated for in the subsequent treatment process and leads to inadequate uranium separation,“ emphasises Jan Laubrich, Head of Water Treatment Plants at Wismut. 

The AEROSTRIP strip diffusers are now used in the first step of this important phase, the so-called pre-stripping. This involves extensive degassing of the contaminated wastewater in elevated tanks in which the aerators are installed. „Pre-stripping and the strip diffusers used in it make a decisive contribution to the success of the entire water treatment process,“ explains Laubrich. The AEROSTRIP®s are ideal for this type of wastewater treatment: „The installed strip diffusers are made of plastic and, after ten years of operation, show no signs of corrosion, defects or malfunctions despite the extreme pH values and high salt loads. Our expectations were met in full,“ says Laubrich.

More than one billion tonnes of radioactive residues stabilised

The remediation of contaminated sites in Seelingstädt is far from complete. Due to the slow decline in pollutant concentrations in the collected water, water treatment is a long-term task that will have to be carried out for many decades to come. With the remediation of the uranium mining legacy, Wismut is also facing one of the greatest ecological and technical challenges in Europe. More than a billion tonnes of radioactive residues have already been stabilised, hazards eliminated and risks minimised. Newly created landscapes, colonised by rare animal and plant species, are evidence of the enormous transformation process. But the tasks of the future remain no less challenging and complex. They will occupy generations to come and require the deployment of material, human and financial resources. „The water treatment processes are the central elements of the overall project and will always account for a large proportion of the financial expenditure,“ says Laubrich. 

With their innovative technology and reliable durability, the strip diffusers from AQUACONSULT will remain an important partial solution for the challenging remediation project in the Bismuth region for a long time to come. The technology from the Lower Austrian company is also proving its enormous suitability for use in wastewater treatment in many other industrial applications, while at the same time offering a long service life and maximum energy efficiency. Due to these numerous advantages, AEROSTRIP®s are used in a wide range of variants in more than 2.500 industrial and municipal wastewater treatment plants worldwide.

Photos:

1: AQUACONSULT Anlagenbau's technology offers a particularly important and unique solution for the central task of uranium mining waste remediation in Seelingstädt, which hardly any other aerator on the market can provide. 
2: Wismut GmbH is facing one of the greatest ecological and technical challenges in Europe with the remediation of uranium mining legacies. AEROSTRIP strip diffusers have been treating extremely contaminated wastewater for over ten years.
3: The water to be treated is extremely salty, acidic and subject to strong temperature fluctuations. This meant that only strip diffusers made of 100% corrosion-resistant material were suitable for this setting: the AEROSTRIP Q series. 
4: AEROSTRIPs are also used in many different industrial wastewater treatment plants due to their performance, durability and maximum energy efficiency.