Lusatian Opencast Mines
Our four Lusatian opencast mines, Jänschwalde and Welzow-Süd in Brandenburg as well as Nochten and Reichwalde in Saxony, belong to Lausitz Energie Bergbau AG. The approved mining fields contain approx 900 million tons of lignite. The opencast mine Cottbus-Nord was closed according to plan in 2015. It is being transformed into a lake, the future Cottbuser Ostsee Lake.
Our Lusatian opencast mines supply the power plants which are nearby: Jänschwalde, Schwarze Pumpe and Boxberg.
The haulage of the lignite is performed by our own central railway system. The total length of our railway network is roughly 360 kilometres.
How does an opencast mine function?
The raw lignite is extracted from a depth of about 60 to 120 meters. It lies between loosely packed sands and gravel layers which are penetrated by groundwater. In total, there are four Lusatian lignite seams. The second one is being mined. A seam is a horizontally deposited layer of raw material with a particular thickness which is proportionately long and wide. The so called second Lusatian seam can be mined economically because of its thickness and properties.
Bucket-wheel excavators and bucket-chain excavators extract the lignite from the ground. By means of conveyor belts it is transported out of the mine. The mine is spanned by the overburden conveyor bridge. This equipment complex with its powerful bucket-chain excavators removes the overburden from above the lignite seam. This overburden is transported by means of a 600 metre long overburden conveyor bridge directly over the pit by the shortest route to the other side of the mine.
The soils are deposited by the overburden bridge to where the lignite has already been mined out. In this way the coaled out areas of the mine are backfilled. The opencast mine dump is created in this way.
Overburden conveyor bridges of the F60 type are able to remove up to 60 metre thick overburden in one go. They are the largest mobile technical systems in the world having a mass of 27.000 tons, a total length of over 600 metres and an average speed of nine metres per minute .
The upper soil layer is removed in what is called the pre-cut. This work is done with bucket-wheel excavators and bucket-chain excavators in advance of the overburden conveyor bridge. The material is transported by means of conveyors once around the top of the mine to the dump side. Spreaders distribute the pre-cut on top of the dump backfill again. In this way the surface is shaped to the contours required for the post-mining landscape.
Pumping up the groundwater under the level of the lignite seam is a precondition for safe mining operations. We dewater only to the extent required for geotechnical safety. Each year about 3,000 filter wells around the opencast mines pump up approximately 400 million cubic metres of groundwater to the surface. About 70 percent is reintroduced into the local and regional water system. The remainder is mostly used in our power plants as cooling and process water. This avoids the extraction of additional water from rivers.
We operate six pit water treatment plants. The groundwater, pumped up, is treated here. It is mostly iron that is removed and the pH is adjusted to a more neutral value.
The lowering of the groundwater in order to mine lignite has the additional effect of lowering the groundwater in the surrounding areas, too, the so-called groundwater depression cone. Next to four of our Lusatian opencast mines underground sealing walls have already been constructed, to limit the lowering of the groundwater to the actual opencast mine and not to dewater neighbouring areas.
Environment and Neighbourhood
In the process of mining lignite land is claimed for a time. In opencast mining operations there are vibrations, dust, noise and other influences. Especially when the weather is dry and windy there is sometimes unavoidable dust in the air from the mine. When large-scale equipment is in operation, conveyor belts or trains are running, noise is created. We are making every effort with a package of organizational and technical measures to avoid or reduce to a minimum any nuisance for the neighbouring communities of the opencast mines.
Measures to reduce the spreading of dust are for example sprayers and high pressure fogging systems as well as protective plantings on the edge of the mine and interim greening of the dump areas. With noise damping protective embankments, technical measures taken on the equipment and replacing acoustic signals with optical ones in the night shift we reduce background noise. All measures against noise and dust are monitored continuously and checked by the responsible approvals authorities.
As a mining company we are obliged to reduce any interference with nature to the unavoidable minimum. The consequences of these interferences have to be compensated for promptly, effectively and in a sustainable way. Thus, parallel to lignite mining activities recultivation work starts on the areas already mined-out. The dumps are created according to detailed planning and experts' assessments in order that the post-mining landscapes lie on stable land also in the future when the groundwater level has risen again fully. If necessary the earth is compacted additionally.
The aim of the subsequent recultivation is a diverse landscape typical of Lusatia in harmony with the surrounding, which is utilizable on the long-term and ecologically valuable. Not a single ton of lignite is mined without establishing ahead how the impact of mining on the existing cultural landscape can be balanced out. On what was an operational area previously there are now forests and agricultural land for future commercial use, habitats close to nature for animals and plants as well as water bodies.
In order to mine a lignite deposit it is sometimes unavoidable that a community has to be resettled. Therefore resettlements in the Lusatian mining district are guided by high standards in order to take the interest of the resettled citizens and municipalities into due account.