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Dumping grounds after hard coal mining as
anthropogenic secondary resources in European
mining regions
Łukasz GAWOR
Silesian University of Technology, Gliwice, Poland Abstract
Post-industrial waste dumps are characteristic signs of mining activities in the European coal basins and ore-exploitation areas. These objects after successful reclamation as well as recovery of secondary resources may be regarded as geotourist attractions. There are three types of coal mining dumping grounds: conical, tabular and landscape dumps. There are many examples of successful reclamation of landscape dumping grounds, which are used as sport, recreation, construction and culture areas. In the paper there are presented different ways of reclamation and managing of post-industrial dumping grounds, exemplified on chosen European mining regions. There are given examples of positive experiences in complex reclamation of dumping grounds in western European regions, which can be used in central and eastern European countries. There is described a problem of recovery of secondary resources from waste material. In many old dumps the content of coal particles or metals may reach over 10%. It is economically and ecologically justified to recover these materials and provide complex management of dumping grounds, consisting of recovery and reclamation processes.
Key words: post-mining waste dumps, post metallurgic waste dumps, recovery of secondary resources.
Zwałowiska pogórnicze jako antropogeniczne złoża wtórne
w europejskich zagłębiach górniczych
Streszczenie
Zwałowiska odpadów wydobywczych i przeróbczych są elementem krajobrazu każdego zagłębia górniczego. Obiekty te po zakończonej sukcesem rekultywacji oraz odzysku odpadowych surowców wtórnych mogą być uznane za interesujące atrakcje geoturystyczne. Wyróżnia się trzy typy zwałowisk: stożkowe, stołowe i krajobrazowe. Istnieje wiele przykładów zakończonej sukcesem rekultywacji zwałowisk krajobrazowych, które są wykorzystywane, jako obiekty sportowe, rekreacyjne, budowlane czy kulturowe. W artykule przedstawiono rożne sposoby rekultywacji i zagospodarowania zwałowisk pogórniczych na przykładzie wybranych europejskich zagłębi górniczych. Podano przykłady pozytywnych doświadczeń w kompleksowej rekultywacji tych obiektów w krajach Europy zachodniej, które mogą zostać wykorzystane w krajach Europy środkowej i wschodniej. Opisano problem odzysku surowców wtórnych z materiału odpadowego. W odpadach zdeponowanych na starych zwałowiskach zawartość węgla lub metali może osiągać wartość nawet ponad 10%. Wydaje się być ekonomicznie i ekologicznie uzasadnione podejmowanie działań związanych z odzyskiem tych materiałów, a także prowadzenie kompleksowego zagospodarowania i rekultywacji opisywanych obiektów.
Słowa kluczowe: zwałowiska pogórnicze, zwałowiska pohutnicze, odzysk surowców wtórnych
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Introduction
All over the Europe there are hundreds of post-industrial areas, where mining and metallurgic wastes are disposed. Post-mining waste dumping grounds are present characteristic signs of industrial activities in the European coal basins and ore-exploitation areas. These objects after successful reclamation (both technical and biological) may be regarded as geotourist attractions. Before planning reclamation processes it is necessary to test possibilities of recovery of different raw materials from the dumps. Many of these objects represent anthropogenic secondary resources, which exploitation is economically justified. Additionally recovery of secondary resources, particularly coal particles, reduces negative environmental impacts as e.g. self-ignition and fire hazards as well as pollution of surface and underground water. Waste dumps generated by coal mining could pose a serious environmental threat if not properly reclaimed. The environmental problems focus on leaching heavy metals from the wastes disposed by the working and closed hard coal mines [5].
There is a possibility of recovery of not only coal but other valuable materials like rare earth elements (REE), especially from wastes disposed together e.g. mining wastes and ashes [1]. Although the recovery of metals (Zn, Pb, Fe) from post-metallurgic dumps in the Upper Silesia is also very important, author decided to focus on coal mining waste dumps, because the technology is well known and there are positive examples of recovery of coal from mining wastes in European coal basins.
The purpose of the paper there is presentation of different ways of reclamation and managing of post-industrial dumping grounds, exemplified on chosen European mining regions. There are given examples of positive experiences in complex reclamation of dumping grounds in western European regions, which can be used in central and eastern European countries. There are discussed problems of recovery of secondary resources from waste material. In the paper there are presented examples from different European mining regions, exemplified on Great Britain (Wales), Belgium, Germany, Czech Republic and Poland.
1. Post-mining dumping grounds
The types of generations of coal mining waste dumps are connected with their genesis and changes of coal preparation technologies. There are three dump categories, which comprise: conical dumps (the most dangerous for the natural environment due to the lack of compaction), tabular dumps (objects built with compaction of waste material in a form of tabular mountain) and landscape dumps (successfully reclaimed objects, with compacted material, designed considering good composition in the landscape (fig. 1.).
Fig. 1. Types of mining waste dumps (after www.ruhrgebiet-industriekultur.de, changed).
Examples of all waste dump types are presented below – phot. 1-3.
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2. Reclamation and management of coal mining waste dumps
The reclamation of coal mining waste dumps may be divided into technical and biological reclamation.
Technical reclamation includes shaping of dumps and compacting material, using heavy equipment. It is connected with three waste dumps generations: conical, tabular and landscape dumps. Technical reclamation used in first generation of dumps (conical) was based on raising the material without compaction, what caused serious environmental problems, e.g. self-ignition and fire hazards. Second dump generation (tabular) was built using compaction of the material, what limited fire hazards, but the shape was still `strange` for the landscape. In the third category (landscape) there was linked compaction of the material with particular vision of the shape of the dump, which suited very well to the landscape.
Biological reclamation methods comprise forestation and sodding and manuring of the land. After over 40 years of field works focused on efficiency of biological reclamation of waste dumps in USCB it can be evaluated that sodding is the most proper reclamation method applied on waste dumps. The forestation of waste dumps is believed as ineffective and nowadays there are tendencies to afforest only parts of waste dumps in a direction of park and recreation cultivation (Gawor, 2011). Development and re-using of the waste dumps belong to the most significant problems connected with disposing of mining waste. The dumps are considered as important elements of cultural landscape in many mining regions (Gawor, 2004). There are different examples of efficient and also spectacular re-using of post mining dumping grounds, particularly in UK, Belgium and Germany. Below there are presented different case studies of development and management of dumping grounds.
3. Case studies
3.1. Ruhr BasinThere are ca. 170 coal mining dumping grounds in Ruhr area [11]. Nowadays there are only 4 active waste dumps connected with the activity of 2 working coal mines (Gawor, 2014). The largest waste dumps in the Ruhr Basin reach the surface of 160 x 104 m2 (waste dump Hoheward in Herten). The coal-mining waste dumps in the Ruhr Basin belong mainly to the third category of dumps, called landscape dumps [2]. These dumps represent recreation and sport areas, with well developed paths or cycling trails, they may also be examples of properly done biological reclamation. Many objects can be considered as geotourist attractions. To the most known attractions from dumping grounds in Ruhr area belong: sightseeing panorama construction `Tetraeder`, mining Way of the Cross, amphitheater and artificial ski-hall in Bottrop, open horizontal astronomic observatory in Herten, sundial in Schwerin, starting point for paragliding in Neukirchen-Vluyn (phot. 4) and many others.
Phot. 4. Starting point for paragliding sports on the dump Norddeutschland in Neukirchen-Vluyn (author).
3.2. Six bells project – Cardiff area
In Wales there was studied a complex of dumps Vivian, Six Bells 1 and Six Bells 2 in the neighborhood of Cardiff. On the dumps there were stored approximately 3 million Mg of coal mining waste material. As far as technical reclamation is concerned the extensive road work has been constructed to permit recovery of coal and environmental restoration of site. During recovery processes all operational processing equipment was situated within buildings, what reduced noise and maintenance, increased safety and allowed all weather operation. Reject material was delivered to heavy equipment for return to site for reconstruction of grassland before biological reclamation via conveyor belts (phot. 5).
Phot. 5. Six bells dump – conveyor belt transporting material from preparation plant (author).
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___________________________________________________________________________ All equipment was monitored to insure efficient operation of the recovery process and immediate identification of problems. The ponds have been built to enhance environmental flora and fauna returning to the site. As the tip has been worked, restoration was continuous. A very important feature of these works was intermediate meeting of restored area with operational area (phot. 6).
Phot. 6. Six bells dump – border between restored area with operational area (author).
What is the most important, the coal which has been recovered and sold, was a financing source for the environmental and safety restoration of the tip area.
3.3. Belgium
The mining industry in Belgium caused presence of ca. 360 waste dumps, which are situated in the provinces Limburg, Liege and Hainaut. After termination of underground coal mining (1960-1980s) the most of the dumps have been left without any anthropogenic interference. A part of them have been levelled, some used for park and recreation purposes [8] and over 30 dumps have been successfully processed (M. Redoute – personal communication). Processing of the tips and recovery of coal were based on the evolution of applied technologies (e.g. liquid dense medium with hydrosizer, barrel technology). After successful recovery of secondary resources the dumps have been re-used as sport, recreation and park areas (phot. 7), as well as places developed for construction purposes (housing, commercial areas). An interesting way of using of the dumps is planting on the southern slopes the vineyards.
Phot. 7. Waste dump Perier – re-using as sport area (author).
3.4. Ostrava-Karvina Coalfield
In the southern (Czech) part of Upper Silesian Coal Basin there are over 280 dumps [12]. A total amount of waste rock extracted in Ostrava-Karvina Coalfield at the time of coal mining activities can be estimated at nearly 0.65 milliard Mg (Martinec et al., 2005). These anthropogenic landforms have been formed at different times during the nearly 200-year tradition of coal mining in Czech Republic. The oldest preserved small mine dumps have been piled up nearby adit collars in Landek. The conical dumps had originated since the half of 19th century until about 1950. During 1950s and 1960s the dumps emerged from the cities and the technology of depositing the wastes have changed. The trend was to form flat (tabular) dumps spread and compacted by the machinery. In 1960s and 1970s waste rock was used for filling up the subsidence basins [9].
There are some examples of successful reclamation and re-using of waste dumps. A conical dump Ema has been classified as historical monument. This dump is situated in Trojice Valley, between Ostrava – Petr Bezruc, Trojice and Michalka mines. There is a geotourist-didactic path on this dump, which with the total height of 325,5 m above sea-level and belongs to the highest dumps in the Upper Silesian Coal Basin [10]. However, plenty of coal mining dumps are not reclaimed at all and many of them are still being facing problems of self-ignition and fire hazards.
3.5. Upper Silesian Coal Basin
The latest inventarization in the Upper Silesian Coal Basin shown presence of ca. 230 coal-mining waste dumps [4]. They concentrate mainly in the central and south-western part of USCB. Altogether the dumping grounds cover more than 4000 x 104 m2 and gather more than 700 million Mg of mining wastes. In the past, due to the
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___________________________________________________________________________ poor coal preparation technology the majority of this waste material was stored in coal mining waste dumps. The coal-mining waste dumps in USCB belong mainly to the first category of dumps – conical dumps and second category of dumps – tabular dumps. The dumping grounds of the first and second category cause serious threats to the natural environment. This threats are predominantly connected with fire hazards, because of the oxygen inflow to the not enough compacted waste material. There are only few objects which belong to the third category – landscape dumps (phot. 8). There is also an opportunity of using such objects as park and recreation areas and geotourist objects, but their development is nowadays in an early stage [3].
Phot. 8. Landscape dumps in Bieruń (author).
4. Recovery of secondary resources
There is a possibility and necessity to recover coal from the coal mining waste dumps. Firstly, coal recovery reduces hazards of self-ignition and dump fires. Secondly, the process of coal recovery is economically justified. In recent years, the economic importance of gangue accompanying coal production has changed and now more and more often it is treated not as waste but as a source of mineral resources for economic use. The quality of mining waste, both those intended for economic use and accumulated in dumps and heaps is very important [6]. From over 230 dumps in the USCB still remain more than 100 dumps which may be considered as anthropogenic secondary deposits (considering objects which are not thermally active). In the past, there were several examples of successful recovery of coal from the dumps (e.g. Central Mining Waste Dump in Smolnica, waste dumps in Buków, Czerwionka – SW of the USCB), some of the dumps are still being exploited – e.g. a waste dump in Panewniki, a waste dump in Knurów (a central part of the USCB). There are several companies which conduct recovery of coal as well as reclamation of the dumps using different preparation technologies. Due to the fact that the amount of coal in the waste material may be up to 10 % (between 3- 10 %, with the assumption that an average amount of coal to be recovered accounts for 5-7 %), it can be estimated that a total potential amount of recovered coal from the dumps in the USCB shall account for more than 45 million Mg [3].
There were also conducted studies on the amount of combustion heat and the calorific value of coal sludge combined with other wastes such as sewage sludge. The proposed methods and actions of recovery materials for energy purposes are part of the current directions of development, but they allow the extension of the scope of use of both extractive waste and products produced on the basis of gangue or coal sludge. Due to the frequent lack of the stable composition of these materials, their current properties should be assessed each time before attempting to use them [7].
The most valuable waste dumps in terms of their recovery are the largest ones. However, one shall take into consideration other features, such as: the ownership title (there are mainly two kinds of owners: coal mine companies and communes), localization as to the neighborhood of protected areas, accessibility (road network, railway network) and local community interest. Past experiences show that there have always been problems with local communities during the planning phase of the coal recovery; nonetheless, as far as its advantages and disadvantages are concerned, benefits for local community are indisputable [4].
Conclusions
Coal mining dumping grounds are present in every coal basin and mining region. There is variety of dumps` generations, they differ in size, height, grade of reclamation and way of re-using. In the issues of management of post-mining dumping grounds there are two main directions: successful and efficient reclamation, both technical and biological and recovery of secondary resources, particularly coal particles, but also waste rock, used for different purposes (aggregates, hydrotechnic constructions, leveling). There are many positive examples of reclamation and sometimes spectacular ways of management of dumping grounds, mostly developed in so called `western countries` (Belgium, Germany, UK). There are of course good examples and practices in central European countries like Czech Republic and Poland, but considering large amount of dumps (hundreds of objects), these examples are rather few. It is possible to use positive experiences from mining regions, where mining activities were undergoing termination dozen years ago.
It must be outlined, that recovery, reclamation and management of post-mining dumping grounds is a complex process and requires detailed planning, using knowledge from different scientific branches – geology, geotechnics, environmental protection, biology as well as modern engineering and technical sciences.
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