Mining waste management of Estonian mineral ...

6th International Conference on Sustainable Development in the Minerals Industry, 30 June – 3 July 2013, Milos island, Greece

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Mining waste management of Estonian mineral resources V. Karu, J. Gulevitš, T. Rahe, R. Roots and R. Iskül Tallinn University of Technology, Department of Mining, Estonia

A. Põlder Tallinn University of Technology, Department of Mechatronics, Estonia

ABSTRACT Mining waste reduction methods include all mining processes beginning from resource distribution until final yield in the plant. For comparing and testing possibilities of mine waste reduction methods, we need to study mining waste sites and provide suggestions to improve testing methods. Currently waste crushing, separating and sampling tests are being carried out. Initial results show some development in cutting and crushing possibilities. 1. INTRODUCTION We need to find new possible technologies to manage waste and how not only reduce new waste production, but also how to reduce already existing mining waste heaps (Valgma et al., 2012). In order to reduce mining waste by considerable amounts we have to make waste interesting for enterprises as a potential new raw material for products. The activities carried out on the regional and transnational level will secure better access to knowledge, state-of-the-art technologies and good practice to Small and Medium Enterprises active in the mineral waste management and prevention sector (Karu, 2011). The study addresses all the waste management challenges and opportunities, which face the Baltic Sea Region mining industry, which should be understood as extending to all forms of extraction of natural non-renewable resources. A comprehensive framework for safe management of waste from extractive industries at EU level is now in place, including: 1) directive 2006/21/EC on management of waste from min-

ing (Directive 2006/21/EC); 2) a Best Available Techniques reference document for the management of tailings and waste-rock in mining activities (Best Available Techniques); 3) an amendment of the Seveso II Directive to include in its scope mineral processing of ores and, in particular, tailings ponds or dams used in connection with such mineral processing (Seveso II Directive). Case study Estonia In addition to the main mineral resource oil shale, there are sufficient reserves of limestone and dolostone, peat, sand, gravel and clay in Estonia (Valgma, 2002, 2003; Valgma and Karu, 2006). Phosphorite and granite are occurrences in current economical situation, in spite of the fact that phosphorite has been extracted for 70 years during earlier times. Oil shale has been mined for 95 years by now (Fig. 1) (Tammeoja et al., 2007; Reinsalu and Valgma, 2007; Karu et al., 2008). All previous mining activities have been produced mining waste, as an example, the total volume of waste rock from oil shale mining is more than 76 million m3 and covers some 790 ha in Estonia itself (Valgma, 2009; Väli et al., 2008). In Estonia, two types of mining

Figure 1: Location of the Estonian oil shale deposit (Estonian Land Board, 2012; Google, 2013).

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waste are currently produced: waste rock from oil shale separation and limestone mining fines (grain size 0-4mm) from crushing and screening. From an environmental point of view Estonia is in good position, not having acidic reactions and having neutralising alkaline limestone rock in all mining areas (Valgma et al., 2012). Thanks to this, reclamation is easily done with the help of the same equipment as mining itself. For underground mining, the main concern is related to stability of the room and pillar mining area (Karu et al., 2007; Karu, 2010b, 2012a). Main problem with limestone fines and oil shale fines are that after blasting the run out mine consists up to 30% fine material (Valgma et al., 2007; Valgma et al., 2010). After the first crushing unit, there is an increase of up to 7% of fine material. Therefore, large amount of usable material ends up into the waste heap and this increase number of waste heaps. The main aim of the study is classify old mining waste sites: which kind of new technologies to use to produce products from waste. Secondly, analyze new optimization methods to decrease production loss and minimize waste. The main question is how much rock can be used for products. 2. METHODS 2.1 Classification of mining waste heaps From previous studies we know where the mining activity has been carried out (Valgma, 2000; Karu, 2010a, 2012b). Classification of mining waste heaps includes defining different parameters of waste heaps, like mining method, process method, quality of waste rock, etc. Classification also gives indication to which kind of technologies we can use to reduce production of new waste (Karu et al., 2013). 2.2 Limestone fines The aim of using mineral resources is that nothing goes to waste just like that, and hills of small particles (such as limestone fines) are not increasing to wait until thrown away but just the opposite - they decrease because are being used in the production process. In order to get two to

four additional aggregate fractions from fines, Limestone Products LLC have implemented washing and sorting technology of small aggregate fractions. Implementation of such technology makes lime processing practically waste free. In the summer of 2007 experimental tests of CDE processing line were held in the Väo quarry. The fraction (or limestone sand) received from the CDE - 0.063-2 mm - is suitable to be used in the road construction, although it has also some limitations that must be considered. 2.3 Optimization of oil shale seam drilling and blasting In oil shale economy the situation is that we are planning to increase heavy oil and decrease electricity production. It means that we need more aggregate rock, because oil factories cannot use fine oil shale (Valgma et al., 2008a,b). At this moment oil shale fine material (025 mm) and oil shale coarse run of mine (25125 mm) ratio is 1:3. Oil factories require coarse oil shale for production. Fine oil shale can only be used in electricity plants. Therefore, Estonia has the situation, where one enterprise producing oil shale hard oil has to buy coarse oil shale run of mine from another enterprise. A huge amount of fine oil shale is left behind. Fine run of mine transport to the power plant is not economical and a lot of fine material will be stored into heaps. The less fine material there is, the less oil shale will be stored in heaps. 2.4 Measurements and analysis with high speed cameras Technological schemes include crushing, screening and sorting units. To get information on each part of technological schemes we need to measure results. If we use optical systems to measure the raw material on a belt conveyor we get the result quickly and we can make future decisions basing on this information. There are several system setups, which could be used for estimating the granulometric composition (particle size distribution) of limestone or oil shale on transportation line such as 3D scanning, image acquisition above the transportation line and image acquisition on material


falling from one line to another. 3D scanning is quite expensive and relatively slow. Selection in between two remaining methods depends strongly on material transportation setup, both methods have their pros and cons. Image acquisition above the transportation line could result in higher material overlapping rate and detection difficulties due to underlying material. With acquisition on material falling, dust might be a source of problems but the material particles can have higher contrast with background. The main problem when using machine vision is overlapping of material particles - this effect can be diminished by using transportation lines with different line speeds. For hardware, a standard gray-scale machine vision camera with sufficient frame-rate and resolution should be acceptable. Depending on the acquisition rate or measuring approach, the camera can take images after predefined time or acquisition can be triggered by using an encoder. Since the task is relatively straightforward, one possibility is to use a smart-camera, resulting with higher compactness and probably lower price of the overall system. Lighting and filter setup of the system depends on spectral properties of the material to be measured, which requires some further research. For preliminary approach, the standard white light together with an IR filter (usually implemented in a camera) can be used. One possible way to estimate the granulometric composition (particle size distribution) is to use edge detection which distinguish edges and after that morphological steps to separate the particles and measure their area. Somewhat similar approaches were used in reference (Põlder, 2010). Due to overlapping of the particles we can not measure the particle granulometrics but estimate it, therefore the final result is supposed to have a high error rate. The output of the estimation would be the approximate percentage of each grain size class in the sampled material.

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3. RESULTS 3.1 Classification results Estonia has 43 mining waste objects, which are situated where mining has been carrying out. All waste heaps can be viewed as prevention stage; waste recovery and land reclamation. Prevention stage is a situation where currently mining waste is reduced and used as products. Waste recovery is a situation where old mining waste heaps are opened and new products being made. When we cannot use the waste rock material as raw material for new products, then the material has been used in land reclamation. 3.1.1 Mining waste management technologies prevention stage Five mining waste objects as in a prevention stage in Estonia: two of them being limestone fines (overburden of the Vasalemma limestone quarry, limestone fines of the Harku limestone quarry), others are oil shale fines (HMS waste rock of the Aidu oil shale open cast, oil shale fines of the Estonia oil shale mine, oil shale fines of the Viru oil shale mine). 3.1.2 Mining waste management technologies waste recovery Fourteen mining waste objects in Estonia are in the waste recovery stage: eleven oil shale fines, one flotation sand of phosphate rock and two limestone fines. The technological line is located in situ. The implemented technology is currently in a production stage, and has been known for ten years. The basic type of mining/processing waste from old oil shale mines originates from heavy media separation and also from hand separation. The grain size is 0-125, and the content of organic matter varies between 3-39%. Basic stages are crushing and screening. Possible uses of these waste products are: aggregates for road basements, oil shale, and limestone sand. Potential technological possibilities for processing of other types of mining waste are crushing phosphate rock, gravel, and dolomite. Flotation sand of phosphate rock was produced in the separation process using the flota-

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tion method. Obtained processing waste product is the flotation sand. In the limestone quarries, the type of mining or processing waste are drilling and blasting, and crushing. The technological scheme is described by two stages: crushing with an impact crusher, and screening with vibrating screens. 3.1.3 Mining waste management technologies land reclamation In Estonia there are nine oil shale waste rock, two phosphate rock overburdens, one limestone fine and one lime plant waste heap, where material is used for land reclamation. The grain size is 0-125, and the content of organic matter varies between 0-60%. Geomorphology of the sites is flat or convex. There is primary risk of igniting in case of open fire but in the Maardu open cast there is also the danger of self-ignition in the case of oxidation. 3.2 More efficient use of limestone fines During last years the large share of production of limestone fines (particle size 0-4 mm) is stored on-site, located at the quarry's bottom. Secondary raw material will be re-extracted during the next 10-12 years and after this time limestone natural deposit, which lies 1.5 m below the bottom of the quarry will be extracted. A waste product remanufacturing line was installed during 2008 - a CDE separation plant. CDE M2500™ is mobile washing equipment offering feeding, screening, sand washing and stockpiling on a compact chassis and enabling the production of four sand and aggregate products to your specification. The CDE washing plant effectively removes minus 63 micron material from the washed fine limestone product. Main use of limestone fines - after the dust removal, using CDE technology - is as raw material for road construction and building material. The principle of the technology is that finest particles of the material are separated with the help flocculant additive and hydrocycloning (Fig. 2). All system performs in circulation, without any dust or water pollution. The flocculant used in the water of CDE performs similarly to the principle used in the production of the drinking water. The flocculant neutralizes in the

Figure 2: CDE process line.

water as time passes. Using a CDE separation unit allows to use 92% of all limestone reserves, the remaining 8% limestone being 0-63 micron meter sized particles. These can be used only in agriculture (for example, for reducing soil acidity). 3.3 Oil shale waste rock The locations of oil shale waste rock heaps are shown in Figure 3. In Estonian oil shale mining, waste rock products can currently be divided as follows (Tohver, 2011): - Blasted and broken limestone is removed during mining operations in order to expose the oil shale. In surface mining, the waste rock is deposited together with overburden and is used for land reclamation purposes. Material is not homogeneous, the size of the waste rock is variable, and pieces of rock can be up to 1.5 m in size. - Reject material, which is also called refuse and results from separation and washing of oil shale. This is composed principally of limestone or marlstone, some sand and clay, and amounts of oil shale, depending on the efficiency of the separation plant operation.

Figure 3: Oil shale waste rock objects in east Estonia.


Refuse is produced and disposed of in a coarse form. Fractions of waste rock are 25/100 and 100/300 mm. Fine refuse is settled and then mixed with trade oil shale. - Unwanted material from crushing and sizing operations in aggregate production. According to model calculations we can increase by 7% the coarse oil shale fraction (particle size 25-125mm) inside run of mine when we are able to optimize drilling and blasting so that it will produce 5% less fine oil shale material. Different blasting plans were used and run of mine samples were taken to analyze its texture (Table 1). 4. DISCUSSION To increase production, some enterprises have been searching innovative technologies where they can use waste rock from sieving (limestone fines 0-4mm) or from an enrichment unit (oil shale waste rock). Limestone Products Factory LLC is holding the leading position amongst the companies producing crushed limestone. Limestone aggregates and crushed limestone is raw material for road construction and building materials. The main problem of limestone crushing is that about 25-30% becomes limestone fines (particle size 0-4mm). This material is stored on-site. It cannot be used without further processing. New technologies are needed to wash the dust from the limestone fines and minimize the amount of waste. Estonian Energy Mining Ltd has improved oil shale enrichment and they can produce limestone aggregate from oil shale waste rock. Table 1: Blasting optimization results.

After blasting run Original of mine texture run of mine after blasting (kg) Run of mine sum 1000 Limestone 300 Coarse oil shale 249 Fine oil shale 451 Coarse oil shale increase (%)

Decrease the fine oil shale production inside run of mine by 5% 1000 300 308 392 7

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Using high speed cameras to control the parameters of production lines allows us to control the product quality and minimize waste. 5. CONCLUSIONS Mining waste reduction methods include all mining processes beginning from resource distribution until final yield in the plant. For comparing and testing possibilities of mine waste reduction methods, we need to study mining waste sites, make suggestions to improve testing methods. We need to find new possible technologies to manage waste and how not only reduce new waste production, but also how to reduce already existing mining waste heaps. Classification of mining waste heaps helps choose technology for reuse of old mining waste heaps. Using a CDE separation unit allows us to use 92% of all limestone reserves, the remaining 8% limestone being 0-63 micron meter sized particles, which can be used only in agriculture. According to model calculations, we can increase 7% coarse oil shale inside run of mine when we are able to optimize drilling and blasting so that it produces 5% less fine oil shale material. Possible uses of these waste products are: aggregates for road basements, oil shale, and limestone sand. ACKNOWLEDGEMENTS The research is supported by project MINNOVATION - http://www.min-novation.eu; ETF8123 “Backfilling and waste management in Estonian oil shale industry” http://mi.ttu.ee/ETF8123 and AR12007 “Sustainable and environmentally acceptable Oil shale mining” - http://mi.ttu.ee/etp. This research work has been supported by the European Social Fund (project “Doctoral School of Energy and Geotechnology II”), interdisciplinary research group “Sustainable mining” http://egdk.ttu.ee

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