Jolanta Sobik-Szołtysek, January Bień, Marcin Milczarek
In the case of insufficiently tight natural geological barrier, the area of landfills should be protected by special artificial barriers (separation screens). The use of natural mineral materials for building the separation screens (loamy minerals, such as a variety of clays) requires their extraction from local deposits, which inevitably generates waste from extraction and treatment of the minerals, causes changes in hydrographic conditions and soil quality in the neighbourhood of the excavations, degraded landscape and additional costs, including the energy and examination of mineral usefulness. Therefore, it seems purposeful to search for replacement materials which are technologically and economically competitive, such as fine grain waste minerals and/or by-products from industrial activity. A fundamental parameter of the separation screen which ensures its efficiency in terms of stopping migration of pollutants outside the landfill is the adequate level of filtration coefficient, which according to legal regulation cannot be greater than 1·10-9 m/s. The aim of the present study was to analyse the filtration coefficient obtained as a result of the mixtures prepared from fine grain mineral waste and by-products from industrial activities under conditions of their maximum densification in order to find the material which shows the best tightness to match the requirements of separation screens for landfill applications. The following minerals were used in the study: coal dust from water and dust circulation system in the Sobieski mine in Jaworzno, Poland, fly ash from combustion of brown coal from Bełchatów power plant, fly ashes from combustion of black coal in conventional and fluidized bed furnaces in Łagisza power plant in Będzin, Poland, post-flotation from Zn-Pb ore dressing from inactive settler in the area of the city of Bytom and barren rock clays from brown coal deposits in the Bełchatów mine. These materials were used for preparation of 8 mixtures with various share of individual components with coal dust as the main component of the matrix, with participation of 50 wt%. Before the determination of filtration coefficient for each of the mixture began, the optimum humidity and maximum bulk density of the soil matrix was measured. In the most of the mixtures, the optimum humidity ranged from 25 to 27.5%, whereas in the case of the mixtures with bottom ash from fluidized bed and fly ash from the conventional furnace it was lower than 20%. Determination of the filtration coefficient was carried out on the specially designed stand under condition of fluid flow from the bottom to the upper part of the sample, with variable hydraulic gradient and i>30. Stabilization of the filtration coefficient was observed for the most of the mixtures after ca. 10–11 days from the beginning of the experiment, at the level typical of the particular mixture. The highest, unstable filtration coefficient of 1.6–2·10-8 m/s was observed for the mixture of coal dust with the ashes from brown coal, which makes it impossible to be used as proposed. Nevertheless, application of another addition to this mixture (floatation waste and clays) considerably improved the coefficient of filtration, which reached the value of ca. 2–2,5·10-9 m/s. The most favourable coefficient was obtained for the mixtures of coal dust with ashes from combustion of hard coal in fluidized bed furnaces, modified with an addition of clays. The value of filtration coefficient ranged from 3 to 6.5·10-10 m/s. The results of the investigations confirmed the ability of achieving the alternative material for building the separation screen which is the mixture of waste and by-products from industrial activities with over-additive properties. It is necessary to continue the research in the area of modification of the mixtures, particularly in the aspect of increased fraction of coal dust in order to optimize filtration coefficient and obtain the screen with satisfactory degree of tightness.
współczynnik filtracji; budowa barier izolacyjnych
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