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RESEARCH OF ELEMENTAL, MINERALOGICAL AND RADIO-NUCLIDIAL COMPOSITION OF SLAVIANSKAYA THERMAL ELECTRIC STATION ASHSLAG WASTES
E. Khobotova, prof., d.ch.s., Ye. Voronova, ass. prof., V. Slishchenko, master, KhNAHU
Summary. Elementary, mineralogical and radionuclidial structures of Slavi-anskaya thermal electric station ashslag wastes have been investigated. It has been established that granulemetrical fractions of slag wastes can be recommended as light concrete contributors.
Key words: fuel slag, granulemetrical fraction, effective, specific radio-activity.
Introduction
The nonwaste technology stimulates the use of industrial wastes for construction materials production. Wastes of the power industry are fuel ash and slags. Thermal electric station’s ash-ab-lation is used abroad basically for manufacturing of cement and various kinds of concrete, in road building, for manufacturing of bricks and light porous aggregates.
However the hydraulic way of ashes and slag removal is carried out at the majority of domestic thermal power stations. Thus the slagash pulp not being uniformed in structure and properties gets into dumps and that complicates the usage of ashslag wastes.
Analysis of publications
Thermal power stations located along Ukraine are large-tonnage sources of ashslag wastes. Their accumulation increases in ash dumps [1] every year. Recycling of ashes and slags is expedient technically and economically as the location of thermal electric stations in densely populated industrial areas of Ukraine facilitates the problem of their waste usage in the construction industry [2].
To make the conclusion about the application of ashes and slags in this or that quality is possible only after their preliminary definition of elemental, chemical, mineralogical and granule-
metrical structures [3]. To define the class of ashslag wastes radiation danger is of important value. Ashes and slags are components of tech-nogenicaly changed radiation background. Their uncontrollable application in manufacture of construction materials can increase the gamma radiation intensity, external irradiation doses at the expense of the ionising radiation and the internal irradiation at inhalation receipt of radon isotopes [4].
Research of ashslag wastes structure
Dispersion of ashslag tests on granulemetric fractions was carried out by means of sieve sets. The granulemetrical structure of ashes varies widely. More often ashes of hydro dumps are polydisperial with prevailing of small fractions [5]. The maximum size of ash particles is
0,2 mm. We allocated fractions of 10 - 20 mm, 5 - 10 mm, <5 mm. Thus all ash particles are transformed into the smallest fraction of <5 mm, two other fractions include slag particles.
The methods of researching were the electronic-zonde microanalysis, x-ray phase and gam-ma-spectrometer analysis.
The x-ray microanalysis gives the idea of the elemental structure of fractions. The fraction <5 mm includes 28,92 % of carbon unlike larger fractions of slag not having any organic components. Then comes: silicon (9,46 %), aluminium (4,72 %) and iron (3,92 %). As the majority
of elements are present as oxides oxygen content constitutes 48,86 %. Conglomerates of the alloyed among themselves unites are the prevailing spatial forms of any fraction. It testifies of the presence of organomineralogacal units fractions worsening ashes quality being used in concrete.
Fractions with diameter of particles 5 - 10 mm include mineral aggregated particles. The microelemental analysis showed the full absence of organic components. Silicon (17,7 %) follows after oxygen (63,87 %), then comes aluminium (8,8 %) and iron (3,59 %). Silicon content has increased by 1,87 time, aluminium - by 1,86 times, iron content practically has not changed in comparison with fraction <5 mm. The prevailing spatial form - caked viewcluster units with the semimelted off external cover is formed as a result of not complete process of external fusion.
Results of x-ray fractional microanalysis of particles in diameter of 10-20 mm testify the absence of any organic component in this fraction. Silicon (19,96 %), aluminium (12,19 %), iron (4,94 %), potassium (2,26 %) have the highest percentage after oxygen. Silicon content has increased 1,13 time, aluminium - 1,39 times, gland - 1,38 times, potassium - 1,65 times in comparison with K20 of 5 - 10 mm which is an undesirable component in ashes if to consider them from the point of view of their usage in construction materials. The spatial structure of slag particles is presented by the glass units filled with caked balls of ashes of various sizes. Thus units of fraction of 5 - 10 and 10 - 20 mm as a matter of fact represent caked of ashslag substances with a wide variation of the ash particles size.
The received roentgenograms of the Slavi-anskaya thermal electric station’s (TES) slag wastes fractions confirmed that all three fractions consisted basically of glass like materials. They have no crystal structure therefore the detailed analysis of phases is impossible. Separate lines are seen on the wavy background of roentgenograms; they are not identical on all three roentgenograms. It is possible to assume that these data contain glasses some crystallized phases.
Measuring of acidity of a film layer of water on the surface of firm particles has shown that fractions of particles <5 mm and 5 - 10 mm have a
souring reaction: pH equals 4,47 and 4,22 accordingly. For particles of 10 - 20 mm the film layer of water is practically neutral, pH 5,82 value is close to that for distilled water.
Fractions of <5 mm and 10 - 20 mm contain compounds of iron and pure iron. They stipulate the increase of the fraction density and the magnetic component of particles. A considerable decrease of hydraulic activity of meltded particles is the property of iron oxide. Meanwhile they can serve as catalysts of siliconforming reactions at use of ashslag fractions as an active additive to cement.
The presence of double calcium aluminate СА2 is a peculiar feature for the crystal phase of the mineral structure of fraction of 5 - 10 mm. This mineral is hydraulically active; the product of its hardening shows a raised stability to the action of many excited environments. It is the main mineral component of clay cement. The miner-alogical values but not only the chemical composition plays a considerable role in the definition of potential ability to hydration.
The possibility of the Slavianskaya TES’s slags usage as an artificial contributor to concretes is not challenged. In this case grains of the wrong form splitted thermally and mechanically being a basic contributor can partially replace rubbles (20 - 60 %) or serve for improving of granule-metric small sands. The granulemetrics of slags is very important especially at their usage as the basic contributor [6]. It is possible to notice that durability of fractions of 5 - 10 mm is 33 - 34 % higher and spliting is 24 - 38 % lower than the same values for 10 - 20 mm fraction.
The results of the chemical analysis have shown that the main oxide of the Slavianskaya TES’s ashslag is SiO2. Then by reducing the quantitative content follows АЬОэ, Fe2O3, CaO and MgO. By inlarging the fraction the quantitative contribution increases SiO2 by 7 %, АЬОэ by 17,7 % and СаО by 27,7 %. Simultaneously oxides contribution decreases Fe2O3 by 18,6 % and MgO by 38,3 %. The calculated fusibility module (М) is an important quantitative characteristics of ashes' fusibility
М I CaOI+jFeA
f (SiO,) + (Al,O,)'
As ashes' microporosity is connected with fusion viscosity, hence, it depends on the specified
oxides ratio. Literary data [5] testify that the temperature of ashes fusion raises with the fall of М/ but its microporosity decreases. Ashes of adsorption activity and ash microporosity depend on Mf more than slag particles. It is necessary to consider their water saturation at the Slavianskaya TES’s ashes usage in light concretes especially in protecting designs. The heat conductivity factor can be increased by 5 - 10 times at full water saturation in comparison with dry concretes. Proceeding from this statement the Mf falling will promote smaller water saturation of light concretes. Hence, large fractions of 5 - 10 mm and 10 - 20 mm are more suitable to be used in light concretes from the investigated fractions.
The chemical ashes compounds without the set of other indicators such as a mineralogical composition cannot characterize objectively the product. In this connection ashslag petrographic researches have been done. Researches were carried out by means of a microscope with the help of a drug for the fraction of < 5 mm and with the clear microsection for other fractions. The results of petrographic researches have shown that the glasphase have the greatest content. With fractions enlarging the increase of mineral mullite content and the reduction of other minerals (magnetite, pyroxenes, calcite, quartz) contents is observed.
The results of gamma-spectrometer research of the Slavianskaya TES’s slag wastes have shown that fractions incorporate two representatives of radioactive families 226Ra and 232Th (a, у - radiators) and 40К (P, у - a radiator), not concerning radioactive numbers. The basic contribution to total activity (more than 80 %) gives 40К isotope. Specific efficient radio-activity of slag fractions is not changed practically as well as the contribution of separate radionuclides to it. Hence, there can not be a restriction in usage of separate granulemetrical fractions in construction. According to the size of (Cef) ashslag as well as its separate fractions refers to the first class of radiation danger for which effective specific activity does not exceed the size of 370 Bk/kg [7]. Similar materials can be used in construction without restriction.
Conclusions
The results of research have shown that the percentage ratio of elemental composition of fractions are different; fractions consist of glass like materials not having a crystal structure; fraction particles of <5 mm and 5 - 10 mm have a sour reaction and particles of fraction of 10 - 20 mm are neutral; there are also differences in granule-metrical properties of slag fractions; materials can be used in construction without any restriction. Everything mentioned above and the difference of the mineral structure of the crystal phase of fractions indicate various areas of application of fractions as components of light concretes.
The fraction of < 5 mm is recommended to be used as an active additive to cement, fractions of 5 - 10 and 10 - 20 mm are small fillers of light concretes.
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Рецензент: В.И. Ларин, профессор, д. хим. н., Научно-исследовательский институт химии при ХНУ им. В.Н. Каразина.
Статья поступила в редакцию 23 декабря 2008 г.
