Elina Khobotova

ELEMENTAL COMPOSITION OF ASH-SLAG WASTES OF SLOVIANSKA THERMAL POWER PLANT

Kharkov National Automobile and Highway University

The low-waste technologies stimulate the use of industrial wastes in various branches of industry. Blast-furnace slag has the properties of effective broken slag, іt can be used for manufacturing various types of cement.

Wastes of the power engineering industry are fuel ash and slag. Ashes from TPP carry-over are widely used for manufacturing cement and various types of concrete, for manufacturing bricks and light porous fillers, as well as in road building. However, at the majority of TPP ashes and slag are removed hydraulically. Thus, the ash-slag being inhomogeneous by its structure and properties gets into dumps and that complicates its further use.

The conclusion about the use of ash and slag for some definite purposes can be made only after preliminary determination of their elemental, chemical, mineral composition and granularity.

Identification of the class of ash-slag wastes radiation safety is also of great importance. Ashes and slag are the components of the technogenically changed radiation background. Their uncontrollable application in the manufacturing of building materials can increase the gamma radiation intensity, external irradiation doses due to electromagnetic radiation, and the internal irradiation doses while inhaling radon isotopes.

The aim of research was to make a conclusion that ash and slag wastes of Slovianska TTP could be used in construction based on determination of their elemental and chemical composition.

Research of the ash-slag wastes composition. Distribution of ash-slag samples by granulometric fractions was carried out by means of sieve sets. The granularity of ashes varies widely. More often ashes of hydro dumps have a polydisperse composition with predomination of small fractions. The maximum size of ash particles is 0.2 mm. We distinguished the following fractions: 10–20 mm, 5–10 mm, <5 mm. Thus, all ash particles are transformed into the smallest fraction <5 mm, two other fractions include slag particles. The research was conducted by the following methods: gamma-spectrometric and electron microprobe analysis.

The results of the gamma-spectrometric research of ash-slag wastes. Gamma-spectrometric analysis was performed on the scintillation gamma spectrometer SEG-001 "AKP-S" which measures the range of energy of gamma radiation from 50 to 3000 keV. The time of measuring activity of natural radionuclides makes up 4 hours on average. To process the results of measurement program Akwin is used. The results of gamma-spectrometric analysis of ash-slag wastes have shown that their fractions include ⁴⁰К and two representatives of radioactive families ²²⁶Ra and ²³²Th (Table 1). The isotope⁴⁰К share is the biggest in the total activity (more than 80 %). Efficient specific activity (C_ef) of slag fractions does not practically change as well as the content

of particular radionuclides in it. Hence, there can not be a restriction in the use of particular granulometric fractions in construction. According to C_ef values of ash-slag and its particular fractions, they refer to the first class of radiation safety at the value of C_еf 370 Bq/kg. Such materials can be used in construction without restriction.

Table 1 − The results of gamma-spectrometric analysis of fractions of ash-slag wastes from the Slovianska TTP

Fraction, mm	С_е_f., Bq/kg	С_sum., Bq/kg	С_і, Bq/kg (% content)
Fraction, mm	С_е_f., Bq/kg	С_sum., Bq/kg	⁴⁰К	²²⁶Ra	²³²Th
<5	237	897	745 (83 %)	83.4 (9.3 %)	68.6 (7.6 %)
5-10	269	984	807 (82 %)	104 (10.6 %)	72.9 (7.4 %)
>10	264	966	792 (82 %)	100 (10.4 %)	73.5 (7.6 %)

The results of electron probe microanalysis of ash-slag fractions. Electron microprobe analysis (EMPA) is carried out by the scanning electron microscope JSM-6390 LV INCA with the system of INCA x-ray microanalysis. The x-ray microanalysis gives an idea about the elemental composition of fractions. The fraction <5 mm includes 28.92 % of carbon unlike larger slag fractions which do not include any organic components. Then, by decreasing quantity, come: silicium (9.46 %), aluminium (4.72 %) and iron (3.92 %). As the majority of elements are present as oxides, the content of oxygen makes up 48.86 % (Table 2).

Table 2 − The results of the electron microprobe analysis of fractions of the Slovianska TTP ash-slag wastes (mass part)

Element	Fraction, mm
Element	<5	5-10	10-20
C	28.92	0.00	0.00
O	48.86	63.87	56.75
Na	0.43	0.96	0.79
Mg	0.45	1.27	0.94
Al	4.72	8.80	12.19
Si	9.46	17.70	19.96
S	0.27	0.10	0.35
Cl	0.10	0.00	0.00
K	1.18	1.37	2.26
Ca	1.40	2.10	1.34
Ti	0.28	0.23	0.48
Fe	3.92	3.59	4.94

The method makes it possible to study the morphological features of the sample surface. Conglomerates of aggregates sintered with each other in contact are the prevailing spatial form (Fig. 1). The availability of organomineral aggregates in fractions worsens the quality of ash from a perspective of its use in concrete. The fraction of 5–10 mm includes mineral aggregates.

a b

Fig. 1 – The surface of the <5 mm fraction particle of the Slovianska TTP ash-slag: а – X1000; b – X 3000.

The microelemental analysis showed the full absence of organic components. The mass fraction of silicon (17.7 %) follows oxygen (63.87 %), then come aluminium (8.8 %) and iron (3.59 %). The silicon content has increased 1.87 times, aluminium – 1.86 times, the iron content practically has not changed in comparison with the fraction <5 mm. The predominant spatial form is the sintered racemose aggregates with the semi-sintered external cover that are formed as a result of the incomplete process of external sintering.

The results of the electron microprobe analysis of the fraction of 10–20 mm prove the absence of any organic components. Silicon, aluminium, iron, potassium have the highest mass percentage after oxygen. The silicon content has increased 1.13 times, aluminium – 1.39 times, iron – 1.38 times, potassium – 1.65 times in comparison with the 5-10 mm fraction. К₂О is an undesirable component in ashes if they are considered from a perspective of their use in building materials.

Conclusions. The elemental composition of fractions is different; fractions include glass as a material without the crystal structure; there are also differences in granulоmetrical properties of slag fractions; materials can be used in construction without any restriction.