Quantitative Chemical Analysis of Slag Ash of Novocherkassk State District Power Plant

Introduction

Novocherkassk SDPP is located in Donskoi housing complex, Novocherkassk, Rostov region of Southern Federal District (Russia). Slag ash are generated after combustion of solid fuel in boilers of Novocherkassk SDPP. Dry ash after combustion is deposited in electric filter. Ash particles with the size from 3-5 µm to 100-150 µm is referred to as fly ash. Ash particles with the size in excess of 150 µm (0.15 mm) is referred to as ash and slag wastes (ASW) or coal slag. Using compressors and pneumatic pumps the ash is conveyed via pipelines to silos. As consequence of pumping the ash particles of various fineness travel with air, a portion of these particles is carried away to transport network. Thus, prior to emission into atmosphere contaminated air should be cleaned. Group cyclone and bag filter are used as mechanical ash collectors.

This article discusses data on quantitative chemical analysis of ash and slag mix of Novocherkassk SDPP, selected before the group cyclone, from group cyclone and from bag filter. Wastes are generated as a consequence of combined removal of fuel slag and ash. Donetsk culm are used as solid fuel. Interim storage (accumulation) of the wastes is performed in ash and slag dump located on the premises of the company.

Related Works

Main technogenic wastes of thermal power plants and SDPP are slag ashes and flue gases. Upon coal combustion in boilers organic portion is burned generating flue gases. Inorganic portion is transformed into slag ash. Fly ash is carried out by flue gases and captured in ash collectors. Ash and slag are unburned residue of solid fuel stored in ash and slag dump. Depending on the coal type and combustion method fly ash and slag ash are characterized by various physicochemical properties and particle size distribution.

Slag and ash are a real challenge for many countries. Let us consider this issue more deeply.

In India with its high density of population thermal power plants generate huge amounts of fly ash, thus affecting environment and water resources. Approximately 260 million tons of cola are consumed annually by 82 thermal power plant in India, which results in generation of 108 million tons of fly ash annually. Fly ash occupies large surface area and is hazardous for environment. Fly ash pollutes air and water, it creates breathing problems. In addition, while depositing on leaves and grain crops in agricultural regions in vicinity of power plants, it reduces harvest. Chemical composition of ash and slag was analyzed by X-Ray fluorescence technique, which is one of the most widely applied method of quantitative analysis (Table 1). It is established that the main components are Si, Al and Fe. In slag ash SiO₂ content is 77.4 wt %, in fly ash Al₂O₃ content is 32.8 wt %. The researchers in [1] arrived to conclusion about reasonability of development of extraction technology of silicon and aluminum, using slag and ash as secondary source for recovery of valuable elements.

Similar issue of impact of Indian coal, nuclear and hydro power plants on environment and human life was discussed in [2]. Many countries of the world aim at increase in electricity production by erection of new power plants. Coal is the only natural resource and fossil fuel abundantly available in India. Coal combustion by thermal power plants results mainly in emission of carbon dioxide (CO₂), sulfur oxides (SO_x), nitrogen oxides (NO_x); CFC trace gases, inorganic macroparticles, such as flue ash and suspended particulate matter (SPM). CO₂, NO_x and CFCs are greenhouse gases. High ash content in Indian coals and inefficient combustion technologies result in emission of particulate contaminants and gases responsible for greenhouse effect. Table 1 summarizes chemical composition of fly ash with high content of Fe₂O₃ (Iron oxide): 63%.

Table 1: Chemical composition of fly ash and slag ash (India)

Component	Wt %
	Fly ash		Slag ash [1]
	Haryana thermal power plant [1]	Chemical Composition of Fly Ash, %  [2]
NOa2	–	0.28	2.02
MgO	0.343	–	1.70
Al2O3	32.8	26	9.97
SiO2	56.1	62	77.4
P2O5	0.562	0.40	0.125
SO3	0.387	–	0.169
Cl	0.0371	–	0.0976
K2O	1.84	1.28	2.19
CaO	1.10	1.13	1.62
TiO2	2.49	1.8	0.494
Fe2O3	4.30	63	4.22
SrO	0.0378	–	–
ZrO2	–	–	0.0357
SO4	–	0.36	–

 

Luohuang power plant, one of the largest thermal power plants in south-west of Chine, consumes approximately six million tons of coals per year with annual generation of fly ash up to two million tons [3]. It is highlighted that coal consumption and, hence, emission of coal fly ash, constantly increases, negatively effecting on environment and human life. Interaction of dust with high amount of silicon dioxide results in development of the most frequent and severe form of pneumoconiosis: silicosis. Coal dust also induces lung cancer. Fluorosis is the disease caused by prolonged intake of fluorine. Loss on ignition (LOI, %) and content of major elements (%) in Luohuang fly ash are summarized in Table 2.

Table 2: Loss on ignition (LOI, %) and the concentrations of major elements (%) in the Luohuang fly ash

LOI	Na2O	MgO	Al2O3	SiO2	P2O5	SO3	K2O	CaO	TiO2	MnO	Fe2O3
4.01	0.77	1.21	21.59	48.27	0.13	0.78	1.21	5.72	1.78	0.09	14.09

 

Data analysis (Table 2) demonstrates that content of SiO₂ and Al₂O₃ in Luohuang fly ash (China) is less than that in Haryana fly ash (India) (Table 1), but is high, nevertheless. Ash composition of lignite (China) was analyzed in [4] (Table 3). Content of SiO₂ (59.04 wt %), Al₂O₃ (18.02 wt %), Fe₂O₃ (5.83 wt %) and CaO (5.80 wt %) is high.

Table 3: Ash composition of lignite, wt %

Na2O	MgO	Al2O3	SiO2	P2O5	SO3	K2O	CaO	TiO2	MnO2	Fe2O3
1.26	2.71	18.02	59.04	0.2	2.5	2.74	5.8	0.93	1.26	5.83

 

Ash and slag in Romania also contain high amount of silica SiO₂ and aluminium oxides Al₂O₃ [4]. It is recommended to use ash and slag for production of building materials. Titanium dioxide TiO₂ is contained in all considered samples but due to its minor content the authors believe that its extraction is inefficient.

The issue of disposal and reprocessing of slag ash wastes as well as researches in the field of development of new technologies attract attention in many countries of the world.

Ordinary Portland cement (OPC) was studied with new binder from locally available slag and fly ash (Malaysia) [5]. Portland cement is widely applied everywhere. It is a hydraulic binder, obtained by combined milling of cement clinker, gypsum and additives with predominant content of calcium silicate (70–80%). Combination of 60% slag and 40% fly ash was used as new binder. The use of slag in concrete increased its strength and decreased porosity. On the basis of chemical analysis it was established that slag and flue ash contain high amount of silicon dioxide and sufficient amount of basic oxides (Table 4). Around the world the fly ash generation rate is about 900 million tons per year. Fly ash and slag are generally disposed to dumps, causing great harm to environment, polluting ground and water. According to preliminary tests of сonsistency, setting time, and flow of binders the researchers [5] concluded that at availability of chemical activator slag and flue ash can be used jointly as an alternative to ОРС. The sodium hydroxide (5% NaOH) and calcium hydroxide (5% Ca(OH)₂) flakes were used as a chemical activator.

Table 4: Chemical properties of materials (wt %)

Material	SiO2	Al2O3	Fe2O3	CaO	MgO	SO3	Na2O	K2O	TiO2	MnO	LOI
Slag	33.05	16.36	0.53	45.0	6.41	1.21	0.13	0.42	–	–	3.05
Fly ash	48.67	14.31	3.51	1.03	0.39	0.14	0.21	0.79	1.13	0.02	6.26
OPC	20.99	4.60	4.44	67.17	2.53	2.98	0.03	0.16	–	–	1.3

 

Physicochemical properties of slag and ash wastes of Yurga thermoelectric plant were analyzed in [6] (Yurga, Kemerovo region, Russia). Chemical composition of slag and ash wastes was determined in samples from electric precipitator and slag ash dump. Chemical composition (Table 5) was obtained using X-ray fluorescent spectrometer. The main components in ash are silicon and aluminum oxides. In order to reveal additional possibilities of application of slag and ash wastes the major classification principles were determined: acidity modulus (electric precipitator –2.9; slag and ash dump –4.7) and basicity modulus (electric precipitator – 0.2; slag and ash dump –0.16), silicate modulus (electric precipitator – 1.7; slag and ash dump – 1.9), and quality coefficient (electric precipitator – 0.7; slag and ash dump –0.54). It was established that Yurga thermoelectric plant slag and ash wastes are referred to acid ashes. Acid ashes are characterized by unstable chemical composition, low content of free calcium oxide and high content of silicon oxide. According to the results of particle size analysis in the study ash the sizes of 60% of the particles in the considered ash are from 10 µm to 70 µm. The material is very fine grained. The use of slag and ash wastes in various fields of building industry would decrease the use of natural resources.

Table 5: Chemical composition of Yurga thermoelectric plant ash, %

Element	SiO2	CaO	Al2O3	MgO	MnO	Fe2O3	FeO	K2O	TiO2	SO3	BaO	P2O5
Ash dump	55.7	6.8	21.83	1.95	0.09	7.44	6.69	3.53	1.11	0.72	0.44	0.38
Electric filter	50.4	13.96	20.52	1.55	0.1	8.55	7.69	1.35	0.97	0.87	0.5	1.08

 

Possibility of application of slag and ash wastes of Khavarovsk thermoelectric plant-3 (Khabarovsk, Far East, Russia) as a secondary source was analyzed in [7]. Ash dump No. 1 is located in the Village of Fedorovka, Khabarovsk region; it was commissioned in 1985. Khabarovsk thermoelectric plant-3 operates mainly with Neryungri black coal, generation of slag and ash is about 300 thousand tpy. Ash and slag are disposed to dump by means of conveying in the form of water slurry. The major component of the considered slag and ash wastes is slag of black, gray and sometimes whitish-gray colors, with porous, pumiceous, sponge and dense structure in the form of fragments with the sizes of 0.01 mm-3.00 mm. Silicate analysis of oxides revealed that the considered slag and ash wastes are characterized by high content of silicon and aluminum oxides and low content of calcium and magnesium oxides (Table 6). Classification properties of the material are determined: basicity modulus (hydraulic modulus) – BM; silicate (silica) modulus – SM; quality coefficient (hydraulic activity) – Q. The basicity modulus is the ratio of content of basic oxides to that of acid oxides. The basicity modulus was 0.06 (BM < 1), hence, these slag and ash wastes are acid and can be used as hydraulic additive. Silicate modulus is the ratio of content of silicon oxide reacting with other oxides to cumulative content of aluminum and iron oxides. Silicate modulus was 3.19. Hydraulic activity was 0.27. Therefore, analysis of chemical composition, physicochemical properties, and hydraulic (chemical) activity of ash and slag of Khabarovsk thermoelectric plant-3 revealed that these wastes are the most efficient as technogenic soils and in road construction, in production of ash–concrete and slag–ash silicate building materials (without additional use of natural materials in the mixes).

Table 6: Composition of ash and slag wastes

Element	SiO2	Al2O3	Fe2O3	P2O5	MnO	MgO	K2O	Na2O	TiO2	CaO
Average content, %	71.58	16.21	6.19	0.13	0.07	0.76	1.22	0.83	0.56	2.44

 

Comprehensive analysis of chemical and phase composition, physicomechanical properties and hydraulic (chemical) activity of ash and slag from Barnaul thermoelectric plant-3 [8] (Barnaul, Altai region, south of Western Siberia, Russia) demonstrated that one of the most efficient filed of their application is production of non-autoclaved ash-concrete and slag ash silicate building materials (without addition of natural materials). This would require for dry removal and storage of slag and ash to provide their subsequent utilization. Barnaul thermoelectric plant-3 operates on Kansk–Achinsk coal with low ash content, hence, generation of slag and ash is 120 thousand tpy. Ash and slag are disposed to dump by transportation in form of water slurry. Existence of hardly hydrated particles of free calcium oxide in Kansk–Achinsk coals prevents their wide application for production of building materials. Upon contact with water free calcium oxide is hydrated being accompanied with increase in volume of generated slaked lime. Building materials and products with such ash are deformed and destroyed with time. Semi-dry method of removal of high calcium slag and ash is proposed, including pneumatic collection of ash and dewatering of slag, damping of ash up to 18%-25% (thus providing dedusting upon loading, conveyance and unloading), transportation of ash and dewatered slag to dump by haulers, leveling and compression of unloaded slag and ash by bulldozers and loaded. Disposed на отвал slag and ash are consolidated in 8-24 hours with generation of monolith ash array. After complete consolidation (28 days) their properties of slag and ash are as follows: density –1.85-1.95 t/m³, strength up to 7 MPa, coefficient of filtration – at least 10 cm/s. The use of effluent waters for consolidation of ash in combination with special plasticizers increases the strength of ash stone up to 9-10 MPa and decrease water permeability to 10^-10 cm/s. Analysis of disposed ash array (monolith) demonstrated that pollution of natural waters with harmful substances from the dump as well as dusting are actually eliminated.

The aspects of development of slag alkaline binders on the basis of fuel slag and ash from thermoelectric plant-2 (Izhevsk, Udmurtia, Russia) and their stability under conditions of sulfate corrosion have been discussed elsewhere [9]. The main component of the binder is milled fuel slag. Sodium liquid glass was used as alkaline components. Chemical composition of ash and slag was determined by X-ray phase analysis and summarized in Table 7.

Table 7: Chemical composition of ash and slag from thermoelectric plant-2, Izhevsk

Material	Oxide content, %
	SiO2	Al2O3	Fe2O3	CaO	MgO	K2O	Na2O
Ash	51.66	19.54	6.99	3.00	0.81	0.54	0.12
Slag	60.4	19.02	6.38	2.63	0.61	0.54	0.13

 

Three compositions were developed for the investigations (Table 8) with liquid glass content of 15%, 20%, and 25%, respectively. After setting the samples, cubes with the size of 20 mm, were stored one day in air-humid conditions, then steamed in 2+4+2 hours at 90^°+5^°С. Finished samples were placed into aggressive medium (1N Na₂SO₄ solution). Reference samples were stored in air-humid and aquatic mediums. In the course of tests the samples were regularly titrated and visually examined, weighed and photographed. Fine cracks were revealed upon examination, destruction of edges was not observed. Physicochemical studies (X-ray phase, differential thermal, electron microscopy and IR spectral analyses) were performed before and after tests in aggressive medium, thus enabling detection of shape and dimensions of new formations, their identification. The obtained data evidence high sulfate resistance of the developed compositions.

Table 8: Studied composition

Content, % (by weight of the slag and ash)
Slag	Ash	Liquid glass	NaOH	Water
60	40	15	10	8
60	40	20	10	4
60	40	25	10	–

 

Modification of slag and ash wastes of thermal power plants by milling for their application upon production of ceramic brick was proposed in [10]. The considered raw materials consisted of ash after combustion of black colas at SDPP-2, Tomsk and clay of Supreme field in Tomsk region, Russia. Chemical composition is summarized in Table 9. Analysis of Table 9 demonstrates that the aluminum oxide content of 12.1% in the clay characterizes it as acid product (Al₂O₃ < 14%). CaO and MgO exist in the form of carbonate compounds. Quantitative combination of aluminum oxide, which characterizes fire resistance of the raw stock, and fusing agents – oxides of magnesium, calcium, and iron – characterizes the raw material as low melting. Loss on ignition below 5% evidences low content of residual fuel, which minimizes shrinkage of products upon roasting. Optimum modes of milling in ball mill were determined on laboratory scale. The researchers [10] established that the milling time should not be higher than 12 hours, since upon further milling the particle size distribution actually does not vary.

Table 9: Chemical composition of raw stock

Name	Oxide content, wt %
	LOI	SiO2	Al2O3	Fe2O3	CaO	MgO	R2O	TiO2
Clay	5.92	64.8	12.1	4.53	5.90	3.08	2.97	0.70
Ash	4.45	61.8	22.4	3.95	3.00	1.81	1.34	1.25

 

Recipe of composite cement [11] was developed with mineral additive in the form of blast furnace granulated slag (FGS) and dumped ash and slag mix (DASM) from thermal power plant, its physicochemical properties satisfy the requirements of Russian standard GOST 31108-2003 General structural Portland clinker cements. Specifications. The composite cement is a hydraulic binder obtained by combined milling of Portland clinker cements, gypsum stone and composite additive composed of at least two mineral components. Chemical composition of the initial materials is summarized in Table 10.

Table 10: Chemical composition of FGS and DASM

Material	Oxide content, wt %
	LOI	SiO2	Al2O3	Fe2O3	CaO	MgO	SO3	K2O	Na2O	TiO2	MnO
FGS	0.6	37.5	13.88	1.52	32.75	7.98	0.88	–	–	4.33	0.56
DASM	6.1	48.8	26.70	5.83	4.80	3.92	0.32	0.98	1.06	–	–

 

Thus, it is obvious that generation of technogenic formations, among which slag and ash are on leading positions, is an urgent global issue. These wastes are generated at power plants upon combustion of solid fuels, accumulated in dumps, occupying large plot of lands and causing environmental damage. Therefore, the use of slag and ash mixes for production of various products will reduce environmental load and decrease expenditures for their disposal.

Experimental

Quantitative composition of slag ash wastes in this work was determined in accordance with approved and valid in RF procedures: PND F 16.1:2:2.2:2.3.46-06, PND F 16.2.2:2.3:3.34-02, Russian standard GOST 26485-85, PND F 16.1:2:2.2:3.65-10, Russian standard GOST 5180-2015.

The procedure PND F 16.1:2:2.2:2.3.46-06 was applied for determination of weight portions of acid soluble forms of heavy metals and toxic elements: cadmium, copper, mercury, nickel, plumbum, zinc, cobalt, iron, manganese, arsenic, selenium, antimony, bismuth. Voltammetric method is based on analysis of current-voltage curves which show current of cell electrochemical reaction as a consequence of redox processes on electrode as a function of its polarization potential.

Calcium content was determine according to the procedure PND F 16.2.2:2.3:3.34-02. This method is based on generation of solid complex of Trilon B with calcium ions at рН=12, accompanied by variation of murexide coloring.

Aluminum content was determined according to Russian standard GOST 26485-85. The essence of the method is to extract exchange (mobile) aluminum form slag wastes by calcium chloride solution, obtaining of colored aluminum complex with chromazurol or xylenol orange in weak acid medium and subsequent photometric measurements of the color solution.

The procedure for determination of weight portion of silicon dioxide (PND F 16.1:2:2.2:3.65-10) is based on gravimetry. At the first stage a sample was fused with soda, at the second stage the fusion cake was leached and the metal salts were converted into chlorides by hydrochloric acid treatment. At the third stage silicic acid was extracted by gelatin. At the fourth stage silicic acid was oxidized to silicon dioxide with its determination by gravimetry.

Moisture content of slag and ash wastes was determined according to Russian standard GOST 5180-2015 by drying to steady weight.

The content of elements was converted into percentage on the basis of ratio of molecular weights of the compounds to relative atomic weight of elements.

Results

Ash collecting facilities of Novocherkassk SDPP are equipped with two bag filters for capturing of particulate ash, aimed at high efficient cleaning of exhaust gases, which are not toxic, aggressive, fire and explosive dangerous, with the temperature not higher than 130-200°C, these units operate in stationary gas flow. The gas flow is maintained by pneumatic pumps in order to override high pressure drop on filter. Group cyclone is used as the cleaning stage I aiming at reduction of dust emissions. This promoted reduction of dust load on the bag filters, which are the cleaning stage II. Cyclone design and analysis of operation of bag filters before and after cyclone implementation are discussed elsewhere [13, 14].

Properties of wastes (slag and ash mix) are summarized in Table 11. Description and code of wastes are given according to Federal Classificatory Catalogue of Wastes (Decree of Ministry of natural resources and ecology of Russian Federation No. 445 dated July 18, 2014) and backgrounds for qualification of materials in terms of environmental hazard class.

Table 11: Properties of wastes (ash and slag mix, Novocherkassk SDPP, Russia)

Description	Property
Code according to Federal Classificatory Catalogue of Wastes	6 11 400 01 20 4
Description of wastes	ash and slag mix after coal combustion, low hazard
Aggregate state	solid (mix of solid forms)

 

In Russian industry the first cleaning stage is more frequently based on mechanical ash collectors operating on the principle of centrifuge forces, where deposition occurs upon flow rotation. Therefore, for preliminary coarse cleaning a TsN-15-500 group cyclone (Scientific-Research Institute for Industrial Gases and Refuse Disposal design, Russia) was installed, comprised of four cyclone units with the diameter of 500 mm. General view of the group cyclone is illustrated in Figure 1. Medium and coarse particles are deposited in cyclone under the action of centrifuge force.

Figure 1: Group cyclone TsN-15-500-4, Wholesale generating company OGK-2, SDPP; top view: cyclone (above), silos (below). Click here to View Figure

 

An FRKI-90K-P3-2-2 bag filter is illustrated in Figure 2. The bag filter is equipped with pulse purge system for recovery of filtering material. Decrease in dust load would permit more efficient operation of filters due to application filtering surface for capturing of fine particles. Dust content before and after implementation of the cyclone demonstrated increase in efficiency of gas scrubbing system [13].

Figure 2: Bag filter FRKI-90K-P3-2-2 (upper part), OGK-2, Novocherkassk SDPP. Click here to View Figure

Chemical composition was determined using ash from handling system prior to installation of group cyclone in the gas scrubbing system. After inclusion of group cyclone and commissioning activities aimed at determination of optimum operation mode the ash was sampled from the cyclone and bag filter (Figure 3).

Figure 3: Appearance of ash and slag mix of Novocherkassk SDPP. Click here to View Figure

 

Quantitative chemical analysis of slag and ash mix was determined according to approved in Russian Federation (RF) procedures: cadmium, copper, mercury, nickel, plumbum, zinc, cobalt, iron, manganese, arsenic, selenium, antimony, bismuth (PND F 16.1:2:2.2:2.3.46-06); calcium (PND F 16.2.2:2.3:3.34-02); aluminum (Russian standard GOST 26485-85); Silicon dioxide (PND F 16.1:2:2.2:3.65-10); Moisture content (Russian standard GOST 5180-2015) (таблицы 12-14).

Table 12: Quantitative chemical analysis of ash and slag mix from handling system prior to inclusion of cyclone

Measured properties	Units of measurement	Results ± error			Measurement procedures
		X1	X2	Xmid
Cadmium	mg/kg	< 0.1	< 0.1	< 0.1	PND F 16.1:2:2.2:2.3.46-06
Copper	mg/kg	33.9	34.9	34.4±8.6
Mercury	mg/kg	< 0.1	< 0.1	< 0.1
Nickel	mg/kg	< 0.5	< 0.5	< 0.5
Plumbum	mg/kg	18	16	17±4
Zinc	mg/kg	< 1.0	< 1.0	< 1.0
Cobalt	mg/kg	< 0.5	< 0.5	< 0.5
Iron	mg/kg	15987	17323	16655±4164
Manganese	mg/kg	1245	1031	1138±285
Arsenic	mg/kg	< 0.1	< 0.1	< 0.1
Selenium	mg/kg	< 0.1	< 0.1	< 0.1
Antimony	mg/kg	< 1.0	< 1.0	< 1.0
Bismuth	mg/kg	< 1.0	< 1.0	< 1.0
Calcium	mg/kg	141326	150103	145714±36429	PND F 16.2.2:2.3:3.34-02
Aluminum	mg/kg	60.3	64.6	62±16	Russian standard GOST 26485-85
Silicon dioxide	%	58	58	58	PND F 16.1:2:2.2:3.65-10
Moisture content	%	1.3	1.3	1.3	Russian standard GOST 5180-2015

 

Table 13: Quantitative chemical analysis of ash from group cyclone

Measured properties	Units of measurement	Results ± error			Measurement procedures
		X1	X2	Xmid
Cadmium	mg/kg	0.40	0.45	0.43±0.11	PND F 16.1:2:2.2:2.3.46-06
Copper	mg/kg	70.9	81.6	76±19
Mercury	mg/kg	< 0.1	< 0.1	< 0.1
Nickel	mg/kg	< 0.5	< 0.5	< 0.5
Plumbum	mg/kg	16.0	15.5	16±4
Zinc	mg/kg	30.4	36.9	34±8
Cobalt	mg/kg	< 0.5	< 0.5	< 0.5
Iron	mg/kg	14582	14896	14739±3685
Manganese	mg/kg	980	898	939±235
Arsenic	mg/kg	< 0.1	< 0.1	< 0.1
Selenium	mg/kg	< 0.1	< 0.1	< 0.1
Antimony	mg/kg	< 1.0	< 1.0	< 1.0
Bismuth	mg/kg	< 1.0	< 1.0	< 1.0
Calcium	mg/kg	98235	97364	97800±24500	PND F 16.2.2:2.3:3.34-02
Aluminum	mg/kg	58.2	56.4	57.3±14.3	Russian standard GOST 26485-85
Silicon dioxide	%	74	73	74	PND F 16.1:2:2.2:3.65-10
Moisture content	%	1.0	1.0	1.0	Russian standard GOST 5180-2015

 

Table 14: Quantitative chemical analysis of ash from bag filter (bunker bags)

Measured properties	Units of measurement	Results ± error			Measurement procedures
		X1	X2	Xmid
Cadmium	mg/kg	0.32	0.36	0.34±0.08	PND F 16.1:2:2.2:2.3.46-06
Copper	mg/kg	42.8	37.8	40±12
Mercury	mg/kg	< 0.1	< 0.1	< 0.1
Nickel	mg/kg	< 0.5	< 0.5	< 0.5
Plumbum	mg/kg	13.2	14.4	14±3
Zinc	mg/kg	12.6	15.7	14±4
Cobalt	mg/kg	< 0.5	< 0.5	< 0.5
Iron	mg/kg	1215	1132	1174±294
Manganese	mg/kg	78	82	80±20
Arsenic	mg/kg	< 0.1	< 0.1	< 0.1
Selenium	mg/kg	< 0.1	< 0.1	< 0.1
Antimony	mg/kg	< 1.0	< 1.0	< 1.0
Bismuth	mg/kg	< 1.0	< 1.0	< 1.0
Calcium	mg/kg	44398	43879	44139±11035	PND F 16.2.2:2.3:3.34-02
Aluminum	mg/kg	< 5	< 5	< 5	Russian standard GOST 26485-85
Silicon dioxide	%	91	91	91	PND F 16.1:2:2.2:3.65-10
Moisture content	%	0.4	0.4	0.4	Russian standard GOST 5180-2015

Preparation to voltammetric analysis is illustrated in Figure 4.

Figure 4: Voltammetric analysis. Click here to View Figure

 

It follows from Table 12 that the slag and ash mix of Novocherkassk SDPP contains significant amount of calcium –145714 mg/kg; iron –16655 mg/kg; manganese – 1138 mg/kg; aluminum –62.47 mg/kg; silicon dioxide –58%, and copper – 34.4 mg/kg. Cadmium, mercury, arsenic, selenium, antimony, bismuth exist in trace amounts < 0,1 mg/kg. The results in Tables 13 and 14 evidence that cadmium, copper, plumbum, zinc, iron, manganese and calcium are contained in coarse and fine particles captured by group cyclone and bag filter. Aluminum, a light metal, is nearly completely captured by cyclone (57.3 mg/kg), since its content in the ash captured by filter is less than 5 mg/kg.

On the basis of quantitative chemical analysis of the slag and ash mix (Table 12) the composition of wastes in Table 15 was determined. The environmental hazard class of the waste was determined by calculations according to the Decree of Ministry of natural resources and ecology of Russian Federation No. 536, dated December 04, 2014 titled On approval of criteria of waste classification as environmental hazard classes I-V. It follows form Table 15 that the total value of K_iis 96.904, which is less than 100, hence, the waste is referred hazard class IV.

Table 15: Composition of wastes (ash and slag mix)

Components	Concentration of the i-th component in wastes, Ci, mg/kg	Coefficient of hazard level of the i-th component of hazardous waste for environment, Wi , mg/kg	Ki = Ci/Wi – hazard level of the i-th component of hazard waste for environment
Calcium oxide	204000.000	2154.43500	94.688
Water	13022.000	1000000.00000	0.013
Mineral components	758000.000	1000000.00000	0.758
Aluminum oxide	118.000	6812.92100	0.017
Iron (II, III) oxides	23000.000	37275.93700	0.617
Manganese (in terms of manganese (IV) oxide)	1800.000	4641.58900	0.388
Lead and its compounds	17.000	76.27000	0.223
Copper (II) oxide	43.000	215.44300	0.200
TOTAL:	1000000.000		96.904

Similarly, the hazard class of ash captured by group cyclone (Table 16) and that captured by bag filter (Table 17) were determined.

Table 16: Composition of wastes (ash removed by group cyclone)

Components	Concentration of the i-th component in wastes, Ci, mg/kg	Coefficient of hazard level of the i-th component of hazardous waste for environment, Wi , mg/kg	Ki = Ci/Wi – hazard level of the i-th component of hazard waste for environment
Calcium oxide	136920.000	2154.43500	63.553
Water	10000.000	1000000.00000	0.010
Mineral components	830987.570	1000000.00000	0.831
Aluminum oxide	108.000	6812.92100	0.016
Iron (II, III) oxides	20354.000	37275.93700	0.546
Manganese (in terms of manganese (IV) oxide)	1485.000	4641.58900	0.320
Lead and its compounds	16.000	76.27000	0.210
Copper (II) oxide	95.000	215.44300	0.441
Zinc	34.000	1467.79900	0.023
Cadmium	0.430	26.90000	0.016
TOTAL:	1000000.000	–	65.966

Table 17: Composition of wastes (ash removed by bag filter)

Components	Concentration of the i-th component in wastes, Ci, mg/kg	Coefficient of hazard level of the i-th component of hazardous waste for environment, Wi , mg/kg	Ki = Ci/Wi – hazard level of the i-th component of hazard waste for environment
Calcium oxide	61795.000	2154.43500	28.683
Water	4000.000	1000000.00000	0.004
Mineral components	929145.660	1000000.00000	0.929
Iron (II, III) oxides	4864.000	37275.93700	0.130
Manganese (in terms of manganese (IV) oxide)	127.000	4641.58900	0.027
Lead and its compounds	14.000	76.27000	0.184
Copper (II) oxide	40.000	215.44300	0.186
Zinc	14.000	1467.79900	0.010
Cadmium	0.340	26.90000	0.013
TOTAL:	1000000.000	–	30.166

It follows from Tables 16 and 17 that total value K_i(65.966; 30.166) is less than 100, hence, the waste is in hazard class IV.

Discussion

It is established that slag and ash mix of Novocherkassk state district power plant after coal combustion has the following composition: iron – 2.3%; mineral components – 75.8%; calcium oxide – 20.4%; aluminum oxide – 0.0118%; water – 1.3022%; manganese oxide – 0.18%; copper oxide – 0.0043%; plumbum – 0.0017%, it is referred to environmental hazard class IV. Hazard class IV leads to noticeable biocenos depression and occurrence of irreversible violations of natural spheres.

Analysis of ash color demonstrates that in total bulk the ash dust is of dark gray color. The ash captured by cyclone contains coarse particles of black color, and the ash captured by bag filter contains fine particles of light colors (gray-yellow color producing silky gloss). This is peculiar for ash dust after combustion of Donetsk culm. The main ash component of silicon dioxide, its content in the ash captured by filter reaches 91%. These fine particles create light tone of this ash.

Conclusions

The issue of disposal and reprocessing of slag and ash wastes is a global challenge. Slag and ash dumps occupy high surface areas, they are a source of pollution of environment, they are hazardous for human life, flora and fauna. Ash dumps are sources of accumulation of heavy metals (plumbum, copper, cadmium), they are characterized by increased radioactivity. Combustion products emitted into atmosphere result in acid rains and increase greenhouse effect, adversely effecting on total environmental situation.

The obtained experimental results evidence that ash and slag are valuable products, after their modification, for instance, by milling, they can be efficiently applied as additive for production of concrete, building materials, dry building mixes. This would permit to decrease cost of production of building materials and negative impact on environment. At present extraction technologies of calcium and iron are being developed.

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