Scientific substantiation of complex extraction and processing of secondary resources for the development of alternative sources of energy

Scientific research on the integrated extraction and processing of secondary resources, such as mine water, technogenic waste, and others, in order to develop alternative energy sources in the diversification of coal mines is an urgent scientific task that will help solve the issues on the economic, social and environmental transformation of coal mining regions. In practice, it is necessary to consider several alternative options and assess the possibility of obtaining different end products from the targeted processing of secondary raw materials. The choice of a rational processing option to obtain the target product is very complicated due to the different composition of the feedstock, as well as a significant variety of primary processing methods and parameters of intermediate processes, which causes certain difficulties in forecasts and calculations. Developing a methodology for typifying actions when choosing options for integrated processing of recyclable materials of different states, defining the basic principles and its structure for comparative analysis of the input, intermediate, and output parameters in terms of composition, physical, chemical, and technological characteristics are urgent modern tasks.


1.Introduction
The global coal industry is currently in a slow decline.This is mainly due to the fact that many governments are seriously developing environmental policies while continuing to reject this energy source as unfriendly.As is well known, one of the main sources СО 2 of emissions is the combustion of carbon-containing fossil fuels, primarily coal.Therefore, most EU countries plan to phase out the use of coal for electricity generation by 2038.
The development trend of international energy markets has always influenced the development and stability of the energy sector, in particular, the coal sector in Ukraine.Therefore, the slightest changes in its performance clearly affect the country's economic sector as a whole.Thus, an increase in the activity of the coal sector ensures the growth of the state's economic potential, and vice versa -the emergence of crises immediately affects the energy sector.
Ukraine's coal industry accounts for about 4% of the world's proven coal reserves, making it one of the top ten global leaders in terms of proven reserves [1].The main consumers of steam coal are power generating companies, which account for 47% of all electricity (Figure 1) [2].
Figure 1 -Segments of the Ukrainian electricity sector: 1 -thermal power plants; 2 -nuclear power plants; 3 -hydroelectric power plants and pumped storage; 4 -other [2] Therefore, the vital activity of the domestic thermal power industry depends on the uninterrupted supply of anthracite coal to thermal power plants.The current situation in the global coal industry is such that it is inevitable that coal deposits will be depleted and coal mines will be closed.These circumstances create environmental and social problems.The current situation associated with the massive closure of mines in coal mining regions, especially in single-industry towns, has created the problem of so-called "depressed areas" and led to the need to diversify the activities of unprofitable coal enterprises that have exhausted their resources and, accordingly, to move to new knowledge, principles and technological levels.

2.Methods
Technogenic deposits formed as a result of mining and processing plants are promising sources of raw materials, but they have always been difficult to work with for a number of reasons, the main of which is the high level of knowledge intensity.However, the prospects of implementing recycling technologies are undoubted and lie in obtaining additional raw materials from production waste by extracting the maximum possible minerals.
In early 2020, the Ministry of Energy presented the Concept of Ukraine's Green Energy Transition until 2050 [3].Focus on gradually reducing the use of coal for energy production.In addition, difficult geological conditions of mining depleted seams and reserves, and the high cost of coal create problems in the coal industry and prompt this step.In addition, Ukraine is a signatory to the Paris Agreement [4].Therefore, the transition to alternative and renewable energy sources is relevant for our country.
In view of the above, let us define the strategic goals of diversification toward the use and processing of carbon-containing raw materials from technogenic deposits: -focusing on improving the environmental condition of the region where coal mining companies are located; -freeing the region's lands from coal enrichment and coal mining wastes and returning them to the agricultural fund or for free sale; -application of advanced environmentally clean technologies for processing coal, coal preparation waste, and coal mine methane to produce electricity and heat for self-sufficiency or sale to consumers; -expanding the range of industrial products manufactured using electricity and heat; -development of technologies for combustion of water-coal mixtures as alternative fuels to replace traditional ones.
To ensure the processing of a technogenic deposit, it is necessary to conduct a comprehensive analysis of the physical, mechanical and physical and chemical properties of waste, chemical composition and structural characteristics, which will allow selecting effective technologies forthe extraction of a useful component.In addition to the requirements to increase the efficiency of development and the well-known environmental component, the main reasons for the development of technogenic deposits can be identified: depletion of existing deposits, which leads to an increase in the volume of technogenic deposits; the need for more complete utilisation of the resulting rock mass through integrated processing; insufficient application of innovations in mining technology; increased negative environmental impact due to the growth of technogenic deposits; increased liability under the law for the creation and improper use of subsoil.
Next, we identify the main areas of dumps use depending on the type of waste.Based on this, it is possible to group the dumps by the mining or processing technologies that led to their formation.Waste dumps may be generated from the activities of an extractive or processing enterprise in the following forms and conditions: dumps formed after open-pit mining; dumps and waste heaps from underground mining; sludge ponds formed after beneficiation or processing.Consequently, all waste can be grouped according to common features, which are divided by the type of mineral that can be extracted from it and the technology of its extraction.
When deciding on the development of dumps, in addition to the main factor, such as the content of the useful component, the following factors should be taken into account for extraction from the dumps: methods of dump formation, their age, and properties of the soils contained in the dump.
The period of formation of dumps for mining can be divided into three parts: the first -1 -5 years; the second -5 -15 years; the third -15 -80 years, which affects the physical and mechanical properties of rocks, their density, caking, and water permeability.
Given the sources of formation of technogenic deposits and the influence of parts of each of them, it is proposed to group the methods of extraction of useful components contained in technogenic deposits.
Several approaches can be used to describe carbon-containing raw materials as an object of study.Firstly, it can be thought of as a binary mixture of coal and rock produced by the use of shearers or redheads.At the same time, the formation of the coal grade composition and the amount of rock depends on the type of combines and the cutting tools used [5].
Secondly, the feedstock can be a mechanical binary mixture of coal and rock that arrives at the concentrator with an ash content of ordinary coal.At the beginning of 2021, there were 51 coal preparation plants in Ukraine with a total production capacity of 148.7 million tonnes.It is known that the operating factories were distributed according to their intended purpose as follows: 19 for coking coal; 19 for steam coal; 23 for anthracite.Factories that enrich coal for coking have a depth of 0 mm and use flotation to enrich slurry.Steam coal enrichment is characterised by schemes with separation of 0-6 mm and enrichment of one class of 6-100 (150) mm in jigging machines or two classes: 6-25 mm in jigging machines and 25-150 (200) mm in heavy surroundings [6].
Third, carbon-containing feedstock can be a mechanical mixture of coal and rock particles formed during beneficiation and fed to the sludge pond in the form of coal sludge, a finely dispersed and highly ash product with high humidity.They can contain from 30 to 86% combustible substances and be used as fuel.However, their sales are limited due to their fine grain size, high moisture content and ash content.
The Law of Ukraine "On Subsoil", among the main principles of the subsoil use policy, encourages subsoil users to "rationally and comprehensively use subsoil to ensure environmental safety» [7].The Law of Ukraine "On Approval of the National Programme for the Development of the Mineral Resource Base of Ukraine until 2030" [8] among the ways of solving existing economic problems is "introduction of rational methods of development of complex deposits and extraction of related components" as one of the main steps.
Integrated development of the deposits will increase the specific value of the extracted minerals and, therefore, reduce the minimum commercial grade limit and expand the development contours, increase the depth of the pit and thereby bring additional mineral reserves into production.On the other hand, if the open pit contour remains unchanged, it is possible to reduce the operating stripping ratio and, consequently, the cost of production [9].
The main areas of integrated development of deposits include: processing of by-product minerals extracted during mining operations; processing of rocks placed in the dumps and suitable for industrial development; processing of beneficiation waste in the tailings and sludge ponds to more fully extract useful components.The technical feasibility of extracting useful components is determined by their content and technological properties.The technical and economic assessment of the feasibility of developing technogenic deposits and the justification of conditions are carried out taking into account the supply and demand for this raw material in the market, the company's economy, the availability of production facilities and the possibility of their reconstruction or construction of new processing complexes, environmental damage, etc.
The gap between the volume of waste accumulation and the volume of waste disposal and neutralisation is deepening the environmental crisis.At the same time, the cost of obtaining primary raw materials for industrial production is steadily increasing.Recently, these factors have been compounded by the problem of Ukraine's resource dependence on external sources of many types of raw materials.All of this demonstrates the importance of recycling.Therefore, the problem of waste should be considered as part of a unified approach to socio-environmental, resource and technological aspects, as a set of three components (problematic aspects) [10, 11]: -resource (development of secondary resource use); -environmental (achievement of environmental safety); -methodological and organisational (scientific, methodological, information and analytical, organisational and legal support for decision-making and regulation).
The resource and environmental aspects of the waste problem have both independent and joint, integral goals, and a separate area is the development of means and methods to address this problem.As a raw material potential, waste can largely replace primary resource sources, thus reducing overall resource consumption.At present, the vast majority of waste is either not used at all or is used according to the simplest technological schemes that do not ensure the full realisation of its resource potential.Therefore, the resource aspect goal block provides for: -determining the resource value of waste and the technological capabilities of its integrated processing; -identification of opportunities to replace primary raw materials with secondary raw materials and recycling; -economic justification of areas and ways of using waste; -creation of a system of resource-closed territorial and production links based on inter-sectoral cooperation, cascade production design.

3.Results and discussion
According to studies [12], the most rational is the processing of technogenic waste, high-ash coal, coal mine methane and other local cheap heat carriers in low-power thermal energy complexes (LTEC) based on coal enterprises for combined heat and power generation.This idea combines the processes of coal mining and its conversion into heat and electricity within a single mining and energy complex, while eliminating the vast majority of intermediate technological operations, which opens up the possibility of significantly improving the economic efficiency, environmental friendliness and safety of the entire complex, and generating electricity from thermal consumption allows for a fairly high efficiency of about 90%, which is impossible for powerful power plants today.Ukrainian coal enterprises spend up to 17% of their coal production on energy supply.And while heat is mainly provided by their own unprofitable boiler houses, electricity is purchased from the grid at a monopoly price, which directly affects the profitability of coal mining companies.Coal mines have all the necessary conditions for creating thermal power plants: a large land allotment; a surface technological complex with an administrative and utility plant; coal, material and timber warehouses; mechanical workshops; transformer substations; stationary installations; railway tracks; motorways; high-voltage power lines, etc.; as well as sludge ponds, water treatment plants and waste heaps.
In general, a combined heat and power plant can include a coal mine, a power module and a process module (Figure 2), where: Fuel module (coal mine) -designed to provide the power module with the required amount of fuel, which can be used as low-grade coal, coal preparation waste, coal mine methane, etc.
Energy module -designed for simultaneous generation of heat and electricity for self-sufficiency and the possibility of selling surplus heat and electricity to third-party consumers, can be made both on the basis of steam turbine generation and gas piston cogeneration.
IOP Publishing doi:10.1088/1755-1315/1319/1/0120086 Technological module -implements the principles of energy and technological processing of fuel at the place of its extraction using own heat and electricity, the possibility to start production of related products, for example, it can be a brick factory, various agricultural companies and other industries with the production of highly liquid goods, such as synthetic petrol, diesel fuel, hydrogen.
The specifics of coal industry enterprises determine the formation of diversification models: 1) Use (utilisation) of concomitantly mined or obtained during primary processing (enrichment) of carbon-containing raw materials.The model features the need to extract and process associated rocks in all development options.Examples include overburden mining and crushed stone production.
2) Integrated use of carbon-containing raw materials, which involves the targeted extraction and processing of other minerals in addition to the main one in demand.The specifics of the model are determined by the qualitative characteristics of the mineral, significant additional investments required for the main processes and infrastructure development, and the complexity of the technological and organisational structure of the enterprise.
3) Comprehensive development of the subsoil of a deposit, which uses the infrastructure created for the extraction of the main or additional minerals for the purpose of developing the underground space.
4) Diversification and production of new products using additional resources.5) Diversification of production and launch of new products from previously produced semifinished products on an innovative basis.
6) The deepest possible processing of raw materials with the integrated use of all possible useful components through production diversification to expand the product range and apply new modern technologies for processing carbon-containing raw materials.
7) Production of new types of products based on increased processing depth and integrated use of mineral raw materials, as well as increased production volumes during the modernisation and reconstruction of existing operations.
The principle of technological efficiency envisages a comprehensive approach to the development and use of existing technologies for processing technogenic waste: 1. Firstly, it is necessary to account for the generated and accumulated waste, study the composition of technogenic deposits, and consolidate existing waste processing technologies into a single information base.Information provided will allow new enterprises to adapt more easily in terms of choosing the most efficient waste processing technologies and convenient production sites, and will serve as a basis for project and research activities in this area and a basis for attracting investors.
2. Secondly, it is necessary to conduct scientific and practical developments of innovative technologies for processing technogenic waste.Both scientists and enterprises are interested in this, and the exchange of scientific experience will lead to an even faster solution to this environmental problem.To develop innovations in the field of technogenic waste treatment, it is necessary to use the dynamics of relations between the state, science and business -the three main factors of the innovation system.

Figure 2 .
Figure 2. Scheme of LTEC based on the coal enterprise [13] Official Bulletin of Ukraine 2016: The Paris Agreement[Internet]. Available from: zakon.rada.gov.ua[5] Kyrychko S and Semenenko Ye 2012 Calculation of parameters of hydrotransport of highly concentrated hydraulic mixtures during the development of technogenic deposits Socio-economic and environmental problems of the mining, construction and energy industries 203-08 [6] Semenenko Ye and Kyrychko S 2012 Improvement of the methodology for calculation of hydraulic transport parameters Hydroaerodynamics in engineering practice 69-70 [7] The Subsoil Code of Ukraine [Internet].Available from: zakon.rada.gov.ua[8] Law of Ukraine: On Approval of the National Programme for the Development of the Mineral Resource Base of Ukraine for the Period up to 2030 [Internet].Available from: zakon.rada.gov.ua[9] Medvedieva O, Lapshyn Ye, Koval N, Zeynullin A and Gupalo O 2020 The resource-saving technology to restore the accumulation ability of tailing ponds.E3S Web of Conferences 168 https://doi.org/10.1051/e3sconf/202016800054[10] Semenenko Ye, Stepan K, Medvedieva O, Nykyforova Nand Tatarko L2019 Calculation of pressure loss and critical velocity for slurry flows with additive agents in vertical polyethylene pipelines E3S Web of Conferences 109 https://doi.org/10.1051/e3sconf/201910900083[11] Blyuss В, Semenenko Ye, Medvedieva O, Kyrychko S and Karatayev A 2020 Parameters determination of hydromechanization technologies for the dumps development as /doi.org/10.33271/mining14.01.051 [12] Bulat A and Chemeris I 2006 Scientific and technical bases of creation of mine cogeneration power complexes (Kyiv:Naukova Dumka) p 175 [13] Slobodiannykova I 2023 Prospects for the diversification of the coal mines at the present stage Materiały Szkoły Eksploatacji Podziemnej 601-07