CREATION OF SOLUTIONS BASED ON INDUSTRIAL WASTE TO STRENGTHEN FRACTURED SURFACES

ABSTRACT

Purpose of work is to conduct research on mining waste for use in the production of building materials. Object and subject of research. Object of study is enrichment tailings and embedded mixtures with and without additives based on them, and subject of study is physical and mechanical properties and features of hardening of embedded mixtures in natural wet conditions.

Research methods. To determine characteristics of input materials and composition of embedded mixtures and their physical and mechanical properties, standard methods were used, and XRF and IR were used to identify their physical and chemical properties.       Phase composition of waste was determined using DRON-3M diffractometer, chemical composition was determined by X-ray fluorescence spectrometer EDX-8000. Particle size distribution analysis was carried out using  Analizette 22 MicroTec Fritsch GmbH (Germany) device.

Results.  A review of foreign and domestic research on the utilization of various industrial wastes in the production of construction products is presented, as well as the results of the work of the Satbayev University Mining and Metallurgical Institute. The tailings of the processing plant of the Akzhal mine were studied as a filler for mixtures to strengthen the quarry sides weakened by fractured rocks, as well as damaged inter-chamber pillars and ceilings in underground workings.    Thus, based on waste from the processing plant, effective solutions have been obtained for strengthening and strengthening fractured rocks in areas of the quarry sides and in underground workings. The significance of the results obtained is the expansion and reproduction of the raw material base of the building materials industry through the processing of industrial waste and the development of resource-saving technologies. The results obtained can be used to improve the level of industrial safety at mines and minimize environmental risks caused by subsoil development.  The recycling of large-scale industrial waste, primarily from the mining, metallurgical and fuel and energy complexes, into building materials is cost-effective and aimed at solving environmental and social problems.

Results obtained can be used to improve level of industrial safety at mines and minimize environmental risks caused by subsoil development. Research results were considered at existing mining enterprises during projects implementation «Development of innovative methods for forecasting and assessing state of rock masses to prevent technogenic emergencies», “Integrated development of sustainable construction industry: innovative technologies, production optimization, efficient use of resources and creation of technological park”, and also used in educational process of university.

АННОТАЦИЯ

Цель работы — проведение исследований по использованию отходов горнодобывающей промышленности для производства строительных материалов.
Объект и предмет исследования. Объектом исследования являются хвосты обогащения и закладочные смеси на их основе с добавками и без них, а предметом исследования — физико-механические свойства и особенности твердения закладочных смесей в естественных условиях увлажнения.
Методы исследования. Для определения характеристик исходных материалов, состава закладочных смесей и их физико-механических свойств использовались стандартные методы, а также методы рентгенофлуоресцентного анализа (XRF) и инфракрасной спектроскопии (IR) для изучения их физико-химических свойств. Фазовый состав отходов определялся с использованием дифрактометра ДРОН-3М, химический состав — с помощью рентгенофлуоресцентного спектрометра EDX-8000. Анализ гранулометрического состава проводился с использованием прибора Analizette 22 MicroTec Fritsch GmbH (Германия).

Результаты. Представлен обзор отечественных и зарубежных исследований по утилизации различных промышленных отходов в производстве строительной продукции, а также результаты работы Горного и металлургического института Университета имени Сатпаева. Хвосты обогатительной фабрики Акжалского рудника были исследованы в качестве заполнителя для смесей, применяемых для укрепления бортов карьера, ослабленных трещиноватыми породами, а также повреждённых межкамерных целиков и перекрытий в подземных выработках.

Таким образом, на основе отходов обогатительной фабрики были получены эффективные решения для укрепления трещиноватых пород в зонах бортов карьеров и в подземных горных выработках. Значимость полученных результатов заключается в расширении и воспроизводстве сырьевой базы промышленности строительных материалов за счёт переработки промышленных отходов и разработки ресурсосберегающих технологий.

Полученные результаты могут быть использованы для повышения уровня промышленной безопасности на горнодобывающих предприятиях и минимизации экологических рисков, вызванных освоением недр. Переработка крупнотоннажных промышленных отходов, прежде всего горно-металлургического и топливно-энергетического комплексов, в строительные материалы является экономически целесообразной и направлена на решение экологических и социальных проблем.

Результаты исследований были учтены на действующих горнодобывающих предприятиях при реализации проектов «Разработка инновационных методов прогнозирования и оценки состояния горных массивов для предотвращения техногенных аварий», «Комплексное развитие устойчивой строительной отрасли: инновационные технологии, оптимизация производства, эффективное использование ресурсов и создание технологического парка», а также использованы в учебном процессе университета.

Keywords: mining waste, enrichment tailings, backfill mixtures, building materials, physical and mechanical properties, hardening, natural moisture conditions, phase composition, particle size distribution.

Ключевые слова: горные отходы, хвосты обогащения, закладочные смеси, строительные материалы, физико-механические свойства, твердение, естественные условия увлажнения, фазовый состав, гранулометрический состав.

Introduction. In the mining and metallurgical complex (MMC) of the Republic of Kazakhstan, over many years, large volumes of waste from overburden rocks and enrichment tailings, slags have been accumulated. Among them, waste from non-ferrous mining and metallurgical enterprises occupies a special place, and the largest reserves are concentrated in tailings dumbs [Table 1]. Since enrichment waste is a finely ground product that does not require additional grinding before use, this reduces economic costs. In addition, process of ore enrichment ensures homogeneity of material both in chemical and mineralogical composition.

Millions of tons of harmful substances are released into the atmosphere and hundreds of millions of cubic meters of polluted wastewater are discharged into water basins. All this leads to serious economic, social and environmental problems. According to modern estimates, enterprises of mining complex of Kazakhstan have accumulated over 50 billion tons of industrial waste and occupy vast territories (more than 150 sq. kilometers of area). Every year, amount of industrial waste increases by approximately 1.5 billion tons, and at the same time, level of use of solid waste is currently low [1].

            Table 1.

Technogenic waste reserves at large mining enterprises

Expansion of the mineral resource base of the building materials industry can be achieved not only by searching for new deposits of non-metallic minerals, but also as a result of involving non-technogenic waste of non-metallic raw materials in production. Technogenic raw materials, as a rule, require industrial processing and evaluation using effective methods and technologies that ensure their full use with maximum preservation of the environment.

1. Comparative analysis. Growing scale of construction in Kazakhstan requires significant amount of mineral raw materials for building materials industry. Intensification in this direction involves use of industrial waste instead of primary natural resources to reduce cost of building materials. Use of solid mining waste in building materials industry is more economical compared to production of building materials based on special mining of mineral raw materials [2-4].

Review of existing scientific works in this area shows that there is significant world practice of conducting research on use of technogenic mineral raw materials. Thus, in foreign countries, mining waste is used to produce bricks, concrete, and glass ceramics [5-7]. Construction materials were obtained from overburden rocks of the Tatar rare metal deposit in the Krasnoyarsk Territory, where concentrates were used as a filler for lightweight concrete, for preparation of plaster mortars, and in environmental protection measures [8-10].

Similar studies on use of mining waste to obtain construction materials and products are being carried out in the Republic of Kazakhstan [9-11].

The use of additives from polymetallic ore tailings increases properties of cement mortars for strengthening fractured rocks. It has been established that developed embedded mixtures with a given high adhesive strength based on enrichment tailings contribute to creation of waste-free technologies for processing mineral raw materials, reducing cost of main industrial products and production building materials, solving environmental problems.

Rational organization of waste recycling process in combination with efficient modern equipment makes it possible to obtain products from secondary raw materials at a cost 2-2.5 times lower than for similar products from primary raw materials, with comparable product quality.

The need to involve enrichment tailings in production is dictated by the following circumstances:

production of enrichment tailings is dictated by following circumstances:

- service life of tailings dumps is limited; filling of many has already been completed or will end in the coming years;

- tailings occupy vast territories and, since they are finely dispersed and easily blown away material, are a source of increased environmental risk for regions where mining and processing complexes operate.

Since enrichment waste is a finely ground product that does not require additional grinding before use, this reduces economic costs. In addition, process of ore enrichment ensures homogeneity of material both in chemical and mineralogical composition. Current and priority direction for recycling above-mentioned waste is using it to obtain construction materials. Review of existing scientific works in this area shows that there is world practice of conducting research on use of technogenic mineral raw materials. Analysis shows that almost all types of construction materials production are experiencing steady growth.

2. Research methods. To determine characteristics of input materials and composition of embedded mixtures and their physical and mechanical properties, standard methods were used, and XRF and ICS were used to identify their physical and chemical properties.

X-ray phase analysis (XPA) was carried out on a DRON-3M X-ray installation (RF) and X-ray structural analysis was carried out with a JCXA-733 “Superprobe” microanalyzer (Japan) with software, scientific research to study waste structure using laboratory polarizing microscope Leica ICH DM2500 (Switzerland), equipped with a powerful 100 W illuminator, which allows you to comfortably work with differential interference contrast; differential thermal analyzes (DTA) were carried out on a derivatographic device MOM-1500 D (Hungary); chemical analysis and microhardness tester PMT-3 (RF). Particle size analysis was performed by three methods: sieve analysis using a multi-frequency sieve analyzer MSA W/D-200 Kroosh Technologies Ltd.; granulometric analysis using a diffraction laser particle size analyzer Helos-KR with Quixel attachments; dispersion analysis in an apparatus for dispersion analysis of powders ADAP type.

3. Presentation of material and discussion.

  Currently, Satbayev University is conducting research on use of mining waste to obtain  solutions components for strengthening disturbed rocks on the sides of quarries and underground workings.

3.1. Research and method development for strengthening fractured rocks on sides of a quarry. Results of sides examination of the Akzhal quarry of Nova-Zinc LLP showed that the largest number of fallouts are confined to fractured rocks, and volume of fallouts increases as sides of quarry stand. Observations of workings driven through fractured rocks revealed that they were stable for a month. After two to three months, cracks up to 10-15 cm in size are formed. Spalling and fallouts develop within six months, roof collapse occurs in the form of domes. This dramatically increases volume and labor intensity of tunneling work, as well as the costs of securing and repairing workings.

Study of rock fracturing and methods development for controlling their properties was carried out for conditions of the Akzhal field. Analysis of mining and geological conditions of the deposit and workings state driven through disturbed rocks showed that systems of steeply dipping cracks have a great influence on workings stability. Deposit is represented by fairly strong rocks and, as a result of folding processes, they were broken by a large number of faults of various orientations. Among these disturbances large tectonic disturbances and small cracks are identified. Intensity of various types of cracks in the rock mass was determined by measuring them using a 1 m long rod or ruler (Fig. 1).

а                                                         b  

Figure 1. Intensity measuring of fracturing in rock mass

One of the most common methods of strengthening is rock cementation. Cementation of rocks in quarries begins from the upper platform of the ledge, where fans of vertical and inclined wells are drilled. Cement mortar is injected into them until mass is completely saturated. Cement mortar is prepared based on cement and water. Technical result is to increase reliability of strengthening slope of quarry benches and to prevent shedding of rocks from surface of slope using mining and metallurgical waste.

This method of ensuring slopes stability and benches of quarries is a complex task, solution of which should include not only determining parameters of stable slopes, but also managing them to achieve better economic results and natural resources. Main task is to develop strengthening solutions at a low cost, with high strength [12].

Essence of this method is that screening inclined wells are drilled parallel to future surface of slope and they are blown up; crushing zones are created, additional inclined wells are drilled, where they install reinforcement and fill them with strengthening solution. Then, wells are drilled at the ledge site, anchors are secured in them, and cables are pulled between reinforcement and anchors. During using this method in existing quarries, we were convinced that method reliably strengthens quarry bench, but is complex.

To achieve this result in the proposed strengthening method of slope of quarry benches, which involves creating a crushing zone by drilling screening inclined wells parallel to future surface of slope and blasting them; After removing blasted rock mass and cleaning surface of slope, reinforcement with hooks is hammered in so that it is adjacent to future surface of slope. A chain-link mesh is attached to hooks over entire surface of slope, and then a layer of strengthening solution is applied to it. Moreover, strengthening solution is prepared based on tailings of quarry processing plant.  

Method is carried out as follows (Fig. 2, a - working platform in plan; b - strengthening quarry slope in isometry):

 а                                                         b  

Figure 2. Description of the method

 a – working platform in plan; b - strengthening quarry slope in isometry

1- Working platform of open cut slope;  2- Inclined hole;  3-Slope surface; 4-Crashing zone; 5-Fittings; 6- Detents; 7-Metal lath; 8-Strengthening solution layer

Based on research, we have proposed solution for strengthening fractured rocks, containing filler, cement, and process water. To reduce solution cost it is proposed to use tailings from enrichment factories as a filler, which are large-tonnage production waste and large areas are allocated for their storage.

Dry superplasticizing additive Neolit 400, which is produced by Neochim with high water-reducing ability and makes it possible to reduce water-binder ratio in systems by more than 20%. By decreasing water-binder ratio, durability and density of solution being developed increases, with a simultaneous decrease in shrinkage and creep deformations as solutions gain strength. The additive is well compatible with Portland cements, cement - up to 37%, tailings from processing plants - up to 52%, superplasticizer Neolit 400 - 0.11-0.16 and the rest is water. Ratio of components shown was obtained experimentally in laboratory conditions. To determine strength, samples of 4x4x16 cm are molded from mixture and compacted on a vibrating platform for 45 seconds, after a day they are removed from molds and stored in humidity conditions for 28 days (starting value), and then physical and mechanical tests are carried out, results of which are presented in table 2.

Table 2.

Physical and mechanical properties of solution

Thus, use of solution described above ensures strengthening of weak areas of sides and can significantly reduce harmful effects of waste from processing plants on environment. Technical novelty of created solution was confirmed by patents of the Republic of Kazakhstan for invention [14]. 

3.2. Development of effective solution for strengthening fractured rocks in underground mines

Analysis of mining and geological conditions of the Akzhal deposit and state of underground workings driven through disturbed rocks showed that rock cracking has a great influence on the stability of workings. Different strength characteristics of rocks in the massif and their sharp decrease upon exposure and contact with air and water predetermine need for a differentiated approach to managing properties of rocks with varying degrees of fracturing. One of the most common methods is shotcrete strengthening of disturbed areas, that is, injection of cement mortar until massif is completely saturated.

To strengthen disturbed fractured rock masses in underground mines, authors of article proposed effective shotcrete solution. Technical result is recycling of mining waste and tailings from processing plants, achieving high fluidity of solution, adhesion to rocks and strength of resulting solution.

To achieve this result, following raw materials were studied: Portland cement PC 400, produced by Central Asia Cement JSC (Karaganda region, Kazakhstan), enrichment tailings from Akzhalskaya Concentrator Plant, functional additive Reparatur, produced by Ading (North Macedonia) and polycarboxylate additive “Neolit 400” (Russia).

Justification for choice of source materials:

1. Use of Portland cement PC 400- produced by Central ASIA cement JSC, is due to location of plant for its production near Balkhash city, not far from the Akzhal mine.

2. Choice of tailings from the Akzhal enrichment plant (EP) is explained by the fact:

- to improve ecological situation of region’s environment through their complete recycling with environmental and economic efficiency;

- to use carbonate composition of tailings to develop special cementing solutions for purpose of more effectively strengthening rock cracks in underground workings with them

3. Use of dispersive polymer powder (DPP) - the Reparatur additive from the Ading company (North Macedonia) in above-mentioned solutions is associated with its properties - increasing the adhesion strength to surface of rock cracks.

4. Use of dry superplasticizing (SP) additive “Neolit 400” (Russia) in the composition of cementitious mortars is due to its high water-reducing properties. By decreasing the water-binder ratio, durability and density of solution being developed increases, with a simultaneous decrease in shrinkage and creep deformations as solutions gain strength.

Figure 3 shows an x-ray diffraction pattern, where it mainly shows reflections (peaks) characteristic of calcium carbonate (CaCO₃), with interplanar distances d, Å: 3.8665; 3.3498; 3.0404; 2.8446; 2.496; 2.2847; 2.0952; 1.9127; 1.77; 1.6287; 1.60; 1.5236; 1.4393. Figure 3 shows DTA analysis, where the endo-effect is recorded at 950 °C, showing dissociation of limestone.

Figure 3. X-ray of the tailings of the Akzhal processing plant

Figure 4 shows DTA analysis, where the endo-effect is recorded at 950 °C, showing dissociation of limestone.

Figure 4. Derivatogram of the tailings of the Akzhal processing plant

Analysis of the mineral and chemical composition of the nonmetallic rock of the Akzhal lead-zinc deposit shows that it mainly consists of calcite - СаСО₃ (about 95...97%) and silica - SiO₂ (about 2.5%); among them there are also impurity elements of magnesium, iron, aluminum, zinc, lead, barium, etc., which are not of industrial interest, since their total content does not exceed 1% [15].    

Tailings from Akzhal processing plant ore enrichment mainly consist of calcite and silica, oxide chemical composition of which is represented by the following individuals: CaO - 54.3; CO₂ - 40.5; SO₃ - 2.3; SiO₂- 1.5; MgO - 1.4 and Fe[S₂]- 0.13%.

Mine and waste process water, respectively, have following characteristics: alkalinity - 0.45 and 0.8; hardness - 11 and 12; pH -7.5 and 8.3. Moreover, the mine one is transparent, and the technological one is turbid, which contains ore enrichment tailings, consisting mainly of calcite - СаСО_3.

Fig.5 shows effect of Neolit 400 SP on strength of samples, from which it can be seen that:

• During injection of SP, samples strength increases by 3...27% compared to their strength without additive;
• At the same time, the more cement in the mortar mixtures, greater positive effect of joint venture on strength; for example, with a cement consumption of 69 kg/m³ and with its optimal content (0.3%), increase in the samples strength in its presence reaches 11%, and with a cement consumption of 265 kg/m³, increase in the strength of samples reaches 29%;
• Positive effect of SP content passes through a maximum, based on this, it can be stated that optimal dosage of the plasticizer is 0.3% of cement content.

Figure 5. Dependence of sample strength on Neolit 400 SP

Thus, composition has been selected to strengthen fractured rocks in underground mines. Components for preparing solution are taken in the following ratio: Portland cement PC 400 - up to 18%, tailings from processing plants - up to 71.2%, "Reparatur" additive - 1.5%; superplasticizer Neolit 400 – 0.3%;  rest is water (water-cement ratio is about 0.5) - 9%.

After dosing components, cement, tailings and additives are loaded into a concrete mixer and mixed thoroughly. Then add water and mix. Finished composition is delivered to underground workings and injected into cracks of disturbed underground mine workings.

To determine strength, samples of 7x7x7 cm were molded from composition and compacted on a vibrating platform for 45 seconds. A day later, samples were removed from molds and stored in humid conditions for 28 days, and then physical and mechanical tests were carried out, results of which are presented in Table 3.

Table 3.

Physical and mechanical properties of the resulting solution

Technical novelty of created solution was confirmed by patents of the Republic of Kazakhstan for invention [16].

Conclusions

1. Use of mining waste as additives or components for production of various building materials contributes to creation of low- and waste-free technologies for processing raw materials, the rational use of mineral resources, and solution of  environmental problem of the biogeo-ecotope - ecosystem.

2. Results of study showed that waste from the Akzhal enrichment plant is an effective component in the production of building materials. Solutions for strengthening fractured rocks were created and put into production, based on MMC waste using polymer powders, which have low cost, sufficient fluidity to fill small cracks and high strength. An increase in the amount of tailings from processing plants by more than 50% will lead to a decrease in the fluidity of the solution and its adhesion to rocks, and a decrease by less than 45% will increase the cost of the composition.

Acknowledgment, funding: This research was carried out within the framework of grant funding from the Ministry of Science and Higher Education of the Republic of Kazakhstan BR21882292 “Integrated development of sustainable construction industry: innovative technologies, production optimization, efficient use of resources and creation of technological park”

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