Latest developments in the utilization of coal mining wastes

Purpose The aim of the work presented in this paper was the construction of a regression model describing the relationship between the experimentally determined value of the maximum temperature observed during the coal mine waste fire and physicochemical parameters characterizing the coal mine waste. Methods The model was constructed with the application of the Partial Least Squares method. The experimental data analysed was acquired through the use of a laboratory test stand with a fixed bed reactor and analytical method of gas chromatography. Results The constructed model was characterized by a good fit of the data used in its construction and the strong predictive ability for the new data. It illustrated the significant impact of the content of H and Fe2O3 and trace elements: Co, Cu, Pb, Sr, V and Zn in a sample on the value of the maximum temperature reached during the fire of coal mine waste. Practical implications The practical importance of the work presented is clear in the light of the role of coal in the Polish economy and environmental aspects related to coal mining and the coal-based energy sector, in particularly to coal waste disposal and utilization. The model constructed contributes to the development of methods of self-ignition and fire risk assessment on coal waste dumps by determining the relationship between waste dump fire occurrence, the temperature observed during the fire and the physicochemical parameters characterizing the coal mine waste. Originality/value The novelty of the study presented in the paper consists in both finding the relationships modelled and the data extraction methods applied in the research field concerned.

In an effort to assist the coal industry in complying with the applicable regulations, to design safe and environmentally acceptable disposal systems, and to encourage secondary use of coal mine waste, the US Department of Energy has initiated research programs to develop coal mine waste disposal and use technology. This study of the properties of mine wastes in the Midwestern coal fields has been limited to the waste materials obtained from underground coal mines and preparation plants attached to both underground and surface mines. The program has been divided into two phases. In Phase I, the 20 most important properties relevant to safe disposal, reclamation, underground disposal, and secondary uses have been identified. An inventory of the significant waste disposal sites in the Midwestern coal fields has been prepared. The site locations have been plotted on USGS maps. Estimates of coal production and coal mine waste production during the next 2 decades have been prepared and are presented in this report. Also, all available information obtained from a search of existing literature on physical and chemical properties, including analysis results of the general runoff from the refuse disposal areas, has been collected and is presented. In order to fill the gaps in information, 20 sites have been identified for drilling and sampling to determine the various physical and chemical properties. They have been selected on the basis of the distribution and quantity of waste at the existing locations (both abandoned and active), the future trends in production and likely locations of waste disposal areas, their geographical and geological distribution, and ease of accessibility for drilling and sampling.

The aim of the study was to evaluate the effect of coal mining waste and its mixtures with municipal sewage sludge and waste rock wool from cover crops on the formation of selected properties of degraded anthropogenic soil. Under the conditions of a pot experiment, coal mining waste and its mixtures with 2.5 and 5% sewage sludge and mixtures supplemented with 1% addition of waste rockwool from cover crops were introduced (in a ratio of 1:1) into the degraded anthropogenic soil. White mustard was grown on the substrates in the first year and maize in the second year. The pH, EC, and sorption properties were determined in soil samples taken before of the plants and after their harvest. The results showed that the addition of coal mining waste and its mixtures with municipal sewage sludge and waste rock wool improved the soil pH and sorption properties. The management of coal mining waste and waste optimising its properties for the production of fertilizing agents can be an effective strategy within a circular economy, which at the same time will increase the efficiency of the management of degraded and poor-quality soils.

Recovering Combustible Matter from Coal Mining Waste and Measures to Extinguish Waste Pile Fire

Globally, coal mining wastes (CMWs) are associated with significant environmental and economic costs. Processing CMW into an ingredient of foam concrete is a promising solution but the behaviour of this particular construction material has not been sufficiently evaluated, especially during the initial period of cement hydration. The purpose of this paper is to present novel laboratory set-up and experimental procedures designed to investigate the early age behaviour of hydrating foam concrete samples made with a CMW from Poland. Two types of tests were devised to simulate air-curing conditions and water-curing conditions, respectively. These tests were carried out in custom-built unsaturated oedometer cells, and the matric suction in the test samples was monitored for approximately 14 days, using Warwick high capacity tensiometers. Experimental results show that in both curing conditions, a higher matric suction during cement hydration corresponds to a denser sample at the end of the monitoring period. A comparison of water-cured and air-cured samples also reveals different responses to CMW inclusion in their mix designs. The responses can be convincingly explained based on complementary test data and idealised capillary tube models adapted for the hydrating foam concrete samples.

Coal production and export are important to the Australian economy. The economic benefits of coal production in Australia, however, come with some sustainability challenges, a major one being the generation of large volumes of waste and the associated environmental issues. Sampling and characterization of some Australian coals and waste have shown promising elevated concentrations of rare-earth elements (REE) with the potential for economic extraction. This represents a significant opportunity to derive additional value from coal production and utilization. CSIRO has developed a multilayered framework from which optimal mine waste utilization pathways may be determined, based on the characteristics of tailings and other wastes. It involves tailings and waste characterization, reprocessing and repurposing, and reuse of the remaining waste resulting in a step-change in the sustainability of coal production. In this paper, we discuss two approaches to capture value from coal mining waste while reducing the safety and environmental risks associated with tailings and waste storage facilities. One aspect of the study involves sampling from selected coal basins and determining REE content in coal-based resources. Identified samples with elevated REE are being used to develop innovative REE beneficiation and extraction technologies in an environmentally acceptable manner. The second aspect of the study involved the use of the washery waste in producing geopolymer concrete products for construction purposes. This part of the study examined the use of coal mine tailings as source material in alkali-activated binder to produce geopolymer concrete. It also studied the suitability of coarse and fine rejects from coal preparation, as substitutes for aggregates and sand, respectively, in geopolymer concrete production. The work involved the formulation and testing of geopolymer mixes for their setting behavior, workability, and strength development. It was determined that coal mine tailings are a suitable precursor material for geopolymer binder formulations in terms of workability and strength development. The optimized 7-day compressive strengths of the geopolymer binder and concrete produced by alkali activation of coal mine tailings were comparable to N32 ordinary Portland cement (OPC).

Oxidation processes result in a number of environmentally adverse phenomenons such as spontaneous combustion of coal in piles, coal mining waste dumps and coal seams, as well as ARD generation in sulfide-bearing coal and ore mining waste dumps. The most efficient way to prevent, attenuate or intercept both adverse processes is to effectively cut off air penetration into the coal- or/and sulfite-bearing material with use of abundant, cost-effective, efficient and easy-to-handle material of high sealing properties against air penetration. Fly ash (FA) from coal-fired power plants in the form of a dense mixture with water (≤1:1 wt.) appeared to be an excellent sealing/insulation material against air penetration that has no competing natural materials in this respect and fulfills all the conditions of efficiency and availability. A series of experiments carried out to evaluate these properties of different FA: Water mixtures showed that penetration resistance of solidified FA: Water mixtures to air is 1–2 orders of magnitude higher than that of the natural sealing materials, while hydraulic conductivity qualifies this material as permeable to water. Full-scale applications of FA: Water dense mixtures for spontaneous ignition control at coal mining waste dumps confirmed high efficiency of this material. Pending projects and potential application fields of dense mixtures of FA with water for these purposes were also discussed, among them the most promising and not yet sufficiently utilized areas of use such as potential for fire control in burning coal seams (exemplified in Jharia Coalfield, India) and prevention of ARD generation in coal/ore mining waste dumps with use of FA: mine water mixtures.

This study assessed the feasibility of cultivating Lavandula dentata in Technosols produced from fine and coarse coal mining waste, focusing on plant development, substrate functionality, essential oil production, and post-mining ecosystem restoration. The Technosols were formulated using coal waste from the Moatize Coal Mine, Mozambique, combined or not in different configurations with agricultural soil and amended with sewage sludge (3% organic matter) and chemical fertilizer to ensure adequate nutrient availability. The experiments were conducted in 30 L containers, performed in triplicate for each experimental group. All settings allowed good plant growth, although the treatment that used only fine waste presented the closest performance to agricultural soil in terms of the production of aerial biomass. In this case, the dried biomass production of the shoots reached an average of 165 g per pot over 8 months (with a standard deviation of 20.3). The study showed a positive correlation between plant development and the available water capacity of the substrates. The plant tissue of L. dentata, in all the Technosols configurations studied, presented a similar composition to the control, with a biomass composition within the standard range established by the literature. The essential oil production ranged from 0.3 to 0.7% (m/m), averaging 0.5% (m/m), with chemical characteristics also alike the control trial. Technosols composed of coal waste from Moatize appear to be an alternative, both to provide a suitable destination for mining waste and to provide conditions for the revegetation and recovery of degraded areas by coal mining. This avoids the commissioning of nearby areas to supply soil for the restoration process. L. dentata, in addition to its various medical, ornamental, and aromatic uses, has potential as an “ecological trigger” in the restoration process with environmental and socioeconomic benefits.

This study focuses on addressing the issues of spontaneous combustion and slope instability at the coal mine waste (CMW) dump located on the north side of the Yumen River in Ximing Mine, China. We conducted slope restoration and environmental treatment of the CMW dump using shotcrete, deep hole grouting, external soil spray seeding technology with multiple soil fixation measures. The stability of the repaired CMW dump was analysed using LiZheng Slope Stability Analysis Software, and the displacement and stress of high-risk zones were assessed using MIDAS GTS NX Software. Our findings provide valuable insights for slope restoration and evaluation.

Wastes from coal mining and processing. Methodological approaches to the assessment of their ecological safety and directions for use. Part 3. Development and validation of test procedure to determine macroand micro-elements contents in coal mining, processing and combustion wastes

Phase I, Interface Overview Investigation, was concerned with evaluating the coal and solid wastes operations associated with converting 50,000 tons per day of Appalachia region coal into high-Btu gas, low-Btu gas, or liquid fuels. Emphasis was placed on defining boundaries for and operations which constitute the interface between coal mining and coal conversion. For Appalachia, two feasible alternatives for providing large quantities of coal were identified; from large, contiguous, integrated coal mining complexes and from isolated mines spread over a specific region or regions. Integrated complexes would provide coal to adjacent coal conversion plants. Regional mines would likely supply coal to remote conversion plants involving a major transport operation. For this movement, rail, barge, slurry pipelines, or combinations of these methods are possible transport alternatives. To define coal operations required within the mining-conversion interface, major operations categories were established. For the integrated mining-conversion alternative these include coal mine, coarse coal, fine coal, and solid wastes operations. For regional mining, these include underground and surface coal mine collection, coal transport, coal slurry, coarse coal, fine coal, and solid wastes operations. Operations associated with these categories are sufficient for design of the interfaces currently proposed for 24 gasification processes and 9 liquefaction processes and include transport, coal preparation, stockpiling, reclaiming, blending, handling, etc. Three cases have been recommended for conceptual engineering and cost estimating.

The main purpose of this paper was to outline a novel approach for the use of industrial by-products generated in coal mines and coal-fired power plants as the components for artificial soils. Several coal combustion by-products, coal mine waste and organic waste materials were tested at laboratory scale for use in the reclamation of areas degraded by coal mining activity. The role of artificial soils was the land rehabilitation of the high acidic waste heap. The results revealed that the amounts of organic matter (14.87–25.01%) and nutrients in the soil substitutes were sufficient to support plant growth, i.e., N (0.37–0.51%), P (0.23–0.47%), K (1.78–3.17%), Ca (4.93–8.39%) and Mg (1.16–1.71%). A phytotoxicity test using white mustard (Sinapis alba) seeds under laboratory conditions showed good germination results (56–66%) for three soil substitutes that did not contain fly ash from biomass combustion, compared to the reference soil (84%). The relationships established for the aqueous leachate parameters of soil substitutes vs. the Sinapis alba germination revealed negative correlations with electrical conductivity (r = −0.88), SO42− (r = −0.91) and Cl− (r = −0.70) ions; the two latter ones were responsible for the salinity which hampered the germination process of the soil substitutes. Moreover, quite similar correlations were obtained between the germination of Sinapis alba and the trace elements of the soil substitutes: Fe (r = −0.69), Cd (r = −0.72), Cu (r = −0.80), Pb (r = −0.78) and Zn (r = −0.74). However, negative and significant correlations in aqueous leachates were shown only with Ni concentration (r = −0.73). The relevance of these results for the effect of salinity on germination and the early growth of S. alba was discussed in detail and was confirmed with the Principal Component Analysis (PCA). The study proved that the physicochemical characteristic of recycled wastes exhibited their potential usefulness for the reclamation of affected areas such as mine waste heaps.

Life cycle assessment of a novel metal recovery method from co-processing of coal mine waste and low-grade printed circuit boards

RESUMO O objetivo desse trabalho foi avaliar o efeito da inoculação de fungos micorrízicos arbusculares (FMA) no crescimento, colonização micorrízica e absorção de P e elementos-traço em leguminosas arbóreas expostas a rejeito de mineração de carvão. Ensaios independentes para as leguminosas Mimosa scabrella Benth. (bracatinga), Mimosa bimucronata (DC.) Kuntze (maricá) e Parapiptadenia rigida (Benth.) Brenan (angico-vermelho) foram conduzidos em casa de vegetação em delineamento inteiramente casualizado com seis tratamentos. Foram avaliados cinco isolados de FMA autóctones de áreas de mineração (Acaulospora colombiana, Acaulospora morrowiae, Dentiscutata heterogama, Rhizophagus clarus e Rhizophagus irregularis), além de um tratamento controle não inoculado, com quatro repetições. Verificou-se que a colonização micorrízica foi superior a 60% para a bracatinga e o maricá, enquanto que, para o angico-vermelho, foi de no máximo 26%. De maneira geral, a inoculação de FMA favoreceu o crescimento das leguminosas arbóreas, atingindo incrementos de até 1430%. A absorção de fósforo foi beneficiada principalmente pela inoculação de A. colombiana, R. irregularis e A. morrowiae. Apesar de se verificar redução nos teores de elementos-traço na parte aérea das plantas, a inoculação de FMA ocasionou incrementos significativos no acúmulo de As, Cu, Zn e Cr para todas as leguminosas avaliadas. Desta forma, os FMA desempenham papel importante para o crescimento de espécies arbóreas em áreas de mineração de carvão, as quais apresentam ambientes pobres, degradados e muitas vezes contaminados.

The main problem of cement production is to reduce energy consumption and reduce the amount of greenhouse gases CO2 emitted into the atmosphere. The prerequisite for solving the problem is: the use of man-made waste and unconventional raw materials in the composition of the charge and the reduction of limestone content from 85% to 70-75% as a source of CO2 gas. The article presents the results of the studied technogenic waste and the suitability of non-traditional raw materials such as tefritobazalt, coal mining waste, and lead slag. The chemical and mineralogical composition of the materials and their suitability for obtaining environmentally friendly clinker have been established. The possibility of obtaining cement clinker using low-energy resource-saving technologies is shown. Clinker formation processes in the developed mixtures are completed at a temperature of 1350 °C, which, with the coal contained in the waste, will reduce the consumption of fuel injectors and reduce CO2 emissions into the atmosphere. In the developed low-energy mixtures, the specific consumption of raw materials for obtaining 1 ton of clinker is reduced to 1516-1525 kg, which is significantly lower than in traditional raw mixtures. Alite crystals are large, reaching 100-140 microns. The content of clinker minerals is C3S-57.88%, C2S-18.82%, C3A-6.46% and C4AF-11.61%. Disposal of large-tonnage waste will reduce environmental pollution and improve the environmental situation in the region.