Secondary raw materials, such as ashes from the combustion of various fuels, are frequently used as alternatives to virgin raw materials. Among these, oil shale ash, a residue from oil shale power production and the shale oil industry, presents significant potential for use in sectors such as construction and agriculture. However, these materials might contain hazardous substances, such as dioxins, which are by-products of thermal treatment and other industrial processes. To date, the dioxin content in oil shale ash has been insufficiently examined. This article provides a comprehensive analysis of the dioxin content in oil shale ash from both a pilot unit and full-scale facilities. Additionally, the study compares the dioxin concentrations in oil shale ash with those in other types of ash and evaluates compliance with regulatory limits. The results showed that dioxin concentrations in the ash were below the limit of detection, regardless of the combustion technology, plant capacity, use of supplementary fuels, or utilisation of wastewater. The findings contribute new knowledge by highlighting the environmental advantages of oil shale ash as a secondary raw material, particularly due to its comparatively lower dioxin content relative to other types of ash.

ABSTRACT European regions long reliant on fossil-intensive energy are undergoing change driven by the European Green Deal, yet the green transition remains uneven across regions. In Estonia’s Ida-Virumaa, one of Europe’s most carbon-intensive regions, the green transition intersects with ethnic diversity, economic precarity, and far-right populism, generating uncertainty in communities whose deep regional ties are rooted in the oil-shale industry and shaped by both the Soviet past and a contested green future. We show that locals hold multiple, overlapping identities, which the green transition can unsettle, fuelling social discontent and perceptions of injustice around green transition policies and measures. The paper further demonstrates how the Estonian far right strategically deploys selective intersectionality by reframing local demands for fairness through identity-selective narratives, such as gender, labour heritage, and land, to broaden political influence while excluding marginalized groups. The findings highlight the need for place-sensitive policies that tackle regional inequalities and strengthen the legitimacy of green transitions.

Evaluating LA-ICP-MS and digestion-based ICP-MS methods for trace elements determination in oil shale and its solid wastes.

Abstract The green transition remains a top priority on the European agenda, with targets to reduce greenhouse gas emissions by 55% by 2030 and achieve climate neutrality by 2050. The European transport sector contributes approximately 20% of total CO₂ emissions, strongly necessitating the need for sustainable transport solutions, so that the assessment of the maritime transport system is considered beyond time and costs to include environmental issues and regional development. This research examines the potential environmental impact of a newly proposed ferry connection between Eastern Finland and Eastern Estonia, focusing on its role in advancing sustainable transport in the region. The study combines case studies, expert interviews, and survey data collected as part of an ongoing EU project between 2023 and 2025. The findings indicate that by 2030, the Sillamäe-Kotka ferry route could reduce annual CO₂ emissions by over 51 million tonnes, which would be a substantial contribution to regional decarbonization, enhanced freight and passenger transport efficiency, and alignment with the International Maritime Organization’s emission reduction targets. At the same time, this research highlights how maritime connectivity can contribute to a just transition process in Estonia’s Ida-Viru County, a region severely affected by the downturn in the oil shale industry, by facilitating new green economic opportunities, regional labour mobility, and sustainable tourism.

The effect of oil shale expansion and the addition of FeCl3 on its pyrolysis behavior was studied by hydrothermal pyrolysis experiments of cylindrical oil shale at 350 °C. The expansion of oil shale promotes the development of pores and fractures, which leads to the drastic pyrolysis of kerogen and the discharge of pyrolysis products. Besides, when the radial swelling increment of the oil shale is 33% of the free expansion, the pyrolysis reaction is basically guaranteed. When the radial expansion increment of the oil shale is greater than 33% of the free expansion amount, FeCl3 can effectively improve the yield of expelled oil by promoting the fracture of polycyclic structure and C-O bond in the kerogen, accelerating the migration of bitumen and urging the water to participate in the reaction. In addition, when the radial swelling increment of oil shale increases, the content of small molecule compounds in the expelled oil is reduced. These findings demonstrated that hydraulic fracturing of oil shale reservoirs and adding FeCl3 can effectively guarantee the success and economy of in-situ oil shale mining.

Oil shale is a rich unconventional energy source that has not been valued in the past due to its high mining costs and low economic benefits. However, with the gradual depletion of conventional crude oil resources, the economic value of oil shale has become increasingly significant. Microwave heating technology, with its efficient energy conversion and good penetration, has become a strong candidate for in situ oil shale mining. For example, studies have shown that microwave heating can achieve a heating efficiency of up to 80% in certain oil shale samples, which is significantly higher than that of traditional methods such as conduction heating (around 50%) and convection heating (around 60%). However, comprehensive reviews on the application of microwave heating technology in oil shale in situ mining are still rare. This review systematically reviews the application progress of microwave heating technology in in situ oil shale mining, including microwave heating devices, dielectric properties of oil shale, numerical simulation techniques, and methods for improving heating efficiency. The research found that optimizing microwave frequency, improving magnetron design, and adding microwave absorbers can significantly improve the heating efficiency and uniformity. In addition, the technology is also environmentally friendly and can achieve crude oil cracking and desulfurization under the action of a catalyst, improving the quality of the crude oil.

Diverse four patterns of mine face development have been implemented in this study; this includes continuous longitudinal single-sided mining development system (Dsl), continuous longitudinal double-sided mining development system (Ddl), continuous cross single-sided mining development system (Dsc) and continuous cross double-sided mining development system (Ddc). This study suggests a progressive development approach that involves the shortest in-pit transport approach from the face of the mine to the reloading station using three options, including a power plant consisting of one Circulating Fluidized Bed (CFB) boiler unit and one steam generator in the first 5 years (first option), two CFB units and two generators in the second 5 years (second option), and three CFB boiler units and three generators in the rest of the mine life (third option). The mineable reserve is estimated at 470,861,070 m³, with a projected mine life of 57.4 years, an annual ore volume of 2,840,075m³, and a total mining capacity (including ore and overburden) of 7,838,607m³. Major Findings: The findings suggest that the minimum in-pit haulage distance of 858.7m for the first option can be attained through the implementation of a continuous cross-double-sided mining development system. The findings also suggest that the continuous cross double-sided mining development system is the optimal selection for the second option, while the continuous longitudinal double-sided mining development system is the optimal selection for the third option.

Coupling mechanism analysis of CO2 non-Darcy flow in multi-scale reservoirs: A case study of the life-cycle process of fracturing-development in shale oil reservoirs

The global demand for resources is escalating in today’s rapidly evolving world. As traditional raw materials become scarcer and more expensive, alternative sources have to be found. One such emerging resource is oil shale ash. This article provides a comprehensive overview of the various fractions of oil shale ash generated in the oil shale industry in Estonia. The ash results from the direct combustion of oil shale with pulverised combustion (PC) and circulating fluidised bed combustion (CFBC) technologies, as well as from shale oil production processes. It offers detailed information about the proportions of ash derived from different technological processes and a thorough analysis of their mineralogical and chemical compositions, trace element content, and leaching characteristics. By examining these diverse characteristics, the study enhances understanding of the ash’s potential implications and applications.

Mining subsidence prevention has not been systematically addressed in Estonia. Despite the presence of numerous shallow and hazardous old mines, including some in urban areas, there are only a few practical examples of land stabilization. This article provides an overview of stabilization methods commonly used elsewhere. By considering the specific characteristics of shallow Estonian mines and existing infrastructure, we propose injectable backfilling through treatment boreholes as the most applicable land stabilization method in Estonia. The backfill typically consists of locally available byproducts or waste materials. We evaluate how Estonian oil shale ash, a residue from power and oil production, compares to the properties required for effective backfilling. Some properties, such as self-cementation, make it suitable for use in backfills. However, it also exhibits less desirable features – high water demand and fast setting. Despite extensive research on oil shale ash, certain material properties that critically impact its usability in backfills – such as its pumpability over longer distances – remain to be fully determined.

In order to prevent leakage of pyrolysed oil and gas and the release of contaminants from the top and bottom strata, it is essential to carry out a comprehensive study of the seepage behaviour of these strata under high temperature triaxial stress conditions. The findings of this study will contribute to the development of effective strategies for the containment and integrity monitoring of subsurface reservoirs and storage environments. Mudstone, serving as both the upper and lower strata, offers an effective barrier due to its inherently low permeability. In order to explore the change rule of mudstone sealing performance under high temperature triaxial stress, an air-heated low permeability rock mass air permeability measurement system is used to measure the ground stress buried 500 m deep and the temperature variation characteristics of mudstone permeability on the roof and floor of Jimsar oil shale in Xinjiang under 100 °C. It was found that the permeability of stressed mudstone decreased with the temperature rising up to 100 °C. The primary factor influencing the outcome was the thermal expansion of the mudstone. The magnitude of the drop value was contingent upon the triaxial stresses that could potentially be induced by the application of significant tensile forces, resulting in a relatively minor drop value. The average hydraulic radius of pore in the mudstone was also calculated, which also exhibited continuous reduction as heating up to 100 °C and the degree of reduction could reach 68%. The capacity, that prevent oil & gas and contaminant from moving cross strata as a barrier, would be strengthened when the mudstone strata from roof and floor experienced the temperature low than 100 °C. The barrier performance of mudstone as a pollutant migration barrier layer to gas pollutant migration during in-situ heat injection mining of oil shale was further evaluated.

Isolation and characterization of a novel bacterium that promotes the degradation of poly(glycolic acid) by its extracellular esterase under thermophilic conditions

Shale oil and gas, deemed as vital alternative resources to conventional oil and gas, have spurred significant interest in information-based exploration and development technologies within the industry in recent years [1]. China boasts extensive shale oil and gas reserves, with the International Energy Agency (EIA) estimating China's shale oil technology capable of extracting approximately 4.393 billion tonnes, ranking third globally. Additionally, China holds shale gas geological resources of about 134.4 trillion cubic meters, ranking first worldwide, showcasing immense development potential. Shale oil and gas, being unconventional resources, are distributed within the pore and fracture systems of organic-rich shale formations. Compared to conventional oil and gas, shale oil and gas exhibit weaker trap control and stronger distribution continuity, typically characterized by poor reservoir physical properties. Conventional extraction methods often struggle to yield industrial oil and gas flow from shale oil and gas resources, necessitating unconventional development technologies such as reservoir monitoring, directional wells, horizontal wells, and segmental fracturing [2]. However, these technologies come with challenges and risks, including complex production operations, high production data density, and environmental concerns such as surface ecological damage and pollutant emissions, further impacting shale oil and gas production. To facilitate the upgrading process of China's shale oil and gas industry, this paper presents the current status of Internet of Things (IoT) application technologies for shale oil and gas development and proposes a research outlook based on the concept of green development. Against the backdrop of energy transformation, it offers a reference framework for the sustainable development of China's extensive shale oil and gas resources.

Real-time high-temperature CT scanning and a rock-mechanics test system were employed to investigate the mechanical properties of oil shale at temperatures from 20 to 600 °C. The results reveal that up to 400 °C, the aperture of fractures initially decreases and then increases when loading is perpendicular to the bedding. However, the number and aperture continuously increase when loading is parallel to the bedding. Beyond 400 °C, the number of pores increases and the aperture of the fractures becomes larger with rising temperature. The changes in microstructures significantly impact the mechanical properties. Between 20 and 600 °C, the compressive strength, elastic modulus, and Poisson’s ratio initially decrease and then increase under perpendicular and parallel bedding loadings. The compressive strength and elastic modulus reach minimum values at 400 °C. However, for Poisson’s ratio, the minimum occurs at 500 °C and 200 °C under perpendicular and parallel bedding loadings, respectively. Simultaneously, while the crack damage stress during perpendicular bedding loading, σcd-per, initially exhibits an upward trend followed by a decline and subsequently increases again with temperature increasing, the initial stress during perpendicular bedding loading, σci-per, parallel bedding loading, σci-par, and damage stress, σcd-par, decrease initially and then increase, reaching minimum values at 400 °C. These research findings provide essential data for reservoir reconstruction and cementing technology in the in situ mining of oil shale.

The emissions of NOx, SO2, CO and decomposition of carbonates during oxyfuel combustion of low heating value semicoke in CFB pilot facility

This article explores the link between the building of the pioneering motor ship Jutlandia by Barclay Curle & Co. Ltd in 1912 for the East Asiatic Company of Copenhagen and the Burmeister & Wain oil engines which powered it, notably through Scottish shale oil. It traces the difficulties in building and installing machinery that was unfamiliar to Clydeside engineers and the impact that the ultimate success of the vessel had on marine engine building on the Clyde. After the Burmeister & Wain licence was awarded to Harland and Wolff, the North British Diesel Engine Works was created as a joint venture between Barclay Curle and Swan Hunter, brokered by the oil and shipping broker Frederick Lane and financed by oil industry capital. Despite early promise, the First World War and state control of the shale oil industry hampered the wholesale adoption of shale oil fuelled commercial motor shipping.

Fast-growing Populus spp. are well-acknowledged to restore contaminated soils from heavy metals in industrial areas. Thus far, there is no knowledge about the phytoremediation capacity of Populus spp. plantations in hemiboreal Estonia conditions to restore industrially polluted areas. The objective of this study was to assess the soil contamination rate of heavy metals (As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb and Zn) and their uptake by mature hybrid aspen (Populus tremula × Populus tremuloides Michx.) in plantations in different industrial pollution areas (e.g. cement factory, oil shale mining). For the reference, industrially polluted plantations were compared with the low pollution area hybrid aspen plantation on former agricultural soil, which was influenced by fertilization and liming before afforestation. Twenty-one years after afforestation, soil samples were collected from the 0-10cm topsoil layer. Aboveground biomass sampling was performed for bark and stem wood by ingrowth cores to separate wood formed during early (1-10years) and late (11-21years) stand development. Two decades after the afforestation of industrially polluted areas, the heavy metal concentrations in the soil were higher than the reference plantation and the standard reference for unpolluted soils in most cases. The highest concentrations of heavy metals in woody biomass were in the oil shale quarry spoil; because of poor growth, the accumulated pools in aboveground biomass were low. Cd differed from other metals and accumulated less in wood and more in bark. The concentration of heavy metals (Cd, Cr, Cu, Fe, Mn, Ni and Zn) was higher in the first decade of stand formation (1-10years) than in the last 10years (11-21years). High pools of heavy metals were accumulated in aboveground biomass in the reference plantation, indicating the considerable removal of heavy metal residues from the previous fertilization and liming source with harvest. Two decades of afforestation with hybrid aspen is too short for complete ecosystem restoration from heavy metals in industrially polluted areas.

Comprehensive evaluation of low-temperature oxidation characteristics of low-rank bituminous coal and oil shale

Analysis of heat transfer performance and system energy efficiency of catalytic combustion heaters for low calorific value waste gas application to oil shale in-situ conversion

The principle and application of oil shale in-situ mining technology are reviewed. Oil shale is rich in resources and is an important supplement to petroleum and natural gas as a source of energy. Currently, ground retorting technology is the primary way to produce shale oil because of its elaborated processing method and equipment. However, this technology has several disadvantages such as low thermal efficiency, high environmental pollution and inability to exploit deeply buried oil shale. A novel method called oil shale in-situ mining technology is efficient and environmentally friendly. This technology can exploit deep oil shale while reducing pollution and greenhouse effect. Based on the data collected, this paper summarizes the development of global underground in-situ oil shale mining technology, introduces four heating transfer principles and mathematical models of conduction heating, convection heating, radiation heating and combustion heating, clarifies the process flow, as well as presents advantages and disadvantages of different technologies. It provides a reference for the research of oil shale in-situ mining technology, and also looks into the technology’s prospects for industrialization, integrating with greenization, information and intelligence.