The mutual impact of low-quality lignite and high-density polyethylene (HDPE) during open system pyrolysis was investigated, aiming to improve utilization of lignite with simultaneous treatment of HDPE waste. Pyrolysis of lignite, HDPE, and their mixture (mass ratio, 1:1) was performed at temperatures 400, 450, 500, 550, and 600 °C. Initial substrates and pyrolysis products were characterized by thermogravimetric analysis (TGA), gas chromatography–mass spectrometry (GC–MS), specific carbon isotope analysis of individual hydrocarbons (δ¹³C), Rock-Eval pyrolysis, and elemental analysis. The positive synergetic effect during co-pyrolysis of lignite/HDPE mixture was observed at temperatures ≥450 °C, with the greatest being at 500 °C. The highest yield of liquid co-pyrolysis products with a similar composition to that of crude oils is also noticed at 500 °C. The yields of liquid and gaseous products and quality of pyrolytic products obtained by co-pyrolysis of lignite/HDPE mixture are notably improved compared with pyrolysis of lignite alone. On the other hand, data obtained from pyrolysis of HDPE alone indicate that it cannot be concurrent to well-developed catalytic thermal processes for polymer recycling. However, concerning the huge amount of produced HDPE, at least part of this plastic material can be reused for advanced thermal treatment of lignite, particularly in countries where this low-rank coal represents the main source of energy.

A detailed analysis of the accident that occurred at the flotation tailings storage facility (TSF) at the inactive mine “Stolice” in 2014 is provided in this paper. All factors that caused the accident have been analyzed, with a review of the consequences of the accident, their accident class according to the Global Industry Standard on Tailings (GISTM), and the implemented measures to rehabilitate the TSF and the surrounding area after the accident. It has been concluded that the TSF had not been properly maintained even before the accident occurred and that the unfavorable weather conditions in Serbia in the May of that year contributed to the filtration disturbance and multiple tailings spillages from the TSF. It has been stated that the consequences according to the GISTM span from “low” to “significant”, with the group of environmental consequences having the highest rank (3). Although the accident occurred without recorded human casualties, with the damage being of a local nature, it is considered one of the most significant accidents at a TSF in Serbia in the last 20 years. The reconstructed TSF is considered stable now, with a low-to-medium risk of failure.

This paper presents the first data on the organic matter and thermal maturity of Mesozoic and Cenozoic sedimentary rocks in the East Herzegovina region of the External Dinarides. Representative, organic-rich samples from outcropping sedimentary rocks of different ages in the area (Triassic to Neogene) were selected and analysed. The organic matter was studied by Rock-Eval pyrolysis and under the microscope in reflected non-polarized light and incident blue light. The results obtained show the presence of different types of organic matter in the area and thermal maturity stages from immature (Cenozoic) to early mature (Mesozoic). Vitrinite is abundant in the samples analysed, with the exception of Cretaceous samples that contain mostly lamalginite and bituminite. While measured vitrinite reflectance in end-member samples (Triassic shale 0.78 % Rr and Neogene coal 0.34% Rr) are in good correlation with the Tmax parameter from Rock-Eval pyrolysis. T max generally shows lower values in most Mesozoic samples. The organic petrographic data indicate that specific kerogen in Cretaceous and some Triassic sedimentary rocks is a probable reason for the significantly lower T max values. In addition, the results of pyrolysis documented before and after extraction revealed that free hydrocarbons (bitumen) in the surface samples analysed suppress the Tmax values.

Serbia’s energy sector is undergoing structural transformation driven by European climate policies, market volatility, and the need for long-term energy security. In this context, geological storage of energy carriers represents a strategically important option. Depleted gas reservoirs, particularly within the Pannonian Basin, constitute a technically validated subsurface infrastructure suitable for repurposing as multifunctional storage systems for natural gas, CO₂, and green hydrogen. This study analyzes trends in European and Serbian natural gas markets, EU decarbonization targets, and Serbia’s energy balance to assess the feasibility of carbon capture and storage (CCS) and underground hydrogen storage. Key geological parameters governing long-term containment—lithology, effective porosity, permeability, caprock integrity, and structural stability—are evaluated, with emphasis on reservoirs combining favorable properties and proximity to existing infrastructure. Quantitative screening based on reservoir depth (approximately 1000–2500 m), effective porosity (15–25%), permeability (typically >50 mD), verified caprock integrity, and estimated geological storage capacities ranging from 0.17 to 1.25 billion m³ demonstrates that several depleted gas reservoirs in Serbia meet explicit fit-for-purpose criteria for underground storage applications. A comparative analysis of the physical and molecular behavior of H₂, CH₄, and CO₂ in porous media indicates that hydrogen storage is the most sensitive to reservoir integrity. The reported results provide quantitative and qualitative evidence that selected depleted gas reservoirs in Serbia satisfy essential requirements for project-level screening, including reservoir capacity, petrophysical suitability, caprock integrity, and infrastructure accessibility. These findings support the technical readiness of such reservoirs for staged deployment of natural gas storage, CO₂ sequestration, and underground hydrogen storage in the post-2035 energy system. Overall, combined subsurface storage of natural gas, CO₂, and hydrogen in Serbia is technically feasible, economically justified, and strategically relevant within the national energy transition framework.

This paper presents the first results of the geothermal evolution modeling in East Herzegovina based on vitrinite reflectance calculations and measurements. Modeling of burial and geothermal was performed using "SimpleMat" software with well known kinetic model of vitrinite reflectance - EASY % Ro. By fitting the calculated reflectance values with mean measured vitrinite reflectances, it was concluded that there was erosion of some 900 m in the area, and that first possible petroleum generation could have started some 100 Ma ago. According to final calibration model that includes additional thickness and subsequent erosion of Paleogene sequence, the Upper Triassic sediments should have maturity from 0.70 to 1.1 % Rr, Lower Jurassic from 0.62 to 0.70 % Rr, whereas Upper Cretaceous sediments should have values from 0.40 to 0.60 % Rr, which is in accordance with measured vitrinite reflectance in 23 samples. Assuming that beginning of oil window in the East Herzegovina correspond to the vitrinite reflectance of 0.50 % Rr, all analyzed Mesozoic samples are at the initial stage of catagenesis ("oil window"), while Cenozoic sediments are at the stage of diagenesis.