The increasing atmospheric CO₂ concentration linked to human activity results in global warming by the greenhouse effect. This anthropogenic CO₂ may be sequestrated into geological formations, e.g., porous basalts, saline aquifers, depleted oil or gas reservoirs, and unmineable coal seams. Furthermore, carbon capture, utilization, and storage (CCUS) methods are an acceptable and sustainable technology to meet the goals of the Paris Agreement, in which Kazakhstan is expected to reduce greenhouse gas emissions by 25% compared with the 1990 level. Unmineable coal seams are an attractive option among all geostorage solutions, as CO₂ sequestration in coal comes with an income stream via enhanced coalbed methane (ECBM) recovery. This paper identifies four carboniferous coal formations, namely Karagandy, Teniz-Korzhinkol, Ekibustuz, and Chu coal basins of Kazakhstan, as CO₂ geostorage solutions for their unmineable coal seams. The ideal depth of CO₂ storage is identified as 800 m to ensure the supercritical state of CO₂. However, the Ekibustuz coal basin fails to meet the required depth of 800 m in its unmineable coal seams. The conventional formula for calculating CO₂ storage in coal basins has been modified, and a new formula has been proposed for assessing the CO₂ storage potential in a coal seam. The CO₂ storage capacities of unmineable coal seam of these coal basins are 24.60 Bt, 0.61 Bt, 14.02 Bt, and 5.42 Bt, respectively. The Langmuir volume of the coal fields was calculated using the proximate analysis of coalfields and found to vary between 36.42 and 98.90 m³/ton. This paper is the first to outline CO₂ storage potential in Kazakhstani coal basins, albeit with limited data, along with a detailed geological and paleographic review of the carboniferous coalfields of Kazakhstan. A short overview of the CO₂-ECBM process was also included in the paper. Instead of any experimental work for CO₂ storage, this paper attempts to present the CO₂ storage capacity of carboniferous coal formation using the modified version of previously determined formulas for CO₂ storage.

This study analyzes 105 coal ash samples from Jurassic and Carboniferous coals from five mines in Kazakhstan, Lenin, Saradyr, Bogatyr, Maikuben, and Shubarkol, focusing on the inorganic elemental compositions, their occurrence, and industrial and environmental implications. Methods include coal ash yield and volatile matter analysis, mineralogical characterization via low-temperature ash X-ray diffraction (LTA-XRD), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). High-temperature ash (HTA) was analyzed using energy-dispersive X-ray fluorescence (EDXRF), highlighting XRF’s potential for rapid multi-elemental analysis. Nine major elements (Al, Si, P, S, Fe, K, Ca, and Ti) and eleven trace elements (As, Cu, Cr, Zn, Pb, V, Ga, Mn, Ni, Y, Yb, and Zr) were identified in HTA samples through EDXRF. SEM and dendrogram analysis confirm their co-occurrence with quartz, kaolinite, pyrite, and accessory minerals such as chalcopyrite, zircon, rutile, and REE-bearing apatite. The elemental content of samples enhances industrial suitability by reducing emissions. Only Yb shows slight enrichment for economic benefits, along with La, Ce, and Nd, while concentrations of potentially toxic elements indicate minimal environmental risk. EDXRF demonstrates its efficiency for large-scale investigations, with all samples analyzed in a few days using automated overnight measurements. This approach shows promise for future studies focusing on trace elements, including REE.

This study aims to comprehensively characterize coal extracted from three active mines in northeastern Kazakhstan: Lenin, Saradyr, and Bogatyr. These mines exploit two Carboniferous coal-bearing formations, Dolyn and Karagandy. Dolyn, extracted by the Lenin underground mine at a depth of 700 m, contrasts with Karagandy, extracted at depths up to 260 m in Saradyr and Bogatyr. Six selected samples from the Lenin, Saradyr, and Bogatyr mines underwent various analyses, including proximate and ultimate analyses, elemental analyses (acid digestions with HCl + HNO₃ + HF, ICP-MS), and determination of mineral matter contents (XRD and SEM-EDS). This research aimed to understand the mode of occurrence of minerals and elements, technological and environmental implications of the coal seams extracted from these mines. Results indicate low sulfur and high ash content in the organic matter of all samples. Quartz and kaolinite dominate, with minor euhedral pyrite present in all samples. Framboidal pyrite, iron oxides, and rare earth element (REE)-bearing minerals are exclusively found in Saradyr and Bogatyr samples. Quartz and kaolinite likely reached the peat swamp through detrital processes, while pyrite formation occurred through both syngenetic and epigenetic processes in the coal samples. Ratios like Ce _n /Ce _n , Eu _n /Eu _n , Y _n /Ho _n , and Gd _n /Gd _n suggest REE deposition in anoxic hydrothermal water environments, possibly indicating a tuffaceous origin for the coal samples. Examining the elements’ mode of occurrence suggests their preferential association with mineral matter. Strong positive correlations among elements like Al, K, Na, Ti, Ba, Be, Ni, Cr, Co, Ga, Sc, V, As, Pb, Cu, Zn, and Zr, along with Eu and Sc of the REEs, suggest association with ash yield, consistent with kaolinite and accessory minerals. Comparative analysis of inorganic geochemical composition of coal worldwide reveals notable depletion of major, trace elements, and REEs in samples from all three mines, suggesting limited economic interest. Furthermore, coal samples containing trace elements pose minimal environmental impact.

The paper comprises new analytical data on the nature and occurrence of gold in solid pyrobitumen, closely associated with the main gold-bearing sulfide arsenic ores of the Bakyrchik gold deposit (Kazakhstan), related to post-collisional magmatic-hydrothermal origin. Gold mineralization of the deposit occurs mainly in the form of an “invisible” type of gold in the structures of arsenian pyrite and arsenopyrite, and the form of gold-organic compounds of pyrobitumen in carbonaceous-terrigenous sequences of Carboniferous formation. Microscopic and electron microscopic analysis, Raman and FT-Infrared analysis, mineralogical and three-step sequential extraction analysis (NH₂OH·HCl, H₂O_2,HNO₃ + HCl) has been carried out using 9 ore samples (from 3 different types of ores) for a comprehensive study of pyrobitumen and sulfide arsenic ores focusing mainly on organic matter. The sequentially extracted precious metal content of pyrobitumen reaches up to 7 ppm gold and other metals like Ag 4 ppm, Pt 31 ppb, and Pd 26 ppb, forming metal–organic compounds, while arsenic sulfide minerals incorporate 11 ppm gold, 39 ppm Ag, 0.49 ppm Pt. The enrichment of gold associating with organic matter and sulfide ore minerals was confirmed in this study. Organic matter was active in the migration of gold and the capture of gold by pyrobitumen. Moreover, the reductive organic matter agent released gold, most likely for the sulfide arsenic ore minerals. Pyrobitumen was a decisive factor in the concentration, transportation, and preservation of gold in the deposit.

Medet Junussov, Ferenc Mádai, János Földessy, Mária Hámor-Vidó. Econ. Environ. Geol. 2024;57:371-86. https://doi.org/10.9719/EEG.2024.57.4.371