Low-temperature Nitrogen Adsorption Research Articles

Shale permeability and microstructural alternation during CO2 pre-fracturing: A mechanistic study

CO2 pre-fracturing technology represents a novel approach to CO2 fracturing, effectively enhancing carbon capture efficiency in shale reservoirs while increasing the recovery of hydrocarbon resources. This study systematically quantifies the impact of water injection on the pore structure and permeability of shale samples saturated with pre-injected CO2. Based on X-ray diffraction (XRD) and low-temperature nitrogen adsorption (LT-NA) results, the dominant mechanism of the swelling-chemical coupling effect in shale property is clarified. Pre-injected CO2 can effectively mitigate the impact of water absorption. After a reaction time of 7 days, the permeability of the CO2-involved hydrated shale samples is four times that of samples without CO2. Nevertheless, the influence of subsequently injected water on shale permeability persists, resulting in an 80% reduction in shale permeability. XRD and LT-NA results indicate that the swelling-chemical coupling effect is the dominant factor in shale property variation during CO2 pre-fracturing. In the initial stage, the decline in calcite and clay mineral content is significant, and chemical dissolution dominates the change in pore structure. As the reaction progresses, the intensity of chemical reactions weakens, and clay mineral swelling becomes the primary factor affecting the shale properties. In this stage, K+ generated from original minerals effectively inhibits clay mineral swelling. Therefore, the swelling-chemical coupling effects should be comprehensively considered during the CO2 pre-fracturing process, and an appropriate soaking time should be selected to maximize CO2 storage efficiency and oil and gas production.

Reservoir Characteristics of the Main Coal Seams in the Longtan Formation, Guxu Coal Mining Area, Sichuan

To facilitate the efficient exploration and development of coalbed methane of the Longtan Formation in the Guxu coal mining area, Sichuan, it is essential to evaluate the reservoir characteristics of the main production layers. In this study, scanning electron microscopy, low-temperature liquid nitrogen adsorption experiments, high-pressure mercury pressure experiments, and isothermal adsorption experiments were conducted to investigate the reservoir characteristics of favorable coalbed methane reservoirs. The results indicate that the main coal seams in the Longtan Formation are medium-to-high ash content anthracite with a well-developed pore–fracture system. The pore size distribution exhibits both unimodal and bimodal types, while the pore morphology includes impermeable pores closed at one end, open permeable pores, and ink bottle-shaped pores. It shows that the middle part of Longtan Formation acts as an enrichment zone for coalbed methane, which is characterized by a stronger adsorption capacity, high Langmuir volume, high gas content, and high gas saturation distribution. The pH value, mineralization degree, and hydrogen–oxygen isotope of the produced water in the main coal seams indicate that the enrichment zone is typically located in a stagnant flow zone with a reducing environment and favorable storage conditions.

Control of complex lithofacies on the shale oil potential in saline lacustrine basins of the Jimsar Sag, NW China: Coupling mechanisms and conceptual models

The heterogeneity of lithofacies is a pivotal factor influencing the shale oil potential. A comprehensive understanding of the intricate influence of rock complexity on hydrocarbon generation properties, microscopic pore-throat structure, and fluid occurrences is crucial for shale oil exploration and development. The Lucaogou Formation in the Jimsar Sag is a type of saline lacustrine shale oil, which was chosen as a research example in this paper. To unravel the causal linkage and confirm the coupling relationship between lithofacies, pores, and fluid mobility in the sedimentary sequence of saline lacustrine basins, a series of experiments were conducted. These included total organic carbon (TOC), X-ray diffraction (XRD), vitrinite reflectance (Ro), Rock-Eval pyrolysis, field emission-scanning electron microscopy (FE-SEM), low-field nuclear magnetic resonance (LF-NMR), mercury intrusion porosimetry (MIP), and low-temperature nitrogen adsorption (LTN2A). The results revealed significant differences in pores, oiliness, and fluid mobility among the four dominant lithofacies. Employing an innovative comprehensive evaluation method, high-carbon silty dolomite manifests significant potential for hydrocarbon generation, substantial storage capacity, effective oiliness and mobility, heightened brittle mineral content, and facile fracture production. Consequently, it was the most favorable lithofacies. Furthermore, TOC, pore size, and pore types emerged as key factors influencing the movable oil content of different lithofacies. More importantly, a detailed multiscale model illustrated potential linkages across the three different scales of lithofacies associations, pores, and fluid mobility. The study’s outcomes can offer enhanced guidance for accurately assessing shale oil resources, particularly in the identification of crucial “sweet spots”.

Bimetallic Pt-IrOx/g-C3N4 Photocatalysts for the Highly Efficient Overall Water Splitting under Visible Light

Two series of bimetallic photocatalysts (0.5% Pt/0.01–0.5% IrOx/g-C3N4 and 0.1% Pt/0.01–0.1% IrOx/g-C3N4) were synthesized by the thermolysis of melamine cyanurate and a successive deposition of platinum and iridium labile complexes (Me4N)2[Pt2(μ-OH)2(NO3)8] and fac-[Ir(H2O)3(NO2)3. The synthesized photocatalysts were studied by a set of physicochemical analysis techniques. Platinum exists in two states, with up to 60% in metallic form and the rest in the Pt2+ state, while iridium is primarily oxidized to the Ir3+ state, which was determined by X-ray photoelectron spectroscopy (XPS). The specific surface area (SBET), which is determined by low-temperature nitrogen adsorption, ranges from 80 to 100 m2 g−1 and the band gap energy (Eg) value is in the range of 2.75–2.80 eV as found by diffuse reflectance spectroscopy (DRS). The activity of the photocatalysts was tested in the photocatalytic production of hydrogen from ultrapure water under visible light (λ = 400 nm). It was found that the splitting of water occurs with the formation of the stochiometric amount of H2O2 as an oxidation product. Two photocatalysts 0.5% Pt/0.01% IrOx/g-C3N4 and 0.1% Pt/0.01% IrOx/g-C3N4 showed the highest activity at 100 μmol h−1 gcat−1, which is among the highest in H2 production published for such systems.

Industrial aluminum hydroxides: Part 1. Phase composition and textural characteristics of industrial aluminum hydroxides/oxides

The most common component in the design of heterogeneous catalysts for oil refining and petrochemistry are aluminum oxides. Each type of hydrocarbon raw materials and technological process corresponds to the optimal characteristics of aluminum oxide supports and catalysts: specific surface area, pore size, phase and impurity compositions. Due to the trend towards import substitution, the research of domestic producers of aluminum hydroxide used for the synthesis of aluminum oxides is becoming more relevant. In this work, domestic industrial samples of aluminum hydroxides were studied by methods of X-ray phase analysis, thermogravimetry combined with differential scanning calorimetry, low-temperature nitrogen adsorption and elemental analysis. It is established that the objects of research are most often phase-inhomogeneous, in which impurities of iron, silicon and calcium are present. The influence of the degree of crystallization and the size of the coherent scattering regions of aluminum hydroxides, mainly with the structure of boehmite and, in some cases, containing bayerite, on the textural characteristics of the resulting aluminum oxides is shown.

Evaluation of Carbonized Corncobs for Removal of Microcystins and Nodularin-R from Water

Microcystins (MCs) and nodularins (NODs) are cyanotoxins that can be found in water bodies during cyanobacterial harmful algal blooms (cyanoHABs). Consumption of water contaminated with cyanotoxins leads to health risks for humans and animals. Herein, corncob-based biochar and activated carbon (AC) were initially investigated for the sorption of six common MC congeners (MC-RR, MC-YR, MC-LR, MC-LA, MC-LW, and MC-LF) and nodularin-R (NOD-R) from spiked water. Biochar was prepared by refluxing commercial corncob with HCl and heating it to 250, 300, or 350 °C. AC was prepared by chemical activation of corncob with H3PO4 at 500 °C under a nitrogen atmosphere. Low-temperature nitrogen adsorption measurements confirmed that H3PO4-AC has a higher specific surface area (≈1100 m2/g) and total pore volume (≈0.75 cm3/g) than biochar and commercial AC. H3PO4-AC showed the maximum efficacy, among all corncob-based sorbents, to remove MCs and NOD-R from water as confirmed by experiments that involved sample analyses by ultrahigh-pressure liquid chromatography-mass spectrometry (UHPLC-MS). The effect of natural organic matter (NOM) on the adsorption of MCs was checked by incubating sorbents with Lake Erie water collected during cyanoHABs from 2020 to 2022. The total concentration (extracellular and intracellular) of studied MC congeners ranged from 1.37 µg/L to 438.51 µg/L and 50 mg of H3PO4-AC completely removed them from 3 mL of lake water. The effect of water pH on cyanotoxin adsorption was studied at pH values of 5.5, 7.0, and 8.5 at both a lower (10 μg/L each) and a higher (50 μg/L each) toxin concentration. Removal was influenced by solution pH at both concentrations when using biochar, while only at higher toxin concentration when using H3PO4-AC. At higher MC and NOD-R concentrations, competitive adsorption was prominent, and overall, the adsorption increased at acidic pH (5.5). The study results suggest that processed corncobs can remove a significant amount of MCs and NOD-R from water, and the measured sorption capacity of H3PO4-AC was ~20 mg of MC-LR and NOD-R per g of this sorbent.

Non-destructive chromatographic determination of surface area in reverse phase chromatographic columns

One of the critical but underutilized parameters that affect chromatographic separation is an adsorbent surface area (S.A.). We introduce a concept of direct determination of the total surface area of chromatographic columns by utilizing a nondestructive measurement of eluent component excess adsorption isotherm measurement and the application of the Standard Excess Adsorption Isotherm from acetonitrile-water and methanol-water binary mixtures for direct determination of the S.A. in chromatographic columns. This nondestructive technique was used to determine the surface area of five commercial columns, including three core-shell particle type columns (Kinetex-C18, Ascentis C18, and Hallo C18) and in-housemade C18 columns. The traditional low-temperature nitrogen adsorption (LTNA) technique was compared to the novel chromatographic method of nondestructive surface area determination for adsorbents modified with octadecylsilanes. The chromatographically determined surface area was in good agreement with the conventional techniques for all columns used. The difference between the three techniques is less than 10%. Columns were characterized in terms of adsorbent geometry (e.g., pore volume, column void volume, interparticle volume), ligands bonding density, and the amount of the packing material in a chromatographic column.

Mesoporous molybdate-substituted hydroxyapatite nanopowders obtained via a hydrothermal route

In the last decade, mesoporous hydroxyapatite (HA) materials have received much attention regarding environmental applications (including adsorption of soil and water contaminants, films for lithium batteries, catalysts, and support systems for catalysis) and open up ample opportunities regarding biomedical devices and structures. Molybdenum ions may strongly influence catalytic and sorption properties of materials. The present study shows an influence of hydrothermal-synthesis conditions (including temperature and duration of the treatment) on phase composition, textural properties, and morphology of molybdate-containing HA. Powders with high crystallinity manifested Brunauer–Emmett–Teller specific surface area up to 55 m2/g with a pore volume of 0.33 cm3/g. The molybdate-containing HA powders were investigated by chemical analysis, X-ray diffraction, Fourier-transform IR spectroscopy, and transmission electron microscopy. Their specific surface area, pore volume, and pore size distributions were determined by low-temperature nitrogen adsorption measurements, zeta potential was quantified, and electron paramagnetic resonance spectroscopy was performed. The concentration of MoO42− preserving the one-phase state was found, and the impact of hydrothermal treatment mode was analyzed by machine learning using artificial neural networks.

Physical Characteristics of Coal Reservoirs and CBM Favorable Area Prediction in the Huaibei Coalfield, Northern China.

To quantitatively characterize middle-high-ranked coal reservoirs, the physical characteristics of seven coal samples from the Huaibei Coalfield in northern China were investigated in detail based on experiments including proximate analysis, coal petrology, low-temperature nitrogen adsorption (LTNA), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and methane isothermal adsorption. The results show that coal maceral in the Huaibei Coalfield is dominated by vitrinite, with a large change in the maximum vitrinite reflectance ranging from 0.7 to 2.5%. The various coal metamorphisms can be attributed to the combined influence of magmatic activities of the Tanlu and Taihang Mountains during the Yanshanian. The coal quality can be characterized by medium-high ash yield, low to very low sulfur content, low phosphorus, and medium-high calorific value. From low-ranked coals to medium-ranked coals, the volume of adsorption and seepage pores decreases but the fracture volume increases due to the stronger dehydration and coal matrix shrinkages. From medium-ranked coals to high-ranked coals, adsorption pores have a significant advantage, suggesting a stronger CH4 adsorption capacity. There is a positive correlation among the fixed carbon content, coal rank, and Langmuir volume, which can be attributed to the transformation of coal chemical composition and structure by coal metamorphism. The deep Xiaoxi in the Suixiao coal mining area, deep Nanping, deep Taoyuan-Qinan, deep Pengqiao, northern Zhuxianzhuang in the Suxian coal mining area, deep Renlou-Zhaoji, and Xutuan deep in the Linhuan mining area are predicted to be favorable areas for CBM exploration in the Huaibei Coalfield.

Optimal selection of inversion method for gas-adsorption pore characterization of shales in Wufeng and Longmaxi Formation, Sichuan Basin

The pore space in gas shale spans multiple scales, ranging from nanometers to micrometers with an extremely complex structure and strong microscopic heterogeneity. Existing low-temperature gas adsorption (LTGA) pore size distribution (PSD) analysis models are based on the assumption of a one-dimensional tubular model and there is a lack of sufficient basis for selecting the most appropriate inversion model among the various types available. In this study, a comprehensive characterization of numerous samples from the Wufeng and Longmaxi Formation in the southern Sichuan Basin was conducted using different methods and inversion models. Based on multiple dimensions, such as fitting errors, the correlation between different methods including low-temperature CO2 adsorption (LTCA), nitrogen adsorption (LTNA), and large-scale mosaic Scanning Electron Microscopy (LAM-SEM), the most suitable one-dimensional models for LTCA and LTNA PSD analysis for the studied shale samples are determined. The simulation of gas condensation processes on LAM-SEM images yielded pore volume (PV) in the range of 32–48 nm comparable to the PV characterized by LTNA. Furthermore, the differences observed in PSDs between the gas condensation simulation procedure and the equivalent circular area diameter method indicate that irregular corner regions within larger pores are attributed to the volume of smaller-sized pores during gas adsorption characterization. It is revealed that the correlation between stitched surface area (SA) and maximum methane adsorption is stronger than individual characterizations, indicating that both micropores and mesopores contribute significantly to adsorption, and both characterization methods need to be employed to obtain SSA that influences methane adsorption. The research findings are helpful to the improvement of the multi-scale pore characterization level and evaluation of shale reservoirs.

Thermo-oxidative degradation of carbon nanotubes and related nanostructures: role of acidic environment and chloride ions

It is shown that acid activation of ultralong carbon nanotubes synthesis products increases their reactivity during subsequent thermochemical treatment in air at 480 °C. Such an integrated approach of CNTs processing provides high purity and maximum yield of the target product. For example, the non-CNT fraction decreases by 3.2 times, while the residual iron content decreases by 17–24 times in comparison with thermochemical treatment without acid. Raman spectroscopy and low-temperature nitrogen adsorption showed that acid activation does not lead to extra surface defects, which could initiate further oxidation of carbon matrix in air. It is suggested that the increased reactivity of CNT synthesis products after acid activation during thermo-oxidative degradation may be due to the formation of an “adduct” of carboxyl groups on the surface of nanotube carbon matrix with hydrogen chloride. It was shown by thermogravimetric studies coupled with mass-spectra investigation of gas evolved, that under the constant heating, at the temperatures of the beginning of intensive oxidation (500–600 °C), the decomposition of the “adduct” occurs, bypassing the stage of formation of more temperature-resistant phenolic groups, which can inhibit further oxidation. Water released during the decomposition of the “adduct” can also accelerate the process of thermal oxidation.

Charge Storage and Magnetic Properties Nitrogen-Containing Nanoporous Bio-Carbon

This article presents the technology for the preparation of a nitrogen-containing nanoporous bio-carbon and investigates its properties. It has been shown that the synthesised bio-carbon is characterised by a high degree of homogeneity, which has been confirmed by energy dispersive spectroscopy. The obtained bio-carbon has a micromesoporous structure, which has been confirmed by the results of studies using the method of low-temperature nitrogen adsorption and desorption. It was found that the specific surface area of biochar is 1247 m2/g. The data on nitrogen adsorption and desorption were compared with the data on small-angle X-ray scattering, and it was found that the micropores in the synthesised bio-carbon are open pores, while mesopores remain closed. The energy dispersion analysis showed that the structure of the bio-carbon does not contain ferromagnetic atoms, but due to the addition of nitrogen, the synthesised bio-carbon in a magnetic field has the properties of a ferromagnet with a characteristic hysteresis of the specific magnetisation. It was found that this material has a saturation magnetisation σs of 1.4 A∙m2∙kg−1 and a coercive force Hc of 10 kA/m. Symmetric supercapacitors were fabricated from the synthesised bio-carbon material with 30% aqueous KOH and 1 M Na2SO4 as electrolytes. It was found that for bio-carbon synthesised at 800 °C, the specific capacitance in a 30% aqueous solution of KOH is 180 F/g, and in a 1 M aqueous solution of Na2SO4, it is 124 F/g. The cyclic voltammetry of the fabricated supercapacitors at different rates of potential expansion was investigated and analysed. Impedance studies on these supercapacitors were carried out. The equivalent electrical circuits describing the electrochemical processes in the studied supercapacitors were constructed and characterised.

Acidification-Induced Micronano Mechanical Properties and Microscopic Permeability Enhancement Mechanism of Coal.

An acid solution improves the pore-plugging problem in hydraulic fracturing, which in turn improves the permeability of the coal seam. The study aimed to investigate the effect of mixed acid on the micronano mechanical properties and permeability of the coal seam. The surface morphology of acidified coal was analyzed from the micronano scale using atomic force microscopy (AFM) and scanning electron microscopy. Additionally, the micronano scale mechanical characteristics of acidified coal were examined using the mechanical mode in an atomic force microscope. Furthermore, the complexity and connectivity of the micronano pores of samples were investigated using the low-temperature nitrogen adsorption and mercury intrusion porosimetry methods and the fractal theory. The results indicated that the surface minerals of acidified coal were dissolved, loosening the coal and increasing the complexity of the pore structure. Mineral deformation and pore deformation weakened the mechanical properties of coal at the micronano scale, and the mean elastic modulus of acidified coal (B# and E#) decreased by 28.78 and 25.66% compared to that of raw coal. The acid solution effectively enlarged the pore diameter, transitioning from micropores to mesopores and macropores, and the total pore volume of acidified coal increased by 1.88 times and 1.25 times, Kn increased from 0.064 to 0.581 and 0.37, respectively. The type of methane diffusion in the diffusion pores changed from Knudsen diffusion to transition-type diffusion. The tortuosity of the pore structure of acidified coal decreased, the fractal dimension of the tortuosity of the pore structure decreased, and the permeability increased by nearly three times. The research results indicate that the mechanical properties of coal decrease after acidification and that the microstructural changes can promote methane migration (diffusion-seepage), which can provide theoretical guidance for coalbed methane extraction in low-permeability coal reservoirs.

Pore Structure Characteristics of Shale Oil Reservoirs with Different Lithofacies and Their Effects on Mobility of Movable Fluids: A Case Study of the Chang 7 Member in the Ordos Basin, China

The Chang 7 member of the Triassic Yanchang Formation in the Ordos Basin is a significant continent shale oil reservoir in China. Therefore, conducting an in-depth investigation into the pore structure and fluid mobility characteristics of the Chang 7 shale oil reservoir holds immense importance for advancing shale oil exploration. This study conducts a detailed analysis of the pore structures and their impact on fluid mobility of the Chang 7 shale oil reservoir using multiple methodologies, i.e., a cast thin section, scanning electron microscopy (SEM), X-ray diffraction (XRD), high-pressure mercury injection (HPMI), low-temperature nitrogen adsorption (LTNA), and nuclear magnetic resonance (NMR). The results show that the sandstone in the Yanwumao area of the Chang 7 shale oil reservoir consists mainly of lithic arkose and feldspathic litharenite, which can be classified into three lithofacies (massive fine-grained sandstone (Sfm), silt-fine sandstone with graded bedding (Sfgb), and silt-fine sandstone with parallel bedding (Sfp)). Moreover, three pore structures (Type I, II, and III), and four pore spaces (nanopores, micropores, mesopores, and macropores) can be characterized. Pore structure Type I, characterized by large pores, exhibits bimodal pore diameter curves, resulting in the highest levels of movable fluid saturation (MFS) and movable fluid porosity (MFP). Pore structure Type II demonstrates unimodal pore structures, indicating robust connectivity, and higher MFS and MFP. Pore structure Type III primarily consists of dissolved and intercrystalline pores with smaller pore radii, a weaker pore configuration relationship, and the least fluid mobility. Furthermore, a correlation analysis suggests that the pore structure significantly impacts the fluid flowability in the reservoir. Favorable petrophysical properties and large pores enhance fluid flowability. Micropores and mesopores with high fractal dimensions have a greater impact on reservoir fluid mobility compared to macropores and nanopores. Mesopores mainly control MFS and MFP, while micropores govern the shift from bound fluid to movable fluid states. Among the lithofacies types, the Sfm lithofacies exhibit the highest fluid mobility due to their significant proportion of macropores and mesopores, whereas the Sfgb lithofacies have lower values because they contain an abundance of micropores. The Sfp lithofacies also dominate macropores and mesopores, resulting in medium fluid mobility levels. This study combines lithofacies types, micro-reservoir pore structure characteristics, and mobile fluid occurrence characteristics to better understand the dominant reservoir distribution characteristics of the Chang 7 shale oil reservoirs in the Ordos Basin and provide theoretical information for further optimization of production strategies.

Catalytic activity of modified silica gel adsorbents under conditions of methanol conversion from water-methanol waste of natural gas

The work is devoted to the analysis of factors affecting the catalytic activity of modified silica gel adsorbents under conditions of methanol conversion to dimethyl ether. The objects of the study were the initial and modified silica gel adsorbents ASM, ASM VS, BASF KC-Trockenperlen H and BASF KC-Trockenperlen WS used in the purification of methanol from water‒methanol waste of natural gas. The purpose of this paper is to study the effect of the specific surface area, elemental and phase composition, and operating time of adsorbents on the catalytic activity of modified silica gel adsorbents under conditions of methanol conversion to dimethyl ether. The composition and structural characteristics of the samples were determined by X‒ray fluorescence, X-ray diffraction analysis and low-temperature nitrogen adsorption. Based on the results of IR‒spectrometric and thermal studies, changes in the structure of the surfaces of adsorbents during their operation by various components of organic origin were evaluated. The catalytic activity of silica gel adsorbents in methanol conversion was studied in a fixed bed reactor at atmospheric pressure in the range of 120-290°C and an optimized rate of methanol-saturated nitrogen flow of 1200 ml/min. The methanol conversion process was controlled by gas‒liquid chromatography. An increase of the catalytic activity of adsorbents in methanol conversion to dimethyl ether was found in the range of ASM VS < BASF KC-Trockenperlen WS < BASF KC-Trockenperlen H < ASM. The maximum catalytic activity at 290°C was shown by the adsorbent ASM with 4.2% aluminum oxide and an amorphous structure, which significantly reduces methanol emissions into the atmosphere. For crystalline adsorbents ASM VS with an alumina content of 13.2%, the catalytic activity was minimal. It is shown that the decrease in the catalytic activity of adsorbents in gas treatment unit during operation is associated with a decrease in the value of the specific surface area of samples with a constant content of aluminum oxide and phase state, which is associated with the possible blocking of the catalytic centers of adsorbents due to the accumulation of components of organic origin in the process of natural gas purification. The establishment of factors affecting the methanol conversion to dimethyl ether on modified silica gel adsorbents will allow managing environmental risks, as well as reducing risks to humans during transportation and disposal of water-methanol waste from natural gas purification.

Reservoir characteristics and formation model of Upper Carboniferous bauxite series in eastern Ordos Basin, NW China

Through core observation, thin section identification, X-ray diffraction analysis, scanning electron microscopy, and low-temperature nitrogen adsorption and isothermal adsorption experiments, the lithology and pore characteristics of the Upper Carboniferous bauxite series in eastern Ordos Basin were analyzed to reveal the formation and evolution process of the bauxite reservoirs. A petrological nomenclature and classification scheme for bauxitic rocks based on three units (aluminum hydroxides, iron minerals and clay minerals) is proposed. It is found that bauxitic mudstone is in the form of dense massive and clastic structures, while the (clayey) bauxite is of dense massive, pisolite, oolite, porous soil and clastic structures. Both bauxitic mudstone and bauxite reservoirs develop dissolution pores, intercrystalline pores, and microfractures as the dominant gas storage space, with the porosity less than 10% and mesopores in dominance. The bauxite series in the North China Craton can be divided into five sections, i.e., ferrilite (Shanxi-style iron ore, section A), bauxitic mudstone (section B), bauxite (section C), bauxite mudstone (debris-containing, section D) and dark mudstone-coal section (section E). The burrow/funnel filling, lenticular, layered/massive bauxite deposits occur separately in the karst platforms, gentle slopes and low-lying areas. The karst platforms and gentle slopes are conducive to surface water leaching, with strong karstification, well-developed pores, large reservoir thickness and good physical properties, but poor strata continuity. The low-lying areas have poor physical properties but relatively continuous and stable reservoirs. The gas enrichment in bauxites is jointly controlled by source rock, reservoir rock and fractures. This recognition provides geological basis for the exploration and development of natural gas in the Upper Carboniferous in the study area and similar bauxite systems.

Assessment of Selected Surface and Electrochemical Properties of Boron and Strontium-Substituted Hydroxyapatites.

Tissue engineering is an interdisciplinary field of science that has been developing very intensively over the last dozen or so years. New ways of treating damaged tissues and organs are constantly being sought. A variety of porous structures are currently being investigated to support cell adhesion, differentiation, and proliferation. The selection of an appropriate biomaterial on which a patient's new tissue will develop is one of the key issues when designing a modern tissue scaffold and the associated treatment process. Among the numerous groups of biomaterials used to produce three-dimensional structures, hydroxyapatite (HA) deserves special attention. The aim of this paper was to discuss changes in the double electrical layer in hydroxyapatite with an incorporated boron and strontium/electrolyte solution interface. The adsorbents were prepared via dry and wet precipitation and low-temperature nitrogen adsorption and desorption methods. The specific surface area was characterized, and the surface charge density and zeta potential were discussed.

Influences of Different Acid Solutions on Pore Structures and Fractal Features of Coal

The effect of different acids on the pore structure and fractal characteristics of micropores and mesopores was determined with the help of low-temperature liquid nitrogen adsorption, X-ray diffraction, and the Frenkel–Halsey–Hill (FHH) model by using Yuwu coal as a sample and placing it in acidic environments, such as HF, HCl, HNO3, and CH3COOH. The results show that the acidization effects of HF and CH3COOH are separately dominated by the micropore and mesopore formation effects, while HCl and HNO3 mainly play their roles in expanding mesopores. After acidization, the surface fractal dimensions D1 and D1′ of micropores and mesopores in coal are always negatively correlated with the total specific surface area SBET, specific surface area Smic of micropores, and specific surface area Smes of mesopores. After being acidized by HF, D2 is negatively correlated with the total volume Vtot and the corresponding micropore volume Vmic, while acidization with HCl and HNO3 leads to the opposite result. After being acidized by CH3COOH, D2 has a negative correlation with Vtot and a positive correlation with Vmic. The structural fractal dimensions D2′ of mesopores in samples acidized by HF and CH3COOH are positively correlated with both the volume Vtot and mesopore volume Vmes, while it is the opposite for samples acidized by HNO3. D2′ of coal samples acidized by HCl is negatively correlated with Vtot while positively correlated with Vmes.

Effects of rock water with different acidity on microstructure and reburning ability of residual coal in goaf

To explore the influences of rock water acidity (PH = 4,5,7) over the microstructure and reburning behaviors of oxidized residual coal in the overlying goaf, the pore morphology, coal surface, functional group content and activity of pre-oxidized coal (O0) and water-immersed oxidized coal (OI) were analyzed by Low-temperature nitrogen adsorption and In-situ diffuse reflection experiments, combining with fractal dimension theory and functional group oxidation kinetics. The oxidation and reburning ability of coal samples has been analyzed by Thermogravimetric-Differential thermal analysis experiment. The results are as follows: Part of the type-III pores of pre-oxidized coal become type-II pores when immersed. The acidic solution has stronger corrosivity to O0 than distilled water, playing a role in smoothing coal and improving the uniformity of pore structure. The order of reburning ability of samples is OI7>OI4>O0>OI5 according to the ignition and stage average mass loss rate (RM). The reactivity of –OH may affect the reburning ability of coal more than its initial content. Soaking is beneficial to the decrease of activation energy of aliphatic groups, and the activity of –C=O- and -C-O- in acid-soaked coal molecules is stronger, so that they can take part in coal-oxygen composite reactions at low temperature.

Study of the influence of pore structure on the radon emission characteristics of terrestrial sedimentary shales after high temperature action.

Heat-assisted development of shale oil and gas is recognized as a vital technique for the efficient extraction of shale gas; however, there is a need for comprehensive investigation regarding radon release during the extraction process. The aim of this study was to investigate the pore structure and radon release characteristics of heat-treated black shale using low-temperature nitrogen adsorption (LTNA) and radon (Rn-222) measurement equipment. The findings reveal that temperature initially enhances radon release, which subsequently decreases. The maximum radon release occurs at 500 °C, reaching 1.46 times the initial stage. The radon release rate is positively correlated with the volume of micropores (< 2 nm) in the shale. Organic pores within the shale serve as the primary storage spaces for radon, and the intricate pore structure of organic matter provides an optimal environment for radon gas retention. These results contribute to elucidating the mechanisms behind the impact of thermal treatment on shale's radon release rate, which is crucial for guiding radon radiation evaluation in thermal treatment processes.