Characterization of silver-kaolinite (AgK): an adsorbent for long-lived 129I species

Bentonite is a preferred buffer and backfill material for deep geological disposal of high-level nuclear waste (HLW). Bentonite does not retain anions by virtue of its negatively charged basal surface. Imparting anion retention ability to bentonite is important to enable the expansive clay to retain long-lived I-129 (iodine-129; half-life = 16 million years) species that may escape from the HLW geological repository. Silver-kaolinite (AgK) material is prepared as an additive to improve the iodide retention capacity of bentonite. The AgK is prepared by heating kaolinite-silver nitrate mix at 400 degrees C to study the kaolinite influence on the transition metal ion when reacting at its dehydroxylation temperature. Thermo gravimetric-Evolved Gas Detection analysis, X-ray diffraction analysis, X-ray photo electron spectroscopy and electron probe micro analysis indicated that silver occurs as AgO/Ag2O surface coating on thermally reacting kaolinite with silver nitrate at 400 degrees C

The hydrology of an ephemerally flooded doline: Pwll-y-Felin, South Wales, UK

The first annual hydrograph from an ephemerally-flooded doline in the UK is described. Flood duration and volume were characterised by combining water-level data with a detailed topographic survey. Rapid surface runoff of Na–SO4-type water is derived from a localized topographic catchment. The inflow stream produced a ‘flashy’ hydrograph with maximum flood depths reaching 7m when the doline can contain 7,383 m3 of water. Flooding occurred over 161 of the 365 day study period, with an average flood depth of 2.4m. Stage dependent drainage properties suggested that water loss is greater when the flood depth is >3m, indicating that there may be additional drainage conduits at higher levels within the doline. A conservative estimate of 138 ML year is provided for net loss of water to the underlying aquifer. The vegetation shows some zonation potentially related to flood duration, with higher diversity in the marginal zone subject to the greatest fluctuation in water levels. The classification of Pwll-y-Felin and other small ephemeral karstic water bodies should be considered not only as geological landforms but as small karstic dependant wetlands. Under-recording of small, isolated temporary water bodies is of concern to international conservation bodies. The methodology presented can help to characterize the hydrology of ephemerally flooded dolines and could be used better to understand karst dependent habitats, recharge in karst aquifers, water budget calculations and to improve management and regulation in karst aquifers

Low enthalpy heat recovery potential from coal mine discharges in the South Wales Coalfield

Fossil fuels generate the majority of space heating and hot water demand in the UK, contributing to greenhouse gas emissions and energy security issues. Concerns about the long term availability of traditional fossil fuels are recognised by the UK government and sustainable, low carbon supplies are being actively investigated. One such option in the renewable energy mix is the use of low enthalpy heat, using open loop ground source technology to recover heat from abandoned flooded coal mines. To assess this potential in the South Wales Coalfield we measured annual temperatures and chemistry at sixteen mine water sites. Mean monthly temperatures ranged from 10.3 to 18.6 °C with an overall mean of 13.3 °C, proving their suitability for low enthalpy heat recovery. Collated data shows the geothermal gradient can vary within the South Wales Coalfield. Exothermic chemical reactions within abandoned mine workings can also contribute to the overall temperature of mine waters. Using discharge and temperature data we estimate that 42 MW of potential heating energy could be generated from currently monitored mine water discharges, however historic dewatering data from operational mines suggests that 72 MW could be generated, enough to heat about 6500 homes. The true potential, if new pumping wells were drilled to exploit flooded workings is likely to be much greater. The use of low enthalpy mine water for space heating and hot water indicate a total emission reduction of around 59% and 76% compare to main gas and electricity heating respectively

Modelling anisotropic adsorption-induced coal swelling and stress dependent anisotropic permeability

To investigate the anisotropy of coal swelling, this study proposes an effective stress model for saturated, adsorptive fractured porous media by considering gas adsorption induced surface stress change on solid-fluid interface. The effective stress model can be used to capture the anisotropic swelling of coal combining anisotropic mechanical properties and to link with the anisotropic permeability. Direction dependent fracture compressibility is used to describe the evolution of anisotropic stress-dependent permeability behaviour. Particularly, the impact of gas adsorption on fracture compressibility is considered in the model. The proposed models were tested against experimental results and compared to relevant existing models available in literatures. The model predicts that the coal swelling in the direction perpendicular to the bedding plane, is greater than that in the parallel plane. Coal permeability in each direction can be affected by the stress changes in any directions. The permeability parallel to the bedding plane is more sensitive to change in stresses than in perpendicular to the bedding due to higher fracture compressibility. The cleat compressibility could increase with gas adsorption, especially for carbon dioxide. Permeability loss in the direction parallel to the bedding plane is more significant than that in the direction perpendicular to the bedding plane. The presented models provide a tool for quantifying gas adsorption-induced anisotropic coal swelling and permeability behaviours

Characterisation of the contaminants generated from a large-scale ex-situ underground coal gasification study using high-rank coal from the South Wales coalfield

Abstract This paper presents an analysis of contaminants generated from large-scale, laboratory-based, underground coal gasification (UCG) experiments using a high-rank coal from the South Wales Coalfield. The experiments were performed at atmospheric and elevated pressures (30 bar) by varying the oxidants’ composition. The experiments were designed to predict the amount of produced water and contaminants generated at each stage of the operating conditions. The mass balance of water supplied and produced in the experiments was accounted for. Chemical analyses of produced water, char and ash contents were performed to quantifytheinorganicandorganicchemicalparameters. Mostof the contaminant concentrationsinthe produced water from the 30-bar pressure experiment were lower than the concentrations generated from the atmospheric pressure experiment. The measured concentrations of theinorganicchemicalspeciesandtheinorganicparameters of the coal seam water from the South Wales Coalfieldwereusedintheoreticalcalculationstopredict the dominant equilibrium species concentrations in a hypothetical scenario of effluent contaminated groundwater.Thebiodegradationoforganiccontaminantssuch as phenol, benzene and sorbed fractions of inorganic contaminants from the produced water on iron oxide in theashresiduewaspredictedusingexistingbiotransformation kinetics and surface complexation models, respectively. The biodegradation of phenol and benzene would be a slow process even at optimum conditions and the iron oxide left in the cavity can act as a sorbent for a few inorganic species. The evidence from the present study suggests future work towards (i) developing an appropriate water treatment process during gas cleaning, (ii) operational procedure (pressure and proportions of oxidant) and (iii) developing UCG-specific experimental prediction of contaminant transportation and transformation kinetics. Keywords High-rankcoal.Undergroundcoal gasification.Highpressure.Producedwater.Inorganic organiccontaminants.As

Modeling Gas Adsorption–Desorption Hysteresis in Energetically Heterogeneous Coal and Shale

Adsorption of gases in porous adsorbents such as coal and shale generally exhibits the phenomenon of hysteresis. Most of the previous studies on desorption hysteresis were conducted via experimental tests. However, few theoretical models that represent adsorption–desorption hysteresis of gases in porous sorbents are available. To address this issue, this work develops a new adsorption–desorption model for describing adsorption and desorption isotherms of gases with hysteresis. Particularly, the energetically heterogeneous surfaces of an adsorbent are considered via the patchwise model. Based on the change in site energy distribution, a logarithmically pressure-dependent hysteresis index, which is used to measure the degree of hysteresis, is derived for quantitative assessment of the degree of hysteresis. Besides, the correlation between the desorption isotherm and initialized pressure for desorption is established. The accuracy of the proposed model to adequately describe the adsorption–desorption hysteresis of gas in coal and shale is demonstrated by validating the model against laboratory experiments obtained from the literature. The results indicate that the adsorption isotherm depends significantly on site energy distribution. By comparing the site energy distributions for adsorption and desorption isotherms, it is found that the desorption hysteresis can be attributed to the change in pore size distribution caused by adsorption-induced deformation. The analyses support that the proposed model can be used as an effective tool to quantitatively predict the amount of released gas during desorption, which is significant for designing coalbed methane or shale gas production and assessing long-term CO2 storage behavior

Low subcritical co2 adsorption-desorption behavior of intact bituminous coal cores extracted from a shallow coal seam

This study focuses on improving fundamental understanding of low, subcritical CO2 adsorption–desorption behavior of bituminous coals with the aim to evaluate the utility of shallow-depth coal seams for safe and effective CO2 storage. Comprehensive data and a detailed description of coal–CO2 interactions, e.g., adsorption, desorption, and hysteresis behavior of intact bituminous coals at CO2 pressures <0.5 MPa, are limited. Manometric sorption experiments were performed on coal cores (50 mm dia. and 30- or 60-mm length) obtained from a 30 m deep coal seam located at the Upper Silesian Basin in Poland. Experimental results revealed that the adsorption capacities were correlated to void volume and equilibrium time under low-pressure injection (0.5 MPa). The positive deviation, observed in the hysteresis of adsorption–desorption isotherm patterns, and the increased sample mass at the end of the tests suggested CO2 pore diffusion and condensation. This behavior is vital for assessing low-pressure CO2 injection and storage capabilities of shallow coal seams where confining pressure is much lower than that of the deeper seams. Overall, CO2 adsorption depicts a type II adsorption isotherm and a type H3 hysteresis pattern of the IUPAC classification. Experimental results fitted better to the Brunauer–Emmett–Teller model than the Langmuir isotherm model. CO2 adsorption behavior of intact cores was also evaluated by characteristic curves. It was found that Curve I favored physical forces, i.e., the presence of van der Waals/London dispersion forces to describe the coal–CO2 interactions. However, analysis of Curve II indicated that the changing pressure-volume behavior of CO2 in the adsorbed phase, under low equilibrium pressures, cannot be ignored

Kinetics of gas phase CO2 adsorption on bituminous coal from a shallow coal seam

This article examines the CO2 adsorption–desorption kinetics of bituminous coal under low pressure injection (0.5 MPa) in the context of CO2 sequestration in shallow level coal seams. This study used two different sizes of intact core samples of bituminous samples from seam no. 30 at the Experimental Mine Barbara (EMB) in Katowice, Poland. Manometric adsorption kinetics experiments were conducted on 50 mm dia. 60 mm long coal core samples (referred to as EMB1) and 50 mm dia. 30 mm long coal core samples (referred to as EMB2). The kinetics of adsorption at injection pressures ranging from 0.1 to 0.5 MPa were compared to those at elevated pressures ranging from 0.5 to 4.5 MPa. For the first time, intact sample adsorption–desorption data were fitted in pseudo first order (PFO), pseudo second order (PSO), and Bangham pore diffusion models. The PSO model fits the data better than the PFO model, indicating that bulk pore diffusion, surface interaction, and multilayer adsorption are the rate-determining steps. Comparing the equilibrium amount of adsorbed (qe) obtained for the powdered samples (9.06 g of CO2/kg of coal at 0.52 MPa) with intact samples (11.68 g/kg at 0.53 MPa and 7.58 g/kg at 0.52 MPa for the intact EMB1 and EMB2 samples) showed the importance of conducting experiments with intact samples. The better fit obtained with the Bangham model for lower pressure equilibrium pressures (up to 0.5 MPa) compared to higher pressure equilibrium pressures (4.5 MPa) indicates that bulk pore diffusion is the rate-determining step at lower pressures and surface interaction takes over at higher pressures. The amount of CO2 trapped within the coal structure following the desorption experiments strengthens the case for intact bituminous coal samples’ pore trapping capabilities