Effects of Permeability and Pyrite Distribution Heterogeneity on Pyrite Oxidation in Flooded Lignite Mine Dumps

<p>In certain reactive transport applications, strong coupling between geochemical reactions and hydrodynamics exists. Dissolution and precipitation of minerals, such as the conversion between gypsum and anhydrite [1] or the precipitation of nesquehonite during CO<sub>2</sub> sequestration [2], as well as gas bubble formation [3] are geochemical processes which modify the multiphase flow dynamics, with direct feedback on reactive transport processes. In addition, heat generation induced by sulphide mineral oxidation can lead to significant increases in temperature [4], impacting flow, transport and geochemical reactions. In these instances, commonly used reactive transport modelling approaches, which rely on decoupling flow and reactive transport processes, have limitations. For density dependent or two-phase flow problems in the presence of a gas phase, the coupling between flow and reactive transport can be accounted for through a Picard iterative approach [3,5,6]. However, this approach is computationally expensive, involving the solution of nonlinear problems multiple times during each timestep, and convergence properties are often poor. More recently, a weak explicit coupling approach was developed to capture the impact of chemistry on flow by integrating water as a component and perform a volume balance calculation [7]. In the current work, a compositional approach is implemented into MIN3P-THCm, in which the flow variables (pressure, density) are expressed based on mass variables. Hence, this global implicit approach does not require solving the flow problem, but instead integrates groundwater flow processes directly into the reactive transport equations. We show that this approach yields very similar results to the commonly used approaches for single and two-phase flow. Finally, we show that, in highly coupled systems, not considering these coupled effects may lead to significant errors in simulating system evolution, highlighting the benefits of the newly developed approach.</p><p> </p><p>[1] Jowett, Cathles & Davis (1993). AAPG Bulletin, 77(3), 402-413.</p><p>[2] Harrison, Dipple, Power & Mayer (2015). Geochimica et cosmochimica Acta, 148, 477-495.</p><p>[3] Amos and Mayer (2006). Journal of contaminant hydrology, 87(1-2), 123-154.</p><p>[4] Lefebvre, Hockley, Smolensky & Gélinas (2001). Journal of contaminant hydrology, 52(1-4), 137-164.</p><p>[5] Henderson, Mayer, Parker, & Al (2009). Journal of contaminant hydrology, 106(3-4), 195-211.</p><p>[6] Sin, Lagneau and Corvisier (2017). Advances in Water Resources, 100, 62-77.</p><p>[7] Seigneur, Lagneau, Corvisier & Dauzères (2018). Advances in Water Resources 122, 355-366.</p>

The impact of organic waste material and fly ash on microbial and chemical pyrite oxidation was investigated in a field experiment, as well as in column tests under laboratory conditions. For the field experiment, pyritic mine spoil was ameliorated with fly ash and treated either with mineral fertiliser, with sewage sludge or with compost. Independent of treatment, during the 18 months following application, the pyrite-S contents decreased steadily in the top spoil (0–30 cm depth). However, high variations of the pyrite-S content were observed. Compared to other pyrite oxidation studies, the pyrite content of the mine spoil at the experimental site was low. Therefore, a model spoil with a higher pyrite content, derived from Tertiary strata of the overburden sequence in the same open-cast mine, was used for the column experiments. For the first column experiment, the model spoil was mixed with fly ash and mineral fertiliser, reflecting the common reclamation practice in the Lusatian open-cast lignite mining district. Columns with this spoil were either inoculated with different cell numbers of autochthonous acidophilic bacteria, isolated from the model spoil, or with a commercial strain of Thiobacillus ferrooxidans. The ratio of sulphate-S to total S was used as a measure for the degree of pyrite oxidation. The ratio of sulphate-S to total S increased within 28 days of incubation. The increase was related to the inoculated cell numbers of bacteria, but independent of the origin of the bacteria. It can be stated, that autochthonous bacteria from the model spoil oxidised pyrite at a similar rate as did the commercial T. ferrooxidans strain. For the second column test, mineral fertiliser, sewage sludge or compost were applied to the model spoil. The columns were inoculated with autochthonous bacteria, isolated from the model spoil. Application of sewage sludge and compost seemed to promote the weathering of pyrite, as the ratio of sulphate-S to total S increased more rapidly in these treatments compared to control or mineral fertiliser application. Both experiments showed an increase of cell numbers of inoculated bacteria, independent of the ratio of sulphate-S to total S.

Decommissioning of lignite mines in the course of phasing-out electric power generation from fossil fuels in the European Union (EU) is one of the strategic key pillars to reduce net greenhouse gas emissions by 55% compared to the 1990 levels until 2030, and achieving climate-neutrality by 2050. Germany’s emission reduction targets are even more ambitious with 65% and 88% scheduled for 2030 and 2040, respectively. Repurposing phasing-out open-pit lignite mines into Hybrid Pumped Hydropower Storage (HPHS) installations for excess energy from the electric grid and renewable sources contributes not only to the EU Green Deal and EU energy supply security, but additionally increases the regional economic value and stabilises the job market. Pumped hydropower is well established for storing excess energy from the electric grid and for load balancing with a total installed capacity of 7.89 GW in Germany and a current total share of 78.6% in the energy storage sector. Total round-trip efficiencies of up to 85% and extraordinary high storage capacities compared to battery-based solutions can be realised. Another advantage of implementing the technology in former open-pit mines is that costs of constructing the two required storage reservoirs are significantly reduced due to the presence of the open-pit hole. Multiple open-pit lignite mines were closed in Germany in the past decades, and nine are expected to cease operation by 2038. Several studies assessing the potentials for PHS based on existing reservoirs have been undertaken, but these do not yet consider the additional potentials of open-pit mines. The aim of the present study was to investigate the potential theoretical and technical power production and storage capacities becoming available by repurposing open-pit mines into HPHS installations. For that purpose, a database of German open-pit lignite mines was established. An analytical model was employed to determine the power production and storage capacities of 34 German open-pit lignite mines, of which 13 meet the previously defined site selection criteria. The results of the present study show that the currently installed energy storage potentials in Germany can be extended by additional 1.42 GW (increase by >18%), increasing the installed PHS capacity by 22.9% at the same time. These findings are essential to guide policy and decision makers involved in the German and EU energy transition. The methodology will be extended to member states of the European Union in the next step. The present study has received funding from the Research Fund for Coal and Steel—2020, under grant agreement No. 101034022 (ATLANTIS).

Heterogeneity in physical and chemical properties is a common characteristic in a subsurface environment. This study investigated the effect of physico-chemical heterogeneity on arsenic (As) sorption and reactive transport under water extraction in a layered system with preferential flow paths. A flume experiment was performed to derive the spatio-temporal data of As reactive transport. The results indicated that the heterogeneous system significantly accelerated downward (vertical direction) As migration as a coupled effect of physical and chemical heterogeneity that led to fast As transport with low As sorption along the preferential flow paths. The results also indicated that such a heterogeneity effect was driven by water extraction that enhanced the downward groundwater flow along the preferential flow paths. Numerical simulations were performed by matching the experimental results to provide insights into the dominant processes controlling the As migration in the heterogeneous systems. The simulation results highlighted the importance of the kinetic oxidation of mineral-bonded Fe(II) to Fe(III) in the clay matrix that dynamically increased As sorption affinity and retarded As reactive transport. A coupled model of reactive transport along the preferential flow paths, sorption-retarded diffusion from the preferential flow paths into the clay matrixes, and reactions that change sorption affinity in the matrix was required to describe the As reactive transport systems with physico-chemical heterogeneities. The results have strong implications for understanding and modeling As downward migration from shallow to deep aquifers under groundwater pumping conditions in field systems with inherent heterogeneity.

Improving the performance of proton exchange membrane fuel cells (PEMFCs) requires deep understanding of the reactive transport processes inside the catalyst layers (CLs). In this study, a particle-overlapping model is developed for accurately describing the hierarchical structures and oxygen reactive transport processes in CLs. The analytical solutions derived from this model indicate that carbon particle overlap increases ionomer thickness, reduces specific surface areas of ionomer and carbon, and further intensifies the local oxygen transport resistance (Rother). The relationship between Rother and roughness factor predicted by the model in the range of 800-1600 s m-1 agrees well with the experiments. Then, a multiscale model is developed by coupling the particle-overlapping model with cell-scale models, which is validated by comparing with the polarization curves and local current density distribution obtained in experiments. The relative error of local current density distribution is below 15% in the ohmic polarization region. Finally, the multiscale model is employed to explore effects of CL structural parameters including Pt loading, I/C, ionomer coverage and carbon particle radius on the cell performance as well as the phase-change-induced (PCI) flow and capillary-driven (CD) flow in CL. The result demonstrates that the CL structural parameters have significant effects on the cell performance as well as the PCI and CD flows. Optimizing the CL structure can increase the current density and further enhance the heat-pipe effect within the CL, leading to overall higher PCI and CD rates. The maximum increase of PCI and CD rates can exceed 145%. Besides, the enhanced heat-pipe effect causes the reverse flow regions of PCI and CD near the CL/PEM interface, which can occupy about 30% of the CL. The multiscale model significantly contributes to a deep understanding of reactive transport and multiphase heat transfer processes inside PEMFCs.

Characteristics of catchments disturbed by lignite mining—case study of Schlabendorf/Seese (Germany)

Sevoflurane induction for general anaesthesia has been reported to be safe, reliable and well accepted by patients. Sevoflurane induction uses either low or high initial concentrations. The low initial concentration technique involves initially administering a low concentration of sevoflurane and gradually increasing the concentration of the dose until the patient is anaesthetized. The high initial concentration technique involves administering high concentrations from the beginning, then continuing with those high doses until the patient is anaesthetized. This review was originally published in 2013 and has been updated in 2016. We aimed to compare induction times and complication rates between high and low initial concentration sevoflurane anaesthetic induction techniques in adults and children who received inhalational induction for general anaesthesia. We defined 'high' as greater than or equal to and 'low' as less than a 4% initial concentration. For the updated review, we searched the following databases: Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 2), MEDLINE (1950 to February 2016), EMBASE (1980 to February 2016), Latin American Caribbean Health Sciences Literature (LILACS) (1982 to February 2016) and the Institute for Scientific Information (ISI) Web of Science (1946 to February 2016). We also searched the reference lists of relevant articles and conference proceedings and contacted the authors of included trials. The original search was run in September 2011. We sought all published and unpublished, randomized controlled trials comparing high versus low initial sevoflurane concentration inhalational induction. Our primary outcomes included two measures of anaesthesia (time to loss of the eyelash reflex (LOER) and time until a weighted object held in the patient's hand was dropped), time to successful insertion of a laryngeal mask airway (LMA) and time to endotracheal intubation. Other outcomes were complications of the technique. We used standardized methods for conducting a systematic review as described in the Cochrane Handbook for Systematic Reviews of Interventions. Two review authors independently extracted details of trial methods and outcome data from reports of all trials considered eligible for inclusion. We conducted all analyses on an intention-to-treat basis, when possible. We estimated overall treatment effects by using a fixed-effect model when we found no substantial heterogeneity, whereas we applied the random-effects model in the presence of considerable heterogeneity. We reran the searches and included one new study (100 participants) in this updated review. In total, we included 11 studies with 829 participants, although most analyses were based on data from fewer participants and evidence of low quality. We noted substantial heterogeneity in the included trials. Thus, our results should be read with caution. It was not possible to combine trials for the primary outcome (LOER), but individual trials reported faster induction times (typically 24 to 82 seconds faster, 41 seconds (31.37 to 50.62)) with high initial concentration sevoflurane (six studies, 443 participants, low-quality evidence). Apnoea appeared to be more common in the high initial concentration sevoflurane group (risk ratio (RR) 3.14, 95% confidence interval (CI) 1.72 to 5.7, two studies, 160 participants, low-quality evidence). We found no evidence of differences between the two groups in the incidence of cough (odds ratio (OR) 1.23, 95% CI 0.53 to 2.81, eight studies, 589 participants, low-quality evidence), laryngospasm (OR 1.59, 95% CI 0.16 to 15.9, seven studies, 588 participants, low-quality evidence), breath holding (OR 1.16, 95% CI 0.47 to 2.83, five studies, 389 participants, low-quality evidence), patient movement (RR 1.14, 95% CI 0.69 to 1.89, five studies, 445 participants, low-quality evidence) or bradycardia (OR 0.8, 95% CI 0.22 to 2.88, three studies, 199 participants, low-quality evidence), and the overall incidence of complications was low. A high initial concentration sevoflurane technique probably offers more rapid induction of anaesthesia and a similar rate of complications, except for apnoea, which may be more common with a high initial concentration. However, this conclusion is not definitive because the included studies provided evidence of low quality.

Sevoflurane induction for general anaesthesia has been reported to be safe, reliable and well accepted by patients. Sevoflurane induction uses either low or high initial concentrations. The low initial concentration technique involves initially administering a low concentration then gradually increasing the dose until the patient is anaesthetized. The high initial concentration technique involves administering high concentrations from the beginning, continuing until the patient is anaesthetized. We aimed to compare the induction times and complications between high and low initial concentration sevoflurane induction in patients who received inhalational induction for general anaesthesia. We defined 'high' as greater and 'low' as less than a 4% initial concentration. We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 9); MEDLINE (1950 to September 2011); EMBASE (1980 to September 2011); LILACS (1982 to September 2011) and ISI Web of Science (1946 to September 2011). We also searched the reference lists of relevant articles, conference proceedings; and contacted the authors of included trials. We sought all published and unpublished, randomized controlled trials comparing high versus low initial sevoflurane concentration inhalational induction. Our primary outcomes were two measures of anaesthesia (time to loss of the eyelash reflex (LOER) and time until a weighted object held in the patient's hand was dropped), time to successful insertion of a laryngeal mask airway (LMA), and time to endotracheal intubation. Other outcomes were complications of the technique. We used the standardized methods for conducting a systematic review as described by the Cochrane Handbook for Systematic Reviews of Interventions. Two authors independently extracted details of trial methodology and outcome data from reports of all trials considered eligible for inclusion. All analyses were made on an intention-to-treat basis, where possible. The overall treatment effects were estimated by using a fixed-effect model when there was no substantial heterogeneity, whereas the random-effects model was applied in the presence of considerable heterogeneity. We used data from 10 studies with 729 participants in the review, though most analyses were based on data from fewer participants. There was substantial heterogeneity in the trials. Thus, our results should be read with caution. It was not possible to combine the trials for the primary outcome (LOER) but individual trials found faster induction times (typically 24 to 82 seconds faster) with high initial concentration sevoflurane. Apnoea appeared to be more common in the high initial concentration sevoflurane group (two trials,160 participants). There was no evidence of a difference in the incidence of cough, laryngospasm, breath holding, bradycardia, salivation and hypotension between the two groups, with the overall incidence of complications being low. A high initial concentration sevoflurane technique probably offers more rapid induction of anaesthesia and a similar rate of complications except for apnoea, which may be more common with a high initial concentration. However, this conclusion is not definitive.

Reactive fronts in chemically heterogeneous porous media: Experimental and modeling investigation of pyrite oxidation

Experiences with open-pit mine flooding in German lignite mining regions show that hydrogeochemical processes can become critical ecological and economic factors for the realisation of Pumped Hydropower Storage (PHS) projects. Depending on sulphide and oxygen availability as well as buffering and dilution processes, acid mine drainage and increased sulphate and metal concentrations can have negative impacts on ecosystems and groundwater resources as well as the installed PHS infrastructure. As part of the ATLANTIS project, this study aimed to quantify changes in water composition in the lower storage reservoir resulting from PHS operation under different hydrogeochemical boundary conditions.For the present parameter study, data sets on hydrochemistry, hydrogeology and morphology of flooded German lignite mines were used to develop a numerical hydrochemical reaction path modelling framework. The chemical calculations were realised with PHREEQC (Parkhurst and Appelo, 2013), while the input and output data were managed via the Python-based simulation framework and PHREEQPY (Müller, 2022). The implemented parallelised workflow made it possible to analyse and evaluate more than 12,000 parameter combinations for various hydrogeological baseline scenarios. The influencing factors considered in these scenarios include the initial flooding of the open-pit mines, source terms due to precipitation, groundwater inflow and surface run-off, mineral availability in the sediments and the pumping cycles between the lower and upper storage reservoirs of the PHS installation.The simulation results show that the volume of water migrating between the lower reservoir and its adjacent aquifers during the pumping cycles is too small to influence the water quality of the reservoir on the short term. The long-term availability of buffer capacities in the reservoir and the present mine waste dumps determine the eventual development of acidic or pH-neutral mine water. Sulphate concentrations are mainly influenced by dilution processes, what underlines the relevance of considering additional source and sink terms. Depending on these as well as the availability of oxygen and quantities of sulphide present in the adjacent sediments, the time required to achieve a chemical equilibrium in the lower storage reservoir varies from a few weeks to several years.In summary, the operation of pumped storage power installations in former open-pit lignite mines can be safely realised if sufficient acid buffer capacities are available and dilution through additional water in- and outflows is sufficiently high.The present study has received funding from the Research Fund for Coal and Steel—2020, under grant agreement No. 101034022 (ATLANTIS).LiteratureMüller, M. (2022): PhreeqPy - Python Tools for PHREEQC. https://www.phreeqpy.com/. Last accessed on 09.01.2024.Parkhurst, D. L., & Appelo, C. A. J. (2013). Description of input and examples for PHREEQC version 3—a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. US geological survey techniques and methods, 6(A43), 497.

The diatom-inferred pH reconstructions for a naturally neutralized pit lake in south-west Poland using the Mining and the Combined pH training sets

Coupled three-phase flow and reactive transport processes are widely encountered in many scientific and engineering problems. In the present study, a pore-scale model based on the lattice Boltzmann method is developed to simulate coupled three-phase flow and reactive transport processes. The model is validated by contact angle test of droplets on a curved surface and confined reactive mass transport in a three-phase system. The pore-scale model validated is then employed to study the three-phase reactive transport in channels and porous media. The evolution of the three-phase distribution, the concentration field, and the contact line length are discussed in detail. For a two-channel structure, the result shows that as the viscosity ratio increases, the phase with higher viscosity is more difficult to be displaced. Moreover, as the surface tension force between two certain phases increases, the third phase tends to form a film between the two phases, thus suppressing the reactive transport between the two phases. Finally, pore-scale simulation results of three-phase flow in a two-dimensional porous medium show that as viscosity of the phase to be displaced increases, the recovery rate of the displaced phase decreases, and the displacing phase tends to follow the mechanism of viscous fingering. Finally, while the viscosity of the displaced phase can be reduced due to the existence of the species, the recovery rate does not necessarily increase and sometimes even reduces due to the combined bypass and lubrication effects.

The injection of a low frequency electrical current in the ground between two electrodes A and B generates a magnetic field that can be measured at the ground surface with sensitive magnetic sensors. The map of the magnetic field, measured at the frequency of the injected current, can be used to determine the paths of the current through the ground. When the current is channelled along preferential conductive paths, the MagnetoMetric Resistivity (MMR) method can be used to detect these paths. Conductive current paths can be associated with preferential flow paths of groundwater when the two electrodes A and B are in the direction of the flow and when the flow path is highly electrically conductive with respect to the background. We first review the background equations for the magnetic field in MMR. Then, we provide the kernel of the problem using Biot and Savart law to connect the components of the observed magnetic field to the current density distribution. We also develop a simple approach to invert the magnetic field in terms of electrical current paths. To illustrate how the method works, we develop five synthetic models to test the sensitivity of the method to the properties of the conductive targets channelling the electrical current. The targets are characterized by different shapes, sizes, depths, and conductivity contrasts with the background. Then, we proceed with a case study for which the MMR method is used to identify and map preferential groundwater flow paths bypassing a mine waste rock dump drainage collection trench into the tailings pond. In this case, the conductivity of the flow paths is much stronger than the background conductivity due to the high mineralization of the ground water along these paths. The method underlines the 3-D architecture of these flow paths.

Scheduled decommissioning of lignite mining in Europe requires innovative and economic strategies to support coal regions in transition. The R&D project ATLANTIS is funded by the European Research Fund for Coal and Steel and started in late 2021, aiming at an integrated feasibility assessment on transforming open-pit coal mines into hybrid energy storage projects. Hereby, repurposing of open-pit mines for hybrid pumped hydropower storage (HPHS) of excess energy from the electric grid and renewable sources available in the vicinity of open-pit mines in abandonment will contribute to the EU Green Deal, while increasing the economic value, stabilising the regional job market and contributing to EU energy supply security. The main objective of ATLANTIS is the elaboration of a technical and economic feasibility study on HPHS in open-pit coal mines. The present contribution will provide insights into the R&D activities within the scope of the project. For that purpose, two target open-pit mines in Greece and Poland were investigated in detail, including analyses supported by geographic information systems (GIS) based on previously defined HPHS design criteria [1] as well as hydro(geo)logical, hydrochemical and geotechnical analyses. At the Polish Szczercow mine located in the Lodz Coal Basin a HPHS capacity of 350 MW can be realised with a hydraulic head difference of approximately 240 m, able to support even more than the currently planned build-out of about 250 MW renewable energy sources made up of wind and photovoltaic parks. A total capacity of 180 MW is feasible at the Kardia mine in the Ptolemais Basin in Greece, whereby the hydraulic head difference amounts to about 100 m. Here, a photovoltaic build-out of 1.2 GW is scheduled. Potential environmental impacts were addressed via an extended risk analysis, consisting of qualitative and quantitative and components integrated by means of feedback loops and supported by the experience of multidisciplinary experts in the fields of hydrogeology, hydrogeochemistry, geotechnics, mining engineering and socio-economics. Based on the findings of this assessment, mitigation measures for the high-ranked risks were defined and are already considered in the course of the specific mine abandonment processes. Dynamic economic models using day-ahead energy market data were implemented to optimise the HPHS operation and support decision making related to the operational modes. Furthermore, the results of the socio-economic footprint assessment undertaken highlight the regional benefits of the HPHS implementation as alternative to the previously envisaged restoration procedure. The elaborated feasibility study on HPHS in abandoned open-pit mines is a key contribution to the industrial partner’s decision making processes and further demonstrates the potentials for application of the project’s findings at the EU level.   [1] Krassakis, P., Karavias, A., Zygouri, E., Roumpos, C., Louloudis, G., Pyrgaki, K., Koukouzas, N., Kempka, T., Karapanos, D. (2023): GIS-Based Assessment of Hybrid Pumped Hydro Storage as a Potential Solution for the Clean Energy Transition: The Case of the Kardia Lignite Mine, Western Greece. Sensors, 23, 2, 593. https://doi.org/10.3390/s23020593   The present study has received funding from the Research Fund for Coal and Steel—2020, under grant agreement No. 101034022 (ATLANTIS).

If a mine waste pile is left open, an active chemical reaction of oxidation is often found due to the commonly high content of pyritic materials. The oxidation of pyrites is an exothermic process and the released heat will promote the flow of fresh oxygen from the surrounding atmosphere into the waste dump. As a result, oxidation reaction will accelerate and temperature within the dump can increase to as high as 60°C above the ambient temperature. The oxidation process also releases sulphuric acid and hydrogen ions into ground water to cause water contamination. Low‐permeability covers such as clay liners have been recently proposed to abate the oxidation process in mine wastes. The effectiveness of using low‐permeability materials to cover mine wastes in order to suppress the pyrite oxidation is examined. By conducting the theoretical analysis of the onset of convective air flow within waste rocks, the conditions under which soil gas flow is significant are identified. By comparing the results with previous field measurements and theoretical analysis for the uncovered conditions, it is shown that low‐permeability covers can effectively suppress soil gas flow and slow down the pyrite oxidation process in mine wastes. Copyright © 2001 John Wiley & Sons, Ltd.