Geothermal Brine Research Articles

Three-chamber electrochemical reactor for selective lithium extraction from brine

Efficient lithium recovery from geothermal brines is crucial for the battery industry. Current electrochemical separation methods struggle with the simultaneous presence of Na+, K+, Mg2+, and Ca2+ because these cations are similar to Li+, making it challenging to separate effectively. We address these challenges with a three-chamber reactor featuring a polymer porous solid electrolyte in the middle layer. This design improves the transference number of Li+ (tLi+) by 2.1 times compared to the two-chamber reactor and also reduces the chlorine evolution reaction, a common side reaction in electrochemical lithium extraction, to only 6.4% in Faradaic Efficiency. Employing a lithium-ion conductive glass ceramic (LICGC) membrane, the reactor achieved high tLi+ of 97.5% in LiOH production from simulated brine, while the concentrations of Na+ K+, Mg2+, and Ca2+ are below the detection limit. Electrochemical experiments and surface analysis elucidated the cation transport mechanism, highlighting the impact of Na+ on Li+ migration at the LICGC interface.

Review of methods for lithium extraction from geothermal brines

Lithium, a highly reactive and valuable metal, is essential for the clean energy transition, powering electronic devices, electric cars, and energy storage systems. With demand for lithium surging, environmentally responsible and economically viable extraction methods are crucial. Traditional sources include brines and mineral clays, but lithium-ion batteries have become a significant secondary source due to their high consumption of lithium. This review explores various extraction methods from geothermal brines, focusing on conventional techniques like solar evaporation, precipitation, and solvent extraction, highlighting their efficiency and limitations. Advanced electrochemical methods are also discussed, including the use of electrochemical ion pumping and electrodialysis, showcasing their potential for high-purity lithium recovery. Direct Lithium Extraction (DLE) technology, which offers over 90% recovery and reduces impurities by over 99%, is identified as a promising approach. The review underscores the need for large-scale field experiments and the development of new lithium sources to meet growing demand.

Investigation of Scaling and Materials' Performance in Simulated Geothermal Brine.

Geothermal energy generation faces challenges in efficiency, partly due to restrictions on reinjection temperatures caused by scaling issues. Therefore, developing strategies to prevent scaling is critical. This study aims to simulate the scaling tendencies and corrosion effects of geothermal fluids on various construction materials used in scaling reactor/retention tank systems. A range of materials, including carbon steel, austenitic stainless steel, duplex stainless steel, two proprietary two-part epoxy coatings, and thermally sprayed aluminium (TSA), were tested in a simulated geothermal brine. Experiments were conducted in a laboratory vessel designed to replicate the wall shear stress conditions expected in a scaling reactor. The tests revealed varying scaling tendencies among the materials, with minimal corrosion observed. The dominant scale formed was calcium carbonate, consistent with geochemical modelling. The findings suggest that despite the high operating temperatures, the risk of corrosion remains low due to the brine's low chloride content, while the wettability of materials after immersion may serve as a useful indicator for selecting those that promote scaling.

Advancing Lithium Extraction: A Comprehensive Review of Titanium-Based Lithium-Ion Sieve Utilization in Geothermal Brine

Advancing Lithium Extraction: A Comprehensive Review of Titanium-Based Lithium-Ion Sieve Utilization in Geothermal Brine

Lithium extraction from geothermal brine using γ-MnO2: A case study for Tuzla geothermal power plant

Geothermal brines contain high concentrations of ions and form a source of various valuable elements. The isolation of the elements from their water systems is a great challenge when the gradual depletion of ores in mining is considered. Attempts have been made for a long time to isolate valuable elements from aqueous mixtures prepared in the laboratory. However, those studies might not reflect the complexity of natural systems and might yield results that deviate significantly from the performance in real field systems. In this study, sorption is used to extract lithium ions from a representative field, Tuzla Geothermal Power Plant (TGPP) Turkey, using a mini-pilot reactor introduced to the reinjection well of the plant. Electrolytic manganese dioxide (γ-MnO2), a relatively inexpensive material widely used as the cathode material in lithium-ion batteries, was employed as a sorbent material for lithium. The sorption/desorption performance of the novel γ-MnO2 was investigated under various conditions. Sorption is performed at 360K and 2 bars. The maximum sorption performance was obtained at 1 h in Tuzla GPP. The desorption experiments were performed in acidic solutions. The concentration of Li+ in the desorption solution was found to be 25 mg/L on average when 10 g of γ-MnO2 was dispersed into 30 mL of the acidic aqueous solution. The first desorption solution was used consecutively for collecting more Li+ ions through the desorption of fresh brine-treated powder samples (cumulative desorption). By repeating this process four times consecutively, 230 mg/L of Li+ was obtained in the desorption solution. Moreover, the reusability of the γ-MnO2 sorbent was examined. The sorbent powder showed almost 40% performance efficiency compared to virgin powder under the conditions employed in this study. The use of electrolytic γ-MnO2 sorbent for lithium adsorption was found to be a promising process for practical use in the separation of lithium from geothermal brines.

Removal of Pb2+ and Cu2+ from artificial geothermal brine by zeolite at various salinity and temperature conditions

Natural zeolite (predominantly clinoptilolite - Ca) was tested for application in geothermal facilities to remove copper (Cu2+) and lead (Pb2+) from formation fluids. Batch and dynamic flow-through (only for lead ions) experiments were performed at different salinities (I = 0.1 and 1 mol/L) in NaCl or CaCl2 solutions at up to 115 °C (batch experiments) and up to 130 °C (flow-through experiments), respectively. The batch experiments resulted in an uptake of up to 24 % at an initial concentration of 0.3 g/L and up to 93 % at 0.03 g/L of Pb2+ and 115 °C. For Cu2+, the uptake reached 100 % from initial 0.004 g/L. The presence of CaCl2 in the solution matrix reduced the uptake of the heavy metals as compared to the NaCl matrix. The Pb2+ uptake by zeolite granulates at dynamic flow-through conditions at 130 °C was 52 % of the initial value of 20.7 mg/L during the 180 min experimental time. Based on the results from batch experiments the data fitting indicated a site density of monovalent exchange sites of 3.0 ± 2.6 mmol/g solid and a cation exchange capacity (CEC) of 295 ± 26 meq/100 g zeolite. The Pb2+ uptake process by zeolite gave a KD value of log K = 1.53. These calculations were not possible for Cu2+ uptake indicating that the uptake mechanisms of Cu2+ at high salinities are too complex to be simulated.To explain the uptake processes at given conditions various structural analysis were performed. Infrared spectroscopy indicated a cation exchange of lighter ions in the crystal structure of zeolite by the heavier ions Cu2+ and Pb2+ at 650 to 750 cm−1. After the treatment with heavy metals, two new bands were detected at 2902 and 2982 cm−1, which were not observed in the natural zeolite. With X-ray diffraction (XRD) new crystalline phases were detected in the treated zeolite samples that could be attributed in case of Pb2+ uptake to cottunite (PbCl2) and laurionite (PbOHCl) and in the case of Cu2+ uptake to Cu2Cl(OH)3 and CuCl2. The simulated G(r)s supported these observations regarding Pb2+ uptake. Using electron microscopy methods, both mechanisms (ion exchange and mineral precipitation) were confirmed: the formation of new Pb2+ and Cu2+ containing mineral phases on the surface of the zeolite granules and the uniform distribution of chloro-coordinated complexes of Cu2+ and Pb2+ on the pore surfaces inside the zeolite.

Technologies of the Integrated Development of Hydrogeothermal Resources of the North Caucasian Region

This paper focuses on the technologies of the integrated development of high-parametric geothermal brines with steam release. They differ from each other depending on initial parameters. Such way of brine utilization will make it possible to transform thermal energy to electrical power along with significant increasing its salinity that contributes to chemical components extraction. The opportunity is considered of this technology application in the Tarumovka geothermal field with electric power generation in steam-turbine and binary power plants, and consequent obtaining valuable mineral components. The geothermal and biogas technologies are given proposing integrated utilization of thermal water for various applications. Such systems make it possible to use resource potential of geothermal well and biomass that will result in improvement of economic and environmental situation in the North Caucasus region.

Optimized Lithium(I) Recovery from Geothermal Brine of Germencik, Türkiye, Utilizing an Aminomethyl phosphonic Acid Chelating Resin

ABSTRACT This study investigates the performance of Lewatit TP 260 ion exchange resin for the efficient recovery of lithium (Li(I)) from geothermal water sourced from the Germencik Geothermal Power Plant in Türkiye. A series of batch sorption experiments were performed to evaluate the influence of key parameters, including resin dosage, solution pH, temperature, initial Li(I) concentration, and contact time, on the Li(I) recovery process. The optimal conditions were determined to be a resin dose of 0.5 g per 25 mL of geothermal water, pH in the range of 6–8, and a temperature of 25°C. Under these conditions, the resin achieved a maximum Li(I) recovery rate of 71% from the geothermal water. Sorption isotherms were further analyzed using the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) models. Among these, the Langmuir model provided the best fit (R² = 0.9841), suggesting a maximum sorption capacity (qm) of 4.31 mg/g. Continuous recovery experiments conducted in column mode confirmed the practical applicability of Lewatit TP 260, achieving a total sorption capacity of 0.41 mg Li(I)/mL resin. The findings exhibit the potential of this resin as a viable sorbent for sustainable Li(I) extraction from geothermal brines, supporting the development of green energy technologies and contributing to the circular economy.

Predicting the performance of lithium adsorption and recovery from unconventional water sources with machine learning

Selective lithium (Li) recovery from unconventional water sources (UWS) (e.g., shale gas waters, geothermal brines, and rejected seawater desalination brines) using inorganic lithium-ion sieve (LIS) materials can address Li supply shortages and distribution issues. However, the development of high-performance LIS materials and the optimization of recovery-related operating parameters are hampered by the variety of production methods, intricate procedures, and experimental expenses. Machine learning (ML) techniques offer potential solutions for enhancing LIS material development. We collected literature data on Li adsorption, categorizing 16 parameters into adsorbent parameters, operating parameters, and solution components. Three tree-based algorithms—Random Forest (RF), Gradient Boosting Decision Trees (GBDT), and Extreme Gradient Boosting (XGBoost)—were used to evaluate the impact of these parameters on lithium adsorption. The grouped random splitting method limited data leakage and mitigated overfitting. XGBoost demonstrated the best performance, with an R² of 0.98 and a root-mean-squared error (RMSE) of 1.72. The SHAP values highlighted that operating parameters were the most influential, followed by adsorbent parameters and coexisting ion concentrations. Therefore, focusing on optimizing operating parameters or making targeted improvements on LIS based on operating conditions will enhance LIS performances in UWS. These insights are crucial for optimizing Li adsorption processes and designing effective inorganic LIS materials.

Evaluation of reflective fiber-optic surface plasmon resonance sensor for monitoring scale deposition.

A reflective surface plasmon resonance (SPR) sensor was evaluated for real-time monitoring of scale deposition. The sensor consists of an optical fiber, only 5mm at the gold-coated tip of the sensing area. The effect of silica growth on the sensor response was evaluated using a Na2SiO3 solution. The sensitivity of the sensor to silica was 1.6 ± 0.3nm per one immersion in the solution of 1000mg/L (as SiO2) at 85°Cand subsequnt air drying, as indicated by theSPR peak shift. The amount of silica deposited on the gold surface was measured by the quartz crystal microbalancemethod, and the SPR sensitivity of 0.089nm/ng to silica mass was obtained. The detection limit (3σ) of the SPR sensor was 17ng, correspondingto a thickness of 2.5nm for amorphous silica. The SPR sensor wastested in geothermal brine sampled at the Sumikawa Geothermal Power Plant, where a clear SPR shift was observed, suggesting the effectiveness of the SPR sensor for scale monitoring.

Fiber Optic-Based Portable Sensor for Rapid Evaluation and In Situ Real-Time Sensing of Scale Formation in Geothermal Water

The formation of scale in hot springs and geothermal brines can be detected quickly and easily using optical fiber-based scale sensors. This paper describes the development of a portable sensor for the in situ detection of scale in geothermal water. This sensor was used to detect the formation of calcium carbonate and silica scale and to assess the effectiveness of their inhibitors. The performance of the sensor was evaluated using calcium carbonate scale. In laboratory experiments using both the newly developed sensor and a conventional nonportable sensor, the strength of the transmitted signal was found to decrease significantly as the amount of scale increased. It was considered that this sensor can accurately evaluate only scale formation without being affected by turbidity. The scale that was deposited on each material (optical fiber core, glass plate, polyvinyl chloride (PVC), and SUS304) was observed using a shape analysis laser microscope. Based on these observations, we concluded that this sensor could be used to predict the amount of scale deposited in real time. In situ evaluation of the sensor was conducted at a blowout carbonated hot spring on Rishiri Island, which is located off the coast of Hokkaido, Japan. The results obtained from experiments using hot spring water showed a similar sensor response within a comparable time range as those obtained from the laboratory experiments. The results of this study thus demonstrate that this novel portable scale sensor is suitable for use in geothermal power plants and investigating effectiveness of inhibiters under different conditions.

Extremely acidic proteomes and metabolic flexibility in bacteria and highly diversified archaea thriving in geothermal chaotropic brines.

Few described archaeal, and fewer bacterial, lineages thrive under salt-saturating conditions, such as solar saltern crystallizers (salinity above 30% w/v). They accumulate molar K+ cytoplasmic concentrations to maintain osmotic balance ('salt-in' strategy) and have proteins adaptively enriched in negatively charged acidic amino acids. Here we analysed metagenomes and metagenome-assembled genomes from geothermally influenced hypersaline ecosystems with increasing chaotropicity in the Danakil Depression. Normalized abundances of universal single-copy genes confirmed that haloarchaea and Nanohaloarchaeota encompass 99% of microbial communities in the near-life-limiting conditions of the Western-Canyon Lakes. Danakil metagenome- and metagenome-assembled-genome-inferred proteomes, compared with those of freshwater, seawater and solar saltern ponds up to saturation (6-14-32% salinity), showed that Western-Canyon Lake archaea encode the most acidic proteomes ever observed (median protein isoelectric points ≤4.4). We identified previously undescribed haloarchaeal families as well as an Aenigmatarchaeota family and a bacterial phylum independently adapted to extreme halophily. Despite phylum-level diversity decreasing with increasing salinity-chaotropicity, and unlike in solar salterns, adapted archaea exceedingly diversified in Danakil ecosystems, challenging the notion of decreasing diversity under extreme conditions. Metabolic flexibility to utilize multiple energy and carbon resources generated by local hydrothermalism along feast-and-famine strategies seemingly shapes microbial diversity in these ecosystems near life limits.

Composite flat-sheet membrane adsorbent of Li2TiO3-Ethylene-co-vinyl alcohol (LTO-EVAL) for lithium extraction

Composite bead adsorbents have been prevalent for the extraction of Li+ from brines. However, adsorbent beads generally demonstrate declining adsorption capacity and require extended equilibrium time when used repeatedly in absorption/desorption cycles. To overcome this challenge, a novel composite flat-sheet membrane adsorbent based on ethylene-co-vinyl alcohol (EVAL) and Li2TiO3 (LTO) is reported herein for highly efficient Li+ extraction from a geothermal brine. At an optimal LTO loading and membrane thickness, the resulting LTO-EVAL membrane was characterized by a large open macrovoid structure for fast ion transport, a fast adsorption rate that reached equilibrium in 0.5 h, and a high capacity of 96 % of that of the powder. The new membrane adsorbent showed adsorption behavior consistent with the Langmuir model and pseudo-second-order kinetic model. For a geothermal brine with a low lithium concentration, the LTO-EVAL membrane showed stable performance in 13 rapid adsorption/desorption cycles, with adsorption capacity at an average adsorption capacity of 7.3 mg/g and a 70 % adsorption efficiency. The average dissolution rate of Ti4+ was below 0.6 % in each cycle. The structure of the adsorbent material showed no discernable changes in chemical structure as confirmed by XRD and SEM results. With the improved extraction efficiency, the reusable membrane adsorbents would be economically viable in the long run and could potentially serve as the next generation of scalable Li+ adsorption material for brines. Further utilization of membrane adsorbent would lead to new design of adsorption modules and systems with reduced footprint. We need to further optimize the stability of the membrane adsorbents so that loss of Li2TiO3 remain at low level to reduce the lost for lithium extraction from the geothermal brine.

Lithium recovery from Mexican geothermal brine via microwave-synthesized ion sieves

This paper investigates for the first time the feasibility of lithium recovery using lithium ion-sieves from a Mexican geothermal brine from a well of Cerro Prieto power plant. The materials were prepared following the microwave-assisted hydrothermal route to favor their sustainability. Also, the effect of the three manganese-based compounds as precursors was evaluated in which the vacancies were generated by acid treatment, by varying the acid concentration and the contact time. The structural characterizations showed that manganese sulfate was an efficient precursor for synthesizing LiMn2O4 spinel. The results of the uptake experiments, varying the pH of the Li solution showed that the highest sorption capacity is obtained at pH 12. The adsorption kinetics was better described by a pseudo second order equation (R2=0.9392). According to the Weber-Morris model, the process seems to be governed by film diffusion rather by intraparticle diffusion. The maximum adsorption capacity that was achieved was 9.64 mg/g and the thermodynamic equilibrium was best described by the Freundlich isotherm (R2=0.9769). Finally, the material was able to retain a competitive uptake capacity after five adsorption-desorption cycles.

Delithiation and lithiation of LiFePO4: Implications for direct Li extraction from synthetic solutions and geothermal brines

The demand for Li is and will be increasing in the future, and the development of a direct Li extraction (DLE) technology from unconventional resources, like geothermal brines, may contribute to a resilient supply in the future. This study investigates the deintercalation from and intercalation of Li in LiFePO4 (LFP) at 25–80 °C, near neutral to acidic pH and the effect of high salinity on the Li extraction performance. The (de-)lithiation is a fully reversible redox process between triphylite and heterosite. Lithium is delithiated from LFP using 0.1 M Na2S2O8 at 42–43 mg/g. The lithiation kinetics increase with temperature, but show a complex relationship to reducing agent (Na2S2O3) concentration. The maximum re-intercalation is achieved in synthetic LiCl + 0.5 M Na2S2O3 solution at 39 mg/g, 25 °C and 7 days, whereas 27 mg/g and 1.3 mg/g Li are intercalated to LFP within 3–4 h in experiments with Bruchsal and synthetic Neustadt-Glewe geothermal brines at 60 °C, respectively. At optimal parameters, >99 % Li are recovered from both geothermal brines in laboratory experiments. This shows that LFP can be used for DLE from geothermal brines under specific conditions in a purely chemical process.

Multi-criteria decision-making method for evaluation of investment in enhanced geothermal systems projects

Deep geothermal energy presents large untapped renewable energy potential could significantly contribute to global energy needs. However, developing geothermal projects involves uncertainties regarding adequate geothermal brine extraction and huge costs related to preparation phases and consequently drilling and stimulation activities. Therefore, evaluating utilization alternatives of such projects is a complex decision-making problem effectively addressed using multi-criteria decision-making (MCDM) methods. This study introduces the MCDM method utilizing analytic hierarchy process (AHP) and weighted decision matrix (WDM) to assess different utilization alternatives (electricity generation, direct heat use and cogeneration). The AHP method determines the weight of each criterion and sub-criterion, while the WDM calculates the final project grade. Five criteria groups - technological, geological, economic, societal and environmental – comprising twenty-eight influencing factors were selected and used for the assessment of investment in Enhanced Geothermal Systems (EGS) projects. The AHP-WDM method was used by 38 experts from six categories: industry, educational institution, research and technology organization (RTO), small- and medium-sized enterprises (SME), local community and other. These diverse expert inputs aimed to capture varying perspectives and knowledge influence investment decisions in geothermal energy. The results were analysed accordingly. The results underscore the importance of incorporating different viewpoints to develop robust, credible, and effective investment strategies for EGS projects. Therefore, this method will contribute to more efficient EGS project development, enabling thus a greater penetration of the EGS into the market. Additionally, the proposed AHP-WDM method was implemented for a case study examining two locations. Locations were assessed and compared on scenario-based evaluation. The results confirmed the method's adequacy for assessing various end uses and comparing project feasibility across different locations.

Is lithium from geothermal brines the sustainable solution for Li-ion batteries?

The rising demand for Li, paramount for energy storage, necessitates expanded supply. As the supply is concentrated in a few countries, this poses supply chain risks for Li-ion battery makers. To diversify suppliers, alternative Li ore deposits such as geothermal brines are being explored. However, Li extraction from geothermal brines is challenging due to the unique chemistry and elevated temperatures. Since Li-extraction from geothermal brines is in its infancy, data availability and quality are still poor, hampering life cycle assessments. Hence, this study provides a parametrized life cycle inventory model of Li carbonate production from geothermal brines. The model accounts for site-specific environmental conditions and technological features. Life cycle impacts at the Salton Sea in the US (1686 cases) and the Upper Rhine Graben in Germany (1982 cases) are quantified. The high case numbers are chosen to mitigate the high uncertainties in input parameters. Specifically, the brine chemistry, adsorption yield, drilling required and energy inputs are varied. Climate change impacts of selected cases vary within 18–59 kg CO2eq/kg Li carbonate at the Salton Sea and within 5.3–46 kg CO2eq/kg Li carbonate at the Upper Rhine Graben, compared to 2.1–11 kg CO2eq/kg Li carbonate in existing ecoinvent data sets. The wide range of potential impacts underscore the necessity of early-stage assessments of the technologies. In case of high drilling demand and use of fossil energy, climate change impacts of Li-ion batteries using Li carbonate from geothermal brines can increase by 30–41 % compared to literature values.

Prediction of Production-Inflow Profile of a Well Producing Single-Phase Flow of Slightly Compressible Fluid from Multilayer Systems by Temperature and/or Pressure Transient Data

Summary This study focuses on the prediction of the production-inflow profile of a well producing a single-phase flow of slightly compressible fluid (water or oil flow) in a multilayered system using the layer permeability and skin values estimated by history matching spatial and temporal temperature and/or pressure data sets along the completion interval. Such data may be acquired by wireline formation testing, production-logging-tool (PLT), or distributed temperature sensing (DTS) fiber-optic cables. We use an in-house thermal, transient coupled reservoir/wellbore simulator developed during this study. It solves transient mass, momentum, and energy conservation equations simultaneously for both reservoir and wellbore. The effects of the Joule-Thomson (J-T), adiabatic expansion, conduction, and convection are all included for predicting the flow profiles across the wellbore. The results from our in-house simulator are verified with the results from a commercial simulator for the single-phase fluid flow of a vertical well producing geothermal brine and oil in a two-zone multilayer system. We also compare the results from our rigorous transient coupled wellbore/reservoir model with the results from a model assuming steady-state thermal wellbore model used in the previous studies. We find that the steady-state thermal wellbore model used in the previous studies that ignore accumulation terms in mass, momentum, and thermal energy balances is a reasonably accurate model for predicting wellbore pressures and temperatures when it is coupled with a nonisothermal reservoir model for slightly compressible fluid because the transient effect in the wellbore is less important with the slightly compressible fluid. We investigate the nonlinear parameter estimation problem based on the use of single or multiple observed temperature and/or pressure (if available) profiles recorded spatially inside the wellbore and at the sandface. The purpose is to identify if the wellbore or sandface data profiles are more useful to accurately estimate the permeability and skin information and predict a production-inflow profile of the well depending on the representation of an actual multilayer system by a reduced-layered or fine-layered model. We show that using an upscaled-layered model (e.g., representing each heterogeneous layer with a lumped single layer with uniform permeability and skin) provides estimates that are more toward the thickness-average permeability and skin factors of the layers and may not provide a good prediction of the well’s production-inflow profile. We show that including the sandface temperature data in regression worsens, while the use of wellbore temperature data sets improves the quality of parameter estimation if an upscaled multilayered model is used. We also show that regressing on multiple temperature profiles, preferably at the sandface, alone could be used to predict the production-inflow profile accurately if a “fine” multilayered heterogeneous model is used. We also investigate if including or excluding the temperature and/or pressure measurements at the nonperforated sections along the completion interval could help enhance the parameter estimation problem. The results show that when multiple profiles of temperatures including the data at nonperforated zones at different production rates are regressed, reliable estimates of the individual layer properties that predict the production-inflow profile accurately can be obtained, though layer permeability and skin factors may often exhibit wide 95% confidence intervals and high correlations among them. Adding sandface or wellbore pressure data, if available, into observed data sets in history matching always improves the quality of parameter estimation.

Quantitative facies analysis of a fluvio-aeolian system: Lower Triassic Buntsandstein Group, eastern France

Understanding the factors that control the temporal and spatial evolution of the Lower Triassic Buntsandstein Group, eastern France, is important not just for palaeoenvironmental reconstruction but also because it is an important reservoir for the lithium-rich geothermal brines in the Upper Rhine Graben region. The interval of interest in this study, the Lower Grès Vosgien Formation (LGV), is made up of c. 200 m of clastic deposits of mixed fluvial and aeolian origin. Given the proximity between the outcrops and the areas of mineral and heat exploration, this region offers a unique opportunity for quantitative analysis and correlation between outcrops and reservoirs. The LGV is the thickest Formation in the Buntsandstein Group. However, hitherto, no detailed architectural analysis has been published to reveal the controlling factors of its depositional elements. In this study, high-resolution facies analysis was applied to thirteen outcrops, and a core, to quantify fluvial and aeolian depositional architectures, and to comprehend palaeoenvironmental conditions during their deposition. Two facies associations were identified. The fluvial channel facies association, composed mainly of sandstones deposited in poorly confined, occasionally ephemeral channels, corresponds to 93 % of the total thickness. The analysis of >800 sets of strata characterised by lower-, transitional-, and upper-flow regime sedimentary structures, distributed within different architectural elements, enabled the distinction of temporal and spatial variabilities, and an estimate of fluvial palaeohydraulic characteristics. The wind- and water-laid facies association, which accounts for 7 % of the total thickness, records an architecture controlled by a fluctuating water-table level, and ephemeral floods. Results revealed that aeolian dunes and sand sheets accumulated in distinct temporal moments. The vertical trends, recorded in the core, indicate an upward increase in the frequency of intercalations between the two facies associations, and a decrease in the occurrences of thicker cross-bedded sandstone sets of fluvial origin, which, associated with the overall retrogradational stacking pattern of the LGV, is interpreted as the preserved record of a large distributive fluvial system (DFS). The occurrence of laterally extensive aeolian deposits, overlying fluvial deposits, is often associated by authors with periods of relatively more arid conditions at a regional scale. However, evidence indicates channel belt avulsion as an alternative interpretation for the establishment of the two facies associations. The findings enhance the knowledge about the depositional controlling factors in braided fluvial and aeolian systems, and improve predictive models that account for reservoir heterogeneity in accumulated successions of this type.

Lithium-rich basement brines: Activity versus concentration geothermometry

Lithium-rich brine plays a crucial role in the energy transition. Specifically, geothermal Upper Rhine Graben brines and the fluid inclusions in the adjacent southwesternmost Black Forest (Germany) are lithium-rich due to their interactions with Variscan basement rocks (granite and gneiss). Given their high salinity, however, conventional empirical geothermometers may prove inadequate, as these rely on elemental ratios in terms of concentration (molar or weight basis) rather than the elements’ activity. This short communication compares several classical geothermometers, such as Na/K, Na/Li, Mg/Li, K2/Mg, Mg/K, with innovative activity geothermometers that use the ion activity products of Ca2+, K+, Li+, Na+ and H2O based on the equilibrium between a generic lithium-mica, quartz, and oligoclase. Activity is calculated using the PhreeqcI code and Pitzer database optimized for LiCl-H2O, CaCl-H2O and NaF-H2O systems. The lithium minerals thermodynamic database, used as a reference for calculating the solubility product, has been further supplemented with Li-tosudite and Li-donbassite. The results of the inferred temperatures highlight the new activity geothermometer's versatility, even when compared with the to activity Na/K geothermometer based on the albite-microcline equilibrium.