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AbstractMicrobially induced calcium carbonate precipitation (MICP) is a geotechnical solution with a low ecological footprint. Conducting MICP inside a porous medium can be used for biocementation. Despite many models and tools being published for simulating MICP, a computationally light, easy-to-use, and freely-available simulation tool is lacking. In this work, we present a reactive transport model using the native capabilities of the Phreeqc software (a free and open-source geochemical solver). We model MICP inside a column packed with sands and inoculated with bacteria. Our model is a one-dimensional representation of the column that accounts for the kinetics of precipitation and ureolysis as well as porosity change. We verify our model by simulating previously published MICP experiments to show our model gives reasonably well predictions. Sensitivity analysis of our model’s input parameters and discussions around their range are presented. Additionally, we calculate the supersaturation of calcite as a function of space and time—a feature that could be important for precipitation, but it is commonly ignored in MCIP modeling. Our scripts developed for running simulations are accessible publicly. Due to the low computational effort required for the simulations, our Phreeqc scripts can be used to design and test different treatment recipes for conducting MICP. [ABSTRACT FROM AUTHOR]

Groundwater is particularly vulnerable to pollution in places with a high population density and extensive human usage of the land, especially in southern parts of Tirupati, India. To assess this, 60 bore-well samples were obtained and assessed for physical specifications, ion chemistry, and heavy metals during the pre- and post-monsoon seasons 2022. The current investigation employed a modified integrated water quality index (IWQI), conventional graphical and human health risk assessment (HHRA) of nitrates and heavy metals to know the groundwater chemistry and its detrimental health effects on humans. The major ions were analyzed using American public health association (APHA) standards, whereas heavy metals were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES). Additionally, pH Redox Equilibrium and C (PHREEQC), a geochemical model written in C programming language was employed to determine the saturation indices of mineral facies and ArcGIS 10.3.1 was used for spatial distribution patterns of IWQI. Then, the HHRA of nitrates and heavy metals was performed using United States environmental protection agency (US EPA) guidelines. The noteworthy outcomes include elevated levels of Ca2+, Mg2+, Cl−, NO3−, Cu, Fe, Mn, and Pb, demonstrating rock-water interaction, silicate weathering, Ca-Mg-HCO3 followed by mixed water facies, dissolution/precipitation, reverse exchange, and anthropogenic contamination are the major controlling processes in groundwater of southern Tirupati, India. The modified IWQI reveals that most groundwater samples (38%) fall under the bad quality class, with (47%) in the poor quality class and only (15%) classified as medium quality class in pre- and post-monsoon seasons. Elevated IWQI were observed in all directions except in the east, which is suitable for drinking. Moreover, the major hazard quotient (HQ) and hazard index (HI) for nitrates (NO3−) and heavy metals like copper (Cu), iron (Fe), manganese (Mn), lead (Pb) and zinc (Zn) are above the critical value of 1, revealing potential risk to humans, especially infants, followed by children and adults, entailing the instantaneous implementation of proper remedial measures and stringent policies to reduce the risk associated with groundwater pollution in the southern parts of Tirupati. [ABSTRACT FROM AUTHOR]

Due to anthropogenic and long-term geological factors, radionuclide leakage may occur in deep geological repositories of radioactive waste when groundwater infiltrates a failed waste canister. The released radionuclides can migrate to near and far field regions through groundwater, posing a serious threat to the ecological environment and human health. As a consequence, knowledge of radionuclide speciation in groundwater is essential for understanding their transport behavior. Uranium is one of the key elements of significant concern for deep geological disposal of high-level radioactive waste. In this study, the uranium species in groundwater from boreholes BS03(pH=9.43) and BS05(pH=7.51) located at the Beishan area(Gansu province) were calculated by the hydrogeochemical software PHREEQC(version 3). The effects of pH, temperature, and initial uranium concentrations on ternary uranyl species are presented. The results indicate that UO2CO3(aq) and (UO2)2CO3(OH)\begin{document}$_3^- $\end{document} are the dominant species in a mildly acidic condition, while CaUO2(CO3)\begin{document}$_3^{2-} $\end{document} and Ca2UO2(CO3)3(aq) are the major species in neutral and weakly alkaline conditions. In BS05 groundwater, the concentration of Ca2+(5.11 mmol/L) is about three times higher than that of Mg2+(1.58 mmol/L). However, the concentration of calcium uranyl carbonate is estimated to be about 250 times higher than that of magnesium uranyl carbonate(MgUO2(CO3)\begin{document}$ _3^{2-}$\end{document}). With an increase of temperature, Ca2UO2(CO3)3(aq), CaUO2(CO3)\begin{document}$_3^{2-} $\end{document} and UO2(CO3)\begin{document}$_3^{4-} $\end{document} concentrations progressively diminish. At uranium concentrations between 4×10−4 and 1×10−1 mmol/L (25 ℃), the dominant uranium species, in order of decreasing concentration are: Ca2UO2(CO3)3(aq)(x＞62%)＞CaUO2(CO3)\begin{document}$_3^{2-} $\end{document}(x≈35%)＞MgUO2(CO3)\begin{document}$_3^{2-} $\end{document}/UO2(CO3)\begin{document}$_3^{4-} $\end{document}(x≈1%), irrespective of the concentrations of Ca2+, Mg2+, and Na+. In the near-neutral and slightly alkaline conditions, the results suggest that the formation of neutral Ca2UO2(CO3)3(aq) and anionic CaUO2(CO3)\begin{document}$_3^{2-} $\end{document} in Beishan groundwater reduces the distribution coefficient between uranium and environmental geo-medium, thereby enhancing the mobility and migration potential of uranium. The research findings contribute to understanding the transport and release mechanisms of uranium, as well as interactions between uranium species and engineered and natural barriers.

As in any other industry, nuclear energy results in the accumulation of some waste, which needs to be managed safely and responsibly due to its radiotoxicity. In the case of highly radioactive waste, geological disposal in stable rock is considered a broadly accepted solution. For the evaluation of the long-term safety of a geological repository, the assessment of radionuclide transport needs to be carried out. Radionuclide transport through engineered and natural barriers of the repository will highly depend on the barriers' transport-related properties, which will be determined by coupled thermal, hydraulic, chemical, mechanical, biological, and radiation processes taking place in those barriers. In this study, the thermo-hydro-chemical (THC) state of bentonite was analysed considering CO2 gas diffusion and temperature-dependent solubility in water. Reactive transport modelling of bentonite under non-isothermal conditions was performed with the COMSOL Multiphysics software (v6.0), coupled with the geochemical solver Phreeqc via the iCP interface. The modelling demonstrated that the consideration of chemical processes in bentonite had no significant influence on non-reactive Cl− transport; however, it would be important for other radionuclides whose sorption in porous media depends on the porewater pH. Based on the modelling results, changes in the bentonite mineralogical composition and, subsequently, porosity depend on the partial CO2 pressure at the bentonite–granite boundary. In the case of low CO2 partial pressure at the bentonite–granite interface, the calcite dissolution led to a slight porosity increase, while higher CO2 partial pressure led to decreased porosity near the interface. [ABSTRACT FROM AUTHOR]

Linear alkylbenzene sulfonate (LAS), a widely used anionic surfactant, is present in wastewater and can be discharged, causing environmental damage. When biodegradation is negligible, adsorption and desorption reactions play an important role, depending on the media characteristics (organic matter and clays) and hydrodynamic parameters. Previously published laboratory column data are modelled with PHREEQC (version 2.18) in three scenarios of LAS input: spill (LAS pulse), continuous discharge (LAS adsorption step) and remediation (LAS desorption step). The distribution coefficients (0.1–4.9 × 10−3 L/g) in the sand columns are lower than those determined in this paper from batch tests and in columns of 25% and 50% agricultural soil mixtures (1–70 × 10−3 L/g). Considering the Freundlich constant parameters from the modelling, the results are similar to the distribution coefficients, but the linear isotherms are more consistent throughout. The mass transfer coefficient from the sand columns is lower than the agricultural soil columns (20–40 h−1), indicating longer elution times for the heavier homologues and a higher percentage of agricultural soil. For lighter homologues, fast migration could cause contamination of aquifers. The great persistence of LAS in the environment necessitates the development of mitigation strategies using reactive transport models, which predict longer times for the remediation of LAS homologues. [ABSTRACT FROM AUTHOR]

Beijing Plain is a very active part of Beijing city regarding the socio-economic and human activities of the region. Over the past four decades, Beijing's economic development and the continuous drought for nearly 10 years in the 2000s have negatively impacted the groundwater quantity and quality. Therefore, it is necessary to investigate the present situation of groundwater chemistry in this region to develop a comprehensive database and orientation for future research on groundwater quality evaluation. Mathematical statistics, Piper's trilinear diagram, Gibbs plots, the ion ratio method and PHREEQC software 3.7.3 were used to analyze the groundwater hydrogeochemical characteristics and formation mechanisms of the quaternary aquifers of the Beijing Plain area. Hydrogeochemical results indicated that the groundwater is slightly alkaline, with pH values ranging from 6.76 to 8.65 and an average value of 7.92. The order of major cations in groundwater was Ca2+ > Na+ > Mg2+ > K+ with average values of 66.54 mg/L, 50.58 mg/L, 23.78 mg/L, and 1.81 mg/L, respectively, while the order of major anions was HCO3− > SO42− > Cl− with average values of 284.89 mg/L, 52.1 mg/L and 35.5 mg/L, respectively. The groundwater chemical types are Mg-Ca-Cl-HCO3, Na-Ca-HCO3, Mg-Ca-HCO3 and Mg-Na-HCO3. Research on the main influencing factors and PHREEQC hydrogeochemical inverse simulations results along the four pathways selected confirmed that rock weathering with sulfate, silicate and carbonate rock mineral dissolution and Na+, Mg2+ and Ca2+ ion reaction exchange influenced groundwater hydrogeochemical characteristics of the quaternary aquifers of the Beijing Plain area. Understanding the formation mechanisms of hydrogeochemistry in quaternary plains provides guidance for future studies and, through suggestions and case studies, facilitates decision-making by policy-makers on the sustainable management of groundwater resources. [ABSTRACT FROM AUTHOR]

The hydrogeochemical research of groundwater in the Bieletan area, China's largest potash producing zone, used a variety of methods, including multivariate analysis, saturation index, and hydrogeochemical modeling. Water samples were collected and analyzed for physicochemical parameters, along with soluble ions from soil cores. The results showed that total dissolved solids (TDS) of groundwater exceeded 300 g/L, with the main hydrochemical characteristics being Cl-Mg type and Cl-Na type. Groundwater is recharged by lake water and canal water, with evaporation being the main factor affecting water chemistry. Hydrogeochemical modeling analyzed the processes occurring from these two different recharge sources: mineral precipitation mainly occurred with lake water recharge, while mineral dissolution mainly occurred with canal water recharge. Regarding potash dissolution, canal water and lake water recharge resulted in 8.860 mmol/L of polyhalite dissolution and 0.278 mmol/L of carnallite dissolution, respectively. This study highlights the complex hydrogeochemical processes controlling groundwater in the potash-rich Bieletan area, providing insights for water resource management and potash mining. [ABSTRACT FROM AUTHOR]

It is critical to develop the methods and technologies of studying the species and concentration in the processing of adsorption, and diffusion of some important radionuclides in spent fuel waste processing such as Beishan granites in domestic institutions and universities for the geological disposal of high-level radioactive wastes. Enrich the models used or constructed and the calculation procedures developed in the past two decades in this field. In order to evaluate the safety of the repository, chemical speciation analysis of nuclides is the premise of research to accurately predict the migration behavior of nuclides. In view of the rapid development of China's nuclear energy industry and the need to establish the identification of nuclides in the environment, it is of great significance to carry out the study of the chemical forms of nuclides around the repository in China. Aiming at the research requirements of element speciation distribution in the environment, a set of B/S architecture element speciation distribution simulation software is developed with JAVA as the development tool, MySQL as the database, and Tomcat as the container. In order to solve the convergence problem of chemical reaction equilibrium nonlinear equations encountered in simulation calculation, the method based on chemical reaction potential energy is introduced to solve the chemical reaction nonlinear equations quickly, and the multi-phase equilibrium calculation can be expanded. SSCS was used to study the species of U in groundwater and the effects of Eh, pH, different ions and concentrations. The calculation results indicate that neptunium mainly exists as NpO2CO-3(aq) in groundwater. Under strong acidic conditions, neptunium maily exists as NpO+2(aq), while in weak acidic, neutral or weak alkaline conditions, the main species are NpO+2(aq) and NpO2OH.When the solution is in strong alkaline conditions, the species are complicated most of neptunium exists as NpO2(CO3)-3(aq), with the possible generation of NpO2(CO3)3-2 or NpO2(CO3)5-3. Np(Ⅴ) is stable in the reduction condition, while Np(Ⅳ) and Np(Ⅵ) are the possible generation. Comparing the neptunium calculation results of the software in the environment with the PHREEQC calculation results, the relative error is within 10 %. For the distribution of trace elements in the environment, a theoretical calculation solution is provided.

The effect of temperature on the solubility of lead-bearing solid phases in water distribution systems for different water chemistry conditions remains unclear although lead concentrations are known to vary seasonally. The study objective is to explore the effect of temperature on the solubility of the lead(II) carbonate hydrocerussite under varying pH and DIC conditions. This is achieved through batch dissolution experiments conducted at multiple pHs (6–10) and DIC concentrations (20–200 mg CL−1) at temperatures ranging from 5 to 40 °C. A thermodynamic model was also applied to evaluate the model's ability to predict temperature effects on lead(II) carbonate solubility including solid phase transformations. In general, increasing temperature increased total dissolved lead at high pHs and the effect of temperature was greater for high DIC conditions, particularly for pH > 8. Temperature also influenced the pH at which the dominant lead(II) solid phase switched from hydrocerussite to cerussite (occurred between pH 7.25 to 10). Finally, the model was able to capture the overall trends observed despite thermodynamic data limitations. While this study focuses on a simple lead solid-aqueous system, findings provide important insights regarding the way in which temperature and water chemistry interact to affect lead concentrations. [ABSTRACT FROM AUTHOR]

Tropical maar lakes are distinct ecosystems with unique ecological features. To comprehend, manage, and conserve these lakes, it is essential to understand their water sources, particularly groundwater, and the hydrogeochemical processes shaping their water chemistry. This research focuses on the maar lake Alchichica in central Mexico, known for harboring 18 new and endemic species and a ring of stromatolites. With groundwater discharge as the primary source, concerns arise over anthropic extraction impacts on water levels and stromatolite survival. Sampling six wells and one piezometer revealed major ion (Ca2+, Mg2+, K+, Na+, Cl−, HCO3−, SO42−) and trace element (Fe, Al3+, SiO2) concentrations. Geochemical evolution was explored through diagrams, geological sections, and inverse geochemical models using the PHREEQC code. Findings indicate groundwater evolving along controlled flow paths, and influencing chemical composition through water–rock interactions. The lake's unique conditions, resulting from the mixing of two flows, enable stromatolite formation. Water level reduction appears unrelated to evaporation at the sampled sites, suggesting a need for a broader study in a larger area. Analyzing the maar lake's hydrochemistry provides valuable insights into unique characteristics supporting high endemism in this ecosystem. This research enhances our understanding of groundwater's geochemical processes and hydrogeochemical evolution in maar lakes, with potential applications worldwide. [ABSTRACT FROM AUTHOR]

Drawing development plans requires evaluating the available resources and assessing their sustainable and subsequent utilization-driven environmental impacts. The current work is concerned with evaluating the sustainability of the halite harvesting process from Al-Qasab Playa, Shaqra, Central Saudi Arabia. The authors integrated, conceptually and quantitatively, ArcGIS-processed SRTM-DEM (Shuttle Radar Topography Mission-Digital Elevation Model) data, hydrogeochemical and thermodynamic-based geochemical modelling, and graphical approaches to achieve the ultimate aims of the study. The watershed is identified as a nonmarine closed basin with a drainage area of 1290 km2, with the slope controlling recharge to the Playa. The Chadha plot including the rainwater exhibits linear regression, with an R2 value of 0.9947, confirming the rainwater origin of the Playa water. The hardness-forming ions are primarily removed in pond 3, eliminating the need for costly and power-consuming steps of softening with ion exchange resins or nanofiltration as it can be used directly as a readily available feed for the chlor-alkali process for producing NaOH, Cl2, and H2 gases through electrolysis. XRD (X-ray diffraction) analysis and the SEM-EDS (Scanning electron microscopy-energy dispersive X-ray spectroscopy) of the harvested halite confirmed its purity. An improved design of the current folkloric harvesting process has been proposed based on the saturation indices calculated thermodynamically to provide a readily available feed intake for the electrolysis chlor-alkali process with or without minimal pretreatment to produce higher value chemicals. The methodological aspects presented here are deemed robust and valid for applications in other study areas, including the assessment of the exploitation of the rejected brine from the desalination plants to achieve the zero liquid discharge approach, as well as other types of sabkhas, regardless of their geographical location. [ABSTRACT FROM AUTHOR]

The exploitation of coal resources has disturbed the equilibrium of the original groundwater system, resulting in a perturbation of the deep groundwater dynamic conditions and hydrochemical properties. Exploring the formation of mine water chemistry under the conditions of deep coal seam mining in the Ordos Basin provides a theoretical basis for the identification of sources of mine water intrusion and the development and utilization of water resources. This paper takes Longwanggou Coal Mine as the research area, collects a total of 106 groups of water samples from the main water-filled aquifers, comprehensively uses Piper trilinear diagram, Gibbs diagram, ion correlation, ion ratio coefficient and mineral saturation index analysis, and carries out inverse geochemical modeling with PHREEQC software, so as to analyze the hydrochemical characteristics and causes of the main water-filled aquifers in deep-buried coal seams in the research area. The results show that the main hydrochemical processes in the study area are leaching and cation exchange, and the groundwater is affected by carbonate (calcite, dolomite), silicate (gypsum) and evaporite. Calculations of mineral saturation indices and PHREEQC simulations have led to the conclusion that the dissolution of rock salt and gypsum in groundwater accounts for most of the ionic action. Na+, Cl− and SO42− are mainly derived from the dissolution of rock salt and gypsum minerals, while Ca2+ and Mg2+ are mostly derived from the dissolution of dolomite and calcite. The results of the inverse geochemical modeling are consistent with the theoretical analysis. [ABSTRACT FROM AUTHOR]

Acid mine drainage (AMD) has resulted in significant risks to both human health and the environment of the Han River watershed. In this study, water and sediment samples from typical mine adits were selected to investigate the hydrogeochemical characteristics and assess the environmental impacts of AMD. The interactions between coexisting chemical factors, geochemical processes in the mine adit, and the causes of AMD formation are discussed based on statistical analysis, mineralogical analysis, and geochemical modeling. The results showed that the hydrochemical types of AMD consisted of SO4–Ca–Mg, SO4–Ca, and SO4–Mg, with low pH and extremely high concentrations of Fe and SO42–. The release behaviors of most heavy metals are controlled by the oxidation of sulfide minerals (mainly pyrite) and the dissolution/precipitation of secondary minerals. Along the AMD pathway in the adit, the species of Fe-hydroxy secondary minerals tend to initially increase and later decrease. The inverse model results indicated that (1) oxidative dissolution of sulfide minerals, (2) interconversion of Fe-hydroxy secondary minerals, (3) precipitation of gypsum, and (4) neutralization by calcite are the main geochemical reactions in the adit, and chlorite might be the major neutralizing mineral of AMD with calcite. Furthermore, there were two sources of AMD in abandoned mine adits: oxidation of pyrite within the adits and infiltration of AMD from the overlying waste rock dumps. The findings can provide deeper insight into hydrogeochemical processes and the formation of AMD contamination produced in abandoned mine adits under similar mining and hydrogeological conditions. [ABSTRACT FROM AUTHOR]

Underground Hydrogen Storage (UHS) in porous media appears to be a promising means for large-scale hydrogen storage, underpinning the full-scale of hydrogen supply chain development. Hydrogen-brine-rock interactions play an important role in hydrogen conversion and contamination during hydrogen cycling process. While the redox reaction triggered by injected H 2 and pre-existing O 2 is unique in UHS compared to other types of gas subsurface storage, few research have been done to understand the role of redox reactions in hydrogen solubility, pH, and fewer works have looked beyond its process on hydrogen conversion and contamination, which may affect the stored H 2 purity and storage efficiency. In this context, we examined the redox reactions on hydrogen-brine-minerals (e.g., calcite, siderite, quartz and pyrite) reactions as a function of dissolved oxygen concentration (from 5.5 to 5500 ppm), temperature, and pressure through geochemical modelling using geochemical solver PHREEQC. Our results showed that increasing dissolved oxygen concentration from 5.5 to 5500 ppm resulted in negligible impact on hydrogen solubility and pH for all tested minerals. As the sensitive minerals, siderite and calcite can react with H 2 through the redox process, leading up to a certain hydrogen loss at the pressure of 20 MPa, respectively. Meanwhile, quartz and pyrite are insensitive minerals to hydrogen, causing less than 0.2% hydrogen loss at the same pressure condition. Our results indicate that the mineral oxidation due to the pre-existing O 2 dissolved in formation brine played a negligible role in H 2 -brine-rock interactions. The results also showed that carbonate minerals such as siderite and calcite may act as electron acceptors, which triggered hydrogen dissociation and thus formed a strong reduction environment based on PHREEQC geochemical database. This process likely causes measurable hydrogen loss associated with abiotic geochemical reactions for the lifetime of the underground hydrogen storage operation. Taken together, we suggest that clean standstone reservoirs will signifcantly reduce the hydrogen conversion and contamination during underground hydrogen storage from abiotic geochemical perspective. • Carbonates minerals likely trigger redox reactions with H 2 based on thermodynamic modelling. • Pre-existing dissolved oxygen contributes negligible impact on hydrogen solubility and pH for all tested minerals. • Abiotic geochemical reactions may lead to an localized pH increase. [ABSTRACT FROM AUTHOR]

It is generally accepted that hydrogen is generated by ferrous iron oxidation and/or water radiolysis but no attempt has been done so far to explain the origin of the nitrogen that is associated to 'hydrogen systems' such as those located in Brazil and Oman and New Caledonian ophiolites. We carried out 25–300 °C geochemical equilibrium calculations on model water and water-mineral systems including ammonium (NH 4 +) to see if this ion could be a 'precursor' in the generation of hydrogen and/or nitrogen. The considered minerals of the water-mineral systems were the magnetite-hematite or fayalite-magnetite-quartz redox-buffering assemblages. The water systems including NH 4 + only or NH 4 + and ferrous iron co-generate hydrogen and nitrogen through the ammonium decomposition reaction: NH 4 + = 1.5 H 2 + 0.5 N 2 + H+ In the water-mineral systems, hydrogen is generated by the magnetite and fayalite ferrous iron oxidation while nitrogen is generated independently by the hematite and magnetite ferric iron reduction by NH 4 +: 3 Fe3+ + NH 4 + = 0.5 N 2 + 3 Fe2+ + 4 H+ With magnetite-hematite, the produced gas is mainly composed of nitrogen. At low temperature with fayalite-magnetite-quartz, the produced gas is mainly composed of hydrogen; approaching 300 °C, and with a sufficient initial ammonium stock, a significant amount of nitrogen is produced to form a mixed gas. If we consider low (magnetite-hematite) or high (fayalite-magnetite-quartz) reducing conditions occurring respectively within the central or peripheral zones of the hydrogen systems, NH 4 + passing through and reacting with these two kinds of redox environments could explain why the central zones release mainly hydrogen (with some amounts of nitrogen) and why mainly nitrogen is emitted at the peripheries. • Modeling of ammonium oxidation in redox-unbuffered and -buffered aqueous systems. • Hydrogen and nitrogen co-generation through ammonium decomposition. • Nitrogen generation through ferric iron reduction by ammonium. • Hydrogen to nitrogen gas ratios as function of redox conditions. • Explanation of hydrogen and nitrogen association within natural hydrogen seepages. [ABSTRACT FROM AUTHOR]

The employment of granular ferric iron-(oxy)hydroxides, a well-known economic and effective method, lowers arsenic concentrations in different water types. However, for direct application in polluted groundwaters, there is a need to develop new injectable adsorbents for aquifers that could also neutralize acidic media. In this context, a granular ferric hydroxide-calcite (GFH-C) adsorbent was size-reduced to 0.4–50 µm by sonication with the aim of improving (i) the adsorption of As(III) and As(V) at different pHs and (ii) the pH control through the dissolution of calcite. Batch experiments were conducted to determine As(III) and As(V) adsorption isotherms and kinetics, as well as calcite dissolution kinetics, using GFH-C of two sizes (granular and sonicated). Results showed that the arsenic binding capacity of sonicated adsorbents did not improve significantly. On the contrary, the As(III) and As(V) adsorption kinetics improved with the sonication, as in the case of calcite dissolution kinetics. The dissolution of calcite from the adsorbent made the water pH increase to around 9.2–9.4. The sonicated adsorbent offers an advantage in depolluting As-containing groundwater due to its smaller size, which is linked with faster arsenic adsorption and effective acidic water neutralization. [ABSTRACT FROM AUTHOR]

As in any other industry, nuclear energy results in the accumulation of some waste, which needs to be managed safely and responsibly due to its radiotoxicity. In the case of highly radioactive waste, geological disposal in stable rock is considered a broadly accepted solution. For the evaluation of the long-term safety of a geological repository, the assessment of radionuclide transport needs to be carried out. Radionuclide transport through engineered and natural barriers of the repository will highly depend on the barriers’ transport-related properties, which will be determined by coupled thermal, hydraulic, chemical, mechanical, biological, and radiation processes taking place in those barriers. In this study, the thermo-hydro-chemical (THC) state of bentonite was analysed considering CO2 gas diffusion and temperature-dependent solubility in water. Reactive transport modelling of bentonite under non-isothermal conditions was performed with the COMSOL Multiphysics software (v6.0), coupled with the geochemical solver Phreeqc via the iCP interface. The modelling demonstrated that the consideration of chemical processes in bentonite had no significant influence on non-reactive Cl− transport; however, it would be important for other radionuclides whose sorption in porous media depends on the porewater pH. Based on the modelling results, changes in the bentonite mineralogical composition and, subsequently, porosity depend on the partial CO2 pressure at the bentonite–granite boundary. In the case of low CO2 partial pressure at the bentonite–granite interface, the calcite dissolution led to a slight porosity increase, while higher CO2 partial pressure led to decreased porosity near the interface.

porousMedia4Foam is a package for solving flow and transport in porous media using OpenFOAM® - a popular open-source numerical toolbox. We introduce and highlight the features of a new generation open-source hydro-geochemical module implemented within porousMedia4Foam, which relies on micro-continuum concept and which makes it possible to investigate hydro-geochemical processes occurring at multiple scales i.e. at the pore-scale, reservoir-scale and at the hybrid-scale. Geochemistry is handled by a third party package (e.g. PHREEQC) that is coupled to the flow and transport solver of OpenFOAM®. We conducted benchmarks across different scales to validate the accuracy of our simulator. We further looked at the evolution of mineral dissolution/precipitation in a fractured porous system. Application fields of this new package include the investigation of hydro-bio-geochemical processes in the critical zone, the modelling of contaminant transport in aquifers, as well as and the assessment of confinement performance for geological barriers.

The thermal springs of the study area are situated in North-eastern Arunachal Himalayas, India along Subansiri and Siang River valleys with surface temperature ranging between 20 and 57 °C. The pH of thermal springs varies from 7.69 to 9.31, indicating near neutral to alkaline nature of thermal and non-thermal waters. The major geochemical processes influencing hydrochemistry are demonstrated using conventional graphical plots, geochemical modelling by PHREEQC and multivariate statistical analysis. The thermal waters of Chetu and Taksing in Subansiri valley are primarily Na–Cl and Na–HCO3 type, while, thermal water of Yangte in Siang valley is also mixed water-type and others of Ca–Mg–HCO3 type. The geochemically distinct type of waters is obvious from dendrogram derived from hierarchical cluster analysis. Quartz geothermometer predicts reservoir temperatures of thermal springs of 88 ± 13 °C; while, Na–K Giggenbach geothermometer predicts 182 °C and 176 °C for Chetu and Taksing hot springs. Thermal waters are immature and highly prone to mixing with meteoric waters as evident from enthalpy-chloride modelling. Evaporite dissolution, silicate weathering and ion exchange processes are found to contribute to total ion budget in geothermal waters. The saturation indices studies depict oversaturation of all thermal waters with calcite and dolomite. Considering all geochemical features, a conceptual hydrological model resembling geomorphology and origin of thermal springs of North-Eastern Arunachal Himalaya has been proposed. The thermal waters of Subansiri valley display very high Sr and F− content which prohibit them from drinking and utilization purposes. High concentration of toxic elements is addressed to geogenic causes over anthropogenic contributions due to lesser accessibilities at hot spring spots.

The study of groundwater hydrogeochemistry is of great significance to the development, utilization and protection of regional groundwater resources. In this paper, a complete and comprehensive analysis of three runoff zones is carried out in the Fengfeng mining area of Handan City, Hebei Province, China. The Piper trilinear diagram is used to analyze the types of karst groundwater hydrochemistry, the ionic proportionality coefficient method is used to analyze the sources of groundwater chemistry and the formation process, the chlorine-alkali index is used to react to the exchange reactions between cations, and PHREEQC software is also used to invert the groundwater simulation. The results are: the type of karst water hydrochemical in the study area is mainly HCO3·SO4–Ca·Mg; the ions are mainly influenced by rock halite, carbonate, sulphate, silicate and cation exchange; in the groundwater runoff zone, aragonite, calcite and dolomite are in saturated state, while gypsum and rock halite are in unsaturated state. The study of karst groundwater hydrochemical types, analysis of water-rock interaction and exploration of hydrogeochemical evolution mechanisms are intended to provide reference for karst water supply security and water resources utilization. [ABSTRACT FROM AUTHOR]

Chott El Beida, North of Algeria (Setif, 585 km2), is an endorheic zone located in a semi‐arid climate. It is among the first chotts listed under the Ramsar Convention on the Wetlands of International Importance. Numerous studies on wetlands in the Setif region have focused on hydrogeology, avifauna, and vegetation. However, only one study has been devoted to soil studies. This study focused on the pedological and geochemical aspects of salinity in this area. This study was conducted on a toposequence of 200 m comprising eight soil profiles. A set of 24 samples were collected from the top to a depth (0–200 cm) and were subjected to a series of physical and chemical analyses. The concentrations of the major elements were used to determine the chemical facies and calculate the saturation indices for each mineral and residual alkalinity using geochemical modelling with PHREEQC. This study shows that the salinity in Chott El Beida is very variable, varying from less saline to extremely saline, moving from the outside to the centre of the chott, with two types of saline profiles: the descending type towards the outside of the chott and the ascending type in the highly saline depression. Geochemical investigations demonstrated that the dominant facies is (Na‐Cl) which is in accordance with the neutral saline pathway. The phenomenon of salinisation in Chott El Beida is controlled mainly by the precipitation of minerals, namely, calcite, aragonite, dolomite, gypsum, and anhydrite, and the dissolution of evaporite minerals. The study of calcite residual alkalinity and generalised residual alkalinity showed that salinisation evolves in the neutral saline path without the risk of alkalinization. [ABSTRACT FROM AUTHOR]

Engineered waterflooding is an effective process for enhanced oil recovery, but it can lead to mineral scale deposition due to the incompatibility of brines. Previous studies on scale mitigation have mainly focused on high‐temperature baryte and anhydrite scales, neglecting gypsum precipitation and inhibitors adsorption at low temperatures. Additionally, earlier research has used simple brines that do not reflect the actual injection and formation water in reservoirs. In this study, the impact of temperature, various brine mixtures, and thermodynamic databases on saturation ratio and scale precipitation is explored using PHREEQC (pH‐REdox‐EQuilibrium‐C program). The study reveals that the copresence of calcium and magnesium ions improves the gypsum inhibition efficiency of scale inhibitors (SIs) at low concentrations to a maximum of 79%. However, this effect is reversed or neutral at higher SI concentrations. The study also shows that the presence of monovalent ions reduces the adsorption of SIs by multi‐walled carbon nanotubes (MWCNTs). Removing sodium ions from seawater while leaving calcium and magnesium ions intact increases MWCNTs' adsorption capability to 93%. This is because monovalent cations attach to the adsorbent surface and block the active sites, whereas divalent cations act as a bridge between MWCNT and SIs. The study establishes that the behaviour of SIs regarding adsorption on MWCNT and crushed sandstone depends on various factors, including molecule size, calcium toleration of the SIs, point of zero charge, and solution pH. Understanding these factors can improve the effectiveness of SIs, reduce chemical costs, and prolong the life of oil wells. [ABSTRACT FROM AUTHOR]

Abstract The expanding geothermal energy sector still faces performance issues due to scalings in pipes and surface level installations, which require elevated operation pressure levels and costly maintenance. For facilities in the North Alpine Foreland Basin, the precipitation of $${\hbox {CaCO}}_{3}$$ CaCO 3 is the main problem which is a consequence of the disruption of the lime-carbonic acid equilibrium during production. The formation of gas bubbles plays a key role in the scaling process. This work presents experiments in a bubble column to quantify the effects of gas stripping on carbonate precipitation and an extension of PhreeqC to include kinetic exchange between a gas phase and water for the simulation of the experimental results. With the same hybrid model not only precipitation of $${\hbox {CaCO}}_{3}$$ CaCO 3 but also the dissolution of scalings by the injection of $${\hbox {CO}}_{2}$$ CO 2 could be quantified. The bubble column was filled with tap water and brine. By varying the ionic strength of the solution, a wider range of geothermal waters was covered. Air and $${\hbox {CO}}_{2}$$ CO 2 were introduced at the bottom. The precipitates built on the column wall were analyzed with Raman spectroscopy: injecting air into tap water at low ionic strength led to the formation of aragonite with 59.8% of the precipitates remaining at the column wall and the rest as particles in dispersion. At moderate ionic strength the dominant polymorph was calcite and 81.5% of the crystals were attached to the wall. At high ionic strength precipitation was inhibited. The presence of crystallization nuclei reduced the time for precipitation, but not the amount of scalings formed. Injecting $${\hbox {CO}}_{2}$$ CO 2 into the solution completely removed the scalings from the column wall. The model and its experimental backup lay the foundation for a process-based prediction of the scales (not only) in geothermal systems.

Copyright of Grundwasser is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The transport and retardation of radioactive elements in hyper-alkaline conditions of radioactive waste repositories is a challenging field that is still poorly understood. In this study, the transport and attenuation of uranium in a column experiment was modelled by considering kinetic reactions, advection–dispersion and chemical/physical retardation processes. The modelling was first performed for three alluvium samples from Yucca Mountain in circumneutral pH to moderately alkaline conditions. Sorption of uranyl ( UO 2 2 + (U VI) ) was found to strongly depend on the surface complexation model assumed, with no significant removal of U VI by precipitation or ion exchange process. The surface/edge site reaction of Al-hydroxyl group in kaolinite was shown to have a high affinity for uranyl adsorption, while the hydrous ferric oxide edge on hematite adsorbed most of the uranyl ions. The model was then used to interpret uranium transport in a laboratory column filled with Hollington sandstone under hyper-alkaline (pH 13) conditions. The simulation results show that uranium adsorption on the Al-hydroxyl edge of kaolinite exceeds adsorption by the calcium silicate hydrate phase. This result may reflect the lack of surface complexation parameters for calcium silicate hydrate minerals. Hence, further studies are required in the field of surface complexation reactions for calcium silicate hydrate phases. Article Highlights: Sorption of uranyl ( UO 2 2 + (U VI) ) was found to strongly depend on the surface complexation model, with no significant removal of U_VI by precipitation or ion exchange process. The aluminol surface edges in kaolinite were shown to have a higher affinity for uranyl adsorption, while the hydrous ferric oxide edge on hematite adsorbed most of the uranyl ions. Uranium adsorption on the aluminol edge of kaolinite exceeds adsorption by the C-S-H phase. This result may reflect the lack of surface complexation parameters for C-S-H minerals. [ABSTRACT FROM AUTHOR]

The crystalline basement aquifer of the Pra Basin in Ghana is essential to the water supply systems of the region. This region is experiencing the ongoing pollution of major river networks from illegal mining activities. Water management is difficult due to the limited knowledge of hydrochemical controls on the groundwater. This study investigates its evolution based on analyses from a previous groundwater sampling campaign and mineralogical investigation of outcrops. The dominant reactions driving the average groundwater composition were identified by means of a combinatorial inverse modelling approach under the hypothesis of local thermodynamical equilibrium. The weathering of silicate minerals, including albite, anorthite, plagioclase, K-feldspar, and chalcedony, explains the observed median groundwater composition in the transition and discharge zones. Additional site-specific hypotheses were needed to match the observed composition of the main recharge area, including equilibration with carbon dioxide, kaolinite, and hematite in the soil and unsaturated zones, respectively, and the degradation of organic matter controlling the sulfate/sulfide content, thus pointing towards kinetic effects during water–rock interactions in this zone. Even though an averaged water composition was used, the inverse models can "bridge" the knowledge gap on the large basin scale to come up with quite distinct "best" mineral assemblages that explain observed field conditions. This study provides a conceptual framework of the hydrogeochemical evolution for managing groundwater resources in the Pra Basin and presents modelling techniques that can be applied to similar regions with comparable levels of heterogeneity in water chemistry and limited knowledge of aquifer mineralogy. The combinatorial inverse model approach offers enhanced flexibility by systematically generating all plausible combinations of mineral assemblages from a given pool of mineral phases, thereby allowing for a comprehensive exploration of the reactions driving the chemical evolution of the groundwater. [ABSTRACT FROM AUTHOR]

This study focuses on determining significant controlling factors of chemical consequences, inverse geochemical modeling, water quality, and human health risk in the Varuna River basin of India. The study interprets that according to pH, total dissolved solids, and total hardness, the maximum number of groundwater samples are alkaline, fresh, and have substantial hardness. The abundance of major ions follows a pattern: Na > Ca > Mg > K, and HCO3 > Cl > SO4 > NO3 > F. Piper diagram shows that Ca–Mg–HCO3 facies are predominant during both seasons. Na-normalized molar ratios of HCO3/Na, Mg/Na, and Ca/Na are 0.62, 0.95, and 1.82 (pre-monsoon) and 0.69, 0.91, and 1.71 (post-monsoon), respectively, elucidating the coupled silicate and carbonate weathering (dolomite dissolution) sources. The Na/Cl molar ratio is 5.3 (pre-monsoon) and 3.2 (post-monsoon), indicating silicate alteration as the primary process rather than halite dissolution. The chloro-alkaline indices confirm the presence of reverse ion- exchange. Geochemical modeling using PHREEQC identifies the formation of secondary kaolinite minerals. The inverse geochemical modeling categorizes the groundwaters along the flow path from recharge area waters (Group I: Na–HCO3–Cl), transitional area waters (Group II: Na–Ca–HCO3), and discharge area waters (Group III: Na–Mg–HCO3). The model demonstrates the prepotency of water–rock interactions in pre-monsoon justified by the precipitation of Chalcedony and Ca-montmorillonite. The mixing analysis shows that in the alluvial plains, groundwater mixing is a significant hydrogeochemical process that affects groundwater quality. The Entropy Water Quality Index ranks 45% (pre-monsoon) and 50% (post-monsoon) of samples as an excellent category. However, the non-carcinogenic health risk assessment shows that children are more susceptible to fluoride and nitrate contamination. [ABSTRACT FROM AUTHOR]

Isothermal evaporation experiment of inland Algerian brine was carried out at 35°C. The study of fractional crystallization during this experiment has been addressed by different approaches. The identification of the solids recovered by X-ray diffraction together with the monitoring of the ionic composition, density, and pH of the evaporated brine. The Jänecke solubility diagram of the quinary system determined both predicted and experimental fractional crystallization pathways. The mass balance of CaSO4, NaCl, MgSO4, and KCl salts was calculated using the Zayani formulates. Finally, PHREEQC forward and inverse modeling has been done with the Pitzer thermodynamic database. The real crystallization sequences obtained are successively: gypsum and halite, halite and schoenite, halite, epsomite and sylvite, and finally halite, epsomite, sylvite, and carnallite. These results corroborate well with those obtained by both forward and inverse PHREEQC modeling but did not agree with those of Jänecke solubility diagram of the studied system at 35°C. This deviation is explained by the metastable equilibria occurred in the late stages of evaporation. Thus, PHREEQC software seems to be better when studying the evaporation of such concentrated inland brines. The calculated mass balance confirmed the possibility of the production of potassium and magnesium salts from these brines. [ABSTRACT FROM AUTHOR]

The production of geothermal fluids can be adversely affected by the formation of free gas bubbles (degassing). Decreasing pressures can cause dissolved gas to exsolve, which can reduce water production. This study aims to improve the understanding of the conditions under which free gas nucleates in geothermal reservoirs. The focus is on CO2 degassing from brines with varying salinity. We report a series of depressurisation experiments at high pressure and temperature using a cell that allows for visual monitoring of the degassing process using a high-speed camera along with pressure and temperature logging. A geochemical model was created for simulating the degassing behaviour at the same conditions as those used in the experiments, thus allowing for direct comparison.

The occurrence, mobilization, and origin of Potentially Toxic Eelements (PTEs) in the environment is always a difficult research question that has not been fully addressed to date; solving this problem would be a major achievement for environmental science and pollution research, a significant scientific breakthrough, and an important contribution to environmental analysis and monitoring. The lack of a holistic methodology that uses chemical analysis to determine the origin of each PTE in the environment is the main motivation for this project. Therefore, the hypothesis tested here is to develop a scientific approach applied to each PTE to determine whether its origin is geogenic (i.e., water-rock interaction with dominance of silicate or carbonate mineral phases) or anthropogenic (i.e., agricultural practices, wastewater, industrial activities). A total of 47 groundwater samples from the Psachna Basin in central Euboea, Greece, were used and plotted on geochemical mole ratio diagrams (i.e., Si/NO3 vs. Cl/HCO3) and used to perform a robust geochemical modeling analysis. The proposed method showed that elevated groundwater concentrations of various PTEs in groundwater were mainly related to intensive fertilization (e.g., Cr, U), water-rock interaction (e.g., Ni), and saltwater intrusion. (i.e., As, Se). This work highlights that a comprehensive framework with sophisticated molar ratios combined with modern statistical methods, multi-isotope signatures, and geochemical modeling could provide answers to unresolved scientific questions about the origin of PTEs in water resources and improve environmental resilience. [ABSTRACT FROM AUTHOR]

In this study, the quality of groundwater has been evaluated for irrigation in Khana and Gokana areas of Rivers State, Nigeria. Standard sampling and analytical methods were used. Chemical features were investigated via chemometric determinations, including major ions and potentially toxic elements (PTEs) and saturation index (SI) of selected mineral phases calculated using the PHREEQC software. Parameters like sodium adsorption ratio (SAR), sodium percentage (Na%), permeability index (PI), magnesium adsorption ratio (MAR), Kelly's ratio (KR), and Potential salinity (PS) were computed to ascertain its quality for irrigation purpose. Results revealed that the principal hydrochemical facies in the studied water samples is Ca–Mg–Cl. Geochemical model indicates the prevalence of dissolution process, since all carbonate and sulfate mineral phases are undersaturated. The occurrence of PTEs could be explained by the prevailing hydrogeochemical conditions and the dissolution/precipitation reactions of key mineral phases such as oxy-hydroxides. For the Khana and Gokana samples, respectively, SAR concentrations range from 0.19 to 0.71 and 0.22 to 0.80; MAR values range from 47.83 to 62.35% and 47.61 to 68.09%; KR ranges from 0.15 to 0.53 and 0.11 to 0.50; %Na ranges from 1.44 to 5.78 and 9.69 to 29.29; while PS are generally < 5. Most of the groundwaters fall into the C1–S1 and C2–S1 categories on the USSL diagram, with low-to-medium salinity hazard; while a few fall into the C3–S1 category. The deductions from the different indices computed in this study revealed that the groundwater is generally considered safe for irrigation purposes. [ABSTRACT FROM AUTHOR]

The Heuningnes Catchment in the Republic of South Africa was used as a case study in this research to describe the application of saltwater fraction/quantification and hydrogeochemistry methods to evaluate the extent of saline intrusion in the coastal aquifers. The argument of the research is that the presence of seawater incursion may be conclusively determined by combining the examination of the major ions, seawater fraction, stable isotopes of water, bromide, and geochemical modeling. Using stable isotopes of oxygen (18O) and deuterium (2H), major ions chemistry, seawater composition, and geochemical modeling, the genesis of salinity and mixing of different water masses were examined. Twenty-nine (29) samples of groundwater were examined. All samples showed water facies of the Na-Cl type, indicating a seawater-related origin. The significance of mixing in coastal aquifers under natural conditions was shown by the hydrogeochemical characteristics of key ions derived from ionic ratios, which demonstrated substantial adherence to mixing lines among endmembers for freshwater as well as saltwater (seawater). The quantification of seawater contribution in groundwater percentages varied from 0.01 to 43%, with three samples having concentrations of seawater above 50%. It was clear from the hydrogeochemical analysis and determination of the proportion of saltwater that the seawater intrusion impacted the coastal fresh groundwater. In addition, the chloride concentration in the groundwater ranged from 81.5 to 26,557.5 mg/L, with the corresponding δ18O values ranging from −5.5‰ to −0.9‰, which suggested that freshwater and saltwater were mixing. The Br−/Cl− ratios showed that evaporation had played a part in elevating groundwater salinity as well. Since saturation indices were below zero, the mineral dissolution could also contribute to the salinization of groundwater. Further proof of seawater incursion in the investigated catchment was supplied by geochemical modeling and bromide. Even though such tools were not verified in multiple coastal aquifers for widespread generalization, the study offered a scientifically significant understanding of the application of such tools on seawater intrusion in coastal aquifers and has useful recommendations for the aquifer setting of similar environments. [ABSTRACT FROM AUTHOR]

NH4+ and Zn2+ are the most abundant cations detected in contaminated groundwater near municipal landfill sites. Remediation strategies were developed accordingly, such as permeable reactive barrier (PRB) that was reported as effective for single contaminant removal with porous reactive materials, including zeolite and activated carbon. However, considering the fact that multiple contaminants coexist in the groundwater, the removal effect of these porous materials and the competitive retention mechanisms between contaminants are unclear. Therefore, this study investigated the removal contributions of zeolite and activated carbon on NH4+ and Zn2+ under single and coexisting conditions. The priorities and competition mechanisms were clarified through batch and column transport tests, microscopic analyses, as well as geochemical reactive transport modeling by PHREEQC. The results indicated that zeolite performed well in removing both contaminants through ion exchange, while activated carbon was only effective in adsorbing Zn2+ through surface complexation. Mixed zeolite and activated carbon promoted each other in NH4+ removal, but inhibited the removal of Zn2+. With the increase of Zn2+ concentration, competitive adsorption occurred that influenced the breakthrough behaviors of both cations. Considering field applications as PRB reactive materials, it is suggested that pure zeolite will be appropriate if NH4+ is the main contaminant, and a mixture of adsorbents with zeolite content larger than 40% can be effective if considerable amounts of heavy metals coexist with NH4+. [ABSTRACT FROM AUTHOR]

The degree of toxic metal and metalloid [metal(loid)] pollution in a tributary creek, which flows along a small-scale gold mining area, was assessed using modeled speciation profile and various environmental pollution indicators. Sediment and water samples were collected from five different locations representing the creek's upstream, midstream, and downstream areas. Concentration of As, Cd, Cu, and Pb in the sediment and aqueous samples were determined. Chemical speciation of the target analytes in the creek system was performed using geochemical software PHREEQC utilizing elemental concentration in sediment and aqueous phase, temperature, pH, dissolved oxygen, and identified minerals as input values. The concentrations of the metal(loids) in the sediments of midstream and downstream were higher compared to the average shale value (ASV) and toxicological reference values (TRV). Similarly, the total concentrations of As and Cu in creek water exceeded the local guidelines for effluent waters. Speciation results identified HAsO42−, Cd2+, CuOH+, and PbOH+ as the major species of the target analytes. Supersaturation of elements in sediment and low solubility in the aqueous matrix point out to resuspension and transport of metals as colloidal suspensions. The enrichment factor (EF) and geoaccumulation index (Igeo) values indicate significant levels of enrichment and pollution in the midstream and downstream areas. The increasing pollution load index (PLI) suggested the progressive deterioration from the upstream (0.8 to 1.7) down toward the midstream (PLI = 2.0 to 18.0) and downstream (PLI = 2.4 to 17.5). Speciation and environmental index results confirmed that anthropogenic sources in the midstream were transported to the downstream catchment. [ABSTRACT FROM AUTHOR]

Copyright of Acta Geoscientica Sinica is the property of Acta Geoscientica Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The expanding geothermal energy sector still faces performance issues due to scalings in pipes and surface level installations, which require elevated operation pressure levels and costly maintenance. For facilities in the North Alpine Foreland Basin, the precipitation of CaCO 3 is the main problem which is a consequence of the disruption of the lime-carbonic acid equilibrium during production. The formation of gas bubbles plays a key role in the scaling process. This work presents experiments in a bubble column to quantify the effects of gas stripping on carbonate precipitation and an extension of PhreeqC to include kinetic exchange between a gas phase and water for the simulation of the experimental results. With the same hybrid model not only precipitation of CaCO 3 but also the dissolution of scalings by the injection of CO 2 could be quantified. The bubble column was filled with tap water and brine. By varying the ionic strength of the solution, a wider range of geothermal waters was covered. Air and CO 2 were introduced at the bottom. The precipitates built on the column wall were analyzed with Raman spectroscopy: injecting air into tap water at low ionic strength led to the formation of aragonite with 59.8% of the precipitates remaining at the column wall and the rest as particles in dispersion. At moderate ionic strength the dominant polymorph was calcite and 81.5% of the crystals were attached to the wall. At high ionic strength precipitation was inhibited. The presence of crystallization nuclei reduced the time for precipitation, but not the amount of scalings formed. Injecting CO 2 into the solution completely removed the scalings from the column wall. The model and its experimental backup lay the foundation for a process-based prediction of the scales (not only) in geothermal systems. [ABSTRACT FROM AUTHOR]

BackgroundPlutonium is an important element for nuclear energy production and radioactive waste disposal, and evaluating its species distribution in natural water systems is essential for investigating its migration behavior. Recently, with the advancements in related research, some new plutonium species have been discovered and confirmed, hence previous related research is now inadequate for accurately describing the species distribution of plutonium in solutions.PurposeThis study aims to understand the speciation distribution of plutonium in different water composition systems.MethodsThe geochemical calculation software PHEEQC was employed to systematically evaluate the effects of the pH value and coexisting ion concentration on the species distribution of plutonium. The plutonium species proportion in different natural water systems was estimated in according with the latest thermodynamic data embedded into PHEEQC software.ResultsThe results reveal that hexavalent plutonium in oxidized groundwater with low hardness mainly exists as PuO22+ or PuO2CO3 under acidic conditions, whereas PuO2(CO3)22- or PuO2(CO3)34- dominate under neutral or alkaline conditions. Although PuO22+ and PuO2CO3 are the main species of plutonium in acidic environments, CaPuO2(CO3)32- is the dominant species under neutral or basic conditions whereas the calcium concentration is high in the solution.ConclusionsTherefore, the hardness of water (particularly, the calcium concentration) can be concluded to be among the important factors affecting the species of plutonium and must be carefully considered in the geological disposal of plutonium.

Underground Hydrogen storage (UHS) is a promising technology for safe storage of large quantities of hydrogen, in daily to seasonal cycles depending on the consumption requirements. The development of UHS requires anticipating hydrogen behavior to prevent any unexpected economic or environmental impact. An open question is the hydrogen reactivity in underground porous media storages. Indeed, there is no consensus on the effects or lack of geochemical reactions in UHS operations because of the strong coupling with the activity of microbes using hydrogen as electron donor during anaerobic reduction reactions. In this work, we apply different geochemical models to abiotic conditions or including the catalytic effect of bacterial activity in methanogenesis, acetogenesis and sulfate-reduction reactions. The models are applied to Lobodice town gas storage (Czech Republic), where a conversion of hydrogen to methane was measured during seasonal gas storage. Under abiotic conditions, no reaction is simulated. When the classical thermodynamic approach for aqueous redox reactions is applied, the simulated reactivity of hydrogen is too high. The proper way to simulate hydrogen reactivity must include a description of the kinetics of the aqueous redox reactions. Two models are applied to simulate the reactions of hydrogen observed at Lobodice gas storage. One modeling the microbial activity by applying energy threshold limitations and another where microbial activity follows a Monod-type rate law. After successfully calibrating the bio-geochemical models for hydrogen reactivity on existing gas storage data and constraining the conditions where microbial activity will inhibit or enhance hydrogen reactivity, we now have a higher confidence in assessing the hydrogen reactivity in future UHS in aquifers or depleted reservoirs.

Nutrient availability after fertilising agricultural soils is affected by many factors, including soil moisture conditions and physicochemical properties. Herein, the availability of potassium in soil enriched with biochar is studied, considering either saturated or unsaturated moisture conditions and questioning key ion exchange approaches, such as equilibrium exchange (E.E.) and kinetic exchange (K.E.). Potassium release is simulated from a soil–biochar mixture of 0, 0.5, 1 and 2% by coupling HYDRUS-1D and PHREEQC models. The water flow, mass transport and geochemical processes are simulated for a cultivation period that imitates agronomic and environmental conditions of a common agricultural field in Northern Greece. Potassium is released gradually during the irrigation period in the case of unsaturated flow conditions as opposed to its complete release over a few days in the case of saturated flow conditions in the soil. Regarding ion-exchange processes, the soluble amount of potassium is more readily available for transport in soil solution when using the E.E. approach compared to the K.E. approach that assumes a kinetically controlled release due to interactions occurring at the solid–solution interface. The increased proportion of biochar in soil results in a doubling of available potassium. Among the four modelling schemes, although the total mass of potassium released into soil solution is similar, there is a significant variation in release time, indicating that simplified saturated conditions may lead to unrealistic estimates of nutrient availability. Further experimental work will be valuable to decrease the uncertainty of model parameter estimation in the K.E. approach. [ABSTRACT FROM AUTHOR]

Electrokinetic remediation (EKR) is a promising technique for the treatment of contaminated soils and sediments. However, the application of EKR to metal(oid)-contaminated mine wastes with varying mineralogy and physicochemical properties has not been fully characterized. This paper evaluates the potential of EDTA-enhanced EKR as a means to remove trace metal(oid)s (Cu, Cd and As) and major metals (Fe, Al and Mg) from a phosphate mine tailings material. Controlled laboratory EKR experiments were performed, in which the electrolyte EDTA concentration was varied between 0.1 and 1 M and the voltage gradient between 24 and 32 V. Migration of the studied contaminants increased proportionally to increasing EDTA concentration and applied voltage gradient, and the obtained average removal efficiencies of Al, Mg, Cu, Cd and As reached up to 29%, 10%, 26%, 28% and 22%, respectively, within a week. Differences in metal mobilization could be explained by their mineral hosts and aqueous speciation under the imposed geochemical conditions during EKR, which were corroborated by aqueous geochemical equilibrium modeling using PHREEQC. Our results suggest that EKR could be a feasible remediation option for select metal(oid)-enriched mine waste fractions following further optimization. [ABSTRACT FROM AUTHOR]

In order to select efficient media and find the optimum operation conditions for contaminant removal in soil aquifer treatment (SAT), column experiments with three different media were carried out under two different dry-wet ratio conditions. Phreeqc and Hydrus-1D were used to simulate the hydrogeochemical interactions. The results based on dissolution kinetics and cation exchange showed that the water-rock interaction in the columns led to the increase of Ca2+ and decrease of K+ in reclaimed water. The transfers of Ca2+ by cation exchange and calcite dissolution were 0.16–0.24 mmol/L and 0.13–0.22 mmol/L, respectively. The adsorption distribution coefficients (Kd) of NH4-N in columns ranged from 0.02 to 4 cm3/g. Higher Kd values were obtained in the columns of finer particle size or with the addition of biochar. The nitrification rates of NH4-N ranged from 0.08 to 0.4 day−1, but the denitrification rates of NO3-N were low (0–0.005 day−1). This indicated that NO3-N removal in the columns was insignificant. The increase of the drying period from 1 to 3 days promoted the microbial-mediated nitrification that transforms NH4-N to NO3-N. Our results indicated that the sand with a 15-cm biochar layer on the top reduced saturated hydraulic conductivity and was suitable for NH4-N removal. A low dry-wet ratio (i.e., 2:2 days) could be selected to prevent the transformation of NH4-N to NO3-N. The findings are helpful to assess hydrochemical characteristic change in SAT and provide a basis for the selection of a reasonable dry-wet ratio. Highlights: Hydrogeochemical processes were studied by 2-m column experiments and modeling. Dissolution kinetics of minerals was considered in reclaimed water chemical change. Cation exchange and dissolution/precipitation were quantified by inverse modeling. Water flux simulation showed that biochar reduced saturated hydraulic conductivity. Biochar addition significantly enhanced NH4+ removal in soil aquifer treatment. [ABSTRACT FROM AUTHOR]

Surface water chemistry evolution of Ekulu River was conducted by inverse geochemical modelling using the PHREEQC computer program. In this study, samples were collected from the Ekulu river at 100m intervals, and were taken to the laboratory for major anions and cations, heavy metal and bacterial content analyses. Inverse geochemical modelling results reveal that the river evolved as a result of dissolution of siderite, quartz, gypsum, galena, sphalerite, pyrolusite and precipitation of goethite and pyrite. The Piper diagram indicates Calcium- Chloride water type, with high Ca2+ + Mg+ and Cl- + SO4² contents, which is typical of water originated from gypsum dissolution and mine drainage. The results of the analyses show that the water cannot be recommended for drinking because the E. coli and coliform contents are higher than the permissible limits. The water chemistry of Ekulu river is as a result of secondary minerals dissolution and mine drainage from Onyeama coal mine whereas the microbial content resulted from pollution from recent faeces. [ABSTRACT FROM AUTHOR]

Selenium has been identified as an element of interest for the safety assessment of a deep geological repository (DGR) for used nuclear fuel. In Canada, groundwaters at DGR depths in sedimentary rocks have been observed to have a high ionic strength. This paper examines the sorption behavior of Se(-II) onto illite, MX-80 bentonite, Queenston shale, and argillaceous limestone in Na–Ca–Cl solutions of varying ionic strength (0.1–6 mol/kgw (m)) and across a pH range of 4–9. Little ionic strength dependence for Se(-II) sorption onto all solids was observed except that sorption at high ionic strength (6 m) was generally slightly lower than sorption at low ionic strength (0.1 m). Illite and MX-80 exhibited the expected results for anion sorption, while shale and limestone exhibited more constant sorption across the pH range tested. A non-electrostatic surface complexation model successfully predicted sorption of Se(-II) onto illite and MX-80 using the formation of an inner-sphere surface complex and an outer-sphere surface complex. Optimized values for the formation reactions of these surface species were proposed.

• Fe2+, Mn2+, and NH 4 + oxidation was simulated for six filters using RTM. • Fe2+ oxidation rates increased at lower pH. • Fe2+ and Mn2+ oxidation sequence is controlled by backwashing and filter media. • Sequential Fe2+ and Mn2+ oxidation results in overall faster Mn2+ oxidation rates. • Dual media filters can be designed to sequentially oxidize Fe2+ and Mn2+. Iron (Fe2+), manganese (Mn2+), and ammonium (NH 4 +) oxidation processes were studied in three single media and three dual media full-scale rapid sand filters (RSFs) using reactive transport modelling (RTM) in PHREEQC and parameter estimation using PEST. Here, we present the insights gained into the spatial distribution of Fe and Mn mineral coatings in RSFs and its influence on the oxidation sequence and rates. Fe2+ and Mn2+ oxidation predominantly occurred simultaneously in the RSFs, contrary to the expected sequential oxidation based on Gibbs free energy calculations. During backwashing, RSF grains become fully mixed, which initiates heterogeneous Mn2+ oxidation on Mn-coated grains that end up in the top layer. The resulting grains have a mixed Fe/Mn mineral coating, which is limiting heterogeneous Mn2+ oxidation due to the limited Mn mineral surface available. Mixed coatings did not seem to affect Fe2+ oxidation rates, instead oxidation rates were increasing at lower pH. We found that RSFs can be designed to spatially separate Fe2+ and Mn2+ oxidation, which results in optimal conditions for Mn2+ oxidation. The RSF needs to consist of two layers with varying density to inhibit mixing and complete Fe2+ oxidation should occur in the top layer. The developed RTM can be used to estimate the depth at which Fe2+ oxidation is complete, and thus the ideal intersection depth of the two layers. A novel perspective is provided on how mineral coating distribution in single and dual media filters influence removal rates and the sequence of oxidation, which contributes to the design of more efficient groundwater filters. [Display omitted] [ABSTRACT FROM AUTHOR]

The injection of circulating fluids (usually water) is the predominant means of heat extraction in an enhanced geothermal system (EGS); however, the additional injection of circulating fluids can cause a water-rock reaction with a dry thermal rock mass, resulting in the generation of a large number of secondary minerals. These secondary minerals cause fracture closure in artificial reservoirs and severely impede the sustainable use of these geothermal systems. Therefore, this study combined laboratory tests with a PHREEQC hydrogeochemical simulation. First, the changes and mechanisms of mineral and aqueous chemical fractions in the artificial reservoir fractures were analyzed after using groundwater from the sandstone aquifer at the Frontier Observatory for Geothermal Energy Research (FORGE) site as a heat transfer fluid in the FORGE project. Second, the dissolution patterns and precipitation of minerals commonly found in artificial fractures were simulated in four different environments with the aid of PHREEQC after completing transconversion. Finally, the effects of different fluids were evaluated for the unblocking of typical minerals. The results show that as a heat transfer fluid, groundwater causes the dissolution of K-feldspar, albite, and illite, partial decomposition of kaolinite and proto-silicate, rapid production of anorthite, decomposition of dolomite, sodization of Ca-montmorillonite, and dolomitization of black mica. Mud acid was more effective in unblocking fissure closures caused by anorthite, chlorite, and kaolinite. NaOH was more effective in unblocking fissure closures caused by illite and Ca-montmorillonite. Groundwater is not suitable as a blockage remover and can easily produce secondary mineral blockages (calcite and aragonite). The effect of ultrapure water is relatively stable; it can be used as a heat exchange fluid or blockage remover, but when used as a remover, it behaves primarily as a physical-mechanical action process.

The Mangkang geothermal field, distributed in the Mediterranean–Himalayas geothermal belt, hosts abundant hot springs whose geneses remain unclear. To determine the hydrochemical characteristics, reservoir temperature, circulation and recharge depths, and water–rock interactions of the geothermal water in the geothermal field, this study analyzed hydrochemical compositions and isotopes (2H, 3H, and 18O), conducted a PHREEQC simulation, and established a conceptual model to illustrate the genesis of geothermal resources in the Mangkang field. Based on the study of hot springs in Meipu, Qvzika, and Zulongpu villages and Rumei town, the following results are reported: The orifice temperatures of these hot springs vary between 18 °C and 67.5 °C. The hydrochemical composition analysis results indicate that the geothermal water in the hot springs is of hydrochemical type HCO3-Ca·Mg. Moreover, the geothermal water has high HBO2 and Na+ concentrations, suggesting protracted water runoff and strong water–rock interactions during its evolution. According to the mineral–water solubility equilibrium and silica geothermometers, it is estimated that the reservoir temperature of the Zulongpu hot spring is 47 °C and other hot springs have much higher reservoir temperatures of 116–130 °C. As indicated by geothermal gradients, annual temperatures, and reservoir temperatures, the geothermal water in Meipu and Qvzika villages has the greatest circulation depth, up to 3600–4300 m, followed by that in Rumei town (3700–4000 m) and Zulongpu village (~1500 m). The 2H-18O isotopic analysis of the geothermal surface water revealed that the geothermal water originates from meteoric water. The recharge elevation was inferred to be ~4700–4900 m. Moreover, the low 3H values (<1 Tu) suggest that the geothermal water is older than 40 years. The PHREEQC inverse simulation results indicated that the variation in the hydrochemical composition of the geothermal water results from the precipitation of chalcedony and dolomite, the absorption of NaX, and the loss of CaX2 during migration and storage. [ABSTRACT FROM AUTHOR]