Silicate Dissolution Research Articles

Hydrochemical evolution characteristics and mechanism of groundwater funnel areas under artificial governance in Hengshui City, North China

The largest groundwater funnel area is located in the North China Plain (NCP) due to long-term and large-scale overexploitation of groundwater from 1970s. Comprehensive control and management measures have been implemented both in national-scale and local-scale since 2015. This paper presented the evolution of hydrochemical characteristics and its mechanism before (2014) and during the artificial governance (2015–2020) in the center of the NCP funnels (Hengshui City) based on water level, water chemical (including concentrations of K+, Na+, Ca2+, Mg2+, Cl−, SO42−, HCO3−, TH and TDS) data. By using Piper diagrams, ion ratio relationships, geostatistical analysis, Gibbs diagrams, chlor-alkali index and inverse hydrogeochemical simulation (PHREEQC), the following conclusions can be drawn:(1)Temporally, the dominant cation and anion were Na+ and HCO3− both in shallow groundwater (SG) and deep groundwater (DG), respectively. Hydrochemical types both in SG and DG tend to be diverse, owing to the increase of SO42− and Cl− proportion after groundwater overdraft management. Spatially, ion concentrations (except for HCO3−) of discharge areas distributed higher due to shorter hydraulic retention time and flow path of recharge area. The impact of groundwater overdraft management on distribution characteristics of DG was lower than that in SG.(2)Compared with 2014 (before artificial management), SG and DG hydrochemical components had stronger correlation relationships with groundwater level. Hydrochemistry field was influenced by groundwater depth fluctuation and the rates of it at varying degree in recharge and discharge areas. Leakage from SG to DG can be deduced by similar alteration of ion concentrations.(3)In SG, the major water chemistry was controlled by evaporation and water–rock interaction, while dissolution of silicate and evaporate companied with ion exchange dominating the groundwater chemistry in DG from 2014 to 2020. Both in SG and DG simulation paths, dissolution/precipitation of mineral phases and artificial governance influence the hydrochemistry. DG also caused by SG leakage. During artificial management, human activities are a factor that cannot be ignored. Ion concentrations increased with the water–rock interaction enhanced, due to the rate of groundwater depth change decreasing.

Interaction between CO2-rich water and hydrated Portland cement and ultramafic rocks

CO2 geological storage in deep rock formations is a possible strategy to mitigate the atmospheric CO2 concentration. In storage sites, CO2 is injected through wells. The space between the metal casing of the wellbore and the host rock is filled with Portland cement in which micro-fractures on flow paths between cement and rock may originate. It has been amply shown that the interaction between CO2-rich water, hydrated Portland cement and sedimentary rocks leads to alteration of cement (dissolution of cementitious phases) and rock (dissolution of silicates) and precipitation of secondary minerals. These processes may enhance or seal the existing microfractures through which CO2 may leak. However, the integrity of the cement and (ultra)mafic rocks under acidic conditions has not been investigated.In this study, the geochemical processes associated with the interaction between CO2-rich water and mortar (composed by hydrated Portland cement and quartz aggregates) and two mafic rocks (peridotite and obsidian) were studied to evaluate the stability of wellbores in mafic rocks, i.e., the role of carbonation and dissolution mechanisms during long-term exposures to CO2-rich brines. Three column experiments were performed at 10 bar pressure, room temperature (20 ± 2°C) and two ionic strengths (4.0·10-4 M and 2.8·10-2 M).The chemical composition of the effluents was examined over time and reproduced by 2D reactive transport simulations. Experimental and model results show that dissolution of the cement phases contributed to cement alteration and buffered the solution pH, rendering low rock alteration. Water residence time affected the precipitation of secondary CO2-bearing minerals.

Batchwise Leaching of Calcium from Demolition Concrete Fines in an Aqueous Ammonium Nitrate Solution: Part 2 Modeling

This article addresses the application of the indirect mineral carbonation process to recycled concrete aggregates (RCA). In such a process, calcium is first leached from the RCA feedstock into an aqueous ammonium nitrate solution and then it is carbonated to precipitate calcium carbonate. The calcium leaching step is modeled in this contribution, whereas it was investigated experimentally in part 1 of this series, where the focus was more on thermodynamic aspects than on kinetics. In this part 2 paper, kinetics aspects are also included by modeling them using two different approaches. In the first approach, the reaction–diffusion model is implemented, accounting for the congruent dissolution of the calcium hydroxide phase and the incongruent dissolution of the calcium silicate hydrate components of concrete fines. In the second approach, a double-shrinking-core model is used, which for the sake of simplicity assumes congruent dissolution of calcium silicate hydrates as well, infinitely fast reaction/dissolution kinetics, and pseudo-steady-state diffusion. The model parameters have been either determined through targeted experiments or estimated by fitting measurements obtained in experiments with two different materials, both in the size range of up to a diameter of 4 mm. Both models exhibit satisfactory accuracy in describing the experimental data; particularly for particles larger than about 0.1 mm in diameter, the two models calculate a nearly identical evolution of the calcium concentration in solution. The simplifications of the double-shrinking-core model lead to a loss of resolution in characterizing the evolution of leaching inside the particles, whereas they enable faster computations. The latter feature makes such a model a convenient tool for studying process performance, namely, productivity, calcium recovery, and solvent efficiency, through parametric analysis; this has been demonstrated as reported in the last part of the article.

Impact of Silicon on Plant Nutrition and Significance of Silicon Mobilizing Bacteria in Agronomic Practices

Globally, rejuvenation of soil health is a major concern due to the continuous loss of soil fertility and productivity. Soil degradation decreases crop yields and threatens global food security. Improper use of chemical fertilizers coupled with intensive cultivation further reduces both soil health and crop yields. Plants require several nutrients in varying ratios that are essential for the plant to complete a healthy growth and development cycle. Soil, water, and air are the sources of these essential macro- and micro-nutrients needed to complete plant vegetative and reproductive cycles. Among the essential macro-nutrients, nitrogen (N) plays a significant in non-legume species and without sufficient plant access to N lower yields result. While silicon (Si) is the 2nd most abundant element in the Earth’s crust and is the backbone of soil silicate minerals, it is an essential micro-nutrient for some plants. Silicon is just beginning to be recognized as an important micronutrient to some plant species and, while it is quite abundant, Si is often not readily available for plant uptake. The manufacturing cost of synthetic silica-based fertilizers is high, while absorption of silica is quite slow in soil for many plants. Rhizosphere biological weathering processes includes microbial solubilization processes that increase the dissolution of minerals and increases Si availability for plant uptake. Therefore, an important strategy to improve plant silicon uptake could be field application of Si-solubilizing bacteria. In this review, we evaluate the role of Si in seed germination, growth, and morphological development and crop yield under various biotic and abiotic stresses, different pools and fluxes of silicon (Si) in soil, and the bacterial genera of the silicon solubilizing microorganisms. We also elaborate on the detailed mechanisms of Si-solubilizing/mobilizing bacteria involved in silicate dissolution and uptake by a plant in soil. Last, we discuss the potential of silicon and silicon solubilizing/mobilizing to achieve environmentally friendly and sustainable crop production.

Seasonal Mg isotopic variation in the middle Yellow River: Sources and fractionation

In order to better understand how stable metal isotope signals in large rivers can be used to constrain present and past weathering, the seasonal riverine MgSr isotopic pattern in the middle Yellow River was systematically investigated based upon weekly collected samples for the whole year of 2013. The results demonstrate that Mg is mainly transported in the dissolved form (65%) in this river system and that 45% of the total dissolved Mg is transported during the monsoon seasons, with 2% exported over 4 days during a single storm event. Dissolved Mg in the middle Yellow River is dominantly derived from both silicate and carbonate (82–89%) in this semi-arid region, with limited evaporite contribution (∼7%). Lithological mixing is the first order control on riverine dissolved Mg and Sr isotopes, with a contribution from ∼40% carbonate dissolution and ∼ 60% from silicate dissolution in the dry seasons, and ∼ 50% carbonate and ∼ 50% silicate during the monsoon seasons according to δ26Mg signals. Furthermore, a significant role of prior calcite precipitation (PCP) can be quantified, which fractionates Mg isotopes by about 0.17‰ to 0.39‰ positively depending on the choice of elemental and isotope partition of Mg in secondary carbonates. Clay formation following the PCP further fractionates riverine Mg isotopes to the negative side. An ∼0.2‰ decrease of riverine Mg isotopes is attributable to (1) a single storm event causing carbonate dissolution and (2) delayed delivery of depleted waters to rivers (∼3 months after the storm event) because of subsurface hydrological circulation. Annually, the weighted average riverine δ26Mg (−1.05‰) in the middle Yellow River is identical to the global average (−1.09‰). Despite the significant impact of lithology on the riverine dissolved Mg isotope signature, the mixing proportions of different Mg sources remain virtually constant, even when there are huge contrast of temperature, hydrology, and precipitation seasonally along the year, providing a basis for dissolved δ26Mg response to climatic forcing on the continental scale. This means that significant changes in the sedimentary Mg isotope records would reflect extreme conditions in deep time.

Analysis of the Formation Mechanism of Medium and Low-Temperature Geothermal Water in Wuhan Based on Hydrochemical Characteristics

Wuhan and its surrounding areas have obvious geothermal spring outcrops, which are unexplored potential geothermal resources. The degree of geothermal resource development in Wuhan is low, and there is a lack of systematic research on their hydrochemical characteristics and formation mechanism. The Wuhan area is bounded by the Xiang-Guang fault, the South Qinling-Dabie orogenic belt in the north, and the Yangtze landmass in the south, with Silurian and Quaternary outcrops and little bedrock outcrops. The Silurian is the main water barrier in the region, which separates the upper Triassic and Paleogene as shallow aquifers and the lower Cambrian and Ordovician as deep aquifers. Different strata are connected by a series of fault structures, which constitute Wuhan’s unique groundwater water-bearing system. Eleven geothermal water (23~52 °C) and six surface water samples (around 22 °C) were collected from the study area. The geothermal water in the study area is weakly alkaline, with a pH of 7.04~8.24. The chemical type of geothermal water is mainly deep SO42− with a higher TDS and shallow HCO3− type water with a lower TDS. Isotopic analysis indicates that atmospheric precipitation and water-rock interaction are the main ionic sources of geothermal water. The chemical composition of geothermal water is dominated by ion-exchange interactions and the dissolution of carbonates and silicates. The characteristic coefficients, correlation analysis, water chemistry type, recharge elevation, geothermal water age, reservoir temperature, and cycle depth were also analyzed. The performance was similar in the same geothermal reservoir, which could be judged as an obviously deep and shallow geothermal fluid reservoir, and the genetic conceptual model of Wuhan geothermal was preliminarily deduced. DXR-8 and DXR-9 had the best reservoir conditions, hydrodynamic conditions, rapid alternation of water bodies, and large circulation depth, which is a favorable location for geothermal resource development and will bring considerable economic and social benefits.

Peridotite dissolution in the presence of green microalgae: Implications for a geoengineering strategy of CO2 sequestration

• Peridotite dissolution rate was significantly enhanced by green microalgae. • Interaction between peridotite and green microalgae showed two stages with first-order reaction in the early stage. • The growth of green microalgae was promoted by the Mg 2+ ion released from peridotite. Enhanced silicate dissolution has been recognized as a potentially promising geoengineering strategy to help remove CO 2 from the atmosphere by applying crushed minerals to aquatic systems. However, it has not yet been fully quantified in the presence of eukaryotic green microalgae. Here, we studied the interaction of peridotite with Chlamydomonas reinhardtii ( C.R. ) and Chlorella pyrenoedosa ( C.P. ). We found that the peridotite dissolution rate was significantly enhanced by green microalgae. Meanwhile, the interaction between peridotite and green microalgae showed two stages with first-order reaction in the early stage (0 - 4 or 5 days). The amount of Mg 2+ released per algal chlorophyll-a biomass and unit time in the early stage is about an order of magnitude higher than that in the late stage (4 or 5 - 9 days). The quantified effect of C.P. on the dissolution rate of peridotite is about two times higher than that for C.R. in the early stage. Based on the stoichiometric relation of peridotite dissolution, it is estimated that one milligram chlorophyll-a biomass of C.R. and C.P can remove 0.44 and 0.24 mg CO 2 from the atmosphere in one day via accelerating dissolution, respectively . Besides, the Mg 2+ ion released from peridotite can promote the growth of green microalgae in turn. Thus, green microalgae play a positive role in CO 2 sequestration via the artificial adding peridotite to aquatic systems, but the issue related to the great deceleration of peridotite dissolution rate after a period of time has to be solved to improve the efficiency of CO 2 sequestration.

Geological carbon cycle in a sandstone aquifer: Evidence from hydrochemistry and Sr isotopes

Sr isotopes have been widely used to quantify silicate versus carbonate weathering reflected in rivers, but there is no such study in groundwater, which is restricted by the difficulty of accurately determining the Sr contents and isotopic ratios of the two endmembers in silicate-dominated aquifers. In a sandstone catchment, we find rainwater, modern groundwater in the recharge area, and old groundwater in the discharge area have contrast 87Sr/86Sr ratios, with mean values of 0.710784, 0.711448, and 0.710269, respectively. If we follow previous studies and use the acetic acid leachate of sandstone to represent the calcite fraction, the resulting 87Sr/86Sr ratio cannot explain most groundwater samples. By considering the simultaneous dissolution of calcite and silicates in the acetic acid leachate, we find the typical 87Sr/86Sr ratio of calcite equals 0.709113, which well explains the 87Sr/86Sr ratios of all groundwater samples. The 87Sr/86Sr ratios of groundwater in the recharge area with abundant dissolved CO2 are contributed by three endmembers (rainwater, silicate and calcite), whereas those of old groundwater in the discharge area with low dissolved CO2 as well as low Cl− and SO42− can be explained by two endmembers (calcite and groundwater in the recharge area). Based on strontium isotopic budget, we find the equivalent concentrations of CO2 consumption by silicates and calcite in groundwater are both larger than those in river waters studied in previous studies, and the majority of dissolved CO2 in groundwater can be fixed by carbonate weathering as long as the residence time is long enough. This study enhances understanding of the roles of silicate and carbonate weathering during long-time groundwater circulation.

Hydrochemical characteristics and processes of groundwater in the Cenozoic pore aquifer under coal mining.

Mining activities considerably affect groundwater quality and resources. It is crucial to investigate water chemistry and hydrochemical processes under coal mining settings for water environment protection and sustainable utilization of groundwater resources. In this study, 36 groundwater samples from the Cenozoic pore aquifer in the Gubei coal mine in Huainan (Anhui Province, China) were analyzed using hydrochemical, multivariate statistical methods, and inverse geochemical modeling. Results revealed a hydrochemical boundary around 100m below the ground surface, forming two flow zones participating in different hydrological cycles. In the shallow (circulation) zone above the boundary, the main hydrochemical processes are silicate dissolution and cation exchange, followed by evaporite dissolution. In this zone, the Na+ + K+, Cl-, and SO42- concentrations are low and stable, forming low-salinity water (total dissolved solids [TDS] < 1g/L) dominated by Na*Ca*Mg-HCO3 and Na*Ca-HCO3 types. At greater burial depths, the pH, TDS, Na+ + K+, Cl-, and SO42- concentrations in the groundwater gradually increase, while the HCO3- concentration gradually decreases, which is mainly due to the enhanced evaporite dissolution and decarbonation in the deep (circulation) zone below the hydrochemical boundary. In this zone, the Na+ + K+, Cl-, and SO42- concentrations are high and variable, forming high-salinity water (TDS > 1g/L) dominated by Na-Cl and Na-Cl*SO4 types. A hydrochemical evolution model of the Cenozoic aquifer was finally established, which advances our understanding of the evolutionary processes of groundwater chemistry under mining drainage.

Effects of precipitation, irrigation, and exploitation on groundwater geochemical evolution in the people’s victory canal irrigation area, China

The People's Victory Canal Irrigation Area is a large gravity irrigation area in the middle and lower reaches of the Yellow River. Groundwater hydrochemistry is controlled by geochemical weathering, precipitation, irrigation from the Yellow River diversion, and artificial exploitation. The Piper diagram, hierarchical cluster analysis, Gibbs diagram, and ion proportion coefficient were applied to improve our understanding of the hydrogeochemical evolution. Our results indicated that groundwater ion concentration has prominent spatial zonation characteristics in the study area. The groundwater ion components in the low salinity area are mainly a result of silicate and carbonate weathering, with the major hydrochemical type being HCO3·Cl–Na·Mg and HCO3–Na·Ca. The soil salt content in the low salinity area is low. The main effect of precipitation on groundwater chemical composition is a reduction in groundwater ion concentration by recharge. The groundwater ion concentration near the canal is similar to the Yellow River water. The groundwater ionic components in the high salinity area are mainly affected by weathering, silicate dissolution, and evaporative salt rocks. The water chemical type is SO4·Cl–Na·Mg. Expectedly, the soil salt content is high in the high salinity area. The Yellow River recharge decreased the ion concentration of groundwater near the canal. In addition, the groundwater exploitation increase results in a change in the flow field, affecting the local groundwater chemistry. The groundwater ion concentration increases as the groundwater flow from the high salinity area to the low salinity area. In contrast, the groundwater ion concentration in the high salinity area decreases. We further discuss these results in the context of the complex influence of precipitation, Yellow River diversion irrigation, and artificial exploitation on the hydrogeochemical evolution.

Effect of citric-acid-modified chitosan (CAMC) on hydration kinetics of tricalcium silicate (C3S)

Studying the mechanism by which organic admixtures affect the hydration and dissolution of tricalcium silicate (C3S) reveals the effect of organic admixtures on ordinary Portland cement and enables target regulation of cement-based materials. In this study, the effects of citric-acid-modified chitosan (CAMC) on the hydration exotherm, hydration products, and microscopic morphology of C3S were investigated. The interface structures, ion adsorptions, and dissolution properties of CAMC and C3S were analyzed using a molecular dynamics simulation method. The results showed the presence of an attraction between the C3S surface and CAMC due to the existence of Op-Hw, Op-Cas, and Hp-Ow ion pairs. CAMC adsorbed most of the Ca ions released upon dissolution of C3S in the aqueous solution and the resulting pairs exhibited low solubilities. The Ca ions were located on the surfaces of C3S particles, preventing the dissolution of the particles and proving the interference effect of additives on the hydration of the cement silicate phase.

Hydrogeochemical evolution of Taiyuan Formation limestone water under the disturbance of water inrush from karst collapse column in Taoyuan Coal Mine, China

Abstract The project implementation of water inrush and its treatment ensures the safe mining of coal mines, but also causes certain disturbance to the hydrogeochemistry of primary limestone water. Based on the water inrush event in Taoyuan Coal Mine of Huaibei coalfield in 2013, the water rock interaction mechanism of Taiyuan Formation limestone water (namely, ‘Taihui water’) was discussed. The results showed that: (1) the relationship of cation mass concentration before and after water inrush was Na+ + K+ &amp;gt; Ca2+ &amp;gt; Mg2+; the correlation of anionic mass concentration before water inrush was SO42− &amp;gt; HCO3− &amp;gt; Cl−, while it was HCO3− &amp;gt; SO42− &amp;gt; Cl− after the event. Before the event, the main water quality types were SO4•Cl-Ca and SO4•Cl-Na; after the event, they mainly included HCO3-Na and SO4•Cl-Na; (2) There is a strong positive correlation between mineral saturation index and pH value, that is, minerals are easy to dissolve under acidic conditions, while alkaline conditions will inhibit the dissolution and transformation of minerals; (3) The hydrogeochemical processes of limestone aquifer mainly included cation exchange, carbonate dissolution, pyrite oxidation, sulfate and silicate dissolution.

Hydrochemical Characteristics and Genetic Mechanism of Geothermal Springs in the Aba Area, Western Sichuan Province, China

Geothermal resources have been a source of significant clean energy in the world. The Sichuan Province is famous for its abundant geothermal resources in China, especially in western Sichuan. The Aba area is a significant minority region in northwestern Sichuan with abundant geothermal resources. In this study, hydrochemical and D-O analyses were conducted on the eight collected geothermal springs to investigate the genetic mechanism of the geothermal resource in the Aba area. The exposed temperatures and pH values of the geothermal springs ranged from 23 °C to 48 °C and from 6.6 to 9.5, respectively. Based on the hydrochemical characteristics, the eight geothermal springs were classified into two types: class A and class B. The class A geothermal springs belonged to the hydrochemical type of Ca-Mg-HCO3-SO4 and Ca-Mg-HCO3 and were affected by the weathering and dissolution of carbonate and silicate. The class B hydrochemical type of geothermal spring was Na-HCO3, which was determined by the weathering and dissolution of evaporite and silicate. A Na-K-Mg triangle diagram revealed that the geothermal springs belonged to immature water. A chalcedony geothermometer indicated that the temperature of the class A shallow geothermal reservoir in the Aba area was 59.70–73.00 °C and 70.65–120.91 °C for class B. Silicon enthalpy approaches showed that the initial reservoir temperature for class A was 181.36–203.07 °C (mixed by 85.76–89.44% cold water) and 271.74–295.58 °C (mixed by 87.39–87.54% cold water) for class B. The recharge elevation of the geothermal spring was 3415–3495 m as calculated by the D-O isotopes. We have proposed these genetic models of the two typical geothermal springs. The achievements provide a vital reference for the further development of geothermal water and the sustainable utilization of geothermal resources in the Aba area.

Insight into the Process and Mechanism of Water-Rock Interaction in Underground Coal Mine Reservoirs Based on Indoor Static Simulation Experiments.

During the storage of underground water reservoirs in coal mines, water–rock interaction occurred between mine water and collapsed rocks, resulting in improved mine water quality, but the water–rock process and mechanism have not been clarified. In this study, six sets of simulated experiments were designed to investigate the water–rock interaction between two types of roof collapse rocks and different water samples in the Daliuta coal mine. The ion ratio method and multivariate statistics are used to reveal the process and mechanism of water–rock interaction during the experimental process from the perspective of input and output water chemical characteristics and rock properties, respectively. The results show that the ion concentration of the effluent water is controlled by water–rock interaction, and the water–rock process mainly involves the dissolution of halite, silicate, pyrite, calcite, dolomite, magnesia chlorite, and gypsum precipitation and is accompanied by ion exchange. Mineral dissolution and precipitation are the most important factors affecting the ion abundance in the effluent. There are differences in the reaction rate, degree of reaction, and dissolution process during the experimental process of fine sandstone and mudstone. Fine sandstone is more reactive than mudstone in terms of reaction rate and degree of reaction, and fine sandstone is dissolved from surface pores to inside and around, while mudstone is generated in new dissolved pores. We found that rock type, ion concentration in the input water, and rock reaction period influence the water–rock interaction during the experiment. The results provide a reference for clarifying the water–rock interaction during the storage of underground water reservoirs in coal mines and predicting the water quality of the effluent.

Multimodal study of the impact of stimulation pH on shale pore structure, with an emphasis on organics behavior in alkaline environments

The tight nature of shale formations calls for hydraulic fracturing techniques able of altering the pore architecture to facilitate the production of hydrocarbon resources. The composition, pH, salinity, density and chemistry of Hydraulic Fracturing Fluids (HFF) vary substantially depending on reservoir characteristics. pH is among the most important stimulation fluid properties, ranging from very acidic, for carbonate reservoirs, to basic, in the case of clay-rich formations. pH regulates what geochemical reactions take place between the stimulation fluid and shale, as well as pore architecture alteration. The dissolution of carbonates and pyrite, and the precipitation of common minerals such as barite, gypsum and iron oxides in acidic environments have been extensively documented. In contrast, alkali stimulation environments and the role of organic components have received less attention. This research provides insight into the role of both minerals and organic components during alkaline stimulation, and the resulting pore architecture alterations. A set of reactive experiments are performed using three different shales, with varying organic matter (OM) content, at different pH (3, 6, 8, 10, 12). The analysis of pore architecture alteration induced by the reaction was performed via nitrogen (N2) gas adsorption and Time-Domain Nuclear Magnetic Resonance (TD-NMR). Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) was used to measure the composition of the stimulation fluid post-reaction. The system with a larger impact on the pore architecture (pH 12) underwent a more extensive analysis through the application of Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) and x-ray Diffraction (XRD). Results show that mineral dissolution contributed to the creation of secondary porosity, mainly through dissolution of clays and silicates. We show that the abundance and distribution of organic matter both play a significant role in changes in pore architecture. Most samples showed an increase in inter-organic porosity, likely due to the organic acids within kerogen reacting with the stimulation fluid. Samples with a larger amount and more widespread distribution of organic matter show the most significant alterations. Finally, we also highlight the dissolution process of iron-rich minerals, including framboidal pyrite, as another important source of secondary porosity.

The risk of scaling in Danish geothermal plants and its effect on the reservoir properties predicted by hydrogeochemical modelling

Injectivity problems have been observed in two of three Danish geothermal plants. The utilized geothermal reservoirs comprise sandstones of Lower Triassic and Upper Triassic – Lower Jurassic. The great variations in the formation mineralogy and the chemical composition of their brines allow for a thorough analysis of the differences in the potential risks of scaling. The key scaling processes upon injection of the cooled brines into the reservoirs were identified and changes in the reservoir porosity assessed by hydrogeochemical modelling. Scaling was predicted to be of importance only in one of the geothermal reservoirs, where barite precipitation in the near field of the injection well was identified as a potential risk and could potentially alter the reservoir porosity. Scaling induced by barite nucleation in the injection well, and precipitation and dissolution of carbonates, silicates and clays in the geothermal reservoirs are all of minor importance.

Influence of coastal alluvial aquifer on groundwater chemistry in Wates, Yogyakarta, Indonesia

Saline groundwater is found far from the coastline, whereas closer groundwater has low salinity in the Wates area, Indonesia. This situation which has led to problems linked to the coastal aquifer, shows different groundwater chemistries. This connection needs to highlight the geochemical evolution of aquifers. This research aims to evaluate the hydrochemical characteristics in Wates Sub-District, Kulon Progo District, Indonesia. The study area is located in the southern part of the Kulon Progo with an aquifer of marine and fluvial deposits. The boundary of the south is the Indian Ocean. The approach is based on analyzing the major ions of 27 groundwater samples, and the XRD results include the Stiff diagram and the Stuyfzand classification. The Stiff diagram showed in agreement with that of the Stuyfzand classification. Results showed that the F2-(CaHCO3)2Ø and F1-(NaMix)Ø types reflect the recharge process and dominate the dissolution of silicate minerals. Halite dissolution originates in topographically flat areas of the Bs1-NaCl (-) water. Total hardness is softer than others as a result of cation exchange. The groundwater chemistry’s geochemical processes are the dissolution of silicate and halite minerals, ion exchange, and fresh and seawater mixing. This research indicates to focus on pumping problems in the aquifer.

Analytical models for predicting the behavior of the Fukushima fuel debris during laboratory tests and long-term storage

The results of the laboratory-based aging experiments with synthesized fuel debris (simulated corium–concrete compound) are discussed. The tests included dynamic (i.e. with periodic solution renewal) experiments with monoliths of the synthesized fuel debris. At the time scale of the experiments, at a temperature of 25 °C, no evolution in the composition of the leachate debris was observed. At the elevated temperature regime, T = 50, 90 and 120 °C and pH ranges from acid to alkaline condition (pH=4, pH=7, and pH=9), the major chemistry changes that occurs during the leaching were the increase of Si, Al and Ca, as structural elements of the concrete fraction of the debris, while the major elements of the melted fuel matrix, U and Zr, were found in the leachate in trace quantities. The release of Si, Al and Ca, was proved to be non-congruent (Ca and Al releases much faster compared to Si) that corresponds to the basic concept of multioxide silicate dissolution. Such system behavior as well as a number of the chemical interactions between the elements limits the classical chemical thermodynamic and kinetic methods and forced us to use a simplified, semi-empirical, effective approach. The component release rates measured in batch tests were fitted to a proposed diffusion and kinetics model which accounts also for the various pH and temperature conditions. Long-term prediction of the glassy phase dissolution and surface enrichment with a poorly dissolved fuel fraction, (U, Zr)O2, is based on a first-order kinetic model inherited the significant properties of the more detailed lab-scale model. To evaluate the growth kinetics of (U, Zr)O2 layer on debris surface, dissolution rate coefficients from the aging laboratory experiments were used. These coefficients calculated for high-temperature (T = 50 and 90 °C) surface reactions, were extrapolated to low-temperature debris storage conditions via the Arrhenius equation. It was shown, that the aging of debris in a water environment at room temperature and neutral pH under no-flow storage conditions results in the density accumulation of the (U, Zr)O2 product up to several g/m2. At the alkaline condition (pH=9) these values increase about five times. The further rise in temperature results in further intensification of the silica leaching process that may dramatically increase the accumulation amount of (U, Zr)O2.

Evolution of hydrochemistry and isotopic characteristics in shallow alluvial aquifers of Poyang Lake Basin, Eastern China

Abstract The hydrochemical characteristics of shallow groundwater and the factors affecting them were analyzed using descriptive statistical analysis, Piper trilinear charts, Gibbs charts, and ion ratios, to help improve the groundwater quality of the Poyang Lake Plain. The results showed that the groundwater was weakly acidic, with an average pH of 6.27. was the main ion component, with high stability in the study area. The chemical ions in groundwater were mainly controlled by rock weathering, and Ca2+ and Mg2+ originated from the dissolution of carbonate, silicate, or evaporite. Cation exchange was an important driving factor in the formation of groundwater chemical components in the study area. The shallow groundwater and surface water in the region around Poyang Lake are replenished by precipitation, but both are more affected by evaporation. The large d-excess value indicated that the groundwater was greatly affected by water–rock interactions. The main source of is chemical fertilizer and levels were less affected by domestic sewage, which may be because the study area is a traditional agricultural area. Rock weathering, leaching, and human activities were the main driving factors for the evolution of the chemical characteristics of the groundwater in the study area. These results provide a technical reference and the basis for regional collaborative efforts to control groundwater and surface water pollution.

Hydrogeochemical characterization, multi-exposure deterministic and probabilistic health hazard evaluation in groundwater in parts of Northern India

This work attempts to identify the latent factors controlling the hydrogeochemistry and assess the groundwater quality and associated health risks in the intermontane valley of Nalagarh in the sub-Himalayan zone in northern India. Analytical results of 64 groundwater samples, 32 each collected during pre monsoon and post monsoon seasons show contrasting results for their major chemical constituents. During pre monsoon period, only 3% of the samples exceed their permissible limits for pH, EC, TH and Mg2+, while during post monsoon period, different parameters, such as TH, Mg2+ and K+, exceed their limits by 9, 16, and 3%, respectively. Gibbs and Piper diagrams reveal that groundwater chemistry is mainly controlled by water-sediment (alluvial) interaction. Geochemical signatures and saturation index (SI) further indicate that the weathering and dissolution of silicate, calcite and dolomite minerals mainly contributed to dominance of Ca2+, Mg2+ and HCO3 - ions in the aquifers. Monte Carlo simulation ascertains non-carcinogenic health risks due to NO3 − and F− in different sub-population groups. Deterministic and probabilistic estimates of these parameters via ingestion and dermal routes confirm their percentage hazard toxicity in the order infants (58.38; 39.62%) >children (15.62; 15.85%) >teens (6.25; 2.73%) >adults (6.25; 1.90%) for pre monsoon. The hazard toxicity for deterministic study implies only on infants (9.38%), whereas, the probabilistic simulation extracted the health risk on infants (6.57%), and children (0.58%) during post monsoon. Minor populations with their lower body weights are more vulnerable to groundwater pollution due to greater consumption of liquid diet. Therefore, treated groundwater is strongly recommended to mitigate health morbidities linked with the non-cancerous risks.