Silicate Dissolution Research Articles

Fundamental effects of using power ultrasound to accelerate C3S hydration

Activation of cement hydration accelerates hardening of concrete, enables faster production rates or production at similar frequency but significantly reduced CO2 emissions. The present study sheds light at the reason for accelerated cement hydration when power ultrasound (PUS) is applied during mixing.The investigations analysed the effect of PUS on dissolution of tricalcium silicate (C3S), homogeneous precipitation of C-S-H as well its effect on C3S-hydration. A combination of analytical techniques such as electric conductivity, optical emission spectroscopy, thermogravimetry, conduction reaction calorimetry, scanning electron microscopy and specific surface analysis were applied. It was revealed that PUS has a significant effect on paste hydration, which is induced by heterogenous nucleation of C-S-H and CH immediately after sonication. These hydrates were formed and dispersed by sonication thus acting as in-situ formed crystal seeds which shorten the induction period of C3S hydration.

Migration of transition metals and potential for carbon mineralization during acid leaching of processed kimberlite from Venetia diamond mine, South Africa

Carbonation of mafic and ultramafic rocks and mineral wastes provides a permanent way to sequester excess atmospheric CO2. Recent research has shown that this method also offers the potential for enhanced recovery of critical metals from mine tailings. In this study, processed kimberlite from the Venetia diamond mine (South Africa) was used in column acid leaching experiments to assess both its carbonation potential and whether critical metals such as nickel could be recovered during mineral carbonation. Processed kimberlite was treated daily with one pore volume of either deionized water or dilute hydrochloric acid (0.04 M, 0.08 M, 0.12 M and 0.16 M) for 28 days. Iron-rich yellow precipitates consistent with yellow ground formed during the experiments both at the top of the residue columns (corresponding to the inlets of the columns) and within the leachates collected from the bases of columns. The carbonation potential and mobility of transition metals were investigated using a combination of quantitative X-ray diffraction (XRD) using Rietveld refinements, inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDXS), transmission electron microscopy (TEM) coupled with EDXS, and synchrotron-based X-ray fluorescence microscopy (XFM). Our results show that the high proportion of clay minerals (e.g., lizardite, smectite, talc, chlorite) in the processed kimberlite act as the primary source for Mg and transition metals such as Ni; however, calcite dissolution is the main source for Ca. The amount of Mg and Ca extracted from processed kimberlite increases with HCl concentration. If acid leaching of processed kimberlite were used at Venetia, the amount of Mg leached from clay minerals would provide an estimated CO2 offset potential ranging from 2.1 to 15.8 % of the mine's total annual emissions. The leached Ca from silicate dissolution could also provide an estimated CO2 offset potential ranging from 2.1 to 8.1 % of the mine's total annual emissions. However, the amount of CO2 released by calcite dissolution during this process is equivalent to 2.1–14.3 % of total annual CO2 emissions at Venetia., thus resulting in a net estimated CO2 offset potential of 2.1–9.6 % if the Ca released from calcite could not be recarbonated. If all of the Ca could be reprecipitated as calcite, the acid leaching techniques employed in this study could offset 4.2–23.9 % of the Venetia mine's CO2 emissions. Ultimately, greater concentrations and/or amounts of acid may be used to access more of the offset potential of Mg phyllosilicates in kimberlite, but the CO2 released by calcite dissolution must also be won back by recarbonation.

Genetic mechanism of geothermal water in the sandstone reservoir of western Sichuan, SW China: Evidence from hydrochemistry and δD − δ18O isotopes

Geothermal energy is the vital clean and renewable energy in the world. In China, most of high−temperature sedimentary − type geothermal waters are developed in western Sichuan, such as geothermal springs in the Litang county. In this study, hydrochemistry and δD − δ18O isotopes were investigated to clarify the genetic mechanism of high−temperature sedimentary − type geothermal waters in the Litang county. The self-organized map and Piper diagram showed three hydrochemical types of geothermal waters: (1) HCO3 − SO4 − Na, (2) HCO3 − Na with low Cl− concentration, (3) HCO3 − Na with high Cl− concentration. Cluster 1 geothermal water of Na − HCO3 − SO4 was dominated by dissolution of silicate and sulfate minerals. Cluster 2 geothermal water of HCO3 − Na with low Cl− concentration was affected by dissolution of silicate and CO2 degassing and mixed by large amounts of shallow cold water. Cluster 3 geothermal water of HCO3 − Na with high Cl− concentration was affected by dissolution of sandstone silicate and CO2 degassing and mixed by less shallow cold water. The recharge elevation of geothermal water in Litang ranges from 4799 to 4972 m, with an average of 4915 m. This suggests that the recharge sources of geothermal water are snow melt water and magmatic water. Cluster 3 geothermal water displayed the largest contribution of magmatic water. The temperature of HCO3 − SO4 − Na geothermal water after mixing is 92−102 °C, with an average of 97 °C; the initial temperature of HCO3 − Na with low Cl− geothermal water is 60−72 °C, with an average of 65 °C; the initial temperature of HCO3 − Na with high Cl− geothermal water is 74−91 °C, with an average of 81 °C. The temperature of geothermal water after mixing is Class 1 > Class 3 > Class 2. From the perspective of reservoir temperature, the Class 3 of geothermal water had the highest values, followed by Class 1 and Class 2 of geothermal water. From the perspective of cold − water mixing ratio, Class 2 and Class 3 of geothermal water had a similar mixing ratio, slightly higher than that of Class 1 of geothermal water. Therefore, the class 3 geothermal water with HCO3 − Na with high Cl− concentration possess the great potential for exploitation.

Stability analysis of a granite-based geopolymer sealant for CO2 geosequestration: In-situ permeability and mechanical behavior while exposed to brine

When considering the use of geopolymers (GPs), as potential alternatives for Portland cement, high durability during exposure to brine at encountered downhole is a key requirement. This study delves into the response of a granite-based GP system designed especially for CO2-geosequestration upon exposure to brines with different concentrations of NaCl. Exposure was carried out by imposed flow in a triaxial apparatus, at 90 °C and 13.8 MPa confining pressure. Mechanical properties were tested in the same apparatus once exposure was completed. A suite of micro-scale analytical techniques was then used to assess the GP's microstructure, mineralogical composition, and chemical bonding. The obtained results revealed increasing compressive strength with increasing brine salinity, suggesting greater resistance to deformation and potential cracking. Concurrently, decreasing Poisson's ratios and increasing Young's moduli could lead to an elevated risk of mechanical failure under strain. In addition, following a 3-week injection period, permeability of NaCl-flooded samples decreased by 20%–35% from initial values. Analysis of the effluents showed fluctuations in the pH and ion content with time, mainly attributed to complex chemical interactions including cation exchange, silicate dissolution and hydrolysis, precipitation of alkali-enriched gels, and mineral alterations. Micro-scale analyses revealed that the improved durability is linked with the formation of new minerals, especially zeolites in the presence of NaCl or portlandite when deionized water was introduced. In conclusion, this study presents new data on the durability of a rock-based GP system when exposed to brine and elevated pressure and temperature, offering insights for optimization to downhole environments.

Importance of early diagenesis of deep-sea sediments to the REY enrichment and oceanic element budget

Deep-sea sediments have become an important new type of rare-earth element (REY) resources that have high potential to meet the increasing demand. However, the enrichment mechanisms of such deposits remain unclear. In this paper, we made a detailed discussion in bulk-sample geochemistry along the core profile of GC26 collected at the western Pacific Ocean. Elements are classified into lithophile-, phosphate-, and metal oxide elements, which have affinities to silicate, phosphate, and Fe–Mn (oxyhydr)oxide phases in sediments, respectively. Biophosphate is the major host of REY in deep-sea sediments. Its accumulation has a substantial effect on bulk-sample strontium isotopes, but a weak effect on bulk neodymium isotopes. Although the bulk neodymium isotopes imply there was a slight change in sedimentary provenances, it cannot explain the different behaviors of the three elemental groups simultaneously. Water-rock interactions at high temperature enlighten us that water–sediment interactions at low temperature, also known as early diagenesis, may be the answer of behaviors of the three element groups. Silicate dissolution during early diagenesis releases elements from the silicate lattice. When biophosphate accumulation occurs, the released phosphate elements (including REY) are preferentially incorporated into biophosphate rather than being released into seawater, which is the key to REY enrichment in deep-sea sediments. This is also the case for metal oxide elements (e.g., Mn, Co, and Ni) when oxygen fugacity is high enough to cause Fe–Mn (oxyhydr)oxide deposition as coatings or micro-nodules. Considerable amounts of silicate elements (e.g., Al, Ti, Fe, Cr, and V) are released into seawater to participate into global oceanic element cycle if they are less compatible in newly formed secondary silicate components (e.g., phillipsite). Our results provide new insights into the importance of early diagenesis of deep-sea sediments to REY enrichment and the global oceanic elemental budget.

Hydrochemical Characteristics and Control Factors of Shallow Groundwater in Anqing Section of the Yangtze River Basin

Shallow groundwater is the main source of water for living and industrial and agricultural production in Anqing City, which is an important basic guarantee to maintain the sustainable development of the social economy and regional ecological environment. In order to further study the water chemical characteristics and controlling factors of shallow groundwater in Anqing City, 196 groups of shallow groundwater samples were collected. A Piper diagram graph, Gibbs chart, ion ratio, and mathematical statistics were comprehensively used to study the water chemical characteristics and controlling factors of groundwater in Anqing City, and the contribution of different sources to the water chemical components of groundwater was quantitatively evaluated. The results showed that the shallow groundwater in Anqing City was weakly alkaline, with pH values ranging from 5.84 to 8.38, with an average value of 7.21. The TDS ranged from 47 to 1 620 mg·L-1, with an average of 324.21 mg·L-1. HCO3- and Ca2+ were the main anions, and the water chemical type was HCO3-Ca type. The chemical components of groundwater were affected by rock weathering leaching, cation alternating adsorption, mineral dissolution and precipitation, and human activities. Ca2+, Mg2+, and HCO3- were mainly derived from the weathering dissolution of carbonate and silicate; Na+, Cl-, and SO42- were affected by industrial activities and domestic sewage discharge; and K+ and NO3- were affected by agricultural activities. The APCS-MLR receptor model analysis further revealed that the chemical components of groundwater were mainly geological factors, industrial factors, agricultural factors, and unknown sources, and their contribution rates were 45.35%, 14.19%, 25.38%, and 15.08%, respectively. Geological factors were important sources of hydrochemical components of shallow groundwater, and human activities aggravated the evolution of groundwater hydrochemistry.

Seasonal variations and water chemical control mechanism of water quality in a suburban river near a coal city: a case study in the Xinbian River of Suzhou City, Anhui Province, China

Abstract To study the seasonal change rules of water quality indicators and water chemical control mechanisms in the nearby city river Xinbian River, in Suzhou City, Anhui Province, China, nine points were selected and periodically sampled for 12 months. Totally 108 water samples were collected, and basic physical–chemical indicators and routine ions (e.g., Ca2+, Mg2+, Na+, K+, SO42−, Cl−, F−, NO3−, CO32−, and HCO3−) were measured. Piper diagram, Gibbs diagram, and ion ratio method were used. The result shows that the seasonal and upstream-to-downstream variations in pH were less varied, whereas the fluctuation in dissolved oxygen was large. Four ions, namely, SO42-, F−, Cl−, and Na+ generally first decreased overall and then changed from spring to winter. The maximum contents of SO42- (406.03 mg/L), Cl− (250.22 mg/L), and Na+ (269.99 mg/L) in single water samples appeared at the S9 sampling point (Suzhou control gate) in March 2020. The dominant hydrochemical types in summer were Na–Ca–HCO3 and Na–Mg–SO4, while Na–Mg–SO4 and Na–Mg–HCO3 were the main hydrochemical types in the other seasons. The control factors of water chemical composition vary according to the season. However, rock weathering (e.g., silicate dissolution) is the dominant control factor of water chemistry in the studied river section.

Heating aluminum dross: Harmless process and utilization as cement admixture

Phosphogypsum (PG) and aluminum dross (AD) with harmful impurities seriously hinder its large-scale engineering utilization. In this paper, the properties of AD and PG as cement admixture were investigated with the aim of reducing the environmental pollution and landfill stockpiling pressure. The migration and transformation rules under crucial factors were analyzed by different characterization methods while AD was heated at different temperature. Then, the compressive strength, soluble phosphorus and fluorine concentration, hydration heat and expansion rate of specimens prepared with AD, PG, and Portland cement (PC) were evaluated to illustrate the hydration mechanism. Compared to the other experiment sets, the results indicated that AD treated at 900°C not only had a higher nitrogen removal rate, but also maintained hydration activity at a relatively high level. Moreover, Heating AD at 900℃ effectively accelerated the dissolution of gypsum and calcium silicate, resulting in increased formation of ettringite (AFt), calcium silicate hydrates (C-S-H) and calcium aluminium hydrates (C-A-H). When the binder consisted of 14% heated aluminium dross (HAD), 6% PG, and 80% PC, the specimen reached the highest compressive strength value at 25.87 MPa. This work provided a new strategy for synergistic utilization of PG and AD, promoting the development of environment-friendly industrial wastes-based cementitious materials effectively.

Self-Assembly of Silicon Nanotubes Driven by a Biphasic Transition from the Natural Mineral Montmorillonite in Molten Salt Electrolysis.

Silicon nanotubes (SNTs) have been considered as promising anode materials for lithium-ion batteries (LIBs). However, the reported strategies for preparing SNTs generally have special requirements for either expensive templates or complex catalysts. It is necessary to explore a cost-effective and efficient approach for the preparation of high-performance SNTs. In this work, a biphasic transformation strategy involving "solid-state reduction" and "dissolution-deposition" in molten salts is developed to prepare SNTs using montmorillonite as a precursor. The rod-like intermediate of silicon-aluminum-calcium is initially reduced in solid state, which then triggers the continuous dissolution and deposition of calcium silicate in the inner space of the intermediate to form a hollow structure during the subsequent reduction process. The transition from solid to liquid is crucial for improving the kinetics of deoxygenation and induces the self-assembly of SNTs during electrolysis. When the obtained SNTs is used as anode materials for LIBs, they exhibit a high capacity of 2791mAhg-1 at 0.2Ag-1, excellent rate capability of 1427mAhg-1 at 2Ag-1, and stable cycling performance with a capacity of 2045mAhg-1 after 200 cycles at 0.5Ag-1. This work provides a self-assembling, controllable, and cost-effective approach for fabricating SNTs.

Hydrochemical Characteristics, Controlling Factors and Strontium Enrichment Sources of Groundwater in the Northwest Plain of Shandong Province, China

To elucidate the hydrochemical characteristics, controlling factors, sources and mechanisms of strontium ion enrichment in groundwater in the northwest plain of Shandong Province, China, 88 groundwater samples were collected, including 51 shallow pore groundwater samples, 29 deep pore groundwater samples and 8 karst groundwater samples. The hydrochemical characteristics of the different types of groundwater were quite different. The karst groundwater samples were all fresh water with a single hydrochemical type, either HCO3-Ca or HCO3-Ca·Mg. The deep pore groundwater samples were mainly brackish water, and the shallow pore groundwater samples were brackish water–salt water, which has complex hydrochemical types. The hydrochemical characteristics of all the types of groundwater were controlled by mineral dissolution and active positive cation exchange. In shallow pore groundwater, deep pore groundwater and karst groundwater, the dissolution of silicate, evaporite and carbonate minerals dominated the hydrogeochemical process. The strontium in groundwater was derived from the dissolution of minerals with strontium isomorphism. The average contents of strontium in shallow, deep and karst groundwater were 1.59 mg/L, 0.58 mg/L and 0.50 mg/L, respectively. The strontium in shallow pore groundwater was mainly derived from the enrichment of groundwater runoff, and its sources are abundant, with silicic rock being the main source. The deep pore groundwater mainly derived from the evaporative minerals containing strontium, and the karst water mainly derived from carbonate rock dissolution with similar characteristics.

Controlling Factors of Groundwater Salinization and Pollution in the Oasis Zone of the Cherchen River Basin of Xinjiang

Groundwater is a vital resource for local human life and production in the oasis zone of the Cherchen River Basin of Xinjiang. Understanding the controlling factors of groundwater salinization and pollution is of great significance for the sustainable utilization of groundwater resources and protection of the ecological environment in desert oasis areas. In light of this, a total of 36 single structure unconfined groundwater samples and 54 multi-layered structure unconfined and confined groundwater samples were collected from the oasis zone of the Cherchen River Basin and evaluated for the distribution characteristics and pollution status of major ions. Hydrogeochemical methods (e.g., Piper diagram, multivariate statistics, Gibbs model, and relationships among ions) were used to determine the main controlling factors of groundwater salinization and pollution. Differences in hydrogeochemical zonation were found from the single structure unconfined aquifers in sloping plains of piedmont areas to the multi-layered structure unconfined and confined aquifers in alluvial-proluvial plain areas, and Cl-Na (87.8%) was the main hydrochemical type in the groundwater of the study area. The quality of single structure unconfined groundwater was starkly better than that of the multi-layered unconfined and confined groundwater, which was mainly caused by Na+ (mean value of 9 969 mg·L-1), Cl- (13 687 mg·L-1), and SO42- (5 840 mg·L-1). Moreover, the natural hydrogeochemical process was the main reason for the deterioration of groundwater quality. The hydrochemistry was mainly controlled by the water-rock interaction and evaporation processes. The mineral dissolution of silicates and evaporites was an important source of chemical ions in the groundwater. Furthermore, the chemical weathering of evaporites combined with the processes of evaporation and cation exchange had a significant influence on the salinization of multi-layered unconfined and confined groundwater in alluvial-proluvial plain areas. In addition, synthetic fertilizers were the main pollution sources of NO3- in groundwater in the intensive agricultural zones.

Hydrochemical Evolution and Nitrate Source Identification of River Water and Groundwater in Huashan Watershed, China

The combined hydrochemical analysis, factor analysis, and isotopic signals of water and nitrate were applied to explore the hydrochemical origin and identify the sources and transformation of nitrate in river water and groundwater in the Huashan watershed. Additionally, a Bayesian isotope mixing model (SIAR) was employed for quantitative assessment of the nitrate sources. The results indicated that both river water and groundwater were dominated by HCO3-Ca and HCO3-Ca·Mg types; both originated from precipitation and were influenced by evaporation. The main constituent ions in the river water and groundwater primarily originated from carbonate and silicate dissolution, with the presence of cation exchange in the groundwater. The water chemistry of river water was greatly influenced by physicochemical factors, while that of groundwater was mainly controlled by water–rock interaction. NO3− in river water was mainly influenced by soil nitrogen (SN) and manure and septic wastes (MSWs), while NO3− in groundwater was jointly affected by ammonium fertilizers (AF), SN, and MSWs. With the exception of denitrification observed in the groundwater at the watershed outlet, denitrification was absent in both groundwater in the piedmont area and in river water. The SIAR model results demonstrated that the contribution rates of atmospheric precipitation (AP), AF, SN, and MSWs to river water were 12%, 21%, 25%, and 42%, respectively, while to groundwater, they were 16%, 27%, 10%, and 47%, respectively. Overall, MSWs were the main sources of nitrate in the river water and groundwater. It is necessary to prevent the leakage of MSWs when managing water resources.

Identifying the source and fate of boron in geothermal water: Evidence from B/Na and B isotopes

High level dissolved B, which poses risks to human health, has been widely observed in geothermal water. In the Guide Basin, NW China, a series of geothermal water samples along a fault show a wide range of B contents ranging from 3.14 to 8.33 mg/L, which are higher than the WHO Guideline value equaling 2.4 mg/L in drinking water. To identify the sources and fate of B, we conduct a comprehensive analysis of hydrochemistry and stable isotopes (D, 18O and 11B) of three thermal fields representing three stages of hydrogeochemical evolution (stages I, II and III). From stage I to III, there are trends of increasing mineral dissolution, which is supported by increasing mean reservoir temperature and concentrations of conservative elements (Cl, Na, K, Li and Si). Geothermal water in stage I with meteoric origin and the lowest reservoir temperature has the highest B/Na resulting from silicate dissolution and falls on the mixing line between granitoids and cold water on the plot of δ11B versus 1/B, showing the control of silicate dissolution. However, geothermal water in stage III has lower Ca, B Sr and B/Na than that in stage II. Because of the occurrence of other processes, geothermal water in stages II and III deviates from the LMWL. Compared with geothermal water in stage I, the increased Sr/Ca and decreased B/Ca show that B are removed by both coprecipitation and vapor separation. With the aid of B isotopes, we find vapor separation dominates in stage II, whereas carbonate precipitation dominates in stage III. Overall, a combined use of three isotopes (H, O and B) and three element ratios (B/Na, B/Ca and Sr/Ca) leads to a complete understanding of B cycle and hydrogeochemical evolution in hydrothermal systems.

Contrasting behavior of K isotopes in modern and fossil groundwater: Implications for K cycle and subsurface weathering

Chemical weathering of rocks largely determines sources of groundwater hydrochemical components, but the superposition of processes removing cations leads to a wide variability of elemental ratios. In this study, potassium (K) isotopes are used for the first time to quantify the roles of silicate dissolution, clay incorporation and clay adsorption in subsurface K cycle. We investigate the behavior of K isotopes in groundwater with contrasting ages from a sandstone aquifer in the Ordos Basin, NW China. For modern groundwater (< 50 yrs) in the recharge area with abundant CO2, the silicate-derived K has been largely removed by 10-year-scale clay incorporation, generating low [K]/[Na] ranging between 0.026 and 0.048 and extremely high δ41K varying between 0.57‰ and 0.69‰; our calculations reveal that 92% of total K released from silicate dissolution has been removed by clay incorporation, suggesting that using measured [K] alone would underestimate the degree of silicate dissolution. For fossil groundwater (∼104 yrs) in the discharge area, clay adsorption during long-time circulation leads to extremely low [K]/[Na] ranging from 0.001 to 0.011 and much lower δ41K varying from -0.32‰ to 0.37‰; as a result of the combined effect of clay incorporation and clay adsorption, up to 99.2% of silicate-derived K has been removed from the dissolved load. This study provides novel insights into the complex processes controlling the K cycle in groundwater and highlights the potential of K isotopes in understanding subsurface weathering and associated elemental cycles.

Hydrogeochemical characteristics and evaluation of groundwater resources of Jilin Province, China

As one of China's nine border provinces, Jilin Province is an important window for China's “Belt and Road” to open up to the north, and an important channel for China's foreign trade and foreign exchanges. Therefore, understanding hydrogeochemical characteristics is very important for effective water resources management in Jilin Province. A total of 64 groundwater samples were collected from 32 monitoring Wells in Jilin Province. Use of hydrogeochemical analysis techniques, WQI index and human health risk index methods to assess hydrogeochemical processes and groundwater quality, including the determination of hydrogeochemical parameters, conventional ions, trace elements and stable isotopes (δD and δ18O). The results show that the groundwater is slightly alkaline, the cations are mainly Na+, Ca2+, Mg2+, and K+, and the anions are mainly HCO3-, Cl−, and SO42-. Most of the groundwater samples belong to Ca-HCO3 and Na-HCO3 types, which are formed by the dissolution of calcite, dolomite, gypsum, silicates and carbonates. Stable isotope analysis shows that groundwater recharge in Jilin mainly comes from atmospheric precipitation at an altitude of 1,430~2,348 m. The strong correlation between trace elements indicates a common source. Most of the groundwater quality index (WQI) in the study area is Class I to Class III, and hazard quotient (HQ) and hazard index (HI) are both below 1. This indicates excellent water quality and minimal health risks associated with human consumption. It is worth noting that trace elements are enriched in the Tanlu fault zone. It provides scientific guidance for the utilization and allocation of groundwater resources in Jilin Province.

Incongruent dissolution of silicates and its impact on the environment: an example of a talc mine

The paper analyzes the process of incongruent dissolution of silicates taking place in close proximity to a talc mine. The chemical and phase composition as well as the concentrations and mobility of potentially toxic elements (PTE) in research material with varying levels of weathering were determined using instrumental (XRF, XRD) and chemical methods (extractions: BCR, aqua regia, water leaching, 0.05 M EDTA). It was demonstrated that the predominant minerals in the weathering crust include weathering-resistant minerals (i.e. quartz and muscovite) and secondary minerals (kaolinite, illite and interstratified minerals, vermiculite/chlorite) and that the predominant processes are hydrolysis and oxidation. The weathering process has an impact on the complexity of the chemical and mineral composition and the diverse structure of the weathering crust. A layer of Fe and Al oxides and hydroxides forms in the upper part of the weathering crust, while the amount of silica decreases. Low-mobility elements (i.e. Si, Al and Fe) react on the phase separation surface, causing the formation of clay minerals (i.e. vermiculite, montmorillonite) or Al and Fe hydroxides (e.g. goethite). The duration of weathering causes an increase in the content of PTEs in solid materials: multifold in the case of Cr (15), Ba (9), Pb (7), Zn (6) and considerably lower in the case of V (1.3), Sr (0.8) and Co (0.4). It was demonstrated that PTEs co-occur in several chemical fractions in the weathering crust and that the highest share of their total concentration are cations incorporated in the crystal lattice of minerals and bound by strong crystalline bonds (F4 46%). The lowest share was observed for the reducible fraction (9%) and the share of the oxidizable fraction was 29% The most mobile cations connected by the weakest bonds comprised only 16% of the total concentration. Based on the content of the readily soluble fraction of PTEs, it was concluded that the degree of weathering does not increase the environmental risk, but actually reduces it for Cr, Cr and Pb. The obtained Ecological Risk Index (ERI) values indicate that the ecological risk associated with the elements tested is low for the entire area, which means that natural weathering processes do not have any impact on environmental pollution.

Acidithiobacillus species drive the formation of ferric-silica cemented microstructure: Insights into early hardpan development for mine site rehabilitation

Hardpan-based profiles naturally formed under semi-arid climatic conditions have substantial potential in rehabilitating sulfidic tailings, resulting from their aggregation microstructure regulated by Fe-Si cements. Nevertheless, eco-engineered approaches for accelerating the formation of complex cementation structure remain unclear. The present study aims to investigate the microbial functions of extremophiles on mineral dissolution, oxidation, and aggregation (cementation) through a microcosm experiment containing pyrites and polysilicates, of which are dominant components in typical sulfidic tailings. Microspectroscopic analysis revealed that pyrite was rapidly dissolved and massive microbial corrosion pits were displayed on pyrite surfaces. Synchrotron-based X-ray absorption spectroscopy demonstrated that approximately 30 % pyrites were oxidized to jarosite-like (ca. 14 %) and ferrihydrite-like minerals (ca. 16 %) in talc group, leading to the formation of secondary Fe precipitates. The Si ions co-dissolved from polysilicates may be embedded into secondary Fe precipitates, while these clustered Fe-Si precipitates displayed distinct morphology (e.g., “circular” shaped in the talc group, “fine-grained” shaped in the chlorite group, and “donut” shaped in the muscovite group). Moreover, the precipitates could join together and act as cementing agents aggregating mineral particles together, forming macroaggregates in talc and chlorite groups. The present findings revealed critical microbial functions on accelerating mineral dissolution, oxidation, and aggregation of pyrite and various silicates, which provided the eco-engineered feasibility of hardpan-based technology for mine site rehabilitation.

Simulations of tricalcium silicate dissolution at screw dislocations: Effects of finite crystal size and mechanical interaction potentials

For many minerals in solution, the relationship between dissolution rate and saturation index displays two distinct regimes, one of slow dissolution near equilibrium and the other of fast dissolution far from equilibrium, with stresses at crystallographic defects controlling the transition between the two. This leads to a characteristic sigmoidal curve between dissolution rate and supersaturation. Here, we use kinetic simulations to predict both regimes and the transition between them in finite-sized crystals with embedded screw dislocations for tricalcium silicate. The simulations employ rate equations which depend on chemical potentials and mechanical stresses and allows us to capture the whole sigmoidal rate curve. We also propose a parametrisation of the interaction potentials between Ca3SiO5 particles that returns consistent interfacial energies with water for different facet orientations. Lastly, we explore the impact of different interaction potentials on the resulting rate curves, contributing to the current discussion on engineering materials and defects to control reactivity.

Hydrogeochemical Characteristics and Evolution Processes of Karst Groundwater Affected by Multiple Influencing Factors in a Karst Spring Basin, Eastern China

Karst groundwater is an important water supply, especially in northern China. With the rapid development of China’s economy, anthropogenic activities have had a significant impact on karst groundwater formation, circulation and other processes. In this paper, the Baotu spring basin, which is closely related to anthropogenic activities, was selected as the research object to carry out a study of water chemical characteristics and evolutionary processes. And, mathematical statistics, Piper trilinear diagram, Gibbs diagram, and ion ratio methods were used to analyze the characteristics and evolution processes of groundwater. The results of this study show that the hydrogeochemical components of karst groundwater are mainly controlled by the weathering of rocks, mainly by the dissolution of carbonate rocks and silicates with the dominant cation of Ca2+ and the dominant anion of HCO3−. Considering the role of anthropogenic activities, including agricultural and industrial activities, the evolution process of karst groundwater is mainly controlled by hydrogeochemical effects such as mineral dissolution and filtration, the mixing of multiple water bodies, anthropogenic activities (domestic sewage, industrial and agricultural wastes), oxidation–reduction and cation alternating adsorption. Moreover, the influence of anthropogenic activities on the formation and evolution of karst groundwater gradually increases, leading to the rise in nitrate content in karst groundwater and accelerating carbonate rock dissolution. The research results of this paper can provide a favorable reference for environmental protection and research on karst groundwater in areas of intensive anthropogenic activity.

Water–Rock Interactions, Genesis Mechanism, and Mineral Scaling of Geothermal Waters in Northwestern Sichuan, SW China

Geothermal resources are the vital renewable energy for resolving energy crisis and environmental deterioration. Understanding hydrogeochemical processes, genesis mechanisms and scaling trends is crucial for securing the sustainable utilization of geothermal resources. In this study, fourteen geothermal waters were collected for hydrochemical and δ2H–δ18O isotopic analyses in northwestern Sichuan, SW China to clarify hydrogeochemical processes, genesis mechanisms, and scaling trends. Geothermal waters were recharged via atmospheric precipitation. Three different types of geothermal waters were identified using a piper diagram. Class 1 geothermal water with HCO3–Na and HCO3–SO4–Na types formed in the contact zone with Yanshanian intrusions and heated by residual radioactive heat. The hydrochemical processes were sodium/potassium silicate dissolution and positive cation–exchange. Class 2 geothermal water with HCO3–Ca and HCO3–Ca–Mg type was carbonate–type and heated by geothermal gradient. The dissolution of carbonate minerals dominated the hydrochemical process. Class 3 geothermal water with the SO4–Ca–Mg type was determined within deep faults. The dissolution of carbonatite and gypsum minerals and the oxidation of sulfides played a vital role in the hydrochemical process. The reservoir temperatures of geothermal waters followed the orders of Class 1 (74.9–137.6 °C) &gt; Class 3 (85.9–100 °C) &gt; Class 2 (38.7–93.5 °C). Calcium carbonate scaling should be paid attention to in Class1 and Class 3 geothermal water, and calcium sulfate scaling merely occurs in Class 3 geothermal water. This study provides vital information for geothermal exploitation in western Sichuan and other similar areas.