Search Results (292)

Iron oxides are crucial for the long-term storage of soil organic carbon (SOC) in paddy soils, making them a key factor in global carbon cycles and important for strategies aimed at combating climate change. This review examines the role of iron oxides in paddy soils, particularly their interaction with SOC, which helps stabilize carbon and contributes to mitigating climate change. These processes of iron oxide phase transformations, wet–dry cycles, and microbial activity help trap carbon in the soil, supporting climate change mitigation efforts. Wet–dry cycles promote mineral dissolution and re-precipitation, forming new reactive surfaces and OC-Fe complexes. Future research should adopt a multi-scale approach to better connect molecular mechanisms with ecosystem-level carbon processes. A deeper understanding of iron oxide behavior in paddy soils will support the development of sustainable soil management practices and improve models for predicting soil carbon sequestration under climate change. Full article

The Qingshan lead–zinc (Pb–Zn) deposit in northwestern Guizhou Province is a structurally controlled, carbonate-hosted system formed from basin-derived hydrothermal processes. Geology, fluid inclusion, and isotopic data reveal a multi-stage hydrothermal circulation after Emeishan Large Igneous Province (ELIP, ~260 Ma) tectono-thermal reactivation within the Sichuan–Yunnan–Guizhu triangle (SYGT) area. Fluid inclusion microthermometry indicates that ore-forming fluids were derived from deep sources influenced by enhanced crustal heat flow linked with possible thermal input from Indo-Caledonian tectonic activity after ELIP. Ore-stage calcite records mixed carbon derived from marine carbonates with additional inputs from organic matter and deep-sourced fluids, reflecting carbonate dissolution and fluid–rock interaction. Sulfide, together with fluid inclusion temperatures > 120 °C, indicates sulfur derived from evaporitic sulfate reduced by thermochemical sulfate reduction (TSR); the heavy sulfur signature and partial isotopic disequilibrium among coexisting sulfides reflect dynamic fluid mixing during ore deposition. Lead isotopes indicate metallogenic metals were leached mainly from Devonian–Permian carbonates with subordinate basement input. Ore precipitated by cooling, depressurization, and mixing of metal-rich, H₂S-bearing fluids in structurally confined zones where the carbonate–clastic interface effectively trapped ore-forming fluids, producing high-grade sphalerite–galena mineralization. Collectively, these data support a Huize-type (HZT) carbonate-hosted Pb–Zn genetic model for the Qingshan deposit. Full article

In the fluid (comprising oil and nutrient solution)–microbe–mineral ternary system of oil reservoirs, current microbial enhanced oil recovery (MEOR) technology lacks investigation into the interactions between the latter two components and their application potential in petroleum production. This may explain why MEOR has achieved only partial success while failing to meet full expectations. This review systematically synthesizes the existing fragmented research on reservoirs regarding rock minerals as direct/indirect microbial substrates in MEOR applications. Currently, microbe–mineral interactions enhance oil recovery primarily through the following mechanisms: clay swelling inhibition, induced mineral precipitation, silicate dissolution, wettability alteration, microbial acids etching, and hydrocarbon degradation modulation. Integrating contemporary findings on microbe–mineral interactions, three strategically prioritized MEOR implementation pathways demonstrate particular promise: microbially mediated weathering processes in silicate/carbonate reservoirs, microbial-induced mineral precipitation/dissolution cycles, and microbial leaching-assisted permeability enhancement. Finally, a total of 20 microorganisms potentially applicable for mineral-targeted MEOR were proposed. If MEOR technology could be re-examined from the perspective of microbe–mineral interactions and thoroughly investigated, integrating the knowledge on fluid–microbe binary systems in oil reservoir, this potentially transformative technology may achieve breakthroughs. Full article

Hydrothermal carbonization (HTC) is an effective method for processing wet sewage sludge without prior drying. This study investigates the influence of temperature (200 °C and 210 °C), residence time (15 and 30 min), and pH (neutral and acidic, pH = 2) on the properties of hydrochar and the liquid fraction. Increasing process severity enhanced carbonization, increasing carbon content from 36% in raw sludge to 43% in acidified samples. Under neutral HTC conditions, ash content exceeded 40%, while acidic conditions reduced it to 28%, indicating mineral dissolution and transfer into the liquid phase. Hydrogen and nitrogen contents remained within 3–6%, contributing to the fuel characteristics. The solid yield decreased from 1.04% in raw sludge to 0.22–0.37% after HTC, confirming intensified organic matter conversion. Acidic conditions significantly improved nutrient release to the liquid phase. PO₄³⁻ concentration increased from 337 to 375 mg/L under neutral conditions to over 675 mg/L, while P₂O₅ exceeded 509 mg/L. Conductivity rose from approximately 2.0 to 4.25 mS/cm, reflecting high ionic content. These results highlight the potential of the liquid fraction as a nutrient-rich stream that can be used for fertilizer recovery, particularly via struvite precipitation, and confirm that precise HTC parameter control supports resource recovery in line with circular economy principles. Full article

Jiaodong Gold Province is a globally rare giant gold cluster, with ongoing debates regarding its metallogenic material sources and mineralization mechanisms. This study focuses on the Linglong quartz-vein-type gold deposit within the Zhaoping Fault Zone, conducting in situ trace element and S-Pb isotope analyses of pyrite from different mineralization stages. The trace element characteristics were investigated to explore the sources of metallogenic materials, the evolution of ore-forming fluids, and the mechanisms of gold precipitation. The main findings are as follows: (1) In the Linglong gold deposit, gold primarily enters the pyrite lattice as a solid solution (Au⁺) through Au-As coupling. From the Py1 to Py3 stages, Co and Ni contents significantly decrease, while Cu, As, Au, and polymetallic element contents continuously increase. Additionally, Cu mainly replaces Fe²⁺ in the form of Cu²⁺, whereas Pb predominantly exists as micro inclusions of galena. (2) The S isotope (Py1: δ³⁴S = +7.60‰–+8.25‰, Py2: δ³⁴S = +6.15‰–+8.15‰, Py3: δ³⁴S = +6.90‰–+9.10‰) and Pb isotope (²⁰⁶Pb/²⁰⁴Pb = 16.95–17.715, ²⁰⁷Pb/²⁰⁴Pb = 15.472–15.557, ²⁰⁸Pb/²⁰⁴Pb = 37.858–38.394) systems collectively constrain the ore-forming materials such that they are dominated by metasomatized enriched lithospheric mantle, with simultaneous mixing of crustal materials. (3) The ore-forming fluid underwent a continuous evolution process characterized by persistently decreasing temperatures and a transition from mantle-dominated to crust–mantle mixed sources. The Py1 stage was predominantly composed of mantle-derived magmatic fluids uncontaminated by crustal materials, representing a high-temperature, closed environment. In the Py2 stage, the fluid system transitioned to an open system with the incorporation of crustal materials. Through coupled substitution of “As³⁺ + Au⁺ → Fe²⁺” and dissolution–reprecipitation processes, gold was initially activated and enriched. During the Py3 stage, pyrite underwent dissolution–reprecipitation under tectonic stress and fluid activity, promoting extraordinary element enrichment and serving as the primary mechanism for gold precipitation. Concurrently, bismuth–tellurium melt interactions further facilitated the precipitation of gold minerals. Full article

The recovery of rare earth elements (REEs) from the spent NdFeB magnets has great strategic significance for ensuring the security of critical mineral resources. This process requires scientifically designed separation technologies to ensure high output and purity of the obtained rare earths. Hydrometallurgy has been widely applied to extract REEs from spent permanent magnets. This paper summarizes and reviews hydrometallurgical technologies, mechanisms, and applications for the separation and recovery of REEs and iron (Fe) from the spent permanent magnets. Key methods include: The hydrochloric acid total solution method, where the spent NdFeB is completely dissolved in hydrochloric acid, iron is precipitated and removed, and then REEs are extracted. The hydrochloric acid preferential dissolution method, where spent NdFeB magnets are first fully oxidized by oxidative roasting, converting Fe²⁺ to Fe³⁺, which hydrolyzes to Fe(OH)₃, and is precipitated and removed, allowing for the subsequent extraction of REEs to obtain rare earth oxides. Acid baking and water leaching, where spent NdFeB is calcined with acidification reagents, and the calcined products are dissolved in water to leach out REEs. At the same time, Fe is retained in the leaching residue. Electrolysis in aqueous solution, where Fe is electrolyzed at the anode or deposited at the cathode to separate it from REES. Organic acids leaching, where organic acids dissolve metals through acidolysis and complexation. Bioleaching, which utilizes microorganisms to recover metal through biological oxidation and complexation. Ionic liquid systems, where Fe or REEs are extracted using ionic liquid or leached by deep eutectic solvents. This paper provides an in-depth discussion on the challenges, advantages, and disadvantages of these strategies for recycling spent NdFeB magnets, as well as the leaching and extraction behavior of REEs. It focuses on environmental impact assessment, improving recovery efficiency, and decreasing reagent consumption. The future development direction for recycling spent NdFeB magnets is proposed, and a research idea of proposing a combined process to avoid the drawbacks of a single recycling method is introduced. Full article

Geological Carbon Sequestration (GCS) plays a crucial role in addressing climate change, particularly in oil and gas development. Understanding the reaction of supercritical CO₂ under in situ conditions and its effects on minerals is essential for advancing GCS technology. This study investigates the reaction mechanisms of feldspar (potassium and sodium feldspar) and clay minerals (chlorite, illite, montmorillonite, kaolinite) in CO₂ environments. The impacts on mineral crystal structures, morphologies, and elemental compositions were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and ion concentration measurements (ICP-OES and ICP-MS). The results show that feldspar minerals exhibit lower reaction rates, with sodium feldspar dissolving faster than potassium feldspar, due to the higher solubility of sodium ions in acidic conditions. Chlorite showed significant crystal structure damage after 30 days, while montmorillonite underwent both dissolution and precipitation, influenced by interlayer cation dissociation. Kaolinite exhibited minimal reaction, primarily showing localized dissolution. Additionally, the formation of siderite (FeCO₃) was observed as Fe²⁺ substituted for Ca²⁺ in CaCO₃, highlighting the role of iron-bearing carbonates in CO₂ interactions. The study provides insights into the factors influencing mineral reactivity, including mineral structure, ion exchange capacity, and solubility, and suggests that chlorite, montmorillonite, and illite are more reactive under reservoir conditions, while kaolinite shows higher resistance to CO₂-induced reactions. These findings offer valuable data for optimizing GCS technologies and predicting long-term sequestration outcomes. Full article

In this study, we investigate the effects of adding varying proportions of fulvic acid during the digestion of pyrite on the iron concentration in both dissolved and diluted sodium aluminate solutions. Based on the occurrence characteristics of iron in the solutions, oxygen was introduced into the diluted solution to examine its iron removal efficiency, and the influence of organic compounds in the solution on iron removal through oxidation was investigated. The results indicate that, during high-pressure digestion, organic compounds forms complexes with iron, disrupting the hydrophilic iron (or ferrous) hydroxide film formed on the pyrite surface, thereby accelerating its dissolution and leading to a sharp increase in sulfur and iron content in the leachate. After cooling and dilution (100 °C, Na₂O_k 170 g/L), the iron content in the sodium aluminate solution continued to be influenced by organic compounds, showing a significant positive correlation. Oxygenation experiments for iron removal were performed using the diluted solution. Under conditions of an oxygen flow rate of 60 mL/min and an oxidation duration of 2 h (95 °C, oxygen partial pressure was 0.05 Mpa), the iron content (calculated as Fe₂O₃) decreased from 0.078 g/L to 0.021 g/L. Characterization and analysis of the iron removal precipitates revealed that the iron-containing minerals were primarily trivalent iron phases, such as goethite and hematite, with minimal ferrous iron content. Additionally, organic carbon also precipitated together with iron, which confirms the synergistic removal of iron and organic compounds. These findings demonstrate that the oxidation of reducing sodium aluminate solutions containing organic compounds, sulfur, and iron with atmospheric oxygen during the Bayer process sedimentation stage can effectively oxidize predominantly ferrous iron into less soluble ferric iron, thereby achieving iron removal. Full article

The geochemical characteristics of reinjection fluids play a crucial role in controlling water–rock interactions and the long-term stability of geothermal reservoirs. This study aims to evaluate how different fluid chemistries affect mineral dissolution–precipitation behavior and ion migration during geothermal reinjection. Five types of reinjection water—including geothermal source water (i.e., formation water from the reservoir), primary and secondary treated waters, and their mixtures—were reacted with carbonate rocks from the Wumishan Formation of the Xiong’an New Area, North China Basin, under reservoir-like conditions (70 °C, 17 MPa). A combination of batch experiments, inverse modeling using PHREEQC, and one-dimensional reactive transport simulations was employed. Results show that fluid pH, ionic strength, and saturation state significantly influence reaction pathways. Alkaline-treated waters enhanced silicate dissolution, increasing Na⁺, K⁺, and Si concentrations, while source water and its mixtures promoted carbonate precipitation, increasing the risk of clogging. Simulations revealed that the early injection stage is the most reactive, with rapid ion front advancement and strong mineral transformations. Reaction-controlled ions such as Ca²⁺ and SO₄²⁻ formed enrichment zones, while conservative ions like Na⁺ and Cl⁻ propagated more uniformly. Moderate alkaline regulation was found to mitigate carbonate scaling and improve silicate reactivity, thereby reducing permeability loss. This integrated approach provides mechanistic understanding and practical guidance for reinjection fluid design in medium-to-deep geothermal systems. Full article

Enhanced Rock Weathering (ERW) is a promising carbon dioxide removal (CDR) strategy that accelerates mineral dissolution, sequestering atmospheric CO₂ while improving soil health. This study builds on prior applications of soil calcimetry by investigating its ability to resolve short-term carbonate fluxes and rainfall-modulated weathering dynamics in wollastonite-amended croplands. Conducted over a single growing season (May–October 2024) in temperate row-crop fields near Port Colborne, Ontario—characterized by fibric mesisol soils (Histosols, FAO-WRB)—this study tests whether calcimetry can distinguish between dissolution and precipitation phases and serve as a proxy for weathering flux within the upper soil horizon, under the assumption that rapid pedogenic carbonate cycling dominates alkalinity retention in this soil–mineral system. Monthly measurements of soil pH (Milli-Q and CaCl₂) and calcium carbonate equivalent (CCE) were conducted across 10 plots, totaling 180 composite samples. Results show significant alkalinization (p < 0.001), with average pH increases of ~+1.0 unit in both Milli-Q and CaCl₂ extracts over the timeline. In contrast, CCE values showed high spatiotemporal variability (−2.5 to +6.4%) without consistent seasonal trends. The calcimetry-derived weathering proxy, log (Σ ΔCCE/Δt), correlated positively with pH (r = 0.652), capturing net carbonate accumulation, while the kinetic dissolution rate model correlated strongly and negatively with pH (r ≈ −1), reflecting acid-promoted dissolution. This divergence confirms that the two metrics capture complementary stages of the weathering–precipitation continuum. Rainfall strongly modulated short-term carbonate formation, with cumulative precipitation over the previous 7–10 days enhancing formation rates up to a saturation point (~30 mm), beyond which additional rainfall yielded diminishing returns. In contrast, dissolution fluxes remained largely independent of rainfall. These results highlight calcimetry as a direct, scalable, and dynamic tool not only for monitoring solid-phase carbonate formation, but also for inferring carbonate migration and dissolution dynamics. In systems dominated by rapid pedogenic carbonate cycling, this approach captures the majority of alkalinity fluxes, offering a conservative yet comprehensive proxy for CO₂ sequestration. Full article

The rise in atmospheric CO₂ intensified the urgency for carbon capture and storage (CCS), yet uncertainties remain in predicting evolution of reservoir properties under CO₂ injection. This study investigates how CO₂–brine–rock interactions alter porosity and permeability in carbonate and sandstone reservoirs. We quantify pore-scale changes and effects of CO₂-saturated brine on rock. In calcite-rich carbonates, CO₂-induced acidification enhances permeability through selective dissolution. Dolomite-rich samples and sandstones exhibit suppressed permeability response due to slower dissolution and pore clogging. μCT and SEM reveal that although bulk porosity changes are small, local changes—especially formation of micropores and mineral occlusions—substantially influence permeability. Geochemical modeling confirms three-stage evolution: early dissolution, intermediate buffering with onset of precipitation, and long-term mineral trapping with near-steady porosity. The results indicate that early injectivity gains may be temporary and that proactive monitoring and management are required to safeguard long-term storage integrity. The findings provide actionable insight for sustainable CCS design, risk assessment, and reservoir stewardship. Full article

To elucidate the hydrochemical characteristics and evolution mechanisms of shallow groundwater in the alluvial–coastal transitional zone of the Tangshan Plain, 76 groundwater samples were collected in July 2022. An integrated approach combining Piper and Gibbs diagrams, ionic ratio analysis, multivariate statistical methods (including Pearson correlation, hierarchical cluster analysis, and principal component analysis), and PHREEQC inverse modeling was employed to identify hydrochemical facies, dominant controlling factors, and geochemical reaction pathways. Results show that groundwater in the upstream alluvial plain is predominantly of the HCO₃–Ca type with low mineralization, primarily controlled by carbonate weathering, water–rock interaction, and natural recharge. In contrast, groundwater in the downstream coastal plain is characterized by high-mineralized Cl–Na type water, mainly influenced by seawater intrusion, evaporation concentration, and dissolution of evaporite minerals. The spatial distribution of groundwater follows a pattern of “freshwater in the north and inland, saline water in the south and coastal,” reflecting the transitional nature from freshwater to saline water. Ionic ratio analysis reveals a concurrent increase in Na⁺, Cl⁻, and SO₄²⁻ in the coastal zone, indicating coupled processes of saline water mixing and cation exchange. Statistical analysis identifies mineralization processes, carbonate weathering, redox conditions, and anthropogenic inputs as the main controlling factors. PHREEQC simulations demonstrate that groundwater in the alluvial zone evolves along the flow path through CO₂ degassing, dolomite precipitation, and sulfate mineral dissolution, whereas in the coastal zone, continuous dissolution of halite and gypsum leads to the formation of high-mineralized Na–Cl water. This study establishes a geochemical evolution framework from recharge to discharge zones in a typical alluvial–coastal transitional setting, providing theoretical guidance for salinization boundary identification and groundwater management. Full article

This study aims to elucidate the geochemical reactions between CO₂-saturated water and rocks in CO₂-enhanced geothermal system (CO₂-EGS) reservoirs by focusing on andesite found in island arc regions, such as Japan. Laboratory flow tests of CO₂-saturated water (3 wt.% CO₂) and rocks (particle size: 0.14–1 mm) were conducted under varying temperature (150–250 °C) and flow rate (0.3 and 1.0 mL/min) conditions using a flow-through reactor. Elevated temperatures enhanced the dissolution of silicate minerals, reflected by increased Na⁺, K⁺, Ca²⁺, and Si concentrations, whereas those of Fe²⁺ and Al³⁺ remained low, suggesting secondary mineral precipitation. The dissolution process was dominant at 150 °C. Al-bearing minerals, such as gibbsite and boehmite, as well as clay minerals, including beidellite and kaolinite, were predominant at higher temperatures (200–250 °C). Carbonate minerals were not observed, attributable to low pH and limited availability of divalent cations. Flow rate substantially influenced Si dissolution rates, with lower flow rates promoting longer residence times and higher Si dissolution rates. These results indicate that the test conditions simulate the environment around the injection well, where the fluid is acidic and dissolution is the main reaction in the rock. Although a small amount of secondary minerals precipitated and the Si dissolution rates were of the same order of magnitude as those for labradorite, it may be considered that andesite has less impact on permeability variations than basalt near the injection well in CO₂-EGS reservoirs. Full article

High-silica–alumina coal gangue is rich in kaolinite, quartz, and other mineral components. The potential for resource utilization is huge, but the silica–aluminate structure is highly stable, and it is difficult to achieve efficient dissociation and elemental enrichment using traditional extraction processes. This study selects typical high-silica–alumina coal gangue as the research object and systematically studies the rules of the physical phase transformation mechanism and ion migration behavior in the activation process of the sodium-based additives stage. In addition, a graded leaching and separation processing route is established, realizing the effective separation and extraction of silica–alumina. The key parameters were optimized using response surface methodology (RSM), obtaining the optimal activation conditions of 800 °C, 30 min, and an additives ratio of 0.8. Under these conditions, the highest dissolution rates of silica and alumina are 82.1% and 92.36%, respectively. Characterization techniques such as XRD, FTIR, and SEM reveal that the activation mechanism of coal gangue involves the decomposition of the aluminosilicate framework and the erosion of sodium ions. At the same time, the chemical bonding reorganization contributes to forming water-soluble sodium silicate (Na₂SiO₃) and insoluble nepheline (NaAlSiO₄), which significantly promotes the release of Si and Al. When the activation temperature is too high, the nepheline phase is transformed into amorphous glassy sodium aluminate and precipitated on the surface, which gradually encapsulates the sodium silicate. This encapsulation restricts dissolution pathways, thereby leading to system densification. Moreover, enhanced resistance to acid attack leads to a decrease in the dissolution rates of Si and Al. This study elucidates the mineral phase reconstruction and element migration mechanisms involved in sodium-based activation and presents a viable approach for the high-value utilization of coal gangue. Full article

The development of hot dry rock needs working fluids, and mineral reactions happen due to contact between hot dry rock minerals and fluids. Mineral reactions influence hot dry rock reservoir characteristics, whereas their impacts on hot dry rock mechanical properties lack understanding. In this study, a simulation study on the influence of reactions between granitic hot dry rock minerals and water on rock non-closed crack compressive shear initiation was conducted. High temperature (180 °C) and high pressure (24 MPa) mineral reaction experiments were performed to obtain reaction kinetics parameters. A model of non-closed crack compressive shear initiation induced by mineral reactions was established. Based on the model, the influences of mineral reactions on the compressive shear initiation of non-closed cracks were analyzed. Results show that the mineral reactions primarily contain feldspar dissolution and quartz precipitation, and their overall effect is crack enlargement. The crack enlargement reduces crack initiation potential for a crack inclination angle of α = 0°, while it increases crack initiation potential for α = 45° and 90°. The difference in crack initiation potential under various α values is attributed to the relative position of the crack to the maximum principal stress direction. This work reveals the influences of mineral reactions on hot dry rock reservoir crack initiation, contributing to achieving sustainable hot dry rock exploitation. Full article