Mineral Interface Research Articles

Multiscale characterisation on the adhesion and selective adsorption at bitumen–mineral interface

The adhesion between bitumen and minerals is essential for the durability of asphalt mixtures, influenced by bitumen composition and mineral structure. The chemical action theory suggests that polar components in bitumen are adsorbed onto the mineral surface, facilitating adhesion. In this study, environmental scanning electron microscopy with energy-dispersive X-ray (ESEM-EDS) is used to analyse bitumen–mineral interfaces at a microscopic level. Elemental analysis reveals selective adsorption of polar substances from bitumen onto the surfaces of four types of minerals. Results show that alkaline rocks (limestone and albite) have a higher adsorption capacity than acidic rocks (granite and quartz). Additionally, treating mineral surfaces with alkaline solutions enhances adsorption. The adhesion properties of bitumen to various minerals are evaluated using the pull-off test. The correlation between ESEM-EDS and pull-off tests demonstrates that the macroscopic adhesion of bitumen to minerals is linked to the microscopic selective adsorption of polar substances.

Density functional theory study on vanadium selective leaching separation from iron in stone coal via Fe2O3 (001) surface passivation

When vanadium is extracted from stone coal, iron impurities readily precipitate and reduce the purity of the vanadium product. Thus, separating vanadium from iron impurities at source is essential. The mechanism of surface passivation of Fe2O3 (001) for the selective leaching separation of vanadium from iron in stone coal was established in the present work. Analysis of mineral phase transformation and microscopic morphology indicates that Fe2O3 in stone coal can undergo a reaction with HF and F-. Subsequently, the hematite surface was covered with FeF3 passivation layer, resulting in the inhibition of hematite dissolving reaction. The results of density functional theory (DFT) computations demonstrate that the HF and F- can reform the Fe2O3 (001) surface via sedimentary behavior at mineral interface, and the adsorption energy can be down to -99.93kJ/mol for the F- adsorption configuration. During sulfuric acid leaching with CaF2 as an aiding agent, the transfer of electrons from Fe atoms to F atoms can weaken the stable Fe-F bonds and decrease the reactive activation of Fe atoms in Fe2O3. This study demonstrates the separation of vanadium from iron by means of hematite passivation in the attendance of fluoride at the atomic level of analysis.

Mineral Interface Doping: Hydroxyapatite Deposited on Silicon to Trigger the Electronic Properties

AbstractDoping silicon wafers without using highly toxic or corrosive chemical substances has become a critical issue for semiconductor device manufacturing. In this work, ultra‐thin films of hydroxyapatite (Ca5(PO4)3OH) are prepared by tethering by aggregation and growth (T‐BAG), and further processed by spike annealing. Via in situ infrared (IR), the decomposition of hydroxyapatite and intermixing with the native silicon oxide is observed already at temperatures as low as 200 °C. Phosphate transport through the native silicon oxide is driven by a phase transformation into a more stable thermal oxide. At 700 °C, diffusion of phosphorus into the sub‐surface region of oxide‐free silicon is observed. In situ IR combined with electrical impedance spectroscopy (EIS), time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), and X‐ray photoelectron spectroscopy (XPS) measurements allows to conclude that the phosphorus is: i) transported through the silicon oxide barrier, ii)) diffused inside the oxide‐free silicon, and iii) finally modified the electrical activity of the silicon wafer. To further explain the experimental findings, density‐functional theory (DFT) is used to demonstrate the extent of the effect of phosphorus doping on the electronic nature of silicon surfaces, showing that even small amounts of doping can have a measurable effect on the electrical performance of semiconductor wafers.

Enhancement of copper mobilization using acidic AlCl3 − rich lixiviant

Copper (Cu) extraction from low-grade ores is limited by the formation of secondary minerals that can passivate the surfaces of Cu-sulphide minerals in these ores. Hence, a novel approach utilizing AlCl3 as a lixiviant was developed to modify coupled dissolution-reprecipitation processes at the mineral interface. The formation of Al-rich phases instead of Fe-hydroxysulphates enhanced Cu extraction through combined ferric-iron and proton-promoted dissolution. AlCl3 accelerated chalcopyrite and bornite dissolution by forming soluble intermediate Cu-phases (e.g., covellite) at consistently high Eh (550–650 mV) and acidity due to the Lewis acid property of AlCl3. X-ray diffraction analysis revealed that Na-bearing jarosite [(K0.61Na0.41)Fe3(SO4)2(OH)] and sideronatrite [Na2Fe(SO4)2(OH)(H2O)] formation in lixiviants without AlCl3 decreased Fe3+(aq) availability for Cu-sulphide minerals dissolution. In contrast, significant amounts of AlSO4+(aq) formed in the AlCl3-rich lixiviant at pH 1–3, which reduced the sulphate activity and decreased the saturation state of the Fe-hydroxysulphates. Further, AlCl3 promoted the formation of amorphous, porous Al-rich phases, facilitating quick Fe diffusion through the passivating layer and improving Cu recovery compared to lixiviants containing CaCl2, NaCl, or acid-only.

In Situ Evolution of Ionic Sites at Clay Mineral Interfaces Facilitates Fluoride and Phosphorus Mineralization.

Soil minerals influence the biogeochemical cycles of fluoride (F) and phosphorus (P), impacting soil quality and bioavailability to plants. However, the cooperative mechanisms of soil minerals in governing F and P in the soil environment remain a grand challenge. Here, we reveal the essential role of a typical soil mineral, montmorillonite (Mt), in the cycling and fate of F and P. The results show that the enrichment of metal sites on the Mt surface promotes the mineralization of F to the fluorapatite (FAP) phase, thereby remaining stable in the environment, simultaneously promoting P release. This differential behavior leads to a reduction in the level of F pollution and an enhancement of P availability. Moreover, solid-state NMR and HRTEM observations confirm the existence of metastable F-Ca-F intermediates, emphasizing the pivotal role of Mt surface sites in regulating crystallization pathways and crystal growth of FAP. Furthermore, the in situ atomic force microscopy and theoretical calculations reveal molecular fractionation mechanisms and adsorption processes. It is observed that a competitive relationship exists between F and P at the Mt interface, highlighting the thermodynamically advantageous pathway of forming metastable intermediates, thereby governing the activity of F and P in the soil environment at a molecular level. This work paves the way to reveal the important role of clay minerals as a mineralization matrix for soil quality management and offers new strategies for modulating F and P dynamics in soil ecosystems.

The generation of a clotted peloidal micrite fabric by endolithic cyanobacteria in recent thrombolites from Cuatro Cienegas, northern Mexico

ABSTRACTCuatro Cienegas is a natural geopark that exhibits a vast reservoir of geological, geochemical and geobiological diversity, including shallow‐water microbial carbonates with clotted micrite textures known as thrombolites. Thrombolites mainly occur as domes and massive irregular carbonates along the margins of Rio Mezquites in Cuatro Cienegas, northern Mexico. Because their clotted textures result from diverse abiotic and biotic interactions at the microbial–mineral interface, the formation of clots in thrombolites continues to be a contentious issue. Through a petrographic, scanning electron microscopy and bulk biogeochemical analysis, this study investigated the role of endolithic cyanobacteria in the generation of thrombolitic clots. Their microclotted fabric is characterized by 50 to 200 μm peloidal clots, pores, fenestrae, crevices and cavities as main components. Thrombolites also contain microbial microstructures, some of them interpreted as the endolithic contribution to the genesis of clotted micrite. Thrombolites and associated fresh microbial mats are composed of cyanobacteria, green algae and diatoms. Petrography and cast‐embedded scanning electron microscopy micrographs also show the presence of filamentous endolithic cyanobacteria inside the thrombolitic framestone. The geochemical bulk characterization for carbon and oxygen isotopes shows average values of −0.7‰ Vienna PeeDee Belemnite and −8.0‰ Vienna PeeDee Belemnite, respectively. The organic matter preserved in their mineral matrix and associated microbial mats indicated the putative presence of cyanobacterial hopanoids. The high diversity of peloids and the microboring evidence, together with observed microstructures, suggest that clots may also form by the concurrent precipitation and dissolution of the thrombolites. Among the known sources of peloidal clots, microbial boring may be an additional micrite source for clot formation. Microbial carbonate dissolution may also promote heterogenous lithification by hydration and dehydration cycles. Thrombolites reflect complex systems due to concurrent interactions among producers (phototrophs), consumers (small invertebrates), mineralization (carbonate precipitation induced by phototrophs) and endolithic dissolution. The microstructures inside thrombolites, in conjunction with biogeochemical attributes of bulk thrombolites, may provide unambiguous sedimentary biosignatures.

Study on cohesion and adhesion behaviors of the zeolite foamed asphalt-warm mix mixture based on molecular dynamics simulation

Zeolite foamed asphalt - warm mix mixture (ZFA-WMM) has been applied in large quantities in asphalt pavement, however, a lower construction temperature, residual zeolite water and zeolite minerals have different effects on the cohesion and adhesion properties of zeolite foamed asphalt (ZFA), which indirectly affects the water stability of its mixture. This study analyzed the interface behavior in ZFA-WMM using molecular dynamics simulation. First, the molecular model of ZFA was constructed, and its thermodynamic properties were calculated and compared with experimental values and related simulated values to validated the reasonable of model. Then, the interface models of ZFA-aggregate (quartz and calcite) and ZFA-ZFA were established, simulating the effects of the zeolite mineral dosage, temperature, and interface moisture (residual zeolite water) content on the cohesion and adhesion of ZFA. Furthermore, the occurrence mode of cohesion or adhesion failures in ZFA-WMM were predicted by comparing the ZFA-aggregate adhesion work with ZFA cohesion work. The simulation results indicated that as the zeolite mineral dosage increased, the ZFA cohesion and ZFA-calcite adhesion increased, while ZFA-quartz adhesion first grew and then dropped, reaching its maximum at 9.4 % zeolite mineral dosage. Under the pavement operating temperature range (-15°C∼65°C), higher pavement temperatures are beneficial to ZFA-aggregate adhesion; the cohesion of ZFA first increases and then decrease as temperature rises, reaching its maximum at 25℃. The larger the interface moisture content, the higher the possibility of water separating ZFA from the aggregate surface and the water sensitivity of ZFA-WMM. The ZFA-WMM is prone to adhesion failure, especially at higher zeolite dosages.

Aluminum substitution stabilizes organic matter in ferrihydrite transforming into hematite: A molecular analysis

The association of soil organic matter (SOM) with iron (Fe) oxyhydroxides, particularly ferrihydrite, plays a pivotal role in the biogeochemical cycling of carbon (C) in both terrestrial and aquatic environment. The aging of ferrihydrite to more crystalline phases can impact the stability of associated organic C, a process potentially influenced by aluminum (Al) substitution due to its abundance. However, the molecular mechanisms governing the temporal and spatial distribution of SOM during the aging process of Al-substituted Fe oxyhydroxides remain unclear. This study aims to bridge this knowledge gap through a comprehensive approach, utilizing batch experiments, solid characterization techniques, and atomic force microscopy (AFM) based peak-force quantitative nanomechanical mapping (PF-QNM). Batch experiments revealed that humic acid (HA) was released into the aqueous phase during aging, with Al inhibiting this release. Various solid characterization methods collectively suggested that Al hindered the crystalline transformation of ferrihydrite and significantly preserved HA on the surface of newly formed hematite, rather than it being occluded within the interior of the new minerals. Results from 3-Dimensional fluorescence spectroscopy (3D-EEM) and Fourier-transform infrared spectroscopy (FTIR) indicated that the structure of HA remained constant, with the carboxyl-rich and hydroxyl-rich portions of HA fixed at the mineral interface during the aging period. Furthermore, we developed AFM-based PF-QNM to both quantify and visualize the interactions between Fe oxyhydroxides and HA, demonstrating variations in HA affinity among different Fe oxyhydroxides and highlighting the influence of the Al substitution rate.

Toward Modeling the Structure of Electrolytes at Charged Mineral Interfaces Using Classical Density Functional Theory.

The organization of water molecules and ions between charged mineral surfaces determines the stability of colloidal suspensions and the strength of phase-separated particulate gels. In this article, we assemble a density functional that measures the free energy due to the interaction of water molecules and ions in electric double layers. The model accounts for the finite size of the particles using fundamental measure theory, hydrogen-bonding between water molecules using Wertheim's statistical association theory, long-range dispersion interactions using Barker and Henderson's high-temperature expansion, electrostatic correlations using a functionalized mean-spherical approximation, and Coulomb forces through the Poisson equation. These contributions are shown to produce highly correlated structures, aptly rendering the layering of counterions and co-ions at highly charged surfaces and permitting the solvation of ions and surfaces to be measured by a combination of short-range associations and long-ranged attractions. The model is tested in a planar geometry near soft, charged surfaces to reproduce the structure of water near graphene and mica. For mica surfaces, explicitly representing the density of the outer oxygen layer of the exposed silica tetrahedra allows water molecules to hydrogen-bond to the solid. When electrostatic interactions are included, water molecules assume a hybrid character, being accounted for implicitly in the dielectric constant but explicitly otherwise. The disjoining pressure between approaching like-charged surfaces is calculated, demonstrating the model's ability to probe pressure oscillations that arise during the expulsion of ions and water layers from the interfacial gap and predict strong interattractive stresses that form at narrow interfacial spacing when the surface charge is overscreened. This interattractive stress arises not due to in-plane correlations under strong electrostatic coupling but due to the out-of-plane structuring of associating ions and water molecules.

Experimental Investigation on Diamond Band Saw Processing of Resin Mineral Composites.

Resin mineral composite (RMC) is a new material with several times the damping properties of gray cast iron and great corrosion resistance. Due to its overall brittleness, sawing with a diamond band saw would be a suitable method. In this research, sawing experiments are carried out to study the sawing force characteristics of the material and its surface morphology during the processing. The results show that the feed force level is in the range of 3.5~5.5 N and the tangential force level is relatively low. The distribution of resin mineral components does not have a significant impact on the average sawing force but increases the fluctuation of the lateral force signal. The maximum fluctuation volume is 94.86% higher than other areas. Uneven lateral force, generated when diamond particles pass through the resin-mineral interface, is one of the causes of fluctuations. The machined surface of RMC has uniform strip scratches and a small number of pits. Maintaining a constant ratio of sawing speed to feed speed can result in approximately the same machined surface. A step structure with a height of about 10 μm appears at the interface of resin minerals. As a processing defect, it may affect the performance of RMC components in some aspects, which need a further precision machining processing.

Distinct photochemistry of adsorbed and coprecipitated dicarboxylates with ferrihydrite: Implications for iron reductive dissolution and carbon stabilization

Although ligand-promoted photodissolution of ferrihydrite (FH) has long been known for low molecular weight organic acids (LMWOAs), such as oxalate (Oxa) and malonate (Mal), photochemistry of coprecipitated FH with Oxa and Mal remains unknown, despite the importance of these mineral-organic associations in carbon retention has been acknowledged recently. In this study, ferrihydrite-LMWOAs associations (FLAs) were synthesized under circumneutral conditions. Photo-dissolution kinetics of FLAs were compared with those of adsorbed LMWOAs on FH surface and dissolved Fe-LMWOAs complexes through monitoring Fe(II) formation and organic carbon decay. For aqueous Fe(III)-LMWOAs complexes, Fe(II) yield was controlled by the initial concentration of LMWOAs and nature of photochemically generated carbon-centered radicals. Inner-sphere mononuclear bidentate (MB) configuration dominated while LMWOAs were adsorbed on the FH surface. MB complex of FH-Oxa was more photoreactive, leading to the rapid depletion of Oxa. Oxa can be readsorbed but in the form of binuclear bidentate and outer-sphere complexation, with much lower photoreactivity. While LMWOAs was coprecipitated with FH, the combination mode of LMWOAs with FH includes surface adsorption with a mononuclear bidentate structure and internal physical inclusion. Higher content of LMWOAs in the FLAs promoted the photo-production of Fe(II) as compared to pure FH, while it was not the case for FLAs containing moderate amounts of LMWOAs. The distinct photochemistry of adsorbed and coprecipitated Fe-LMWOAs complexes is attributed to ligand availability and configuration patterns of LMWOAs on the surface or entrapped in the interior structure. The present findings have significant implications for understanding the photochemical redox cycling of iron across the interface of Fe-organic mineral associates.

Controls of Multi-Scale Fractures in Tight Sandstones: A Case Study in the Second Member of Xujiahe Formation in Xinchang Area, Western Sichuan Depression

Abstract Different scales of fractures affect the reservoir quality in tight sandstone. There are more studies on macroscopic tectonic fractures but less on bedding fractures and microfractures. The control factors of multi-scale fractures are unclear. In this paper, we analyzed the types and controls of fractures in the second member of the Xinchang region in Western Sichuan. We use core and outcrops observations, imaging logging, scanning energy spectra, and rock slices. Natural fractures can be classified into tectonic, bedding, and microscopic types. The tectonic fractures are mainly low- to medium-angle tensile fractures. The bedding fractures are nearly horizontally distributed along the bedding surface, including parallel, dark mineral interface, and carbonaceous fragments interface bedding fractures. The microfractures develop intra-grain, edge-grain, and inter-grain types. The intra-grain microfractures are inside quartz or feldspar grains, whereas inter-grain types penetrate multiple grains with larger extension lengths. The tectonic fractures are related to the stress, grain size, mineral component, argillaceous content, and lithologic thickness. Parallel bedding fractures are controlled by the coupling of water depth and flow velocity. Bedding fractures at the interface are controlled by rock component. The microfractures are controlled by the length-width axis ratio of the grain, grain element content, and brittleness index. Fractures of different scales form a three-dimensional fracture system that has a substantial impact on the gas production.

Overlooked role of aqueous chromate (VI) as a photosensitizer in enhancing the photochemical reactivity of ferrihydrite and production of hydroxyl radical

The reactive oxygen species (ROS) photochemically generated from natural iron minerals have gained significant attention. Amidst the previous studies on the impact of heavy metal ions on ROS generation, our study addresses the role of the anion Cr(VI), with its intrinsic photoactivity, in influencing ROS photochemical generation with the co-presence of minerals. We investigated the transformation of inorganic/organic pollutants (Cr(VI) and benzoic acid) at the ferrihydrite interface, considering sunlight-mediated conversion processes (300–1000 nm). Increased photochemical reactivity of ferrihydrite was observed in the presence of aqueous Cr(VI), acting as a photosensitizer. Meanwhile, a positive correlation between hydroxyl radical (•OH) production and concentrations of aqueous Cr(VI) was observed, with a 650% increase of •OH generation at 50 mg L−1 Cr(VI) compared to systems without Cr(VI). Our photochemical batch experiments elucidated three potential pathways for •OH photochemical production under varying wet chemistry conditions: (1) ferrihydrite hole-mediated pathway, (2) chromium intermediate O-I-mediated pathway, and (3) chromium intermediates CrIV/V-mediated pathway. Notably, even in the visible region (> 425 nm), the promotion of aqueous Cr(VI) on •OH accumulation was observed in the presence of ferrihydrite and TiO2 suspensions, attributed to Cr(VI) photosensitization at the mineral interface. This study sheds light on the overlooked role of aqueous Cr(VI) in the photochemical reactivity of minerals, thereby enhancing our understanding of pollutant fate in acid mining-impacted environments.

Study of Asphalt Behavior on Pre-Wet Aggregate Surface Based on Molecular Dynamics Simulation and Surface Energy Theory

The improvement of the performance of asphalt mixtures has been studied by scholars. This research proposes a new asphalt–mineral interface formation method, which is a pre-wet bitumen–mineral mixture. The formation process of the pre-wet asphalt–mineral interface was simulated by molecular dynamics simulation software. The diffusion coefficient, concentration distribution, and interfacial energy of the asphalt on the surface of the pre-wet mineral material and non-pre-wet mineral material were compared and analyzed. The simulation results show that the mineral surface diffusion rate of the asphalt after pre-wetting is increased by more than 50%, and the concentration in the X, Y, and Z directions is reduced by 0.8%, 4.6%, and 7.8%, respectively. At the same time, the interface energy between the bitumen and the pre-wet mineral was increased by more than 8%. The results of the molecular dynamics model are verified based on the surface energy theory and contact angle test. The experimental results show that the contact angle of the asphalt is smaller and the diffusion performance is better after pre-wetting. At the same time, the interface adhesion work between the asphalt and wet mineral surface increased by 4.3% in a dry environment, and the peeling work decreased by 41.1% in a water environment. Therefore, the author believes that the pre-wetting technology of the asphalt mixture has a certain feasibility and practicability.

Effects of loading rates on interfacial adhesion between aggregates and asphalt binders

Effects of loading rates on the adhesion between aggregate minerals and asphalt materials were elucidated through combined simulation and experimental studies. Silica, calcium carbonate and alumina represented the primary aggregate minerals, whereas saturate, asphaltene, resin, and aromatic represented the primary asphalt components. In the experiments and simulations, asphalt components and binders were pulled away from mineral interface at various loading rates. The relation between adhesion and loading rates was identified for the low-speed, transition and high-speed regions. Microstructural evolutions were characterized at different loading rates. Results showed that alumina generated higher adhesion to asphalt than silica and calcium carbonate, which agreed with prior experimental findings using particle probe scanning force microscopy. At low velocities, the gradual delamination of mineral-asphalt interfaces resulted in small adhesive forces. But at high velocities, the breakage of many bonds within a short period led to high adhesive forces. The study provided further understandings of the interfaces between aggregate and asphalt, which might promote the design and utilization of asphalt material.

New insights on the breakage mechanism of magnetite quartzite via high voltage pulse discharge: liberation, property difference, micro morphology, and numerical simulation

Herein, new insights on the breakage mechanism of magnetite quartzite via high voltage pulse discharge were proposed. The liberation of magnetite quartzite was significantly enhanced by high voltage pulse discharge. The ground products liberations of pulse numbers 300 were improved by 20.93% at grinding time 3 min. The iron distribution rate of high voltage pulse breakage in −0.074 mm were improved by 29.04 percentage points at pulse numbers 300. The linear thermal expansion coefficient of magnetite and quartz were 7.52 × 10−6 °C and 5.70 × 10−7 °C, thus different expansion deformation and thermal stress of grain boundary expansion generated to promote the grain boundary separation of quartz and magnetite. The impact wave force destroyed the intergranular force rather than the intragranular force preferentially during the high voltage pulse breakage. A distorted electric field was generated at the mineral interface to produce grain boundary cracks and realized the macro fracture of magnetite quartzite.

Application of molecular dynamics simulations in interface interaction of clay: Current status and perspectives

AbstractTo understand the research progress of molecular dynamics (MD) method in the field of clay minerals, the application of MD in the interface interaction of clay minerals is reviewed in this paper. MD simulations have become the indispensable means to study mineral interface effects. Clay minerals are common associated minerals with hydrophilic surface, the ease of argillization, negative electricity, and the ability of forming impurities and defects. They are widely concerned in the fields of mine wastewater treatment, fine clay mineral flotation, shale oil and gas exploitation, and so forth. In addition, clay minerals are considered as natural adsorbents due to their large specific surface area, but their complex interface interactions hinder their effective utilization. Therefore, it is particularly important to reveal the interaction mechanism of clay interface at the atomic/molecular level by means of software simulation technology. In this review, our focus is on the applications of MD method in the field of clay mineral interface interaction, such as clay/gas interface, clay/water interface, agents and clay/water interface, and mineral particle and clay/water interface. Furthermore, the history and shortcomings of MD simulation are summarized. The research and effective utilization of clay interface are summarized and prospected as well.

Chemical and Structural Insights of the Nano Organo–Mineral Interfaces in Growing Abalone Nacre

Chemical and Structural Insights of the Nano Organo–Mineral Interfaces in Growing Abalone Nacre

Graphite ore flotation efficiency using bio ester collector formed by transesterification

Bench scale flotations were carried out to investigate an alternative collector reagent with a more sustainable bias, with selective action at the mineral interface to replace the standard hydrocarbon-base collector used for graphite’s flotation, the kerosene. A soy bio oil was produced by a transesterification reaction to perform as a collector. The study used graphite ore with 5.85% carbon content obtained from Salto da Divisa/MG region, in Bahia-Minas Province, Brazil. The design of experiments showed that the bio ester performed 11% higher than kerosene as a graphite’s collector, improving the flotation’s selectivity with 62% ore grade by bio oil and 88% recovery, against 54% ore grade using kerosene and 77% recovery. The chemical composition investigated with XPS analysis for both concentrates with kerosene and bio ester demonstrated the influence of esters and oxigenated-groups on oxidized graphite surfaces.

Water Vapor Condensation on Iron Minerals Spontaneously Produces Hydroxyl Radical.

The hydroxyl radical (•OH) is a potent oxidant and key reactive species in mediating element cycles and pollutant dynamics in the natural environment. The natural source of •OH is historically linked to photochemical processes (e.g., photoactivation of natural organic matter or iron minerals) or redox chemical processes (e.g., reaction of microbe-excreted or reduced iron/natural organic matter/sulfide-released electrons with O2 in soils and sediments). This study revealed a ubiquitous source of •OH production via water vapor condensation on iron mineral surfaces. Distinct •OH productions (15-478 nM via water vapor condensation) were observed on all investigated iron minerals of abundant natural occurrence (i.e., goethite, hematite, and magnetite). The spontaneous •OH productions were triggered by contact electrification and Fenton-like activation of hydrogen peroxide (H2O2) at the water-iron mineral interface. Those •OH drove efficient transformation of organic pollutants associated on iron mineral surfaces. After 240 cycles of water vapor condensation and evaporation, bisphenol A and carbamazepine degraded by 25%-100% and 16%-51%, respectively, forming •OH-mediated arene/alkene hydroxylation products. Our findings largely broaden the natural source of •OH. Given the ubiquitous existence of iron minerals on Earth's surface, those newly discovered •OH could play a role in the transformation of pollutants and organic carbon associated with iron mineral surfaces.