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Fungi actively enhance the local dissolution of nutrient-bearing minerals through the combined biomechanical and biochemical actions of their hyphal tips to obtain mineral-bound inorganic nutrients (MINs). However, little is known about the dynamic processes underlying hyphal tip-mineral interactions. Here, we assess the adhesive force between a single hypha of the common fungus Talaromyces flavus and the Fe-bearing silicate lizardite and quartz (as a control), as well as hyphal tip-induced lizardite weathering and hyphal Fe uptake. We showed that T. flavus hyphae formed their maximal adhesive force with lizardite at the growing tips, reaching 6.11 ± 0.69 nN after a contact time of one minute. The adhesive forces of the tip-lizardite interface within two minutes were > 2.65 times stronger than those of the tip-quartz interface. Examination of the hyphal tip-lizardite interface after 18 h indicated the formation of dissolution channels with a depth of 27.7 ± 8.0 nm. Furthermore, the hyphal tips resulted in an altered lizardite up to 46 nm. The thickness of the altered lizardite increased to ∼130 nm after contact with the mature regions of the hyphae for ∼173 min. And the altered lizardite was found to have depleted Fe levels that increased with increasing contact time. The total content of Fe in T. flavus associated with the lizardite surface after 18 h was 52.98 ± 12.20 nmol mg-1, which was 6 times greater than the total amount of Fe in quartz surface-associated T. flavus after 24 h of culture. These results demonstrate that fungi access MINs by the active development of a strong adhesive force with target minerals through their hyphal tips, effectively enabling fungi to flourish in heterogeneous environments and be major geological agents for biogeochemical transformation.

Knowledge of Sn(II) speciation in aqueous and gaseous phases and the corresponding isotope effects are critical for understanding the transport and deposition of Sn in various geological and cosmochemical processes. In this study, we use first principles method to investigate the speciation of stannous (Sn(II)) chloride in fluids under hydrothermal and supercritical conditions. The results show that SnCl3−, SnCl2(H2O) and SnCl(H2O)2+ are stable in hydrothermal solutions at temperatures of up to 300 °C, with SnCl3− being the dominant species, whereas SnCl2 and SnCl2(H2O) are the stable species in vapor phases. Notably, SnCl2 is found to be stable under supercritical conditions. The reduced partition function ratios (β factors) for the stable Sn(II) species and three major Sn minerals (cassiterite, megawite, and romarchite) are also calculated by first principles methods. The calculation results show that under equilibrium, heavy Sn isotopes are preferentially partitioned into stannic (Sn(IV)) species, and gaseous species enrich heavy Sn isotopes relative to aqueous species. Based on the equilibrium Sn isotope fractionation factors derived in this study, we use a transport-precipitation model to evaluate the Sn isotope response to cassiterite precipitation in hydrothermal fluids. The modeling results show that significant Sn isotope variability could be produced during cassiterite precipitation, with temperature and Sn speciation being the primary controlling factors. Furthermore, by comparing the Sn isotope variability in natural cassiterite and those derived from the model, we argue that Sn should occur predominantly as Sn(IV) species in hydrothermal fluids during cassiterite precipitation in tin mineralizing systems.

Fungus-mineral interactions influence a variety of geochemical and biological processes on and near the Earth’s surface. The secondary metabolites produced by fungi during these interactions control mineral weathering and affect geochemical element cycling; however, the extent to which minerals exert their influence on fungal metabolism has not been quantitatively determined in detail. Here, we used mass spectroscopy to investigate the exometabolome of Talaromyces flavus, a serpentine soil-inhabiting fungus, during interactions with antigorite, chlorite, hornblende, lizardite, magnetite, and quartz at 28 °C under aerobic conditions. Our experimental results showed that all the minerals used promoted spore germination and hyphal growth. The glucose consumption rate during the initial stages of the fungus-mineral interactions indicated that the metabolic activity of T. flavus was enhanced by a factor of ∼7 by lizardite, antigorite, chlorite, hornblende, and magnetite and by a factor of ∼3 by quartz. A total of 1198 secondary metabolites were detected at 166 h, and 977 (81.55%) of them were common to the T. flavus interactions with antigorite, chlorite, hornblende, lizardite, and magnetite. Statistical and comparative analyses of the 28 most common organic acids revealed that the production of these secondary metabolites by T. flavus was highly mineral-specific and that their content varied significantly in response to the different minerals. Moreover, the component composition of the secondary metabolites of T. flavus interacting with lizardite was more similar to chlorite and magnetite than to antigorite, hornblende, and quartz. Strong correlations were found between the production of gluconic, oxalic, citric, and itaconic acid and the bioavailability of certain elements. Fumaric and orsellinic acid production were stimulated by magnetite and chlorite, respectively. These results demonstrate that fungi can significantly regulate their metabolic behavior during interactions with minerals and that their metabolic regulation is primarily related to the chemical composition, weatherability, and surface properties of the minerals. Such biotic and abiotic responses have important implications for the fungus-induced geochemical transformation of minerals and metals.

Subduction of atmospheric noble gases has been considered to play an important role in altering the primordial isotopes of Earth’s mantle over geological time. Analysis of natural samples and experiments indicate that large quantities of noble gases can be dissolved in volatile-bearing hydrous minerals in the subduction slabs. To quantitatively investigate the recycling efficiency of noble gases and relevant consequences on the mantle noble gas isotopic evolution, the diffusivities of noble gases in these minerals are needed. In this study, diffusion of He, Ne, Ar, Kr and Xe in lizardite, antigorite and tremolite have been calculated by first-principles methods based on density functional theory. Our results disclose that diffusion is slower with increasing radius of the noble gas atom (DHe > DNe > DAr > DKr > DXe) as expected. The common ring-structures in hydrous silicate minerals provide incorporation sites for the noble gas atoms and control their mobility. The diffusion activation energies are 84.9, 157.3, 287.5, 347.4, 414.9 kJ/mol from He to Xe in lizardite, and despite the very similar lattice structure between lizardite and antigorite, the activation energies are found to be significantly higher in antigorite, which are 120.6, 267.3, 449.6, 497.9 and 550.0 kJ/mol, respectively. In tremolite, the energy barriers are 93.6, 158.2, 266.3, 322.2 and 385.0 kJ/mol, which are also found to be in very good agreement with available experimental values and similar to those in lizardite. We also calculated diffusion activation energies at higher pressures (1 GPa for liazardite, 3 GPa for antigorite and tremolite) to better understand how much noble gases can be preserved against diffusive loss during subduction. Our result show that the oceanic crust and the lithospheric mantle of the subduction slab play different roles in delivering noble gases into the mantle. We find that all Ar, Kr, Xe and possibly part of the Ne can be entrained by the serpentine-dominated lithospheric mantle into the deep mantle due to the high diffusive energy barriers in antigorite. In contrast, noble gases in the amphibole-enriched oceanic crust would be characterized by fractionated noble gas signature, with the concentrations of retained noble gases in the crust following their respective ionic radius (Ne

In this study, clay-soil organic matters (SOMs) interactions were investigated by combining first principles molecular dynamics (FPMD) and classical molecular dynamics (CMD) techniques. FPMD was employed to quantify the binding mechanisms of reactive SOMs groups on clay surfaces and to derive parameters for the bonding of the reactive groups on edge surfaces. By integrating the derived parameters with CVFF–CLAYFF force fields, CMD simulations were carried out to investigate the structures of large models of clay-SOMs associations. All possible reactive SOMs groups, including carboxylate, phosphate, quinone species and ammonium groups were taken into account. FPMD results showed that all these groups are important to the complexation of SOMs on clay surfaces under dry conditions but only chemical bonding of carboxylate and phosphate and cation bridging are of significance under wet conditions. pH dependence of carboxylate and phosphate and Eh-pH dependence of quinone species are presented. CMD simulations showed that SOMs bound on clay surfaces via direct bonding of carboxylate and Ca2+ bridging and revealed the effect of water on structures of the clay-SOMs association. Based on the computational results, a procedure was proposed for constructing realistic molecular models for soils. Possible applications and further improvements of these models are discussed.

The solubilization and mobilization of elements from silicate minerals during fungal weathering are predominantly promoted by acidification and complexation reactions. However, stark differences exist in the release rates of different elements driven by fungal-derived low molecular weight organic compounds (LMWOCs) when acidity maintains constant, raising the question of whether the release of individual element during dissolution is ligand-specific. In this work, we investigate this question by characterizing the release of Mg, Si, Fe, and Ni from lizardite [(Mg, Fe, Ni)3Si2O5(OH)4]. Miniaturized batch reactors (microplate wells of 250 µL) were used in dissolution experiments in the presence and absence of the indigenous fungus Talaromyces flavus. Abiotic chemical weathering experiments with metabolically relevant organics and HCl were also carried out to isolate the vital effects of elemental releases. The initial release rates of Mg, Si, Fe, and Ni were obtained from determining the dissolved elemental concentrations. The results show that T. flavus enhances the release of Mg and Si by a factor of ∼2, but that of Fe and Ni by a factor of >10, relative to the rates measured in the control experiment. Additionally, the measurements show an overexcretion of siderophores and oxalic acid, as well as acidification of bulk solution, during bioweathering. Abiotic chemical dissolution of lizardite confirms the release of Fe and Ni proceeds mainly via a ligand-promoted pathway. In addition, the results indicate that siderophores and oxalic acid are responsible for the solubilization of Fe and Ni, respectively. These findings provide direct evidence that the rate and mechanism of elemental release from silicate during bioweathering are ligand-specific, and both synergistic and inhibitory effects may be involved. Given that siderophore- and oxalic acid-producing fungi are highly active in soils, these results may have the potential to advance our understanding of the critical roles of fungi in rhizosphere geochemistry and ecology.

Aiming at an atomistic mechanism of heavy metal cation complexing on clay surfaces, we carried out systematic first principles molecular dynamics (FPMD) simulations to investigate the structures, free energies and acidity acidity constants of Ni(II) complexes formed on edge surfaces of 2:1 phyllosilicates. Three representative complexes were studied, including monodentate complex on the SiO site, bidentate complex on the Al(OH)2 site, and tetradentate complex on the octahedral vacancy where Ni(II) fits well into the lattice. The complexes structures were characterized in detail. Computed free energy values indicate that the tetradentate complex is significantly more stable than the other two. The calculated acidity constants indicate that the tetradentate complex can get deprotonated (pKa = 8.4) at the ambient conditions whereas the other two hardly deprotonate due to extremely high pKa values. By comparing with the 2 Site Protolysis Non Electrostatic Surface Complexation and Cation Exchange (2SPNE SC/CE) model, the vacant site has been assigned to the strong site and the other two to the weak site, respectively. Thus a link has been built between atomistic simulations and macroscopic experiments and it is deduced that this should also apply to other heavy metal cations based on additional simulations of Co(II) and Cu(II) and previous simulations of Fe(II) and Cd(II)). This study forms a physical basis for understanding the transport and fixation of heavy metal elements in many geologic environments.

In the pursuit of a microscopic understanding of the effects of temperature on the surface reactivity of clay minerals, we conducted first principles molecular dynamics (FPMD) simulations to study the interfacial structures and acidity of clay edge surfaces at elevated temperatures. The common edge surfaces ((0 1 0) and (1 1 0) types) of phyllosilicates were investigated at 348 K and 423 K, and the results were compared with those previously derived at ambient conditions. We found that the stable surface sites are the same as at ambient conditions, including Al(OH2)2 (6-fold Al), Al(OH2) (5-fold Al) and Si(OH) on the (0 1 0) facet, and Al(OH2), Al(OH)Si and Si(OH) on the (1 1 0) surface. The FPMD-based vertical energy gap technique was applied to compute the acidity constants of edge sites and the resulting pKa values show a decreasing trend with temperature. The results demonstrate that although changes in the point of zero charge of the entire material are insignificant up to 348 K, the decrease in surface pKa can be 3 pKa units, while it can be as large as 6 pKa units up to 423 K. The derived interface structures and pKa values can be used in future experimental and modeling research, e.g., in interpreting experiments and predicting the surface complexation of metal cations and organics. This study therefore provides a physical basis for investigating the interfacial processes of clay minerals in environments that experience elevated P–T conditions, such as sedimentary basins and geological nuclear waste repositories.

We report a first principles molecular dynamics (FPMD) study of the acid chemistry of 2:1-type dioctahedral phyllosilicates. Using the FPMD based vertical energy gap method, we computed intrinsic acidity constants of phyllosilicate edge sites. The investigated models include both neutral and charged frameworks (i.e., Mg for Al replacement in octahedral sheets and Al for Si replacement in tetrahedral sheets) and the common edge surface types (i.e., (0 1 0) and (1 1 0)). The result of the neutral framework agrees with the experiment of pyrophyllite. For charged frameworks, it is found that Al(OH) sites in T-sheets (i.e., Al-sub) and Mg( OH 2 ) sites (i.e., Mg-sub) have extremely high pKas and thus they all keep protonated. Both types of substitutions increase pKas of the apical oxygen sites on (1 1 0) surfaces and Mg substitution also increases the pKas of neighboring silanol sites. With the calculated pKas, we explore the mechanism of heavy metal cations complexation on edge surfaces. As a quantitative basis, the results in this work can be used in future modeling and experimental studies for understanding acid reactivity of phyllosilicates.

In supergene environments, microbial activities significantly enhance sulfide oxidation and result in the release of heavy metals, causing serious contamination of soils and waters. As the most commonly encountered arsenic mineral in nature, arsenopyrite (FeAsS) accounts for arsenic contaminants in various environments. In order to investigate the geochemical behavior of arsenic during microbial oxidation of arsenopyrite, (2 3 0) surfaces of arsenopyrite slices were characterized after acidic (pH 2.00) and oxidative decomposition with or without an acidophilic microorganism Acidithiobacillus ferrooxidans. The morphology as well as chemical and elemental depth profiles of the oxidized arsenopyrite surface were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. With the mediation of bacteria, cell-shaped and acicular pits were observed on the reacted arsenopyrite surface, and the concentration of released arsenic species in solution was 50 times as high as that of the abiotic reaction after 10 days reaction. Fine-scale XPS depth profiles of the reacted arsenopyrite surfaces after both microbial and abiotic oxidation provided insights into the changes in chemical states of the elements in arsenopyrite surface layers. Within the 450 nm surface layer of abiotically oxidized arsenopyrite, Fe(III)-oxides appeared and gradually increased towards the surface, and detectable sulfite and monovalent arsenic appeared above 50 nm. In comparison, higher contents of ferric sulfate, sulfite, and arsenite were found in the surface layer of approximately 3 μm of the microbially oxidized arsenopyrite. Intermediates, such as Fe(III)-AsS and S0, were detectable in the presence of bacteria. Changes of oxidative species derived from XPS depth profiles show the oxidation sequence is Fe > As = S in abiotic oxidation, and Fe > S > As in microbial oxidation. Based on these results, a possible reaction path of microbial oxidation was proposed in a concept model.

In this paper, we report a first principles molecular dynamics (FPMD) study of the acid–base chemistry of gibbsite. With FPMD based vertical energy gap technique, the acidity constants of the sites on the basal surface (i.e. (0 0 1)) and the edge surface (1 0 0) are derived and the results overall indicate that l(OH 2 ) 2 groups on the edge surface are the major acidic sites. The free-energy calculation indicates that both the 6-fold (i.e. Al(OH 2 ) 2 ) and 5-fold (i.e. Al(OH 2 )) coordination states of edge Al atoms are probable with the former being much more stable. The 6-fold forms have very similar 1st and 2nd acidity constants in 9.0–10.0, which agrees with the experimental PZC (point of zero charge) range. The 5-fold forms have a very low p K a of about 2.0, which indicates that its common form is Al(OH) within normal pH range. The doubly coordinated site (i.e. Al 2 (OH)) on the edge surface has a very high p K a of about 13.0, indicating that the proton dissociation rarely happens. For the basal surface, the hydroxyl groups almost do not have contribution to the acid–base chemistry of gibbsite. On this surface, some OHs keep orientation parallel to the surface and therefore they can only perform as proton acceptors. However, their protonated states have very low p K as of around 1.3. The other OHs have an extremely high p K a (about 22.0), indicating no dissociation in common pH. Overall, this study provides atomic-scale understanding on the acid–base chemistry of gibbsite and the derived interfacial structures and acidity constants form a basis for future research on the interfacial processes of Al–hydroxides.

Acid–base chemistry of clay minerals is central to their interfacial properties, but up to now a quantitative understanding on the surface acidity is still lacking. In this study, with first principles molecular dynamics (FPMD) based vertical energy gap technique, we calculate the acidity constants of surface groups on (0 1 0)-type edges of montmorillonite and kaolinite, which are representatives of 2:1 and 1:1-type clay minerals, respectively. It shows that Si–OH and Al–OH2OH groups of kaolinite have pKas of 6.9 and 5.7 and those of montmorillonite have pKas of 7.0 and 8.3, respectively. For each mineral, the calculated pKas are consistent with the experimental ranges derived from fittings of titration curves, indicating that Si–OH and Al–OH2OH groups are the major acidic sites responsible to pH-dependent experimental observations. The effect of Mg substitution in montmorillonite is investigated and it is found that Mg substitution increases the pKas of the neighboring Si–OH and Si–OH2 groups by 2–3 pKa units. Furthermore, our calculation shows that the pKa of edge Mg–(OH2)2 is as high as 13.2, indicating the protonated state dominates under common pH. Together with previous adsorption experiments, our derived acidity constants suggest that Si–O– and Al–(OH)2 groups are the most probable edge sites for complexing heavy metal cations.

We report first-principles molecular dynamics (FPMD) studies on the structures of interfaces between phyllosilicate edges and water. Using FPMD, the substrates and solvents are simulated at the same first-principles level, and the thermal motions are sampled via molecular dynamics. Both the neutral and charged silicate frameworks are considered, and for charged cases, the octahedral (Mg for Al) and tetrahedral (Al for Si) substitutions are taken into account. For all frameworks, we focus on the commonly occurring (0 1 0)- and (1 1 0)-type edge surfaces. With constrained FPMD, we calculated the free energy of the leaving processes of coordinated water of octahedral cations; therefore, the coordination states of those edge cations are determined. For (0 1 0)-type edges, both the 5- and 6-fold coordination states of Al are stable and occur with a similar probability, whereas only the 5-fold coordination is stable for Mg cations. For (1 1 0)-type edges, only the 6-fold states of Al cations are stable. However, for Mg cations, both coordination states are stable. In the 5-fold case, the solvent water molecules form H-bonds with the bridging oxygen atoms (i.e., Mg O Si ). The free energy results indicate that there should be a considerable number of 5-fold coordinated octahedral sites (i.e., Mg OH/ Al OH) at the interfaces. The interfacial structures and acid/base groups were determined by detailed H-bonding analyses. (1) Bridging oxygen sites. For (0 1 0) edges, the bridging oxygen atoms are not effective proton-accepting sites because they are inaccessible from the solvent. For (1 1 0) edges, the oxygen atoms of neutral and octahedrally substituted frameworks (i.e., M O Si for M Al/Mg) are proton-accepting sites. For T-sheet substituted cases, the bridging oxygen site becomes a proton-donating group (i.e., Al OH Si ) through the capture of a proton. (2) T-sheet groups. All T-sheet edge groups are M OH (M Si/Al) and act as both proton donors and acceptors. (3) O-sheet groups. For (0 1 0) edges with 6-fold Al, the active surface groups include Al (OH)(H2O) and Al (OH)2, whereas for Mg cations, the edge group is Mg (OH2)2. For 5-fold coordination, the active groups are Al OH. At (1 1 0) edges, proton-donating sites include Al OH, Al OH2 and Mg OH2 groups. Overall, our results reveal the significant effects of isomorphic substitutions on the interfacial structures, and the models provide a molecular-level basis for understanding relevant interfacial processes.

The acid chemistry of confined waters in smectite interlayers have been investigated with first principles molecular dynamics (FPMD) simulations. Aiming at a systematic picture, we establish the model systems to take account of the three possible controlling factors: layer charge densities (0 e, 0.5 e and 1.0 e per cell), layer charge locations (tetrahedral and octahedral) and interlayer counterions (Na+ and Mg2+). For all models, the interlayer structures are characterized in detail. Na+ and Mg2+ show significantly different hydration characteristics: Mg2+ forms a rigid octahedral hydration shell and resides around the midplane, whereas Na+ binds to a basal oxygen atom and forms a very flexible hydration shell, which consists of five waters on average and shows very fast water exchanges. The method of constraint is employed to enforce the water dissociation reactions and the thermodynamic integration approach is used to derive the free-energy values and the acidity constants. Based on the simulations, the following points have been gained. (1) The layer charge is found to be the direct origin of water acidity enhancement in smectites because the neutral pore almost does not have influences on water dissociations but all charged pores do. (2) With a moderate charge density of 0.5 e per cell, the interlayer water shows a pKa value around 11.5. While increasing layer charge density to 1.0 e, no obvious difference is found for the free water molecules. Since 1.0 e is at the upper limit of smectites’ layer charge, it is proposed that the calculated acidity of free water in octahedrally substituted Mg2+-smectite, 11.3, can be taken as the lower limit of acidities of free waters. (3) In octahedrally and tetrahedrally substituted models, the bound waters of Mg2+ show very low pKa values: 10.1 vs 10.4. This evidences that smectites can also promote the dissociations of the coordinated waters of metal cations. The comparison between the two Mg2+-smectites reveals that different layer charge locations do not lead to obvious differences for bound and free water acidities.

To shed light on gold speciation in sulfur-containing ore-forming fluids, we perform first principles molecular dynamics (FPMD) simulations to investigate gold–hydrosulphide complexing under representative geological conditions. With this advanced technique, the electronic structures of solutes and solvents are calculated with density functional theory and the thermal motions are sampled with molecular dynamics. The molecular structures, solvated structures and stabilities of possible complexes are characterized in detail and the following insights have been gained. (1) The previously hypothesized species Au(HS)(H2S)3 and Au(HS) are found unstable under ore-forming conditions. Au(HS)(H2S)3 would dissociate to LAu(HS) (L = H2S or H2O) and free H2S molecules spontaneously. Au(HS) is highly reactive and tends to capture a second ligand to form a double-coordinated complex. (2) In the thin vapor-like phases of low pressures, the stable complexes include Au(HS)(H2O), Au(HS)(H2S) and Au(HS)2− and their relative stability is Au(HS)2− > Au(HS)(H2S) > Au(HS)(H2O). In dense aqueous phases of high pressures, Au(HS)(H2S) would spontaneously deprotonate to Au(HS)2− and thus Au(HS)(H2O) and Au(HS)2− are the stable forms. All of these complexes can retain to the upper-limit of ore-forming temperatures. (3) The gold ions in the complexes do not favor coordinating more molecules and therefore the solvations happen mainly through H-bonding interactions between the ligands and environmental waters. H-bonds are found in vapor, liquid, and dense supercritical phases, whereas in the thin supercritical phase the hydration is very weak. These results provide quantitative and microscopic basis for understanding the speciation of gold in hydrothermal fluids.

To explore the complexation mechanisms of carboxylate on phyllosilicate edge surfaces, we simulate acetate complexes on the (0 1 0) type edge of pyrophyllite by using density functional theory method. We take into account the intrinsic long-range order and all the possible complex sets under common environments. This study discloses that H-bonding interactions occur widely and play important roles in both inner-sphere and outer-sphere fashions. In inner-sphere complexes, one acetate C–O bond elongates to form a covalent bond with surface Al atom; the other C–O either forms a covalent bond with Al or interacts with surface hydroxyls via H-bonds. In outer-sphere complexes, the acetate can capture a proton from the surface groups to form an acid molecule. For the groups of both substrate and ligand, the variations in geometrical parameters caused by H-bonding interactions depend on the role it plays (i.e., proton donor or acceptor). By comparing the edge structures before and after interaction, we found that the carboxylate binding can modify the surface structures. In the inner-sphere complexes, the exposed Al atom can be stabilized by a single acetate ion through either monodentate or bidentate schemes, whereas the Al atoms complexing both an acetate and a hydroxyl may significantly deviate outwards from the bulk equilibrium positions. In the outer-sphere complexes, some H-bondings are strong enough to polarize the metal–oxygen bonds and therefore distort the local coordination structure of metal in the substrate, which may make the metal susceptible to release.

To explore the effects of layer-charge distribution on the thermodynamic and microscopic properties of Cs-smectites, classical molecular dynamic simulations are performed to derive the swelling curves, distributions and mobility of interlayer species, and Cs binding structures. Three representative smectites with distinct layer-charge distributions are used as model clay frameworks and interlayer water content is set within a wide range from 0 to 380 mgwater/gclay. All the three smectites swell in a similar way, presenting the characteristic swelling plateaus and similar trends of swelling energetic profiles. The full-monolayer hydrate, corresponding to the global minima of the immersion energy, is the most stable hydrated state of Cs-smectites. The calculated diffusion coefficients of interlayer species disclose the confining effects in all smectites: both water molecules and ions diffuse slower than corresponding bulk cases and they are much more mobile in the direction parallel to the clay surfaces than perpendicular to them. The formed inner-sphere complex structures are very similar in different smectites: ions bind on the H-sites or T-sites and water molecules form cage-like caps covering the ions. Layer-charge distribution is found to have significant influences on the mobility of interlayer species and preference of ion binding sites. A general sequence is proposed to elucidate the preferences of various hexagonal sites (H-sites) and triangular sites (T-sites), that is, tetrahedrally substituted H-sites > nonsubstituted H-sites > tetrahedrally substituted T-sites > nonsubstituted T-sites, but the influence of octahedral substitutions on the preference of the neighboring sites is not obvious. Analysis of mobility indicates that H-sites are more stable Cs-fixation positions than T-sites and smectite with higher fraction of octahedral charges seems to be the most effective barrier material no matter how water content varies although all smectites can immobilize Cs ions in relatively dry conditions. These findings will not only facilitate basic research in geochemistry and material sciences, but also promote the barrier material designing.