Montmorillonite Surface Research Articles

Adsorption mechanism of Pb2+ in montmorillonite nanopore under various temperatures and concentrations

Adsorption of lead (Pb2+) onto the montmorillonite (Mt) surface is one of the key approaches to remove Pb2+ in geological and environmental engineering. Temperature and initial Pb2+ concentration are two essential factors that influence the adsorption capacity of Mt on absorbing Pb2+. However, the nanoscale governing mechanism of temperature and initial concentration on Pb2+ adsorbing of Mt is still unclear. This research performed comprehensively molecular dynamics (MD) simulations to investigate how temperature and initial concentration affect the dynamic Pb2+ adsorption of Mt nanopore. The Pb2+ removal ratio shows a two-stage variation with the increase of initial Pb2+ concentration. Temperature controls the maximum initial Pb2+ concentration for complete Pb2+ removal by changing the maximum adsorption energy of Mt. Temperature also influences the maximum adsorption capacity and Pb2+ removal ratio of Mt nanopore indirectly by changing diffusion and hydration state of Pb2+. The initial Pb2+ concentration corresponding to the maximum adsorption energy coincides with the maximum initial Pb2+ concentration determined by the Pb2+ removal ratio. Lower adsorption energy and higher level of hydration and diffusion make Pb2+ absorbing on Mt surface become more difficult, reducing the Pb2+ adsorbing capacity of Mt. The initial Pb2+ concentration influences adsorption capacity and Pb2+ removal ratio not only via altering the quantity of Pb2+ but also through controlling the adsorption energy of Mt, as well as the diffusion and hydration state of Pb2+. With the increase of initial Pb2+ concentration, the hydration of Pb2+ is weakened while the adsorption energy of Mt and diffusion of Pb2+ are enhanced.

Competitive Adsorption Processes at Clay Mineral Surfaces: A Coupled Experimental and Modeling Approach

Quantification of adsorption processes on clay mineral surfaces is often necessary to predict the extent and the evolution of contaminants’ migration in surficial and underground environments. Many studies have been dedicated to retention measurement as a function of pH and ionic strength in relation with the two main identified adsorption processes for clay minerals, that is, cation exchange on their basal surfaces and surface complexation on their edge surfaces. The latest process has been repeatedly assessed as an effective retention mechanism at circumneutral pH conditions, which often prevail in natural environments. This assessment must however be tempered by the lack of information about competitive processes that can take place with the numerous chemical species present in natural settings, compared to simplified systems investigated in laboratory experiments. In this study, we quantified experimentally the competition between Pb2+, Co2+, Zn2+, and Mg2+ for specific adsorption on montmorillonite edge surfaces. Zn2+ was an effective competitor with Pb2+ and Co2+, and our results showed also unambiguously the influence of Mg2+ concentration levels on the specific adsorption of Pb2+ and Co2+. Because of the high ionic strength used in the experiments, cation exchange with Mg2+ was dismissed as a possible reason for such competition process, leaving specific competitive adsorption on edge surfaces as a unique explanation for our observations. Modeling of Pb2+ adsorption data with a state-of-art electrostatic complexation model for montmorillonite edge surfaces, supported by state-of-the-art, made it possible to distinguish two types of possible competition driving forces: Zn2+ competition for adsorption site occupancy but also detrimental changes in surface electrostatic potential following Mg2+ adsorption on sites neighboring those of Pb2+ adsorption. Mg2+ competition observed in our experiment should apply in most of clayey environments. Consequently, adsorption data obtained on pure clay mineral phases, and the associated models that have been built based on these data without considering the geochemical background in competitive species, may overestimate the retention properties of clay minerals when applied to natural settings.

Interaction of Indigo carmine with naturally occurring clay minerals: An approach for the synthesis of nanopigments

Dyes are organic colorants used in textile, paint, printing and many more industries for different purposes, especially to make the products more attractive. However, these organic compounds can not be removed easily from water bodies due to their non-biodegradable nature. In this context, this paper aims at the application of clay minerals and their organo forms which were used to remove the anionic dye, Indigo Carmine from aqueous media at different conditions such as pH, contact time and initial concentration by employing batch extraction method. Synthesis of organo clay was done through ion-exchange method using cationic surfactant (Cetylpyridinium chloride). The adsorbents (before and after adsorption of dye) were characterized using different analytical techniques like X – Ray diffraction, Fourier Transform Infra-Red spectroscopy, UV–vis spectroscopy. During the study, it was found that the efficiency for uptake of anionic dye was more for organo clay (Organo Montmorillonite − 330 mg g−1 and Organo Bentonite − 468 mg g−1) at favorable acidic condition as the surface of Montmorillonite and Bentonite become positively charged after interaction with surfactant results in electrostatic interaction between dye and organo clays. As there was no significant change in diffraction peak of adsorbent after interaction with dye suggested the surface interaction of dye which was further supported by FT-IR studies.

Smectite, sepiolite, and palygorskite for inactivation of pyocyanin, a biotoxin produced by drug-resistant Pseudomonas aeruginosa

Pyocyanin is an important virulence factor in the resistance of Pseudomonas aeruginosa to antibiotics. This study evaluated the potential of three clay minerals (smectite, sepiolite, and palygorskite) in binding and degrading pyocyanin. A combination of adsorption experiments, in-situ variable-temperature x-ray diffraction (VTXRD), energy dispersive x-ray spectrometry (EDS), and UV spectroscopy were employed to investigate the (1) adsorption affinity (K) and capacity (Q max ) of clay minerals for pyocyanin, (2) binding sites for adsorption on clay minerals and (3) the degradation/transformation of pyocyanin on clay surfaces. Adsorption experiments were performed at pH3, 4.9, and 7 at which pyocyanin occurred as ∼100% protonated, ∼50% protonated and zwitterionic, and ∼100% zwitterionic species, respectively. Overall, the estimated Q max was 0.23-0.53 mol/kg for sepiolite, 0.21-0.43 mol/kg for palygorskite, and 0.43-0.68 mol/kg for montmorillonite. The Q max and K were pH dependent: pH3 < pH7 for sepiolite, pH3 > pH7 for palygorskite, and pH3≈pH4.9>pH7 for montmorillonite. Pyocyanin was mainly adsorbed in the tunnels of sepiolite, external surface of palygorskite, and the interlayer of montmorillonite. The clays did not degrade pyocyanin, instead the structure was slightly transformed on the surfaces of sepiolite and montmorillonite. These results demonstrated the potentials of clay minerals in disarming P. aeruginosa through adsorbing the virulence factor pyocyanin. • Adsorption of pyocyanin by sepiolite, palygorskite and montmorillonite was investigated. • Adsorption (mol/kg) ranged from 0.23 to 0.53 (sepiolite), 0.21 to 0.43 (palygorskite), and 0.43 to 0.68 (montmorillonite). • The surfaces of sepiolite have higher affinity for zwitterionic pyocyanin. • Palygorskite and montmorillonite surfaces have higher affinity for protonated pyocyanin. • Adsorption occurred mainly in the tunnels of sepiolite, external surface of palygorskite and interlayer of montmorillonite.

THE ORGANIC MODIFICATION OF PRE-LITHIATED MONTMORILLONITE

The use of mineral/polyimide composites for lithium-ion battery separators provides an outstanding development direction. Minerals that can be used for lithium-ion battery separators are minerals that have good pores size and distribution, can be intercalated with lithium-ions, and are hydrophobic. Montmorillonite is a natural mineral belonging to the smectite group, and has the capacity to exchange cations but is hydrophilic so it is necessary to modify it to make it hydrophobic and to keep it rich in lithium ions for such purpose. In this study, organic modification has been carried out to change the hydrophilic nature of montmorillonite to become hydrophobic under lithium-ion-rich conditions. Montmorillonite was first isolated by sonicating the dispersion, then carefully separating its suspension after several days of aging. Afterward, the suspension was precipitated by centrifugation and finally dried at 80°C. Thereafter, carbonate cations, organic compounds, and metal oxides, especially ferrous oxide, are removed. The purified isolated montmorillonite is then lithiated with lithium chloride. Finally, the surface of the pre-lithiated montmorillonite was modified with cetyltrimethylammonium bromide to obtain organic-modified pre-lithiated montmorillonite. The results of characterization with an infrared spectrophotometer showed vibration peaks at 2928 cm-1, 2854 cm-1, and 1476 cm-1 as evidence of the presence of attached cetyltrimethylammonium, and vibration peaks at 520 cm-1 and 463 cm-1 as evidence of the presence of attached lithium. The results were also characterized by SEM and XRD which shows that the montmorillonite was organically modified, and lithium intercalated.

Insights into the Influence Mechanism of Different Interlayer Cations on the Hydration Activity of Montmorillonite Surface: A Dft Calculation

Insights into the Influence Mechanism of Different Interlayer Cations on the Hydration Activity of Montmorillonite Surface: A Dft Calculation

Adsorption of cationic surfactant as a probe of the montmorillonite surface reactivity in the alginate hydrogel composites.

Adsorption of a cationic surfactant allowed to probe the surface reactivity of montmorillonite encapsulated in a composite of alginate hydrogels (A-MMT). Dodecylbenzyldimethylammonium chloride (BAC-12) was the surfactant used for these studies. BAC-12 is part of the widely used surfactant mixture known as benzalkonium chloride. XRD showed that up to three different types of basal spacing (d 001) were present within the composite indicating that as the concentration of adsorbed BAC-12 increases, populations with different adsorption conformational arrangements are present, even unexpanded clay remains. From the SEM-EDS spectra it is observed that the clay is distributed in the whole composite. In addition, the effect of the presence of cationic and anionic biocides on BAC-12 adsorption was studied. Cationic biocides such as tetradecyllbenzyldimethylammonium chlorides (BAC-14) and paraquat (PQ) show a competitive behavior for the clay adsorption sites at BAC-12 low concentration indicating an electrostatic adsorption mechanism. However, the presence of anionic contaminants such as 2,4-D and metsulfuron methyl do not affect surfactant adsorption. In all scenarios is observed an abrupt increase of BAC-12 adsorbed amount reaching values higher than the clay CEC suggesting strong tail-tail interactions. This occurs at concentrations 10 times lower than the CMC of BAC-12 promoted by clay encapsulation in the composite. In these composites the alginate does not affect the surface reactivity of the clay, but the formation of the hydrogel allows it to be easily extracted from aqueous media which makes it an interesting material with a potential use in water remediation.

Molecular Dynamic (MD) Simulations of Organic Modified Montmorillonite

This study complements the knowledge about organobentonites, which are intended to be new binders in foundry technology. In the developed materials, acrylic polymers act as mineral modifying compounds. Modification of montmorillonite in bentonite was carried out in order to obtain a composite containing a polymer as a lustrous carbon precursor. The polymer undergoes thermal degradation during the casting process, which results in the formation of this specific carbon form, ensuring the appropriate quality of the casting surface without negative environmental impact. The present paper reports the results of computational simulation studies (LAMMPS software) aimed at broadening the knowledge of interactions of organic molecules in the form of acrylic acid and acrylate anions (from sodium acrylate) near the montmorillonite surface, which is a simplified model of bentonite/acrylic polymer systems. It has been proven that the –COOH group promotes the adsorption of acrylic acid (AA) to the mineral surface, while acrylate ions tend to be unpredictably scattered, which may be related to the electrostatic repulsion between anions and negatively charged clay surfaces. The simulation results are consistent with the results of structural tests carried out for actual organobentonites. It has been proven that the polymer mainly adsorbs on the mineral surface, although it also partially intercalates into the interlayer spaces of the montmorillonite. This comprehensive research approach is innovative in the engineering of foundry materials. Computer simulation methods have not been used in the production of new binding materials in molding sand technology so far.

Cellulose hydrogel coated nanometer zero-valent iron intercalated montmorillonite (CH-MMT-nFe0) for enhanced reductive removal of Cr(VI): Characterization, performance, and mechanisms

Cellulose hydrogel coated nanometer zero-valent iron intercalated montmorillonite (CH-MMT-nFe0) was innovatively designed and fabricated, and applied for the removal of Cr(VI). The composite was characterized with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The addition of MMT and CH improved the dispersity, oxidation resistance and stability of nFe0, and the removal rate of Cr(VI) was up to 98%. At the same time, the interlayer limit of montmorillonite reduced the particle size of nFe0 and increased the activity of nFe0. The formation of “micro reactor” between montmorillonite and iron surface promoted the adsorption and degradation of Cr(VI). Hydrogels had good mesoporous network structure and functional groups such as amides and carboxylic acids. They provided.additional active sites and promoted mass transfer. The multiple interaction mechanisms of CH– MMT-nFe0 on Cr(VI), such as adsorption, reduction and co-precipitation were realized. The material was a potential Cr(VI) polluted wastewater remediation material.

Recent advances in engineering montmorillonite into catalysts and related catalysis

ABSTRACT Montmorillonite, a ubiquitous clay mineral, has been engineered into a variety of porous and nanostructured catalysts, owing to its peculiar layered structure with characteristic surface and intercalation chemistry. Such a class of catalysts have continuously received considerable attention in both science and industry. This review examines recent advance in engineering montmorillonite into metal ion-exchanged montmorillonite catalysts, acid-activated montmorillonite catalysts, organo-montmorillonite catalysts, pillared interlayered montmorillonite catalysts and montmorillonite-supported catalysts. The former two types of montmorillonite-based catalysts have been used in the catalytic cracking, dehydration, hydrolysis, esterification, polymerization, alkylation, and Fischer-Tropic synthesis. The introduction of oxide pillars in the interlayer space of montmorillonite and the immobilization of metal oxides or zero-valent metals on the surface of montmorillonite allow montmorillonite to be used in the catalytic oxidation, reduction, isomerization and coupling reactions. Currently, the role of montmorillonite in acid catalysis, redox catalysis, and free radical catalysis have been partly revealed. The effect of the structures and the active sites of modified montmorillonite on its catalytic performance need to be investigated in more detail. Future work is suggested to focus on solving engineering problems and exploring novel catalytic applications of montmorillonite, in particular exfoliated montmorillonite nanolayers.

Effect of γ-Fe2O3 nanoparticles on the composition of montmorillonite and its sorption capacity for pyrene

Fe content and distribution on montmorillonite would probably enhance its sorption capacity for hydrophobic organic pollutants. Thus, Fe modified montmorillonites with different ratios of FeSO4·7H2O and Ca-montmorillonite were prepared. The results indicated that γ-Fe2O3 nanoparticles were not only generated at the montmorillonite surfaces, but that the γ-Fe2O3 also extended the edges of montmorillonite surfaces. The sorption capacities for pyrene were enhanced and even reached 834.79 μg g−1 with increase in ferrous iron content, but were then suppressed due to aggregation of γ-Fe2O3 on montmorillonite surfaces. Furthermore, pyrene was directly observed on γ-Fe2O3-montmorillonite surfaces with a lattice spacing parameter of approximately 0.27 nm, indicating that a new phase that mainly contained pyrene was generated during the sorption process. Additionally, after regenerating the γ-Fe2O3-montmorillonite composites, they could be reused for at least 5 cycles. It is therefore proposed that the prepared γ-Fe2O3-montmorillonite could be exploited as a potential green composite for remediation of hydrophobic organic pollutants in soil and sediment.

Reactive Transport Modelling of the Long-Term Interaction between Carbon Steel and MX-80 Bentonite at 25 °C

The geological disposal in deep bedrock repositories is the preferred option for the management of high-level radioactive waste (HLW). In some of these concepts, carbon steel is considered as a potential canister material and bentonites are planned as backfill material to protect metallic waste containers. Therefore, a 1D radial reactive transport model has been developed in order to better understand the processes occurring during the long-term iron-bentonite interaction. The numerical model accounts for diffusion, aqueous complexation reactions, mineral dissolution/precipitation and cation exchange at a constant temperature of 25 °C under anoxic conditions. Our results suggest that Fe is sorbed at the montmorillonite surface via cation exchange in the short-term, and it is consumed by formation of the secondary phases in the long-term. The numerical model predicts precipitation of nontronite, magnetite and greenalite as corrosion products. Calcite precipitates due to cation exchange in the short-term and due to montmorillonite dissolution in the long-term. Results further reveal a significant increase in pH in the long-term, while dissolution/precipitation reactions result in limited variations of the porosity. A sensitivity analysis has also been performed to test the effect of selected parameters, such as corrosion rate, diffusion coefficient and composition of the bentonite porewater, on the corrosion processes. Overall, outcomes suggest that the predicted main corrosion products in the long-term are Fe-silicate minerals, such phases thus should deserve further attention as a chemical barrier in the diffusion of radionuclides to the repository far field.

Anisotropic hydrogels with enhanced mechanical and tribological performance by magnetically oriented nanohybrids

Most current hydrogels have weak mechanical properties and unordered structures, which limits their applications. However, soft tissues with highly ordered hierarchical nanocomposite structures exhibit anisotropic mechanical performance and function to adapt the complex environments. Therefore, the introduction of an ordered nanocomposite structure into hydrogel is an effective strategy to endow the hydrogel with superb mechanical strength and excellent anisotropic functions. Here, we develop a method to create anisotropic hydrogels with significantly enhanced mechanical and tribological properties. Based on mussel adhesion chemistry, polydopamine (PDA) was used as a mediator to control the formation of Fe3O4 nanoparticles on the surface of montmorillonite (MMT). Subsequently, the obtained PDA-Fe3O4-MMT nanohybrids in the polyvinyl alcohol/polyacrylic acid (PVA/PAA) hydrogel matrix were aligned to form an ordered structure using magnetic-induced technology and then frozen in hydrogel form by freezing-thawing and annealing methods. The resulting hydrogels showed an anisotropic microstructure and exhibited outstanding mechanical properties with a tensile strength of 10.65 MPa, toughness of 52.2 MJ/m3, and compressive strength of 4.86 MPa, which is higher than that of the corresponding isotropic hydrogel. More interestingly, the friction coefficient of hydrogel is significantly reduced to as low as 0.038 due to the presence of ordered structure. This work not only improves magnetic induction technology for the preparation of anisotropic hydrogels but also provides a simple and effective method to obtain hydrogels with anisotropic structure, high mechanical strength, and anisotropic properties for potential application in tissue engineering.

Synergistic sorption/photo-Fenton removal of typical substituted and parent polycyclic aromatic hydrocarbons from coking wastewater over CuO-Montmorillonite

Polycyclic aromatic hydrocarbons (PAHs) and substituted PAHs (SPAHs) are commonly persistent organic pollutants that are found in different industrial and agricultural wastewaters. In the present research study, we investigated the purification of coking wastewater containing mixed 16 PAHs and 18 SPAHs using CuO decorated montmorillonite (CuO-M) under solar light. For better removal efficiency, H2O2 was added to make the photo-Fenton reaction into action. Due to the complexity of this coking wastewater, the purification was carried out in two runs. The results showed that, by using CuO-M/H2O2/light, 66% of the total yield of PAHs and SPAHs was removed from coking wastewater within 4 h. The second treatment run led to a further increase in the removal rate up to 91% of total pollution. Different synergetic mechanistic pathways such as the adsorb & shuttle process, generation of reactive oxygen species (ROSs) by photoactive CuO on the montmorillonite surface, and photo-Fenton ROSs generation in bulk water catalyzed by CuO and H2O2 are responsible for the effective removal of PAHs and SPAHs. Even though the study was established under well-controlled lab conditions, we should say that the CuO-M/H2O2/light system showed excellent performance in removing a significant part of PAH and SPAH compounds that might make it a potential alternative/cooperative to be involved in wastewater treatment plant (WWTP) to purify the same coking wastewater.

Determination of Surface Acidity on The Natural and Synthetic Montmorillonite Clays by Titration Method

Determination of surface acidity on the natural and synthetic montmorillonite clays has been carried out using the acid-base titration method to count the number of bound acid sites per gram of clay. The total acidity of natural and synthetic montmorillonite surfaces obtained was 4.67 and 5.33 mmol/g, respectively. FTIR analysis results indicate the presence of functional groups from the tetrahedral and octahedral constituents. Both samples have similar absorption patterns. The similarity of absorption patterns was followed by a decrease in intensity and shift in some absorption bands, and the appearance of new absorption bands.

Montmorillonite facilitated Pb(II) biomineralization by Chlorella sorokiniana FK in soil

In this study, Chlorella sorokiniana FK, isolated from lead-zinc tailings, was employed for Pb(II) biomineralization with or without montmorillonite (MMT) addition in soil. Batch experiment results showed that montmorillonite facilitated Pb3(CO3)2(OH)2 formation on the surface of Chlorella-MMT composite, thus increasing algal cells’ tolerance to Pb(II) poisoning. Surprisingly, Pb(II) adsorbed and biomineralized by Chlorella-MMT composite was 2.69 times and 3.76 times as much as that by Chlorella alone, respectively. The montmorillonite facilitated Chlorella-induced Pb biomineralization by promoting both photosynthesis and urea hydrolysis, mainly due to more hydroxyl functional groups generated during its binding with Chlorella and its high pH buffering capacity. Moreover, the SEM-EDS analysis indicated that the biomineral particles shifted from algal cell surface to montmorillonite surface in the composite during long-term Pb-detoxification. In-situ soil Pb(II) remediation experiments with Chlorella-MMT composites further showed that Pb was immobilized as carbonate form in the short term and as residue fraction in the long term. This study made the first attempt to explore the facilitating effects of montmorillonite on metal-carbonate precipitation mediated by microalgae and to develop a green, sustainable, and effective strategy for immobilization of heavy metal in soil by combining clay minerals and microalgae.

Cation adsorption at permanently (montmorillonite) and variably (quartz) charged mineral surfaces: Mechanisms and forces from subatomic scale

In this study, the adsorption behavior of monovalent cations Li+, Na+, and Cs+ in LiCl, NaCl, and CsCl solutions, respectively, on montmorillonite and quartz surfaces were investigated to reveal adsorption mechanisms at the subatomic scale. The results showed that on the permanently charged montmorillonite surface, both strong-force zero-order and weak-force first-order kinetics were present, whereas only weak-force first-order kinetics were observed on the variably charged quartz surface. Based on the recently established asymmetric orbital hybridization theory to describe cation adsorption at charged surfaces, the origins of the adsorption forces of cations on the two differently charged surfaces were evaluated and quantitatively distinguished. It was concluded that the different forces and their strengths resulted in the differences between the cation adsorption mechanisms at montmorillonite and quartz surfaces. For each type of cation, the total adsorption energy at the montmorillonite surface was much larger than that at the quartz surface; the former was up to three times larger than the latter, depending on the cation concentration. The main forces for cation adsorption at the montmorillonite surface were the electrostatic force and force from asymmetric orbital hybridization, depending on cation type. The main force for cation adsorption at the quartz surface was electrostatic force at a cation concentration of 0.001 mol/L, whereas at a cation concentration of 0.01 mol/L, the electrostatic force approached zero and adsorption was driven by the dispersion force.

Immobilization of aldehyde dehydrogenase on montmorillonite using polyethyleneimine as a stabilization and bridging agent

In the following study the tetrameric enzyme, aldehyde dehydrogenase (ALDH - 228 kDa), was immobilized on montmorillonite using polyethyleneimine (PEI) as a bridging agent. Previous studies have shown that small enzymes such as laccases and peroxidases exhibit increased stability and enhanced activity over time when immobilized on the surface of clay minerals. However, low-cost immobilization methods for high MW, multimeric enzymes, are lacking because these enzymes are prone to disassociation and deactivation upon adsorption. Herein, ALDH was successfully immobilized by pre-stabilization with a polyelectrolyte prior to adsorption on the surface of montmorillonite. The resulting complex was characterized in terms of enzyme conformation and loading using zeta potential, SEM, FTIR, and TGA measurements. Aldehyde transformation activity was measured by following benzaldehyde transformation to benzoic acid and NADH formation. An optimal ALDH:PEI ratio of 4:1 (w/w) was identified, yielding the highest activity at the adsorbed state due to conformational stability. The adsorption isotherm best fit the dual Langmuir-Freundlich model and revealed a significantly high loading capacity of 6.2 mg protein per mg montmorillonite. Rate experiments showed that although activity was maintained at the adsorbed state, the immobilization slowed aldehyde transformation, probably due to diffusion limitations caused by aggregation and heterogeneity of the material. Overall, the results suggest that this method has the potential to efficiently immobilize large multimeric proteins. This in turn can help solve separation issues and advance the design of efficient platforms for bio-catalysis and bioremediation technologies.

Mechanistic understanding of antimony(V) complexation on montmorillonite surfaces: Insights from first-principles molecular dynamics

Clay minerals play a vital role in retaining antimony (Sb) by surface complexation, which can largely attenuate its mobility and availability. However, a profound understanding of the environmental process of Sb on clay-water interface is insufficient. In this study, aiming to quantitatively revealing the complexation mechanism of Sb(V) onto montmorillonite at the molecular scale, we performed first-principles molecular dynamics (FPMD) simulations to systematically investigate the related structural and energetic information. In interlayer space, [Sb(OH)6]- anion can bind with Ca2+/Na+/Al3+/Fe3+ as stable inner-sphere complexes, and the Sb-Al/Fe complex is much more favorable than Sb-Na/Ca complex. On edge surfaces, the ligand exchange processes on possible sites in a wide range of pH have been examined. At (010) edge, [Sb(OH)6]− was adsorbed as bidentate complex on Al-(H2O)(H2O) and Mg-(H2O)(H2O) and monodentate complex on Al-(H2O)(OH), and at (110) edge [Sb(OH)6]− formed monodentate complex on Al-(H2O) and Mg-(H2O). The desorption free energies indicated that the Sb-Al bidentate complex is the most stable and favorable edge species, followed by the Sb-Mg bidentate complex. Overall, this work provides the molecular-scale insights into the fate of antimony in natural environments, and the derived fundamental data contribute to improving the experiment-based surface complexation models (SCM).

Polyacrylic Acid to Improve Flotation Tailings Management: Understanding the Chemical Interactions through Molecular Dynamics

Molecular dynamic simulations of polyacrylic acid polyelectrolyte (PAA) analyzed its interaction with the main minerals that make up characteristic tailings of the mining industry, in this case, quartz, kaolinite, and montmorillonite. The simulations were carried out with the package Gromacs 2020.3. The interaction potentials used were General AMBER Force Field (GAFF) for PAA and CLAYFF-MOH for mineral surfaces. The SPC/E model described water molecules and Lennard-Jones 12-6 parameters adjusted for SPC/E model were used for Na+ and Cl− ions. The studied systems were carried out at pH 7, obtaining stable adsorption between the PAA and the studied surfaces. Interestingly, the strongest adsorptions were for montmorillonite at both low and high salt concentrations. The effect of salinity differs according to the system, finding that it impairs the absorption of the polymer on montmorillonite surfaces. However, a saline medium favors the interaction with quartz and kaolinite. This is explained because montmorillonite has a lower surface charge density and a greater capacity to adsorb ions. This facilitated the adsorption of PAA. It was possible to identify that the main interaction by which the polymer is adsorbed is through the hydroxyl of the mineral surface and the COO−Na+ complexes. Molecular dynamics allows us to advance in the understanding of interactions that define the behavior of this promising reagent as an alternative for sustainable treatment of complex tailings in highly saline environments.