Montmorillonite Surface Research Articles

Inversion of Montmorillonite Ion-Exchange Characteristics

The mechanism of montmorillonite modification with sodium metasilicate for inversing its ion-exchange characteristics has been studied. The blockage of the interlayer space in montmorillonite by amorphous silicon–oxygen clusters, which are formed as a result of sodium metasilicate hydrolysis, hinders the access of ions to the internal negatively charged surface of the mineral and increases the strength of bonding between aluminosilicate layers. As a result, adsorption becomes possible only on the outer surface of particles, namely, on active silanol and aluminol groups. This fact has been confirmed by the high rate of the process, as well as by the appearance of the ability to adsorb anions only after the reversal of montmorillonite surface charge. The value of the adsorption of Cr(VI) oxoanions by modified montmorillonite has appeared to be 0.26–1.05 mg/g depending on the synthesis conditions of the samples.

Phototransformation of perfluorooctane sulfonamide on natural clay minerals: A likely source of short chain perfluorocarboxylic acids

In this study, a new phototransformation pathway for perfluorooctane sulfonamide (FOSA) and underlying degradation mechanisms are described. Phototransformation of FOSA in a natural clay mineral (montmorillonite) suspension was compared to that in an aqueous solution. Results showed that the presence of montmorillonite can significantly promote the transformation of FOSA to perfluocarboxylic acids (increasing rate). The phototransformation reaction was found to be initiated by the activation of adsorbed oxygen molecules on the surface of montmorillonite, which generate superoxide anion and hydroxyl radicals. Hydroxyl radicals can then attack FOSA adsorbed onto the surface of montmorillonite, promoting the transformation process. In this reaction, clay minerals played a dual role: providing hydroxyl radicals and concentrating FOSA on their surfaces. This helped to promote the contact and reaction between FOSA and hydroxyl radicals. This study provides the first evidence that heterogeneous oxidation of FOSA at the surface of natural clay minerals may act as an important source of perfluocarboxylic acids (PFCAs), especially short chain PFCAs (i.e. trifluoroacetic acid, TFA).

Connections between Macroscopic Wettability and Lipid Structures on Clay Montmorillonite

Soil organic matter, which includes lipids from bacterial membranes, influences characteristics of soil such as soil water repellency. However, the mechanism that governs the distribution of lipids on mineral surfaces and the consequent alteration of macroscale wettability is unclear. This project investigates phospholipid-clay films to understand how lipids influence wettability. Previous investigations conducted to study the physical characteristics of the lipid-mineral surfaces focused on phosphoethanolamine (PE) lipids on the clay mineral montmorillonite. In this study, the physical characteristics of phosphoglycerol (PG) lipids on montmorillonite were studied. As PE lipids are zwitterionic and PG lipids are negatively charged, these lipids interact with the clay surface differently and can be used to determine how lipid-clay interaction alters wettability. The physical characteristics of the lipid-mineral films were studied using atomic force microscopy and fluorescence microscopy. Atomic force microscopy experiments were conducted to study the topography of the PG-montmorillonite surfaces while fluorescence microscopy was employed to map the distribution of the lipids on the montmorillonite surface. Additionally, wettability experiments were conducted on the surface of the PG-montmorillonite samples to determine the kinetics of water soaking into the film. Physical characteristics were then compared to wettability data to establish causative relationships. We find that the small-scale distribution of lipid aggregates has the most impact on macroscopic wettability for PG lipids, whereas, for PE lipids, the lipid distribution across hundreds of microns was the main influence.

Identification of montmorillonite particle edge orientations by atomic-force microscopy

Statistical information on the edge surface area and edge crystallographic orientation of clay nanoparticle surfaces is essential for proper accounting of the protonation-deprotonation reactions as a part of mechanistic surface complexation models. A combination of atomic-force microscopy (AFM) measurements and molecular dynamics computer simulations made it possible to quantify the relative contributions of the most frequently occurring montmorillonite edge surfaces to the total edge surface area. Edge surfaces normal to the [110] and [010] crystallographic directions are found to be the most abundant (~60% and ~20%, respectively), in agreement with previous estimations.

Effects of salts and adsorption on the performance of air entraining agent with different charge type in solution and cement mortar

In this paper, the effect of salts in solution and the adsorption of surfactant are studied to give the answer why the air entraining agents fail. The high valence cations (e.g. Ca2+) weaken the surface activity of anionic surfactant solution but have no effect on the surface activity of cationic and nonionic surfactant solution. The calcium induces the decreased surface activity of anionic surfactant solution, the low foamability, the big bubble size, and the depressed the air-entraining performance. Anionic surfactant has stronger adsorption on surface of cement than that on surface of montmorillonite, granite and limestone. But cationic and nonionic surfactants have much stronger adsorption on surface of montmorillonite and granite than that on surface of cement. When montmorillonite, granite and limestone are added into cement mortar, the air-entraining performance of anionic surfactant is not depressed, but the air-entraining performance of cationic and nonionic surfactants are obviously depressed.

Chemisorption mechanism of crude oil on soil surface

One of the main challenges in cleaning crude oil-contaminated soil is the unknown adsorption mechanism between residual oil and soil. Herein, infrared spectrometer (IR) is used to detect the existence of dibutylphthalate (DBP) and pelargonamide on montmorillonite (MMT) surface. In addition, after the adsorption of DBP and pelargonamide on MMT, the bands in fingerprint region of the two IR spectra are almost identical, indicating coordination bonds were formed on the surface of MMT. X-ray photoelectron spectroscopy (XPS) is employed to detect the chemical environment of N, O and Al. The reverse migration of Al2p spectrum and forward migration of N1s and O1s spectra indicate the coordination adsorption of carbonyl and amine groups on MMT surface. Then, density functional theory (DFT) calculations are applied to make a further explanation of the bonding mechanisms of DBP and pelargonamide onto MMT surfaces. The result shows that there are two types of aluminum on the surface of MMT acting as Lewis acid sites in coordination adsorption, namely Al3+/Si4+ isomorphic substitutions and Al3+ adsorbed on MMT by means of electrostatic adsorption. Meanwhile, the oxygenium on the surface of MMT acts as Brønsted bases in hydrogen bonding adsorption.

Effect of synthetic Beishan site water and cement solutions on the mineralogy and microstructure of compacted Gaomiaozi(GMZ) bentonite

The mineral alteration and microstructure evolution of compacted GMZ bentonite was investigated during the long-term in the Beishan area, a candidate for a high-level radioactive waste repository in China. The compacted GMZ bentonite samples at initial dry densities of 1.5 and 1.7 Mg/m3 were infiltrated by synthetic Beishan Site Water (BSW) and two synthetic cement solutions (Young Cement Water -YCW and Evolved Cement Water - ECW) under constant volume conditions for about 2 months in this study. X-Ray diffractometry (XRD), mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM-EDS) tests were carried out to observe the mineralogy and microstructure of the specimens after experiencing the three types of pore solutions.There is evidence of cation exchange reactions, some zeolites and C-S-H in the GMZ bentonite after the infiltration of alkaline solutions. The hydration of alkaline solutions and mineralogy alteration result in changes to the microstructure of compacted GMZ bentonite. The generated secondary mineral on the surface of montmorillonite leads to the clogging of inter-aggregate pores. In the case of high dry density, this resulted in pore occlusion.

Research of structure and sorption properties of montmorillonite modified with hexadecylthymethylammonium bromide

The object of research is a natural layered silicate – montmorillonite of the Cherkasy deposit (Ukraine) with the general formula (Ca,Na)(А1,Mg,Fe)2(OH)2[(Si,А1)4О10]×nH2O. The chemical composition of the mineral: SiO2 – 51.9 %, Аl2O3 – 17.10 %, Fe2O3 – 7.92 %, MgO – 1.18 %, Na2O, K2O and CaO up to 2 % and Н2О – 8.78 %. Montmorillonite is characterized by a significant dispersion of particles and the presence of a large number of sorption centers on its surface is capable of cation exchange. One of the most problematic places is that montmorillonite is practically incapable of removing pollutants present in water as anions. In order to obtain sorbents capable of removing heavy metal anions, the surface of montmorillonite was modified with the cationic surfactant hexadecyltrimethylammonium bromide.During the study, X-ray diffraction analysis, scanning electron microscopy, infrared spectroscopy, and thermal analysis were used to study the structure of the initial montmorillonite and its organomodified forms. The spectrophotocolorimetric method is used to study the sorption properties of composites.The work confirms that hexadecyltrimethylammonium bromide molecules are sorbed not only on the outer surface of the particles, but also migrate between the aluminosilicate packets of the layered structure of montmorillonite. Sorption studies have confirmed that the use of organomodified forms of montmorillonite has increased the degree of extraction of chromium (VI) ions from 32 % to 96 %. The resulting sorbents make it possible to purify contaminated water with a chromium (VI) concentration of 1 mg/dm3 to the maximum permissible concentrations. This is due to the fact that the organomodification of the surface of montmorillonite has a number of features and allows to change the structure of the original mineral, as well as recharge the clay surface from negative to positive. This makes it possible to use organoclay to remove inorganic toxicants in anionic forms. Compared with similar known ones, the obtained composites provide the removal of even trace amounts of heavy metal anions from aqueous media.

Binary adsorption of Cu(II) and Ni(II) on Lai'yang bentonite: Kinetics, equilibrium, competition quantitative and mechanisms investigation

AbstractIn this study, the competitive adsorption of Cu(II) and Ni(II) adsorption onto bentonite were investigated. The effects of initial adsorbate concentration, pH, contact time, temperature on adsorption and the kinetics, thermodynamic, quantification of adsorption competition and competitive mechanisms have been studied. The results indicated that Cu(II) has a higher affinity than Ni(II) for adsorption on bentonite. But the inhibition effect was not noticeable under alkaline conditions. The Langmuir and pseudo‐second‐order kinetics models can be applied to simulate the isothermal adsorption and adsorption dynamic, respectively. Under a single system/binary system, the maximum adsorption capacity of bentonite for Cu(II) and Ni(II) is 12.76/10.57 and 11.12/9.11 mg/g, respectively. The equilibrium adsorption capacity reduction rate is suitable for quantitative characterization of adsorption competition under any concentration conditions; adsorption competition coefficient is more suitable for low concentration adsorption; although the distribution coefficient is not suitable for quantitative adsorption competition at high concentrations, it can be used to characterize the variation of adsorption competitiveness of Cu(II) at different concentrations. The higher electronegativity, lower first hydrolysis constant and Misono softness, and a better “guest‐host” consistency between Cu(II)O6 and the vacancies in the montmorillonite octahedral sheet make the higher affinity of Cu(II) to bentonite and result in the possible ion exchange between Cu(II) in solution and adsorbed Ni(II). In addition, at high concentrations, Cu(II) and Ni(II) precipitates formed on the surface of montmorillonite may cause remained Cu(II) ions in the solution unable to enter the internal space of the montmorillonite octahedron.

Emerging WS2/montmorillonite composite nanosheets as an efficient hydrophilic photocatalyst for aqueous phase reactions

Tungsten disulfide (WS2) as one of transition metal dichalcogenides exhibits excellent catalytic activity. However, its catalytic performances in aqueous phase reactions are limited by its hydrophobicity. Here, the natural hydrophilic two-dimensional clay was used to enhance the dispersibility of WS2 in aqueous phase. WS2/montmorillonite (WS2/MMT) composite nanosheets were prepared via hydrothermal synthesis of WS2 on the surface of montmorillonite from WCl6 and CH3CSNH2. The microstructure and morphology show that WS2 nanosheets are assembled parallelly on the montmorillonite with the interface interaction. Through the support of montmorillonite, WS2/MMT possesses higher photocatalytic ability for aqueous phase reactions than WS2, which could be due to the synergistic effect of higher adsorption property, higher hydrophilicity, dispersibility and more catalytic reaction site. The strategy could provide new ideas for obtaining novel hydrophilic photocatalyst with excellent performance.

The immobilized Cu nanoparticles on magnetic montmorillonite (MMT@Fe3O4@Cu): As an efficient and reusable nanocatalyst for reduction and reductive-acetylation of nitroarenes with NaBH4

In this study, the immobilization of copper nanoparticles on superparamagnetic montmorillonite, MMT@Fe3O4@Cu, was studied. Magnetically nanoparticles (MNPs) of iron oxide (Fe3O4) were primarily prepared by a chemical co-precipitation method. Next, the prepared Fe3O4 MNPs were intercalated within the interlamellar spaces and external surface of sodium-exchanged montmorillonite. Finally, Cu NPs were immobilized on magnetic montmorillonite by a simply mixing of an aqueous solution of CuCl2·2H2O with MMT@Fe3O4 followed by the reduction with NaBH4. Characterization of MMT@Fe3O4 clay system represented that through the immobilization of Fe3O4 MNPs, disordered-layers structure of MMT was easily reorganized to an ordered-layers arrangement. The synthesized composite systems were characterized using FT-IR, SEM, EDX, XRD, VSM, BET and ICP-OES analyses. SEM analysis exhibited that dispersion of Cu NPs, with the size distribution of 15–25 nm, on the surface of magnetic clay was taken place perfectly. BET surface analysis indicated that after the immobilization of Fe3O4 and Cu species, the surface area and total pore volume of MMT@Fe3O4@Cu system was decreased. Next, the Cu-clay nanocomposite system showed a perfect catalytic activity towards reduction of nitroarenes to anilines as well as reductive-acetylation of nitroarenes to acetanilides using NaBH4 and Ac2O in water as a green and economic solvent. The copper magnetic clay catalyst can be easily separated from the reaction mixture by an external magnetic field and reused for six consecutive cycles without the significant loss of its catalytic activity.

Distribution and Mobility of Crude Oil-Brine in Clay Mesopores: Insights from Molecular Dynamics Simulations.

The value of crude oil accommodated in shale has been recognized and has attracted increasing attention from the academic and industrial society. The occurrence and mobility of crude oil in clay pores, therefore, become essential issues for evaluation and recovery of shale oil. The distribution, structure, and transport of the oil-brine mixture confined in a slit-shaped montmorillonite mesopore with different water amounts have been investigated using equilibrium molecular dynamics and nonequilibrium molecular dynamics (NEMD) simulations. A mimic model of crude oil, a mixture of 19 organic molecules, was employed, and thus the behavior of different organic molecules could be characterized in detail. A temperature of 410 K and a pressure of 300 atm corresponding to a buried depth of 3 km were employed. The simulations indicate that the water amount determines the distribution of crude oil. Water and metal ions prefer to cover on hydrophilic montmorillonite surfaces, while nonpolar hydrocarbons tend to be far away from clay surfaces. As the water amount is too low to completely cover the clay surfaces, some polar organic molecules will come into contact with the uncovered clay surface. Abundant organic acid molecules adsorb onto montmorillonite surfaces mainly through participating in the inner-sphere complexes of Na+ ions closely located at montmorillonite surfaces (i.e., Na+ cation bridge) and forming hydrogen bonds with water molecules in the vicinity. Carbazole molecules tend to aggregate together due to π-π stacking, while thioether molecules mix within alkane molecules and exhibit no characteristic distributions. The mobility of all oil components decreases with the decrease of the water amount, and the mobility of polar components (i.e., organic acid and carbazole) is relatively lower than that of nonpolar hydrocarbons. NEMD simulations clearly indicate that the transport velocity of crude oil markedly increases with the water amount under a specific pressure gradient. The brine covering on clay surfaces significantly weakens oil-clay interfacial interactions. Polar components, especially organic acid, exhibit relatively low transport velocity compared with nonpolar hydrocarbons. These findings highlight the understanding of physical-chemical behaviors of shale oil and provide atomistic information for technology development for enhancing oil recovery.

Layer Charge Effects on Adsorption and Diffusion of Water and Ions in Interlayers and on External Surfaces of Montmorillonite

Molecular simulations using classical force fields were performed to study the adsorption and diffusion properties of water and ions in the high-charge (Arizona-type) montmorillonite clays with var...

Montmorillonites Can Tightly Bind Glyphosate and Paraquat Reducing Toxin Exposures and Toxicity.

Among the numerous contaminants of soil, glyphosate and paraquat are two of the most widely used herbicides that are commonly detected in the environment. Soil and sediment contaminated with glyphosate, paraquat, and other environmental toxins can be mobilized and redistributed to lawns, vegetable gardens, parks, and water supplies in vulnerable communities at the site of disasters such as hurricanes and flooding. Glyphosate and paraquat bind strongly to soils containing clays, making their bioavailability (bioaccessibility) from these types of soil very low. Because of their affinity for clay-based soils, it is possible that montmorillonite clays could be administered as a therapeutic agent in the diet of animals and humans to decrease short-term exposure and toxicity. In this study, we investigated the sorption mechanisms of glyphosate and paraquat onto active surfaces of calcium montmorillonite (CM) and sodium montmorillonite (SM) clays and derived binding parameters, including capacity, affinity, and enthalpy. Additionally, we used these parameters to predict the reduction in bioavailability under different pH and temperature conditions and to estimate the theoretical dose of clay that could protect against severe paraquat toxicity and lethality. Computational modeling and simulation studies depicted toxin sorption mechanisms at different pH values. Additionally, a toxin-sensitive living organism (Hydra vulgaris) was used to confirm the safety of the clay and its ability to protect against toxicity from glyphosate and paraquat. The high efficacy of CM and SM shown in this study supports the natural binding activity of glyphosate and paraquat to clay-based soils. Following disasters and medical emergencies, montmorillonite clays could be administered by capsules and tablets, or added to food and flavored water, to reduce toxin bioavailability and human and animal exposures.

Electron transfer between sorbed Fe(II) and structural Fe(III) in smectites and its effect on nitrate-dependent iron oxidation by Pseudogulbenkiania sp. strain 2002

Iron redox cycling in clay minerals plays important roles in nutrient cycling and contamination migration in soils and sediments. Studies have shown interfacial electron transfer (IET) between sorbed Fe(II) and structural Fe(III) in clays, but the impact of IET on biological redox reactions has not been investigated. Here we studied the impact of such IET process on an example redox reaction, i.e. coupled Fe(II) oxidation and nitrate reduction, in the presence of the nitrate-reducing bacterium Pseudogulbenkiania sp. strain 2002. Aqueous Fe2+ was sorbed to basal surface (pH 6) and edge sites (pH 8) of nontronite (NAu-2) and montmorillonite (SWy-2). The amount of Fe(II) sorption was lower at pH 6 than at pH 8. At pH 6, the extent of IET from basal Fe(II) to structural Fe(III) was higher in SWy-2 than in NAu-2, resulting in a higher proportion of structural Fe(II) in SWy-2. Because structural Fe(II) is more reactive than basal Fe(II), such IET resulted in a higher reactivity of SWy-2-associated Fe(II) than that of NAu-2-associated Fe(II) towards biologically-mediated nitrate reduction. At pH 8, extensive IET from highly reactive edge-Fe(II) to structural Fe(III) in NAu-2 resulted in formation of structural Fe(II) and Fe oxides, which lowered the reactivity of NAu-2-associated Fe(II). In contrast, due to limited IET in SWy-2 at pH 8, a large fraction of sorbed Fe(II) remained and was associated with SWy-2 and/or goethite/mixed Fe(II)-Fe(III) nanoparticles, which were highly reactive. As a result, SWy-2-associated Fe(II) is more reactive than NAu-2-associated Fe(II) at pH 8. The results of this study have important implications for understanding clay redox reactions in such environments where clay minerals and aqueous Fe2+ are in contact and IET occurs.

Adsorption of U(VI) on montmorillonite in the presence of ethylenediaminetetraacetic acid

The adsorption, diffusion and migration behaviors of uranium may be highly influenced by organics in natural environments. Ethylenediaminetetraacetic acid (EDTA) is one of the most important small organics in groundwaters, especially at the radioactive contaminated sites. In this work, we studied U(VI) adsorption on montmorillonite in the presence of EDTA with batch method. Our results indicated that U(VI) adsorption was significantly different in the presence and absence of EDTA. The equimolar EDTA inhibited the U(VI) adsorption at a wide pH range while only enhanced the adsorption at pH ˜7.0. The pseudo-second-order model showed the best fit for describing the adsorption kinetics in comparison with three other popular models. The influence of different addition sequences on adsorption of EDTA and U(VI) on montmorillonite was also investigated, and the results indicated that EDTA played the role as a bridge between montmorillonite surface sites and U(VI). The X-ray photoelectron spectroscopy and attenuated total reflectance Fournier-transform infrared spectroscopy also suggested the formation of EDTA-bridge inner-sphere surface complexes on montmorillonite. This work provides the valuable information of U(VI) adsorption on montmorillonite in the presence of EDTA, and helps us understand the diffusion and migration behaviors of uranium in natural environments.

Cadmium decontamination through ball milling using an expandable clay mineral

Mechanochemical treatments have been widely used for the remediation of soils and sediments polluted by organic and inorganic pollutants. However, there has been still limited knowledge about the molecular mechanisms underlying the mechanochemical transformations responsible of heavy metals immobilization on clay minerals.In the present study, the ability of a dioctahedral smectite to retain cadmium (Cd) as induced by mechanochemical treatments was investigated. The smectite was ground with different amounts of Cd (from 0.3 to 5.2% w/w). Solid-state characterizations (XRF, XRD, XPS, FT-IR, NMR) as well as desorption isotherm experiments were carried out to understand the critical metal sorption mechanisms onto dioctahedral smectite occurring in mechanochemical interactions. The “entrapping efficiency” and the type of interaction between clay surfaces and cadmium were evaluated. Cd immobilization degree was assessed by extract analyses and expressed as leachable fraction of cations. Leaching was both performed with deionized water and 1 M MgCl2 solution. Spectroscopic analyses evidenced that long time grinding (24 h) allowed Cd sorption on two sites: Type I, exhibiting characteristic of an outer-sphere complex likely localized in the montmorillonite interlayers and coordinated by two water molecule shells, i.e. in an exchangeable position; Type II sites, where Cd was more tightly bound to the TOT layers, either onto broken edges via the new OHs formed during the mechanochemical treatments or onto montmorillonite surfaces likely bridged via a water molecule. Desorption isotherms also confirmed a two-adsorption site model. This information could be useful to understand, develop and manage new remediation technologies based on mechanochemical treatments.

Elaboration and Characterization of Active Films Containing Iron-Montmorillonite Nanocomposites for O2 Scavenging.

Iron particles of sizes between 6 and 20 nm forming aggregates of 57 ± 17 nm were synthesized by chemical reduction of iron precursors on the surface of montmorillonite (MMT). This active MMT-Fe powder was then uniformly distributed in a linear low-density polyethylene (LLDPE) matrix by extrusion at atmospheric conditions, as confirmed by wide-angle X-ray scattering (WAXS), which also detected a partial exfoliation of the nanoclays. Thermogravimetric analysis (TGA) did not detect any significant modification of the degradation temperature between nanocomposites and active nanocomposites. 57Fe Mössbauer spectroscopy evidenced the formation of a majority of iron boride in MMT-Fe as well as in the active film containing it. The LLDPE.Fu15.MMT-Fe3.75 and LLDPE.Fu15.MMT-Fe6.25 films had oxygen-scavenging capacities of 0.031 ± 0.002 and 0.055 ± 0.009 g(O2)/g(Fe), respectively, while the neat powder had an adsorption capacity of 0.122 g(O2)/g(Fe). This result confirms that the fresh film samples were partially oxidized shortly after thermomechanical processing (60% of oxidized species according to Mössbauer spectroscopy). No significant difference in oxygen permeability was observed when MMT-Fe was added. This was related to the relatively small film surface used for measuring the permeability. The reaction–diffusion model proposed here was able to reproduce the observed data of O2 adsorption in an active nanocomposite, which validated the O2 adsorption model previously developed for dried MMT-Fe powder.

Comparison of the Phase Transition and Degradation of Methylene Blue of TiO2, TiO2/Montmorillonite Mixture and TiO2/Montmorillonite Composite.

Nano-TiO2 (T), TiO2/montmorillonite mixture (Mix), and TiO2/montmorillonite composite (Com) were prepared by using TiOSO4•2H2O as the precursor of TiO2 and montmorillonite as the matrix. The phase transition process of TiO2 and the degradation of methylene blue (MB) in T, Mix, and Com were studied by x-ray diffraction (XRD), infrared spectrum (IR), scanning electron microscopy with energy spectrum (SEM-EDS), and other methods. The results show that, except for the fact that the heating temperature has a great influence on the phase transition and grain growth of TiO2, the introduction of montmorillonite has an obvious inhibition effect on the phase transition and grain growth of TiO2, and the inhibition effect of the Com is obviously stronger than Mix. In Com, Ti–O–Si chemical bond was formed between TiO2 and oxygen atoms with negative charge on the bottom of the structure layer of montmorillonite, which is the main reason for inhibition effect. However, in Mix, TiO2 only covers the surface of montmorillonite without breaking the degree of order of montmorillonite and forming no chemical bond with montmorillonite, so the inhibition effect is small. From degradation of MB, it was found that before the structure of montmorillonite was destroyed (400–600°C), the total degradation percentage in Mix (85.3–99.5%) was higher than T and Com. At high temperature (above 700°C), because of the inhibition effect, the total degradation percentage of MB in Com is much larger than T and Mix, even above 1,100°C, the total degradation percentage can still reach at 47%. Therefore, in industrial applications, Mix and Com can be selected to degradation MB, according to the actual application temperature range.

Chromium(VI) and lead(II) accumulation at the montmorillonite/aqueous solution interface in the presence of polyacrylamide containing quaternary amine groups

Nowadays, due to increasing environment pollution, the amount of heavy metals in soil becomes higher and higher. The introduced metals are usually toxic and harmful for plants and animals. Taking this fact into account, in this paper it was checked if common clay mineral – montmorillonite, modified by soil flocculant (cationic polyacrylamide, CT PAM) can immobilize chromium(VI) and lead(II) ions and thus decreases their bioavailability. The adsorbed amounts of polymer, ions and polymer/ions on the montmorillonite surface were measured spectrophotometrically. The electrical double layer structure formed around montmorillonite particles without and with heavy metal ions/polymer was also determined. The obtained results indicate that cationic polyacrylamide captures both lead and chromium ions and increases their adsorbed amount on the montmorillonite surface. Thus, the cationic flocculant usage may enhance the heavy metal immobilization.