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This study presents the chemical and mineralogical composition of clay deposits and associated rock types within the Ropp Complex in order to assess the influence of parent lithology on the kaolinization, genesis, and utility of the deposit. Representative kaolin samples from E horizons of the weathering profiles and their bedrocks were collected from six sites in the Ropp Complex. Clay mineralogy was determined via the XRD technique, while a geochemical analysis was conducted using XRF, SEM coupled with EDS, and ICP-MS. The results showed that all kaolins dominantly contain kaolinite with a content of 77%–98% except for the AS1 kaolin with only minor kaolinite (20%) but mainly illite (65%). The notably lower crystallinity of kaolinite (HI value of 0.53–1.1) as well as its markedly small grain size is consistent with the formation of kaolinite from intensive chemical weathering of igneous rocks. The AS1 kaolin was probably formed from hydrothermal alteration in the burial stage due to the heating of groundwater by the late volcanism. Mobile trace elements (Sr, Ba, and Eu) exhibited a depletion trend, while immobile elements (Hf, Ta, Th) showed enrichment. The relatively more zirconium in kaolins implies the formation of low-temperature kaolinization. The notably high kaolinite content, accompanied by reasonable levels of Fe2O3 and TiO2, signifies a medium-grade quality. Furthermore, chondrite-normalized rare earth element (REE) patterns exhibit congruent trends in rocks and kaolin samples, indicating a relative enrichment in light rare earth elements (LREEs) alongside a discernible negative Eu anomaly. The abundant kaolinite and silicon–aluminum composition make the kaolins suitable for refractories, pharmaceutics, cosmetics, and supplementary cementitious material (SCM). [ABSTRACT FROM AUTHOR]

The boundary between Cretaceous and Paleogene (K/Pg) plays an important role in deciphering the Earth's history and biological evolution from Mesozoic to Cenozoic. As such, the delineation and characterization of the boundary layer has attracted significant attention. In this study, X-ray diffraction (XRD) and elemental analyses were conducted to characterize the samples of boundary layer and the layers around Agost and Caravaca, Spain. The XRD results showed that the layers immediately above and below the boundary layer are made of limestone, while in the boundary layer, a significant increase in the clay minerals smectite, kaolinite, and illite was observed. The major element analyses revealed an increase in Si and Al contents, confirming the presence of clay minerals. The trace element analyses showed elevated concentrations of V, Cr, Ni, Zn, Pb, and Th, but not for Rb, Cu, and U. The rare Earth element (REE) analyses showed elevated La, Ce, and Nd concentrations in the boundary layer. Correlation analyses between selected trace elements and REE showed good agreements, with R2 values of about 0.9. The results agreed well with the finding in the area, except the lower contents of Rb, Cu, and U; thus, they may promote further studies to make detailed comparisons. [ABSTRACT FROM AUTHOR]

The extensive use of synthetic materials in modern society presents a great challenge to environmental and water quality. As such, numerous studies were dedicated to the removal of emerging contaminants from water using novel materials as sorbents or catalysts. With large reserves and low material costs, Earth material has also attracted great attention for contaminant removal. Halloysite is a 1:1 layered clay mineral with moderate cation exchange capacity that can be used for the removal of cationic contaminants. On the other hand, as it may bear positive charges on the aluminum hydroxyl sheets, it could be used to remove anionic contaminants. In this study, the removal of a cationic dye, methylene blue (MB), and an anionic dye, alizarin red S (ARS), from the water was evaluated from single and mixed solutions. The results suggested that from single solutions, MB removal was via cation exchange while ARS removal could have originated from anion exchange. From mixed solutions, their removal was mutually increased, which may be due to a synergistic effect in the presence of a type of charged dyes serving as counterions to enhance the sorption of dyes of opposite charges. This finding suggests that halloysite may serve as a sorbent for the removal of organic contaminants of different charges at the same time, which is a new perspective that needs further evaluation and expansion. [ABSTRACT FROM AUTHOR]

Using Earth materials for the removal of environmental contaminants attracted great attention. In this study, the mechanism of safranin O (SO) removal by 1:1 layered clay minerals was investigated. The specific surface area and cation exchange capacity of the minerals played a key role, while solution pH and ionic strength had less influences on SO removal. The sorption of counterion Cl– on halloysite nano clay (HNC) at high loading levels resulted in bilayer SO formation on HNC surfaces. Lack of Cl– sorption on kaolinite (KAO) suggested monolayer SO formation on KAO surfaces. These speculations were confirmed by molecular dynamic simulation. [ABSTRACT FROM AUTHOR]

The increased use of color dyes in industry imposes a great threat to the environment. As such, developing cost-effective techniques for dye removal from wastewater attracted great attention. Earth materials, particularly those with large specific surface area (SSA) and high cation exchange capacity (CEC), were evaluated for their potential use for wastewater treatment. In this study, palygorskite, sepiolite, and clinoptilolite were evaluated for their removal of cationic dyes using safranin O (SO+) as a model compound. The CEC values of the materials played a key role in SO+ removal while other physicochemical conditions, such as temperature, equilibrium solution pH, and ionic strength, had less influence on SO+ removal. Sorbed SO+ cations were limited to the external surfaces of the minerals, as their channel sizes are less than the size of SO+ cation. Molecular dynamic simulations showed dense monolayer SO+ uptake on palygorskite due to its relatively large CEC value. In contrast, loosely packed monomer SO+ uptake was adopted on sepiolite for its large SSA and low CEC. Dense multilayers or admicelles of SO+ formed on zeolite surfaces. As such, for the best SO removal, palygorskite is better than sepiolite, though both are fibrous clay minerals. [ABSTRACT FROM AUTHOR]

• Uptake of Triethylenetetramine (TETA) on rectorite was via a complexation mechanism. • Uptake of Cu2+ and Cu-TETA on rectorite was via a cation exchange mechanism. • Interlayer cation Ca2+ complexed with TETA could be exchange with Cu2+. • Under high loading levels, Cu-TETA adoption a vertical bilayer configuration. • Results suggest that TETA-modified clay minerals could be used as sorbent for metals. Uptake of metals, organics, and formation of metal-organic complexes on the surface or in the interlayer of clay minerals had been studied extensively over the last half century. In this study, we investigated the uptake mechanisms of Cu2+, triethylenetetramine (TETA), and Cu-TETA on rectorite and its use for metal removal via metal-TETA complexation. The uptake of Cu2+, TETA, and Cu-TETA by rectorite occurred on the external as well as in the interlayer space, resulting in a change of d 001 -spacing due to differences in sizes of interlayer cations or complexes. Although the uptake of Cu2+ and Cu-TETA by rectorite was via a cation exchange process as evidenced by the stoichiometric desorption of dominant interlayer cation Ca2+, the uptake of TETA alone on rectorite was via complexation with interlayer cation Ca2+. Due to strong affinity of TETA for Cu2+, significant amounts of Cu2+ uptake occurred on TETA-rectorite. Desorption of Ca2+ from TETA-rectorite confirmed the replacement of interlayer cation Ca2+ by Cu2+. However, the replacement of Ca2+ by Cu2+ in TETA-rectorite did not involved in removal of TETA. As such, TETA-modified clay minerals may serve as a type of sorbents for the removal of selected heavy metals via surface or interlayer via complexation. [ABSTRACT FROM AUTHOR]

Highlights • Antimicrobial activity (AMA) of tetracycline (TC) was drastically reduced in the presence of different clays. • The reduction in AMA was attributed to significant removal of TC from solution by the clays. • The reduction in AMA was more obvious in the presence of MMT due to its higher cation exchange capacity. • The reduction in AMA may contribute to elevated TC resistance of both TC sensitive and resistant bacteria. Abstract Antibiotics are extremely effective against bacterial infections due to their selective toxicity for bacteria rather than the host. Extensive use and misuse of antibiotics resulted in significant increases in antibiotic levels in aquatic and soil environments. Bacteria exposed to antibiotics with low concentrations may develop antibiotic resistance. In this study a swelling 2:1 clay mineral montmorillonite (MMT) and a non-swelling 1:1 clay mineral kaolinite were premixed with tetracycline (TC) of varying concentrations. The gram-negative bacteria Escherichia coli (E. coli) and Salmonella enterica (S. enterica) of both TC sensitive and TC resistant strains were tested for their growth in the presence TC-loaded clay minerals of different amounts and under different physico-chemical conditions. The antimicrobial activity of TC was significantly decreased in the presence of MMT. In the absence of MMT, no bacteria growth was found at a TC concentration 0.25 mg/mL and above. On the contrast, in the presence of MMT, 50% growth was still found for a TC resistant E. coli at a TC concentration of 5 mg/g. The influence of kaolinite was to a lesser degree. These results suggest that antimicrobial agents present in clayey soils could be responsible for possible mutation of bacteria of high antibiotic resistance. [ABSTRACT FROM AUTHOR]

With an increased use of color dye in textile industries and elevated fabrics output, more scientific studies and technology developments are needed to effectively treat wastewater containing dyes. However, better understanding of the interactions between dyes and suspended solids is a necessity to advance such developments. In this study the interactions between rhodamine 6G (R6G), a cationic dye, and different types of clays minerals, commonly found in the wastewater sludge, were elucidated. The uptake of R6G on the clay minerals was attributed to cation exchange on the external surfaces of non-swelling clays, and at both external and interlayer spaces for swelling clays. In the interlayer of montmorillonite, the R6G molecules form monolayer and bilayer configurations under low and high uptake levels. The significant amounts of R6G uptake indicate that clay minerals are good sorbents for the removal of cationic dyes from water. And the R6G could be readily removed in wastewater treatment by adding small amount of clays and flocculated the clays out. [ABSTRACT FROM AUTHOR]

This Special Issue is a collection of five original articles devoted to both experimental and theoretical studies of phenomena and processes occurring at surfaces of clay minerals and related materials. Shi et al. [[4]] consider clinoptilolite zeolite as a candidate for removal of cationic dyes safranin O and toluidine blue from single and binary solutions. The works of Jiang et al. [[3]] and Shi et al. [[4]] are devoted to investigations of color dyes sorption on different types of clay minerals and zeolites. [Extracted from the article]

Abstract: The widespread use of antibiotics in human medicine and animal husbandry has resulted in their frequent detection in municipal wastewater, surface water, ground water, soils and sediments. Clay minerals are important components of soil and sediment. Adsorption of antibiotics to clay minerals is an important factor influencing the fate and transport of these compounds in the environment. Furthermore, clay minerals are low-cost adsorbents, which are widely used to remove inorganic and organic pollutants from aqueous solution. An adsorption study of nalidixic acid (NA), a quinolone antibiotic, on montmorillonite (SAz-1) and kaolinite (KGa-1b), two important components of soils, was conducted under different pH and initial concentration conditions. Adsorption of NA were well-described by the Freundlich isotherm and an adsorption equilibrium could be reached within 24h. On the other hand, repetitive NA adsorption on montmorillonite at low pH obeyed the Langmuir isotherm. Adsorption of NA increased as solution pH increased up to 5.5, above which a further increase in solution pH resulted in a decreased NA adsorption. When solution pH was below its pKa, NA existed mainly in a neutral form NA0, and hydrophobic interaction was responsible for relatively high NA adsorption on clay minerals. At solution pH above its pKa, electrostatic repulsion between the anionic form NA− and negatively charged mineral surface reduced NA adsorption. XRD analysis indicated that NA adsorption to montmorillonite at pH 4.0 resulted in a basal spacing expansion of 0.9Å, suggesting adsorption and intercalation of NA in the interlayer space. FTIR analyses revealed the formation of a coordination bond between the keto oxygen in the pyridine ring or the C N group in the pyridine ring and the exchangeable cation in the interlayer space, thus promoting NA uptake on montmorillonite. [Copyright &y& Elsevier]

Abstract: Desorption from soil clay components may affect the transport and fate of antibiotics in the environment. In this study, ciprofloxacin (CIP) desorption from a kaolinite and a montmorillonite was investigated under different pHs, different concentrations of metal cations of various valencies (Na+, Ca2+ and Al3+) and a cationic surfactant hexadecyltrimethylammonium (HDTMA), and different desorption cycles. Desorption of CIP from kaolinite and montmorillonite was strongly pH-dependent and desorption isotherms were well fitted with the Langmuir equation. The percentage of CIP desorbed increased with increasing initial CIP loadings, desorbing cation concentrations, and desorption cycles. Comparatively, CIP was more readily desorbed from kaolinite than from montmorillonite. Moreover, the hysteresis index values were all negative, suggesting that the presence of metal cations and HDTMA in solution promoted CIP desorption from clay minerals, owing to cation exchange. The XRD analyses indicated that desorption of CIP occurred from both external and interlayer surfaces of montmorillonite. Formation of Al–CIP complex on solid surface and then detachment of Al–CIP from the solid surface may contribute to the higher CIP desorption by Al3+ in comparison to Na+ and Ca2+. [Copyright &y& Elsevier]

Abstract: The removal of tetracycline (TC) from aqueous environment by illite (IMt-2) was studied in a batch system at different pH and ionic strength conditions. Adsorbent characterizations were determined by XRD and FTIR. The TC adsorption capacity on IMt-2 was 32mg/g at pH 5–6 and the adsorption equilibrium data obeyed the Freundlich isotherm. The kinetics of TC adsorption was moderately fast and almost reached equilibrium in 8h and the results followed pseudo-second-order kinetic model and Elovich model. The X-ray diffraction patterns before and after TC adsorption revealed no changes in basal spacing and intensity under two kinetic adsorption and a few initial TC concentration conditions, indicating that the adsorbed TC molecules were on the external surface of the mineral in contrast to intercalation of TC into swelling clay minerals, such as montmorillonite and rectorite. In spite of its low TC adsorption capacity, the results suggested that IMt-2 could be a good candidate to remove TC from wastewater containing higher amounts of TC and illite would be an important environmental sink for the fate and transport of TC in soils. [Copyright &y& Elsevier]

Abstract: Frequent detection of antibiotics in natural environment and wastewater effluent requires systematic investigations of various clay minerals. Dioctahedral 2:1 clay minerals are major constituents of soil and sediments. Interaction of these clay minerals and ciprofloxacin (CIP) was studied. The CIP adsorption capacities on montmorillonite, rectorite, and illite were 1.19, 0.41, and 0.10mmol/g, corresponding to 1.0, 1.0, and 0.9 CEC. Desorption of the equivalent amounts of exchangeable cations suggested that the cation exchange was mainly responsible for the CIP adsorption on montmorillonite and rectorite. The expansion of the basal spacing and shifts of characteristic FTIR bands indicated the intercalation of CIP ions with tilted orientation in montmorillonite and rectorite. The displacement of exchangeable cations and associated FTIR band shifts also indicated the cation exchange as important for CIP adsorption on illite but hydrogen bonding between CIP carboxylic groups and basal oxygen atoms on external surface apparently made a significant contribution to the adsorption. [Copyright &y& Elsevier]

Higher levels of arsenic in the aquifers of Chia-Nan Plain in southwestern Taiwan were attributed to the cause of Blackfoot disease in the area half a century ago. Although extensive studies were conducted on the occurrence, speciation, mobility, and transport of arsenic in the region, the relationship between arsenic adsorption by different aquifer materials and the concentration and speciation of arsenic in these aquifers was poorly delineated. This study focused on characterization of sediments in the region, as well as determination of relations between arsenic adsorption and other geochemical and clay mineralogical properties of the sediments. The arsenic adsorption capacity was positively related to the clay minerals, Fe, and Mn contents in the sediments. The higher arsenic adsorption capacity of the sediments served as a sink for the arsenic during its transport from the central mountains to the coast and as a source for its release under reduced environment and in the presence of humic substances. [ABSTRACT FROM AUTHOR]

Abstract: Frequent detection of pharmaceuticals in surface water and wastewater attracted renewed attention on studying interactions between pharmaceuticals and sludge or biosolids generated from wastewater treatment. Less attention was focused on studying interactions between pharmaceuticals and clay minerals, important soil and sediment components. This research targeted on investigating interactions between diphenhydramine (DPH), an important antihistamine drug, and a montmorillonite, a swelling clay, in aqueous solution. Stoichiometric desorption of exchangeable cations accompanying DPH adsorption confirmed that cation exchange was the most important mechanism of DPH uptake by the swelling clay. When the solution pH was below the pK a of DPH, its adsorption on the swelling clay was less affected by pH. Increasing solution pH above the pK a value resulted in a decrease in DPH adsorption by the clay. An increase in d 001 spacing at a high DPH loading level suggested interlayer adsorption, thus, intercalation of DPH. The results from this study showed that swelling clays are a good environmental sink for weak acidic drugs like DPH. In addition, the large cation exchange capacity and surface area make the clay a good candidate to remove cationic pharmaceuticals from the effluent of wastewater treatment facilities. [Copyright &y& Elsevier]

Abstract: Kaolinite is a major type of clay minerals in soils of warm and humid climate. Although it has a much lower cation exchange capacity (CEC) and specific surface area compared to swelling clays, its ubiquitous existence as well as its pH-dependent surface charge makes it an important component to study the interactions between contaminants and soils. Tetracycline (TC) is a group of broad spectrum antibiotics used extensively in human and veterinary medicine. It has a high aqueous solubility and a long environmental half-life. In this study, the interactions between TC and kaolinite in aqueous solution were investigated in batch tests and supplemented by FTIR analyses. The adsorption of TC on kaolinite was mainly on the external surfaces via cation exchange as confirmed by stoichiometric desorption of exchangeable cations and simultaneous adsorption of H+ rather than due to complexation. Under acidic conditions, a reduction in surface charge, thus the CEC, resulted in more desorption of exchangeable cations compared to TC adsorption. Fitting of the experimental data to the adsorption of different species revealed that TC+ accounted for 4/5 of the total TC adsorbed with the remaining by zwitterion TC0, possible via hydrogen bonding. At higher temperature, the pKa2 and pKa3 values seem to shift a pH unit lower. Due to its pH-dependent charge of kaolinite, TC adsorption is more pH dependent. The TC adsorption capacity on kaolinite was much lower compared to that on swelling clays. However, the adsorption rate constant was faster than that on swelling clays owing to surface adsorption instead of intercalation. Despite its low TC adsorption capacity, the ubiquitous existence of kaolinite in soils of warm climate may play a vital role in the fate and transport of TC in these soils. [ABSTRACT FROM AUTHOR]

Abstract: Many of commonly used pharmaceuticals are hydrophilic. In aqueous solutions, these molecules will have strong interaction with swelling clay minerals, resulting in intercalation of these compounds in the interlayer of the minerals and retention by these minerals. In this research, we studied the intercalation of tetracycline (TC) into swelling clay minerals as represented by montmorillonite and rectorite of different surface charges and different charge densities. The maximum interlayer expansion was seen at a higher pH when the TC molecules adopted an extended conformation, even though, the amount of TC intercalated at higher pH is lower. Under pH 4–5, the intercalated TC produced an interlayer gallery height of 9.2 Å compared to 10.3 Å produced at pH 8.7 in the interlayer space of rectorite. Due to TC intercalation, the full width at half maximum (FWHM) becomes much broader, suggesting that the number of fundamental layers stacking along c axis decreased to 2–3. Depending upon the nature of the swelling clay minerals and the TC concentration, the intercalation process can be transitional, involving in the occurrence of mechanical mixtures, materials of intermediate layer thicknesses, and/or mixed layering of different ordering states. [Copyright &y& Elsevier]

Acridine orange (AO) is a cationic fluorescent dye commonly used in DNA analyses. Extensive studies were conducted for its metachromasy under different solution concentrations and different amounts of AO sorbed on a solid surface. Meanwhile, for the safe disposal of wastewater, AO removal from water using different materials was also evaluated extensively. Clay minerals, due to their large specific surface area, high cation exchange capacity, and vast reserves, have been evaluated as potential sorbents for the removal of a variety of different types of contaminants, including color dyes. In this study, the sorption of AO on different types of clay minerals was contrasted. The sorption of co-presenting Zn2+ was much less than the sorption of AO, suggesting that clay minerals have higher affinities for AO in comparison to inorganic Zn2+. The desorption of exchangeable cations was linearly related to AO sorption, and the amounts of AO sorbed were close to the CEC values of the minerals, confirming that cation exchange is the dominating mechanism for AO sorption. Molecular dynamics simulation results showed that, under low and high AO loading levels, the sorbed AO formed monolayers and bilayers on the mineral surfaces of non-swelling clay minerals, except halloysite, as well as in the interlayer of swelling clay minerals, due to its relatively large dimer constant in solution. Overall, clay minerals are good candidates for the removal of cationic dyes from solution even in the presence of competing inorganic cations. [ABSTRACT FROM AUTHOR]

Abstract: Rectorite is an interstratified clay mineral made at 1:1 ratio of an orderly arrangement of a nonswelling component illite and a swelling component smectite. Due to the presence of two distinct types of components, it is of great interest to study the adsorption of long chain alkylammonium in rectorite. In this study, we conducted batch experiments and used X-ray diffraction (XRD) and Fourier Transform infrared (FTIR) spectroscopy to characterize the interlayer configuration of intercalated long chain hexadecyltrimethylammonium (HDTMA) in rectorite. The FTIR results showed that a monomer-like intercalation with extensive gauche conformers was formed at surfactant loading less than the cation exchange capacity (CEC) of the mineral. At a higher surfactant loading the CH2 c and anti-symmetric vibrations shifted to lower frequencies, suggesting a more ordered all-trans surfactant interlayer configuration. The thermogravimetric and derivative of thermogravimetric analayses showed a high pyrolysis temperature for the monomer-like gauche conformers and lower pyrolysis temperature for the all-trans configuration of the intercalated HDTMA. The XRD analysis confirmed the monomer-like conformation with a d-spacing of 25.2Å at the low surfactant intercalation and a vertical all-trans configuration with a d-spacing of 49.5Å at an HDTMA intercalation of 3.20 CEC. In addition to conformation analyses of intercalated surfactant in the interlayer using FTIR, the absorbance measured by peak height at 1470, 2850, and 2917cm−1 increased linearly with surfactant loading, providing a faster, yet efficient method to quantify the amount of surfactant adsorbed. [Copyright &y& Elsevier]

The studies on dye removal from solutions attracted great attention due to the increased use of color dyes in different fields. However, most of the studies were focused on dye removal from a single solution. In reality, wastewater from the fabric industry could contain mixed dyes. As such, evaluating different dye removal from mixed solutions may have more practical importance. In terms of sorbents evaluated for dye removal, most of them were an organic type generated from agricultural wastes. Clay minerals and zeolites were also studied extensively, because of the vast reserves, inexpensive material cost, larger specific surface area (SSA) and high cation exchange capacity (CEC). However, evaluating the factors controlling the dye removal from mixed dye solutions was limited. In this study, the removal of cationic dyes safranin O (SO) and toluidine blue (TB) by clinoptilolite zeolite (ZEO) was evaluated under single and binary systems. The results showed that removal of TB was preferred over SO by approximately a 2:1 ratio. The counterion Cl− sorption from mixed dye solution helped the formation of mixed dye aggregates on mineral surfaces. Molecular dynamic simulation confirmed the multilayer mixed dye formation on ZEO under high loading levels. [ABSTRACT FROM AUTHOR]

Interactions between cationic dyes and negatively charged mineral surfaces have long attracted great attention from clay mineralogists, environmental scientists, and chemical engineers. In this study, the interactions between a cationic dye toluidine blue (TB) and palygorskite and sepiolite were investigated under different experimental conditions. The results showed that in addition to cation exchange, the specific surface area (SSA) of the minerals, particularly the formation of dimer molecules on the surface of both minerals, also accounted for the much higher TB uptake in comparison to their cation exchange capacities (CEC). The TB molecules were sorbed to the external surfaces, as no d-spacing expansion was observed in X-ray diffraction analyses. FTIR analyses showed strong interactions between the C=N or N-(CH3)2 group and the mineral surfaces, suggesting net electrostatic interactions if either of these functional groups bears a positive charge. Results from molecular dynamic simulations suggested dense monolayer TB formation on palygorskite because of its limited SSA and large CEC values. In comparison, a loosely dimeric formation was revealed on sepiolite for its large SSA and limited CEC values. Therefore, palygorskite is a better carrier for the sorption of cationic dyes, as evidenced by Maya blue paintings. [ABSTRACT FROM AUTHOR]

Excipients play an important role in pharmaceutical formulations. Many clay minerals, because of their large specific surface area and inert behaviour in reactions with active ingredients, are commonly used as excipients. In this study, the uptake of ranitidine (RT), the active ingredient of Zantac, on and released from palygorskite (Pal), kaolinite (Kao), and talc was evaluated under different physicochemical conditions. The results showed that the uptake of RT on these minerals was limited to the external surface areas only. Cation exchange and electrostatic interactions were responsible for the RT uptake on Pal and Kao, resulting in a monolayer sorption. In contrast, multilayer RT uptake was found on the talc surfaces. Under different desorbing conditions, significant amounts of sorbed RT remained on the solid surface after 5 h of desorption. The results suggest that the sorptive interactions between the active ingredients and the excipients may not be neglected in pharmaceutical formulations, should these minerals be used as additives and/or excipients. [ABSTRACT FROM AUTHOR]

• Rectorite is an effective sorbent to ethidium bromide (EtBr) from water. • EtBr sorption on rectorite could be as high as 160 mg/g in less than an hour. • Cation exchange was the most important mechanism for EtBr removal. • Under low and high loading sorbed EtBr forms monomers and dimers in the interlayer. • Intercalated EtBr could be thermally decomposed and spent rectorite thus regenerated. Ethidium bromide (EtBr) is an intercalating agent commonly used as nucleic acid fluorescent tag in various techniques of life science field. It is considered as a serious biohazard due to its mutagenicity and carcinogenicity. As such, developing high efficiency and low cost materials as cleanup kits is in urgent need although many methods have already been developed. In this study we take use of the affinity of organic cations for clay minerals of high cation exchange capacity (CEC) and large specific surface area (SSA) and tested the removal of EtBr using rectorite, a type of clay mineral made of 1:1 regularly mixed layers of illite and montmorillonite. Our results showed that the uptake of Et+ on rectorite could be as high as 400 mmol/kg and the removal of Et+ was extremely fast. Desorption of inorganic cation Ca2+ and sorption of counterion Br− revealed that cation exchange was the dominating mechanism of Et+ removal using rectorite. Thermal analyses revealed that the EtBr could be thermally destructed inside the interlayer of rectorite and the material could be thermally regenerated. Thus, clay minerals could have a great potential to be fabricated into cleanup kits for the removal of EtBr in case of spill. [ABSTRACT FROM AUTHOR]

The adsorption of atenolol (AT) from aqueous solutions by Ca-montmorillonite (SAz-2) was investigated in batch studies under different physicochemical conditions. The AT existed in neutral un-dissociated form at pH 10, and was adsorbed on dioctahedral smectite (SAz-2) obeying the Langmuir isotherm with a maximum adsorption capacity of 330 mmol/kg. The kinetic adsorption suggested that both strong and weak adsorption sites existed on SAz-2 and participated in the adsorption mechanisms. The amount of exchangeable cations desorbed from SAz-2 during AT adsorption was linearly correlated with the amounts of adsorbed AT having slopes of 0.43, which implied that a cation exchange based adsorption mechanism was also in place. A comprehensive basal spacing change of SAz-2 was observed after AT adsorption on the clay mineral when tested with or without AT recrystallization. The intercalation of AT into the SAz-2 interlayers did not result in swelling due to the low adsorption capacity of the drug. Prominent interactions between the pharmaceutical molecule and SAz-2 were evidenced by apparent shifts of the infrared absorption bands after adsorption. The interlayer configurations and hydrogen bonding of AT on SAz-2 were also supported by infrared, X-ray diffraction and thermogravimetric analyses. This study suggested that SAz-2 is an excellent material to remove not only AT from pharmaceutical wastewater, but can potentially remove many other β-receptor blocker drugs. The results helped us to understand the possible interlayer configurations and adsorption mechanisms of the drugs on natural clay mineral based adsorbents. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the interaction between ciprofloxacin (CIP), a fluoroquinolone antibiotic, and rectorite, a regular mixed-layer clay mineral, in aqueous solution was studied by X-ray diffraction, Fourier transform infrared, and thermal gravimetric analyses in conjunction with solution chemistry. The uptake of CIP by rectorite was mainly via a cation exchange mechanism as evidenced by quantitative desorption of exchangeable cations accompanying CIP adsorption. The dehydration of rectorite accompanying CIP adsorption as indicated by infrared and gravimetric analyses also pointed to the cation exchange mechanism between CIP and hydrated cations previously occupied in the interlayer. The intercalated CIP is thermally more stable in comparison to crystalline CIP, suggesting that the presence of swelling clay minerals in soil and wastewater treatment systems may provide a place for contaminant accumulation and shelter to protect CIP from thermal degradation. [Copyright &y& Elsevier]

Abstract: Clay mineralogy analyses were carried out on Cenozoic sedimentary rocks collected from the southwestern margin of the Tarim Basin, northwest China, using X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. These investigations were aimed at determining the paleoclimate of the area in early Cenozoic times, especially during the late Eocene to early Oligocene. The proportion of clay mineral species and clay mineral indices, as well as the proportion of non-clay minerals, gypsum, and morphology of the clays showed that the paleoclimate of the Tarim Basin underwent a distinct change from warm and humid to cold and dry during the late Eocene to early Oligocene. The climate evolution derived from the clay mineralogical study in the Tarim Basin is consistent with the effects of Eocene–Oligocene climate cooling. Combined with the retreat of the Neo-Tethys Sea, cooling of global ocean temperatures reduced the moisture supply to continental interiors, leading to cooling and aridification in the Asian interior. [Copyright &y& Elsevier]

The stability and persistence of organic matter (OM) in source rocks are of great significance for hydrocarbon generation and the global carbon cycle. Clay-OM associations commonly occur in sedimentation and diagenesis processes and can influence the pyrolytic behaviors of OM. In this study, clay-OM complexes, i.e., interlayer clay-OM complexes and clay-OM mixture, were prepared and exposed to high-pressure pyrolysis conditions in confined gold capsule reactors to assess variations in OM pyrolysis products in the presence of clay minerals. Three model organic compounds, octadecanoic acid (OA), octadecy trimethyl ammonium bromide (OTAB), and octadecylamine (ODA), were employed and montmorillonite (Mt) was selected as the representative clay mineral. The solid acidity of Mt plays a key role in affecting the amount and composition of the pyrolysis gases generated by the clay-OM complexes. The Brønsted acid sites significantly promote the cracking of hydrocarbons through a carbocation mechanism and the isomerization of normal hydrocarbons. The Lewis acid sites are primarily involved in the decarboxylation reaction during pyrolysis and are responsible for CO 2 generation. Mt exhibits either a catalysis effect or pyrolysis-inhibiting during pyrolysis of a given OM depending on the nature of the model organic compound and the nature of the clay-OM complexation. The amounts of C 1–5 hydrocarbons and CO 2 that are released from the Mt-OA and Mt-ODA complexes were higher than those of the parent OA and ODA, respectively, indicating a catalysis effect of Mt. In contrast, the amount of C 1–5 hydrocarbons produced from the pyrolysis of Mt-OTAB complexes was lower than that of OTAB, which we attribute to an inhibiting effect of Mt. This pyrolysis-inhibiting effect works through the Hoffmann elimination that is promoted by the catalysis of the Brønsted acid sites of Mt, therefore releasing smaller amounts of gas hydrocarbons than the nucleophilic reaction that is induced by the halide ions in OTAB. In particular, the interlayer space of Mt acts as an ‘amplifier’ that magnifies the above-mentioned catalysis or pyrolysis-inhibiting effect, due to the greater number of Brønsted acid sites with high acidity in the interlayer space. These findings are potentially important for understanding the storage and transfer mechanisms of natural OM in sedimentation and diagenesis processes. [ABSTRACT FROM AUTHOR]

The presence and persistency of pharmaceuticals and personal care products (PPCPs) in the environment attracted great attention recently. Among them, antibiotics and pain-killers accounted for a large quantity. Although many works were devoted to the investigation of their removal in wastewater treatment processes, most of the PPCPs studied were of cationic nature. The net repulsive interactions between anionic PPCPs and negatively charged sorbents make them difficult to be removed in wastewater treatment. In this study, 2:1 clay minerals illite and montmorillonite (MMT) were modified with different amounts of cationic surfactant cetyltrimethylammoium bromide (CTAB). The types and sites of interactions between the surfactant-modified clays and the anionic drug diclofenac (DC) were investigated. The uptake of DC on the modified clays was controlled by the CTAB loading level and its surface configuration on the clays. The adsorption sites of DC were limited to the external surfaces of modified illite due to its non-swelling nature. On the contrary, both the external and interlayer sites were available for the adsorption of DC on modified MMT. A CTAB bilayer formation resulted in significant increase in DC adsorption due to the formation of extensive admicelles. FTIR results showed participation of the benzene ring, N H, and CH 2 CH 3 for the interactions between DC and modified MMT, suggesting that partitioning of DC into the admicelles of CTAB played a significant role in DC uptake. The results could extend the application of surfactant-modified clays for the removal of anionic PPCPs in the wastewater treatment processes. [ABSTRACT FROM AUTHOR]

Halloysite is a clay mineral similar to kaolinite and can be found in soils and weathered rocks in different particle shapes and hydration states. Due to misfit between the SiO 4 tetrahedral sheets and Al(OH) 6 octahedral sheets, it may form tubular structure with the SiO 4 tetrahedral sheets on the outer surfaces. The isomorphous substitution resulted in substantial cation exchange capacity (CEC). In this study, we tested the uptake of selected pharmaceutical compounds (PCs) by halloysite nanotubes (HNTs) under different physico-chemical conditions. The uptake capacity of these PCs were slightly lower than the CEC values of the HNTs, while the stoichiometric relation between the amounts of PC uptake and desorption of exchangeable cations supported cation exchange as the major mechanism for the uptake of PCs by the HNTs. The uptake of PCs was on the external surfaces of HNTs, whilst the surface area was not a limiting factor for the uptake of PCs. The finding from this study could extend the application of HNTs as a carrier for ionizable pharmaceuticals. [ABSTRACT FROM AUTHOR]

Although they are both 1:1 layered phyllosilicates, their TB sorption capacity was 47 and 149 mmol/kg in comparison to their CEC values o 37 and 120 meq/kg and SSA values of 65 and 25 m2/g for KAO and HNC. As such, both CEC and SSA values played a significant role on TB removal. At the sorption capacity, TB molecules formed mostly monolayer and bilayer surface configuration on KAO and HNC as revealed by molecular dynamic simulation. Top and bottom views are along [0 0 1] and [1 0 0] crystallographic directions. [Display omitted] • Removal of toluidine blue (TB) by 1:1 layered clay minerals studied. • At high loading, sorbed TB molecules formed dimer or bilayer on halloysite. • In contrast, dense TB monolayer formed on kaolinite at high loading. • Both surface area and cation exchange capacity played vital roles in TB removal. Extensive use of color dyes in modern society resulted in their potential release into the environment. Dye removal often involved in sorption or reaction. For sorptive removal, materials with low cost and high efficiency are of great potential. In this study, the removal of toluidine blue (TB), a cationic dye, by 1:1 layered clay minerals kaolinite (KAO) and halloysite (HNC) was systematically studied under different physicochemical conditions. The TB removal was fast and equilibrium could be reached within an hour. The TB removal capacities were 47 and 149 mmol/kg by KAO and HNC slightly larger than their cation exchange capacity (CEC) of 37 and 120 meq/kg. The results indicated that both the CEC and specific surface area (SSA) of the minerals played a critical role in TB removal. Equilibrium solution pH and ionic strength had less effect on TB removal, suggesting preferred affinity of TB over other inorganic cations for mineral surfaces. X-ray diffraction data showed no interlayer expansion, indicating TB sorption sites were on the external surfaces of both minerals. The FTIR results indicated participation of N+ on the dimethyl group for TB sorption on negatively charged mineral surface. At the sorption capacities, TB may form a condensed monolayer on KAO surfaces, and a dimer or bilayer coverage on HNC surfaces, as suggested by molecular dynamic simulation. The results from this study suggest that clay minerals of high CEC and large SSA values would be good candidates for the removal of cationic dyes form water. [ABSTRACT FROM AUTHOR]

Mixed-layer illite–vermiculite (I/V) clays of the Xuancheng red earth were investigated using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectrometer, and high-resolution transmission electron microscopy (HRTEM) methods. The XRD results indicated that the mixed layer I/V clays were characterized by the broad 10–14Å peak with a maximum intensity at ~12Å in air-dried sample, which decomposed into two peaks at 10Å and 14Å peaks respectively after ethylene glycol treatment. After K+ saturation, the 14Å peak changed to 10Å, which reverted back to 14Å after saturation with Mg2+ with a notable decrease in intensity of the 10Å peak. The broad 10–14Å peak collapsed to 10Å on heating to 400°C. These suggested that the broad 10–14Å peak resulted from randomly interstratified illite–vermiculite clays together with discrete illite and also vermiculite. HRTEM observation showed that straight 10Å illite layers were interstratified with 12Å vermiculite layers, suggesting that transformation of illite to vermiculite involves an exchange of K+ by hydrated cations associated with a swelling of the illite. The (060) spacing of I/V clay is 1.50Å, indicating a dioctahedral precursor of illite and thus reinforcing the transformation from illite to vermiculite. FTIR analysis suggested that most band positions of vermiculite and illite in mixed-layer I/V did not change in comparison with those of the discrete clay species, indicating that the basic crystal structure of mixed-layer illite–vermiculite remains the same as the discrete clays. The interlayer cations in the interlayer region of vermiculite layers of the I/V clays are mainly Ca and minor Mg, Al, and Fe. The abundant Ca makes the I/V clays to behave like I/S on glycolated and thermal treatment, while the Mg, Al, and Fe complex ions in the interlayer region cause the vermiculite layer to lose its expandability and to behave like chlorite. The mixed-layer I/V clays were widely formed in late Quaternary alluvial fans in subtropical to tropical areas, where the sediments experienced synchronous pedogenic modification. The syndepositional pedogenesis process leads to an incomplete transformation of illite to vermiculite and causes the formation of metastable intermediates of mixed-layer illite–vermiculite. [ABSTRACT FROM AUTHOR]

Abstract: The use of antibiotics and hormones in human and veterinary has resulted in frequent detection of these pharmaceuticals in groundwater and wastewater. Thus, it is of great interest to study the interaction between common pharmaceuticals and clay minerals. In this research, we investigated the sorption and intercalation of tetracycline (TC) from water onto rectorite, a regular interstratified clay mineral made of 1:1 ratio of illite and montmorillonite, under different pH and initial concentration conditions. The TC sorption capacity on rectorite reached to 140mgg−1 at pH 4–5 and decreased to 54mgg−1 at pH 11. The intercalation of TC into the interlayer space of the montmorillonite component resulted in an increase in d-spacing. Under acidic condition, the intercalated TC produced an interlayer gallery height of 10Å, compared to 17Å at pH 11, although the amount of TC intercalated is much less than that under acidic condition. Thermogravimetric analyses showed a peak decomposition temperature (T peak) of 230°C for crystalline TC, which increased to 410–420°C after intercalated in rectorite. Both XRD patterns and FTIR spectra showed different interlayer configurations of TC at low and higher amounts of intercalation. The results indicate that rectorite could be a good candidate as sorbent to remove TC from water. [Copyright &y& Elsevier]

Increased use of color dyes in textile industries resulted in great needs of treating dye-containing wastewater. As such, researches and developments for effective removal of dyes from wastewater have been conducted extensively and good progresses have already been made. However, there are still needs to understand the mechanisms of interactions between dyes and solids and to evaluate factors controlling such interactions. In this study, the interactions between different types of clay minerals and rhodamine B (RhB), a zwitterionic dye, were examined under different physic-chemical conditions. The solution pH, ionic strengths, and temperature had minimal influence of RhB uptake on these clay minerals. Uptake of RhB was limited to the external surfaces for the non-swelling clay minerals kaolinite and palygorskite. In contrast, both external and interlayer spaces are responsible for the uptake of RhB on swelling clay mineral montmorillonite. The RhB molecules intercalated into the interlayer of montmorillonite may adopt a monolayer or a bilayer configuration under low and high uptake levels. Under neutral pH condition, the RhB molecules exist as zwitterionic species in solution. The extensive uptake of RhB by the clay minerals, up to their cation exchange capacity (CEC) values, was attributed to electrostatic interactions between cationic end of the amine and the negatively charged clay minerals surfaces. The significant RhB uptake suggested that clay minerals are also good sorbents for the removal of zwitterionic dyes. [ABSTRACT FROM AUTHOR]

Many dye molecules form different aggregation states in aqueous solution under different concentrations. Acridine orange (AO) is a cationic fluorescence dye and is commonly used in DNA analyses. Most measurements for light absorption and fluorescence emission of dyes sorbed on solid matrix reported in literature were performed in clay-dye suspension. Rarely, it was evaluated in solid state. In this study, the fluorescence effect of AO, after being sorbed on 2:1 layered clay minerals montmorillonite (MT), rectorite (RT), and illite (IT), was evaluated in terms of contributions by different forms of AO (monomer, dimer, H- and J -aggregates). As the amounts of AO sorbed increased, the proportion of absorption spectra made by monomer and dimer decreased, while that made by of H- and J -aggregates increased. In sorbed state, the absorbance of AO monomer and dimer was obvious while that attributed to H- and J -aggregates was higher in comparison to that in AO solution. At AO loading of 30 μmol/g on MT and 24 μmol/g on RT and IT, fluorescence emission reached maximum intensity. While the majority of the fluorescence was attributed to monomer and dimer, an unknown peak at 580–590 nm was resolved in the fluorescence spectra. Due to its red shift, it was attributed to J -aggregates on the surface of the minerals. The contribution by H-aggregates was observed in absorption spectra, but not in fluorescence spectra, which was speculated that the blue shift caused by H-aggregates overlapped with the excitation wavelength of 490 nm. The 2:1 clays could serve as a substrate for optimal dye sorption to achieve maximum fluorescence emission effect and practical applications of such dye-clay composites in powder form could be further explored. • Fluorescence of acridine orange on 2:1 dioctahedral clays in powder form was tested. • Maximal fluorescence emission obtained when the dye was in monomer formation. • Fluorescence emission was optimized at dye loading of 24–30 μmol/g on the clays. • Higher dye loading levels resulted in significant fluorescence quenching. • Exploration of dye-loaded clay powders for fluorescence applications is promising. [ABSTRACT FROM AUTHOR]