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In this study, the removal of ciprofloxacin hydrochloride (a fluoroquinolone antibiotic) by using various effective adsorbents such as activated carbon, montmorillonite, modified montmorillonite (commercial name Cloisite 20A), and alumina was investigated. Adsorption experiments were performed to determine and compare the adsorption capacities of these adsorbents. The adsorption capacities of adsorbents were examined at different initial concentrations of ciprofloxacin hydrochloride. Activated carbon was found to be having the best adsorption capacity for the removal of ciprofloxacin hydrochloride. For the solution having an initial ciprofloxacin hydrochloride concentration of 4 ppm, the adsorption capacities of adsorbents were obtained as 1.86 mg g−1 for activated carbon, 1.67 mg g−1 for modified montmorillonite, 1.15 mg g−1 for alumina, and 0.60 mg g−1 for montmorillonite. And also, about 92% of the ciprofloxacin hydrochloride was removed from the water using the activated carbon. In addition, Langmuir, Freundlich, and Temkin isotherm models were employed to express the adsorption process. For all adsorbents, Freundlich isotherm model provided best fitting to the experimental data because of very high values of R2 (> 0.99). Kinetic models of pseudo-first order, pseudo-second order, Elovich, and Weber-Morris intraparticle diffusion model were utilized to evaluate the experimental adsorption data. Adsorption kinetics data were well represented by pseudo-second order kinetic model with values of R2 (> 0.999).

Heavy metal pollution such as water contamination by Pb, Hg, Cu, Cd and Cr ions is induced by rapid urbanization and industrialization and is a major threat to human health. One of the most efficient processes to clean contaminated water is adsorption. Adsorbents such as clay minerals and modified clays are efficient for the removal of metal ions from wastewater. This manuscript reviews current research in heavy metal adsorption by clay minerals such as halloysite, bentonite, montmorillonite, vermiculite and attapulgite, from 2013 to 2017, and highlights the main adsorption mechanisms. The structure, composition and synthesis of various clay minerals and modified clays are presented.

As a type of atmospheric particulates, it is important to understand the characteristics of the atmospheric microbial-mineral aerosol. This paper focuses on the montmorillonite/bacteria complex, which is prepared by combining montmorillonite and three common strains of bacteria (Escherichia coli, Staphylococcus aureus, and Bacillus pumilus) in the solution system. The particle size, morphology, surface potential, and surface group characteristics of the extracted montmorillonite/bacteria complex were analyzed by modern analysis and testing technology. Results demonstrate that both montmorillonite and three common strains of bacteria can form the mineral/bacteria complex. The scanning electron microscopy results showed that S. aureus adheres to the montmorillonite in a multi-layered manner, while E. coli and B. pumilus cement the montmorillonite particles to form the complex. Additionally, the presence of the globular bacteria outnumbered the rod-shaped bacteria. The particle size of the montmorillonite/bacteria complex increased, ranging from 1.53 to 4.71 times larger than that of the original particles. The matching trend results suggest that the formation of the montmorillonite/bacteria complex does not follow a one-to-one relationship. The surface potential of the complex was negatively charged within a pH range of 2~11, without an isoelectric point. The potential value of the complex tends toward that of montmorillonite, indicating that non-electrostatic interactions primarily govern the complex formation. The most prominent FTIR spectra of the montmorillonite/bacteria complex corresponded to the peaks of montmorillonite, with additional peaks representing protein and polysaccharide from the bacteria. These signify the adherence of bacteria to the surface of the montmorillonite. The β-sheet/α-helix ratio of bacteria in the montmorillonite/bacteria complex increased indicating that the hydrogen bonding plays a dominant role in the complex formation.

Abstract We investigated the effects of substrate (cellulose or starch) and different clay contents on the production of microbial extracellular polymeric substances (EPS) and concomitant development of stable soil aggregates. Soils were incubated with different amounts of montmorillonite (+ 0.1%, + 1%, + 10%) both with and without two substrates of contrasting quality (starch and cellulose). Microbial respiration (CO2), biomass carbon (C), EPS-protein, and EPS-polysaccharide were determined over the experimental period. The diversity and compositional shifts of microbial communities (bacteria/archaea) were analysed by sequencing 16S rRNA gene fragments amplified from soil DNA. Soil aggregate size distribution was determined and geometric mean diameter calculated for aggregate formation. Aggregate stabilities were compared among 1–2-mm size fraction. Starch amendment supported a faster increase than cellulose in both respiration and microbial biomass. Microbial community structure and composition differed depending on the C substrate added. However, clay addition had a more pronounced effect on alpha diversity compared to the addition of starch or cellulose. Substrate addition resulted in an increased EPS concentration only if combined with clay addition. At high clay addition, starch resulted in higher EPS concentrations than cellulose. Where additional substrate was not provided, EPS-protein was only weakly correlated with aggregate formation and stability. The relationship became stronger with addition of substrate. Labile organic C thus clearly plays a role in aggregate formation, but increasing clay content was found to enhance aggregate stability and additionally resulted in the development of distinct microbial communities and increased EPS production.

A highly resourceful, environmentally benign, and recyclable magnetic montmorillonite composite (MMT/CF) was obtained through a simple one-step hydrothermal method and exhibited excellent Pb (II) removal. The as-synthesized adsorbent was then characterized by XRD, SEM–EDX, FTIR, BET, and TGA-DTA. The operating parameters including adsorbent dosage, initial Pb (II) concentration, solution pH, and time were studied. Also, a comparative approach was formed between response surface methodology (RSM) and artificial neural network (ANN) to optimize and model the removal efficiency of Pb (II) by MMT/CF. The results indicated that the ANN model was more precise and quite trusted optimization tool than RSM in consideration of its higher correlation coefficient ( R 2  = 0.998) and lower prediction errors (RMSE = 0.851 and ADD = 0.505). Langmuir isotherm provided the best fit to the experimental data, and the maximum adsorption capacity was 101.01 mg/g. Additionally, the kinetic studies showed that the pseudo-second-order model fitted well with the experimental data. The magnetic MMT/CF composite possesses high adsorption capacity and is suitable for reuse. Therefore, this study shows that MMT/CF composite can be a potential adsorbent in Pb (II) uptake from aqueous media.

Expansive soil is blamed for many engineering problems such as foundation damages, subgrade heave, and road surface bulking. Lime is one of the most widely utilized materials in the stabilization of expansive soil. However, the stabilization mechanism of lime-treated expansive soil has not been thoroughly studied from the nanoscale level. This paper employed montmorillonite (Mt) and portlandite (Po) to represent expansive soil and the hydration product of lime. Four types of portlandite-montmorillonite (Po-Mt) molecular models with different surface charges and interlayer cations revealed the nanoscale stabilization mechanism of Po-Mt. The results show that volume change of Po-Mt samples is not only related to adsorption energy of Mt, but also controlled by competitive adsorption of Po and interaction between lime and Mt. The interface energy between Po and Mt generated by Ca ions migration from Po to Mt surface plays a most significant role in governing the swelling behavior of Po-Mt by providing strong repulsive force to confine the swelling of Mt layers.

Two novel adsorbents – montmorillonite (Mnt)-hyamine and Mnt-hyamine-sodium dodecyl sulfate (SDS) – were synthesized using Mnt nanoparticles. The modified Mnt and Mnt nanoparticles were used for the removal of crystal violet from water, and they were characterized using various techniques. The effects of pH, time, temperature, adsorbent dosage and initial dye concentration on the dye-removal efficiency were investigated using response surface methodology. The optimum conditions for maximum dye removal were obtained. The optimum conditions for crystal violet adsorption on Mnt-hyamine, Mnt-hyamine-SDS and Mnt nanoparticles are temperatures 25.00°C, 29.97°C and 27.28°C; pH values 9.00, 10.41 and 9.40; adsorbent dosages 1.00, 1.15 and 1.06 g L –1 ; and initial dye concentrations 30.00, 98.74 and 99.44 mg L –1 , respectively. The adsorbent dosage is the most critical variable for dye removal. Temkin and Langmuir are the best isotherms for studying adsorption equilibria. In the kinetic study, the fractal-like integrated kinetic Langmuir model was the most appropriate model, and the thermodynamic parameters were also determined. The synthesized adsorbents could be easily separated from solution. The Mnt-hyamine-SDS adsorbent has a high adsorption capacity (690.69 mg g –1 ) for the removal of crystal violet.

Metal cations are often used to regulate montmorillonite, but the mechanism is still unclear. In this paper, the regulation of different cations in montmorillonite was studied, and it was found that the regulation of different cations had significant effects on the structure of montmorillonite. Firstly, the viscosity is negatively correlated with particle size, and the order of particle size is trivalent > divalent > monovalent cation. Secondly, the swelling capacity is positively correlated with the absolute value of zeta potential, and the order of the zeta potential is monovalent > trivalent > divalent cation. Thirdly, the smaller hydrated ion radius and static electricity of monovalent cations significantly reduce the layer spacing. Meanwhile, isomorphism displacement results in a significant increase in the proportion of cis-vacant configuration due to changing the electronegativity of the octahedron. The comprehensive performance is that the particle size is significantly reduced and the absolute value of zeta potential is significantly increased. It is easy to peel off and expand in water to form a uniform and stable colloidal substance, which has the best gel performance. The research results can provide theoretical support for the regulation of montmorillonite structure and gel properties by different valence metal cations.

Gaomiaozi (GMZ) bentonite is the most extensively used buffer/backfill material in deep geological repositories used for the disposal of high-level nuclear waste in China. Highly alkaline ground water solutions derived from the cement dissolution may cause changes in the mineralogical composition and in the adsorption capacity of bentonite, and may affect the long-term performance of the engineering barrier system. In the present study, the alteration of montmorillonite and its influence on the adsorptive properties of GMZ bentonite were investigated. The X-ray diffraction patterns of the mineral composition showed that the main compound of the GMZ bentonite is montmorillonite. By contrast, its hydration with a solution of KOH at 80 °C produced cementitious materials, and transformation could likely lead to kaolinisation. Thermodynamic results show that the adsorption of Sr (II) on GMZ bentonite is exothermic and follows quasi-secondary adsorption kinetics. For an initial Sr (II) concentration C0 = 100 mg/L, the maximum amount of Sr (II) adsorbed (qe) on GMZ bentonite was 9.72 mg/g. The adsorption capacity of GMZ bentonite on Sr (II) decreased gradually and as a function of the mineral transformation time in a mixture of GMZ bentonite and KOH. The Freundlich isotherm adsorption model can describe in a satisfactory manner the adsorption of Sr (II) on GMZ bentonite or the transformation of bentonite at different degrees of mineral transformations.

Mineral dusts are among the most active ice-nucleating particles present in cloud droplets, with their properties influencing radiative properties and precipitation formation. To improve weather predictions and climate projections, it is important to understand under which conditions ice will form on mineral dusts. Laboratory experiments have primarily focused on single minerals, and field samples are complex mixtures that cannot be controlled in their composition or particle size. To fill this gap, a bottom-up investigation of suspensions containing pure or binary mixtures of microcline, montmorillonite, or quartz at concentrations between 0.0001 and 0.1 wt % is presented. Arrays of monodisperse aqueous droplets (diameters of 75 µm) are generated using a microfluidic device and subsequently cooled at a rate of 1 K min.sup.-1 . The probability of freezing in the presence of binary mixtures generally follows that of the most ice-active mineral. Each pure mineral's nucleation site density is fit as a function of temperature and used to predict the frozen fraction curves for each binary mixture assuming additivity of mineral surface area. Predictions are also made for Arizona Test Dust from the obtained pure mineral fits, and general agreement with experiments is observed. This work presents a systematic study of ice formation in the presence of pure and binary mixtures of common mineral dusts, providing information for the future design of composition-aware parameterizations for ice nucleation in the atmosphere.