EFFECT OF MECHANOACTIVATION OF THE NATURAL AND ENRICHED BY SEDIMENTION BENTONITE ON THE RHODAMINE B ADSORPTION EFFICIENCY

Bentonite, due to its physical and chemical properties, is considered to be one of the most promising candidates for decontamination and disposal of high-level heavy metal wastes. Magnetic particles and their composites are also extremely suitable in water treatment. Therefore, the possibility to enhance the sorption properties of natural clay rock bentonite by its magnetic modification was investigated. The bentonite/iron oxide composites were prepared in different weight ratios at two selected temperatures 20°C and 85°C. The surface and pore changes of natural bentonite after magnetic modification was studied by nitrogen adsorption measurements. It was found that the composite prepared in weight ratio 1:1 of bentonite/ iron oxide at 85°C, denoted as A85, showed the highest increase in total pore volume (0.216 cm3/g) and the specific surface area from the value 39.4 m2/g of the natural bentonite to 82.8 m2/g of A85. The natural bentonite and composite materials were characterized by powder x-ray diffraction (XRD) analysis in order to quantify the structural changes. The magnetic properties were measured by superconducting quantum interference (SQUID) magnetometer and the morphology of the investigated samples was observed by scanning electron microscopy (SEM). The natural bentonite and composites A85 and E20 were chosen to study the sorption of cadmium from model solutions.

Introduction. One of the methods for improving the properties of sintered materials is mechanical activation of powders. It ensures milling the powders, changing its energy state, intensifying the sintering of powder materials, and forming a fine-grained structure in it. When tungsten powders are mechanically activated in planetary centrifugal mills, nanoparticles can be formed, which have a high reactive power. The objective of the paper is to study the effect of mechanical activation of tungsten particles on the structure and properties of the sintered Sn-Cu-Co-W powder material. Research technique: Mechanical activation of W16,5 grade tungsten powder is carried out in a planetary centrifugal ball mill AGO-2U for 5…120 minutes with carrier speeds of 400…1,000 rpm. The mixture of tungsten, tin, copper, and cobalt powders are compacted by static pressing in molds and then sintered in vacuum at 820 °C. The morphology and size of powder particles, as well as the structure of the sintered samples, are studied by scanning electronic microscopy, X-ray microanalysis, and optical metallography. Porosity of the sintered samples is identified by the gravimetric method. Microhardness of the structural constituents and macrohardness of the sintered materials are measured, too. Results: in the modes under study, mechanical activation is accompanied by the formation of tungsten nanoparticles with the minimum size of 25 nm. Alongside this, the powder is exposed to cold working, which hinders further milling. Tungsten nanoparticles, characterized by high surface energy, have a significant effect on the dissolution-precipitation of cobalt during liquid-phase sintering of Sn-Cu-Co-W powder material. Addition of nanodispersed tungsten into the material slows down the growth of cobalt particles during sintering and contributes to the formation of a fine-grained structure. The sintered Sn-Cu-Co-W material, containing mechanically activated tungsten, features higher hardness of 105…107 HRB, which is explained by cold working of tungsten particles and dispersion hardening. The results can be applied for improving mechanical properties of Sn-Cu-Co-W alloys used as metallic binders in diamond abrasive tools.

The adsorption of the cationic dyes rhodamine B (RhB) and methylene blue (MB) was investigated on natural montmorillonite (MM) and its mechanoactivated form (MAMM). Mechanical modification of MM was carried out in a planetary mill using zirconia grinding media (MM-to-media mass ratio 7.5:1) at a rotor speed of 1500 rpm for 3 minutes. The adsorption efficiency increased significantly for both dyes when using MAMM compared to MM: by 26.9% for RhB and 29.8% for MB. A comparison of the physicochemical properties of the adsorbents was performed using small- and wide-angle X-ray diffraction, solid-state NMR (Si, Al, Na), scanning electron microscopy, IR spectroscopy, TG-DSC thermal analysis, low-temperature nitrogen adsorption/desorption, and static laser light scattering. The improved adsorption properties of MAMM are attributed to structural and textural changes caused by mechanoactivation, which leads to delamination of aluminosilicate layers, enhanced pore characteristics, and a reduction in clay particle size in aqueous dispersions. Additionally, MAMM retains a high degree of crystallinity of aluminosilicate layers, exhibits partial dehydroxylation, and shows a slight shift of the ζ-potential toward less negative values.

Nanoceria was synthesized by reaction of cerium nitrate deposition in an aqueous medium without stabilizers at room temperature. Nano-sized cerium oxide was dried at 20 °C and calcinated in air for 1 hour at 120, 300, 500, 800 °C. SEM images of samples demonstrated that the morphology of the obtained cerium oxide does not significantly change with the increase of the temperature of heat treatment. Electron microscopy showed that the average diameter of CeO2 particles varies in the range of 12.4–15.9 nm. Sample element content was determined by the energy-dispersive X-ray spectrometry method. The Oxygen:Cerium elements ratio in the samples is in the range 1.7–2.1. X-Ray Diffraction method was used to determine the structural characteristics of materials. It was demonstrated that with increasing annealing temperature, the average crystallite diameter increases from 10 to 23 nm, and the degree of crystallinity changes from 60 % for Ce-20 to 100 % for Ce-800. The characteristics of the porous structure were determined based on low-temperature nitrogen adsorption/desorption isotherms. The specific surface area (BET) of the samples heated to 500 °C varies within 46–61 m2/g. The total pore volume varies from 0.19 to 0.22 cm3/g. After heating to 800 °C, the specific surface area and total pore volume decrease to 17 m2/g and 0.13 cm3/g, respectively. By TGA method was found that 5 % mass loss between 20 and 300 °C is attributed to adsorbed water, while 9 % starting at around 500 °C refers to release from the surface of chemically bonded water molecules. The IUVS Ce4+/IUVS Ce3+ ratio in samples was found from UV-spectra of diffuse reflectance; it varied in the range of 1.60 to 2.08. Calcination of nanoceria samples at temperatures above 500 °C leads to the oxidation of Ce3+ to Ce4+ and reduction of nanoceriа surface defects. The catalytic activity of the synthesized materials was evaluated by the determination of the reaction rate constant (k) of the H2O2 decomposition reaction at the different concentrations (1–10 %) at room temperature and within pH 8.0–11.0. Materials calcinated at different temperatures demonstrate maximum catalytic activity at pH 10.0, which is determined by the increase in the content of deprotonated ceranol groups on the surface of cerium oxide with an increase in the pH from 8.0 to 10.0, and the formation of insoluble Cerium compounds with a further increase in pH. The activation energy (Ea) of the reaction of hydrogen peroxide decomposition by nanoceria in the temperature range of 20–40 °C at pH 10 was determined by kinetic data. The Ea for un-annealing sample Ce-20 is 127 kJ/mol. Increasing temperature to 120 °C does not change the Ea. It was shown that the smallest value of activation energy is 77 kJ/mol for the sample calcinated at 300 °C. Heating the samples at temperatures 500 and 800 °C causes growth of Ea – to 94 and 95 kJ/mol, respectively. We did not find correlation between degree of crystallinity, specific surface area, total pore volume, crystallite size and calcinated samples catalytic activity. The dependence of the rate constant (activity) on the calcination temperature is extreme with a maximum at 300 °C was found. A sample Ce-300, which has the highest O:Ce ratio (2.08), the largest O content (67.5 %), the lowest Ce4+/Ce3+ ratio (0.15) among the calcinated samples, and therefore the largest number of surface defects exhibits the highest catalytic activity and has the lowest activation energy for the hydrogen peroxide decomposition reaction. Presumably, when heating CeO2 samples, some parallel processes occur. Changes in the values of structural parameters either have no effect or are insignificant and also do not affect the catalytic activity of nanoceria. Desorption of physically adsorbed water, which inactivates the catalytic centers, leads to an increase in catalytic activity of the material. In addition, destruction of ceranol groups on the surface of cerium oxide with loss of oxygen and oxidation of Ce3+ to Ce4+ reduces catalytic activity.

In this paper, the mineral and pore structure characteristics of Longmaxi shale gas reservoir have been studied with a series of parallel experiments on core samples drilled from Jiaoshiba gas field, southern Sichuan Basin, China, including X-ray diffraction (XRD) tests, total organic carbon (TOC) analysis, field emission scanning electron microscopy (FE-SEM), low temperature nitrogen adsorption/desorption (LTNA), and nuclear magnetic resonance (NMR). The relations among TOC, mineralogical compositions and pore structure parameters, and comparison of pore size distribution (PSD) of shales obtained by LTNA and NMR are discussed. The results show that the Longmaxi shales are rich in organic matter, with an average content of 2.73%. The mineralogical compositions are dominated by quartz and clay minerals, with an average content of 43.72 and 36.32%, respectively. The TOC has strong positive correlations to the quartz and pyrite, but negative correlations to clay mineral. There are three types of pores, including organic pores, inorganic pores (inter-crystalline pores and intergranular pores), and microfractures (diagenetic shrinkage joints and organic evolution abnormal-pressure fracture), which can be seen from FE-SEM, with pore sizes following the order of organic pores <inorganic pores < micro-fractures. The organic matter and quartz have a positive influence on the specific surface (ranging from 7.27 to 14.705 m2/g) and total pore volume (ranging from 0.004 to 0.02 cm3/g), whereas clay minerals have a negative effect on the specific surface and total pore volume. Compared with LTNA, the NMR can better reveal pores, indicating pore size ranging from smaller than 1 nm to several tens of micrometers. The PSDs acquired from NMR present tri-modal distribution when TOC content is higher than 2.5% and clay mineral content lower than 40%. On the contrary, the PSDs present bi-modal distribution when TOC content is lower than 2.5% and clay mineral content higher than 40%.

The influence of the combined impact of shear stress and cavitation on the structure and sorption properties of chitin

BASF to invest EUR 4.5 bn in EV battery recycling

A characterization study of some aspects of the adsorption of aqueous Co 2+ ions on a natural bentonite clay

Characteristics of shale pore structures may play an important role in natural gas accumulation and consequently estimating the original gas in place. To determine the pore structure characteristics of Niutitang marine shale in the Sangzhi block, we carried out N2 adsorption-desorption (LP-N2GA), CO2 adsorption (LP-CO2GA), and methane isothermal adsorption on shale samples to reveal the pore size distribution (PSD) and its impact on the adsorption capacity. Results indicate that the Niutitang Shale is in stages of maturity and overmaturity with good organic matter, and they also indicate well-developed interparticle, intraparticle, and organic pores. Quartz and clay are found to be the main minerals, and the high illite content means that the Niutitang Shale is experiencing the later stage of clay mineral transformation. Various-sized shale pores are well-developed, and most of them are narrow and slit-like. For pores with diameters of 2–300 nm measured with LP-N2GA, mesopores (2–50 nm) contribute most of the total specific surface area (SSA) and total pore volume (TPV) in comparison to macropores (50–300 nm). For micropores (&amp;lt;2 nm) tested by LP-CO2GA, the PSD appears to be multimodal; shale pores of 0.50–0.90 nm diameter contribute most of the SSA and TPV. CO2-SSA and N2-SSA indicate positive correlations with their corresponding TPV. The total organic matter (TOC) has good correlation with the SSA and TPV of micropores. The Langmuir volume positively correlates with the total SSA. Additionally, the TOC content has a good correlation with the Langmuir volume, which is consistent with the observation of well-developed fossils of diatoms and organic pores. As an important source of organic matter, more diatoms mean more organic matter, larger TOC values and quartz content, larger SSA and TPV of micropores, and, of course, stronger shale adsorption capacity. The results provide important guidance for the exploration and development of shale gas existing in the Sangzhi block.

The effect of mechanical treatment of natural montmorillonite in a planetary-centrifugal mill on the efficiency of intercalating aluminum polyhydroxocomplexes [Al30O8(OH)56(H2O)26]18+ in the formation of pillared structures was studied. Measurements made using the photometry method showed that in the montmorillonite matrix, after intercalation of the Al30 polyhydroxocomplexes using mechanical treatment, an increase in the content of Al3+ cations by 13% was observed. According to the electrophoretic light scattering data, the particle size for the suspension of mechanically activated montmorillonite dispersed in water was about 100 nm. The raw, mechanically activated and pillared montmorillonites are characterized by the methods of low-angle X-ray diffraction, scanning electron microscopy, and low-temperature nitrogen adsorption-desorption. It was shown that preliminary mechanical activation of the initial substrate increases the basal distance d001 and significantly (approximately by 45–50%) increases the specific surface area and the total pore volume of Al30-pillared montmorillonite; in this case, both meso- and microporosity increase, and the pore size decreases by about 12%. The special importance of the size of montmorillonite particles during the intercalation and further formation of the pillared structure is shown. А decrease in the size of the montmorillonite particles during mechanical treatment increasing the area of the interphase boundary through which ion exchange takes place. It was shown that the small sizes of tactoids (about 100 nm) in an aqueous suspension play a key role in increasing the cation exchange capacity of mechanically activated montmorillonite. To a lesser extent, the efficiency of intercalation is influenced by the processes of defect formation and the related changes in the electrical properties of the silicate layers of montmorillonite. Based on the structural properties, the obtained pillared materials can be recommended for use as selective adsorbents, molecular sieves and catalysts.

The effect of carbon dioxide (CO2) on global warming is serious problem. The adsorption with solid sorbents is one of the most appropriate options. In this study, the most interesting adsorbent is granular activated carbon (GAC). It is suitable material for CO2 adsorption because of its simple availability, many specific surface area, and low-cost material. Afterwards, GAC was impregnated with chitosan solution as impregnated granular activated carbon (CGAC) in order to improve the adsorption capacity of GAC. This research aims to compare the physical and chemical characteristics of GAC and CGAC. The experiment was carried out to evaluate the efficiency of CO2 adsorption between GAC and CGAC. The results indicated that the iodine number of GAC and CGAC was 137.17 and 120.30 mg/g, respectively. The Brunauer-Emmett-Teller results (BET) of both GAC and CGAC show that specific surface area was 301.9 and 531.3 m2/g, respectively; total pore volume was 0.16 and 0.29 cm3/g, respectively; and mean diameter of pore was 2.18 and 2.15 nm, respectively. Finally, the CO2 adsorption results of both GAC and CGAC in single column how the maximum adsorption capacity was 0.17 and 0.25 mol/kg, respectively; how degeneration time was 49.6 and 80.0 min, respectively; and how the highest efficiency of CO2 adsorption was 91.92% and 91.19%, respectively. Keywords: Carbon dioxide adsorption, Chitosan, Global warming, Granular activated carbon

Changes in the pore structure of lignite after repeated cycles of liquid nitrogen freezing as determined by nitrogen adsorption and mercury intrusion

Influence of pyrolysis conditions of modified corn cob bio-waste sorbents on adsorption mechanism of atrazine in contaminated water

Soil is a particulate material and its constituent particles have a wide range of sizes. Nanoparticles of usually 1 to 100 nm are the smallest particles in soil environments and exist in one of the three different forms: nanoplatelets, nanowires or nanotubes, and nanodots. Due to their tiny size, soil nanoparticles usually exhibit special enhanced surface properties and hence interact more actively with other soil particles and solution. In this paper, some commonly occurring nanoparticles and their properties are briefly summarized, including specific surface area, particle morphology, nanoporosity, and surface charges. Owing to the extremely large specific surface area, surface charges, and sometimes nanoporosity, these particles, even preset at a small fraction, may significantly affect soil's physico-chemical behavior and engineering properties. Soils containing nanoparticles with nanoscale intraparticle voids usually exhibit much higher liquid and plastic limits that usually show irreversible changes upon drying, while the presence of fibrous nanoparticles usually makes the soil more thixotropic and enhances its shear strength. To reflect the difference between nanoparticles and classical clay sized particles, a new type of soil particle "nanosol" is proposed to define soil nanoparticles.

Characterization of organo-modified bentonite sorbents: The effect of modification conditions on adsorption performance