Applied Clay Science最新文献

Rare earth elements (REYs) originate from the weathering of parent granite, whose clay-sized fractions are pivotal in the regolith-hosted rare earth elements (REEs) deposits. Regarding microbial action on REY mobilization and fractionation, their patterns remain unclear. Chemical extraction and bio-leaching experiments utilizing sulfate-reducing bacteria (SRB) were performed to exemplify the chemical and microbial effects on REY mobilization among the clay-sized phases. Our results indicate that the REYs occur primarily in the three fractions: i.e., amorphous FeMn phase, crystalline Fe phase, and carbonate in chemical reactors wherein the mineral phase was critical to the adsorption of REY. The 30-day SRB-leaching experiments led to an increase in the percentage of REY from 6% to 45% in the residue phase, implying that the residue phase, R_{Amor iron} phase, and R_Org phase hosted the REYs. The disorder of iron-bearing minerals, formation of iron-organic matters (Fe-OM), and secondary iron-bearing minerals represented a significant bio-leaching mechanism. Compared to chemical extraction, relatively higher MREY and HREY release efficiencies were obtained via bio-leaching, with average LREY/HREY ratios of 1.34–5.91 and 0.2–2.24 in chemical and bio-reactors, respectively. Our findings exhibited high potential microbial effects on the mobilization and fractionation of REY among mineral phases, offering real insights into the biogeochemical processes between minerals and bacteria.

Amorphous mesoporous materials derived from synthetic saponite (Sap) by acid treatment have been used in catalysis for several decades. Uncovering the transformation process of Sap from layered to amorphous structure under acid attack is beneficial to optimize the structure of Sap-derived mesoporous materials, yet such transformation process remains unclear. Herein, a magnesium-Sap was synthesized by hydrothermal method and then treated with sulfuric acid. By studying the changes in phase composition, morphology, chemical state of elements and surface area of the synthetic Sap after acid attack, a specified transformation mechanism of synthetic Sap to amorphous silica is clarified. The experimental results indicate that after leaching of Mg and Al cations from the Mg/AlO₆ octahedral sheets of Sap during acid attack, the retained SiO₄ tetrahedral sheets of Sap were transformed into amorphous short-range ordered silica phases and nanoscrolls with pseudohexagonal side pores. The transformation process of synthetic Sap under acid attack can be divided into leaching of metal ions from octahedral sheets of Sap to form layered silica particles, splitting and crimping of surface nano-silica layers from the formed silica particles, and completely amorphous transformation. The distortion of SiO bonds in SiO₄ tetrahedral sheets during acid attack might be the driving force for such transformation. This work provides specific transformation process of synthetic Sap under acid attack which is conductive to the controllable preparation of acid-treated Sap derivates, and has certain significance for understanding of structural transformation of clay minerals with MgO₆ octahedral structure.

Lithium (Li)-bearing clays have emerged as new types of Li resources. The structure and elemental composition of clay minerals play a crucial role in determining the Li leaching efficiency. The elemental composition and structural transformation of Li-bearing mica from Inner Mongolia (IMS) and Jiangxi (JS), China, were studied during the calcination-leaching process by using X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR) and electron microprobe analysis (EMPA). The findings indicate that Mica is the predominant Li-bearing mineral in both IMS and JS. Notably, the IMS mica contains a significantly higher concentration of fluorine compared to the JS mica. Fluorine exerts a minor inhibitory effect on Li leaching, whereas the hydroxyl group (OH) significantly inhibits the leaching of Li from mica. The removal of residual oxygen atoms post-dehydroxylation is crucial to extract Li from mica. Both defluorination and dehydroxylation reactions occur within the temperature range of 800 °C to 900 °C. When calcined at 900 °C, the IMS mica was transformed into sanidine, while the JS mica was transformed into microcline. The acid leaching of products calcined at this temperature represents a process that further disrupts the residual mica structure and facilitates a cation exchange reaction.

Managing clay-containing slurries during drying process remains a persistent challenge in various industries. Despite challenges of drying clay-containing-slurries, limited information is available. The aim of this study is to explore the drying performance of slurries containing kaolin and bentonite and gain insights into the underlying drying mechanisms. The research presented integrates drying experiments, rheology measurements, settling experiments, zeta potential measurements, FTIR, TGA/DTA, and SEM analysis. Bentonite-containing slurries retained more moisture due to their high-water adsorption capacity, with higher bentonite percentages extending drying times. The addition of Ca²⁺ ions reduced moisture content by replacing Na⁺ ions with smaller Ca²⁺ ions, making the slurries less viscous. The addition of Ca²⁺ disrupted the gel-like structure of bentonite as confirmed by SEM and FTIR. In contrast, kaolin-containing slurries maintain lower moisture levels owing to the non-swelling structure of kaolinite. SEM showed the formation of agglomerates for kaolin when Ca²⁺ was added The addition of Ca²⁺ ions had a subtle impact on drying rates, despite a slight increase in slurry viscosity probably due to the agglomeration of kaolinite particles. Both slurries exhibited three drying phases: rapid drying due to high moisture, a moderate phase with reduced rates, and a final phase of slowed drying as tightly bound moisture was harder to remove. This paper demonstrated the significance of understanding the drying processes of clay-containing slurries to enhance the overall drying efficiency.

In the proposed Swiss repository location at Nördlich Lägern, in an Opalinus Clay formation, at the depth of about 850–900 m, the ambient temperature due to geothermal gradient is expected to be about 45–50 °C.

In this study, constant-volume swelling pressure experiments were performed to assess the effect of such elevated temperatures (25 - 60 °C) on granular Wyoming bentonite performance around designed buffer dry density of 1450 kg/m³. Bentonite was hydrated with a saline solution closely simulating reference Opalinus clay groundwater, and the bentonite dry density was varied between 1300 kg/m³ and 1600 kg/m³ to evaluate density dependency. Tests included isothermal, as well as increasing (incremental) and decreasing (decremental) temperature programs following different thermo-hydraulic paths: full saturation-first and complete heating-first. The dependency of swelling pressure on both bentonite density and temperature was analyzed by pressure-temperature slope (kPa/°C) and obtained results were compared to previous similar tests with Wyoming bentonite at different bentonite densities.

Overall conclusion is that granular Wyoming-type bentonite swelling pressure response to elevated temperature at designed dry density of 1450 kg/m³ is small (−6.5 ± 2.0 kPa/°C), and robust against changes in the thermo-hydraulic path or in the density.

2D/2D van der Waals heterojunctions have been proved to be a feasible strategy to enhance photocatalytic activity. In this work, two-dimensional (2D) BiOCl and layered double hydroxides (NiAl-LDHs) were composited using a simple mechanical mixing method at room temperature. The 2D/2D BiOCl/NiAl-LDHs S-scheme heterojunctions with a sheet-on-sheet interface contact were formed. The effects of interface contact and band structure between BiOCl and NiAl-LDHs on the photocatalytic properties were investigated. Experimental results showed that the reaction rate constants of BiOCl/NiAl-LDHs S-scheme heterojunctions for the degradation of methyl orange, methylene blue and levofoxacin were 13, 59 and 3 times of BiOCl and 141, 83 and 27 times of NiAl-LDHs, respectively. BiOCl/NiAl-LDHs heterojunctions displayed good stability and regeneration capacity. After four times of recycling, the degradation rates were more than 97 % for methyl orange and methylene blue, and 94.5 % for levofoxacin. The enhancement in photocatalytic activity was attributed to the formation of S-scheme van der Waals heterojunctions with sheet-on-sheet contact, which provided a short charge transfer distance and enabled rapid charge separation at the interface. The formation of S-scheme heterojunctions was confirmed by X-ray photoelectron spectroscopy, experimental calculations and radical trapping experiments. Using the same method, BiOX(X = Br and I)/NiAl-LDHs composites with sheet-on-sheet contact were also obtained. This work could provide valuable reference for constructing 2D/2D van der Waals heterojunctions.

Natural kaolinite is widely used in the field of photocatalysis as the support material of photocatalyst. However, its weak photochemical activity has severely limited its application as a photocatalyst in photocatalysis. Herein, kaolinite/NiFe layered double oxide (Kaol/NiFe-LDO) heterostructure photocatalyst was successfully constructed to activate peroxymonosulfate for degradation of organic pollutants. The chemical bonds formed at the interface of Kaol/NiFe-LDO heterostructures (HCs) greatly improve the photocatalytic ability of natural Kaol. Additionally, systematic characterization results validate that the Kaol/NiFe-LDO HCs possesses a direct Z-scheme band structure. By utilizing both interfacial chemical bonding and direct Z-type heterostructure effects, the optimized Kaol/NiFe-LDO HCs demonstrates a 2-fold increase in rhodamine B (RhB) degradation and a 6.5-fold increase in orange II (OII) degradation compared to natural Kaol in the presence of PMS as an oxidant. The Kaol/NiFe-LDO HCs photochemically activate the PMS to produce sulfate radicals through photo-generated hole oxidation, thus improving the photocatalytic performance of the system. The present study offers novel insights into the activation of PMS by natural clay minerals for environmental applications.

The response of clay minerals to changes in pore fluid salinity, particularly in coastal areas such as bays, lagoons, sounds, sloughs, and estuaries, has not been extensively studied. Herein, the influence of salinity exchange on the microscopic interaction and sedimentation behavior of halloysite nanotubes in an aqueous condition was investigated. In-situ microscopic observations and macro-scale sedimentation experiments reveal that halloysite nanotubes tend to disperse in pore fluids with high ionic strength because salt ions weaken the edge-to-face halloysite fabrics. Salinity exchange experiments demonstrate the permanent alteration of flocculation and sedimentation behavior due to the residual salt ions on the HNT surfaces. Even when the salt concentration is restored to its initial value, the presence of residual salts leads to the formation of a large and open floc structure, resulting in slower settling and a loosely packed final sediment. Our study provides a thorough understanding of the salt effect on sediment formation, including changes in the microscopic clay particle fabrics during salinity exchange.

Rectorite has a regular lamellar structure, and its structure tends to result in a high adsorption capacity. Prior research has examined the adsorption characteristics of rectorite on antibiotics by various analytical techniques, including X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The results demonstrated that the adsorption capacity of Na-Rec for both ciprofloxacin (CIP) (18.3 mg g⁻¹) and tetracycline (TC) (25.0 mg g⁻¹) was stronger than that of Ca-Rec for both CIP (17.7 mg g⁻¹)and TC (23.5 mg g⁻¹), and that both rectorites were stronger than CIP for TC (23.5 mg g⁻¹ > 17.7 mg g⁻¹, 25.0 mg g⁻¹ > 18.3 mg g⁻¹). Rectorites were characterized both before and after adsorption, and the effects of a number of variables on the adsorption process were investigated. During the adsorption process, ions are liberated in the interlayer structure and exchange with pollutant molecules in the interlayer. This study reveals that rectorites with different ionic hydrates states have distinct adsorption behaviors and loading capabilities, which is worthy of providing theoretical direction for future groundwater remediation including local stratigraphic mineral soils.