Applied Clay Science最新文献

Layered double hydroxides (LDH) have undergone extensive investigation, showing potential for application in the corrosion protection of reinforced concrete. However, the chloride consolidation ability of LDH is sensitive to the anions in the environment. In this paper, based on the isomorphic substitutes for cement hydration products (AFm), Ag was deposited on layered double oxide of calcium and aluminium (CaAl-LDO@Ag) to improve the stability of chloride capture. The anti-bacterial performance of CaAl-LDO@Ag was also tested. The results indicated a significant enhancement in chloride binding capacity due to Ag deposition. The mechanism of capturing chloride ions was mainly the structural memory effect of LDO and the combination of Ag⁺ and Cl⁻. On this basis, CaAl-LDO@Ag exhibited a better corrosion inhibition effect in the simulated concrete pore (SCP) solution, which was potentially attributed to the enhanced chloride threshold of steel bars. Moreover, antibacterial experiment demonstrated that CaAl-LDO@Ag effectively inhibits the reproduction of Escherichia coli (E. coli).

This study achieved a selective separation through evaluating the role of the network structure of illite in apatite flotation, when flotation performance could not be manipulated through mainly modifying the pulp rheology. The presence of a complex depressant, acidified sodium silicate (ASS), changed both apatite rheology and illite rheology slightly, while apatite and illite settled differently. Focused beam reflectometry (FBRM) indicated that the size of illite network structure was largest at 100 g/t ASS. Combining the rheology, settling tests and FBRM measurements suggested a potential ASS dosage for flotation separation of apatite from illite, which was in accordance with the flotation results. Cryo-SEM observation further verified that face-to-face (F-F) aggregated and edge-to-face (E-F) flocculated association of illite was the ideal mode for selective separation between apatite and illite. The results in this study justified that the network structure of clay minerals has a more direct relationship with the flotation performance.

In an attempt to maintain the sustainable development goals in the construction sector via reducing the raw-materials/energy consumption and greenhouse-gas emissions related to cement production, a green nano-modified slag/bentonite-based alkali-activated material was developed. Firstly, the green composites were prepared by mixing slag and bentonite with a ratio of 2:1. Several factors like NaOH-concentration (6, 8, 10 wt%); thermal treatment of bentonite (as-received “RB” and thermally treated at 650 °C “TB”); curing conditions (normal-curing for 3 and 28-days as well as hydrothermal-curing at 3, 6, 9, 15 bar for 4 h) and meso-porous tungsten oxide nano-particles “WO₃-NPs” inclusion (0.25, 0.5 and 1 wt%) were studied to assign the optimum conditions for fabricating composites with adequate mechanical properties and radiation-shielding ability. The mechanical performance and radiation shielding were evaluated by measuring the compressive-strengths and linear attenuation coefficient “μ”/ half value layer “HVL” using ¹³⁷Cs, respectively. The results reveal the feasibility of using 8 wt% NaOH, TB, hydrothermal-curing at 3 bar/4 h and 0.5 wt% WO₃-NPs in fabricating low-cost/pre-cast/environmentally friendly building material with superior compressive-strength (53.6 MPa). Also, the radiation shielding results substantiate that this developed composite achieved adequate μ and HVL values, referring to its efficiency as a radiation-blocker. The synergistic impact of alkali-hydrothermal-activation, the high pozzolanicity of TB and the nucleation-site/potential-seeds effect of WO₃-NPs are the main reasons behind forming strength-giving-phases from stratlingite, hydrogarnet, analcime and pentasil zeolitic phase (ZSM-5), as proved by X-ray diffraction (XRD), thermogravimetric analysis (TGA/DTG) and scanning electron microscopy (SEM). The presence of such phases reinforced the microstructure, thus improving the mechanical performance and radiation shielding capability.

This study reports the in-situ transformation of geopolymers into molecular sieve using a method with mild conditions. The application of geopolymer zeolites for dynamic adsorption in continuous fixed beds has been less studied, and the application of adsorbents after adsorption has been less studied. Different metakaolin-based geopolymer molecular sieve microspheres (NaA-MSM, SOD-MSM) were prepared by in-situ conversion of metakaolin as raw material and NaOH as an alkali activator. The continuous fixed-bed adsorption performance was evaluated by varying the influent flow rate, initial metal concentration, and adsorbent dosage. The maximum adsorption capacities of NaA-MSM and SOD-MSM for Cu (II) were 698.14 and 523.84 mg·g⁻¹, respectively. In the simulated solution of real lake water, the adsorption capacities of NaA-MSM and SOD-MSM for Cu (II) were 202.94 and 154.97 mg·g⁻¹, respectively. The results show that the synthesized molecular sieve is an excellent adsorbent for Cu (II)-containing wastewater, and the application design of recycling heavy metals in wastewater by adsorption technology and degrading dyes has been successfully constructed.

Olivine dissolution applications in coastal environments hold great promise for both ocean alkalinity enhancement and carbon dioxide storage. Yet the dissolution mechanism of olivine and the influence of metal ions, such as Mg²⁺ and Ca²⁺, remain unclear. Moreover, the weathering products, such as clay minerals are usually mixed with olivine, and the influence of the associated minerals on the dissolution also unexplored. In this study, an 80-day dissolution experiment was performed in Ca²⁺-free artificial seawater (ASW-Ca) and ASW lacking both Ca²⁺ and Mg²⁺ (ASW-CaMg), to elucidate the mechanism of olivine dissolution and the impact of Ca²⁺ and Mg²⁺ on the presence of an associated clay mineral, kaolinite. To evaluate the mineral properties before and after dissolution, X-ray diffraction spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy analyses were used. Etch pits were observed on olivine's surface as well as its reduced crystallinity. The atomic ratio of Mg/Si in olivine decreased from 1.49 ± 0.56 in the raw samples to 1.29 ± 0.53 in the samples obtained from ASW-CaMg after undergoing the 80-day dissolution, whereas it was much higher, at 1.85 ± 0.32, in the samples from ASW-Ca. The increasing Mg/Si was attributed to the Mg²⁺ adsorption on the surface of olivine, which inhibited the release of structural Mg²⁺. Hence, Mg²⁺ was a key environmental factor influencing the process of olivine dissolution, and estuaries, which have low Mg²⁺ content and low pH may be the promising areas for the olivine application. Moreover, in ASW-CaMg, the total alkalinity (TA), dissolved inorganic carbon (DIC) concentration, and charge concentration of alkaline earth metal ions increased by 3392 ± 28, 2922 ± 3, and 3740 ± 91 μmol kg⁻¹, respectively, compared to the data from the blank experiment. Notably, TA and DIC had strong linear relationships with the alkaline earth metal ions (Mg²⁺ and Ca²⁺). The release of free alkaline earth metal cations during olivine dissolution was a controlling factor for long-term carbon dioxide storage in ASW-CaMg. Finally, during the 80-day dissolution experiment, no dissolution of the associated kaolinite was observed, however, kaolinite may influence the olivine dissolution by adsorbing the released Si.

In this study, composite adsorbents were prepared as mixtures of aluminosilicates from Central European deposits (clinoptilolite and bentonite) and two types of fly ash from Czech operations that differed in fuel type and combustion temperature. The composites were tested for the adsorption of individual toxic cations (cadmium (Cd²⁺) and caesium (Cs⁺)) and anions (arsenate (AsO₄³⁻) and chromate (CrO₄²⁻)) and for cation–anion co-adsorption in appropriate model solutions under laboratory conditions. The clay–fly ash combinations were more selective for cation adsorption, with an efficiency of about 80% or higher, and unsuitable for anion adsorption, with a maximum efficiency of 30% for AsO₄³⁻ and <20% for CrO₄²⁻. In the co-adsorption systems, the co-adsorption of all tested ions was more efficient than the adsorption of individual ions—by >20%, on average, for Cd²⁺, Cs⁺ and AsO₄³⁻ and by about 6% for Cr. Because the composite sorbents combined the properties of both components, they exhibited variability in active adsorption sites for effective cation and anion binding. The co-adsorption efficiency was up to 50% higher than that of the adsorption of any single kind of ion.

Developing a greater understanding of kaolinite dehydroxylation upon calcination is crucial for several industrial applications, including cements. Aluminium coordination in meta-kaolinite indicates the extent of its dehydroxylation and its potential chemical reactivity, and it is typically determined using ²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. This technique however presents limitations for Fe-rich materials, given the magnetic properties of Fe ions and minerals containing Fe. In this study, the effect of calcination on Al coordination was assessed in a low-Fe clay used as a reference system, and a Fe-rich clay. Al coordination in the low-Fe clay was quantified via ²⁷Al MAS NMR spectra deconvolution, using data collected at 9.4 T and 11.7 T. Energy dispersive X-ray spectroscopy (EDX) maps and electron energy loss spectroscopy (EELS) measurements were carried out in a scanning transmission electron microscope (STEM) on both clays. Al K-edge EEL spectra showed distinguishable 4/5-fold Al and 6-fold Al sites in both clay types. Differences in line-profile indicated a higher proportion of 4/5-fold Al in kaolinite in the Fe-rich clay compared to the low-Fe clay. Conversely, the Fe-rich clay contained a lower proportion of 4/5-fold Al in meta-kaolinite after calcination, relative to the low-Fe clay. These differences are consistent with the greater structural disorder of the meta-kaolinite identified in the Fe-rich clay by X-ray diffraction and the geological origins of both clays. Overall, this study demonstrates the potential of EELS to provide information about Al coordination for individual kaolinite and meta-kaolinite particles.

The present study aims to evaluate five clay samples from different pits in the Teruel province, Spain. While these clays are primarily utilized as raw materials in ceramics, their potential applications in pharmaceutical and cosmetic domains, notably in sun protection and thermal mud products, are under investigation. Characterization of these clays entailed X-ray diffraction, X-ray fluorescence, scanning electron microscopy, pH measurement, analysis of technological properties, rheological assessment, and thermal property evaluation. Furthermore, given the predominant composition of kaolin in most of the samples, their Sun Protection Factor (SPF) in suspensions and physical stability were assessed. The studied samples exhibited varied mineralogical compositions, primarily consisting of kaolinite (70% to 15%), quartz (75% to 5%), and illite (26% to 7%). The pH values of these dispersions closely matched the skin's pH, exhibiting anti-thixotropic behavior at 50% w/w and demonstrating suitable viscosity for skin application. Based on their composition and rheological properties, the samples exhibited potential for use as therapeutic thermal muds. Analyses of cooling kinetics were performed to validate this potential. Results showed that the dispersions systems attained temperatures between 33.89 °C and 34.62 °C within 20 min (the common application time for thermal muds) and reached 32 °C (skin temperature) in 24.3 to 26.22 min, confirming their appropriateness as therapeutic muds. The SPF values of the dispersions varied from 7.46 to 16.65, with the majority of samples showing significant stability during 45 h. Consequently, it can be inferred that most of the studied samples show advantageous characteristics for inclusion in topical formulations, especially in sun protection and thermal mud products.

One of the earliest known settlements of Pre-Roman Padua, Veneto Region (north-eastern Italy) was located in the very centre of the present-day city. The archaeological excavations revealed structures related to craft activities (metallurgical and pottery workshops) and residential areas datable from the late 9th to the 1st century BCE. A large pyrotechnic structure formed by an earthen block densely filled and covered by broken ceramic vessels was found, bringing to light the earliest foundry of the Pre-Roman Padua known to date. Many potsherds found in the site correspond to a regional ceramic class that included coarse and fine wares mainly composed of very dark ceramic bodies. A multi-analytical study based on macroscopic and petrographic descriptions as well as mineralogical, geochemical and microstructural analyses, was carried out in order to state the technological choices adopted for producing these dark vessels and the provenance of the raw materials. A poorly manufacturing was adopted to produce the common pottery, resulting coarse wares uneven textured, while the fine wares were produced by adopting the purification of the base clays and/or the tempering of the clay pastes. Common geo-resources were used, consisting in illitic-chloritic clays rich in quartz and feldspars, the firing regime conditions covered a range of maximum temperatures (normally under 850 °C) and the temper was constituted by silicate (chiefly quartzite, rhyolite and trachyte rock fragments) and/or carbonate (calcite and/or dolomite) inclusions, that were added after having been grounded and/or sieved. The specific mineral and lithic markers of provenance identified in the sherds confirmed the correspondence of this pottery with a local production. However, the specific technological choices that were carried out must be taking into consideration, since the purification removed the larger grains originally present in the base clays and the tempering influenced the chemical composition of the sherds. The different degree of purification of the base clays and the differential tempering procedures that were accomplished point out the adoption of very specific recipes to produce the fine wares, suggesting the correspondence of this local ceramic class with diverse sub-productions and the high level of specialization achieved by the potters in southern Veneto during the Early Iron Age.

Accurate determination of solid acidity is essential for evaluating the catalytic activity of clay minerals. However, the conventional Fourier-transform infrared (FTIR) method using NH₃ as the probe encounters challenges in measuring the solid acidity owing to the presence of water on the surface or within interlayer spaces of clay minerals as well as the influence of environmental water during the detection process. To mitigate water interference, a NH₃-probe X-ray photoelectron spectroscopy (XPS) approach was adopted as an alternative to the FTIR method for the identification and semi-quantification of solid acidity of clay minerals. Following NH₃ adsorption, the types of solid acid sites in clay minerals were identified through the chemical shift in N1s XPS spectra. The ratio of Brønsted and Lewis acid sites in a given sample and the relative concentration of acid sites across different samples were determined by examining the specific N1s peak area ratio. According to the XPS data, the ratios of Brønsted and Lewis acid sites in Ca-montmorillonite (SAz-2) and Na-montmorillonite (SWy-2) were nearly 1:1, whereas that for the illite–smectite mixed-layer mineral (ISCz-1) was 4. The acid site contents in SAz-2 were more than twice those of SWy-2. This work highlights the promising application prospects of the NH₃-probe XPS method in solid acidity investigations of clay minerals.