Hydrogen wettability of clays: Implications for underground hydrogen storage

This study investigates the ability of hydrogen (H₂) to wet clay surfaces in the presence of brine, with implications for underground hydrogen storage in clay-containing reservoirs. Rather than measuring contact angles directly with hydrogen gas, a suite of other gases (carbon dioxide (CO₂), argon (Ar), nitrogen (N₂), and helium (He)) were employed in the gas-brine-clay system under storage conditions (moderate temperature (333 K) and high pressures (5, 10, 15, and 20 MPa)), characteristic of a subsurface environment with a shallow geothermal gradient. By virtue of analogies to H₂ and empirical correlations, wettabilities of hydrogen on three clay surfaces were mathematically derived and interpreted. The three clays were kaolinite, illite, and montmorillonite and represent 1:1, 2:1 non-expansive, and 2:1 expansive clay groups, respectively. All clays showed water-wetting behaviour with contact angles below 40° under all experimental set-ups. It follows that the presence of clays in the reservoir (or caprock) is conducive to capillary and/or residual trapping of the gas. Another positive inference is that any tested gas, particularly nitrogen, is suitable as cushion gas to maintain formation pressure during hydrogen storage because they all turned out to be more gas-wetting than hydrogen on the clay surfaces; this allows easier displacement and/or retrieval of hydrogen during injection/production. One downside of the predominant water wettability of the clays is the upstaged role of biogeochemical reactions at the wetted brine-clay/silicate interface and their potential to affect porosity and permeability. Water-wetting decreased from kaolinite as most water-wetting clay over illite to montmorillonite as most hydrogen-wetting clay. Their wetting behaviour is consistent with molecular dynamic modelling that establishes that the accessible basal plane of kaolinite's octahedral sheet is highly hydrophilic and enables strong hydrogen bonds whereas the same octahedral sheet in illite and montmorillonite is not accessible to the brine, rendering these clays less water-wetting.     

Tuning and controlling photocatalytic performance of TiO2/kaolinite composite towards ciprofloxacin: Role of 0D/2D structural assembly

Lamellar kaolinite supported monodispersed TiO₂ was prepared through rational design and 0D/2D structural assembly, which showed significantly improved photocatalytic performance towards ciprofloxacin. After systematic evaluation, the pseudo-first-order kinetic constant rate of TiO₂/kaolinite composite can reach to 0.04549 min⁻¹, which was 6.90 and 1.81 times higher than that of pure TiO₂ and P25, respectively. The nano-TiO₂/kaolinite composite photocatalyst also displayed good reusability performance, only a slight decline occurred after four repeated experiments, which is beneficial for the large-scale application of photocatalysts. Various characterizations indicated that enhanced photocatalytic performance can be ascribed to the synergistic effect between natural kaolinite and the well distributed TiO₂, which enhanced the light absorption ability, assisted the dispersion of pure TiO₂, resulted in co-catalysis effect, improved the separation facilitation of photo-induced carriers and promoted the stronger adsorption capacity, etc. These merits effectively regulated the carriers’ lifetime and migration velocity of the photogenerated charge carriers. Considering the excellent properties of natural kaolinite (low cost, abundance, stability, etc.), our study provides a promising candidate for effective degradation of trace amounts of pharmaceutical and personal care product (PPCP) or contaminants with potential high-toxic risk.     

Synthesis of iron red hybrid pigments from oil shale semi-coke waste

Oil shale semi-coke (SC) is a bulk solid waste produced after shale oil being extracted from oil shale. It is abundant on the earth, but most of them are discarded or piled up as solid waste, and their reuse as resources is very limited. In this paper, adhering to the concept of “waste to materials“, the α-Fe₂O₃/SC hybrid pigments with the red color (a* = 29.68) better than commercial iron red pigments (a* = 26.92) were synthesized by an one-pot hydrothermal reaction of pretreated SC with Fe(III), using SC as a cheap starting material. The microscopic structure, chemical composition and color of the hybrid pigments were studied, and the reaction parameters for synthesizing the best hybrid pigments from SC were optimized. The results indicate that the hybrid pigments are mainly composed of SiO₂ and Fe₂O₃, where α-Fe₂O₃ particles grow on the surface of SC-derived silicate substrate with a better dispersion. The hybrid pigments showed a good stability, especially an outstanding high temperature-resistant stability. The secondary heat treatment induced the further improvement of red color value of the hybrid pigments. This work provides a new way and solution for the rational disposal and functional application of SC waste.     

An investigation into the effects of lime on compressive and shear strength characteristics of fiber-reinforced clays

To meet the ever-increasing construction demands around the world during recent years,reinforcement and stabilization methods have been widely used by geotechnical engineers to improve the performances and behavior of fine-grained soils.Although lime stabilization increases the compressive strength of soils,it reduces the soil ductility at the same time.Recent research shows that random fiber inclusion modifies the brittleness of soils.In the current research,the effects of lime and polypropylene(PP) fiber additions on such characteristics as compressive and shear strengths,failure strain,secant modulus of elasticity(E_(50)) and shear strength parameters of mixtures were investigated.Kaolinite was treated with 1%,3% and 5% lime by dry weight of soil and reinforced with 0.1% monovalent PP fibers with the length of 6 mm.Samples were prepared at optimum conditions and cured at 35℃ for 1 d,7 d and28 d at 90% relative humidity and subsequently subjected to uniaxial and triaxial compression tests(UCT and TCT) under cell pressures of 25 kPa,50 kPa and 100 kPa.Results showed that inclusion of random PP fibers to clay-lime mixtures increases both compressive and shear strengths as well as the ductility.Lime content and curing period were found to be the most influential factors.Scanning electron microscopy(SEM) analysis showed that lime addition and the formation of cementitious compounds bind soil particles and increase soil/fiber interactions at interface,leading to enhanced shear strength.The more ductile the stabilized and reinforced composition,the less the cracks in roads and waste landfill covers.     

Kaolinitic calcined clays: Factors affecting its performance as pozzolans

Five natural kaolinitic clays from different regions of Argentine, with different kaolinite content, different impurities and different degree of crystallinity were calcined in a fixed-bed electrical furnace at 700 °C. Clays were characterized by X-ray diffraction (XRD) and Fourier transformed infra-red spectrometry (FTIR) that provides an index about the order/disorder of the structure. After heat treatment, the structural changes were characterized by XRD and FTIR, and pore size distribution and specific surface were determined. Their pozzolanic activity was evaluated with the Frattini test, electrical conductivity in saturated Ca(OH)₂ solution and compressive strength on mortars at 7, 28 and 90 days. Among tested clays, four of them can be classified as pozzolan by the Frattini test. The pozzolanic activity of the natural clays showed good correlation with the content of kaolinite, the inversed of structure order determined by FTIR, and the specific surface of calcined clays. This study confirms that natural clays other than pure kaolinite can be interesting pozzolanic materials when thermally activated.     

Solid solution limit of Fe2O3 in mullite crystals,produced from kaolin by solid state reactions

Porcelain, wall/floor tiles, and roofing tiles are classified as traditional ceramics and are produced from natural raw materials such as clay, quartz, and feldspar. The raw materials are selected by the oxide content which provides the desired properties of the final product. However, impurities such as Fe₂O₃ and TiO₂ may have a significant influence on both physical/mechanical properties and aesthetic appearance. Fe₂O₃, which is of particular importance, causes black maculation formation in tablewares, in which whiteness is essential. The only way to overcome the black maculation is to corrupt the Fe₂O₃ crystal structure and to employ Fe^2+/3+ cation, making a solid solution with a host crystal (i.e. mullite-3Al₂O₃·2SiO₂). The aim of this study is to identify the solubility limit of Fe₂O₃ in mullite crystals. With the scope of the study, an illite/kaolinite was utilized by adding an increasing amount of Fe₂O₃ (e.g. 1–2–4–6–8–10?wt%) into the recipes fired at 1300?°C for 3?h after homogenization. According to the mullite phase content, it is concluded that ~ 5?wt% of Fe₂O₃ could be dissolved in mullite crystal structure on the basis of the Rietveld refinement of the XRD patterns.     

An experimental study of the relationship between settling flocs and eroded flocs of kaolinite in aqueous media

Aspects of the relationship between flocs in suspension and those held in a cohesive sediment bed were investigated experimentally using an erosion rig with kaolinite as the sample material under different medium conditions. The critical shear-stress, τ_c, required to initiate the erosion were measured, and the floc sizes of the eroded products (d_E) were analysed in situ using macro-photography. Factors such as age, density, pH and ionic strength were investigated. Separate experiments were performed to measure the floc size in the settling zone (d_A). The results show that the floc sizes from the above two different measurements show the same variance with respect to physico-chemical (pH and ionic strength) changes in the environment. This work has been very successful in showing the relationship between the flocs in suspension and those eroded from a bed of sediment, so one property can be predicted from knowledge of another.     

焦炉热修补用半干法喷补料的开发与应用

以煅烧高岭土、硬质黏土熟料、SiO2微粉等为主要原料,选用不同的结合剂和添加剂,研制出适合于焦炉炭化室炉壁喷补用半干法喷补料,此种焦炉热修补用喷补料加水量少、反弹率低、挂料时间长,达到并超过国外同类产品。     

芦溪高岭土增白实验研究

研究了提纯剂（柠檬酸钠和NaOH按一定比例配制）、还原剂（Na2S2O4）和稳定剂（草酸）用量对高岭土增自效果的影响。实验结果表明：当提纯剂用量为0．4％、还原剂用量为0．2％、稳定剂用量为0．3％时,试样的白度达到最高,由原来的74．75。提高到了86．50°。     

芦溪高岭土增白实验研究

研究了提纯剂(柠檬酸钠和NaOH按一定比例配制)、还原剂(Na2S2O4)和稳定剂(草酸)用量对高岭土增白效果的影响。实验结果表明:当提纯剂用量为0.4、还原剂用量为0.2、稳定剂用量为0.3时,试样的白度达到最高,由原来的74.75°提高到了86.50°。