Knowledge Gap: The aggregation of clay minerals-layered silicate nanoparticles-strongly impacts fluid flow, solute migration, and solid mechanics in soils, sediments, and sedimentary rocks. Experimental and computational characterization of clay aggregation is inhibited by the delicate water-mediated nature of clay colloidal interactions and by the range of spatial scales involved, from 1 nm thick platelets to flocs with dimensions up to micrometers or more. Simulations: Using a new coarse-grained molecular dynamics (CGMD) approach, we predicted the microstructure, dynamics, and rheology of hydrated smectite (more precisely, montmorillonite) clay gels containing up to 2,000 clay platelets on length scales up to 0.1 mu m. Simulations investigated the impact of simulation time, platelet diameters (6 to 25 nm), and the ratio of Na to Ca exchangeable cations on the assembly of tactoids (i.e., stacks of parallel clay platelets) and larger aggregates (i.e., assemblages of tactoids). We analyzed structural features including tactoid size and size distribution, basal spacing, counterion distribution in the electrical double layer, clay association modes, and the rheological properties of smectite gels. Findings: Our results demonstrate new potential to characterize and understand clay aggregation in dilute suspensions and gels on a scale of thousands of particles with explicit representation of counterion clouds and with accuracy approaching that of all-atom molecular dynamics (MD) simulations. For example, our simulations predict the strong impact of Na/Ca ratio on clay tactoid formation and the shear-thinning rheology of clay gels.

Formulation of sustainable slow-release phosphate (SRP) fertilizers using low-cost carrier materials is a growing area of research. This fertilizer can prevent its nutrient loss caused by surface runoff or soil leaching. Here, we investigated the mechanochemical activation of halloysite-rich kaolin clay by planetary ball milling and produced an enhanced SRP fertilizing substrate. The milling process was carried out under dry (clay only and KH2PO4 solution added after milling) and wet conditions (slurry of clay and KH2PO4) over varying durations (e.g., 1-8 h). Changes in crystallinity and microstructure of materials induced by milling were characterized by X-ray diffraction and electron microscopy. The retention and release of phosphate from the water-extractable phase of the fertilizer were also analyzed. High-resolution transmission electron microscopy mapped the elemental distribution at the crystal scale. The milling method had a pronounced effect on the phosphate release behavior. Dry-ground materials (3-5 h) showed better retention and controlled release (similar to 40% phosphate released in the first wash followed by similar to 5% in two successive washes). However, wet-ground samples released more phosphate initially (similar to 50%), leaving less for later release. Compared to wet milling, dry milling caused greater crystal damage, particularly halloysite tube breaks, and increased the amorphousness of the material. These affected the containment of KH2PO4 salt into halloysite lumen and the release of phosphate ions in the water phase. This provides a choice of fertilizer formulations simply by adjusting milling conditions. To move forward, we need to study the scale-up of this potentially sustainable slow-release phosphate fertilizer and test it in soil and crops. This will benefit raw mineral resources and improve the nutrient efficiency.

The use of nanoparticles has emerged as a popular amendment and promising approach to enhance plant resilience to environmental stressors, including salinity. Salinity stress is a critical issue in global agriculture, requiring strategies such as salt-tolerant crop varieties, soil amendments, and nanotechnology-based solutions to mitigate its effects. Therefore, this paper explores the role of plant-based titanium dioxide nanoparticles (nTiO2) in mitigating the effects of salinity stress on soybean phenotypic variation, water content, non-enzymatic antioxidants, malondialdehyde (MDA) and mineral contents. Both 0 and 30 ppm nTiO2 treatments were applied to the soybean plants, along with six salt concentrations (0, 25, 50, 100, 150, and 200 mM NaCl) and the combined effect of nTiO2 and salinity. Salinity decreased water content, chlorophyll and carotenoids which results in a significant decrement in the total fresh and dry weights. Treatment of control and NaCl treated plants by nTiO2 showed improvements in the vegetative growth of soybean plants by increasing its chlorophyll, water content and carbohydrates. Additionally, nTiO2 application boosted the accumulation of non-enzymatic antioxidants, contributing to reduced oxidative damage (less MDA). Notably, it also mitigated Na+ accumulation while promoting K+ and Mg++ uptake in both leaves and roots, essential for maintaining ion homeostasis and metabolic function. These results suggest that nTiO2 has the potential to improve salinity tolerance in soybean by maintaining proper ion balance and reducing MDA level, offering a promising strategy for crop management in saline-prone areas.

The increasing generation of industrial waste sludge poses a serious worldwide problem with detrimental effects on the environment and the economy. Effective utilization of waste sludge in sustainable construction practices offers a universal solution to mitigate environmental impacts. As the mining industry continues to extract clay from clay mines, the demand for sustainable practices in both clay mineral extraction and brick production is growing. Bricks are fundamental in masonry construction, and current research is exploring the integration of industrial waste materials into fired clay bricks to enhance their properties and mitigate environmental impacts. This study investigates the incorporation of waste sludge in brick manufacturing to assess its potential for reducing environmental burdens while maintaining technical performance. X-ray Fluorescence Spectrometry (XRF) analysis reveals that both clay soil and mosaic sludge contain high levels of silicon dioxide (SiO2) and aluminum oxide (Al2O3), supporting their suitability as partial substitutes for clay soil. Incorporating up to 30% of body mill sludge (BS) and polishing sludge (PS) into the brick mix significantly enhances physical and mechanical properties, resulting in reduced shrinkage, increased porosity, and improved compressive strength, reaching up to 25 N/mm(2). Initial rate of suction tests shows values below 5 g/mm(2), indicating optimal water absorption characteristics. Various leachability assessments, including the Toxicity Characteristic Leaching Procedure (TCLP), Synthetic Precipitation Leaching Procedure (SPLP), and Static Leachate Test (SLT), confirm that bricks containing up to 30% BS and PS comply with United States Environmental Protection Agency (USEPA) and Environment Protection Authority Victoria (EPAV) standards for heavy metals, making them environmentally safe for use. Additionally, indoor air quality assessments confirm that these bricks meet Industry Codes of Practice on Indoor Air Quality (ICOP-IAQ) guidelines. This study demonstrates that using BS and PS as alternative raw materials offers a sustainable, cost-effective solution aligned with Sustainable Development Goals (SDGs), promoting cleaner production practices in brick manufacturing.

Interactions among microbes, minerals, and organic matter are key controls on carbon, nutrient, and contaminant dynamics in soils and sediments. However, probing these interactions at relevant scales and through time remains an analytical challenge due to both their complex nature and the need for tools permitting nondestructive and real-time analysis at sufficient spatial resolution. Here, we demonstrate the ability and provide analytical recommendations for the submicron-scale characterization of complex mineral-organic microstructures using optical photothermal infrared (O-PTIR) microscopy. Compared to conventional infrared techniques, O-PTIR spectra collected at submicron resolution of environmentally relevant mineral and organic reference compounds demonstrated similar spectral quality and sensitivity. O-PTIR detection sensitivity was greatest for highly crystalline minerals and potentially for low molecular weight organic compounds. Due to photothermal effects, O-PTIR was more sensitive toward organics than minerals compared to conventional IR approaches, even when organics were mineral-bound. Moreover, O-PTIR resolved mineral-bound and unbound organics in a complex mixture at submicron (<500 nm) resolution. Finally, we provide best practices for artifact-free analysis of organic and mineral samples by determining the appropriate laser power using damage thresholds. Our results highlight the potential of O-PTIR microscopy for nondestructive and time-resolved analysis of dynamic microbe-mineral-organic matter interactions in soils and sediments.

Nanoclay, a processed clay, is utilized in numerous high-performance cement nanocomposites. This clay consists of minerals such as kaolinite, illite, chlorite, and smectite, which are the primary components of raw clay materials formed in the presence of water. In addition to silica, alumina, and water, it also contains various concentrations of inorganic ions like Mg2+, Na+, and Ca2+. These are categorized as hydrous phyllosilicates and can be located either in interlayer spaces or on the planetary surface. Clay minerals are distinguished by their two-dimensional sheets and tetrahedral (SiO4) and octahedral (Al2O3) crystal structures. Different clay minerals are classified based on the presence of tetrahedral and octahedral layers in their structure. These include kaolinite, which has a 1:1 ratio of tetrahedral to octahedral layers, the smectite group of clay minerals and chlorite with a 2:1 ratio. Clay minerals are unique due to their small size, distinct crystal structure, and properties such as high cation exchange capacity, adsorption capacity, specific surface area, and swelling behavior. These characteristics are discussed in this review. The use of nanoclays as nanocarriers for fertilizers boasts a diverse array of materials available in both anionic and cationic variations. Layered double hydroxides (LDH) possess a distinctive capacity for exchanging anions, making them suitable for facilitating the transport of borate, phosphate, and nitrate ions. Liquid nanoclays are used extensively in agriculture, specifically as fertilizers, insecticides, herbicides, and nutrients. These novel nanomaterials have numerous benefits, including improved nutrient use, controlled nutrient release, targeted nutrient delivery, and increased agricultural productivity. Arid regions face distinct challenges like limited water availability, poor soil quality, and reduced productivity. The addition of liquid nanoclay to sandy soil offers a range of benefits that contribute to improved soil quality and environmental sustainability. Liquid nanoclay is being proposed for water management in arid regions, which will necessitate a detailed examination of soil, water availability, and hydrological conditions. Small-scale trial initiatives, engagement with local governments, and regular monitoring are required to fully comprehend its benefits and drawbacks. These developments would increase the practicality and effectiveness of using liquid nanoclay in desert agriculture.

Different chemical solutions can significantly change the contact angle (CA) of soil, but few studies have studied the change rule and action mechanism of the CA from the mineral composition of soil essence. In unsaturated soil mechanics, the CA is an important parameter to calculate the wet suction between soil particles in unsaturated soil. When the chemical composition of the soil pore liquid changes, the CA will also change, which will affect the wet suction and other parameters, thus changing the macroscopic mechanical properties of the soil. In this study, the CA of air-solution-mineral phases with different solution components (pH, type and concentration of salt solution) of different minerals (quartz, orthoclase and plagioclase) were measured. The results show that the CAs of quartz, orthoclase and plagioclase all rise first and then drop with the rise of pH. The peak CAs are pH = 5, pH = 4 and pH = 3, respectively. Quartz, orthoclase and plagioclase all have valley values in different concentrations of NaCl and KCl solutions. In CaCl2 solution, only quartz has valley value, while orthoclase and plagioclase increase monotonously. Quartz in soil plays a main role in the influence of soil CA, followed by orthoclase and plagioclase. The CA of different minerals in different chemical solutions is mainly controlled by electric double layer interaction and functional groups interaction. In different salt solution environment, in addition to the above two effects, the mineral CA is also affected by the surface tension.

The stabilization and application of expansive geomaterials are critical in geotechnical engineering. These naturally expansive materials exhibit complex hydro-chemo-mechanical properties because they undergo volumetric changes in response to variations in moisture content and/or temperature. The characteristic shrink-swell behavior of these materials makes their use problematic and plays a substantial role in influencing the stability of geo-infrastructure applications. However, there is a lack of comprehensive knowledge of the mechanisms and factors impacting their behavior to ensure mechanical integrity in natural and built infrastructure and geo-engineering projects. This work provides a comprehensive review of the intrinsic and extrinsic factors contributing to the shrink-swell behavior and expansion mechanisms of frost-heaving and natural-expansive geomaterials, such as expansive clays and sulfate minerals. We reviewed and synthesized peer-reviewed published works in various databases and academic repositories in the last 100 years. The influence of shrink-swell behavior of these geomaterials and the critical role they play in engineering infrastructure were highlighted, explicitly focusing on their involvement in geotechnical-related hazards, such as the freeze-thaw cycle, and the damage and sulfate-attack of geo-infrastructure. We analyzed the interactions between clay minerals, especially how bentonite enhances grout stability and acts as a buffer material in high-level nuclear waste repositories. The findings indicate that water interaction with geomaterials and concrete can cause about a 10% volume expansion when frozen. Also, the exposure of fractured rocks to low (0 degrees C) temperatures can greatly change rock deformation and strength. Finally, gypsum interacting with water can theoretically increase in volume by 62% to form ice crystals. This forward-leading review presents the advantages, disadvantages, and unresolved issues of expansive natural geotechnical materials that improve the resiliency and sustainability of geological infrastructure.

Plant growth requires a complex network of arbuscular mycorrhizal (AM) fungi and bacteria to supply organic compounds and major (C, N, P, etc.) and trace nutrients to the roots. Hyperaccumulation by certain plant species is based on the threshold 'maxima' a plant can safely ingest/absorb an element from soils without tissue damage. The latter criteria for hyperaccumulation vary between elements. The amount of an element a plant can absorb depends both on the ability of the species to uptake the element and on the element concentrations and bioavailability in the substrate. A plant growing directly on a mineral-rich substrate or a short height above the soil should be able to access inorganic matter via the roots. In contrast, a plant capable of accumulating inorganic elements, but growing on a peat without direct root contact with the inorganic soil fraction, would suffer a dearth of mineral nutrients. Partitioning of elements occurs within hyperaccumulators. For example, the preferential binding of heavy rare earth elements (HREE) to organic ligands leads to the relative enrichment of HREE in aerial plant structures. The presence of hyperaccumulators in a wide range of present-day plant species suggests that this mechanism was present among peat-forming plants in the fossil record. Examples from peats through low-rank coals to high volatile A bituminous coals show that hyperaccumulation provides a viable hypothesis for the consequent enrichment of certain elements. Complications from the depositional history and diagenetic alteration of the peat; metamorphism and mineralization through the history of the coal; and, not the least, the problems implicit in sampling suitable intervals in working mines, cores, natural exposures, etc., present problems in the extrapolation of the modern plant mechanisms to coals. Coal represents natural settings and, apart from Miocene and younger coals produced from vegetation with known relatives in modern setting, we cannot experiment on the ancient plants. The analogies between the geochemical appearance of coals and the element uptake and partitioning behavior of modern plants, however, does offer hope that hyperaccumulation might have been a mechanism, potentially one of many mechanisms, for the organic associations of inorganic elements in coals.

There is a lack of research on the molecular interactions between clay minerals and geopolymers at the nanoscale, as well as the interfacial mechanism and mechanical behavior of geopolymers, as a highly promising sustainable soft soil reinforcement stabilizer (grouting reinforcement method). In this study, molecular dynamics simulations were used to reveal the interfacial characteristics and the molecular behavior of geopolymer stabilizers and clay minerals. Molecular models of two geopolymers (calcium aluminosilicate hydrate (C-A-S-H) and sodium aluminosilicate hydrate (N-A-S-H)) and two major minerals (montmorillonite and illite) in soft Hangzhou clays were developed. Then, the interfacial characteristics, interaction mechanisms and mechanical behaviors of different geopolymer/clay mineral interface systems were compared. It was found that montmorillonite and illite attract water molecules to aggregate on the mineral surfaces and promote the migration and diffusion of Ca2+ and Na+ at the interfaces. The interfacial interactions of the geopolymer/clay mineral system mainly consisted of electrostatic interactions. Stronger hydrogen bonding interactions occur at the interface of the geopolymer/clay mineral system. The metal cations and the geopolymer stabilizer between the clay mineral layers form a complex ion nest in concert with the aggregated water molecules to stabilize their interfacial interactions. In terms of the mechanical properties, the C-A-S-H stabilizer has a stronger interfacial shear strength. The shear strength of the illite system is stronger than that of the montmorillonite system, but montmorillonite can produce stronger interfacial bonding with the ground polymer stabilizer, and the curing effect is more obvious.