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 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.

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.

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.