As a primary raw material for rare earth production, monazite is often associated with radioactive isotopes such as lanthanum and cerium. In order to further reduce the possibility of diffusion and enhance the stability of tailings dams, this study attempts to solidify the flowable monazite waste into solid or semisolid states by adding different types and proportions of solidifying materials. The strength characteristics of the modified soil were studied through strength tests, and the results showed that blast furnace slag exhibited the best solidification effect. Discrete element method was employed to conduct numerical calculations on the stability of tailings dams, analyzing the stability of tailings dams under different solidification schemes and slope ratios. It was found that increasing the slope ratio would lead to a decrease in the stability of tailings dams. Macroscopic and microscopic deformation characteristics of the tailings dam were analyzed: the distribution patterns of dam body velocity and displacement were generally consistent, and the simulated principal stresses were slightly larger but distributed similarly to finite element results. Microstructure analysis revealed a significant increase in contact force after solidification compared to before. This study demonstrates that employing solidification measures for monazite waste tailings dams can enhance stability, reduce environmental pollution, save cement consumption and is crucial for establishing a green ecological production system.

Trichloroethylene (TCE) with trace concentrations is often detected in soils and groundwater, posing potential damages to public health. The elimination of TCE can be achieved through reductive dechlorination using zero-valent iron (ZVI). However, ZVI usually suffers from the presence of passive iron (hydro)oxides layer and low electron transfer rate, thus leading to the unsatisfactory reactivity. Herein, we fabricated oxalated ZVI (Ox-ZVI(bm)) by mechanical ball-milling of micro-scale ZVI and H2C2O4 center dot 2H(2)O to modify the ZVI surface composition. To be specific, the modification of the iron oxide shell by oxalic acid facilitated the generation of unsaturated coordination Fe(II), enhancing TCE adsorption. Furthermore, the formed FeC2O4 on the iron oxide shell improved electron transfer efficiency, contributing to the enhanced TCE reductive dechlorination. Impressively, the rate of TCE degradation by Ox-ZVI(bm) was 10-fold higher than that of ZVI(bm) without oxalate modification. Moreover, Ox-ZVI(bm) samples were filled in a laboratory Permeable Reactive Barriers (PRB) column to treat actual underground wastewater containing TCE pollutants. The effluent concentration of TCE maintained steadily below 0.21 mg/L for over 10 days, complying with the National Groundwater Class IV standard (GBT 14848-2017). This marks a significant step toward practical groundwater treatment.

The performance of a geogrid-stabilized structure affected by dynamic loadings is significant. This study investigates the microscale deformation mechanism of the geogrid-aggregate interface cyclic shear behavior using the discrete element method (DEM). Spheres and nonspherical clumps are generated to form aggregate samples. The DEM models are able to capture the macroscopic dynamic shear laws of the aggregate layers stabilized with a geogrid in a similar way to those tested experimentally. The microscale mechanical responses of the cyclic shear tests (e.g., shear strain, fabric evolution, and confined zone), which vary with the particle shape as well as the measurement volume, are analyzed. The rib flexural rigidity has a minor influence on the peak shear strength of the geogrid-aggregate interface cyclic shear test, but is a key factor influencing the shape of the hysteretic loop, which is closely related to the micromechanical responses at the geogrid-aggregate interface. The particles in the upper and lower shear boxes show different motion patterns in response to the aperture ratio. In the case of A/ D50 = 2.53, the cumulative plastic deformation of the soil layers extending beyond the interface during the loading and reversal loading process is effectively restrained.

Soil supports life by serving as a living, breathing fabric that connects the atmosphere to the Earth's crust. The study of soil science and pedology, or the study of soil in the natural environment, spans scales, disciplines, and societies worldwide. Soil science continues to grow and evolve as a field given advancements in analytical tools, capabilities, and a growing emphasis on integrating research across disciplines. A pressing need exists to more strongly incorporate the study of soil, and soil scientists, into research networks, initiatives, and collaborations. This review presents three research areas focused on questions of central interest to scientists, students, and government agencies alike: 1) How do the properties of soil influence the selection of habitat and survival by organisms, especially threatened and endangered species struggling in the face of climate change and habitat loss during the Anthropocene? 2) How do we disentangle the heterogeneity of abiotic and biotic processes that transform minerals and release life-supporting nutrients to soil, especially at the nano-to microscale where mineral-water-microbe interactions occur? and 3) How can soil science advance the search for life and habitable environments on Mars and beyond-from distinguishing biosignatures to better utilizing terrestrial analogs on Earth for planetary exploration? This review also highlights the tools, resources, and expertise that soil scientists bring to interdisciplinary teams focused on questions centered belowground, whether the research areas involve conservation organizations, industry, the classroom, or government agencies working to resolve global chal-lenges and sustain a future for all.

Climate change in Arctic landscapes may increase freeze-thaw frequency within the active layer as well as newly thawed permafrost. Freeze-thaw is a highly disruptive process that can deform soil pores and alter the architecture of the soil pore network with varied impacts to water transport and retention, redox conditions, and microbial activity. Our objective was to investigate how freeze-thaw cycles impacted the pore network of newly thawed permafrost aggregates to improve understanding of what type of transformations can be expected from warming Arctic landscapes. We measured the impact of freeze-thaw on pore morphology, pore throat diameter distribution, and pore connectivity with X-ray computed tomography (XCT) using six permafrost aggregates with sizes of 2.5 cm3 from a mineral soil horizon (Bw; 28-50 cm depths) in Toolik, Alaska. Freeze-thaw cycles were performed using a laboratory incubation consisting of five freeze-thaw cycles (-10 C to 20 C) over five weeks. Our findings indicated decreasing spatial connectivity of the pore network across all aggregates with higher frequencies of singly connected pores following freeze-thaw. Water-filled pores that were connected to the pore network decreased in volume while the overall connected pore volumetric fraction was not affected. Shifts in the pore throat diameter distribution were mostly observed in pore throats ranges of 100 mu m or less with no corresponding changes to the pore shape factor of pore throats. Responses of the pore network to freeze-thaw varied by aggregate, suggesting that initial pore morphology may play a role in driving freeze-thaw response. Our research suggests that freeze-thaw alters the microenvironment of permafrost aggregates during the incipient stage of deformation following permafrost thaw, impacting soil properties and function in Arctic landscapes undergoing transition.