A novel iron-based phosphate cement (IPC), derived from iron-rich smelting slag (ISS), was developed as a sustainable and efficient binder for the stabilization/solidification of trivalent chromium (Cr3+). The mechanical properties, hydration behavior, microstructure, leaching toxicity, chromium chemical forms, and environmental safety of chromium-stabilized iron phosphate cement (CIPC) were thoroughly evaluated. The results showed that, with a mass ratio of ISS to ammonium dihydrogen phosphate (ADP) of 2.0, and even with the addition of 20 % chromium nitrate nonahydrate (CN), the compressive strength of CIPC reached 4.2 MPa after curing for 28 d. Furthermore, chromium leaching was well below 1 mg/L, significantly lower than the GB 5085.3-2007 standard limit of 15 mg/L, demonstrating the effective encapsulation of Cr3+ due to IPC's high early strength. In the IPC system, Cr3+ was primarily stabilized by forming CrPO4 and CrxFe1-x(OH)3 co-precipitates, which were further solidified through the physical encapsulation of IPC hydration products, such as (NH4)2Fe(PO3OH)2 center dot 4H2O, (NH4) (Mg,Ca)PO4 center dot H2O, and FePO4. This process resulted in a solidification efficiency of up to 99 %. BCR analysis confirmed that more than 98 % of the chromium in the CIPC remained in a stable residual form. Finally, the ecological risk index (PERT) was found to be 23.52, far below the safety threshold of 150, indicating the solidified material's long-term environmental safety. This study provides an innovative approach for the reutilization of ISS while effectively stabilizing/solidifying chromium.

When uranium heap leaching tailings (UHLT) are used as filling aggregates, their discontinuous and non-uniform grading characteristics can easily cause segregation, settlement of the filling slurry, and deterioration of cemented body mechanical properties, seriously affecting the safety of the filling system and filling quality. To address the bimodal distribution defects of UHLT, characterized by excessively high proportions of coarse and fine particles with a lack of intermediate particle sizes, this study simulated its particle size characteristics using inert materials such as loess, fine sand, sand, and gravel. The study systematically verified the impact of grading defects on flow stability and mechanical properties. The filling slurry exhibited a spread of 222.5 mm with obvious segregation, and the uniaxial compressive strength at 28 days was 9.09 MPa. To overcome this bottleneck, this research innovatively proposed optimization strategies of qualitative reconstruction (QLR) and quantitative reconstruction (QTR). QLR involves adding medium-sized particles in stages and replacing equal amounts of coarse and fine particles, reducing the spread to 202.7 mm under an optimized quantity of 50 g, with a uniaxial compressive strength of 6.84 MPa at 3 days. However, slurry segregation still occurred. QTR established a multi-particle-size independent calculation model based on the extended Talbot gradation theory, and through the staged quantitative reconstruction of UHLT with aggregate having a grading index of 0.4, the spread decreased to 168.4 mm without segregation, achieving a uniaxial compressive strength of 5.58 MPa at 3 days and 9.11 MPa at 28 days. The study shows that both QLR and QTR can effectively improve the grading of UHLT, with QLR being simple and QTR offering precise control. The research provides new approaches for regulating filling slurries with similar discontinuous and non-uniform graded aggregates, and its innovative methodology can be extended to multiple fields such as concrete aggregate optimization.

Mato Grosso is the largest consumer of pesticides in Brazil, and although their role in phytosanitary control is evident, environmental contamination is a concern due to their intensive use. Therefore, identifying the behavior of pesticides in the environment can assist in risk management, and the Environmental Risk Index (ERI) is an indirect way of knowing the potential of these compounds. This study was aimed at evaluating the ERI of the most sold insecticides in Mato Grosso used for the control of lepidopteran pests. The parameters evaluated were persistence in the soil, leaching, volatility, toxicological profile and recommended dose. Our findings reported on 24 insecticides, which totaled an annual amount of 23,046,348 kg of active ingredients, with acephate at the top of the ranking with 8,974,413 kg sold in 2020. This insecticide, despite being widely used, had the lowest ERI due to low persistence, leaching and volatility, and its critical factor was animal toxicity. Malathion, methoxyphenozide, chlorantraniliprole, flubendiamide, and beta-cyfluthrin had the highest ERI, with toxicological profile and persistence in the environment as critical factors. In general, all compounds exhibited medium to very high levels of toxicity, indicating the need to manage risks associated with insecticide use and select those with lower impact, to minimize damage to agroecosystems.

To enhance the applicability of multiple solid waste road base materials in seasonally frozen soil areas and reduce the negative impact of red mud (RM) on the environment owing to its strong alkalinity, this paper utilizes untreated bayer method RM, fly ash (FA), and phosphogypsum (PG) as raw materials for preparing the road base materials. The mechanical properties, leaching characteristics, and Freeze-thaw (F-T) resistance of the materials from different solid waste systems were investigated through F-T cycle tests, unconfined compressive strength (UCS) tests, and leaching tests. The hydration, sodium solidification, and F-T deterioration mechanisms were revealed using an X-ray diffractometer and a scanning electron microscope. Results indicated that when the mix ratio of RM: FA: PG: cement was 64:28:2:6 (RFP2), the specimen exhibited the best F-T resistance. After 10 F-T cycles, the compressive strength retention rate (BDR) of the specimen was 91.43 %, and the Na+ leaching concentration was 390 mg/L, which still met the Chinese standard. The main hydration products of the material include C-S-H gel and ettringite crystals. These crystals and gels are intertwined and connected to form a dense mesh structure, which improves the material's F-T resistance and sodium solidification effect. The F-T cycle results in the expansion of cracks within the material, which leads to the destruction of the adhesion of the cementitious products, thus causing a deterioration of the strength of the specimen and the reduction of the sodium solidification effect.

The solidification effect of contaminated soil degrades under wet-dry (W-D) cycles and acid rain. Acidic dry-wet cycle tests for Cr-contaminated soil solidified by alkali-activated granulated blast furnace slag (GGBS) are carried out. Toxic leaching test and accelerated leaching test are performed to study the leaching characteristic and mechanism. Scanning electron microscopy and energy spectrum analysis are used to investigate the microscopic mechanism. The long-term stability is evaluated through the apparent diffusion coefficient. The results show that a few W-D cycles at pH=7 will cause additional hydraulic reaction of GGBS and thus reduce the leaching concentration of total Cr and Cr(VI). Along with W-D cycles more AFt is generated. The expansion of AFt results in micro-fracture and thus more Cr leaching. In acidic W-D cycles, AFt dissolves first, releasing Cr immobilized by ion exchange. With the increasing acidity, C-S-H gels dissolve and more gypsum is generated, resulting in more micro-fractures. Consequently, the encapsulation effect weakens, resulting in more Cr leaching. However, the C-A-S-H gels remain stable. The slopes of the logarithmic curves of cumulative leached fraction versus time range from 0.373 to 0.675. The errors of fitting by a pure-diffusion analytical solution are mainly below 0.5%, indicating that diffusion is the dominant leaching mechanism. However, after 18 W-D cycles at pH=3, the effect of dissolution increases and the diffusion-dominated criteria are not satisfied. The mobility of Cr under neutral, weak acidic, and strong acidic W-D cycles is low, moderate, and high, respectively. It is necessary to take measures to reduce acid rain infiltration and W-D cycles when utilizing solidified soil. This research provides a reference for evaluating the long-term stability of solidified contaminated soil.

Hydrothermal solidification offers an effective, sustainable method for stabilizing clay soil, addressing environmental concerns while improving geotechnical properties. Facilitating pozzolanic reactions between lime and clay under controlled temperature and pressure significantly enhances compressive strength and soil durability. This process promotes calcium silicate hydrate (C-S-H) formation, reduces industrial waste, and supports lime reuse, making it an energy-efficient soil improvement approach. This study investigates the impact of lime addition (0-20%) and various chemical and physical parameters on clay soil compressive strength. Key chemical components include SiO2 (20.1-76.9%), Al2O3 (7.6-34.8%), Fe2O3 (0.6-32.9%), CaO (0.1-43.5%), MgO (0-9.56%), Na2O (0.01-2.8%), and K2O (0.1-3.9%). Physical properties such as density, plasticity index (6-34.5%), and liquid limit (24-65.2%) were analyzed alongside process parameters like heating temperature (60-1000 degrees C), curing time (0-120 days), and curing temperature (20-41 degrees C). Using a dataset of 152 samples divided into training and testing groups, the statistical analysis focused on the leaching coefficient (Lc) and silica-sesquioxide ratio (Kr). Lc emerged as the most significant factor, achieving an R2 of 0.89 and an RMSE of 1.13 MPa. This study found that the compressive strength of lime-treated clay soils varied from 0.02 MPa to 11.9 MPa, influenced by lime concentration, chemical composition, and processing factors. Increased lime additions, particularly when combined with hydrothermal treatment, led to significant strength enhancements owing to improved pozzolanic activity. The plasticity index (PI) markedly diminished with lime stabilization, enhancing workability and mitigating volumetric variations. The density of treated soils rose from 0.8 g/cm3 to 2.1 g/cm3, signifying improved particle compaction and less porosity. The mechanical enhancements indicate that hydrothermal solidification efficiently converts expanding clay into a robust and stable material appropriate for geotechnical applications. Increased Lc improved compressive strength through enhanced pozzolanic activity and density, while higher Kr values, indicating lower CaO availability, yielded limited strength gains. Lc consistently outperformed Kr and other chemical compositions in enhancing clay soil compressive strength.

Municipal solid waste incineration bottom ash (MSWIBA) emerges as a potential alternative to natural aggregates due to its similar mineral composition and engineering properties as embanking fillings. However, the instability and environmental pollution risks of MSWIBA limit its large-scale application. This study proposes to employ Enzyme Induced Carbonate Precipitation (EICP) technology to enhance the mechanical properties of MSWIBA and reduce its environmental impact. Initial analyses focused on the basic physicochemical properties and morphological changes of MSWIBA before and after modification. Then the modified MSWIBA exhibited improvements in shear resistance, resilient modulus, and permanent deformation behavior. It was also found that existing resilient modulus and permanent deformation predicting models for soils are applicable to EICPmodified MSWIBA. The column leaching tests were conducted on samples subjected and not subjected to freeze-thaw and dry-wet cycles. The results revealed the modified MSWIBA released reduced heavy metal concentrations in both water and acid leaches. These findings establish a solid theoretical foundation for employing EICP-modified MSWIBA as an embankment fill material, highlighting the potential for wider adoption of this eco-friendly alternative in road constructions.

The existence of dispersive clay soils can cause serious erosion, void, and structural damage due to an imbalance of the electrochemical forces within the particles, which causes the soil particles to be repulsive instead of being attracted to each other. Dispersivity is observed in several highway embankments in Mississippi, and the embankments have eroded and developed voids over time. The current study investigated the root cause of the voids observed within the subgrade of the state highway 477 in Mississippi and evaluated the dispersivity of high cations-based soil. As part of an investigative initiative, a 2D Ground Penetration Radar (GPR) of the highway embankment road to make a 2D profile of the soil subsurface media was surveyed to reveal that potential hotspots were overlooked, leading to suspected soil dispersivity and subsequent issues. To assess the extent of visible voids and sinkholes, dispersive tests, including the Double Hydrometer Test (DHT), were conducted to evaluate the dispersivity of the clay soils. A series of boreholes were drilled along the roadway to collect the soil samples, determine their physical properties, and identify clay soil dispersity within the soil profile. Following the confirmation of dispersive soil existence through these tests, advanced analyses, such as Scanning Electron Microscope (SEM) to identify the microstructures and the ionic compositions of the soil particles and Toxicity Characteristic Leaching Procedure Tests (TCLPT) to assess the solubility of high concentrated elements in liquid, were performed to comprehend the root cause of the soil dispersion. Based on the results of the analysis, the GPR wave cannot pass through the subgrade, which mostly happens due to the presence of the charge within the soil. Based on SEM, DHT, and TCLP test results, the soil samples have high cations, including the presence of K + . Moreover, a similar distribution of the ionic compositions was observed among the majority of the soil samples; however, the percent of dispersion regarding clay soil particles varied.

Despite early hydrological studies of 234U/238U in groundwaters, their utilization as a paleoclimatic proxy in stalagmites has remained sporadic. This study explores uranium isotope ratios in 235 datings (230Th) from six stalagmites in Ejulve cave, northeastern Iberia, covering the last 260 ka. The observed 234U enrichment is attributed to selective leaching of 234U from damaged lattice sites, linked to the number of microfractures in the drip route and wetness frequency, which under certain conditions, may result in the accumulation of 234U recoils. This selective leaching process diminishes with enhanced bedrock dissolution, leading to low S234U. Temperature variations significantly influence bedrock dissolution intensity. During stadial periods and glacial maxima, lower temperatures likely reduced vegetation and respiration rates, thereby decreasing soil CO2 and overall rock dissolution rates. This reduction could enhance the preferential leaching of 234U from bedrock surfaces due to lower bulk rock dissolution. Additionally, the temperature regime during cold periods may have facilitated more frequent freeze-thaw cycles, resulting in microfracturing and exposure of fresh surfaces. Conversely, warmer temperatures increased soil respiration rates and soil CO2, accelerating rock dissolution rates during interstadials and interglacials, when low S 234 U is consistent with high bedrock dissolution rates. The contribution of a number of variables sensitive to bedrock dissolution and wetness frequency processes successfully explains 57% and 74% of the variability observed in the S 234 U in Andromeda stalagmite during MIS 3-4 and MIS 5b-5e, respectively. Among these variables, the growth rate has emerged as crucial to explain S 234 U variability, highlighting the fundamental role of soil respiration and soil CO2 in S 234 U through bedrock dissolution. I-STAL simulations provides the potential for a combination of Prior Calcite Precipitation (PCP) indicators like Mg/Ca with PCP- insensitive indicators of bedrock dissolution such as S234U, along with growth rate data, may be useful to diagnose when PCP variations reflect predominantly changes in drip intervals and when changes in bedrock dissolution intensity contribute. The relationship between stalagmite S234U, bedrock dissolution, and initial dripwater oversaturation suggests two significant advancements in paleoclimate proxies. First, S 234 U could serve as a valuable complement to S13C since it is significantly influenced by soil respiration and soil CO2, thereby reflecting soil and vegetation productivity sensitive to both humidity and temperature. Secondly, since PCP does not fractionate uranium isotopes, S 234 U could be used in combination with Mg/Ca or S44Ca to deconvolve PCP variations due to changing drip rates from those due to changes in initial saturation state. This study emphasizes the overriding climatic control on S234U, regardless of the absolute 234U/238U activity ratios among samples and their proximity or distance from secular equilibrium, and advocates for its application in other cave sites.

Nitrate leaching from soil presents a significant threat to soil health, as it can result in nutrient loss, soil acidification, and structural damage. It is crucial to quantify the spatial heterogeneity of nitrate leaching and its drivers. A total of 509 observational data points regarding nitrate leaching in northern China were collected, capturing the spatial and temporal variations across crops such as winter wheat, maize, and greenhouse vegetables. A machine learning (ML) model for predicting nitrate leaching was then developed, with the random forest (RF) model outperforming the support vector machine (SVM), extreme gradient boosting (XGBoost), and convolutional neural network (CNN) models, achieving an R-2 of 0.75. However, the performance improved significantly after integrating the four models with Bayesian optimization (all models had R-2 > 0.56), which realized quantitative prediction capabilities for nitrate leaching loss concentrations. Moreover, the XGBoost model exhibited the highest fitting accuracy and the smallest error in estimating nitrate leaching losses, with an R-2 value of 0.79 and an average absolute error (MAE) of 3.87 kg/ha. Analyses of the feature importance and SHAP values in the optimal XGBoost model identified soil organic matter, chemical nitrogen fertilizer input, and water input (including rainfall and irrigation) as the main indicators of nitrate leaching loss. The ML-based modeling method developed overcomes the difficulty of the determination of the functional relationship between nitrate loss intensity and its influencing factors, providing a data-driven solution for estimating nitrate-nitrogen loss in farmlands in North China and strengthening sustainable agricultural practices.