This investigation examines the development of titanium slag-flue gas desulfurized gypsum-Portland cement ternary composites (the ternary composites) for the solidification and stabilization of Pb-contaminated soils. The efficacy of the ternary composites is systematically evaluated using a combination of experimental methodologies, including mechanical properties such as unconfined compressive strength, stress-strain behavior and elastic modulus, leaching toxicity, XRD, TG-DTG, FTIR, XPS, and SEM-EDS analyses. The results indicate that the mechanical properties of Portland cement solidified Pb-contaminated soils are inferior to those of Portland cement solidified Pb-free soil, both in the early and later stages. However, the mechanical properties of Pbcontaminated soils solidified by the ternary composites are superior to those of the ternary composites solidified Pb-free soils in the early stage but somewhat inferior in the later stage. The ternary composites significantly decrease the leached Pb concentrations of solidified Pb-contaminated soils, which somewhat increase with the Pb content and with the pH value decrease of the leaching agent. Moreover, with much lower carbon emissions index and strength normalized cost, the ternary composites have comparable stabilization effects on Pbcontaminated soils to Portland cement, suggesting that the ternary composites can serve as a viable alternative for the effective treatment of Pb-contaminated soils. Characterization via TG-DTG and XRD reveals that the primary hydration products of the ternary composite solidified Pb-contaminated soils include gypsum, ettringite, and calcite. Furthermore, FTIR, XPS and SEM-EDS analyses demonstrate that Pb ions are effectively adsorbed onto these hydration products and soil particles.
Foamed lightweight soil (FLS) is frequently used for roadbed backfilling; however, excessive cement use contributes to higher costs and energy consumption. Desulfurized gypsum (DG), a by-product of industrial processing with a chemical composition similar to natural gypsum, presents a viable alternative to cement. This study evaluates the potential of DG to replace cement in FLS, creating a new material, desulfurized gypsum foamed lightweight soil (DG-FLS). This article is conducted on DG-FLS with varying DG content (0-30%) to assess its flowability, water absorption, unconfined compressive strength (UCS), durability, and morphological characteristics, with a focus on its suitability for roadbed backfilling, though its performance over the long term in engineering applications was not evaluated. Results show that as DG content increased, flowability, water absorption, and UCS decreased, with values falling within the range of 175-183 mm, 8.24-12.49%, and 0.75-2.75 MPa, respectively, all of which meet embankment requirements. The inclusion of DG enhanced the material's plasticity, improving failure modes and broadening its applicability. Durability tests under wet-dry and freeze-thaw cycles showed comparable performance to traditional FLS, with UCS exceeding 0.3 MPa. Additionally, the incorporation of SO42- in DG-FLS reduced sulfate diffusion, decreased C-S-H content, and increased calcium sulfate content, improving sulfate resistance. After 120 days of exposure to sulfates, the durability coefficient of DG-FLS surpassed 100%, with a 25% improvement over traditional FLS. A sustainability analysis revealed that DG-FLS not only meets engineering strength requirements but also offers economic and environmental benefits. Notably, DG-12 showed a 20% reduction in environmental impact compared to conventional FLS, underscoring its potential for more sustainable construction.
Soft soil foundations need to be reinforced because of their low bearing capacity and susceptibility to deformation. Ordinary portland cement (OPC) is widely used in foundation treatment due to its strong mechanical properties. However, the production process for OPC curing agents involves high energy consumption and significant CO2 emissions. Given these problems, this paper proposes a fly ash-slag-based geopolymer to replace OPC curing agents, which can solidify soil while reducing OPC consumption. Another issue is that variability in environmental conditions influences the strength of soil solidified with fly ash-slag-based geopolymer, leading to subpar mechanical properties. However, by adding desulfurized gypsum as an admixture, the rich SO42- can react with Ca2+ and active silicate in the geopolymer to form Aft, thereby improving the mechanical properties. In the experiment, desulfurized gypsum is added as an admixture to a fly ash-slag-based geopolymer curing agent, and the resulting solidified soil is investigated through various macroscopic and microscopic tests. These tests include unconfined compressive strength measurements, water stability tests, scanning electron microscopy analyses, and X-ray diffraction tests. The results of these tests are combined with the response surface method to optimize the alkali-solid ratio, the modulus of the alkali activator, and the amount of desulfurized gypsum to 0.6%, 0.809%, and 15.96%, respectively. On this basis, an optimal mixing ratio was proposed and applied to form a geopolymer-solidified soil. The compressive strength and microstructure of this soil were then investigated using the single-variable method. An unconsolidated undrained triaxial test was performed on geopolymer-solidified soils of different curing times to investigate their shear performance. The water stability test was carried out to explore the influence of soaking time on the strength of solidified soil. Through microscopic observation, it was found that the fly ash-slag-based geopolymer generated significant amounts of (N, C)-A-S-H and C-S-H in solidified soil. With the addition of desulfurized gypsum, soil particles become filled with Aft and the solidified soil becomes more brittle instead of plastic, resulting in a significant increase in compressive strength. In addition, the cohesion and internal friction angle increase with curing time. With the increase of soaking time, the softening effect of long-term water soaking reduced the strength of the solidified soil.
This study investigates the stabilization of lateritic soil through partial replacement of cement with flue gas desulfurization (FGD) gypsum, aiming to enhance its engineering properties for pavement subgrade applications. Lateritic soils are known for their high plasticity and low strength, which limit their utility in infrastructure. To address these challenges, soil specimens were treated with varying cement contents (3%, 6%, 9%) and FGD gypsum additions (1%-6%). Laboratory tests were conducted to evaluate plasticity, compaction, permeability, unconfined compressive strength (UCS), California Bearing Ratio (CBR), and fatigue behaviour. The optimal mix 6% cement with 3% FGD gypsum demonstrated significant improvements: UCS increased by over 110% after 28 days, permeability reduced by 26%, and soaked CBR improved by 56% compared to untreated soil. Additionally, fatigue life showed remarkable enhancement under cyclic loading, indicating increased durability for high-traffic applications. To support predictive insights, machine learning models including Decision Tree, Random Forest, and Multi-Layer Perceptron (MLP) were trained on 168 data samples. The MLP and Random Forest models achieved high prediction accuracy (R2 approximate to 0.98), effectively capturing the non-linear interactions between mix proportions and UCS. SHAP (SHapley Additive exPlanations) analysis identified curing duration as the most influential factor affecting strength development. This integrated experimental-computational approach not only validates the feasibility of using FGD gypsum in sustainable soil stabilization but also demonstrates the effectiveness of machine learning in predicting key geotechnical parameters, reducing reliance on extensive laboratory testing and promoting data-driven pavement design.
Our recent investigations have discovered inward diffusion (in-gassing) of moderately volatile elements (MVEs; e.g., Na, K and Cu) from volcanic gas into volcanic beads/droplets. In this work, we examine the distribution of sulfur in lunar orange glass beads. Our analyses reveal that sulfur exhibits a non-uniform distribution across the beads, forming U or W shaped profiles typical of in-gassing. A model developed to assess sulfur contributions from different sources (original magmatic sulfur versus atmospheric in-gassed sulfur) in the orange beads indicates that atmospheric sulfur in-gassed during eruption contributes approximately 9-24 % to the total sulfur content of an orange bead, averaging around 16 %. This in-gassed sulfur is derived from the eruption plume, where atmospheric sulfur could undergo photochemical reactions induced by UV light, leading to mass independent fractionation and a distinct sulfur isotope signature. Interestingly, a recent study discovered a small mass independent isotope fractionation of sulfur in lunar orange glass beads in drive tube 74002/1 and a lack of such mass independent isotope fractionation in black glass beads in the same lunar sample. This finding contrasts with sulfur in lunar basalts, which typically exhibit mass dependent fractionation. With our work, the observed mass independent fractionation signal in sulfur isotopes of orange beads can be attributed to the in-gassing of photolytic sulfur in the optically thin part of the eruption plume where UV light can penetrate. Using the sulfur isotope data of lunar orange beads, we estimate that the 033S value of atmospheric sulfur is approximately -0.18 %o. Our study provides new insights into the complex dynamics of volatile elements in lunar volcanic processes, highlighting the role of in-gassing in shaping sulfur isotope signatures in volcanic glass beads.
Acid sulfate soils impact surrounding ecosystems with pronounced environmental damage via leaching of strong acidity along with the concurrent mobilization of toxic metals present in the soils and, in consequence, they are often described as the nastiest soils on Earth. Within Sweden, acid sulfate soils are distributed mainly under the maximum Holocene marine limit that stretches the length of the country, some 2000 km north to south. Despite only minor geographical differences in the geochemical composition of the Swedish acid sulfate soils, their field oxidation zone microbial community compositions differ along a north-south regional divide. This study compared the 16S rRNA gene amplicon-based microbial community compositions of field oxidation zones (field tested pH 6.5) collected from the same field sites throughout Sweden that had acidified (final pH = 20 degrees C) greater than what was experienced by the field oxidation zone samples when sampled (similar to 2 degrees C-9 degrees C). These data suggested that in the absence of significant geochemical differences, temperature was the predominant driver of microbial community composition in Swedish acid sulfate soil materials.
Cadmium (Cd) contamination in agricultural soil and accumulation in rice poses serious threat to human health. It is reported that Selenium (Se) can mitigate the toxic effect of Cd in rice. But the underlying mechanism of Se preventing the Cd accumulation and restoring the micronutrient content in rice grains have not been studied before. Therefore, our main aim is to reduce Cd content and restore micronutrient content in rice grain and study the mechanism. Two indigenous rice genotypes (Maharaj and Jamini) were exposed to 10 and 50 mu M Cd in presence and absence of Se (5 mu M) with a control set and assessed for plant growth, biomass, Cd content, ROS and antioxidants for Cd induced toxicity and amelioration. Genes for micronutrient transporters were studied by RT-PCR. Grain Cd and micronutrient content and agronomic parameters were also studied. Se supplementation increased plant growth, biomass, and yield under Cd stress. SEM and EDX analysis revealed that Se-Cd complex formed on root surfaces restricted Cd uptake by the roots preventing root damage. Soil analysis confirmed that Se decreased Cd bioavailability, restricted root to shoot Cd translocation, ultimately reducing Cd accumulation and restoring micronutrients in grain. This was further validated by fluorescent Leadmium dye staining. In (Se + Cd) treated seedlings, up-regulation of S metabolism and nutrient transporter genes also contributed to the mitigation of Cd stress. The Se supplementation can be considered as a cost-effective, ecofriendly and sustainable approach to produce Cd free rice cultivation in Cd polluted soil.
Human activities involving combustion and agricultural practices, among others, lead to the release of acidifying compounds such as nitrogen oxides (NOx), sulfur oxides (SOx), and ammonia (NH3). These substances are the main drivers of human-induced terrestrial acidification, a geochemical process resulting mainly in the decline of soil pH, causing ecosystem damage and biodiversity loss. A relevant tool to quantify impacts of human activities is Life Cycle Assessment where characterization factors are used to estimate the potential environmental impacts per unit of emission. These are derived from models of environmental processes occurring along the stressor's impact pathway, connecting an emission to its potential environmental damage. Here, new ecosystem quality characterization factors for terrestrial acidification were developed, assessing the potential global loss of vascular plant species. The final values combine four elements: existing fate factors, updated soil response factors, recently revised effect factors, and the Global Extinction Probability. The latter allows to convert the local decline in species richness into a global species loss. The regionalized marginal characterization factors provided represent the aggregated global biodiversity impact in all the world's ecoregions due to an acidifying emission (of NOx, NHx, or SOx) from a specific country. The values cover five orders of magnitude (from 10- 16 to 10-11 PDFglobal.yr.kgemitted- 1 ), and the comparison to currently implemented values has helped both validate the calculation pathway and confirm the need for updated factors. Following current harmonization recommendations, terrestrial acidification impacts can now be compared to those from other stressors estimated in global Potential Disappeared Fraction of species.
Strongly alkaline dispersive soils pose a significant global challenge to both engineering applications and agricultural production, particularly in arid and semi-arid regions. Conventional soil modifiers used to address this issue not only present environmental and economic concerns but also fail to effectively improve soil alkalinity. This study investigates the potential application of acidic desulfurization gypsum (DG) as a soil modifier for dispersive soils, aiming to achieve high-value utilization of industrial solid waste. The dispersibility of soil under hydrostatic and dynamic conditions are studied using the mud ball test and pinhole test. The engineering properties and modification mechanism of DG consolidated soils were revealed by combining the unconfined compressive strength (UCS), Brazilian split tensile strength (BTS), microstructure, and mineral evolution. Results show that 3% DG significantly reduces soil dispersibility and improves disintegration and erosion resistance, with UCS and BTS increases of 210% and 94%, respectively. The mechanism involves DG releasing hydrogen ions to reduce soil alkalinity, which in turn activates cation activity of DG, replacing sodium ions on the soil surface and forming a binding hydrate within 7 days. Tests on natural dispersive soil from check dams confirmed effectiveness of DG. Advanced machine learning techniques quantitatively analyzed the impact of DG on soil dispersibility, highlighting the relationship between soil dispersibility and chemical/mechanical properties. This study establishes a novel link between hydraulic erosion parameters, mechanical parameters, and soil stressstrain relationships, providing valuable insights for future soil stabilization. The results show potential of waste acidic DG in practical engineering applications and contribute to the sustainable advancement of dispersive soil stabilization technology. Alkaline dispersive soils also aid in regulating the acidity and alkalinity of DG and controlling toxic emissions.
Apatite is ubiquitous in lunar samples and has been used widely for estimating volatile abundances in the lunar interior. However, apatite compositional and isotopic variations within and between samples have resulted in varying and ambiguous results. Understanding apatite petrogenesis will help with both identifying the appropriate composition for volatile estimation and interpreting isotopic variations. Here we report a comprehensive petrogenetic investigation of apatite in Chang'E-5 (CE5) basaltic sample CE5C0800YJYX013GP. Apatite displays both intra-grain and inter-grain compositional variations with F and Cl contents falling in the ranges of 0.97-2.47 wt% and 0.24-1.09 wt%, respectively. These apatite compositions show relatively low F and high Cl characteristics in comparison to apatites of Apollo high-Ti and low-Ti mare basalts, but are similar to those reported for lunar meteorites LAP 04841 and MIL 05035. We discern three zoning profiles: fractional crystallization (FC)-dominated, degassing-induced and a third indicated by REE-enriched cores, which are interpreted as representing different generations of apatite. FC-dominated zoning is characterized with decreasing F and increasing Cl and S contents from core to rim; while the opposite is true for the degassing-induced zoning. Regardless of the zoning patterns, apatite Cl and S contents display positive correlations, with S contents up to similar to 3000 ppm, much higher than previous reports for Apollo samples (up to similar to 600 ppm). We demonstrate that the fractional crystallization model proposed by Boyce et al. (2014) in combination with H2O degassing and high S contents in melt (likely at sulfide saturation) can explain these high Cl and S contents observed in CE5 apatite. Based on the core composition of the FC-dominated zoning profile, which has the lowest incompatible element concentrations, bulk F, Cl and H2O contents in the parental melt are estimated to be similar to 72 +/- 21, similar to 43 +/- 14 and similar to 1576 +/- 518 ppm, respectively. These estimates have lower F/Cl ratios than those measured in olivine-hosted melt inclusions from Apollo mare basalts. By adopting the petrogenetic model for CE5 basalt proposed by Su et al. (2022), i.e., 10 % partial melting of a hybrid mantle source, followed by similar to 30-70 % fractional crystallization (similar to 50 % for our sample), we estimate the F, Cl, H2O and S contents in the mantle source are in the ranges of similar to 2.5-4.6, similar to 0.7-1.4, similar to 53-105 and similar to 38-125 ppm, respectively, similar to estimates for both depleted Earth mantle and primitive lunar mantle. However, by adopting the model of Tian et al. (2021), 2-3 % partial melting of a mantle source composed of 86 PCS+2% TIRL (PCS, percent crystallized solid; TIRL, trapped instantaneous residual liquid), followed by 43-88 % fractional crystallization, these estimates will be 5-10 times lower. To be certain whether the relatively low F and high Cl characteristics of CE5 apatite imply an enriched mantle source requires further evaluation of the petrogenetic models for CE5 basalt.