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Serpentinite carbonation contributes to the deep carbon (C) cycle. Recently, geophysical and numerical studies have inferred considerable hydrothermal alteration in plate bending faults, opening the possibility of significant C storage in the slab mantle. However, there is a lack of quantitative determination of C uptake in serpentinized mantle rocks. Here, we experimentally constrain serpentinite carbonation in H2O–CO2–NaCl fluids to estimate C uptake in hydrated mantle rocks. We find that serpentinite carbonation results in the formation of talc and magnesite along the serpentinite surface. The presence of porous reaction zones (49.2% porosity) promotes the progress of carbonation reactions through a continuous supply of CO2-bearing fluids to the reaction front. Added NaCl effectively decreases the serpentinite carbonation efficiency, particularly at low salinities (< 5.0 wt%), which is likely attributed to the reduction in fluid pH and the transport rate of reactants, and the increase in magnesite solubility. Based on previous and our experiments, we fit an empirical equation for the reaction rate of serpentinite carbonation. Extrapolation of this equation to depths of plate bending fault systems suggests that serpentinite carbonation may contribute to an influx of up to 7.3–28.5 Mt C/yr in subduction zones. Our results provide new insights into serpentinite carbonation in environments with high fluid salinities and potentially contribute to the understanding of the C cycle in subduction zones. [ABSTRACT FROM AUTHOR]

Interfacial processes involving metal (oxyhydr)oxide phases are important for the mobility and bioavailability of nutrients and contaminants in soils, sediments, and water. Consequently, these processes influence ecosystem health and functioning, and have shaped the biological and environmental co-evolution of Earth over geologic time. Here we employ reactive molecular dynamics simulations, supported by synchrotron X-ray spectroscopy to study the molecular-scale interfacial processes that influence surface complexation in ferrihydrite-water systems containing aqueous MoO 4 2 - . We validate the utility of this approach by calculating surface complexation models directly from simulations. The reactive force-field captures the realistic dynamics of surface restructuring, surface charge equilibration, and the evolution of the interfacial water hydrogen bond network in response to adsorption and proton transfer. We find that upon hydration and adsorption, ferrihydrite restructures into a more disordered phase through surface charge equilibration, as revealed by simulations and high-resolution X-ray diffraction. We observed how this restructuring leads to a different interfacial hydrogen bond network compared to bulk water by monitoring water dynamics. Using umbrella sampling, we constructed the free energy landscape of aqueous MoO 4 2 - adsorption at various concentrations and the deprotonation of the ferrihydrite surface. The results demonstrate excellent agreement with the values reported by experimental surface complexation models. These findings are important as reactive molecular dynamics opens new avenues to study mineral-water interfaces, enriching and refining surface complexation models beyond their foundational assumptions. [ABSTRACT FROM AUTHOR]

This study explores the optimization of iron electrocoagulation for treating laundry greywater, which accounts for up to 38% of domestic greywater. Characterized by high concentrations of surfactants, detergents, and suspended solids, laundry greywater presents complex challenges for treatment processes, posing significant environmental and health risks. Utilizing response surface methodology (RSM), this research developed a second-order polynomial regression model focused on key operational parameters such as the area-to-volume ratio (A/V), current density, electrolysis time, and settling time. Optimal treatment conditions were identified: an A/V ratio of 30 m2/m3, a current density of 10 mA/cm2, an electrolysis duration of 50 min, and a settlement period of 12 h. Under these conditions, exceptional treatment outcomes were achieved, with turbidity removal reaching 94.26% and COD removal at 99.64%. The model exhibited high effectiveness for turbidity removal, with an R2 value of 94.16%, and moderate effectiveness for COD removal, with an R2 value of 75.90%. The interaction between the A/V ratio and electrolysis time particularly underscored their critical role in electrocoagulation system design. Moreover, these results highlight the potential for optimizing electrocoagulation parameters to adapt to daily fluctuations in greywater production and meet specific household reuse needs, such as toilet flushing. This tailored approach aims to maximize contaminant separation and coagulant efficiency, balance energy use and operational costs, and contribute to sustainable water management. [ABSTRACT FROM AUTHOR]

Background and aims: Ensuring adequate and balanced nutrient supply is crucial for enhancing citrus fruit quality. Some plants could modulate nutrient bioavailability in soil through the enhancement of root exudation. The study aimed to reveal how citrus change its root exudates metabolism profile to adapt to the soil with secondary nutrients and micronutrients deficiency. Methods: Citrus sinensis Osbeck cv. Newhall ×Poncirus trifoliate (L.) Raf grown in Ganzhou citrus orchards was used to evaluate the effect of soil applied and foliar sprayed secondary nutrients and micronutrients (Ca, Mg, B, Fe, Zn, Se) on the mineral elements concentration, external and intrinsic quality of citrus. The hydroponic experiment was conducted with Poncirus trifoliate (L.) Raf grown either in full nutrient solutions or in specific nutrient shortage conditions (Ca, Mg, B) for 45 days to obtain root exudate and perform untargeted metabolomic analysis (UHPLC-MS/MS). Results: Adequate supplementation of secondary nutrients and micronutrients effectively enhanced the nutritional value and intrinsic quality (TSS/TA) of citrus. 791 features were identified in citrus root exudates. Some metabolites was identified as root exudates for the first time, such as hecogenin, bergaptol and limonin. In the absence of secondary nutrients and micronutrients, citrus roots will secrete more substances related to plant disease resistance, nutrient acquisition and plant-microbial interactions, such as resveratrol, cinnamaldehyde, scopoletin, and phloretin. Conclusion: These findings highlight the value of secondary nutrients and micronutrients in regulating fruit quality and root exudates metabolism profile of citrus. It reveal the strategies of citrus to mitigate the nutrient deficiency in soils. [ABSTRACT FROM AUTHOR]

CO2 capture and storage in geological reservoirs have the potential to significantly mitigate the effects of anthropogenic gas emissions on global climate. Here, we report the results of the first laboratory experiments of CO2 injection in continental flood basalts of South America. The results show that the analyzed basalts have a mineral assemblage, texture and composition that efficiently allows a fast carbonate precipitation that starts 72 h after injection. Based on the availability of calcium, chemical monitoring indicates an estimated CO2 storage of ~ 75%. The carbonate precipitation led to the precipitation of aragonite (75.9%), dolomite (19.6%), and calcite (4.6%). [ABSTRACT FROM AUTHOR]

Environmental pollution is a pressing and widespread issue in contemporary society that necessitates innovative solutions to meet the growing demand for clean water resources. One crucial development in the realm of nanomaterials involves the creation of multifunctional materials with specific adsorption properties and ease of recovery, which are integral to water purification efforts. Among these materials, magnetic nanocarriers have emerged as a versatile and efficient means of immobilizing target pollutants for water decontamination. Their effectiveness stems from their expansive surface area, relatively straightforward fabrication, and diverse applications, particularly in environmental remediation processes. This comprehensive review aims to delve into the various classes of magnetic carriers and their roles in removing contaminants from water sources. Each class is examined critically, providing insights into synthesis methodologies, accompanied by noteworthy examples from the literature, and an exploration of the significant contributions these materials offer to the field. Through this review, we seek to provide a thorough understanding of the use of magnetic nanocarriers in addressing the crucial issue of water pollution and highlight their potential to play a pivotal role in achieving cleaner and more sustainable water resources for our growing population. [ABSTRACT FROM AUTHOR]

Soil contamination by uranium presents a burgeoning global environmental concern, exerting detrimental effects on both agricultural production and soil health. Biochar, a carbonaceous material derived from biomass pyrolysis, exhibits considerable potential for remediating uranium-contaminated soils. However, a comprehensive review of the effects of biochar on the fate and accumulation of uranium in soil–plant systems remains conspicuously absent. In this paper, uranium sources and contamination are reviewed, and the impact of biochar on uranium immobilization and detoxification in soil–plant systems is analyzed. We reviewed the status of uranium contamination in soils globally and found that mining activities are currently the main sources. Further meta-analysis revealed that biochar addition significantly reduced the soil uranium bioavailability and shoot uranium accumulation, and their effect value is 58.9% (40.8–76.8%) and 39.7% (15.7–63.8%), respectively. Additionally, biochar enhances the soil microenvironment, providing favourable conditions for promoting plant growth and reducing uranium mobility. We focused on the mechanisms governing the interaction between biochar and uranium, emphasising the considerable roles played by surface complexation, reduction, ion exchange, and physical adsorption. The modification of biochar by intensifying these mechanisms can promote uranium immobilisation in soils. Finally, biochar alleviates oxidative stress and reduces uranium accumulation in plant tissues, thereby mitigating the adverse effects of uranium on plant growth and development. Overall, our review highlights the capacity of biochar to remediate uranium contamination in soil–plant systems through diverse mechanisms, providing valuable insights for sustainable environmental remediation. Highlights Biochar reduces uranium mobility through a variety of mechanisms, including surface complexation, reduction, ion exchange, and physical adsorption. Biochar significantly reduces uranium bioavailability in soil and limits its accumulation in plants. Modified biochar has been shown to enhance its effectiveness in immobilising uranium. Biochar application to soil not only promotes uranium remediation but also improves soil quality. [ABSTRACT FROM AUTHOR]

Phosphate solubilizing fungi Penicillium oxalicum (POX) and Red yeast Rhodotorula mucilaginosa (Rho) have been applied in Pb remediation with the combination of fluorapatite (FAp), respectively. The secretion of oxalic acid by POX and the production of extracellular polymers (EPS) by Rho dominate the Pb remediation. In this study, the potential of Pb remediation by the fungal combined system (POX and Rho) with FAp was investigated. After six days of incubation, the combination of POX and Rho showed the highest Pb remove ratio (99.7%) and the lowest TCLP-Pb concentration (2.9 mg/L). The EPS combined with POX also enhanced Pb remediation, which has a 99.3% Pb removal ratio and 5.5 mg/L TCLP-Pb concentration. Meanwhile, Rho and EPS can also stimulate POX to secrete more oxalic acid, which reached 1510.1 and 1450.6 mg/L in six days, respectively. The secreted oxalic acid can promote FAp dissolution and the formation of lead oxalate and pyromorphite. Meanwhile, the EPS produced by Rho can combine with Pb to form EPS-Pb. In the combined system of POX + Rho and POX + EPS, all of the lead oxalate, pyromorphite, and EPS-Pb were observed. Our findings suggest that the combined application of POX and Rho with FAp is an effective approach for enhancing Pb remediation. [ABSTRACT FROM AUTHOR]

Deinococcus radiodurans (DR) exhibits strong resistance to ionizing radiation. In this study, by constructing a radiation-resistant genetically engineered strain overexpressing the Cs gene, the tolerance of the bacterium to aluminum ions was enhanced, thereby achieving the goal of microbial sustainable remediation of uranium-contaminated environments. Methods: 1. Extraction of the recombinant plasmid pRADK-Cs, transformation into DR, and verification. 2. Investigation of factors such as time and initial uranium concentration on the efficiency of uranium accumulation by the recombinant strain, characterized by changes in functional groups and surface morphology before and after accumulation using techniques such as scanning electron microscope. Conclusions: The recombinant strain Deino-Cs can reduce the inhibitory effect of aluminum ions on uranium accumulation capability, and it exhibits a higher uranium accumulation rate compared to the wild-type strain. [ABSTRACT FROM AUTHOR]

TiO2 nanoparticles were synthesized using Phyllanthus acidus leaf extract. The presence of amines, aliphatic alcohol, phenolic acids and hydroxyl group in the Phyllanthus acidus leaf extract may be responsible for the reduction of TiO2 nanoparticles from a precursor. Green synthesized TiO2 nanoparticles were characterized with the help of UV–visible spectroscopy, XRD, FTIR, FESEM-EDX, TEM and BET analysis. The size of nanoparticles was determined to be 20–40 nm with a surface area of 108.31 m2/g, a pore size of 1.347 nm and a total pore volume of 0.1456 cc/g. The performance of heavy metal adsorption of TiO2 nanoparticles was assessed. The process variables such as metal initial concentration, adsorbent dosage, pH and contact time for the adsorption of lead were optimized using response surface methodology (RSM) with central composite design (CCD). The lead removal efficiency of 98.6% was achieved using green synthesized TiO2 nanoparticles under optimum conditions, an initial lead concentration of 89 mg/L, a dosage of adsorbent at 0.32 g, pH of 7.8 and a contact time of 89 min. The fitting of different isotherm models was carried out with the experimental and observed data, which confirmed that the Langmuir model best fit to describe the adsorption isotherm with an adsorption capacity of 2.633 mg/g. The first-order model is the optimum kinetic model, illustrating the rate of the equation of the adsorption of lead on TiO2 nanoparticles. [ABSTRACT FROM AUTHOR]

Basaltic rocks, owing to their vast geological presence, have been identified as potential reservoirs for carbon dioxide (CO2) sequestration. Their inherent attributes, namely, a pronounced mineral trapping capability, distinct structural intricacies, and a potential storage capacity surpassing 100Gt, earmark them as prime candidates for CO2 storage. However, knowledge gaps exist in understanding the modifications in the petrophysical and mechanical characteristics of these rocks post-CO2 sequestration. Comprehending these CO2-induced petrophysico-mechanical alterations is crucial for assessing their potential for long-term carbon mineralization-based storage. Thus, this study provides a critical review of key parameters that can induce post-CO2 injection changes in the mechanical and petrophysical properties of basaltic rocks. Also, the implications of these changes for long-term CO2 storage efficiency in Basaltic rocks are succinctly presented. Findings from this review work show that the mineralogical composition of basaltic rocks can alter the petrophysical and mechanical behaviors during CO2 injection. The reaction processes tend to enhance CO2 storage and mineralization via an increase in the porosity of the basaltic tuff, which was caused mainly by their dissolution. Laboratory simulations of CO2 storage in basaltic rocks had revealed that when the experiment was run for a longer length of time, the distribution/concentration of reaction minerals, reaction rates of the minerals, and/or permeability development of the rock matrix either decreased, increased, or remained the same. Furthermore, the strength indices for all types of basalts demonstrate that as exposure duration increases, the material strength steadily decreases. Core experiments and laboratory simulations have revealed that permeability increased at a higher flow rate and decreased at a lower flow rate. This is because a higher flow rate (increased injection pressure) will yield more pore spaces. Also, precipitation of carbonate minerals is favored under alkaline conditions since this condition necessitates increased production of divalent cations. Understanding these changes is essential since they can be detrimental to the immediate environment of the storage site, especially when there is CO2 leakage and consequent contact with freshwater resources. Similarly, we highlighted how several reports have correlated the occurrence of low-scale seismic events bounding the storage sites, to CO2 storage. Lastly, based on the reviews synthesized, we recommend promising directions to provide more profound insights into CO2 storage in basaltic rocks. [ABSTRACT FROM AUTHOR]

Guided by the concept of treating the wastes with wastes, the efficient use of bone residuals as separation materials is worthy of study. Since bone chars (BCs) are composed of hydroxyapatite and carbon matrix, it is desired to extend the carbon component with improved pore structure and abundant modified groups further, which is favorable to capture metal ions. In this work, phosphorus-modified BCs (PBCs) were fabricated by pretreating bone residuals with phytic acid, achieving improved surface areas (208.7–517.6 m2/g, 37.9–8.2-fold of enhancement) and abundant surface phosphorus contents (5.63–7.54 at.%, 2.8–5.8-fold of enhancement) than BCs. PBCs could adsorb heavy metals with fast kinetics (10.0 h) and excellent maximum capacities (463.9, 156.5, and 80.9 mg/g for Pb(II), Cu(II), and Cd(II)). Spectroscopic results demonstrated that the formation of precipitation was crucial for the enrichment of Pb(II). Moreover, the coordination with functional groups (O-/reductive N-species), the cation exchange with inorganic Ca2+, the electrostatic attraction with deprotonated O−, and the cation-π coordination should also be considered for the sorption. Our study facilitated the application of activated bone wastes as a promising candidate to remediate aquatic heavy metals. [ABSTRACT FROM AUTHOR]

The processes of acid in situ leaching (ISL) uranium (U) mines cause the pollution of groundwater. Phosphate (PO43−) has the potential to immobilize U in groundwater through forming highly insoluble phosphate minerals, but the performance is highly restricted by low pH and high sulfate concentration. In this study, hydrogen peroxide (H2O2) and PO43− were synergistically used for immobilizing U based on the specific properties of groundwater from a decommissioned acid ISL U mine. The removal mechanisms of U and the stability of U on the formed minerals were elucidated by employing X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and kinetic experiments. Our results indicated that the removal of U by simultaneously adding H2O2 and PO43− was significantly higher than the removal of U by individually adding H2O2 or PO43−. The removal of U increased with increasing PO43− concentration from 20 to 200 mg L−1 while decreased with increasing H2O2 concentration from 0.003 to 0.3%. Specifically, the removal efficiency of U from groundwater reached 98% after the application of 0.003% H2O2 and 200 mg L−1 PO43−. Amorphous iron phosphate that preferentially formed at low H2O2 and high PO43− concentrations played a dominant role in U removal, while the formations of schwertmannite and crystalline iron phosphates may be also contributed to the removal of U. This was significantly different from the immobilization mechanism of U through the formation of uranyl phosphate minerals after adding phosphate. The kinetic experimental results suggested that the immobilized U had a good stability. Our research may provide a promising method for in situ remediating U-contaminated groundwater at the decommissioned acid ISL U mines. [ABSTRACT FROM AUTHOR]

The radioactive uranyl and thorium ions discharged into freshwater have been the imperative environmental issue arousing great concern. Biochar, owing to its low cost, operational ease, and high efficiency, is touted as the promising sorbent for the U(VI) and Th(IV) removal in aqueous solutions. This study employed several characterization techniques and batch experiments to investigate mechanisms of U(VI) and Th(IV) adsorption on biochar. The kinetic results exhibited the fitness of the pseudo-second-order model. Both U(VI) and Th(IV) removals were influenced by pH, while only the ionic strength effects on U(VI) adsorption were observed. The adsorption of either the U(VI) or the Th(IV) fitted to the Langmuir and Freundlich model well. Natures such as endothermicity, increasing randomness, feasibility, spontaneity, and temperature favor of the adsorption reaction could be found in U(VI) and Th(IV) adsorption (U: ΔH0 = 36.28, ΔS0 = 108.84 and ΔG0 < 0; Th: ΔH0 = 63.42, ΔS0 = 134.12 and ΔG0 < 0). Our results highlighted the importance of biochar as the potentially green adsorbent and provided a practical strategy for radioactive contaminant remediation. [ABSTRACT FROM AUTHOR]

Electroplating sludge is a typical heavy metal-containing hazardous waste with tens of millions of tons produced annually in China. Acid leaching is the most common method to extract valuable heavy metals for resource recycling and environmental protection. However, the coexisting elements, which are released from electroplating sludge to the leaching solution, will hinder the recycling of valuable heavy metals. In this work, dynamic acid-leaching experiments, X-ray diffraction analysis, and simulation calculations were conducted. It was found that coexisting elements (mainly Ca, Fe, and Al) account for a large proportion, and calcium salts as coexisting mineral phase (especially CaCO3) are ubiquitous in electroplating sludge. Moreover, the evolution of coexisting mineral phase plays an essential role in the acid-leaching process: (1) the dissolution of CaCO3 contributed a strong acid-neutralization capability and released Ca2+; (2) H2SO4 is the optimal extracting reagent, since it triggered the transformation of calcium salts to CaSO4·2H2O, reducing the Ca2+ concentration; (3) the coexisting elements Fe and Al would form ferrous and aluminum salt minerals with the acid-leaching process, which reduces the leaching of low-value elements. This work provides a new perspective on the acid-leaching mechanism of electroplating sludge, where the evolution of the mineral phase effect the release of valuable heavy metals and coexisting elements. This work also provides as comprehensive information as possible on electroplating sludge and inspires the improvement of the acid-leaching method. [ABSTRACT FROM AUTHOR]

Separation materials have received increasing attention given their broad applications in the management of environmental pollution. It is desired to balance the contradiction between high separation efficiency and selectivity of separation materials. The integration of ball-milled bone chars with electrospun membranes might achieve this balance. In this study, electrospun cellulose/chitosan/ball-milled bone char (CL/CS/MB) membranes were by well-dispersing ball-milled bone chars with nanoscale size (98.9–167.5 nm) and developed porosity (40.2–373.1 m2/g) in the electrospinning solvent. The synergistic integration of distributed MBs (5.4–31.5 wt.% of loading hydroxyapatite on the membrane matrix) allowed the efficient sorption of Pb(II) with fast kinetics (20.0 min), excellent capacity (219.9 mg/g at pH 5.0, T 298 K), and favorable selectivity coefficients (2.76–6.79). The formation of minerals was dominant for the selective sorption of Pb(II) by combining the spectral analysis and quantitative determination. The surface complexation with O-/reductive N-species, the cation exchange with inorganic Ca2+, the electrostatic attraction with deprotonated O−, and the cation-π coordination with the aromatic carbon via the π-electrons should be not ignored for the capture of Pb(II). This work demonstrated the feasibility of electrospun CL/CS/MB membranes as a promising candidate for the remediation of aquatic pollutants. [ABSTRACT FROM AUTHOR]

A reinforced composite aerogel absorbent was synthesized using a green chemistry method and an environmentally friendly freeze-drying technique. The absorbent consisted of sodium alginate, polyethyleneimine (PEI), and graphene oxide (GO). The ability of the absorbent to remove Cr (VI) ions from aqueous solutions was studied. PEI was a nitrogen source for Cr (VI) removal and a cross-linking agent for GO sheets, while SA was a reinforcing material. The aerogel was investigated using X-ray diffraction, scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, texture analysis, Raman spectroscopy, and thermogravimetric analysis (TGA). Batch studies were conducted to investigate the effect of pH and contact time on adsorption. The results indicated that the SA/PEI/GO aerogel had a maximum adsorption capacity of 174.05 mg·g−1 for Cr (VI) at pH 2. The adsorption mechanism was described using the Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamic studies revealed that the adsorption process was spontaneous and endothermic. The aerogel demonstrated good regeneration ability and satisfactory recovery for Cr (VI) even after five cycles. These findings suggest that the composite aerogel could be a promising adsorbent for efficiently removing Cr (VI) from wastewater. [ABSTRACT FROM AUTHOR]

This study reports Zn2+-mediated supramolecular composite hydrogels from the mixtures of sodium alginate and polyethyleneimine in the aqueous solutions. The composite hydrogels, consisting of both carboxylate and amino groups, show enhanced uptake capacity of 718 mg-U/g in a 20 mg/L uranium-spiked water at pH = 6. Furthermore, uranium uptake by the composite hydrogels, an endothermic and spontaneous process, follows pseudo-second-order kinetic model and Langmuir model. Importantly, the composite hydrogels can reach a high uranium uptake capacity of 692 mg-U/g in a simulated uranium wastewater with other metal ions. [ABSTRACT FROM AUTHOR]

Purpose: The modification of clay minerals by exopolysaccharides (EPS) may significantly increase their adsorption capacity for heavy metals. Therefore, this study focused on the characterization of two typical clay minerals, montmorillonite, and kaolinite modified with EPS (produced by Rhizobium tropici), their impact on the adsorption of uranium, U(VI), and the influence of pH, sulfate, and phosphate. Materials and methods: The characterization of clays, EPS, and clay-EPS composites were carried out using X-ray power diffraction (XRD), fourier transform infrared spectroscopy (FTIR), atomic force microscope (AFM), and scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) analysis. Results: Results showed that EPS partially entered and dehydrated cations in the interlayers of montmorillonite, resulting in the decrease in interlayer d-spacing, which were confirmed by XRD and FTIR. Montmorillonite had better EPS adsorption capacity than kaolinite. The EPS-clay mineral composites significantly increased U(VI) adsorption capacity by 650% and 60% for montmorillonite and kaolinite, respectively. The adsorption capacity for U(VI) was ordered as montmorillonite-EPS > EPS > montmorillonite > kaolinite-EPS > kaolinite. Montmorillonite-EPS modification for U(VI) was maximized at pH 4, while the high pH such as pH 9 inhibited the U(VI) adsorption. Sulfate or phosphate has a negligible effect on the adsorption of UO22+ on montmorillonite-EPS. Conclusion: The current study provides a new insight for the application of biopolymers in remediation of U(VI) contaminated area. [ABSTRACT FROM AUTHOR]

Natural uranium is a crucial resource for clean nuclear energy, which has brought significant economic and social benefits to humanity. However, the development and utilization of uranium resources have also resulted in the accumulation of vast amounts of uranium mill tailings (UMTs), which pose a potential threat to human health and the ecological environment. This paper reviews the research progress on UMTs treatment technologies, including cover disposal, solidification disposal, backfilling disposal, and bioremediation methods. It is found that cover disposal is a versatile method for the long-term management of UMTs, the engineering performance and durability of the cover system can be improved by choosing suitable stabilizers for the cover layer. Solidification disposal can convert UMTs into solid waste for permanent disposal, but it produces a large amount of waste and requires high operating costs; it is necessary to explore the effectiveness and efficiency of solidification disposal for UMTs, while minimizing the bad environmental impact. Backfilling disposal realizes the resource utilization of solid waste, but the high radon exhalation rate caused by the UMTs backfilling also needs to be considered. Bioremediation methods have low investment costs and are less likely to cause secondary pollution, but the remediation efficiency is low, it can be combined with other treatment technologies to remedy the defects of a single remediation method. The article concludes with key issues and corresponding suggestions for the current UMTs treatment methods, which can provide theoretical guidance and reference for further development and application of radioactive pollution treatment of UMTs. [ABSTRACT FROM AUTHOR]

Various applications in science and engineering involve porous materials where the fluid erodes the solid either chemically or mechanically and transports the finer particles through the larger pore spaces of the residual solid. In soil mechanics, the process is called suffusion. In rocks, erosion is mainly due to chemical dissolution. Irrespective of the manner in which the solid erodes, the much finer particles mix with the pure fluid to form a thick fluid whose mass density is greater than that of the pure fluid but less than that of the intact solid. As the solid loses mass, its porosity increases and its mechanical properties degrade, thus impacting the deformation and fluid flow responses of the system. This paper formulates the complex kinematics and conservation equations governing the solid–fluid interaction with internal erosion. We use the classic u / p formulation in which u is the displacement of the residual solid and p is the pressure in the thick fluid. We focus on the case of chemical erosion in rocks where the eroded particles are so small that the interface between them and the pure fluid may be neglected. We then present numerical examples demonstrating the flow and deformation processes in porous materials subjected to internal erosion. [ABSTRACT FROM AUTHOR]

The rise in environmental pollutant levels in recent years is mostly attributable to anthropogenic activities such as industrial, agricultural and other activities. Additionally, these activities may produce excessive levels of dangerous toxicants such as heavy metals, organic pollutants including pesticide and herbicide chemicals, and sewage discharges from residential and commercial sources. With a focus on environmentally friendly, sustainable technology, new technologies such as combined process of nanotechnology and bioremediation are urgently needed to accelerate the cost-effective remediation process to alleviate toxic contaminants than the conventional remediation methods. Numerous studies have shown that nanoparticles possess special qualities including improved catalysis and adsorption as well as increased reactivity. Currently, microorganisms and their extracts are being used as promising, environmentally friendly catalysts for engineered nanomaterial. In the long term, this combination of both technologies called nano-bioremediation may significantly alter the field of environmental remediation since it is more intelligent, safe, environmentally friendly, economical and green. This review provides an overview of soil and water remediation techniques as well as the use of nano-bioremediation, which is made from various living organisms. Additionally, current developments related to the mechanism, model and kinetic studies for remediation of agricultural contaminants have been discussed. [ABSTRACT FROM AUTHOR]

Here, we describe surface functionalized, superparamagnetic iron oxide nanocrystals (IONCs) for ultra-high PFAS sorption and precise, low energy (magnetic) separation, considering perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). As a function of surface coating, sorption capacities described are considerably higher than previous studies using activated carbon, polymers, and unmodified metal/metal oxides, among others. In particular, positively charged polyethyleneimine (PEI) coated IONCs demonstrate extreme sorption capacities for both PFOA and PFOS due to electrostatic and hydrophobic interactions, along with high polymer grafting densities, while remaining stable in water, thus maintaining available surface area. Further, through a newly developed method using a quart crystal microbalance with dissipation (QCM-D), we present real-time, interfacial observations (e.g., sorption kinetics). Through this method, we explore underpinning mechanism(s) for differential PFAS (PFOA vs PFOS) sorption behavior(s), demonstrating that PFAS functional head group strongly influence molecular orientation on/at the sorbent interface. The effects of water chemistry, including pH, ionic composition of water, and natural organic matter on sorption behavior are also evaluated and along with material (treatment) demonstration via bench-scale column studies. [ABSTRACT FROM AUTHOR]

Background and aims: Uranium (U), a highly deleterious radionuclide, has attracted global attention because its radiotoxicity and chemical toxicity causes severe damage to terrestrial and marine organisms. In the past few decades, numerous research has been done on immobilization, tolerance, remediation approaches and sources of U in the polluted media, and appraising the uptake and toxicity to the terrestrial plants. There are few literature reviews that elucidated the impact of soil and microbial properties on uranium immobilization and remediation methods to overcome U contamination in the natural environment. In this review, we tried to discuss biogeochemical cycling, sources, impact of soil properties on uranium immobilization and different remediation techniques involved in U treatment. Method: This review synthesized the available evidence of potential sources of Uranium, remediation techniques, and biogeochemical cycling, and further discussed the impact of soil properties on uranium immobilization based on available literature. Results: In this comprehensive review, we presented the key sources of U contamination, their occurrences, utility, and biogeochemical cycling. Moreover, the impact of U on biochemical properties and detoxification mechanisms in plants has been briefly discussed and proposed nanotechnology-based strategic engineering solutions to reduce the U in the natural environment. Conclusions: The information provided and explained in this literature review is useful for the policymakers/decision makers/environmentalists to provide serious challenges, research directions, alternative technologies and methods for recovery of U contamination in the environment. [ABSTRACT FROM AUTHOR]

Copyright of Mine Water & the Environment is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Three modified biochar (Cunninghamia lanceolata) with iron and manganese elementals (FMBCs) were successfully prepared and used to remove hexavalent chromium (Cr(VI)) from aqueous solutions. The biochar before and after decoration were characterized by advanced instruments. The adsorption capacities of modified biochar in different Cr(VI) (20 mg·L− 1, 1 mg·L− 1) solutions were 4868.28 mg·kg− 1 and 300 mg·kg− 1. The Cr(VI) removal was highest at pH 2. The possible adsorption was considered to be ion exchange adsorption, chemisorption, and electrostatic attraction. Meanwhile, interfering ions are conducive to increasing the adsorption content. FMBCs prepared at different temperatures showed different characteristics, single-use and cycle-use performance, and high and low concentration removal superiority. The result indicated that FMBCs had a promising potential as an adsorbent to remove toxic and harmful Cr(VI) from aqueous solutions. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Understanding the binding configuration of uranium on biotite is crucial for elucidating the environmental behavior of U(VI) and addressing emergency scenarios in disposal repositories. This investigation demonstrated that U(VI) adsorption on biotite was significantly affected by pH, while a lesser impact from ionic strength. Moreover, the presence of phosphate and humic acid (HA) exerted a substantial enhancing influence on U(VI) adsorption (adsorption rate increased by over 20%). X-ray photoelectron spectroscopy (XPS) analysis revealed that elevated Fe(II) contents within biotite structures facilitated the reduction of partial U(VI) to form U(V/IV)/U(IV), i.e., mineralization products, under both aerobic and anaerobic conditions. [ABSTRACT FROM AUTHOR]

In the context of rising anthropogenic activities and world conflicts, there is an urgent need for energy supply, such as nuclear power from uranium minerals. Nonetheless, uranium is one of the most radioactive and hazardous metals due to its long half-life and chemical toxicity to living organisms, thus requiring advanced methods to clean uranium-contaminated waters and ecosystems. Silicate minerals, which constitute about 90% of the Earth's crust, have been widely studied as a means of removing radionuclides and heavy metals, including uranium, due to their abundance, low cost, and high efficiency. Here, we review uranium removal by silicate minerals, focusing on the sorption and reduction of uranium (VI) by silicate minerals with well-defined pore structures, including kaolinite, montmorillonite, silica, zeolites, and other natural or modified silicate minerals. The treatment process is influenced by the pH, uranium (VI) concentration, ionic strength, temperature, and the presence of carbon dioxide and organic ligands. In particular, the pore structure and surface charge of silicate minerals play critical roles in the sorption process, whereas the modification of silicate minerals and preparation of silicate mineral composites can substantially enhance the sorption of uranium (VI). The reduction of uranium (VI) produces sparingly soluble uranium (IV), which prevents the migration of uranium and facilitates the sorption process. Molecular dynamic simulations and density functional theory calculations can provide valuable insights into the mechanism of uranium (VI) sorption and reduction, especially when used in correlation with experimental studies. Future studies could focus on improving the alkali resistance and sorption selectivity of silica minerals for extracting uranium from seawater. [ABSTRACT FROM AUTHOR]

The predominant mineral, montmorillonite, in smectite-rich clays, the most promising buffer & backfill, controls their sorption characteristics towards radionuclides. The role of sulphate on Am(III) sorption by Na-montmorillonite has been investigated. The influence of pH, ionic strength & [SO 4 2 - ] on Am(III) sorption by Na-montmorillonite has been studied. The contribution of Am(III) hydroxo complexes in aqueous speciation is ~ 50% at pH 7.5 while that of Eu(III) hydroxo complexes is ~ 10%. In contrast to Eu(III), Am(III) sorption could be modeled by either ≡SOAmOH+ or ≡SOAmCO3. Log K for Am(III) ion exchange & ≡SOAmCO3 is less than that for similar Eu(III) species. [ABSTRACT FROM AUTHOR]

In this work, we synthesized activated alumina biochar composites (γ-Al2O3/BC) by sol–gel method, which improved the problem that the surface charge of γ-Al2O3 was not conducive to the removal of heavy metal cation in a neutral solution, and then explored the feasibility of removing Pb(II) by γ-Al2O3/BC as well as reusing Pb-laden waste sludge to remove phosphorus (P) and its micro-adsorption mechanisms. The results show that the maximum adsorption capacity of γ-Al2O3/BC for Pb(II) is 182.48 mg/g, and the removing capacity of recycled Pb-laden slag for P also reaches 87.13 mg/g. It was found that the presence of Pb in the slag makes P removal more effective. In addition, in the process of P removal, the Pb in the slag will not be released, which will not cause secondary pollution to the water. The micro-adsorption mechanism of Pb(II) and P on the composites was investigated by XPS, XRD, and FTIR. It demonstrates that special functional groups such as hydroxy-aluminum, hydroxyl, and carboxyl groups can remove Pb(II) through strong surface complexation and electrostatic attraction. Furthermore, the removal mechanism of P from Pb-laden sludge includes chemisorption and complexation, and the precipitation of P and Pb on the adsorbent surface is the main reason for the removal of P. Therefore, it is feasible to further effectively remove P by using the waste biochar containing Pb. The idea of this paper provides a potential method for the reuse of waste adsorbent. [ABSTRACT FROM AUTHOR]

Americium is a highly radioactive actinide element found in used nuclear fuel. Its adsorption on aluminum (hydr)oxide minerals is important to study for at least two reasons: (i) aluminum (hydr)oxide minerals are ubiquitous in the subsurface environment and (ii) bentonite clays, which are proposed engineered barriers for the geologic disposal of used nuclear fuel, have the same ≡AlOH sites as aluminum (hydr)oxide minerals. Surface complexation modeling is widely used to interpret the adsorption behavior of heavy metals on mineral surfaces. While americium sorption is understudied, multiple adsorption studies for europium, a chemical analog, are available. In this study we compiled data describing Eu(III) adsorption on three aluminum (hydr)oxide minerals—corundum (α-Al2O3), γ-alumina (γ-Al2O3) and gibbsite (γ-Al(OH)3)—and developed surface complexation models for Eu(III) adsorption on these minerals by employing diffuse double layer (DDL) and charge distribution multisite complexation (CD-MUSIC) electrostatic frameworks. We also developed surface complexation models for Am(III) adsorption on corundum (α-Al2O3) and γ-alumina (γ-Al2O3) by employing a limited number of Am(III) adsorption data sourced from literature. For corundum and γ-alumina, two different adsorbed Eu(III) species, one each for strong and weak sites, were found to be important regardless of which electrostatic framework was used. The formation constant of the weak site species was almost 10,000 times weaker than the formation constant for the corresponding strong site species. For gibbsite, two different adsorbed Eu(III) species formed on the single available site type and were important for the DDL model, whereas the best-fit CD-MUSIC model for Eu(III)-gibbsite system required only one Eu(III) surface species. The Am(III)-corundum model based on the CD-MUSIC framework had the same set of surface species as the Eu(III)-corundum model. However, the log K values of the surface reactions were different. The best-fit Am(III)-corundum model based on the DDL framework had only one site type. Both the CD-MUSIC and the DDL model developed for Am(III)-γ-alumina system only comprised of one site type and the formation constant of the corresponding surface species was ~ 500 times stronger and ~ 700 times weaker than the corresponding Eu(III) species on the weak and the strong sites, respectively. The CD-MUSIC model for corundum and both the DDL and the CD-MUSIC models for γ-alumina predicted the Am(III) adsorption data very well, whereas the DDL model for corundum overpredicted the Am(III) adsorption data. The root mean square of errors of the DDL and CD-MUSIC models developed in this study were smaller than those of two previously-published models describing Am(III)-γ-alumina system, indicating the better predictive capacity of our models. Overall, our results suggest that using Eu(III) as an analog for Am(III) is practical approach for predicting Am(III) adsorption onto well-characterized minerals. [ABSTRACT FROM AUTHOR]

Enhanced rock weathering (ERW) in soils is a promising carbon removal technology, but the realistically achievable efficiency, controlled primarily by in situ weathering rates of the applied rocks, is highly uncertain. Here we explored the impacts of coupled biogeochemical and transport processes and a set of primary environmental and operational controls, using forsterite as a proxy mineral in soils and a multiphase multi-component reactive transport model considering microbe-mediated reactions. For a onetime forsterite application of ~ 16 kg/m2, complete weathering within five years can be achieved, giving an equivalent carbon removal rate of ~ 2.3 kgCO2/m2/yr. However, the rate is highly variable based on site-specific conditions. We showed that the in situ weathering rate can be enhanced by conditions and operations that maintain high CO2 availability via effective transport of atmospheric CO2 (e.g. in well-drained soils) and/or sufficient biogenic CO2 supply (e.g. stimulated plant–microbe processes). Our results further highlight that the effect of increasing surface area on weathering rate can be significant—so that the energy penalty of reducing the grain size may be justified—only when CO2 supply is nonlimiting. Therefore, for ERW practices to be effective, siting and engineering design (e.g. optimal grain size) need to be co-optimized. [ABSTRACT FROM AUTHOR]

Coal thermal power plants are critical sources of heavy metal pollution in groundwater with a significant health hazard. The current study assessed the seasonal (pre and post-monsoon) concentration of aluminum, arsenic, iron, cobalt, manganese, nickel, copper, chromium, cadmium, lead and zinc concentrations in groundwater along with heavy metal pollution index and human health risks. Further, multivariate statistical approaches i.e. correlation, principal component analysis and hierarchical cluster analysis were used to estimate the groundwater's interactions with heavy metals to know their possible sources of contamination. The results showed the mean higher concentration (µg/L) for aluminum (387.65, 399.184), arsenic (11.368, 17.288), lead (7.92, 9.59), iron (126.22, 272.24) and manganese (248.69, 825.82) throughout both seasons than the standard acceptable limits of national and international agencies. Considering the heavy metal pollution index, the mean value was noticed less than the critical value (> 100) for pre-monsoon (19.92) and post-monsoon season (44.42), denoting low-level pollution. Concerning health risks, arsenic, lead, manganese and zinc were the most significant metals causing health hazards with hazard index (105) exceeding the United States Environmental Protection Agency's standard limit and affecting children's population more than adults. Further, high values of toxic metals were noticed during the post-monsoon season. Besides, multivariate analysis showed that anthropogenic and natural activities are attributed to metal pollution. The present study suggests unsuitability of groundwater for drinking purposes as this can cause a potential health risk. Hence, the study area needs routine groundwater quality monitoring as it is susceptible to heavy metal contamination. [ABSTRACT FROM AUTHOR]

Celestine and barite mineralizations occur in the Upper-Paleocene unit of marly-clay within curdled limestone of the Siouf-Cherahil area, North–South axis, Central Tunisia. The particularity of celestine is the high contents of U and it has never been studied as same as the Ba-rich deposit of Cherahil zone. This work was undertaken to narrow this gap. For this, mineralogical and geochemical characteristics of celestine and barite nodules were investigated using X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. At the Siouf zone, the mineralogical and geochemical data indicate that celestine contains more than 45% of Sr and U rate has a wide distribution and can reach 0.64%. Similarly, the values of P2O5 are around 3.50%. Statistical analysis showed a high positive correlation between U and P, indicating that U had a strong affinity with P. In Cherahil zone, barite record considerably high barium values. The Siouf-Cherahil deposit reports huge proportions of sulfate minerals along the solid solution (Ba, SrSO4). These deposits display high contents of BaO, SrO, and SO4 and significant amounts of U and P with trace amounts of Y, Ni, Zn, Zr, Cr. The main process responsible for celestine and barite crystallization is the early diagenesis from interstitial fluids. The mineralization is located in trap structures and privileged zones created by synsedimentary tectonic events. In such available spaces, celestine concretions could be developed under several textural types: fibrous, granular, saccharoid, and hyaline automorph. [ABSTRACT FROM AUTHOR]

Copyright of Mine Water & the Environment is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Purpose: Aluminum- and iron-impregnated food waste biochar (Al-FWBC and Fe-FWBC) have been suggested for the remediation of dredged sediments contaminated with arsenic (As). Materials and methods: Sediment was obtained from a reservoir surrounded by several abandoned gold mines. High As concentration (102.7 mg kg−1) of the sediment corresponded to a severely contaminated level, but other heavy metals were in acceptable ranges without toxic concerns. Al-FWBC and Fe-FWBC, successfully synthesized in a previous study to remove As from aqueous solutions, were used as stabilization/solidification (S/S) agents in the current study. A sequential extraction procedure was applied to investigate the fractionation and stability of As in sediments. Results and discussion: Amendment of Al-FWBC and Fe-FWBC for 6 months reduced the non-specifically and specifically sorbed fractions but increased the residual fraction. Fe-FWBC 1% was most efficient in stabilizing As in the sediment and it decreased 45.4% of non-specifically and specifically sorbed fractions. The effect of Al-FWBC and Fe-FWBC amendments was further confirmed by measuring potential ecological risk, and the contamination factor decreased from a considerably polluted to moderately polluted level. Arsenic and other heavy metals that leached from the S/S-treated sediments via toxicity characteristic leaching procedure did not exceed the values prescribed by the US Environmental Protection Agency. Conclusions: Stabilization/solidification treatment using Al-FWBC and Fe-FWBC, converted from waste to value-added substances for environmental pollution control, can be applied to remediate sediments contaminated with As. [ABSTRACT FROM AUTHOR]

Aluminium (Al)-rich palaeosols—i.e., palaeobauxite deposits—should have formed in karst depressions in carbonate sequences as a result of acidic solutions from oxidative weathering of sulfide minerals during the Great Oxidation Event (GOE), but no GOE-related karst-palaeobauxite deposits have so far been recorded. Here, we report results of in situ uranium–lead (U–Pb) dating of detrital zircon and spatially associated rutile from a metamorphosed Al-rich rock within a dolomite sequence in the Quadrilátero Ferrífero (QF) of Minas Gerais, Brazil, known as the Gandarela Formation. Rutile grains are highly enriched in thorium (Th = 3–46 ppm; Th/U ratio = 0.3–3.7) and yielded an isochron, lower-intercept age of ca. 2.12 Ga, which coincides with the final phase of the GOE—i.e., the Lomagundi event. The rutile age represents either authigenic growth of TiO2 enriched in Th, U and Pb during bauxite formation, or subsequent rutile crystallisation during metamorphic overprint. Both cases require an authigenic origin for the rutile. Its high Th contents can be used as a palaeoenvironmental indicator for decreased soil pH during the GOE. Our results also have implications for iron (Fe)-ore genesis in the QF. This study demonstrates that in situ U–Th–Pb-isotope analyses of rutile can place tight constraints on the age and nature of palaeosols. [ABSTRACT FROM AUTHOR]

Cr(III)-organic complexes are stably presented in tanning, electroplating, and other industrial wastewaters, and their safe and efficient removal remains a current challenge. Available oxidation processes can remove Cr(III) complexes but readily result in highly toxic Cr(VI) accumulation. Herein, negligible Cr(VI) accumulation was achieved during photo-oxidation of Cr(III) complexes using a simple strategy of decreasing dissolved oxygen (DO). At the DO concentration of 5.0 mg·L−1 or less, the in-process formation of intermediate Cr(VI) was totally abated by in situ formed reductive species, and total Cr was reduced from 9.0–11.0 mg·L−1 to below 1.0 mg·L−1. A complete curtailment of Cr(VI) was observed after 30–60 min at pH 6.0–9.0. Increasing Cr(III)-EDTA concentration and decreasing pH value facilitated the in situ reduction of intermediate Cr(VI). Based on the identification of intermediates and additional Cr(II) and quenching experiments, the possible key species involved in intermediate Cr(VI) reduction were the photogenerated Cr(II) and some C-centered radicals from Cr(III)-EDTA decomplexation, and the possible mechanisms of Cr(III)-EDTA decomplexation and intermediate Cr(VI) reduction were thus proposed. The process also showed efficient treatment on other Cr(III) complexes (citrate, oxalate, and tartrate) and realistic Cr(III) complexed wastewater. This study would provide an insignificant Cr(VI)-accumulated alternative for efficient and safe removal of Cr(III) complexes from contaminated water. [ABSTRACT FROM AUTHOR]

The diversity of flora in Kalimantan influences the presence of microbe-associated with rhizosphere on their activities and functions in ecosystems. However, abiotic stress such as acidification, drought, and toxic soil residues negatively impacted soil health and plant growth in some regions of Kalimantan's soil. The Plant-growth promoting rhizobacteria (PGPR) can alternate by producing phytohormone, solubilizing phosphate, nitrogen fixation, and biofilm production. Rhizobacteria will be beneficial for plant growth, soil aggregation, and bioremediation. Those benefit of rhizobacteria is essential to investigate. However, the study of the role of plant-rhizobacteria interaction in soil Kalimantan was limited. Therefore, this review focused on the presence of indigenous rhizobacteria and their mechanism to adapt and be tolerant in harsh environments. [ABSTRACT FROM AUTHOR]

Developing novel adsorbents for efficient U(VI) adsorption from wastewater is of great significance in both nuclear energy development and environmental protection. Herein, a novel functional resin (AO67/MA33-resin) with large particle size (100–200 μm) was controllably synthesized and employed for U(VI) elimination. The AO67/MA33-resin overcomes the shortcoming of small particle size of traditional adsorbents and shows strong antacid and high-temperature resistance stability and reusability. Meanwhile, the AO67/MA33-resin also exhibits excellent U(VI) removal ability including wide pH adaptability, fast adsorption kinetic, and high adsorption capacity. The adsorption mechanism was determined to involve chelation between amidoxime carboxyl functional groups and uranyl ions. A further application for U(VI) removal from real uranium mine wastewater was evaluated by dynamic column experiments. The present work indicated that the AO67/MA33-resin would be a promising adsorbent material for uranium removal from wastewater. [ABSTRACT FROM AUTHOR]

Ex situ mineralization of CO2 is a promising technology that employs Ca- and Mg-rich industrial wastes but it simultaneously produces end products. Although Mg is a major mineralization source, it can adversely impact carbonate precipitation and crystal stability during co-precipitation in combination with Ca2+. In this study, the effects of Mg2+ ions on the mineralization process and its products were investigated using precipitates formed at different aqueous concentrations of Mg2+. The final phases of the precipitates were quantitatively evaluated at the end of each process. The alterations undergone by the calcite crystals, which constituted the dominant carbonate phase in each experiment, were analyzed using a sophisticated crystallographic approach. Aragonite was detected at high Mg2+ concentrations (Mg2+/Ca2+ ratio of 2.00), although brucite was the sole phase of the Mg crystal. The increase in Mg2+ ion concentration induced the formation of an amorphous solid. The results revealed that a drastic transformation of the calcite lattice occurred when the ratio of Mg2+/Ca2+ exceeded 1.00, agreeing with the shifts observed in the calcite structure upon comparing the precipitates formed at the Mg2+/Ca2+ ratios of 1.00 and 2.00, wherein microstrain and crystallite sizes changed from 0.040 and 55.33 nm to 0.1533 and 12.35 nm, respectively. At a Mg2+/Ca2+ ratio of 2.00, 6.51% of the Ca2+ ions in the calcite structure were substituted by Mg2+, increasing the surface energy of the crystal and the solubility of the carbonate. Therefore, Mg2+ is a potential hindrance that can impede the precipitation of carbonates and increase instability at certain concentrations. [ABSTRACT FROM AUTHOR]

Metastable ferrihydrite is omnipresent in environments and can influence the fate of Pb(II) during ferrihydrite transformation. Ferrihydrite is rarely pure and often coexists with impurities, which may influence the mineralogical changes of ferrihydrite and Pb(II) behavior. In this work, we investigated the effect of malic acid or phosphate on Pb(II)-ferrihydrite coprecipitates (Fh-Pb) transformation and the subsequent fate of Pb(II) during the 10-day aging of Fh-Pb. Results showed that both malic acid and phosphate retarded Fh-Pb transformation and prevented the release of Pb(II) from Fh-Pb back into solutions. Pb(II) was beneficial to goethite formation by inhibiting hematite formation while both malic acid and phosphate inhibited goethite formation since they could act as templates of nucleation. Besides, malic acid and phosphate improved the proportion of non-extracted Pb(II) during Fh-Pb transformation, indicating that Pb(II) was incorporated into secondary minerals. Pb(II) could not replace Fe(III) within the crystal lattice due to its large radius but was occluded into pores and defect structures within the secondary mineral lattices. This work can advance our understanding of the influences of malic acid and phosphate on Pb(II) immobility during Fh-Pb aging. [ABSTRACT FROM AUTHOR]

Iron (Fe) oxides can rapidly recrystallize in the presence of aqueous Fe(II) (Fe(II)aq) under anoxic conditions. Since different Fe oxides have diverse affinities and redox reactivities for metal(loid)s, nutrients, and organic matters, recrystallization of Fe oxides significantly alters their speciation and environmental behavior. Therefore, the major reaction steps, rates, and influencing factors of Fe(II)aq-catalyzed recrystallization have gained increasing attention. This paper aims to review the latest advances, especially in redox cycling between Fe(II)aq and Fe oxide and in the kinetics of Fe atom exchange. The mineralogical recrystallization pathways and intermediate processes of different Fe oxides when exposed to Fe(II)aq are discussed. The influencing factors such as morphological natures of Fe oxides and typical environmental substances governing the kinetics of isotopic exchange between Fe(II)aq and Fe oxides are summarized. Several major analytical methodologies in this realm are also illustrated. Finally, some unsolved issues and future research directions in the field of Fe(II)aq-catalyzed Fe oxide recrystallization are outlined. [ABSTRACT FROM AUTHOR]