Removal of uranium contaminant from aqueous solution by chitosan@attapulgite composite

Microbial production of methyl-uranium via the Wood-Ljungdahl pathway

The misuse of uranium is a major threat to human health and the environment. In microbial ecosystems, microbes deploy various strategies to cope with uranium-induced stress. However, the exact ecological strategies and mechanisms underlying uranium tolerance in microbes remain unclear. Therefore, this study aimed to investigate the survival strategies and tolerance mechanisms of microbial communities in uranium-contaminated soil and groundwater. Microbial co-occurrence networks and molecular biology techniques were used to analyze the properties of microbes in groundwater and soil samples from various depths of uranium-contaminated areas in Northwest China. Uranium pollution altered microbial ecological strategies. Uranium stress facilitated the formation of microbial community structures, leading to symbiosis. Furthermore, microbes primarily resisted uranium hazards by producing polysaccharides and phosphate groups that chelate uranium, releasing phosphate substances that precipitate uranium, and reducing U(VI) through sulfate- and iron-reducing processes. The relative abundance of metal-methylation genes in soil microorganisms positively correlated with uranium concentration, indicating that soil microorganisms can produce methyl uranium via the Wood-Ljungdahl pathway. Furthermore, soil and groundwater microorganisms demonstrated different responses to uranium stress. This study provides new insights into microbial responses to uranium stress and novel approaches for the bioremediation of uranium-contaminated sites.

Simple and scalable preparation of lignin based porous carbon coated nano-clay composites and their efficient removal for the diversified iodine

Here, lignin and nano-clay were used to prepare novel composite adsorbents by one-step carbonization without adding activators for radioactive iodine capture. Specially, 1D nano-clay such as halloysite (Hal), palygorskite (Pal) and sepiolite (Sep) were selected as skeleton components, respectively, enzymatic hydrolysis lignin (EHL) as carbon source, lignin based porous carbon/nano-clay composites (ELC-X) were prepared through ultrasonic impregnation, freeze drying, and carbonization. Characterization results indicated lignin based porous carbon (ELC) well coated on the surface of nano-clay, and made its surface areas increase to 252 m2/g. These composites appeared the micro-mesoporous hierarchical structure, considerable N doping and good chemical stability. Results of adsorption experiments showed that the introduction of ELC could well promote iodine vapor uptake of nano-clay, and up to 435.0 mg/g. Meanwhile, the synergistic effect between lignin based carbon and nano-clay was very significant for the adsorption of iodine/n-hexane and iodine ions, their capacity were far exceed those of a single material, respectively. The relevant adsorption kinetic and thermodynamics, and mechanism of ELC-X composites were clarified. This work provided a class of low-cost and environmentally friendly adsorbents for radioactive iodine capture, and opened up ideas for the comprehensive utilization of waste lignin and natural clay minerals.

Recent advances in clay minerals for groundwater pollution control and remediation

Clay minerals are abundant on Earth and have been crucial to the advancement of human civilization. The ability of clay minerals to absorb chemicals is frequently utilized to remove hazardous compounds from aquatic environments. Moreover, clay-based adsorbent products are both environmentally acceptable and affordable. This study provides an overview of advances in clay minerals in the field of groundwater remediation and related predictions. The existing literature was examined using data and information aggregation approaches. Keyword clustering analysis of the relevant literature revealed that clay minerals are associated with groundwater utilization and soil pollution remediation. Principal component analysis was used to assess the relationships among clay mineral modification methods, pollutant properties, and the Langmuir adsorption capacity (Qmax). The results demonstrated that pollutant properties affect the Qmax of pollutants adsorbed by clay minerals. Systematic cluster analysis was utilized to classify the collected data and investigate the relationships. The pollution adsorption mechanism of the unique structure of clay minerals was investigated based on the characterization results. Modified clay minerals exhibited changes in surface functional groups, internal structure, and pHpzc. This review provides a summary of recent clay-based materials and their applications in groundwater remediation, as well as discussions of their challenges and future prospects.

Synthesis and characterization of chitosan-vermiculite-lignin ternary composite as an adsorbent for effective removal of uranyl ions from aqueous solution: Experimental and theoretical analyses

Chitosan (Ch), vermiculite (V) and lignin (L) were used as the components of a natural composite adsorbent (Ch-VL) for the removal of the UO₂²⁺ ions in aqueous solutions. During the study, we recorded and analyzed the initial UO₂²⁺ ion concentration, initial pH, contact time, temperature, and recovery. The recycling performance of the Ch-VL composite was assessed by three sequential adsorption/desorption experiments. Adsorption performance of the Ch-VL composite for UO₂²⁺ ions was 600 mg L^-1 at pH 4.5 and temperature of 25 °C. Thermodynamic findings, ΔH⁰:28.1 kJ mol^-1, and ΔG⁰:-14.1 kJ mol^-1 showed that adsorption behavior was endothermic and spontaneous. Its maximum adsorption capacity was 0.322 mol kg^-1, obtained from the Langmuir isotherm model. The adsorption kinetics indicated that it followed the pseudo-second-order and intraparticle diffusion rate kinetics. The adsorption thermodynamic shown indicated that the UO₂²⁺ ion adsorption was both spontaneous and endothermic. The adsorption process was enlightened by FT-IR and SEM-EDX analyses. The study suggested a simple and cost-effective approach for the removal of toxic UO₂²⁺ ions from wastewater. To highlight the adsorption mechanism, DFT calculations were performed. Theoretical results are in good agreement with experimental observations.

Preparation of a Heterogeneous Catalyst CuO-Fe2O3/CTS-ATP and Degradation of Methylene Blue and Ciprofloxacin

A heterogeneous particle catalyst (CuO-Fe2O3/CTS-ATP) was synthesized via injection molding and ultrasonic immersion method, which is fast and effective. The particle catalyst applied attapulgite (ATP) wrapped by chitosan (CTS) as support, which was loaded dual metal oxides CuO and Fe2O3 as active components. After a series of characterizations of catalysts, it was found that CuO and Fe2O3 were successfully and evenly loaded on the surface of the CTS-ATP support. The catalyst was used to degrade methylene blue (MB) and ciprofloxacin (CIP), and the experimental results showed that the degradation ratios of MB and CIP can reach 99.29% and 86.2%, respectively, in the optimal conditions. The degradation mechanism of as-prepared catalyst was analyzed according to its synthesis process and ∙OH production, and the double-cycle catalytic mechanism was proposed. The intermediate products of MB and CIP degradation were also identified by HPLC-MS, and the possible degradation pathways were put forward.

3D printed biocompatible graphene oxide, attapulgite, and collagen composite scaffolds for bone regeneration

Tissue-engineered bone material is one of the effective methods to repair bone defects, but the application is restricted in clinical because of the lack of excellent scaffolds that can induce bone regeneration as well as the difficulty in making scaffolds with personalized structures. 3D printing is an emerging technology that can fabricate bespoke 3D scaffolds with precise structure. However, it is challenging to develop the scaffold materials with excellent printability, osteogenesis ability, and mechanical strength. In this study, graphene oxide (GO), attapulgite (ATP), type I collagen (Col I) and polyvinyl alcohol were used as raw materials to prepare composite scaffolds via 3D bioprinting. The composite materials showed excellent printability. The microcosmic architecture and properties was characterized by scanning electron microscopy, Fourier transform infrared and thermal gravimetric analyzer, respectively. To verify the biocompatibility of the scaffolds, the viability, proliferation and osteogenic differentiation of Bone Marrow Stromal Cells (BMSCs) on the scaffolds were assessed by CCK-8, Live/Dead staining and Real-time PCR in vitro. The composited scaffolds were then implanted into the skull defects on rat for bone regeneration. Hematoxylin-eosin staining, Masson staining and immunohistochemistry staining were carried out in vivo to evaluate the regeneration of bone tissue.The results showed that GO/ATP/COL scaffolds have been demonstrated to possess controlled porosity, water absorption, biodegradability and good apatite-mineralization ability. The scaffold consisting of 0.5% GO/ATP/COL have excellent biocompatibility and was able to promote the growth, proliferation and osteogenic differentiation of mouse BMSCs in vitro. Furthermore, the 0.5% GO/ATP/COL scaffolds were also able to promote bone regeneration of in rat skull defects. Our results illustrated that the 3D printed GO/ATP/COL composite scaffolds have good mechanical properties, excellent cytocompatibility for enhanced mouse BMSCs adhesion, proliferation, and osteogenic differentiation. All these advantages made it potential as a promising biomaterial for osteogenic reconstruction.

Indole-functionalized cross-linked chitosan for effective uptake of uranium(VI) from aqueous solution

Herein, a novel indole-modified cross-linked chitosan aerogel (IAA-CTSA) was fabricated by grafting 3-indoleacetic acid onto chitosan and adding glutaraldehyde as crosslinking agent through a facile two-step one pot method. The...

The Adsorption Characteristics of Uranium(VI) from Aqueous Solution on Leonardite and Leonardite-Derived Humic Acid: A Comparative Study

The humic substance is a low-cost and effective adsorbent with abundant functional groups in remediating uranium (U) (VI)-contaminated water. In this research study, leonardite together with leonardite-derived humic acid (L-HA) was used to eliminate U(VI) from water under diverse temperatures (298, 308, and 318 K). L-HA showed a higher adsorption volume for U(VI) than leonardite. U adsorption was varied with pH and increased with temperature. The adsorption kinetics of L-HA had a higher determination coefficient (R²) for pseudo-second-order (R² > 0.993) and Elovich (R² > 0.987) models, indicating possible chemisorption-assisted adsorption. This was further supported with the activation energies (15.9 and 13.2 kJ/mol for leonardite and L-HA, respectively). Moreover, U(VI) equilibrium adsorption on leonardite was better depicted with the Freundlich model (R² > 0.970), suggesting heterogeneous U(VI) adsorption onto the leonardite surface. However, U(VI) adsorption onto L-HA followed the Langmuir equation (R² > 0.971), which implied the dominant role of monolayer adsorption in controlling the adsorption process. Thermodynamic parameters, including standard entropy change (ΔS⁰ > 0), Gibbs free energy (ΔG⁰ < 0), and standard enthalpy change (ΔH⁰ > 0), suggested a spontaneous and endothermal adsorption process. In addition, ionic species negatively affected U(VI) adsorption by leonardite and L-HA.

TiO2/CTS/ATP adsorbent modification and its application in adsorption-ultrafiltration process for dye wastewater purification

Industrial dyeing produces highly polluting wastewater and threatens the environment. Effective treatment of dyeing wastewater is a crucial step to prevent toxic chemicals from entering receiving waters. This study aimed to assess a modified attapulgite (ATP)-based adsorbent for dyeing wastewater purification by introducing chitosan (CTS) and titanium dioxide (TiO₂) into the adsorbent material named TiO₂/CTS/ATP. It was found that after modification, the adsorbent showed a lower hydrophilicity, as demonstrated by an increase in the water contact angle from 9.1° to 42°, which could reduce the water adsorption tendency and potentially facilitate contaminants adherence. The modification also led to a significantly increased specific surface area of 79.111 m²/g from 3.791 m²/g and exhibited more uniform and smaller particle size (reduced from 3.99 to 2.52 μm). When the TiO₂/CTS/ATP adsorbent was applied to the adsorption of Congo red solution, the adsorption efficiency was observed to reach to 97.6% at the dosage of 0.5 g/L. Furthermore, the combination of adsorption and ultrafiltration was able to achieve 99% Congo red removal. Adsorption pretreatment prior to the ultrafiltration also enabled to reduce membrane fouling, increased the reversible membrane fouling, and resulted in a considerably lower transmembrane pressure as compared with the direct ultrafiltration filtration system.

The synergistic effect of attapulgite in the highly enhanced photoreduction of Cr(VI) by oxalic acid in aqueous solution

Attapulgite (ATP), a widely existed clay in nature, was firstly and successfully applied to enhance the photoreduction of highly toxic Cr(VI) by oxalic acid (Ox). In ATP + Ox + UV system, batch effects (Ox concentration, initial Cr(VI) concentration, ATP dosage, and reusability of ATP) were investigated. By studying the impact of the initial pH in the solution, the change of pH and Fe species concentration as well as Ox concentration during the reaction, the free radical scavenging test, and the role of ATP, the mechanism of Cr(VI) removal by ATP + Ox + UV system was revealed. The methyl orange (MO) removal of ATP + Ox + UV system was also inspected. The results indicated that ATP showed the obvious enhancement in efficient photoreduction of Cr(VI) by Ox in water. The Fe and Si components in ATP played an important role in Cr(VI) removal by ATP + Ox + UV system: most of Cr(VI) was reduced by Fe(II) and CO₂^•‒ produced by the Fe(III)-Ox complex from the dissolved Fe component in ATP under UV irradiation. Some of Cr(VI) was reduced by e^- and CO₂^•‒ from the oxidation of Ox by h⁺ generated by the photocatalyzed SiO₂ in ATP. Furthermore, ATP + Ox + UV system also showed excellent MO removal performance, indicating the great potential in practical applications.

An Efficient Uranium Adsorption Magnetic Platform Based on Amidoxime-Functionalized Flower-like Fe3O4@TiO2 Core-Shell Microspheres

Efficient removal of uranium (U) from aqueous solutions is crucial for ecological safety. Functionalized magnetic nanoparticles provide a promising strategy for radionuclide recovery and separation. However, designing and synthesizing magnetic adsorbents with high sorption capacity and selectivity, accompanied by excellent stability and reusability, remain a challenge. In this work, novel amidoxime-functionalized flower-like magnetic Fe₃O₄@TiO₂ core-shell microspheres are designed and synthesized to efficiently remove U(VI) from aqueous solutions and actual seawater. The magnetic Fe₃O₄ core facilitates easy separation by an external magnetic field, and flower-like TiO₂ nanosheets provide abundant specific surface areas and functionalization sites. The grafted amidoxime (AO) groups could function as a claw for catching uranium. The maximum adsorption capacity on U(VI) of the designed nanospheres reaches 313.6 mg·g^-1 at pH 6.0, and the adsorption efficiency is maintained at 97% after 10 cycles. In addition, the excellent selectivity of the magnetic recyclable AO-functioning Fe₃O₄@TiO₂ microspheres endows the potential of uranium extraction from seawater. The designed material provides an effective and applicable diagram for radioactive element elimination and enrichment.

Assembly of three-dimensional ultralight poly(amidoxime)/graphene oxide nanoribbons aerogel for efficient removal of uranium(VI) from water samples

Assembling graphene oxide nanoribbons (GONRs) into three-dimensional (3D) materials with controllable and desired structure is an effective way to expand their structural features and enable their practical applications. In this work, an ultralight 3D porous amidoxime functionalized graphene oxide nanoribbons aerogel (PAO/GONRs-A) was prepared via solvothermal polymerization method using acrylonitrile as monomer and GONRs as solid matrices for selective separation of uranium(VI) from water samples. The PAO/GONRs-A possessed a high nitrogen content (13.5%), low density (8.5 mg cm^-3), and large specific surface area (494.9 m² g^-1), and presented an excellent high adsorption capacity of uranium, with a maximum capacity of 2.475 mmol g^-1 at a pH of 4.5, and maximum uranium-selectivity of 65.23% at a pH of 3.0. The results of adsorption experiments showed that U(VI) adsorption on PAO/GONRs-A was a pH-dependent, spontaneous and endothermic process, which was better fitted to the pseudo-second-order kinetic model and Langmuir isotherm model. Both X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations revealed that U(VI) adsorption on PAO/GONRs-A mainly did rely on the amidoxime groups anchored on the aerogel while UO₂(PAO)₂(H₂O)₃ was dominant after interaction of uranyl with PAO/GONRs-A. Therefore, as a candidate adsorbent, PAO/GONRs-A has a high potential for the removal of uranium from aqueous solutions.

Preparation of graphene oxide-modified palygorskite nanocomposites for high-efficient removal of Co(II) from wastewater

Removing Co(II) from wastewater is urgent due to the threat to the environment and human health. In the work, the nanocomposite of graphene oxide-modified palygorskite (mPal-GO) is synthesized by cross-linking one-dimensional palygorskite (Pal) with two-dimensional material graphene oxide (GO), and used to remove Co(II) from wastewater. Its structure is characterized by Fourier transformed infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area measurement. The parameters, such as mass ratio (GO:mPal), temperature, pH, and contact time, are carefully investigated. The results indicate that pseudo-second-order equation and Langmuir isotherm model are the best fitting one in the adsorption process of Co(II) onto mPal-GO. The maximum adsorption capacity achieves 16.9 mg/g at pH = 6.0 and T = 298 K according to the Langmuir model analysis. Furthermore, mPal-GO can be reused more than 5 times with a slight decrease according to the adsorption-desorption cycle experiments. Finally, mPal-GO with the low-cost and easy separation is a promising candidate for removing of Co(II) from wastewater.

Macroscopic and spectroscopic characterization of U(VI) sorption on biotite

Knowledge of the geochemical behavior of uranium is critical for the safe disposal of radioactive wastes. Biotite, a Fe(II)-rich phyllosilicate, is a common rock-forming mineral and a major component of granite or granodiorite. This work comprehensively studied the sorption of U(VI) on biotite surface with batch experiments and analyzed the uranium speciation with various spectroscopic techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and time-resolved fluorescence spectra (TRFS). Our results indicated that uranyl ions could penetrate into the interlayer of biotite, this ion-exchange process was pH-dependent and only favorable under acidic condition. Instead of precipitation or reduction to uraninite, the TRFS results strongly suggests U(VI) forms surface complexes under the neutral and alkaline condition, though the number and structure of surface species could not be identified accurately. Besides, the oxidation of biotite with peroxide hydrogen showed that structural Fe(II) would have a very low redox reactivity. With leaching experiments, zeta potential analysis and thermodynamics calculation, we discussed the possible reasons for inhibition of U(VI) reduction at the biotite-water interface. Our results may provide insight on interaction mechanism of uranium at mineral-water interface and help us understand the migration behavior of uranium in natural environments.

Clever use of natural clay materials in the synthesis of non-symmetric carbonates by utilizing CO2 as a feedstock: Ag/attapulgite nano-catalyst

Using natural minerals seems to be one of the most novel and environmentally friendly strategies to design catalysts for CO₂ conversion. Herein, we report a facile and efficient nano-catalyst for the synthesis of non-symmetric carbonate by utilizing a magnesium-aluminium silicate nano-mineral-attapulgite (ATP). Thanks to the unique structure of ATP and its ability to absorb carbon dioxide, the Ag/attapulgite nano-catalyst has excellent catalytic activity and stability in the carbon dioxide fixation reaction. The design of this Ag/attapulgite nano-catalyst provides a novel idea for realizing CO₂ conversion and clay resource utilization.

Development of highly efficient bundle-like hydroxyapatite towards abatement of aqueous U(VI) ions: Mechanism and economic assessment

The exploration of emergency materials with ultra-fast adsorption rate and great adsorption capability of released U(VI) ions is essentially urgent. The present work successfully fabricated bundle-like hydroxyapatite (B-HAP) microstructures which composed of numerous nanorods by employing a facile and green method. The B-HAP was applied to treat the U(VI) containing wastewater. The abatement of U(VI) by B-HAP was very rapid and the saturated adsorption capacity was superior; over 96.7 % of U(VI) was abated within 5 min, and the maximum adsorption capacity was as high as to 1305 mg/g, signifying the feasibility and effectiveness of this B-HAP in the treatment of uranium-contaminated wastewater due to nuclear accidents. It is worthy to note that other ions in solution exhibited relatively low interference on its performance, indicating that B-HAP has great application potential to capture U(VI) from radioactive-contaminated wastewater as well. The U(VI) removal mechanism by B-HAP was confirmed with results from XRD, FT-IR and XPS. Chernikovite [H₂(UO₂)₂(PO₄)₂·8H₂O] was newly formed after U(VI) abatement by B-HAP. Economic assessment suggested B-HAP and its application on U(VI) abatement were cost-effective. With characteristics of high adsorption rate, large capacity, and strong antijamming ability, B-HAP has great application potential as an emergency treatment material for nuclear accidents.

Removal of U(VI) from aqueous and polluted water solutions using magnetic Arachis hypogaea leaves powder impregnated into chitosan macromolecule

In this study m-AHLPICS (magnetic Arachis hypogaea leaves powder impregnated into chitosan) was prepared and utilized as an adsorbent to remove U(VI) from aqueous and real polluted wastewater samples. m-AHLPICS was characterized by using the BET, XRD, FTIR, SEM with elemental mapping and magnetization measurements. Different experimental effects such as pH, dose, contact time, and temperature were considered broadly. Chitosan modified magnetic leaf powder (m-AHLPICS) exhibits an excellent adsorption capacity (232.4 ± 5.59 mg/g) towards U(VI) ions at pH 5. Different kinetic models such as pseudo-first-order, and pseudo-second-order models were used to know the kinetic data. Langmuir, Freundlich and D-R isotherms were implemented to know the adsorption behavior. Isothermal information fitted well with Langmuir isotherm. Kinetic data followed by the pseudo-second-order kinetics (with high R² values, i.e., 0.9954, 0.9985 and 0.9971) and the thermodynamic data demonstrate that U(VI) removal using m-AHLPICS was feasible, and endothermic in nature.

Enhanced dark adsorption and visible-light-driven photocatalytic properties of narrower-band-gap Cu2S decorated Cu2O nanocomposites for efficient removal of organic pollutants

The Cu₂S-decorated Cu₂O nanocomposites were synthesized by a facile co-precipitation and calcination method, and used as adsorbent and photocatalyst to remove organic pollutants from wastewater. Batch adsorption experiments were conducted to investigate the influences of molar ratio of Cu₂O to Cu₂S, initial solution pH, coexisting anion and temperature on the adsorption performances. As-obtained Cu₂O/Cu₂S-9/1 nanocomposite with high specific surface area (45.88 m²/g) exhibited superior adsorption ability towards Congo red, methyl orange and tetracycline in aqueous solution. The adsorption of organics onto the nanocomposite was a spontaneous and exothermic process, and the adsorption processes could be well described by the Freundlich isothermic and Pseudo-second-order kinetic models. The Cu₂O/Cu₂S-9/1 nanocomposite also showed excellent photocatalytic degradation activities for organic pollutants. Optical properties characterization suggested that the decoration of Cu₂S could effectively enhance visible-light absorption and inhibit the recombination of photo-generated electron-hole pairs. ESR tests and trapping experiments of reactive species indicated that both superoxide radicals (O₂^-) and holes (h⁺) were crucial for the photocatalytic degradation of organic pollutants. Moreover, the photocatalytic efficiency of Cu₂O/Cu₂S-9/1 nanocomposite had no significant decrease even after four consecutive runs. The bifunctional nanocomposite as adsorbent and photocatalyst presents a great potential in treating organic-contaminated wastewater.

Surface-Bound Humic Acid Increased Propranolol Sorption on Fe3O4/Attapulgite Magnetic Nanoparticles

This study explored the feasibility of utilizing a novel sorbent humic acid (HA) coated Fe₃O₄/attapulgite (MATP) magnetic nanoparticles (HMATP) for the sorption of propranolol from aqueous solutions. MATP and bare Fe₃O₄ nanoparticles were also synthesized under similar preparation conditions. The FTIR, Zeta potential, XRD, VSM, TEM, and TGA analyses were conducted to characterize the sorbent materials. The effects of pH, sorbent dosage, ionic strength, HA in the aqueous solution, contact time and initial sorbate concentration on sorption of propranolol were investigated using batch sorption experiments. The results suggested that the sorption capacity of HMATP showed little change from pH 4 to 10. Na⁺ and Ca²⁺ slightly inhibited the sorption of propranolol on HMATP. While HA in solution enhanced both MATP and HMATP, which indicated that HMATP can resist HA interference in water. Further, the less leaching amounts of Fe and HA suggested a good stability of HMATP. In all conditions, sorption capacity of propranolol on HMATP was obviously higher than that on MATP, which indicated that surface-coated HA played an important role in the propranolol sorption process. Electrostatic interaction, cation exchange, hydrogen bonding, and π–π electron donor acceptor interactions were considered as the sorption mechanisms.

Magnetically modified hydroxyapatite nanoparticles for the removal of uranium (VI): Preparation, characterization and adsorption optimization

Recently, magnetically modified nanomaterials have gained a great interest in the field of wastewater remediation. In this regard, the present work introduces a facile microwave-assisted pathway for the preparation of magnetically modified hydroxyapatite nanoparticles (MNHA) and evaluates its adsorption capability towards the removal of uranium (VI) ions from wastewaters. The prepared magnetic nanocomposite went through a full characterization procedure using different techniques, such as transmission electron microscope (TEM), X-ray diffraction (XRD), FT-IR, Brunauer-Emmett-Teller (BET) surface area measurements and magnetization curve. Involvement of the prepared MNHA in the remediation of wastewater containing U(VI) ions was investigated and the factors that influence the adsorption capacity were considered and optimized. The adsorption's optimum pH was found to be 5.0 and equilibrium was attended after 120 min. A maximum adsorption capacity of 310 mg/g was achieved after 120 min at 25 °C. The experimental data were well explained by Langmuir adsorption isotherm model. Kinetically, the adsorption process follows the pseudo-second order model. Thermodynamically, it is endothermic, irreversible and spontaneous adsorption process. Removal of U(VI) ions was found to take place via complex formation between the phosphate groups on the adsorbent and uranyl ions. The recovery of U(VI) ions from MNHA beads and the reusability of the spent beads were also explored. It was concluded that the prepared MNHA nanocomposite is simple, fast, ecofriendly adsorbent for the removal of U(VI) ions from water with excellent adsorption capacity.

Functionalized Biochar/Clay Composites for Reducing the Bioavailable Fraction of Arsenic and Cadmium in River Sediment

Biochar has frequently been used for the treatment of heavy metal pollution in water and soil; its effect on contaminated sediments requires further research. To improve the ability of biochar to immobilize heavy metals in sediment, we prepared a functionalized biochar/attapulgite composite by pyrolysis of the clay attapulgite and zinc chloride-pretreated rice straw biomass. Compared with the original biochar, the biochar/attapulgite composite had a large increase in specific surface area, pore volume, oxygen-containing functional groups, and cation exchange capacity. Biochar effectively improved the dispersibility of attapulgite as a matrix. The results showed that the biochar/attapulgite composite effectively reduced the bioavailable fraction of arsenic (As) and cadmium (Cd) in river sediment, which was a great improvement compared with the raw biochar. After the sediment was treated with different biochar/attapulgite composites, the concentrations of As and Cd in the overlying water and the porewater, and the content of acid-extractable and toxicity characteristic leaching procedure (TCLP)-extractable As and Cd in the solid phase of the sediment decreased significantly. Both zinc chloride activation and attapulgite improved As and Cd immobilization in sediment when we used the biochar/attapulgite composite. The results suggest that biochar/attapulgite composite can be used as an efficient in situ sorbent amendment to improve the heavy metal immobilization ability of the sediment. Environ Toxicol Chem 2019;38:2337-2347. © 2019 SETAC.

Preparation of Attapulgite/CoFe2O4 Magnetic Composites for Efficient Adsorption of Tannic Acid from Aqueous Solution

The use of attapulgite (ATP)-based materials for adsorption of pollutants from water and wastewater has received growing attention. However, recovering ATP-based adsorbents remains a challenge. In this study, a magnetic adsorbent ATP/CoFe₂O₄ with high tannic acid (TA) adsorptive capacity was fabricated via a facile co-precipitation approach and was well characterized. The loaded CoFe₂O₄ particles were embedded into the adsorbent surfaces to allow magnetic separability. For this material, its TA adsorption kinetics, isotherm behavior, and magnetic separation efficiency are reported. The developed magnetic composites had rapid sorption kinetics of 3 h, high sorption capacity of 109.36 mg/g, and good magnetic separation efficiency of 80%. The used ATP/CoFe₂O₄ was successfully regenerated by NaOH and reused five times without a substantial reduction in TA removal and magnetic performance. Intermolecular hydrogen bonding formation and surface complexation were identified as the sorption mechanisms of TA by ATP/CoFe₂O₄.

Preparation of a magnetic reduced-graphene oxide/tea waste composite for high-efficiency sorption of uranium

The preparation and application of adsorptive materials with low cost and high-efficiency recovery of uranium from nuclear waste is necessary for the development of sustainable, clean energy resources and to avoid nuclear pollution. In this work, the capacity of tea waste and tea waste hybrids as inexpensive sorbents for uranium removal from water solutions was investigated. Composites of graphene oxide (GO) and tea waste (TW) exhibited a promising adsorption performance for uranium from aqueous solutions. The composites GOTW and magnetic rGO/Fe₃O₄/TW show high adsorption capacities (Q_{m (TW)} = 91.72 mg/g, Q_{m (GOTW)} = 111.61 mg/g and Q_{m (rGO/Fe3O4/TW)} = 104.95 mg/g) and removal rates (~99%) for U(VI). The equilibrium sorption of the adsorbents fitted well to the Langmuir model, and the sorption rate fitted well to a pseudo-second-order kinetic model. The thermodynamic parameters indicated that sorption was spontaneous and favourable. The prepared adsorbents were used for the removal of uranium from real water samples as well. The results revealed that GOTW and rGO/Fe₃O₄/TW can be used to remediate nuclear industrial effluent as a potential adsorbent.

Spectroscopic studies on U(VI) incorporation into CaCO3: Effects of aging time and U(VI) concentration

In this study, the incorporation of U(VI) into CaCO₃ under different aging times and U(VI) concentrations was studied by combining batch experiments, X-ray diffraction (XRD), attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR), and extended X-ray absorption fine structure (EXAFS) approaches. Batch sorption experiments showed that the sorption of U(VI) on calcite was strong pH-dependence, and high pH was beneficial for U(VI) sorption possibly due to the electrostatic attraction between positively charged calcite and negatively charged uranyl tri-carbonate species. XRD patterns showed that the [104] facet of calcite shifted toward low angle at pH ∼10.0, which indicated that the uranyl tri-carbonate species of U(VI) possibly diffused into calcite lattice by replacing Ca atoms, and then induced the expansion of calcite crystal cell. The incorporation of U(VI) into CaCO₃ showed that the uptake of U(VI) gradually decreased within the first 200 h, and then significantly increased with the increasing aging time. U(VI) incorporation into CaCO₃ might experience vaterite, transition from vaterite to calcite, and calcite stages, which were confirmed by XRD, ATR-FTIR, and X-ray absorption near-edge structure (XANES) spectroscopy. As the U(VI) concentration increased, the transition time from vaterite to calcite correspondingly increased, indicating that U(VI) incorporation into CaCO₃ can stabilize vaterite phase. EXAFS analyses suggested that the local structure of uranyl moiety was changing during the incorporation process, and the species of U(VI) incorporation into vaterite was similar to uranyl carbonates, however indeed different from the species of uranyl tri-carbonate presented in calcite.

Preparation of PVDF/Hyperbranched-Nano-Palygorskite Composite Membrane for Efficient Removal of Heavy Metal Ions

In this work, three kinds of hyperbranched polyamidoamine-palygorskite (PAMAM-Pal) were designed and synthesized by grafting the first generation polyamidoamine (G1.0 PAMAM), G2.0 PAMAM and G3.0 PAMAM onto Pal surfaces, respectively. Then, these PAMAM-Pals were used as additives to prepare polyvinylidene fluoride (PVDF)/hyperbranched polyamidoamine-palygorskite bicomponent composite membranes. The structures of the composite membranes were characterized by Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TEM), X-ray photoelectron spectroscopy (XPS), field-emission scanning electronmicroscopy (SEM), atomic force microscope (AFM) and Thermogravimetric analysis (TGA). The adsorption properties of composite membranes to heavy metal ions was studied, and the results found that the maximum adsorption capacities for Cu(II), Ni(II) and Cd(II) could reach 155.19 mg/g, 124.28 mg/g and 125.55 mg/g, respectively, for the PVDF/G3.0 PAMAM-Pal membrane, while only 23.70 mg/g, 17.74 mg/g and 14.87 mg/g could be obtained for unmodified membranes in the same conditions. The high adsorption capacity can be ascribed to the large number of amine-terminated groups, amide groups and carbonyl groups of the composite membrane. The above results indicated that the prepared composite membrane has a high adsorption capacity for heavy metal ions removal in water treatment.

Retardation of hexavalent uranium in muscovite environment: a batch study

The sorption of hexavalent uranium on muscovite as a function of pH, background electrolyte, temperature and humic acid (HA) was investigated in detail using batch experiments. The results showed that the uranium sorpiton on muscovite was kinetic fast, the kinetic process was fitted well by pseudo-second-order kinetic model. The sorption of uranium depended strongly on pH while weakly on background electrolyte concentration, indicating that surface complexation dominated the sorption process. The escalation of temperature and humic acid concentration were favorable to uranium sorption on muscovite. The sorption isotherms at pH 6.0 could be described better by Langmuir model than Freundlich or Dubinin-Radushkevich (D-R) model, thermodynamic data indicated that the uranium sorption process on muscovite was spontaneous and endothermic process. The findings in present work can provide important experimental reference for understanding the environmental behavior of uranium in mica-rich terrains.

Efficient decontamination of naturally occurring radionuclide from aqueous carbonate solutions by ion flotation process

The present study evaluates the performance of ion flotation process for removal of uranyl tricarbonate complex, UO2(CO3)3 4−, which is the dominant species in many aqueous media particularly seawater, from aqueous solutions using cetyltrimethylammonium bromide, CTAB, as a cationic surfactant. Flotation of UO2(CO3)3 4− as a function in the solution pH is investigated in absence and in presence of carbonate. Removal percentage >99% is achieved in the pH range 8.5–11.5 in presence of 5×10−3 M carbonate. The influence of concentrations of ethanol (0.1–2% v/v) and CTAB (5×10−5–1.4×10−3 M) show that UO2(CO3)3 4− is efficiently removed at concentrations of 0.5–1.5% v/v and 4×10−4–1×10−3 M, respectively. Based on the obtained kinetic data, the flotation mechanism and the flotation rate are investigated using two different flotation models. Floatability of UO2(CO3)3 4− in presence of different cations (Ba2+, Ca2+, Mg2+ and Sr2+) and anions (NO3 −, Br−, Cl−, SO4 2− and HPO4 2−) is studied. Except for Mg2+ and NO3 −, the flotation efficiency of UO2(CO3)3 4− is significantly decreased at concentrations higher than 1×10−3 and 5×10−3 M of the studied cations and anions, respectively. Ion flotation process is efficiently applied for removal of uranium(VI), R%>98.5%, from seawater. Accordingly, ion flotation can be considered as a promising technique and thus its feasibility for removal and/or recovery of uranium(VI) from many aqueous environment.