Functionalized Sugarcane Bagasse for U(VI) Adsorption from Acid and Alkaline Conditions

Exploring recyclable alginate-enhanced GCN-LDO sponge for U(VI) and Cd(II) removal: Insights from batch and column studies

Developing effective water treatment materials, particularly through proven adsorption methods, is crucial for removing heavy metal contaminants. This study synthesizes a cost-effective three-dimensional material encapsulating graphitic carbon nitride-layered double oxide (GCN-LDO) in sodium alginate (SA) through the freeze-drying method. The material is applied to remove uranium (U(VI)) and cadmium (Cd(II)) in real water systems. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analyses conclusively verified the elemental composition and successful encapsulation of GCN-LDO within the SA matrix. Removal effectiveness was tested under various conditions, including adsorbent dose, ionic strength, contact time, temperature, different initial pollutant concentrations, and the impact of co-existing ions. The adsorption of U(VI) and Cd(II) conformed to the pseudo-second-order (PSO) kinetic model, signifying a chemical interaction between the sodium alginate-graphitic carbon nitride-layered double oxide (SA-GCN-LDO) sponge and the metal ions. The Langmuir isotherm indicated monolayer, homogeneous adsorption for U(VI) and Cd(II) with capacities of 158.25 and 165.00 mg/g. SA-GCN-LDO recyclability was found in up to seven adsorption cycles with a removal efficacy of 70%. The temperature effect study depicts the exothermic nature of the U(VI) and Cd(II) ion removal process. Various mechanisms involved in U(VI) and Cd(II) removal were proposed. Further, continuous fixed bed column studies were performed, and Thomas and the Yoon-Nelson model were studied. These insights from this investigation contribute to advancing our knowledge of the material's performance within the context of U(VI) and Cd(II) adsorption, paving the way for optimized and sustainable water treatment solutions.

Reduction and adsorption of uranium(VI) from aqueous solutions using nanoscale zero-valent manganese

Nano zero-valent manganese (nZVMn) is theoretically expected to exhibit high reducibility and adsorption capacity, yet its feasibility, performance, and mechanism for reducing and adsorbing hexavalent uranium (U(VI)) from wastewater remain unclear. In this study, nZVMn was prepared via borohydride reduction, and its behaviors about reduction and adsorption of U(VI), as well as the underlying mechanism, were investigated. Results indicated that nZVMn exhibited a maximum U(VI) adsorption capacity of 625.3 mg/g at a pH of 6 and an adsorbent dosage of 1 g/L, and the co-existing ions (K⁺, Na⁺, Mg²⁺, Cd²⁺, Pb²⁺, Tl⁺, Cl^-) at studied range had little interference on U(VI) adsorption. Furthermore, nZVMn effectively removed U(VI) from rare-earth ore leachate at a dosage of 1.5 g/L, resulting in a U(VI) concentration of lower than 0.017 mg/L in the effluent. Comparative tests demonstrated the superiority of nZVMn over other manganese oxides (Mn₂O₃ and Mn₃O₄). Characterization analyses, including X-ray diffraction and depth profiling X-ray photoelectron spectroscopy, combined with density functional theory calculation revealed that the reaction mechanism of U(VI) using nZVMn involved reduction, surface complexation, hydrolysis precipitation, and electrostatic attraction. This study provides a new alternative for efficient removal of U(VI) from wastewater and improves the understanding of the interaction between nZVMn and U(VI).

A Critical Review of the Removal of Radionuclides from Wastewater Employing Activated Carbon as an Adsorbent

Radionuclide-contaminated water is carcinogenic and poses numerous severe health risks and environmental dangers. The activated carbon (AC)-based adsorption technique has great potential for treating radionuclide-contaminated water due to its simple design, high efficiency, wide pH range, quickness, low cost and environmental friendliness. This critical review first provides a brief overview of the concerned radionuclides with their associated health hazards as well as different removal techniques and their efficacy of removing them. Following this overview, this study summarizes the surface characteristics and adsorption capabilities of AC derived from different biomass precursors. It compares the adsorption performance of AC to other adsorbents, such as zeolite, graphene, carbon nano-tubes and metal-organic frameworks. Furthermore, this study highlights the different factors that influence the physical characteristics of AC and adsorption capacity, including contact time, solution pH, initial concentration of radionuclides, the initial dosage of the adsorbent, and adsorption temperature. The theoretical models of adsorption isotherm and kinetics, along with their fitting parameter values for AC/radionuclide pairs, are also reviewed. Finally, the modification procedures of pristine AC, factors determining AC characteristics and the impact of modifying agents on the adsorption ability of AC are elucidated in this study; therefore, further research and development can be promoted for designing a highly efficient and practical adsorption-based radionuclide removal system.

Polymer Nanorings with Uranium Specific Clefts for Selective Recovery of Uranium from Acidic Effluents via Reductive Adsorption

Nanostructured polymeric materials, functionalized with an appropriate receptor, have opened up newer possibilities for designing a reagent that shows analyte-specific recognition and efficient scavenging of an analyte that has either a detrimental influence on human physiology and environment or on its recovery for further value addition. Higher active surface area, morphological diversity, synthetic tunability for desired surface functionalization, and the ease of regeneration of a nanostructured material for further use have provided such materials with a distinct edge over conventional reagents. The use of a biodegradable polymeric backbone has an added significance owing to the recent concern over the impact of polymers on the environment. Functionalization of biodegradable sodium alginate with AENA (6.85% grafting) as the receptor functionality led to a unique open framework nanoring (NNRG) morphology with a favorable spatial orientation for specific recognition and efficient binding to uranyl ions (U) in an aqueous medium over a varied pH range. Nanoring morphology was confirmed by transmission electron microscopy and atomic force microscopy images. The nanoscale design maximizes the surface area for the molecular scavenger. A combination of all these features along with the reversible binding phenomenon has made NNRG a superior reagent for specific, efficient uptake of UO₂²⁺ species from an acidic (pH 3-4) solution and compares better than all existing UO₂²⁺-scavengers reported till date. This could be utilized for the recovery of uranyl species from a synthetic acidic effluent of the nuclear power. The results of the U uptake experiments reveal a maximum adsorption capacity of 268 mg of U per g of NNRG in a synthetic nuclear effluent. X-ray photoelectron spectroscopy studies revealed a reductive complexation process and stabilization of U(IV)-species in adsorbed uranium species (U@NNRG).

Preparation and uranium (VI) biosorption for tri-amidoxime modified marine fungus material

The preparation, characterization, and uranium (VI) adsorption properties of tri-amidoxime modified marine fungus material (ZZF51-GPTS-EDA-AM/ZGEA) were investigated in this study. ZGEA was synthesized by four steps of condensation, nucleophilic substitution, electrophilic addition, and nitrile amidoxime and characterized by a series of methods containing FT-IR, TGA, SEM, and BET. Contrasted with uranium (VI) adsorption capacity of original fungus mycelium (15.46 mg g^-1) that of the functional material (584.60 mg g^-1) was great under the optimal factors such as uranium (VI) ion concentration 40 mg L^-1, solid-liquid ratio 50 mg L^-1, pH of solution 5.5, and reaction time 120 min. The above data were obtained by the orthogonal method. The cyclic tests showed that ZGEA had good regeneration performance, and it could be recycled at least five adsorption-desorption processes. The thermodynamic experimental adsorption result fitted Langmuir and Freundlich models, which explored monolayer and double layers of uranium (VI) adsorption mechanism, and the kinetic adsorption results were in better consistent with the pseudo-second-order and pseudo-first-order dynamic models (R² > 0.999).

Magnetically Functionalized Moss Biomass as Biosorbent for Efficient Co2+ Ions and Thioflavin T Removal

Microwave synthesized iron oxide nanoparticles and microparticles were used to prepare a magnetically responsive biosorbent from Rhytidiadelphus squarrosus moss for the rapid and efficient removal of Co2+ ions and thioflavin T (TT). The biocomposite was extensively characterized using Fourier transformed infrared (FTIR), XRD, SEM, and EDX techniques. The magnetic biocomposite showed very good adsorption properties toward Co2+ ions and TT e.g., rapid kinetics, high adsorption capacity (218 μmol g-1 for Co and 483 μmol g-1 for TT), fast magnetic separation, and good reusability in four successive adsorption-desorption cycles. Besides the electrostatic attraction between the oxygen functional moieties of the biomass surface and both Co2+ and TT ions, synergistic interaction with the -FeOH groups of iron oxides also participates in adsorption. The obtained results indicate that the magnetically responsive biocomposite can be a suitable, easily separable, and recyclable biosorbent for water purification.

Environmental geochemistry and bioaccumulation/bioavailability of uranium in a post-mining context - The Bois-Noirs Limouzat mine (France)

Knowledge on the bioavailability of trace elements is essential in developing environmental quality standards. The purpose of this study was to explore the relationships between trace elements (in particular Uranium (U)) in sediments, porewater and their bioaccumulation by Chironomus riparius on a uranium mining site and river sediments upstream of the mine. The mobility and speciation of U in sediments was investigated using DGT. Geochemical modelling using CHESS provided insight on sorption behavior of U on ironoxyhydrite (HFO) and aqueous speciation of U. In the upstream site U concentrations found were 0.05 μmol g^-1 in surface sediment, 0.84 nmol L^-1 in porewater and 2.4 nmol g^-1 in Chironomus riparius whereas in the ferrihydrite deposits on the mining sites the concentrations found were up to 9.4 μmol g^-1 in surface sediment, 0.37 μmol L^-1 in porewater and 0.684 μmol g^-1 in in Chironomus riparius. Despite the large differences in concentrations of U between the two sites, sediment to dissolved partitioning coefficients, bioconcentration factor (BCF) and biota sediment accumulation factors (BSAF) were very comparable. In the upstream sediment binding of U to organic matter controls sorption and aqueous speciation of U, whereas in the HFO rich sediments, sorption on HFO and the formation of HFO colloids are the determining factors. The low BSAF factors and high BCF factors indicate that the bioaccumulation is due to uptake from the dissolved phase. The DGT probes with different binding resins provide information on the colloidal nature and lability of the dissolved U species.

Nano-sized Prussian blue immobilized costless agro-industrial waste for the removal of cesium-137 ions

For human health and safety, it is of great importance to develop innovative materials with a vast capacity for powerful removal of radioactive ions from aqueous solutions. Prussian blue functionalized sugarcane bagasse (PB-SCB) was successfully prepared for the efficient elimination of radioactive cesium (¹³⁷Cs) using a nontoxic, environmentally friendly, and costless method. The prepared renewable material was characterized using different techniques to emphasize morphology, functional groups, crystal structure, and the adsorption process. The adsorption of Cs(I) was better fitted to the pseudo-second-order model than pseudo-first-order model which revealed a chemical adsorption mechanism. The experimental isotherm results were best illustrated by the Freundlich model (R² = 0.98). Besides, the obtained values for the thermodynamic parameters indicating that the adsorption process was endothermic and spontaneous in nature. In addition to demonstrating high adsorption capacity for Cs ion removal (56.7 mg/g at 30 °C), PB-SCB might consider being an efficient and cost-effective adsorbent for the decontamination of cesium, where an estimated cost analysis revealed that the expenditure for the removal of 1000 mg/L cesium from alkaline radioactive wastewater is likely to be US$0.12. Graphical abstract.

A Sugarcane-Bagasse-Based Adsorbent Employed for Mitigating Eutrophication Threats and Producing Biodiesel Simultaneously

Eutrophication is an inevitable phenomenon, and it has recently become an unabated threat. As a positive, the thriving microalgal biomass in eutrophic water is conventionally perceived to be loaded with myriad valuable biochemical compounds. Therefore, a sugarcane-bagasse-based adsorbent was proposed in this study to harvest the microalgal biomass for producing biodiesel. By activating the sugarcane-bagasse-based adsorbent with 1.5 M of H2SO4, a highest adsorption capacity of 108.9 ± 0.3 mg/g was attained. This was fundamentally due to the surface potential of the 1.5 M H2SO4 acid-modified sugarcane-bagasse-based adsorbent possessing the lowest surface positivity value as calculated from its point of zero charge. The adsorption capacity was then improved to 192.9 ± 0.1 mg/g by stepwise optimizing the adsorbent size to 6.7–8.0 mm, adsorption medium pH to 2–4, and adsorbent dosage to 0.4 g per 100 mL of adsorption medium. This resulted in 91.5% microalgae removal efficiency. Excellent-quality biodiesel was also obtained as reflected by the fatty acid methyl ester (FAME) profile, showing the dominant species of C16–C18 encompassing 71% of the overall FAMEs. The sustainability of harvesting microalgal biomass via an adsorption-enhanced flocculation processes was also evidenced by the potentiality to reuse the spent acid-modified adsorbent.

Sorption behavior of Co-radionuclides from radioactive waste solution on graphene enhanced by immobilized sugarcane and carboxy methyl cellulose

Novel graphene-sugarcane bagasse-carboxy methyl cellulose (GSCCMC) nanocomposite have been synthesized via freeze-drying technique after preparation of graphene from natural graphite by modified Hummer method and evaluated as adsorbent for sorption of 60Co(II)-radionuclides from radioactive waste solution and real wastewater samples using a series of batch adsorption experiments and compared with graphene. The synthesized (GSCCMC) nanocomposite was characterized using Fourier transformer infrared (FT-IR), Transmission electron microscope (TEM), Thermal analysis, Elemental analysis, Specific Surface area (SBET) and X-ray diffraction (XRD), which confirmed the successful formation of graphene-sugarcane bagasse-carboxy methyl cellulose (GSCCMC) nanocomposite. Different parameters affecting the removal process including pH, contact time and metal ion concentration were investigated. Isotherm and kinetic models were studied. Adsorption kinetics described well by pseudo-second-order. The Langmuir model provides a better fitting than the Freundlich and Temkin models and the maximum adsorption capacity from Langmuir model were found to be 0.4186 and 0.2424 mol/g for (GSCCMC) nanocomposite and graphene (G), respectively. From Dubinin–Radushkevich (D–R) isotherm model, the sorption energy (E)-values of graphene (G) and (GSCCMC) are 10.16 and 10.564 kJ/mol, respectively and this mean the adsorption of 60Co(II)-radionuclides can be explained by chemisorption process, which is characteristic of ion exchange. Desorption of 60Co(II)-radionuclides from loaded (GSCCMC) nanocomposite was studied using different eluents (0.1 M HCl, 0.1 M NaOH and H2O). The data illustrated that 0.1 M HCl solution showed maximum desorption percent (D%) than other eluents. The economic viability of the adsorption process for the removal of 60Co(II) from wastewater samples was studied. The result indicated that the cost for preparation of (GSCCMC) nanocomposite is lower than for (GSCCMC) nanocomposite that prepared from purchase the graphene powder. Therefore, the synthesized (GSCCMC) nanocomposite was used as regenerated material for sorption of 60Co(II)-radionuclides from aqueous solutions and can be used for many times as a cost-effective and environmental friendly material in wastewater treatment.