Plant polyphenol surfactant construction with strong surface activity and chelation properties as efficient decontamination of UO22+ on cotton fabric

Chemically synthesized surfactants have promising applications in the treatment of uranium, however, their hazardous environmental effects, non-biodegradability, and numerous drawbacks prevent them from being widely used in practice. Herein, we successfully synthesized a green chelating and foaming integrated surfactant (BTBS) by Mannich reaction and acylation of bayberry tannin for the effective removal of UO22+ from aqueous environments or solid surfaces. The as-prepared surfactant was systematically characterized by FT-IR, showing that the hydrophobic groups were successfully grafted onto tannin. The modified material showed better foaming and emulsifying properties, which proved this method could improve the amphiphilicity of tannin. Moreover, for the first time, a foam fractionation method in conjunction with a tannin-based surfactant was applied for UO22+ removal from water. This surfactant was used as a co-surfactant and could readily remove 90 % of UO22+ (20 mg L-1) from water. The removal of UO22+ could be completed in a short time (30 min), and the maximum adsorption capacity was determined as 175.9 mg g-1. This surfactant can also be used for efficient decontamination of uranium-contaminated cotton cloth with a high removal rate of 94.55 %. In addition, the mechanism studies show that the adsorption of BTBS for UO22+ can be mainly attributed to a chelating mechanism between UO22+ and the adjacent phenolic hydroxyls. The novel biomass-derived BTBS with advantages such as high capture capacity, environmental friendliness, and cost-effectiveness suggests that it plays an important role in the remediation of radionuclide pollution.

Removal of uranium from contaminated groundwater using monorhamnolipids and ion flotation

Mining of uranium for defense-related purposes has left a substantial legacy of pollution that threatens human and environmental health. Contaminated waters in the arid southwest are of particular concern, as water resource demand and water scarcity issues become more pronounced. The development of remediation strategies to treat uranium impacted waters will become increasingly vital to meet future water needs. Ion flotation is one technology with the potential to address legacy uranium contamination. The green biosurfactant rhamnolipid has been shown to bind uranium and act as an effective collector in ion flotation. In this study, uranium contaminated groundwater (∼440 μg L-1 U) from the Monument Valley processing site in northeast Arizona was used as a model solution to test the uranium removal efficacy of ion flotation with biosynthetic (bio-mRL) and three synthetic monorhamnolipids with varying hydrophobic chain lengths: Rha-C10-C10, Rha-C12-C12, and Rha-C14-C14. At the groundwater's native pH 8, and at an adjusted pH 7, no uranium was removed from solution by any collector. However, at pH 6.5 bio-mRL and Rha-C10-C10 removed 239.2 μg L-1 and 242.4 μg L-1 of uranium, respectively. By further decreasing the pH to 5.5, bio-mRL was able to reduce the uranium concentration to near or below the Environmental Protection Agency maximum contaminant level of 30 μg L-1. For the Rha-C12-C12 and Rha-C14-C14 collector ligands, decreasing the pH to 7 or below reduced the foam stability and quantity, such that these collectors were not suitable for treating this groundwater. To contextualize the results, a geochemical analysis of the groundwater was conducted, and a consideration of uranium speciation is described. Based on this study, the efficacy of monorhamnolipid-based ion flotation in real world groundwater has been demonstrated with suitable solution conditions and collectors identified.

Preparation of novel porous Al2O3-SiO2nanocomposites via solution-freeze-drying-calcination method for the efficient removal of uranium in solution

In this work, the efficient extraction of uranium in solution using Al₂O₃-SiO₂-T was reported. Kinetics and isotherm models indicated that the removal process of uranium on Al₂O₃-SiO₂-T accorded with pseudo-second-order kinetic model and Langmuir isotherm model, which showed that the adsorption process was a uniform mono-layer chemical behavior. The maximum adsorption capacity of Al₂O₃-SiO₂-T reached 738.7 mg g^-1, which was higher than AlNaO₆Si₂(349.8 mg g^-1) and Al₂O₃-SiO₂-NT (453.1 mg g^-1), indicating that the addition of template could effectively improve the adsorption performance of Al₂O₃-SiO₂to uranium. Even after five cycles of adsorption-desorption, the removal percentage of uranium on Al₂O₃-SiO₂-T remained 96%. Besides, the extraction efficiency of uranium on Al₂O₃-SiO₂-T was 72.5% in simulated seawater, which suggested that the Al₂O₃-SiO₂-T was expected to be used for uranium extraction from seawater. Further, the interaction mechanism between Al₂O₃-SiO₂-T and uranium species was studied. The results showed that the electrostatic interaction and complexation played key roles in the adsorption process of Al₂O₃-SiO₂-T to uranium.

Organo-modification of montmorillonite for enhancing the adsorption efficiency of cobalt radionuclides from aqueous solutions

Montmorillonite clay was organically modified with thoron (TH) and was employed as an adsorbent for removal of cobalt(II) radionuclides from aqueous solutions. Batch adsorption experiments, under several operational parameters such as pH, contact time, initial adsorbate concentration, adsorbent dosage, ionic strength, and temperature, were conducted to determine the optimum conditions for efficient removal of cobalt(II) radionuclides. The obtained data showed that almost complete removals were achieved for cobalt(II) at pH values ≥ 3.5 using TH-modified montmorillonite (TMM), while only 63% were obtained by unmodified clay at pH ≥ 5.4. Adsorption kinetic data of cobalt(II) were better fitted by the pseudo-second order kinetic model and its adsorption rate was controlled by film diffusion. Both Langmuir and Freundlich models had the ability to well describe the equilibrium data of cobalt(II) radionuclides at the studied temperatures. The adsorption capacity of TMM (0.85 mmol/g) was found to be not only nine times that of unmodified montmorillonite (0.097 mmol/g), but also higher than those reported in literature using various unmodified and modified clays. Thermodynamic parameters (ΔH°, ΔS°, and ΔG°) were calculated. Among the examined desorbing agents, both Al³⁺ and EDTA were succeeded to desorb most of cobalt(II) radionuclides (desorption % ~ 90%) loaded onto TMM. The results of this study clarified that TMM can be considered as an effective adsorbent for removal of cobalt(II) radionuclides from aqueous solutions.

Highly efficient carbonaceous nanofiber/layered double hydroxide nanocomposites for removal of U(VI) from aqueous solutions

The three-dimensional (3D) carbonaceous nanofiber and Ni-Al layered double hydroxide (CNF/LDH) nanocomposite was successfully prepared by a facile one-step hydrothermal methodology. Characterization of scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), XRD, and Fourier transformed infrared spectroscopy (FTIR) provided a demonstration that the modified CNF/LDH nanocomposite possessed abundant functional groups, for instance, metal-oxygen surface bonding sites (Ni–O as well as Al–O) and free-metal surface bonding sites (C–O, C–O–C, as well as O–C=O). The elimination of representative radionuclide (i.e. U(VI)) on the CNF/LDH nanocomposite from aqueous solutions was explored as a key function of pH, ionic strength, contact time, reaction temperature as well as radionuclide preliminary concentrations with the use of the batch methodology. As revealed by the findings, the sorption of radionuclides on CNF/LDH nanocomposite adhered to the pseudo-second-order kinetic model as well as Langmuir model. The maximum elimination capacity of U(VI) amounted to be 0.7 mmol/g. The independent of ionic strength shed light on the fact that inner-sphere surface complexation mainly overpowered radionuclide uptake by the CNF/LDH nanocomposite, which was further verified through the combination of FTIR and XPS spectral analyses. The abovementioned analyses shed light on the fact that the CNF/LDH nanocomposite can be regarded as a latent material to preconcentration radionuclides for environmental remediation.