Uranium is not only a strategic resource for nuclear power but also a highly toxic contaminant in the environment. Although a series of traditional capturing materials including zeolites, metal–organic frameworks, mesoporous silica, and carbon-based nanomaterials have been investigated and developed, the combined advantages of decent stability, ultrafast removal kinetics, high sorption capacity, great selectivity, and potential recyclability have yet to be integrated into a single material. Herein, a new synthesis strategy was developed to synthesize a novel phosphorylated graphene oxide (GO)–chitosan (CS) composite (denoted as GO–CS–P) for U(VI) removal. The crosslinking of GO with CS and the subsequent phosphorylation of the GO–CS composite were demonstrated by scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), zeta potential measurement, thermogravimetric (TG) analysis, and scanning transmission electron microscopy (STEM). Batch experiments and spectroscopic analysis were performed to explore the removal performance and mechanism of GO–CS–P towards U(VI). The results showed that the uptake of U(VI) was ultrafast as the sorption equilibrium could be reached within 15 min. The maximum sorption capacity of U(VI) at pH 5.0 and 293 K was calculated to be 779.44 mg g−1, one of the highest values among the currently reported adsorbents. GO–CS–P also exhibited an excellent selectivity for capturing U(VI) from a mixture containing multiple competing metal ions. According to the desorption experiments, FTIR, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) analysis, the highly efficient immobilization of U(VI) in GO–CS–P was predominantly controlled by inner-sphere surface complexation with a minor contribution of surface reduction. The experimental findings demonstrated the feasibility of using GO–CS–P for used nuclear fuel partition and uranium-bearing wastewater remediation.

In this work, a carboxymethyl cellulose (CMC)-modified Fe3O4 (denoted as Fe3O4@CMC) composite was synthesized via a simple co-precipitation approach. Fourier transform infrared spectroscopy, zeta potential and thermogravimetric analysis results indicated that CMC was successfully coated on the Fe3O4 surfaces with a weight percent of ~30 % (w/w). The prepared Fe3O4@CMC composite was stable in acidic solution and could be easily collected with the aid of an external magnet. A batch technique was adopted to check the ability of the Fe3O4@CMC composite to remove Eu(III) as a function of various environmental parameters such as contact time, solution pH, ionic strength, solid content and temperature. The sorption kinetics process achieved equilibrium within a contact time of 7 h. The sorption isotherms were well simulated by the Langmuir model, and the maximum sorption capacity at 293 K was calculated to be 2.78 × 10−4 mol/g, being higher than the series of adsorbent materials reported to date. The ionic strength-independent sorption behaviors, desorption experiments by using ammonium acetate and disodium ethylenediamine tetraacetate as well as the spectroscopic characterization suggested that Eu(III) was sequestrated on the hydroxyl and carboxyl sites of Fe3O4@CMC via inner-sphere complexation. Overall, the Fe3O4@CMC composite could be utilized as a cost-effective adsorbent for the removal of trivalent lanthanide/actinides (e.g., 152+154Eu, 241Am and 244Cm) from radioactive wastewater.

This study highlights the simultaneous sequestration of U(VI) and arsenate at the goethite/water interface. The uptake trends and speciation of these two components were related with molar arsenate/U(VI) ratio, solution pH, contact order and aging time. A metastable [UO2(H2AsO4)2·H2O] was observed after 3 days and then this solid completely transformed into Na2(UO2AsO4)2·3H2O after 7 days. The disodium ethylenediamine tetraacetate ligand gave rise to the complete dissolution of Na2(UO2AsO4)2·3H2O phase and the release of U(VI) and arsenate back into the solution. The experimental findings facilitated us better comprehend the migration and fate of coexisting U(VI) and arsenate in the aquatic environment.

The permeable reactive barrier (PRB) technique has attracted an increasing level of attention for the in situ remediation of contaminated groundwater. In this study, the macroscopic uptake behaviors and microscopic speciation of Eu(III) on hydroxyapatite (HAP) were investigated by a combination of theoretical modeling, batch experiments, powder X-ray diffraction (PXRD) fitting, and X-ray absorption spectroscopy (XAS). The underlying removal mechanisms were identified to further assess the application potential of HAP as an effective PRB backfill material. The macroscopic analysis revealed that nearly all dissolved Eu(III) in solution was removed at pH 6.5 within an extremely short reaction time of 5 min. In addition, the thermodynamic calculations, desorption experiments, and PXRD and XAS analyses definitely confirmed the formation of the EuPO4·H2O(s) phase during the process of uptake of dissolved Eu(III) by HAP via the dissolution–precipitation mechanism. A detailed comparison of the present experimental findings and related HAP–metal systems suggests that the relative contribution of precipitation to the total Eu(III) removal increases as the P:Eu ratio decreases. The dosage of HAP-based PRB for the remediation of groundwater polluted by Eu(III) and analogous trivalent actinides [e.g., Am(III) and Cm(III)] should be strictly controlled depending on the dissolved Eu(III) concentration to obtain an optimal P:M (M represents Eu, Am, or Cm) ratio and treatment efficiency.

The speciation, migration and transport of radionuclides in the environment are significantly influenced by their interactions with the natural minerals and humic substances therein. In view of this, the effect of temperature and contact order on the sorption behaviors of trivalent Eu(III) in the γ-Al2O3/Eu(III) and γ-Al2O3/HA/Eu(III) systems was studied using batch experiments and the extended X-ray absorption fine structure spectroscopy (EXAFS) technique. The endothermic sorption behavior of Eu(III) in the γ-Al2O3/Eu(III) systems was induced by the hydrolysis reaction of Eu(III) in solution and the complexation of Eu(III) with the γ-Al2O3 surface sites. The endothermic sorption of Eu(III) in the γ-Al2O3/HA/Eu(III) systems was attributed to the endothermic binding of HA on γ-Al2O3 and the endothermic complexation between Eu(III) and HA. EXAFS analysis suggested the formation of type B ternary complexes and their thermodynamic stability improves with rising temperature. The different sorption percentages under various contact orders were closely related to the binding mode of Eu(III) on the exposed γ-Al2O3 surfaces or the γ-Al2O3/HA colloids. The findings obtained herein are important to evaluate the security of the radioactive waste repository and predict the fate of trivalent actinides (e.g., Am(III), Cm(III), Pu(III), etc.) near the geological repository.

•Core–shell structured Fe3O4@CD MNPs are prepared via chemical co-precipitation approach.•Fe3O4@CD MNPs are low-cost and eco-friendly as the raw materials are abundant and harmless.•Fe3O4@CD MNPs can be easily separated from the aqueous phase with a magnet.•Fe3O4@CD MNPs exhibit favorable performance toward the removal of Co(II) and 1-naphthol.•Fe3O4@CD MNPs show great application potential in environmental protection field.Herein, β-cyclodextrin (β-CD) was introduced on the surfaces of Fe3O4 particles via the chemical co-precipitation approach. The as-prepared Fe3O4@CD MNPs can be easily separated from the aqueous phase with a magnet. The removal performance of Fe3O4@CD MNPs toward Co(II) and 1-naphthol were investigated by using the batch technique. The maximum sorption capacities of Fe3O4@CD MNPs toward Co(II) and 1-naphthol are higher than a series of adsorbent materials. The simultaneous removal of Co(II) and 1-naphthol is achieved via the binding of Co(II) on the external surface sites of Fe3O4@CD MNPs and the incorporation of 1-naphthol into the hydrophobic cavity of surface-coated β-CD. The Fe3O4@CD MNPs exhibit favorable removal performance toward Co(II) and 1-naphthol from the simulated effluent. The experimental results herein suggest that Fe3O4@CD MNPs can be used as cost-effective material for the purification of co-contaminated water systems.