Adsorption of U(VI) from aqueous solution by sulfonated ordered mesoporous carbon

Uranium extraction using hydroxyapatite recovered from phosphorus containing wastewater

A considerable amount of uranium (U(VI))-containing industrial wastewater is generated from both uranium mining and processing, and nuclear electrical power generation. Discharge of U(VI) containing wastewater causes severe damage to the environment and leads to a loss of resources. Uranium sorption on hydroxyapatite (HAP) has been studied extensively to address the abovementioned issues. In the present study, BC-HAP was recovered through phosphate sorption from wastewater, which was first reused as a potential sorbent for extracting uranium from aqueous solutions comparing to commercially available nano-HAP. The sorption behavior of uranium and its transformation on the recovered BC-HAP were investigated by conducting batch experiments as well as Fourier-transform infrared, scanning electron microscopy, and x-ray diffraction analyses. BC-HAP had superior sorption ability for uranium extraction. Autunite precipitant at nano-scale is observed after uranium sorption. Partial desorption of uranium was observed in the presence of Na₂CO₃ and NaHCO₃. Surface complexation and phosphate dissolution precipitation contributed to the favorable uranium sorption. Thus, recovered BC-HAP can be widely used as a promising and cost-effective adsorbent to extract uranium from aqueous solution.

Recovery of phosphorus rich krill shell biowaste for uranium immobilization: A study of sorption behavior, surface reaction, and phase transformation

Increased generation of shrimp shell from exploitation of krill results in emerging biowaste pollution, in addition, uranium pollution has drawn public concern due to the rapid development of nuclear power, uranium mining, and nuclear fuel processing. In this study, krill shells were recovered and used as a potential natural biosorbent for uranium immobilization, thereby enabling both uranium decontamination and krill shell reutilization. Interaction of uranium with krill shell surface and their transformation were investigated by using batch sorption experiments, scanning electron microscopy, and transmission electron microscopy. Krill shell had high uranium sorption ability. Uranium was transformed into a nano-scale precipitate. The mapping of phosphorus and uranium was related to the nano-scale precipitate, indicating that sorption of uranium was dependent on phosphorus. Surface chemisorption between phosphate in krill shell and uranium as well as the formation of the nano-scale precipitate were interpreted as the mechanism of uranium immobilization. Thus, natural krill shell waste has potential for extensive use as a promising and cost-effective sorbent for uranium immobilization and krill shell reutilization.

Synthesis of FC-supported Fe through a carbothermal process for immobilizing uranium

The abundant generation of uranium (U), a radioactive nuclide, engenders a severe hazard to the environment. Iron based materials were used to immobilize U from water, however, the immobilization is limited by the agglomeration of nanoparticle Fe. In this study, a novel carbothermal process was proposed to synthesize flour carbon (FC) supported nano-flake Fe (Fe-FC). Scanning electron microscopy (SEM) and nitrogen isotherm adsorption-desorption analysis were conducted to characterize Fe-FC. The immobilization characteristics were investigated through batch sorption experiments. Results indicated that nano-flake was appropriately dispersed on the surface. The sorption capacity reached 19.12 mg/g when the initial concentration of U and the dosage of Fe-FC were 20 mg/L and 1 g/L, respectively. Langmuir isotherm sorption and pseudo-second-order models were fitted well to sorption experimental data. The sorption mechanism is ascribed to surface chemisorptions between U(VI) and Fe-FC. Subsequently, X-ray diffraction (XRD) analysis validated that formation of Fe₂UO₃ contributed to the favorable immobilization of U and that Fe₂UO₃ was the fate of U.

Uranium biosorption from aqueous solution by the submerged aquatic plant Hydrilla verticillata

The biosorption characteristics of U(VI) from aqueous solution onto a nonliving aquatic macrophyte, Hydrilla verticillata (dry powder), were investigated under various experimental conditions by using batch methods. Results showed that the adsorption reached equilibrium within 60 min and the experimental data were well fitted by the pseudo-first-order kinetic model. U(VI) adsorption was strongly pH dependent, and the optimum pH for U(VI) removal was 5.5. Isotherm adsorption data displayed good correlation with the Langmuir model, with a maximum monolayer adsorption capacity of 171.52 mg/g. Thermodynamic studies suggested that U(VI) adsorption onto H. verticillata was an exothermic and spontaneous process in nature. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that the amino and hydroxyl groups on the algal surface played an important role in U(VI) adsorption. The mechanisms responsible for U(VI) adsorption could involve electrostatic attraction and ion exchange. In conclusion, H. verticillata biomass showed good potential as an adsorption material for the removal of uranium contaminants in aqueous solution.

Enhanced adsorption capacity and selectivity towards strontium ions in aqueous systems by sulfonation of CO2 derived porous carbon

Sulfonated porous carbon (PC-SO₃H) shows enhanced Sr²⁺ adsorption performance in terms of removal capacity, kinetics, and selectivity.

Simultaneous reduction and adsorption for immobilization of uranium from aqueous solution by nano-flake Fe-SC

Uranium containing radioactive wastewater is seriously hazardous to the natural environment if it is being discharged directly. Herein, nano-flake like Fe loaded sludge carbon (Fe-SC) is synthesized by carbothermal process from Fe-rich sludge waste and applied in the immobilization of uranium in aqueous. Batch isotherm and kinetic adsorption experiments are adopted to investigate the adsorption behavior of Fe-SC to uranium in aqueous. XPS analyses were conducted to evaluate the immobilized mechanism. It was found that the carbonized temperature played significant role in the characteristics and immobilization ability of the resulted Fe-SC. The Fe-SC-800 carbonized at 800°C takes more advantageous ability in immobilization of uranium from aqueous than the commercial available AC and powder zero valent iron. The adsorption behavior could be fitted well with the Langmuir isotherm adsorption model and pseudo-second order model. The equilibrium adsorption amount and rate for Fe-SC-800 is high to 148.99mgg^-1 and 0.015gmg^-1min^-1, respectively. Both reductive precipitation and physical adsorption are the main mechanisms of immobilization of uranium from aqueous by Fe-SC-800.

Uranium biosorption from aqueous solution onto Eichhornia crassipes

Batch experiments were conducted to investigate the biosorption of U(VI) from aqueous solutions onto the nonliving biomass of an aquatic macrophyte Eichhornia crassipes. The results showed that the adsorption of U(VI) onto E. crassipes was highly pH-dependent and the best pH for U(VI) removal was 5.5. U(VI) adsorption proceeded rapidly with an equilibrium time of 30 min and conformed to pseudo-second-order kinetics. The Langmuir isotherm model was determined to best describe U(VI) biosorption with a maximum monolayer adsorption capacity of 142.85 mg/g. Thermodynamic calculation results indicated that the U(VI) biosorption process was spontaneous and endothermic. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis implied that the functional groups (amino, hydroxyl, and carboxyl) may be responsible for the U(VI) adsorption process, in which the coordination and ion exchange mechanisms could be involved. We conclude that E. crassipes biomass is a promising biosorbent for the removal of uranium pollutants.

Functionalization of mesoporous materials for lanthanide and actinide extraction

Recent advances in the field of functionalized mesoporous solid-phase sorbents designed for rare earth element and actinide separation/concentration could provide answers to limitations occurring in the industrial separation processes of these critical elements.