A cascade electro-dehydration process for simultaneous extraction and enrichment of uranium from simulated seawater.

Uranium extraction from seawater has become a crucial issue that has raised tremendous attention. The transport of water molecules along with salt ions through an ion-exchange membrane is a common phenomenon for typical electro-membrane processes such as selective electrodialysis (SED). In this study, a cascade electro-dehydration process was proposed for the simultaneous extraction and enrichment of uranium from simulated seawater by taking advantage of water transport through ion-exchange membranes and the high permselectivity of membranes for monovalent ions against uranate ions. The results indicated that the electro-dehydration effect in SED allowed 1.8 times the concentration of uranium with a loose structure CJMC-5 cation-exchange membrane at a current density of 4 mA/cm2. Thereafter, a cascade electro-dehydration by a combination of SED with conventional electrodialysis (CED) enabled approximately 7.5 times uranium concentration with the extraction yield rate reaching over 80% and simultaneously desalting the majority of salts. Overall, a cascade electro-dehydration is a viable approach, creating a novel route for highly effective uranium extraction and enrichment from seawater.

Electrodialysis for the volume reduction of the simulated radionuclides containing seawater.

In this study, electrodialysis (ED) was performed to concentrate the radionuclides containing seawater for volume minimization. The concentration behaviors of the trace radioactive elements were also explored. Under the optimal voltage drop of 6 V and the volume ratio of 1:40, the concentration times of Cs+, Co2+, Sr2+ and I- could reach 9.9, 9.5, 20.1 and 32.5, respectively. Furthermore, it enabled over 80% volume reduction and over 90% removal of all hazardous radionuclides. Hence, ED is a feasible and promising method to manage the radioactive wastewater due to its high concentration and decontamination performances. For identical ion contents, the concentration rate for the cations presented the order of Na+ > Cs+ > Sr2+ > Co2+; the hydration radius and hydration free energy played the dominant roles in ion concentration. In contrast, for the ED concentration of trace radioactive elements, of which the contents are several magnitudes lower than the predominant salt concentration, the concentration rate presented the order of Sr2+ > Cs+ > Co2+ > Na+; the specific charge began to play an important role when the predominant ion approached its saturated salt concentration. For the anions, I- always migrated faster than Cl- at diverse concentrations.

Electrodialytic Desalination of Tobacco Sheet Extract: Membrane Fouling Mechanism and Mitigation Strategies.

In the papermaking industry (reconstituted tobacco), a large number of tobacco stems, dust, and fines are discharged in the wastewater. This high salinity wastewater rich in ionic constituents and nicotine is difficult to be degraded by conventional biological treatment and is a serious threat that needs to be overcome. Electrodialysis (ED) has proved a feasible technique to remove the inorganic components in the papermaking wastewater. However, the fouling in ion exchange membranes causes deterioration of membranes, which causes a decrease in the flux and an increase in the electrical resistance of the membranes. In this study, the fouling potential of the membranes was analyzed by comparing the properties of the pristine and fouled ion exchange membranes. The physical and chemical properties of the ion exchange membranes were investigated in terms of electrical resistance, water content, and ion exchange capacity, as well as studied by infrared spectroscopy (IR) spectra, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analyses. The results indicated that the membrane fouling is caused by two different mechanisms. For the anion exchange membranes, the fouling is mainly caused by the charged organic anions. For the cation exchange membrane, the fouling is caused by minerals such as Ca2+ and Mg2+. These metal ions reacted with OH- ions generated by water dissociation and precipitated on the membrane surface. The chemical cleaning with alkaline and acid could mitigate the fouling potential of the ion exchange membranes.