A Prussian blue analog-based copper-aluminum layered double hydroxide for cesium removal from water: fabrication, density functional theory-based molecular modeling, and the adsorption mechanism.

A new type of adsorbent, a Prussian blue analog-based copper-aluminum layered double hydroxide (PBA@CuAl-LDH), was successfully synthesized using a one-step method for the removal of radioactive Cs+ from wastewater. The adsorption performance, characteristics and the underlying adsorption mechanism of PBA@CuAl-LDH were systematically examined. The results showed that PBA@CuAl-LDH exhibited excellent adsorption performance, with a maximum adsorption capacity of 109.2 mg g-1. Over 85% of PBA@CuAl-LDH can be recycled, and the material exhibited only a 6.6% loss in adsorption performance. The adsorption process was well-fitted using the pseudo-second-order kinetic model and the Freundlich isotherm model, revealing the surface heterogeneity of the composite adsorbent. A molecular model of PBA@CuAl-LDH was constructed by combining density functional theory and multiple instrumental characterization techniques. Our results indicate that PBA crystals can be generated between layers and on the surface. Ion exchange was revealed as the main adsorption mechanism of Cs+ by PBA@CuAl-LDH. Specifically, the interstitial spaces of the PBA crystals generated between the layers and on the surface played an important role in ion exchange. These findings provide concrete theoretical support for radioactive pollution control and have significant value in directing the fabrication of cesium removal materials and their future engineering application.

Leaching behaviour and mechanism of U, 226Ra and 210Pb from uranium tailings at different pH conditions.

A large number of radionuclides remain in uranium tailings, and U, 226Ra and 210Pb leach out with water chemistry, causing potential radioactive contamination to the surrounding environment. In this paper, uranium tailings from a uranium tailings pond in southern China were collected at different depths by means of borehole sampling, mixed and homogenised, and analysed for mineral and chemical composition, microscopic morphology, U, 226Ra and 210Pb fugacity, static leaching and dynamic leaching of U, 226Ra and 210Pb in uranium tailings at different pH conditions. The variation of U, 226Ra and 210Pb concentrations in the leachate under different pH conditions with time was obtained, and the leaching mechanism was analysed. The results showed that the uranium tailings were dominated by quartz, plagioclase and other minerals, of which SiO2 and Al2O3 accounted for 65.45% and 13.32% respectively, and U, 226Ra and 210Pb were mainly present in the residue form. The results of the static leaching experiments show that pH mainly influences the leaching of U, 226Ra and 210Pb by changing their chemical forms and the particle properties of the tailings, and that the lower the pH the more favourable the leaching. The results of dynamic leaching experiments during the experimental cycle showed that the leaching concentration and cumulative release of U, 226Ra and 210Pb in the leach solution were greater at lower pH conditions than at higher pH conditions, and the leaching of U, 226Ra and 210Pb at different pH conditions was mainly from the water-soluble and exchangeable states. The present research results are of great significance for the environmental risk management and control of radioactive contamination in existing uranium tailings ponds, and are conducive to ensuring the long-term safety, stability and sustainability of uranium mining sites.

Theoretical and experimental investigations of enhanced uranium(VI) adsorption using a nitrogen doping strategy.

With the ongoing development and utilization of nuclear energy, uranium pollution has become an increasingly serious issue. Although many adsorbents are able to remove hexavalent uranium (U(VI)) from aqueous solution, the development of a high capacity adsorbent exhibiting superior stability would be beneficial. Grafting poly(amidoxime) (PAO) onto reduced graphene oxide (rGO) provides suitable U(VI) adsorption performance but the PAO is prone to agglomeration. The present work used density functional theory calculations to predict that PAO would bond with pyrrolic N atoms in nitrogen-doped rGO (N-rGO). To confirm this, PAO-grafted rGO (PAO-rGO) and PAO-grafted N-rGO (PAO-N-rGO) were prepared and characterized and the successful grafting of PAO on N-rGO was demonstrated. Adsorption experiments demonstrated that PAO-N-rGO exhibit superb U(VI) adsorption performance compared with the original PAO-rGO under acidic conditions. As for competing metal ions, Cu2+, Al3+, and Ca2+ have a greater impact on U(VI) adsorption than Na+, Mg2+, and K+ both for PAO-rGO and PAO-N-rGO. The maximum adsorption capacities of PAO-rGO and PAO-N-rGO for U(VI) were calculated to be 1500.26 and 1545.95 mg g-1, respectively. The mechanism of nitrogen doping promoting uranium(VI) adsorption can be attributed to enhanced PAO grafting and improvement of adsorption performance of the rGO. This work demonstrates that nitrogen doping is a viable strategy for enhancing the U(VI) adsorption performance of PAO-rGO.

NORM survey within the second census on pollution sources in China.

The Second Census of Pollution Source in China was conducted from 2017 to 2020, and the radioactive target in this census was Naturally Occurring Radioactive Material (NORM).The census plan for the radioactive component was prepared by the Nuclear and Radiation Safety Centre of the Ministry of Ecology and Environment in accord with the work requirement of the overall census. The work steps involved in performing the census included establishing the organization structure, document formulation, conducting a pilot survey, relevant training, screening of preliminary survey data, quality assurance, detailed data collection and analysis, data verification and reporting, and final summarizing. The survey mainly involved 15 kinds of NORM industries, which include the rare earth, niobium/tantalum, zircon, zirconia and tin industries, etc. Almost 30,000 enterprises were investigated in the screening phase, and nearly 2000 enterprises were determined to satisfy the screening criteriafor the presence of NORM. A total of 3500 samples including discharge water, raw ore, milling ore and solid waste were obtained and measured resulting in about20,000 individual datum. The Nuclear and Radiation Safety Centre of the Ministry of Ecology and Environment had responsibility for the NORM census and has completed a comprehensive statistical analysis of the data including analysis of the characteristics from different perspectives.

A study of 110mAg in aquatic and terrestrial ecosystems.

Experiments on a simulated terrestrial agricultural ecosystem were carried out using the pot culture approach. The most representative plants in local vegetable gardens were selected to investigate the root uptake of (110m)Ag. The results show that carrot, kale and flowering cabbage have the largest transfer factor values among the vegetables. Flowering cabbage, as the most popular leafy vegetable in Hong Kong and the South China area, can be used as a biomonitor for radioisotope contamination in vegetables. Soil column and adsorption tests were also carried out to study the leaching ability of the silver isotope in soil and (110m)Ag was mainly adsorbed in the top 1 cm of soil regardless of the pH value. Experiments on a simulated aquatic ecosystem for freshwater fish and marine organisms were carried out in glass aquaria. The freshwater fish Cyprinus carpio, the marine fish Cuvier and some local abundant seashore molluscs were selected to investigate the kinetic metabolism of (110m)Ag in the compartmental system. The results show that molluscs absorb (110m)Ag much more than fish. Clibanarius infraspinatus has the largest concentration factor among the marine organisms selected. Fish liver, although representing a minor portion of the total body mass, shows the highest (110m)Ag concentration factor, whereas muscle, although representing a major portion of the total body mass, is characterized by an absence of (110m)Ag.