Surface charge property governing co-transport of illite colloids and Eu(Ⅲ) in saturated porous media

The transport of colloids and radionuclides is sophisticated because of the variety of charge properties between colloidal particles and host subsurface media, which causes great difficulty in establishing a reliable model of radionuclides migration by taking the colloid phase into consideration. In this work,the co-transport of illite colloids(IC) and Eu(Ⅲ) in the quartz sand and iron-coated sand porous media was investigated by column experiments to address the predominant mechanism of charge properties on co-transport. Results showed that Eu(Ⅲ) transport was driven by the illite colloids and electrostatic interaction was critical in governing the co-transport patterns. The promotion of Eu(Ⅲ) transport by IC was attenuated in the iron-coated sand systems;more IC-Eu(Ⅲ) complexes were retained uniformly in the column. The pore throat shrinkage caused by electrostatic attachment between aggregated IC and iron oxides exacerbated the physical straining and size exclusion effect of IC-Eu(Ⅲ) complexes. An aggravated irreversible retention of IC-Eu(Ⅲ) was detected in iron-coated sand column due to the electrostatic attraction of IC-Eu(Ⅲ) to host media. The findings are essential for improving the understanding on the potential transport, retention and release risk of colloids associated radionuclides, and imply that the positively charged permeable reactive barrier is an effective strategy to reduce the transport risk of colloid associated radionuclides.

Synthesis of novel nanomaterials and their application in efficient removal of radionuclides

With the development of nuclear energy, large amounts of radionuclides are inevitably released into the natural environment. It is necessary to eliminate radionuclides from wastewater for the protection of environment. Nanomaterials have been considered as the potential candidates for the effective and selective removal of radionuclides from aqueous solutions under complicated conditions because of their high specific surface area, large amounts of binding sites, abundant functional groups, pore-size controllable and easily surface modification. This review mainly summarized the recent studies for the synthesis, fabrication and surface modification of novel nanomaterials and their applications in the efficient elimination and solidification of radionuclides,and discussed the interaction mechanisms from batch experiments, spectroscopy analysis and theoretical calculations. The sorption capacities with other materials, advantages and disadvantages of different nanomaterials are compared, and at last the perspective of the novel nanomaterials is summarized.

Sorption of uranyl ions on TiO_2:Effects of pH,contact time,ionic strength,temperature and HA

Sorption of U(VI) onto TiO_2 as functions of pH, ionic strength, contact time, soil humic acid(SHA), solid-to-liquid ratio and temperature was studied under ambient conditions using batch and spectroscopic approaches. The sorption of U(VI) on TiO_2 was significantly dependent on pH and ionic strength. The presence of SHA slightly enhanced the sorption of U(VI) on TiO_2 below pH 4.0, while it inhibited U(VI) sorption in the higher pH range. U(VI)sorption on TiO_2 was favored at high temperatures, and the sorption process was estimated to be endothermic and spontaneous. Reduction of U(VI) to lower valent species was confirmed by X-ray photo-electron spectroscopy analysis. It is very interesting to find that U(VI) sorption on TiO_2 was promoted in solutions with higher back-ground electrolyte concentrations. In the presence of U(VI), higher back-ground electrolyte made more TiO_2 particles aggregate through(001) facets, leading more(101) facets to be exposed. Therefore, the reduction of U(VI) was enhanced by the exposed(101) facets and more U(VI) removal was observed.

China's progress in radionuclide migration study over the past decade(2010–2021):Sorption,transport and radioactive colloid

The radionuclide(RN)migration study is not only helpful to understand environmental behavior of RNs,but also can establish the basis for the safety assessment of geological disposal of high-level radioactive waste(HLW).In the context of China’s HLW disposal,this review briefly summaries the progress of China’s RN migration studies over the past decade regarding three aspects,RN sorption,RN transport and radioactive colloid.Domestic studies from other disciplines(such as geology and environmental science)are also included in this review because they can provide references for the RN migration study.Overall,China has achieved clear progress in RN migration study over the past decade,although large-scaled field experiments are lacked and a gap still exists comparing with the international advanced level.Finally,several suggestions are proposed for future RN migration research in China.

Opportunities and challenges of high-pressure ion exchange chromatography for nuclide separation and enrichment

With the rapid development of the nuclear industry,more-stringent requirements are proposed for highlevel radioactive waste liquid treatment and the enrichment of isotope products.High-pressure ion exchange chromatography has been widely accepted for the fine separation of elements and nuclides due to its advantages,such as high efficiency,environmental friendliness,ease of operation,and feasibility for large-scale industrial applications.Here,we summarized the evolution of high-pressure ion exchange chromatography and the relevant research progress in ion exchange equilibrium and related separation technology.The prospects for application of high-pressure ion exchange chromatography to rare earth elements,actinide elements and isotope separation were discussed.High-pressure ion exchange chromatography represents a promising strategy for the extraction of rare earth elements and actinide elements from high-level radioactive waste liquid,as well as being an effective method for the automated production of high purity isotope products with great environmental benefits.

Efficient photoreduction strategy for uranium immobilization based on graphite carbon nitride/activated carbon nanocomposites

Uranium removal from aqueous solutions using environmentally friendly photocatalytic technology is a novel approach for resource recovery.Herein,carbon nitride/activated carbon composite materials(CN/AC)were investigated for U(Ⅵ)reduction under visible light.An exceptional boost in photocatalytic activity was observed for CN/AC composites(up to 70 times over the conventional bulk g-C_(3)N_(4)).The strong interactive conjugatedπ-bond structure between g-C_(3)N_(4) and AC accelerated the migration of carriers and then prolonged the electron lifetime.CN/AC composites exhibited excellent compatibility with different water substrates and were resilience to a wide range of p H changes and abundant competitive anions/cations.Quenching experiments and electron microscopy characterization indicated that U(VI)was reduced by photogenerated electrons and deposited on the edge of CN/AC composites.The low-cost,high-performance carbon-based composite material proposed in this work is a potential candidate for the efficient treatment of radioactive wastewater.