Peroxide-treated metal-organic framework templated adsorbents for remediation of high level nuclear waste

Application of hybrid MOF composite in extraction of f-block elements: Experimental and computational investigation

An attempt was made to understand the sorption behaviour of UO₂²⁺, Th⁴⁺ and Eu³⁺ on novel hybrid metal-organic framework composites, FeBDC@CoBDC. The XRD pattern revealed the composite nature of the hybrid MOF materials, while FTIR and Raman spectroscopic analyses evidenced the presence of different functional moieties. The thermal stability of the hybrid MOF composites was investigated through thermogravimetric analysis. The sorption predominantly followed Langmuir isotherm with sorption capacity of 189 mg g^-1, 224 mg g^-1 and 205 mg g^-1 for UO₂²⁺, Th⁴⁺ and Eu³⁺ respectively. The sorption proceeded through chemisorption following pseudo 2^nd order rate kinetics. The processes were found to be thermodynamically favourable and endothermic in nature. However, they were entropically driven. Multiple contacts of complexing agents were necessary for quantitative elution of f-elements from loaded MOF. The MOF showed moderate stability towards radiation exposure. DFT calculation was used for the optimization of structures, estimation of bond length and estimation of binding energy. In hybrid MOF composites, the Fe atom was having six coordination with 4 O atoms of BDC moieties and 2 O atoms of -OH groups. The O atoms of BDC and -OH groups were coordinated to Eu, Th and U atoms during their sorption.

Endowing 2,6-bis-triazolyl-pyridine of poor extraction with superior efficiency for actinide/lanthanide separation at high acidity by anchoring to a macrocyclic scaffold

Exploring nitrogen-containing extractants for recovering hazardous minor actinides that are workable in solutions of high acidity has been a challenge in nuclear waste treatment. Herein, we report our findings that 2,6-bis-triazolyl-pyridine (PyTri), which is ineffective as a hydrophobic ligand for minor actinide separation, turns into an excellent extractant that exhibits unexpectedly high efficiency and selectivity (SF_Am/Eu = 172, 1 M HNO₃) when attaching to pillar[5]arene platform. Surprisingly, the distribution ratio of Am(III) (D_Am) is 4300 times higher than that of the acyclic PyTri ligand. The solvent extraction performance of this pillar[5]arene-achored PyTri not only far exceeds the best known pillar[5]arene ligands reported to date, but also stays comparable to other reported outstanding extractants. Slope analysis indicates that each P[5]A-PyTri can bind two metal ions, which is further corroborated by spectroscopic characterizations. Thermodynamic studies imply that the extraction process is exothermic and spontaneous in nature. Complexation investigation via EXAFS technique and DFT calculations strongly suggest that each Eu(III) ion is coordinated to three PyTri arms through a nine-coordination mode. This work provides a N-donor extractant that can operate at high acidity for minor actinide partitioning and implicates a promising approach for transforming poor extractants into superior ones.

Highly efficient actinide(III)/lanthanide(III) separation by novel pillar[5]arene-based picolinamide ligands: A study on synthesis, solvent extraction and complexation

Selective extraction of highly radiotoxic actinides(III) is an important and challenging task in nuclear wastewater treatment. Many proposed ligands containing S or P atoms have drawbacks including high reagent consumption and possible secondary pollution after incineration. The present work reports five novel pillar[5]arene-based extractants that are anchored with picolinamide substituents of different electronic nature by varying spacer. These ligands reveal highly efficient separation of actinides(III) over lanthanides(III). Specifically, almost all of these ligands could extract Am(III) over Eu(III) selectively at around pH 3.0 (SF_Am/Eu>11) with fast extraction kinetics. Variation of the pyridine nitrogen basicity via changing para-substitution leads to an increase in the distribution ratios by a factor of over 300 times for Am(III) with an electron-withdrawing group compared to those with an electron donating group. Investigation of complexation mechanism by slope analysis, NMR, IR, EXAFS, and DFT techniques indicates that each ligand binds two metal ions by pyridine nitrogen and amide oxygen. Finally, these ligands do not show obvious decrease in both extraction and separation ability after being exposed to 250 kGy absorbed gamma radiation. These results demonstrate the potential application of pillar[5]arene-picolinamides for actinide(III) separation.

Power production waste

The storage of large amount of power production waste occupies huge land resource; moreover, the stored or discarded waste may pollute the water environment through changing the water pH, releasing the trace and toxic elements even radioactive elements, and so on by leachate. Therefore, the recycling and disposal of power production waste are important and necessary. This paper reviews the research literatures published in 2019 on power generation waste from coal-fired and nuclear power plants, mainly including the recycling of fly ash and flue gas desulfurization gypsum in construction industry and environmental application, the recovery and immobilization of different metals from coal combustion products and selective catalytic reduction catalysts, and the treatment and disposal of radioactive elements from nuclear power plants. Practioner points Coal-fired power plant waste can be applied for material preparation and wastewater purification. Valued and toxic metals are normally recovered or removed from spent selective catalytic reduction catalyst. Recovery and removal of radioactive elements is essential for nuclear power plant wastes disposal.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.

Long term corrosion estimation of carbon steel, titanium and its alloy in backfill material of compacted bentonite for nuclear waste repository

The container of high-level radioactive waste (HLRW) being in deep geological disposal, the backfill material is needed to serve as the second defense for HLRW and the highly compacted bentonite is generally selected. As the time goes, the underground water will infiltrate the backfill, causing the corrosion of materials for the building of containers in the formed electrolyte. Carbon steel, titanium and its alloy are the potential candidate materials for the fabrication of HLRW containers. The current investigation aims at assessing the safety of HLRW container in deep geological disposal for hundreds of thousands of years and facilitating the material selection for future container fabrication by estimating their corrosion behavior in compacted bentonite with a series of moisture content at different temperatures through electrochemical methods including open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curve (PC) measurements. The corrosion rates were estimated for a carbon steel, a pure titanium and a titanium alloy in compacted Gaomiaozi Bentonite infiltrated with simulated underground water in Beishan area of China over an expected disposal period up to 10⁶ years respectively, showing that titanium and its alloy are more reliable materials for building HLRW containers than carbon steel.