Removal of Cs, Sr, U and Pu species from simulated nuclear waste effluent using graphene oxide

Caesium adsorption on a zeolitic imidazolate framework (ZIF-8) functionalized by ferrocyanide

¹³⁷Cs is one of the most hazardous radionuclides in nuclear waste owing to its toxicity. Developing an adsorbent for Cs⁺ with a high capacity and selectivity is a challenging task. A metal-organic framework (MOF) is a material with a high surface area that has been widely applied in wastewater treatment. Exploiting the affinity between ferrocyanide (FC) and Cs⁺, zeolitic imidazolate framework-8 (ZIF-8) was chemically functionalized with FC, ZIF-8-FC to selectively capture Cs⁺. After functionalization, ZIF-8-FC has a hollow morphology and small FC related crystals, which might result in better migration of Cs⁺ inside ZIF-8-FC. This synergistic effect was proven by the Q_max of ZIF-8-FC, 422.42 mg g^-1, which is 15.9 times higher than that of ZIF-8. Additionally, ZIF-8-FC retained its good adsorption performance within a pH range of 3-11 and an excellent Cs⁺ selectivity even in artificial seawater conditions. The structure of ZIF-8-FC after adsorption proves its stability. Furthermore, the thermodynamic adsorption implied that higher temperatures are more favorable for Cs⁺ uptake. This work demonstrates the remarkable adsorption and selectivity of ZIF-8-FC, which make it a promising candidate for remediation of radioactive Cs⁺.

Microwave irradiation assisted sodium hexametaphosphate modification on the alkali-activated blast furnace slag for enhancing immobilization of strontium

An inadvertent leakage of ⁹⁰Sr into the environment can induce an easy accumulation in biosphere and cause a continuous radiation to the surrounding ecosystem. In this study, sodium hexametaphosphate (Na₆O₁₈P₆) was employed to modify the blast furnace slags (BFS) to enhance the chemical stabilization of Sr²⁺ ions in the BFS-based cementitious materials. Microwave irradiation (MW) was used to further increase the binder activity of BFS samples and strengthened the mechanical strengths and durability of BFS-based blocks. A combination of experimental factors including the mass ratio of Na₆O₁₈P₆ to BFS-Sr_0.1 of 15%, the ratio of solid to liquid of 1:4 mg/L, the output power of 650 W, and the activation time of 3 min was most conductive to achieving an optimal microwave-irradiation process. Four extraction solutions were sorted by their leaching abilities following as MgSO₄ solution > H₂SO₄ solution > CH₃OOH solution > deionized (DI) water based on their leaching results. Compared with microwave irradiation, an addition of Na₆O₁₈P₆ to BFS samples obtained a better compressive strength for BFS-based blocks. However, a microwave-irradiation treatment was more effective in improving the resistances of blocks to gamma irradiation and thermal-thaw changes. Exposing to gamma irradiation over 6 months and enduring to thermal-thaw tests over 15 cycles, the microwave-treated blocks only lost 3.29% and 2.23% of leaching removal efficiencies in deionized water, respectively. Microwave irradiation increased the mechanical strengths of BFS-based blocks and inhibited leaching of Sr²⁺ ions from matrices mainly by strengthening hydration reactions and Sr²⁺ encapsulation.