Immobilization of NPP evaporator bottom high salt-bearing liquid radioactive waste into struvite-based phosphate matrices

Study of Modified Magnesium Phosphate Cement for Fluoride Removal

In this study, we used a novel composite material based on magnesium phosphate cement (MPC) to explore the retention of fluoride from used water. Dead-burned magnesium oxide (MgO), ammonium dihydrogen phosphate (NH4H2PO4), and a few retarders were used to create this particular substance. Several studies have corroborated the performance of using aluminum in the capture of fluoride. From this perspective, we attempted to reinforce our matrix with different quantities of aluminum, which increased the resistance of the composite in water. The optimal conditions that were obtained were evaluated and scrutinized using a range of techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transforms infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET). The adsorbents demonstrated a powerful ability to remove fluoride from contaminated water and the defluoridation capacity was evaluated at 4.84 mg/g. Equilibrium modeling was carried out, and the experimental data were expressed in accordance with the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms.

Dittmarite-type magnesium phosphates for highly efficient capture of Cs. JOURNAL OF HAZARDOUS MATERIALS 2023;453:131385. [PMID: 37043858 DOI: 10.1016/j.jhazmat.2023.131385] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The presence of cesium ions (Cs⁺) in radioactive wastewater has attracted considerable attention owing to their extreme toxic effects. Thus, there is an urgent need to develop adsorbents for Cs⁺ with high adsorption capacities (q). While phosphate-based adsorbents have advantages for their disposal, previous adsorbents have shown limited q because of their limited capacity for ion exchange, despite showing high theoretical q values. In this study, two dittmarite-type magnesium phosphates, KMgPO₄·H₂O (KMP) and NH₄MgPO₄·H₂O (NMP), were synthesized because of their ability to contain readily exchangeable cations in their interlayers. KMP and NMP demonstrated remarkable adsorption capacities for Cs⁺ (q_e^KMP = 630 mg g^-1 and q_e^NMP = 711 mg g^-1), which were the highest among all reported adsorbents and are ∼84 % of their theoretical values. Their distribution coefficients in waters with high divalent ion concentrations were low, which limits their use for the adsorption of Cs⁺ from such environments. After adsorption, KMP and NMP were structurally transformed into struvite-type CsMgPO₄·6H₂O (CsMP), which has two different stacking structures, either cubic or hexagonal, depending on the pH of the solution. The high q values of KMP and NMP enable them to reduce the volume of radioactive waste for disposal.

Minimization of radioactive waste volume from nuclear power plants using precipitation-membrane technologies

The purpose of this study is the development and experimental testing on simulation solutions of a precipitation-membrane method for fractionation of liquid radioactive waste and sorption post-treatment of the filtrate. The choice of processing method is based on the analysis of factors affecting the efficiency of ion-exchange purification of solutions; properties of complex compounds of polyvalent metals; characteristics of commercially available membrane elements and economic aspects of the preparation and disposal of radioactive waste. The basic idea is to use the internal properties of solutions to isolate polyvalent cations and acidoligands in the form of poorly soluble compounds in the volume of an inert polypropylene element, which will increase the efficiency of ion-exchange post-treatment and reduce the amount of waste. The architecture and operating parameters of the experimental setup are designed to provide favorable conditions for the formation in solution of complexes (ion pairs) of polycharged cations with acid ligands of various nature.

Toward Sustainable Cementitious Radioactive Waste Forms: Immobilization of Problematic Operational Wastes

Developing effective radioactive waste management practices is essential for ensuring the sustainability of the nuclear industry. The immobilization of radioactive wastes is one of the main activities conducted during the management of these wastes; it aims to produce a durable waste form that has sustainable performance over long periods of time. In this work, the challenges that face the design of durable cementitious waste forms are addressed for problematic operational wastes. In this respect, the problematic characteristics of evaporator concentrates, spent ion exchangers, and organic liquid wastes are overviewed, and the factors that affect the durability of their cementitious waste forms are identified. A summary of potential conventional and innovative cementitious matrices is presented by reviewing the cementation practices in national programs and recent research devoted to developing durable matrices. Finally, a guide to optimize the mix design of these waste forms was proposed that includes the selection of the testing procedure, factors that affect the waste form performance, and the optimization technique. This guide was presented with special focus on leaching tests, which are a means to test the stabilization performance of nuclear waste forms.