Adsorption and separation behavior of strontium and yttrium using a silica-based CMPO adsorbent

Review on Synthesis of Silica-Based Hybrid Sorbents and Their Application in Radionuclide Separation and Removal via Chromatographic Technique

The efficient separation and removal of key nuclides is important for the nuclear fuel cycle from the aspects of radioactivity reduction and potential resource recycling. The urgent objective is to design and develop functional materials for the separation and removal of important nuclides. Porous silicon-based adsorbents are considered highly advantageous materials for separating and removing radioactive nuclides in complex environments due to their excellent mechanical properties, high porosity, and functionalization ability. In this review, we compiled the applications of porous silica-based materials in recent years in the separation and removal of key nuclides, such as actinides, lanthanides, strontium, cesium, iodine, and platinum group metals; discussed their separation and removal performances; analyzed the constitutive relationship between key radionuclides and porous silica-based adsorbents; and systematically described the properties and mechanisms of different types of porous silica-based adsorbents. This article aims to provide some ideas for the design of an advanced separation process in the nuclear fuel cycle.

A negatively-charged supramolecular trap for precisely catching strontium ion

Due to the analogous physicochemical properties and weak coordination ability of alkali and alkaline earth metals, accurate separation of radioactive 90Sr from groundwater or seawater still presents a big challenge in environmental radioactivity remediation. Here we mimic the complexation behavior of molecular crown-ether carboxylic acids to construct an elegant negatively charged supramolecular trap in an anionic crown ether-based metal-organic framework (ZJU-X99) for precisely catching Sr2+. Owing to the synergistic effects of electrostatic interactions arising from the In(COO)4- nodes and supramolecular host-guest recognition from the 18-crown-6 rings, ZJU-X99 exhibits rapid adsorption kinetics (1 min), high adsorption capacity (263 mg/g), and exceptional selectivity for Sr2+ even when 1000-fold of Na⁺, K⁺ and Cs⁺ coexist. Relative to alkali metals, Sr2+ ions are intricately ensconced within the supramolecular trap, resulting in lowest binding energy and minimal structural alterations. Dynamic column experiments and radioactive 90Sr decontamination trials further validate its practical application prospects. Our findings offer valuable insights into the design of supramolecular frameworks featuring tailored binding sites for targeted ions.

Development of N,N,N',N'-tetra-2-ethylhexyl-thiodiglycolamide silica-based adsorbent to separate useful metals from simulated high-level liquid waste

A novel silica-based adsorbent was synthesized by impregnating macroporous silica polymer composite (SiO₂-P) particles with a mixture of N,N,N',N'-tetra-2-ethylhexyl-thiodiglycolamide (TEHTDGA) and tri-n-octylamine (TOA). Then, the possibility of separating Pd(II) and other metal ions from simulated high-level liquid waste (HLLW) using the newly synthesized adsorbent (TEHTDGA + TOA)/SiO₂-P was evaluated based on various adsorption characteristics obtained via batch-adsorption experiments, such as the HNO₃ concentration, contact time, reaction temperature, adsorption isotherm, and chemical stability of the adsorbent. Furthermore, column separation experiments were performed based on the characteristics obtained from the batch-adsorption experiment, and the possibility of simultaneous separation of multiple metal ions was examined. The experimental results revealed that (TEHTDGA + TOA)/SiO₂-P performs well in the separation of multiple metal ions from simulated HLLW.

An asymmetric pulsed current-assisted electrochemical method for Sr(Ⅱ) extraction using supramolecular composites

The development of effective, economical, and sustainable seawater extraction strontium techniques is of great significance to the environment and industrial needs. In this paper, an asymmetric pulsed current-assisted electrochemical (AP-CE) method was used to extract Sr(Ⅱ) from seawater using a carbon electrode modified by dibenzo-18-crown-6-ether and cellulose acetate. An asymmetric pulsed current was used to prevent unwanted cations from blocking adsorption sites to prevent water splitting. It also prevented the cellulose acetate membrane from sealing the crown ether. Compared with traditional physicochemical adsorption of Sr(Ⅱ), the AP-CE method achieved a higher removal efficiency and adsorption capacity. When the concentrations of Sr(Ⅱ) were 10, 20, 50, and 100 mg L^-1, the removal efficiencies of Sr(Ⅱ) were 99.3%, 97.6%, 97.3%, and 96.1%, and the adsorption capacities of Sr(Ⅱ) were 14.9, 29.3, 73.0, and 144.2 mg g^-1, respectively. This method exhibited excellent selectivity for Sr(Ⅱ) adsorption from simulated seawater, suggesting that the asymmetric pulse electrochemical method is promising for extracting strontium ions from seawater.

Amidoxime Functionalization of Algal/Polyethyleneimine Beads for the Sorption of Sr(II) from Aqueous Solutions

There is a need for developing new sorbents that incorporate renewable resources for the treatment of metal-containing solutions. Algal-polyethyleneimine beads (APEI) (reinforced with alginate) are functionalized by grafting amidoxime groups (AO-APEI). Physicochemical characteristics of the new material are characterized using FTIR, XPS, TGA, SEM, SEM-EDX, and BET. AO-APEI beads are tested for the recovery of Sr(II) from synthetic solutions after pH optimization (≈ pH 6). Uptake kinetics is fast (equilibrium ≈ 60-90 min). Sorption isotherm (fitted by the Langmuir equation) shows remarkable sorption capacity (≈ 189 mg Sr g-1). Sr(II) is desorbed using 0.2 M HCl/0.5 M CaCl2 solution; sorbent recycling over five cycles shows high stability in terms of sorption/desorption performances. The presence of competitor cations is studied in relation to the pH; the selectivity for Sr(II) is correlated to the softness parameter. Finally, the recovery of Sr(II) is carried out in complex solutions (seawater samples): AO-APEI is remarkably selective over highly concentrated metal cations such as Na(I), K(I), Mg(II), and Ca(II), with weaker selectivity over B(I) and As(V). AO-APEI appears to be a promising material for selective recovery of strontium from complex solutions (including seawater).