Hollow fiber supported liquid membrane studies using a process compatible solvent containing calix[4]arene-mono-crown-6 for the recovery of radio-cesium from nuclear waste

Remarkable enhancement in radio-cesium uptake from acidic feeds into an extraction chromatography resin containing a calix[4]arene-mono-crown-6 ligand

An extraction chromatography resin, prepared by the impregnation of bis-octyloxy-calix[4]arene-mono-crown-6 (BOCMC)onto an acrylic ester based polymeric support material, gave excellent uptake data for the removal of radio-cesium (Cs-137) from nitric acid feed solutions. The weight distribution coefficient (Kd) value of >300 obtained during the present study at 3 M HNO3 was the highest reported so far while using a calix-crown-6 based extraction chromatographic resin material. Analogous resin reported previously has yielded a Kd value <100 at comparable feed conditions. The sorbed metal ions could be efficiently desorbed with de-ionized water. Kinetic modeling of the uptake data indicated that both the film and the intra-particle diffusion mechanism are simultaneously operating in the sorption of Cs+ion onto the BOCMC resin. The metal ion sorption data were fitted to the sorption isotherm models and did not conform to the chemisorptions of physisorption models and indicated a pi-pi interaction between the benzene rings of the calix-crown-6 ligand and the Cs+ ion. The reusability of the resins was quite satisfactory after 5 cycles and the radiation stability of the resin material was very good upto an absorbed dose of 500 kGy. The results of column studies were quite encouraging with 15 mL (9 bed volumes) as the breakthrough volume while the elution was complete in about 12 bed volumes of de-ionized water.

State-of-the-Art Organic- and Inorganic-Based Hollow Fiber Membranes in Liquid and Gas Applications: Looking Back and Beyond

The aggravation of environmental problems such as water scarcity and air pollution has called upon the need for a sustainable solution globally. Membrane technology, owing to its simplicity, sustainability, and cost-effectiveness, has emerged as one of the favorable technologies for water and air purification. Among all of the membrane configurations, hollow fiber membranes hold promise due to their outstanding packing density and ease of module assembly. Herein, this review systematically outlines the fundamentals of hollow fiber membranes, which comprise the structural analyses and phase inversion mechanism. Furthermore, illustrations of the latest advances in the fabrication of organic, inorganic, and composite hollow fiber membranes are presented. Key findings on the utilization of hollow fiber membranes in microfiltration (MF), nanofiltration (NF), reverse osmosis (RO), forward osmosis (FO), pervaporation, gas and vapor separation, membrane distillation, and membrane contactor are also reported. Moreover, the applications in nuclear waste treatment and biomedical fields such as hemodialysis and drug delivery are emphasized. Subsequently, the emerging R&D areas, precisely on green fabrication and modification techniques as well as sustainable materials for hollow fiber membranes, are highlighted. Last but not least, this review offers invigorating perspectives on the future directions for the design of next-generation hollow fiber membranes for various applications. As such, the comprehensive and critical insights gained in this review are anticipated to provide a new research doorway to stimulate the future development and optimization of hollow fiber membranes.

Theoretical calculation assisted materials screening of BiOX (X = F, Cl, Br, I) for electrochemical absorption of cesium ions

The electrochemical switching ion exchange (ESIX) technique has been widely used for the separation and recovery of radioactive cesium ions (Cs⁺) from wastewater. In this study, a series of BiOX (X = F, Cl, Br, I) materials were first evaluated for their absorption properties to Cs⁺ through density functional theory (DFT) calculations. The calculations predict that BiOBr has the best absorption performance among the four materials, BiOF, BiOCl, BiOBr, and BiOI, due to its high absorption energy and low ion migration energy barrier to Cs⁺. Simultaneously, the selectivity calculations revealed that BiOBr also showed the best selectivity for Cs⁺ compared with Li⁺ and Na⁺. Subsequently, four materials were prepared using the hydrothermal synthesis method and their electrochemical absorption performance was tested. The results showed that BiOBr has the highest electroactivity, and its absorption capacity was up to 16 mg Cs⁺/g BiOBr in a solution mixture of 50 ppm Li⁺, Na⁺, and Cs⁺. Based on our theoretical calculations and experiments, our findings provide prospective insights for predicting the electrochemical absorption performance of materials using first-principles calculations.

Highly ordered macroporous silica dioxide framework embedded with supramolecular as robust recognition agent for removal of cesium

Owning to highly mechanical strength and non-interference effectivity, silica dioxide is often explored as a stable supporter commonly with mesopore. It is known that a macroporous framework has larger mass transfer channel, possibly beneficial to adsorption process. Herein highly ordered macroporous silica dioxide framework (homogeneous pore size of 194.20 nm) was synthesized and embedded with supramolecular (CC/OMS). Cs cation adsorption onto CC/OMS was explored under different pH (presence or absence of humic acid), initial cesium concentration, shaking time, competing ions. The robust cesium uptake capacity demonstrated by a theory adsorption amount of 150.01 mg/g highlighted unique CC/OMS properties combining large mass transfer channel and superior complex capacity of supramolecular. The adsorption was well fit with Langmuir and pseudo-second-order model. Sodium and potassium at a lower concentration showed little influence on cesium adsorption. The results demonstrated that CC/OMS was an alternative material for cesium capture from acidic aqueous solution.

Theoretical and experimental investigations of BiOCl for electrochemical adsorption of cesium ions

BiOCl was found to have excellent electrochemical adsorption properties for cesium ions (Cs⁺) in electrochemically switched ion exchange (ESIX). In this work, BiOCl nanosheets were synthesized by a hydrothermal method and used for electrochemical adsorption of Cs⁺. The experimental results showed that BiOCl exhibited higher electrochemical adsorption selectivity for Cs⁺ than Li⁺ and Na⁺. Quantum chemical calculations based on density functional theory (DFT) were first performed to compare the adsorption and migration mechanisms of three ions Li⁺, Na⁺, and Cs⁺ in BiOCl crystals. The calculation results revealed that the excellent electrochemical adsorption performance of BiOCl for Cs⁺ is due to the interaction of embedded Cs with Cl and Bi in BiOCl crystals. This makes it have a higher adsorption energy and a lower ion migration energy barrier due to the balance of interaction forces. In this work experimental and theoretical calculations were used to systematically analyze the adsorption and migration of three ions in BiOCl, which has important guiding significance for the design of highly-efficient electroactive materials for electrochemical adsorption of Cs⁺.

Stable solidification of silica-based ammonium molybdophosphate by allophane: Application to treatment of radioactive cesium in secondary solid wastes generated from fukushima

Silica-based ammonium molybdophosphate (AMP/SiO₂) is an absorbent material that can effectively remove Cs from radioactive-contaminated wastewater (RCW) generated by Fukushima nuclide accident. Pressing/sintering method was used for final disposal of secondary waste (spent absorbent) to achieve the volume reduction of AMP-Cs/SiO₂ (AMP/SiO₂ saturation adsorption of Cs) and stable solidification of Cs by adding natural allophane. The structure of AMP-Cs completely collapsed at approximately 700°C, and most Mo and P species in AMP sublimed. The optimal sintering temperature was estimated as 900°C. The stable crystalline phase of Cs₄Al₄Si₂₀O₄₈ was recrystallized by the reaction of Cs₂O, Al₂O₃, and SiO₂, and the immobilization ratio of Cs was approximately 100%. The leachability of Cs from the sintered product in distilled water was approximately 0.41%. The high immobilization and low leachability of Cs were attributed to the excellent solidification properties of the sintered products of AMP-Cs/SiO₂-allophane.