First successful synthesis of an Al-rich mesoporous aluminosilicate for fast radioactive strontium capture

Al-rich zeolites such as NaA (Si/Al = 1.00) have been widely applied to remove radioactive ⁹⁰Sr²⁺ because of their high surface charge density enabling efficient ion-exchange of multivalent cations. However, due to the small micropore diameters of zeolites and large molecular size of strongly hydrated Sr²⁺, Sr²⁺-exchange with zeolites suffers from very slow kinetics. In principle, mesoporous aluminosilicates with low Si/Al ratios close to unity and tetrahedrally coordinated Al sites can exhibit both high capacity and fast kinetics in Sr²⁺-exchange. Nonetheless, the synthesis of such materials has not been realized yet. In this study, we demonstrate the first successful synthesis of an Al-rich mesoporous silicate (ARMS) using a cationic organosilane surfactant as an efficient mesoporogen. The material exhibited a wormhole-like mesoporous structure with a high surface area (851 m² g^-1) and pore volume (0.77 cm³ g^-1), and an Al-rich framework (Si/Al = 1.08) with most Al sites tetrahedrally coordinated. Compared to commercially applied NaA, ARMS exhibited a dramatically improved Sr²⁺-exchange kinetics (>33-fold larger rate constant) in batch adsorption while showing similarly high Sr²⁺ capture capacity and selectivity. Due to the fast Sr²⁺-exchange kinetics, the material also exhibited 3.3-fold larger breakthrough volume than NaA in fixed-bed continuous adsorption.

Sensitive and accurate methods for determination of low activity level of 90Sr and 137Cs in grass/vegetable samples

Sensitive, precise and accurate methods for determination of low activity level of ⁹⁰Sr and ¹³⁷Cs in grass/vegetable samples by a low background β-counter were developed. The method for ⁹⁰Sr determination was based on coprecipitation as carbonate, elimination of ²¹⁰Bi and iron with a Microthene-TOA column, separation of ⁹⁰Y with a Microthene-HDEHP column, and source preparation as Y₂(C₂O₄)₃. The method for ¹³⁷Cs determination was based on Cs adsorption on ammonium molybdophosphate and precipitation as Cs₃Bi₂I₉ for source preparation. The quality control tests indicated that the methods could provide accurate results. The method application showed that: (1) The mean yields of yttrium and cesium were 79 ± 6% and 84 ± 2%, respectively. (2) The activity concentrations of ⁹⁰Sr in 9 grass/vegetable samples were in the range of 0.04-1.8 Bq kg^-1, while that of ¹³⁷Cs in the range of 0.022-0.18 Bq kg^-1. And (3) the uptake rate of ⁹⁰Sr from soil to grass/vegetable was much higher than that of ¹³⁷Cs.

Recent developments in nanostructured inorganic materials for sorption of cesium and strontium: Synthesis and shaping, sorption capacity, mechanisms, and selectivity-A review

Liquid wastes containing non-ferrous heavy metal ions and some radionuclides, ¹³⁷Cs and ⁹⁰Sr in particular, represent one of the most dangerous sources of environmental contamination. The remediation of wastewater containing such pollutants continue to be among the biggest challenges of Sustainable Development and Environmental Safety. Sorption-based technologies have proven their efficiency also in reducing the radionuclide content in aqueous streams to low-level residual activity, with the concomitant decrease in the amount of ultimate solid waste generated. Although sorption of cesium and strontium by resins, clays, and zeolites has been investigated intensively and even used in real applications, there is still considerable scope for improvement in terms of retention capacity and selectivity. Recent progress in design and preparation of nanostructured inorganic materials has attracted growing interest based on the potential for improving the retention performance when coupling such functionalities as ion exchange capacity, structural flexibility that may result in steric retention effects, as well as the propensity to interact specifically with the target metal cations. Titanate, vanadate, and tungsten based materials, manganese oxides, hexacyanoferrates, metal sulfides, ammonium molybdophosphates, or hydroxyapatite, characterized by various structures and morphologies, are reviewed with the emphasis being put on synthesis and shaping of such materials, their structure in relationship with the capacity and selectivity of trapping cesium and strontium from either single or multi-component aqueous solutions, as well as the possible retention mechanism. The potential candidates for remediation uses are selected with regard to their sorption capacity and distribution coefficient towards target cations, and also the pH window for an optimum cation capture.

Synthesis and radiometric evaluation of diglycolamide functionalized mesoporous silica for the chromatographic separation of actinides Th, Pa and U

Grafting of DGA on mesoporous silica affords a sorbent with the potential to separate U from Pa and Th.

The novel composite mechanism of ammonium molybdophosphate loaded on silica matrix and its ion exchange breakthrough curves for cesium

Long-lived ¹³⁷Cs (over 30 years), a byproduct of the spent fuel fission processes, comprises the majority of high-level and prolific heat-generating waste in downstream processing. This study reports a novel sequential annealing mechanism with cross-linked network of polyvinyl alcohol, fabricating the composite of ammonium molybdophosphate loaded on silica matrix (SM-AMP20, 20wt% AMP) as an excellent granular ion exchanger for removal Cs⁺. When the matrix is remarkably sequential annealed, well-dispersed SM-AMP20 particles are formed by firmly anchoring themselves on controlling the porous characteristics and stable structure. The material crystallizes in the complex cubic space group Pn-3m with cell parameters of crystalline AMP formation. The breakthrough curve of Cs⁺ by SM-AMP20 follows the Thomas model with a high removal rate of 88.23% (∼10mg/L of Cs⁺) and breakthrough time as high as 26h (flow rate Q≈2.5mL/min and bed height Z≈11cm) at neutral pH. We also report on sorbents that could efficiently remove Cs⁺ ions from complex solutions containing different competitive cations (Na⁺, Al³⁺, Fe³⁺, and Ni²⁺, respectively) in large excess. Furthermore, this study shows that there is a probability for SM-AMP20 to recycle cesium using an eluent of 2-3mol/L NH₄NO₃ solution.

Fabrication of calix[4]arene-attached mesoporous ammonium molybdophosphate–silica hybrid and its application as an adsorbent for cesium ions

The cesium cation is a common contaminant in medical and industrial products as well as in nuclear wastes, and it can present a serious risk to human health.

Functionalization of mesoporous materials for lanthanide and actinide extraction

Recent advances in the field of functionalized mesoporous solid-phase sorbents designed for rare earth element and actinide separation/concentration could provide answers to limitations occurring in the industrial separation processes of these critical elements.

Synthesis of SBA-15 encapsulated ammonium molybdophosphate using Qaidam natural clay and its use in cesium ion adsorption

The ordered hexagonal mesoporous silica (SBA-15) encapsulated ammonium molybdophosphate (AMP) was successfully synthesized using low-grade natural clay from Qaidam Basin as silica and aluminum source, through a one-pot synthesis method.