Activated Carbon/Transition Metal (Ni, In, Cu) Hexacyanoferrate Nanocomposites for Cesium Adsorption

Amino modified nanofibers anchored to Prussian blue nanoparticles selectively remove Cs+ from water

To improve the selective separation performance of silica nanofibers (SiO2 NFs) for cesium ions (Cs+) and overcome the defects of Prussian blue nanoparticles (PB NPs), PB/SiO2-NH2 NFs were prepared to remove Cs+ from water. Among them, 3-aminopropyltriethoxysilane (APTES) underwent an alkylation reaction with SiO2, resulting in the formation of a dense Si-O-Si network structure that decorated the surface of SiO2 NFs. Meanwhile, the amino functional groups in APTES combined with Fe3+ and then reacted with Fe2+ to form PB NPs, which anchored firmly on the aminoated SiO2 NFs surface. In our experiment, the maximum adsorption capacity of PB/SiO2-NH2 NFs was 111.38 mg/g, which was 31.5 mg/g higher than that of SiO2 NFs. At the same time, after the fifth cycle, the removal rate of Cs+ by PB/SiO2-NH2 NFs adsorbent was 75.36% ± 3.69%. In addition, the adsorption isotherms and adsorption kinetics of PB/SiO2-NH2 NFs were combined with the Freundlich model and the quasi-two-stage fitting model, respectively. Further mechanism analysis showed that the bond between PB/SiO2-NH2 NFs and Cs+ was mainly a synergistic action of ion exchange, electrostatic adsorption and membrane separation.

Synthesis of Prussian blue-embedded magnetic micro hydrogel for scavenging of cesium from aqueous solutions; Batch and dynamic investigations

A magnetic micro porous structure composite based on alginate and Prussian blue (M-SA-PB) was simply prepared for cesium removal from the aqueous solutions. The gelation and formation of PB proceeded through the same step, which made the PB homogenously distributed and firmly attached to the alginate matrix. The homogenizer was applied to break down the bulky gel structure into micro-ones, and the lyophilizer will provide the porous structure. Batch cesium sorption experiments showed that the adsorption kinetics and isotherms were attributed to the pseudo-second-order model and Langmuir isotherm. Moreover, the Cs-ion is favorably adsorbed on the M-SA-PB composite surface as a monolayer towards Cs, with a maximum adsorption capacity reach of 191.0 mg/g. Furthermore, the M-SA-PB adsorbent showed excellent adsorption selectivity of Cs from multiple-ion solutions. Our work was extended to use the M-SA-PB composite in dynamic cesium sorption. The column studies showed that the removal efficiency of Cs+ increased with increasing bed depth as well as the initial cesium concentration. Finally, as previously mentioned, the M-SA-PB could be considered an excellent Cs+ scavenger employing both batch and dynamic approaches, which makes it a promising adsorbent for practical investigations.

Efficient removal of cesium ions using Prussian blue loaded on magnetic porous biochar synthesized by one-step calcination

Prussian blue (PB) is widely used for the selective removal of radioactive cesium ions (Cs+) from aqueous solutions. Due to its small size and easy dispersion in water, PB requires a carrier that is both inexpensive and easily separable. Magnetic porous biochar (MPBC) was formed by activating starch with FeCl3 through a one-step calcination method. MPBC can be used as a carrier for Prussian blue, which is easily separated from the solution. This composite material (PB/MPBC) has a rich pore structure and maintains effective surface area, which can facilitate the penetration of Cs+ into the adsorbent. Besides, PB/MPBC exhibits high selectivity and good adsorption capacity achieving a large removal capacity of 101.43 mg/g. Thus, this study provides a novel approach for preparing composites with efficient removal of Cs+.

Efficient Co-Adsorption and Highly Selective Separation of Cs+ and Sr2+ with a K+ -Activated Niobium Germanate by the pH Control

¹³⁷ Cs and ⁹⁰ Sr are hazardous to ecological environment and human health due to their strong radioactivity, long half-life, and high mobility. However, effective adsorption and separation of Cs⁺ and Sr²⁺ from acidic radioactive wastewater is challenging due to stability issues of material and the strong competition of protons. Herein, a K⁺ -activated niobium germanate (K-NGH-1) presents efficient Cs⁺ /Sr²⁺ coadsorption and highly selective Cs⁺ /Sr²⁺ separation, respectively, under different acidity conditions. In neutral solution, K-NGH-1 exhibits ultrafast adsorption kinetics and high adsorption capacity for both Cs⁺ and Sr²⁺ (q_m ^Cs  = 182.91 mg g^-1 ; q_m ^Sr  = 41.62 mg g^-1 ). In 1 M HNO₃ solution, K-NGH-1 still possesses q_m ^Cs of 91.40 mg g^-1 for Cs⁺ but almost no adsorption for Sr²⁺ . Moreover, K-NGH-1 can effectively separate Cs⁺ from 1 M HNO₃ solutions with excess competing Sr²⁺ and M^{n +} (M^{n +}  = Na⁺ , Ca²⁺ , Mg²⁺ ) ions. Thus, efficient separation of Cs⁺ and Sr²⁺ is realized under acidic conditions. Besides, K-NGH-1 shows excellent acid and radiation resistance and recyclability. All the merits above endow K-NGH-1 with the first example of niobium germanates for radionuclides remediation. This work highlights the facile pH control approach towards bifunctional ion exchangers for efficient Cs⁺ /Sr²⁺ coadsorption and selective separation.

Nanodispersion of ferrocianides for purification of man-made contaminated water containing caesium

A method of obtaining a nanodispersion of nickel-potassium ferrocyanides intended for purification of man-made polluted waters is proposed. It is applicable to purify effluent and floor drain water at nuclear power plants, which contains caesium, strontium, cobalt, manganese and other transition metals. The optimal conditions for the synthesis of nanodispersion have been determined, which is represented by clusters of nanoparticles associated with water molecules and nitrates dispersed in a dilute solution of nickel and potassium nitrates. On the surface of the formed nanocrystals there are fragments of structures of smaller formations. The mechanism of sorption of ions of alkali, alkaline earth and transition metals is investigated considering the ion charge density. The effect of competing ions (strontium, cobalt, manganese) on the sorption of caesium is taken into account. An integrated method of purification of multi-component man-made solutions including drainage waters of nuclear power plants is based on the use of nanodispersion of nickel-potassium ferrocyanides in combination with bentonite clay, which allows removing caesium from the drainage simulator with an efficiency of 96%, and strontium and transition metal ions (cobalt, manganese, copper, iron) with an efficiency of at least 98%.

A Critical Review of the Removal of Radionuclides from Wastewater Employing Activated Carbon as an Adsorbent

Radionuclide-contaminated water is carcinogenic and poses numerous severe health risks and environmental dangers. The activated carbon (AC)-based adsorption technique has great potential for treating radionuclide-contaminated water due to its simple design, high efficiency, wide pH range, quickness, low cost and environmental friendliness. This critical review first provides a brief overview of the concerned radionuclides with their associated health hazards as well as different removal techniques and their efficacy of removing them. Following this overview, this study summarizes the surface characteristics and adsorption capabilities of AC derived from different biomass precursors. It compares the adsorption performance of AC to other adsorbents, such as zeolite, graphene, carbon nano-tubes and metal-organic frameworks. Furthermore, this study highlights the different factors that influence the physical characteristics of AC and adsorption capacity, including contact time, solution pH, initial concentration of radionuclides, the initial dosage of the adsorbent, and adsorption temperature. The theoretical models of adsorption isotherm and kinetics, along with their fitting parameter values for AC/radionuclide pairs, are also reviewed. Finally, the modification procedures of pristine AC, factors determining AC characteristics and the impact of modifying agents on the adsorption ability of AC are elucidated in this study; therefore, further research and development can be promoted for designing a highly efficient and practical adsorption-based radionuclide removal system.

Copper ferrocyanide chemically immobilized onto a polyvinylidene fluoride hollow-fibre membrane surface for the removal of aqueous cesium

A method of chemically bonding copper ferrocynide (CuFC) to the surface of a PVDF hollow-fibre membrane (PVDF-CuFC) was designed and the resulting PVDF-CuFC was applied to the effective removal of aqueous cesium (Cs). In order to chemically immobilize CuFC on the surface of the PVDF hollow-fibre membrane, carboxyl groups were introduced onto the membrane surface (PVDF-COOH) to peptide bond with amine groups from CuFC. The introduction of the carboxyl group onto the surface of the PVDF hollow-fibre membrane was confirmed by Fourier-transform infrared spectroscopy (FT-IR), while the immobilization of CuFC was confirmed by scanning electron microscopy with energy dispersed spectroscopy, FT-IR, and thermogravimetric analysis. The PVDF-CuFC showed higher Cs adsorption kinetics and adsorption capacity than PVDF-COOH. Moreover, as the initial pH increased, the amount of Cs adsorption by PVDF-CuFC also increased. However, the amount of Cs adsorption at pH 10 was slightly less. The applicability of PVDF-CuFC as a filter type adsorbent for the treatment of a Cs-contaminated water source is demonstrated by continuous filtration experiments.

Decontamination of radioactive cesium-contaminated soil/concrete with washing and washing supernatant- critical review

We reviewed washing of radioactive Cs-contaminated concrete and soil based on the fate of Cs in concrete and soil, including sorption materials for treatment of supernatant solution. In non-aged cement materials (the calcium silicate hydration (C-S-H) phase), it was possible to decontaminate Cs using ion exchange with monovalent cations, such as NH₄⁺. The clay components in the soil and aggregates were important factors in optimization of the efficiency and mechanism for Cs decontamination with washing solution. The parameters (reagent component, pH, and temperature) of the washing solution should be determined considering soil mineral type (here, weathered biotite (WB) with vermiculite), since monovalent cations such as NH₄⁺ and K⁺ can inhibit Cs decontamination due to collapse of the hydrated and expanded interlayer regions with cation exchange. In this case, hydrothermal treatment or H₂O₂ dosing was necessary to expand the collapsed interlayer region for Cs removal by washing with cation exchange or organic acids. Acid and a chelating agent significantly enhanced Cs-release with dissolution of the adsorbent layer containing iron and aluminum oxides. The important characteristics of important and emerging sorption materials for treatment of the radioactive Cs-contaminated supernatant after washing treatment are discussed. Sorbents for treatment of washing supernatant are divided in to two main categories. Clay minerals, metal hexacyanoferrates, and ammonium molybdophosphates are discussed in the inorganic class of materials. Hypercrosslinked polymers, supramolecular sorbents, carbon nanotubes, and graphene oxide are covered in the carbon-based sorbents for Cs removal from water.

CAESIUM RETENTION CHARACTERISTICS OF KNIFC-PAN RESIN FROM RIVER WATER

The caesium retention characteristics of a potassium-nickel hexacyanoferrate resin in a polyacrylnitrile (KNiFC-PAN) matrix were tested in fresh water over the range of 2.5-400 mL min-1. The experimental setup used 2 mL resin and 4-L aliquots of freshwater samples. The results showed nearly 100% retention at speeds below 10 mL min-1, above 80% up to 100 mL min-1, and approached 50% at 400 mL min-1. Using 100 mL min-1 flow rate and KNiFC-PAN resin in a well-type HPGe detector, the minimum detectable concentration was reduced to 3 mBq kg-1 for 4-L aliquots of water samples from the previous 15 mBq kg-1 achieved by Powdex ion-exchange resin and a planar type HPGe detector.