A novel method for separating Cs<Superscript>+</Superscript> from liquid radioactive waste using ionic liquids and a selective extractant

Selective separation of Cs ⁺ from liquid radioactive waste by “precipitation” was observed in a hydrophobic ionic liquid containing the Cs ⁺ -selective extractant dicyclohexano-18-crown-6. The precipitate was formed by the cation exchange mechanism, which simplified the treatment of Cs ⁺ after extraction. Solid–liquid extraction is a more economical extraction system than liquid–liquid extraction because it uses smaller quantities of ionic liquids. This work showed the possibility of developing a new method for removing Cs ⁺ from liquid radioactive waste using solid–liquid phase separation instead of the conventional liquid–liquid separation in an ionic liquid extraction system.     

Spontaneous reductive decomposition behavior of hydrogen permanganate in water for chemical decontamination of nuclear power plants

The spontaneous reductive decomposition behavior of HMnO₄ in water as a function of the initial HMnO₄ concentration and reaction temperature was investigated. The decomposition of HMnO₄ was fast in the early stage of the reaction and thereafter slowed down significantly, regardless of the initial HMnO₄ concentration. The loss of HMnO₄ by spontaneous reductive decomposition increased with increasing reaction temperature. Based on the experimental results and the classical nucleation theory, a mathematical model was developed using a combination of two first-order reactions representing the nucleation and crystal growth of MnO₂ to predict the spontaneous reductive decomposition behavior of HMnO₄.     

Studies on a new solid–liquid Cs separation using the ionic liquid extraction system in comparison with the conventional adsorption

The process characteristics of a new solid–liquid Cs⁺ separation from the radioactive liquid waste using a crown ether dicyclohexano-18-crown-6 as an extractant and an ionic liquid of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide were studied. The physicochemical properties of the precipitate containing Cs⁺ which is an solid–liquid extraction product were investigated to identify the solid–liquid phase separability and Cs⁺ loading. The Cs⁺ separation process performances were compared experimentally with those of the conventional adsorption system for pretreatment requirement and the amount of Cs⁺ waste. It was observed that the solid–liquid separation method using ILs has high Cs⁺ separation performance especially in the low Cs⁺ concentration.

     

Removal of cobalt and strontium from groundwater by sorption onto fishbone

Fishbone as a main backfill material of permeable reactive barrier to remediate groundwater contaminated with Co and Sr was investigated through single- and bi-solute competitive sorptions. The single-solute sorption data were fitted by Freundlich, Langmuir and Dubinin-Radushkevich models. The coefficients of determination (R ² > 0.91) indicated that all models fitted well. Maximum sorption capacities (q _mL ) of Co and Sr predicted by the Langmuir model were 0.55 mmol/g and 0.50 mmol/g, respectively. The bi-solute competitive sorption of the metals was analyzed by the Langmuir, competitive Langmuir, Sheindorf-Rebhun-Sheintuch (SRS) and P-factor models. The sorbed amount of one solute in bi-solute system decreased due to competition with the other solute. Langmuir model parameters for single- (q _mL and b _L ) and bi-solute (q _mL ^* and b _L ^* ) competitive sorptions were compared to analyze the effect of competition between the metals. The competitive Langmuir, SRS and P-factor models predicted the bi-solute competitive sorption data well (R ² > 0.93).     

Effect of chlorine on adsorption/ultrafiltration treatment for removing natural organic matter in drinking water

In drinking water treatment, prechlorination is often applied in order to control microorganisms and taste-and-odor-causing materials, which may influence organics removal by adsorption and membrane filtration. Thus, the addition of chlorine into an advanced water treatment process using a hybrid of adsorption and ultrafiltration (UF) was investigated in terms of natural organic matter (NOM) removal and membrane permeability. A comparison between two adsorbents, iron oxide particles (IOP) and powdered activated carbon (PAC), was made to understand the sorption behavior for NOM with and without chlorination. Chlorine modified the properties of dissolved and colloidal NOM in raw water, which brought about lower TOC removal, during IOP/UF. The location of IOPs, whether they were in suspension or in a cake layer, affected NOM removal, depending on the presence of colloidal particles in feedwater. Chlorine also played a role in reducing the size of particulate matter in raw water, which could be in close association with a decline in permeate flux after chlorination.     

Modeling manganese removal in chelating polymer-assisted membrane separation systems for water treatment

The removal of manganese from groundwater, using water-soluble chelating polymers such as polyacrylic acid (PAA) in combination with ultrafiltration (UF), was investigated. The effects of the solution pH and polymer dosages on the manganese removal were evaluated, and the removal efficiency was modeled considering the relevant chemical equilibria. In the absence of polymer, manganese removal with UF membranes alone was negligible at acidic pH values, but the removal increased substantially when polyacrylic acid (PAA) was added to the feed solution. The increase can be attributed to the formation of Mn²⁺–PAA chelates which are rejected by the membranes. A mathematical model was developed to explain this phenomenon based on chemical equilibria, including complex formation and precipitation. The chelation number (i.e., the number of carboxyl groups in the PAA binding to a single metal ion) and the equilibrium constants for metal–PAA chelation reactions were obtained by fitting experimental data at acidic pH in single-divalent metal systems. The model was able to predict Mn removal in chelation/UF systems at various pH levels and polymer dosages, and to account for the competitive interactions of PAA with the target (Mn²⁺) and background species (Ca²⁺, Mg²⁺) in multi-component systems. The predicted Mn removal efficiency was most sensitive to the chelation number.     

Sorptive removal of cobalt, strontium and cesium onto manganese and iron oxide-coated montmorillonite from groundwater

Applicability of montmorillonite, manganese oxide-coated montmorillonite (MOCM) and iron oxide-coated montmorillonite (IOCM) as backfill materials in permeable reactive barrier (PRB) to remediate contaminated groundwater was investigated. Single- and bi-solute competitive sorptions of Co, Sr and Cs were conducted. The Freundlich, Langmuir and Dubinin-Radushkevich models fitted the single-solute sorption data well (R ² > 0.95). Maximum sorption capacities (q _mL) of Co and Sr predicted by the Langmuir model were in the order of MOCM (0.37 mmol/g for Co and 0.28 mmol/g for Sr) > montmorillonite (0.27 mmol/g for Co and 0.19 mmol/g for Sr) ≈ IOCM (0.23 mmol/g for Co and 0.21 mmol/g for Sr), while those of Cs were in the order of montmorillonite (1.11 mmol/g) > MOCM (0.68 mmol/g) > IOCM (0.62 mmol/g). In the bi-solute sorptions, the sorbed amount of one solute decreased due to the presence of the other competing metal ion. Langmuir model parameters for single-solute (q _mL and b _L) and bi-solute ( q_\textmL^* q_{\text{mL}}^{*} and b_\textL ^* b_{\text{L}}^{ *} ) sorptions were compared to analyze the effect of competition between the metal ions. The competitive Langmuir (R ² > 0.81) and P-factor (R ² > 0.82) models predicted the bi-solute competitive sorption data well but not the SRS model (0.003 < R ² < 0.97).     

Amine-functionalized graphene oxide/zinc hexacyanoferrate composites for cesium removal from aqueous solutions

Journal of Radioanalytical and Nuclear Chemistry - Amine-functionalized graphene oxide/zinc hexacyanoferrate (amino-rGO/ZnHCF) composites were successfully synthesized for the removal of Cs+ from...