Sorption Behavior of Cesium and Strontium Ions on Mixtures of Clay Sorbents

The sorption behavior of Cs and Sr ions on natural clay minerals such as sand, bentonite and loam, and mixtures of bentonite-sand and loam was studied under static condition.

It was found that the distribution ratio of Sr ion on bentonite and loam are influenced by loam concentration of solution, along with the concentration of ion of interest. The obtained results revealed that the distribution ratio of ion the clay mixture can be expressed,in terms of distribution ratio of each constituent of the mixed sorbent, provided that the corrections for pH and sorbed ion concentration of solution are made.     

Migration of Cesium,Strontium and Cobalt in Water-Saturated Inada Granite

Diffusivities of C_s, Sr and Co were measured in a water-saturated granite in an attempt to investigate the migration of radionuclides into the matrix of the rock. The measured penetration profiles of every tracer were composed of two parts. There were a steep slope near the surface and a gradual slope in the deeper part. These profiles were successfully explained by considering two diffusion paths in the granite. One diffusion path was fissure with a width of a few microns and another was network of submicron pores. The volume of submicron pores was approximately 80% of the total pore volume in the granite. The orders of magnitude of apparent diffusivities for all nuclides were 10^?11 to 10^?12m²/s through the fissure and 10^?14 m²/s through the network of pores. The ratio of geometrical factors in the two paths was also calculated from each apparent diffusivity and was almost unity. This calculated ratio suggests that the pore network in the granite matrix has a similar shape to the fissure, thus the microstructure of the granite seems to be fractal.     

Selective Uptake of Cesium by Ammonium Molybdophosphate (AMP)-Calcium Alginate Composites

The uptake properties of Cs+ for ammonium molybdophosphate (AMP, (NH₄)₃PMo₁₂O₄₀.3H₂O) and its composite with alginate gel polymer have been studied by the batch and column methods. The free energy for the ion exchange ([NH⁺ ₄]_ad+Cs⁺NH⁺ ₄+[Cs⁺]_ad) was found to have a relatively low value of -9.7 kJ/mol compared to other inorganic ion exchangers, indicating high selectivity of AMP for Cs⁺ ions. The fine crystals of AMP exchanger were granulated with calcium alginate (CaALG) gel polymer as an immobilization matrices. The uptake rate of Cs+ for AMP-CaALG composite was fairly fast and the uptake attained equilibrium within 3 h; the uptake was above 96% even in the presence of 5M (=mol/dm³) NaNO₃. The distribution coefficient of Cs+, Kd-Cs, decreased in the order of coexisting ions, H⁺>Na⁺>K+>NH⁺. In a wide HNO₃ concentration region of 10^-2-5M, the K_d,cs value for the composite was around 10⁴cm³/g, while those for other elements, Na⁺, Sr²⁺, Co²⁺, Eu³⁺ and Am³⁺, were less than 10²cm³/g. The uptake of Cs⁺ followed a Langmuir adsorption isotherm, and the uptake capacity of Cs⁺ increased with the content of AMP immobilized in the composite. The trace amounts of Cs⁺ in the presence of HNO3 were selectively adsorbed on the composite column.     

Separation of Heat-Generating Nuclides from High-Level Liquid Wastes through Zeolite Columns

Heat-generating nuclides Cs and Sr were separated from simulated high-level liquid wastes (HLLW) by successive adsorption on columns of ferrierites (F) and zeolite A. Adsorbed Cs and Sr were efficiently eluted with NH₄NO₃ and EDTA solutions, respectively, yielding the recovery over 96%. A simulated waste solution containing 29 components was denitrated with a formic acid up to pH 7.92. The amounts of nuclides adsorbed from this denitrated solution were experimentally estimated to be 0.33 mmol Cs/g·F and 0.19 mmol Sr/g·A, respectively.     

Diffusion Behavior of Cesium,Strontium and Cobalt in Pellet Waste Package

A leaching model for a radioactive pellet package for nuclear power plant wastes was studied. Calculated results obtained in term of the model were compared with experimental ones, where volumetric averages of diffusion coefficients in the Na₂SO₄ pellet and in the cement-glass were used to solve the diffusion equation in the pellet package. Since Na₂SO₄ pellets dissolved quickly, the pellet part were simulated by saturated Na₂SO₄ solution. The leaching ratios were meaured with different volume ratios of cement-glass in the package to discuss the validity of the model. The cement glass diffusion coefficient and distribution factor, which were required to solve the equation, were also measured. The calculated results agreed with the experimental ones within a 20% error.     

Alkali Hydrothermal Synthesis of Zeolites from Coal Fly Ash and Their Uptake Properties of Cesium Ion

Zeolites were synthesized from coal fly ash by hydrothermal treatment with KOH solutions. K-H zeolite (K₂Al₂Si₄O₁₂-nH₂O) was produced under optimum conditions of 160°C, 3 d, 1 M (=mol/dm³) KOH and liquid-solid ratio of 15cm³/g. The uptake behavior of radioactive cesium for the products was investigated by batch and column methods. The uptake equilibrium of Cs+ for the above product was attained within 2h yielding the distribution coefficient of above 10⁴ cm³/g. The uptake of Cs⁺ was followed by a Langmuir adsorption isotherm and the maximum uptake capacity was estimated to be 3.34 mmol/g. The successive removal of Cs⁺ was accomplished through the column packed with granular composites of product-alginate gel polymer.     

Analysis of Adsorption Behavior of Cesium onto Quartz Using Electrical Double Layer Model

The adsorption behavior of Cs onto quartz was investigated with the use of a high performance liquid chromatograph. The surface-based distribution coefficient (K_a) of Cs onto quartz was determined in the solution of which pH ranged from 6 to 11 and ionic strength from 10^?3 M to 10^?1 M. The K_a values were found to increase with increasing pH and with decreasing ionic strength. The obtained data were successfully analyzed by an electrical double layer model and the optimum parameter values of the double layer electrostatics and adsorption reactions were obtained. The adsorption mechanisms of alkali metal ions was discussed on the basis of the present analysis.     

Migration of Radionuclides (60Co, 85Sr and 137Cs) in Alkaline Solution (pH 12) through Sandy Soil Layer

Column experiments have been carried out on the migration of ⁶⁰Co, ⁸⁵Sr and ¹³⁷Cs in an alkaline solution (pH 12) through a sandy soil layer. Radionuclide--concentration distributions in both an effluent and a sandy soil layer were measured after pouring 200ml of aqueous solution containing the radionuclides on the layer, followed by eluting with 3,800 ml of distilled water.

Strontium-85 and ¹³⁷Cs gave a similar distribution pattern in the soil layer, while ⁶⁰Co migrated deeper into the layer. The migration velocity followed the order; ⁶⁰Co>⁸⁵Sr≧¹³⁷Ca. The order was different from that obtained with the radionuclides existed in a neutral solution. This suggested that the migration behavior of the radionuclides is significantly affected by the pH of the solution in which the radionuclides exist.

The sandy soil layer used here is considered as a linear system for the migration of in the solution of pH 12.     

Sorption and Desorption Behavior of 60Co, 85Sr,and 137Cs in a Porous Tuff

Sorption experiments of ⁶⁰Co, ⁸⁵Sr and ¹³⁷Cs were carried out to study sorption characteristics onto a porous tuff. Sorption kinetics and rate controlling step were examined. The effects of particle size on sorption and distribution ratio were also investigated. Desorption experiments were carried out by using extracting reagents to distinguish sorption mechanisms such as reversible sorption in groundwater condition, ion exchange, association with ferro-manganese oxides or oxyhydroxides, and irreversible fixation. Strontium sorbed onto the tuff surface mainly by the ion exchange reaction which was fast and reversible. Cobalt and cesium do not sorb by simple step. The main sorptive binding of cobalt was the association with ferro-manganese oxides and the secondary one was the irreversible fixation. Diffusion into the lattice of rock minerals controlled the sorption rate of cobalt. The main sorption of cesium was the irreversible fixation, secondary one was the ion exchange.     

Synthesis of a Magnetic Composite Resin and Its Cobalt Removal Characteristics in Aqueous Solution

A series of stepwise procedures to prepare a new organic-inorganic composite magnetic resin with phenolsulphonic-formaldehyde and freshly formed iron ferrite was established, based upon wet-and-neutralization method for synthesizing iron ferrite and pearl-polymerization method for synthesizing rigid bead-type composite resin. The ion exchange and sorption characteristics of the composite resin prepared by the above method at various conditions were experimentally disclosed. The composite resin prepared shows stably high removal efficiency to Co(II) species in aqueous solution in a wide range of solution pH. The overall isotherm is qualitatively explained by the generalized adsorption isotherm concept proposed by McKinley. The standard enthalpy change derived from van't Hoff equation conforms to the typical range for chemisorption or ion exchange. The selectivity of the PSF-F (phenolsulphonic formaldehyde-iron ferrite) composite resin to Co(II) species and other competing chemicals (i.e. Na₂EDTA, Ca(II) and Na) was compared. It is anticipated that the composite resin can also be used for column-operation with process-control by applying external magnetic field, since the rigid bead-type composite resin shows magnetic-susceptibility due to its paramagnetic inorganic constituent (i.e. iron ferrite).