This paper is a study on a stable destruction method of radioactive waste ion exchange resins. According to the resin TGA
results, its decomposition occurred through three stages. And a sufficient retention time of the resins and an effective retention
capacity of SO2 gases and the doped metal compounds were required to destruct resins doped with radioactive metals stably. The resins doped
with radioactive metal surrogates were effectively destructed in the lab-scale MCO system. CO and SO2 emissions were below 100 and 1 ppm, respectively. And the surrogates were collected more than 99.9% in the molten carbonate.
Thus, the resins can be destructed stably in the MCO process.
Authors:H. Shin, B. Lee, H. Yang, S. Yun, and H. Moon
Complexation of trivalent europium by a well characterized soil fulvic acid was investigated by equilibrium dialysis titration method ([FA]=24 mg·dm–3, [Eu]t=9.0·10–7–3.5·10–6 mol·dm–3, pH 6.0). The concentrations of the fulvate bound and free europium were measured radiometrically using152Eu as a tracer. The experimental results were evaluated using a bimodal normal distribution model and a plot with two overlapping normal distributions was obtained which gave two means logK (µI=7.0,
II=0.5) values for binding of europium by two classes of sites in fulvic acid. A multiligand model was assumed for fulvic acid, based upon the Eu(III) luminescence studies (7F05D0 excitation) on many organic acids as model ligands.
A preconcentration method of 13 rare earth elements (REES) was studied for neutron activation ananlysis (NAA). Hydrated magnesium oxide was used as the preconcentration agent to absorb the REES ions from aqueous solution onto the solid magnesium oxide, which was separated and analyzed. It was observed that the Langmuir equation for isothermal adsorption was well obeyed by the REES under the condition studied. The efficiency of the preconcentration process using hydrated magnesium oxide was critically examined for each of REE and for mixture of REES by preparing a known volume of solution containing known amount of trace REES. NAA was used to analyze REES recovered by the preconcentration process. It was found that the REES recoveries were satisfactory and the preconcentration process is reliable. There are several resort resort areas in Taiwan where local people are enjoying its hot spring water. It is generally believed that the hot spring water spa would bring about some sorts of therapeutic functions. The preconcentration method developed above, was applied to analyze the trace amounts of REES in hot spring wate in Taiwan.
The distributions of 210Po and 210Pb in the intermediate layer (400–2000 m) of the northwestern North Pacific were determined to elucidate the export flux of
particulate matter. 210Po generally showed depletion relative to 210Pb in the intermediate layer, suggesting that 210Po was scavenged by particles. Because the removal rate constants of 210Po in the western region were higher than those in the eastern region and this trend coincided with that of the particle fluxes
in the surface layer, the export production in the surface layer was assumed to influence the particle flux in the intermediate
layer of the northwestern North Pacific.
The stability constants of Eu3+ and Am3+ with the site specific humic acid (YKHA) have been determined. The humic acid has been extracted from the soil of Yongkwang
area belonging geologically to the Okchon Basin of the Korean Peninsula, where the nuclear power plant is located. The total
carboxylate capacity, the acidity constant (pKa), and the binding constants with Eu3+ and Am3+ have been determined for humic acid.
The complexation of Eu3+ and Am3+ ions with the humic acids has been investigated at various pH (4.0, 4.5, 5.0, 5.4) in 0.1M NaClO4 solution using solvent extraction technique. Two humic acids are used in this study: humic acid extracted from the soil of Taejon on the Okchon Basin of Korea (TJHA) and commercially available one from Aldrich Chemical Co. (AHA). The total carboxylate group concentrations were determined to be 3.58 meq/g and 4.59 meq/g for Taejon and Aldrich humic acids, respectively. The conditional stability constants (log
1 and log
2), dependent on the pH of the solution, of the complexes of Eu3+ and Am3+ ions with the humic acids have been determined at the ionic medium of 0.1M NaClO4. The values of stability constants with the degree of ionization of TJHA for Eu and Am complexes are quite well agreed with those of Lake Bradford humic acid (LBHA), indicating that structural characteristics of TJHA and LBHA may be quite similar to one another.
Authors:H. Yang, Y. Cho, H. Eun, E. Kim, and I. Kim
Kinetics of a thermal dechlorination and oxidation of gadolinium oxychloride (GdOCl) originating from a molten salt process
was investigated under various oxygen partial pressures by using a non-isothermal thermogravimetric (TG) analysis. The results
of isoconversional analysis of the TG data suggests that the dechlorination and oxidation of GdOCl follows a single step reaction
and the observed activation energy was determined as 137.7�4.1 kJ mol−1. The kinetic rate equation was derived for a conversion of the GdOCl with a linear-contacting boundary reaction model. The
power dependency for oxygen and the pre-exponential factor was determined as 0.306 and 1.012 s−1 Pa−0.306, respectively.
Authors:H. Eun, H. Yang, Y. Cho, H. Park, H. Lee, and I. Kim
Distillation and condensation characteristics of LiCl-KCl eutectic salts containing rare earth precipitates were investigated
and a conversion of the rare earth oxychlorides to oxides was performed. The distillation flux was increased by about 1,000
times by reducing the pressure from 760 Torr to 0.5 Torr. The composition of the recovered salts was changed according to
the condensed spot. The conversion temperature of the multicomponent oxychlorides was decreased when compared to that of a
single component. It was found that the concentration of the chloride gas in the flue gas is an index to establish whether
the conversion is completed or not.
Authors:H.-S. Kim, H.-S. Yang, H.-J. Kim, and H.-J. Park
The thermal degradation and thermal stability of rice husk flour (RHF) filled polypropylene (PP) and high-density polyethylene
(HDPE) composites in a nitrogen atmosphere were studied using thermogravimetric analysis. The thermal stability of pure PP
and HDPE was found to be higher than that of wood flour (WF) and RHF. As the content of RHF increased, the thermal stability
of the composites decreased and the ash content increased. The activation energy of the RHF filled PP composites increased
slowly in the initial stage until α=0.3 (30% of thermal degradation region) and thereafter remained almost constant, whereas
that of the RHF filled HDPE composites decreased at between 30 and 40 mass% of RHF content. The activation energy of the composites
was found to depend on the dispersion and interfacial adhesion of RHF in the PP and HDPE matrix polymers.
Authors:H.-S. Yang, M. P. Wolcott, H.-S. Kim, and H.-J. Kim
In the TG analysis of the bio-composites, their thermal stability was found to slightly decrease and the ash content to increase
as the lignocellulosic filler loading increased. This is a logical consequence of the lower thermal stability of the lignocellulosic
filler compared to that of the matrix polymer. The dispersion and interfacial adhesion between the lignocellulosic filler
and thermoplastic polymer were important factors affecting the thermal stability of the composite system. In order to improve
their compatibility and interfacial adhesion, the incorporation of a compatibilizing agent into the lignocellulosic material-thermoplastic
polymer composites is recommended. In the TMA analysis, the thermal expansion of the composites was found to decrease with
increasing filler loading and incorporating compatibilizing agent. Lignocellulosic filler is a suitable material for preventing
the thermal expansion of the composite materials caused by atmospheric changes.