Heiichiro Obanawa

Recovery of 3%-Enriched Uranium by Means of a Chemical Method

Continuous bench-plant operation for about 4 months has resulted in the first recovery of 3%-enriched uranium by means of a chemical-exchange process. This confirms the reduced development time and uranium adsorption band stability predicted by mathematical models, which are derived by application of mass transfer concepts to redox chromatography and extension of addition reaction equilibrium equations to include multiphase systems. Furthermore, it confirms the achievement of a reduction in stage time by >10/sup 3/ through catalytic acceleration of the isotope-exchange rate and employment of an adsorbent with a high adsorption/desorption rate.

Process energy of the advanced chemical uranium enrichment process

Process energy of the chemical uranium enrichment process is discussed using the dynamic enrichment factor, avoiding a cluster of commonly used equations that correlate relevant engineering parameters. An advanced process, whose process energy was found to be much smaller than in the original process in both laboratory and bench tests, has been recently developed and applied to a pilot plant. The basic principle underlying the improvement is an inverse redox reaction induced by the increased sorbability of multi-coordinated metal-complex ions onto an ion-exchange resin. The energy requirement for the advanced process will be reduced to <100 kW . h/kg . separative work unit.

Equilibrium behavior in acid-base chromatography for carbon isotope separation

Abstract The separation of 12C and 13C isotopes by acid-base chromatography using an anion-exchange resin was investigated. In order to design the separation system, equilibria with respect to a carbon band were examined with reduction potential strength. Simulation and analysis with the potential strength and the newly derived S and L potentials were found useful for determining experimental conditions. Isotopic separation factors between CO2 and HCO3 observed in the chromatographic experiments were nearly equal to those in the corresponding solutions. The experiments at 25 or 90[ddot]C gave values of about 1.25 to 1.26 × 10−2 as the isotropic molar ratio of 13C at the rear boundary of the carbon band.

The Equilibrium Principle of Displacement Chromatography

Abstract Displacement chromatography, an alternate method to elution chromatography in terms of operation, is described. The principle of displacement is conveniently explained using the concept of an ‘addend’ which is regarded as a species essential to any equilibrium reaction consisting of association of two species and its reverse reaction. Microscopic equilibria in a chromatographic column can be characterized by use of reduction potential strengths (Δμ° and Δμ) and its derived quantities, S and L potentials that we introduced for expression of equilibria. The method for evaluating the separation factor of displacement chromatography is also described. Further, a profile of simulated separation produced by iterative applications of the distribution function to the multistage equilibrium in the column is presented.

Energy Consumption of Chemical Uranium Enrichment

Abstract A quantitative study of chemical separation energy for enriching uranium-235 by the redox chromatography was conducted. Isotope exchange reactions between U4+-UO2 2+ ions in the enrichment column are maintained by the redox reactions. The chemical separation energy is ultimately supplied by hydrogen and oxygen gas for regenerating redox agents. The redox energy for the isotope separation is theoretically predicted as a function of the dynamic enrichment factor observed in the chromatographic development of uranium adsorption band. Thermodynamic treatments of the equilibrium reactions implies an “inverse redox reaction” which can be enhanced by the chemical potential of the ion-exchange reaction of oxidant. Experimental results showed 30 to 90% recovery of the redox energy by the inverse reaction. These results will devise a simplified redox chromatography process where a number of columns in one module is reduced.

Ion Exchange of Uranyl-chloro Complexes and its Chemical Composition in an Ion Exchanger

The inside of ion-exchanger has conventionally assumed to be a kind of homogeneous electrolyte solution. This assumption may inevitably lead to the result that the complexes UO2Cl53- and UO2Cl64- exist as sorbed species in the present uranyl-chloride system, which can hardly be considered from the potential energy calculation of coordination. We considered that an ion-exchanger phase can be divided into two parts, one being a region around the exchange sites and the other a Donnan invasion region. By the equilibrium analysis besed on this model, we reached a reasonable conclusion that main uranyl chloride complexes are UO2Cl3- and UO2Cl42- in the anion-exchange resin phase.

Theory and industrial use of ultra multistage separation with adsorption-desorption reactions: Separation unit with chemical reactions and formation of displacement boundaries.

吸脱着による超多段精密分離の分離ユニットとしては, 吸脱着反応だけではなく溶液内の化学反応を伴う分離ユニットが望ましい.また, 超多段精密分離には置換型界面の形成が必要であり, さらに工業的規模の分離を効率良く行うためには三界面を置換型に維持することが必要である.置換界面は吸着剤の吸着選択性だけでは維持し得ず, 界面での反応が必要であることを明らかにし, これらの平衡反応の定量的な検討のために付加ポテンシャル強度Δμを導入し, 炭素, ウランの同位体分離について理論計算, および実験により検討した.また付加子について考察し炭素, ホウ素の同位体分離においてはプロトン, ウラン同位体分離では電子, 希土類元素分離ではEDTA等の配位子が分離ユニット内の化学反応を行う分離付加子であること, さらにそれぞれの場合の界面形成反応での付加子を明らかにした.

Recovery of separation energy by inverse redox reactions

Abstract An “inverse redox reaction”, in which ferrous, Fe(II), and titanyl, TiO(IV), ions are converted to ferric, Fe(III), and trivalent titanium, Ti(III), ions, was observed to occur within an anion-exchange resin in adsorption-desorption experiments, even though the standard reduction potential (E 0 ) of the Fe(III) / Fe(II) couple is approximately 0.57 V higher than that of TiO(IV) / Ti(III) in acidic solution. This type of reaction had been predicted by a thermodynamic treatment developed to describe the multiple chemical equilibria of redox chromatography for uranium enrichment, in which the standard reduction chemical potentials of ligand-exchange, redox and ion-exchange reactions can be obtained by theoretical calculations and measurements. Utilization of the inverse reaction in redox chromatography was found to result in 30% to 90% reduction of the separation energy required for uranium enrichment.