Kenichi Akiba

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.

Transport of Uranium(VI) through a Supported Liquid Membrane Containing LIX 63

Abstract The carrier transport of U(VI) has been studied by means of the liquid membrane of LIX 63 (HR) held on a porous support. U was effectively transported from the dilute feed solution (pH = 4–5) to the product solution of 0.1 M H2SO4. Its concentration in the feed decreased according to [U]f, t = [U]f, o exp (-k obs t). The apparent rate constant (k obs) increased with an increase in carrier concentration up to 0.05 M, but it became nearly constant in the range of [HR] = 0.05–0.2 M. The rate of transport was inversely proportional to the feed volume. More than 99% of U was recovered and the final concentration ratio in the product to the feed ([U]p/[U]f) exceeded 103.

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 Kd,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.

Selective Removal of Cesium from Sodium Nitrate Solutions by Potassium Nickel Hexacyanoferrate-Loaded Chabazites

Potassium nickel hexacyanoferrate(II)s (KNiFC) were incorporated in the porous matrix of chabazite by successive impregnation with Ni(NO3)2 and K4Fe(CN)6. The loading percentage of KNiFC crystals on chabazite increased with repeated times of impregnation. The ion-exchange equilibrium of Cs+ in KNiFC-loaded chabazite (CFC) was attained within 2 days. Relatively large distribution coefficients of Cs+, K d,Cs, above 104 cm3/g were obtained, irrespective of coexisting NaNO3 concentration. There is a large difference between the K d value of 137Cs and those of other nuclides; the separation factor of Cs/Sr (αCs/Sr = K d,Cs/K d,Sr) was estimated to be above 104. The breakthrough curve for Cs+ through the column packed with CFC exhibited a symmetrical S-shaped profile, and this exchanger proved to be effective for the selective removal of radiocesium from waste solutions containing highly concentrated NaNO3.

Uptake behavior of americium on alginic acid and alginate polymer gels

The uptake behavior of Am3+ was investigated by using alginic acid and alginate polymer gels. The affinity of radioactive nuclides for carboxyl groups in gel matrices increased in the order of Na+ < Cs+ < Co2+ < Pd2+, Sr2+, Fe3+ < Eu3+, Am3+. Among alginate gels, calcium alginate exhibited relatively higher uptake rate and distribution coefficient of Am3+. The column packed with calcium alginate beads was effective for the removal of trace amounts of Am3+ from acidic nitrate solutions.

Selective Uptake and Recovery of Palladium by Biopolymer Microcapsules Enclosing Cyanex 302 Extractant

Selective uptake and recovery of platinum group metals are an important subject in the high level liquid waste treatment. An extractant having a strong affinity for palladium, bis(2,4,4-trimethylpentyl) monothiophosphinic acid (Cyanex 302, HA), was enclosed into microcapsules by utilizing highly immobilizing ability of biopolymer (alginate and alginic acid gel polymers). The uptake of Pd2plus, Ru(NO)3+ and Rh3+ for granular microcapsules has been studied by batch and column methods. A relatively large distribution coefficient of Pd2plus, Kd,Pd, of above 104 cm3/g was obtained in the presence of 0.2–0.5 M HNO3 and the separation factors of Pd/Ru and Pd/Rh were estimated to be above 102. The uptake of Pd2+ on microcapsules followed a Langmuir-type uptake isotherm and the maximum uptake capacity was estimated to be 0.72–0.96 mmol/g. These metal cations were chromatographically separated through the column packed with HA-alginate microcapsules.

Adsorption Behavior of Cesium and Strontium on Synthetic Zeolite P

Abstract Adsorption behavior of Cs and Sr on a synthetic zeolite P has been studied. Natural zeolites, clinoptilolite and mordenite, were converted into the zeolite P having a high crystallinity through hydrothermal treatment with NaOH solutions. The distribution coefficient (Kd) for Cs+ and Sr2+ depended on pH in acidic region, while attained nearly constant values around 103cm3/g in neutral and alkaline regions. This value is almost the same as that for Cs+ and about ten times that for Sr2+ on the original clinoptilolite. The adsorption obeys Langmuir-type isotherms, and the saturated amounts of Cs and Sr were respectively estimated to be 1.76 and 1.84 mmol/g. The zeolite P containing these cations was readily converted into a stable solid form consisting of pollucite and Sr-feldspar by calcination above 1,000°C.

Effect of diluent on synergic extraction of europium by thenoyltrifluoroacetone and tri-n-octyl phosphine oxide

Abstract Effects of organic diluents have been studied on the adduct formation of thenoyltrifluoroacetone (TTA;HA) chelate of europium(III) with a strong neutral donor, tri- n -octyl phosphine oxide (TOPO;S). The tris-TTA chelate EuA 3 forms two types of synergic adducts EuA 3 ·S and EuA 3 ·2S. Adduct formation constants K S, m ( m = 1, 2) determined in thirteen diluents are strongly diluent-dependent, e.g. log K S,2 = 15.08 in pentane to 7.68 in chloroform. The log K S, m values are correlated to the solubility parameter δ org of the organic diluent by the linear equation, log K S, m = 2B δ org + constant, where B is a negative constant characterized by the composition of the adduct.

Mutual Separation of Lanthanoid Elements by Centrifugal Partition Chromatography

Abstract Multistage separation based on liquid-liquid extraction has been investigated by means of centrifugal partition chromatography (CPC). A kerosene solution of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (EHPA) was employed as a stationary phase without any solid support. Metal ions eluted by the aqueous mobile phase were detected by the post-column reaction with Arsenazo III. The retention volumes are approximately linear with the distribution ratios of metals. The mutual separation of adjacent lanthanoids was accomplished by CPC.

Uptake and Recovery of Platinum Group Metals Ions by Alginate Microcapsules Immobilizing Cyanex 302 Emulsions

This paper deals with a novel preparation method for the microencapsulation of emulsified extractant into alginate gel polymer matrices, characterization of microcapsules and chromatographic separation of PGMs (Platinum Group Metals) ions in nitric acid solutions.