A new and highly effective adsorbent has been synthesized through immobilization of Cd(II) protected active sites of humic acid (HA) on chitosan (Chit) using glutaraldehyde (Glu) cross-linker and followed by elution of the Cd(II) protector from the produced material by using Na₂EDTA. The adsorbent (Chit-Glu-Cd-HA) was then utilized to adsorb Cd(II) in an aqueous solution. The stability of the Chit-Glu-Cd-HA adsorbent towards dissolution at various aqueous medium acidities was the best if compared to the stability of adsorbents obtained through direct immobilization of unprotected HA on chitosan (Chit-HA) and through the glutaraldehyde assisted immobilization of the unprotected HA on chitosan (Chit-Glu-HA). Within the medium acidity range from pH 2 to 12, the dissolved AH from the synthesized Chit-Glu-Cd-HA adsorbent was ≤ 2.1 %(w/w), while that from Chit-Glu-HA and Chit-HA was ≤ 11.2 and 20.1 %(w/w), respectively. For the Chit-Glu-Cd-HA adsorbent, every g of adsorbent contained 497 mg of AH. On the other hand, AH contained in every g of Chit-HA and Chit-Glu-HA was remarkably lower, i.e. 30 and 291 mg, respectively. With 80 % degree of Cd(II) elution from the Chit-Glu-Cd-AH by using Na₂EDTA 0.05 M, the maximum adsorption ability of the adsorbent for Cd(II) was 5.67 × 10⁻³ mol/g and this capacity was significantly higher compared to that of Chit-HA and Chit-Glu-HA, i.e. 1.67 and 0.41 × 10⁻³ mol/g, respectively. These adsorption capacity data may indicate that glutaraldehide utilized to immobilize unprotected HA on chitosan consumes the active site of the formed adsorbent. The protection of active sites of HA with Cd(II) before immobilization to chitosan using glutaraldehyde releases the active sites of HA from their obligation to interact with glutaraldehyde and therefore after eluting the Cd(II) protector, the active sites of the immobilized HA are available to be occupied by Cd(II) adsorbed from the aqueous solution.

View full abstract

We have synthesized a new type monolithic porous ion exchange resin which has a co-continuous porous structure. The pore structure is obtained by a two-step polymerization process. In the first step, an open-celled porous styrene-divinylbenzene (St-DVB) copolymer is synthesized by preparation of waterin-oil (W/O) emulsion and polymerization. In the second step, the obtained copolymer is soaked and polymerized in a solution containing a polymeric initiator, styrene and DVB. In order to obtain the monolithic ion exchange resin, functional groups, such as sulfonic acid and trimethylammonium, were introduced into the copolymer. The ion exchange capacities of the monolithic cation and anion exchange resins that have co-continuous porous structures were both over 4 meq/g. The pressure drop of the new monolith was about 5 times lower than that of previously reported open-celled monoliths. The ion exchange band length of the new monolith was about 10 times shorter than that of conventional ion exchange resins. As one application of the new monolith, we have developed a palladium-loaded monolithic anion exchange resin (Pd-AEMR) to decompose hydrogen peroxide (H₂O₂) in ultrapure water. TEM and EPMA data indicated that Pd particles of about 50 nm were loaded uniformly on the surface layer of Pd-AEMR. H₂O₂ decomposition rate when using Pd-AEMR was about 10 times faster than that of Pd-loaded bead-type resin.

View full abstract

This paper describes the separation of sulfuric acid and monosaccharides with an amphoteric ion exchange resin to reduce the tailing of sulfuric acid. The amphoteric ion exchange resin of snake cage type was prepared by polymerizing p-styrenesulfonate ions contained in a strong-base anion exchange resin (Dowex 1X4) as counter ion. First, chloride form Dowex 1X4 (100-200 mesh) was changed into p-styrenesulfonate ion form. Then, p-styrenesulfonate ions in the resin were polymerized for 3 h at 72.5±2.5℃ and for more 3 h at 82.5±2.5℃ using a water soluble radical initiator. The resulting resin named Dowex 1X4-SS was treated with 1 M (M = mol dm⁻³) NaCl and finally washed with water in a columnmode. FT-IR spectra and elemental analyses of Dowex 1X4-SS suggested its amphoteric structure of snake cage type. The separation of glucose and sulfuric acid was tested by using a column (i.d. 1.5 cm, resin bed length 29-30 cm) at 50℃. The tailing of sulfuric acid was markedly reduced in case of Dowex 1X4-SS, compared to that of the parent resin Dowex 1X4. In addition, the newly developed Dowex 1X4-SS successfully applied to the continuous separation of monosaccharides and sulfuric acid in concentrated sulfuric acid hydrolyzates of bamboo by means of a simulated moving bed chromatography.

View full abstract

Germanium is a kind of rare metal. For the recovery of germanium ion, the novel recovery process is proposed using the complexation of germanium ion with catechol in solution; germanium ion is complexed with catechol forming anion, and then the anion-containing solution is flowed through quaternary-ammonium-group-containing membrane. In permeation mode, germanium ion is adsorbed to the membrane with catechol via ionic interaction. In actual wastewater of solar panel, silicate ion existed with germanium ion. At pH 3.0, germanium ion was selectively adsorbed to the membrane in the presence of silicate ion. The remained catechol in the effluent from the membrane was removed by solvent extraction with TOPO.

View full abstract

Separation of europium (Eu³⁺) and yttrium (Y³⁺), using a solvent impregnated resin (SIR) containing 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, coated by water-soluble chitosan crosslinked by glutaraldehyde, was investigated. Coating of the SIR successfully suppressed leakage of the extractant during adsorption processing. Adsorption of Eu³⁺ with both coated and uncoated SIRs was progressed with Langmuir mechanism, and the maximum adsorption amount of Eu³⁺ at equilibrium pH = 2.27 was 0.294 mol/kg with coated SIR and 0.310 mol/kg with uncoated SIR. Decrease in the maximum adsorption amount by coating SIR with polymer can be suppressed rather than the other coated SIRs previously reported. The coated SIR was then applied to column separation of Eu³⁺ and Y³⁺. Complete separation of the metals could be achieved by gradient elution with a gradual increase in the concentration of a dilute nitric acid. The coated SIR could also be reused for repeated adsorption-elution processing.

View full abstract

The dynamic adsorption/elution properties of a fibrous grafted adsorbent having sulfonic acid (SO₃H) groups was evaluated by column-mode adsorption/elution tests for various cations. The fibrous grafted adsorbent could efficiently function even under high flow rate condition. The breakthrough points at 25, 50, 100, 200, 500 and 1000 h⁻¹ in space velocity were 369, 333, 322, 314, 294 and 265 bed volume (BV), and the breakthrough capacity of the six flow rates were 1.38, 1.25, 1.25, 1.18, 1.10 and 0.99 mmol-Cu²⁺/g-adsorbent, respectively. The affinity order of the fibrous grafted adsorbent for cations depended on the cationic size and valence: the larger the cationic size and valence, the greater the affinity became. As for the different-charged cations, the SO₃H group had a higher affinity for the more multiply-charged cations. All the adsorbed cations could only be eluted by 1 M HNO₃ aqueous solution of less than 30 BV, and the recovery of each cation was reached over 90%. When the cationic mixture aqueous solution consisting various cations was continuously supplied to the column, the cation with stronger affinity for the SO₃H groups expelled the cation with weaker affinity previously adsorbed by the SO₃H groups with increasing feed volume. When the mixture aqueous solution consisting of monovalent, divalent and tervalent cations, was used, the fibrous grafted adsorbent preferentially adsorbed than the monovalent and divalent cations.

View full abstract

Fibrous phosphoric acid adsorbents for scandium were synthesized using two methods; by radiation-induced graft polymerization of glycidyl methacrylate (GMA) with subsequent chemical modification (GMA-gP), and by direct radiation grafting with phosphoric monomer having both vinyl and phosphoric groups (HMP-g) onto a polypropylene coated by polyethylene nonwoven fabric. The resulting grafted fibrous adsorbent, HMP-g, having the grafted long side chain, has high affinity for scandium (Sc(III)) adsorption even under the coexistence with Fe(III) ion. The breakthrough capacity for 0.5 ppm Sc(III) solution with Fe(III) interference was 10.9 μmol-Sc(III)/g-adsorbent for GMA-gP, and 17.8 μmol-Sc(III)/g-adsorbent for HMP-g, respectively.

View full abstract

A large amount of arsenic waste solution which was dissolved in neutral aqueous media, was generated from the manufacturing process of gallium arsenide component in semiconductor industry. As for arsenic removal, an adsorbent was developed by radiation graft polymerization and subsequent chemical modification with N-methyl-D-glucamine (NMDG) as a functional group. Furthermore, the grafting and the modification were carried out using water based solvent instead of organic solvent in view of an environmental emission and a working environment. The solvents were comprised of water and surfactant, and the adsorption performances compared with a conventional method synthesized in 1,4-dioxane of organic solvent. An optimal degree of grafting (D.g.) was around 200% because the grafted adsorbent with highly D.g. was sustained physical damages. When arsenic adsorption amount was expressed as the amount of arsenic per 1 mol of NMDG groups, the amount of adsorptions for arsenic(III) and arsenic(V) at pH 6.5 were 3.2 times and 2.1 times higher than our previous fibrous adsorbent. From the pH dependency studies, the developed grafted adsorbent gave high removal ratio in a neutral media area for both arsenic species. Breakthrough capacities in the column mode tests for arsenic(III) and arsenic(V) were 0.3 and 18 mg/g at pH 6.5, respectively.

View full abstract

Adsorption of Au(III) in multi-metal systems Au/Cu/Ni on mercapto modified silica coated on magnetite (Fe₃O₄/SiO₂-SH) has been studied. Fe₃O₄/SiO₂-SH was synthesized via sol-gel process by using magnetite obtained through co-precipitation of Fe²⁺/Fe³⁺ salt mixture with NH₄OH as the precipitating solution, sodium silicate solution extracted from rice hull ash and 3-mercaptopropyltrimethoxysilane (MPTMS) as the mercapto group source. Fe₃O₄/SiO₂-SH was characterized with Fourier transform infrared (FTIR) spectrophotometer, X-ray diffraction (XRD) and ion chromatography for sulfur analysis. Optimization of Au(III) adsorption in a batch system was carried out as function of pH, contact time and ion concentration. Adsorption kinetics was evaluated with pseudo-first order and pseudo-second order models based on the data of contact time variation, while the adsorption isotherm was studied based on Langmuir and Freundlich models. The adsorbed metal ions Au(III), Cu(II) and Ni(II) quantitatively were calculated based on the difference of metal concentrations before and after adsorption analyzed with flame atomic absorbance spectrophotometer (FAAS). Results of characterization showed that Fe₃O₄/SiO₂-SH has been successfully synthesized. Adsorption of Au(III) on Fe₃O₄/SiO₂-SH slightly decreased with increasing the pH in a range of 2.0-6.0 and fits to pseudo-second order model with the rate constant of 1.37×10⁻³ g mg⁻¹ min⁻¹. Fe₃O₄/SiO₂-SH shows a linear plot of Langmuir isotherm model with adsorption the capacity for Au(III) of 125 mg/g. Adsorption on multimetal systems shows that capacity of Au(III) on Fe₃O₄/SiO₂-SH is higher than that of Cu(II) and Ni(II), and high selectivity for Au(III) toward Cu(II) and Ni(II) ions.

View full abstract

The cesium adsorption behavior of vermiculite from a pure aqueous solution was studied in terms of the vermiculite grain size and reactant concentrations. Although a relation between grain size and the cesium adsorption percentage was not observed when the concentration of cesium in the reactant was high, the adsorption rate decreased at a certain grain size when cesium concentration was low. Reverse ion-exchange reactions were insignificant when water was used as an eluent.
Vermiculite with a grain size of 500-599 μm was used in the column method. As the flow rate increased, the breakthrough point decreased. Although a considerably low flow rate was required to obtain significant recovery of cesium from contaminated water, it is suggested that vermiculate with a relatively large grain size could be used in the column method.

View full abstract

4-Methyl-1,3-dioxolan-2-one is well known solvent in the name of propylene carbonate (PC) and has good solvent properties, e.g. low toxicity, less flammable, high density and less viscous, nevertheless the application of PC in solvent extraction has only been considered in a few cases. Then, availability of PC to solvent extraction was examined by applying it to the extraction of three different kinds of analyte, hydrophilic neutral species, a chelate and an ion association complex. At first, 6 water miscible solvents, i.e., methanol, isopropanol, tert-butanol, acetone, acetonitrile and tetrahydrofuran were arbitrarily selected as hydrophilic neutral species and the extractability of PC and cyclohexane for these solvents were examined. Dioctyldiglycolamic acid (Abbreviate as DODGAA) complex of lanthanide (Ln³⁺) was chosen as an example of chelate extraction and was extracted with PC and n-hexane, respectively. Ion association extraction was investigated with the extractability of bis(1,10-phenanthroline) iron(II) complex (Fe(phen)₃²⁺2X⁻) by using PC, toluene and nitrobenzene. In all cases, PC showed the significant extractability compared to common solvents.

View full abstract

To investigate the adsorption behavior of metal ions with β-diketone type chelating agents, thenoyltrifluoroacetone (Htta) and benzoyltrifluoroacetone (Hbfa) supported on mesoporous silicate MCM-41 that has been hydrophobized (hMCM-41) using trimethylchlorosilane was synthesized. The hexagonally arranged pore structure of MCM-41 was not significantly changed by the hydrophobic treatment and attachment of chelating agents, although the pore size, pore volume and surface area were slightly smaller than those of untreated MCM-41 as a result of the chemical modification of the surface. The amount of chelating agents adsorbed on hMCM-41 was 0.47 for Htta and 0.33 mmol g⁻¹ for Hbfa, respectively. All metal ions examined, except for Cd²⁺, were quantitatively adsorbed on hMCM-41 as metal complex, M(tta)₂ or M(bfa)₂. The order of the adsorption selectivity of the metal ions was similar to the stability constants of metal ions with Htta or Hbfa. Furthermore, most of the metal ions adsorbed onto hMCM-41 at lower pH compared with the results of having used MCM-41 as a support of chelating agents. This suggests that the adsorption ability of metal ions with chelating agents was improved by the hydrophobic treatment of MCM-41.

View full abstract

p-t-Octylcalix[4]arene derivatives as extraction reagents have been prepared to investigate silver extraction rate in nitrate media by batch-wise method. The interfacial tension was also measured by the drop volume method to investigate the effect of interfacial activity on silver extraction rate with the calix[4]arene derivatives in chloroform / nitric acid media by varying the concentrations of the extraction reagent and nitric acid. Interfacial activities of calix[4]arene derivatives were evaluated by comparing the obtained interfacial tension values. The interfacial excess and the average area per the adsorbed extractant molecule at chloroform / nitric acid interface were estimated from the Gibbs' adsorption equation and were used to investigate the relationship with silver extraction by using calix[4]arene derivatives in nitrate media. From the result, silver extraction rate with calix[4]arene derivatives in nitrate media was significantly related to their interfacial activities.

View full abstract

Two bipyridinium-benzocrown ether conjugates, 1 and 2, each appending styrene and naphthalene units at the nitrogen atom of pyridine in pyridyl-pyridinium-benzocrown ether conjugates via methylene spacer, respectively, have been prepared to investigate their guest responsive color changes and sensing abilities. Non-crown ether compounds, 3 and 4, have been also prepared as the analogue of 1 and 2, respectively. All compounds showed yellow color associated with intramolecular charge transfer (CT) absorptions, where the benzocrown ether or non-crown ether unit and bipyridinium unit act as π-electron donor and π-electron acceptor, respectively. Upon addition of metal ions as the guest, 1 and 2 showed color change to colorless with the blue shift in their CT absorptions, although 3 and 4 did not changed their color by the presence of the guest. This is due to the formation of host-guest inclusion complexes of 1 and 2 with metal ions. Such guest-induced color changes of 1 and 2 were used for alkali and alkaline earth metal ion sensing. The high sensitivities of 1 and 2 were observed for Li⁺ and Mg²⁺ among alkali and alkaline earth metal ions, respectively. The sensitivity value of 1 was roughly proportional to its binding constants. Similar trend of 2 was observed for alkali metal ions but not for alkaline earth metal ions. The substituent introduced at N-position in the bipyridinium-benzocrown ether conjugate may affect the ion sensing property.

View full abstract

Phenylboronic acid azoprobe (B-Azo-Cb) for saccharide recognition was synthesized. B-Azo-Cb/polyamidoamine (PAMAM) complex was synthesized by the condensation reaction of terminal carboxylic group of B-Azo-Cb and surface amine of PAMAM dendrimer. Thin porous cellulose acetate membrane embedded with B-Azo-Cb/PAMAM dendrimer complex was prepared from cellulose acetate, formamide, acetone, and B-Azo-Cb/PAMAM dendrimer complex by casting on the glass plate at various temperatures. The saccharide transportability was evaluated by measuring the amount of saccharide in receiving solution. The amount of saccharide transport of porous cellulose acetate membrane embedded with B-Azo-Cb/PAMAM dendrimer complex was higher at low temperature-treated membrane, and low pH of receiving solution. In contrast, the saccharide transportabilities through non-treated cellulose acetate membrane were the same at any pH of receiving solution. Saccharide transportability was in the order of galactose > glucose > fructose (B-Azo-Cb/PAMAM G4 modified membrane), and glucose > galactose > fructose (B-Azo-Cb/PAMAM G5 modified membrane). These orders were the same of the saccharide response in solution. These results indicated that the saccharide transport of B-Azo-Cb/PAMAM-embedded membrane is successfully mediated by the phenylboronic acid.

View full abstract

The ability of humin to remove AuCl₄⁻ from aqueous solution was affected by the conformation of humin macromolecules. By esterification using ethanol, macromolecule aggregates of humin which were bound each other by inter-hydrogen bonding and their functional groups which were in position of inward direction due to intra-hydrogen bonding would be, in some extents, disrupted so that the aggregate size of humin became smaller and the functional group direction changed outward. It means the surface area increases and the outer surface is more hydrophilic. As a result, although esterification reduced approximately 50 % of the content of carboxyl group but the ability of the esterified humin in removing AuCl₄⁻ was still higher compared to humin. Esterification using ethanol, in fact, consumed also hydroxyl group and only 26.2 % of the hydroxyl group remained after esterification. In spite of the content of hydroxyl group abruptly decreased, but its role in reducing AuCl₄⁻ to gold (Au) metal was still significant.

View full abstract

Several syntheses of metal ion adsorbents using modified banana fibers having Schiff bases were investigated. In addition, adsorption properties of a metal ion adsorbent were also evaluated. Alkalitreated (BF)-g-(glycidyl methacrylate)(BF-GMA) were synthesized. The Schiff base, 2-2'{iminobis[ethane-2,1-diylnitrilo(E)methylidine]}bisphenol derivative was synthesized by the reaction of diethylenetriamine and salicylaldehyde derivatives in methanol. The metal ion adsorbents were synthesized by the reaction of 2,2'-{iminobis-[ethane-2,1-diylnitrilo(E)methylidine]}bisphenol derivative, and BF-GMA. Where, C₁: R=H, C₂: R=Cl, C₃: R=Br. The concentration of metal ion was measured by an inductively coupled plasma atomic emission spectroscope. Metal ion adsorption percentage (%) of BFGMA(C₃) was higher than those of BF-GMA(C₁) and BF-GMA(C₂). Especially, adsorption property to Co²⁺ was higher than that to the other metal ions. This result suggests that the acid dissociation constant of BF-GMA(C₃) is larger than that of BF-GMA(C₁). Therefore, BF-GMA(C₃) can be chelated with metal ions more easily than BF-GMA(C₁) can be. These results show a definite feasibility of the use of banana fibers for the metal ion adsorbent.

View full abstract

Ethylenediaminetetraacetic acid (EDTA) forms a stable complex with copper. Electrodialysis treatment accompanied by electrochemical reaction was studied for the regeneration of EDTA and Cu from a solution of the complex. The electrodialysis stack consisted of three units of two cells containing cathode and anode compartments, and bipolar electrodes set between the units. The cells in a unit were separated by a cation-exchange membrane. Electrochemical reactions for the regeneration of EDTA and Cu were successfully achieved by electrodialysis with one unit in a stack. Both the rate of EDTA-Cu disappearance and the rate of EDTA formation were almost proportional to the current density. The Cu deposition on the cathode also proceeded well. Experiments were also conducted using electrodialysis with bipolar electrodes in a stack, and the rates of EDTA formation and EDTA-Cu disappearance were faster than those for the single unit experiments, and increased with the current density. The current efficiency of the electrochemical reaction on the cathode was close to 100%, and the current leakage from the bipolar electrode in the stack was negligibly small under the conditions employed. The results suggest that electrodialysis with bipolar electrodes enables the effective regeneration of Cu and EDTA from a solution of the complex. All the experimental results were analyzed using a mathematical model that considered electrochemical reaction on the cathode, ionic flux in the cation-exchange membrane, and the material balances of EDTA, EDTA-Cu, and sodium. The simulated results were in good agreement with the experimental results.

View full abstract

The adsorption properties of cesium ion and potassium ion to iron(III) hexacyanidoferrate(II) (IF) and copper(II) hexacyanidoferrate(II) (CF) immobilized in silica gel were investigated. The selectivity of cesium to potassium and the maximum adsorption amount were about the same for these adsorbents, but some adsorption properties were different for these adsorbents. The adsorption amount was dependent on the counter anion species and proton was desorbed alongside the adsorption of cations for IF, while the adsorption amount was independent on the counter anion species and proton was not desorbed alongside the adsorption for CF. The adsorption amount increased with the temperature for both adsorbents and the dependence on the temperature for IF was much more significant than that for CF.

View full abstract

A lot of contaminated wastes have been produced by decontamination works at contaminated areas around Fukushima prefecture, Japan, and piled up at temporary storage sites. At some temporary sites, it was found that leaching water was accumulated under stacks of contaminated “plant” wastes and contained radioactive cesium. To handle the wastes and the solution properly, decontamination tests of the leaching water were examined with molybdophosphate type cesium adsorbents synthesized by radiation-induced graft polymerization method. At batch adsorption tests, 75% of radioactive cesium was successfully removed with radiation graft cesium adsorbents. At column adsorption tests, radioactivity concentration of the leaching water could be reduced under 75 Bq/L as an indication of the provisional limit value up to around 500 times volume as large as an adsorbent volume. Moreover, brownish-red color of leaching water was succeeded to be decolored by amine type radiation graft adsorbents for water discharge. For development of volume reduction method of contaminated plant wastes, radioactive cesium extraction tests from the wastes and removal tests from the extracts were executed using contaminated oil cakes of sunflower seeds as a model of contaminated plant wastes. As a result, 65% of radioactive cesium was successfully extracted from the oil cakes to liquid phase, and more than 65% of radioactive cesium could be collected from the extract by radiation graft cesium adsorbents. These results showed a possibility of an application of these processes to volume reduction method for contaminated plant wastes.

View full abstract

Paper sludge (PS) was converted into a novel zeolitic material with the ability to simultaneously remove NH₄⁺ and PO₄³⁻ from an aqueous solution using calcination and alkali treatment. The sludge was calcined at 200–1000 ℃ for 6 h to have PO₄³⁻ removal ability, and was then converted into a zeolitic material upon reaction with a 1 – 4 M NaOH solution at 80 ℃ to have NH₄⁺ removal ability. Also, the both removal abilities of the product was tried to improve using diatomite during the alkali reaction. Without the addition of diatomite, hydroxysodalite and katoite were obtained in the product, and with the addition of diatomite, zeolite-P appeared in the product. The product from the calcined PS with diatomite has a higher NH₄⁺ removal ability than those calcined without diatomite, and the product obtained from the 2 M NaOH solution with addition of diatomite has a high removal ability because of the zeolite-P phase in the product. On the other hand, regardless of diatomite addition or NaOH concentration the product from the PS calcined at 800 ℃ had a high PO₄³⁻ removal ability due to the present of active sites to remove PO₄³⁻. The observed concentrations of Si, Al and Ca in the solutions during the reaction explain the crystallization behavior of these phases. The product synthesized from the PS calcined at 800 ℃ in 2 M NaOH solution with the addition of diatomite was able to simultaneously remove NH₄⁺ and PO₄³⁻ from the aqueous solution.

View full abstract

Removal of perchlorate ion in tap water with montmorillonite which modified with hexadecylpyridinium chloride (CPC-montmorillonite) was investigated by column chromatography. Almost all anions except Cl⁻ ion in a tap water containing 0.518 and 0.540 mg dm⁻³ on average of perchlorate ion (ClO₄⁻) and bromate ion (BrO₃⁻), respectively, through the CPC-montmorillonite bed, are adsorbed at the beginning of the column experiment, whereas the Cl⁻ concentration in effluent immediately increases steeply. The anions exhibit breakthrough in the order of F⁻, SO₄²⁻, BrO₃⁻, NO₃⁻, Br⁻ and ClO₄⁻. These results suggest that the anion uptake on CPC-montmorillonite proceeds through anion-exchange process, and the anion affinity of CPC-montmorillonite becomes F⁻ < SO₄²⁻ < BrO₃⁻ < NO₃⁻ < Br⁻ < ClO₄⁻. The ClO₄⁻ concentration in effluent solution passing through the CPC-montmorillonite bed falls below detection limits of ion chromatography up to 4,500 bed volumes (BV) at the feed solution rate of space velocity (SV) 15 h⁻¹, thus the ClO₄⁻ ion in the tap water can be reduced to less than 0.025 mg dm⁻³ of the target value under consideration as a standard of water-purity for tap water at Ministry of Health, Labour and Welfare of Japan. The ClO₄⁻ concentration increases gradually between 5,000 and 10,000 of BV and becomes nearly constant at above near 10,000 of BV. The ClO₄⁻ uptake amount on the column experiment can be estimated as 0.04 mmol g⁻¹ from the adsorption breakthrough curve of ClO₄⁻ ion. During 37 consecutive days of column experiment, 86 % of hexadecylpyridinium chloride molecules were eluted from an interlayer of CPC-montmorillonite and the basal spacing, (001) plane, of CPC-montmorillonite decreased from 4.05 nm to 2.11 nm.

View full abstract

A mixed bed ion exchange (MBIE) column producing ultrapure water will be removed from service well before its capacity is exhausted. There is usually an operational criterion for replacing or regenerating the bed; for example, defining 50 parts per trillion (ppt) Na as an endpoint in Pressurized Water Reactors (PWRs). These plant-specific criteria depend on the water treatment objectives and include low day-today concentrations or the ability to handle an upset event such as a concentration spike. In mixing the bed initially the cation to anion resin ratio is frequently set to where the equivalence of cation capacity equals the equivalence of anion capacity. An alternative approach is to define the resin ratio based on the feedwater pH so that the initial breakthrough time of cations and anions are the same. This ratio calculation procedure using feedwater analysis and a rate limited ion exchange model is described and the impact of this approach is discussed.

View full abstract

The adsorption behavior of Cs(I), Sr(II), I(I), and Ln(III) species on the novel synthesized tannic acid-type resin embedded in high-porous silica beads (TA resin) in seawater with initial pH 7.7 has been studied at room temperature, compared with those of typical resins such as bisphenol A-type (BA), DIAION CR10, WK10, and PK228 resins. As a result, it was found that the obtained distribution coefficients (K_d) of these metal ions using the examined resins increase in order of WK10, CR10, BA, and TA resins (≒ PK228 resin) for Cs(I) species, in order of WK10, BA, TA, CR10, and PK228 resins for Sr(II) species while these resins have no adsorption ability of I(I) species. Moreover, it was also revealed that these resins can adsorb stronger trivalent lanthanides from La to Lu except for Pm in order of PK228, WK10, BA, TA, and CR10 resins. These results imply that the adsorption ability of our synthesized TA resin for the metal ions such as Cs(I), Sr(II), and Ln(III) species are much higher than those of commercial resins, that is, we have succeeded in the synthesis of the novel effective resin for removal of Cs(I), Sr(II), and Ln(III) species in seawater. The K_d values of Ln(III) species with TA resin were relatively larger than those of Cs(I) and Sr(II) species. The obtained K_d values of Ln(III) species with TA resin increased sharply with increasing the pH (1.5, 2.8, 6.3, 7.2, 7.4, and 8.1) in seawater due to the dissociation of OH groups in TA resin and decreased gradually with an increase of the dilution factor (1.0, 2.0, 3.0, 5.0, and 10.0) of seawater because the complexation reactions between Ln(III) species and CO₃²⁻ contained in seawater are depressed. In addition, we have examined the adsorption isotherms and thermodynamics (Temp. = 297 - 330 K) of Ln(III) species on TA adsorbent in seawater. As a result, it was found that the adsorption processes between TA resin and Ln(III) species are strongly influenced by the components contained in seawater. Furthermore, their processes were found to be endothermic and spontaneous reactions in nature. From these results, we concluded that the developed TA resin is suitable for removal of Ln(III) species rather than that of Cs(I) and Sr(II) species in contaminated seawater.

View full abstract

We investigated the Cs-adsorption behavior of weathered biotites collected from Domeki, Mankei, Tozawa, and Yatsuzaku (in Ono-Niimachi, Tamura-Gun, Fukushima Prefecture) by changing the initial concentration of Cs in a solution. The degree of weathering (i.e. vermiculitization) of the samples increased in the following order: Domeki sample → Tozawa → Mankei → Yatsuzaku. A characteristic feature of the Domeki sample was distortion of the biotite layer. The Tozawa sample had an even greater degree of distortion of the biotite layer. In the Mankei sample, hydrobiotite and randomly interstratified biotite-vermiculite were observed with distorted biotite. The Yatsuzaku sample contained vermiculite with hydrobiotite and distorted biotite. The Cs adsorption ratio was associated with the initial Cs concentration of the solution. The Cs adsorption ratio of samples in an initial solution of 1 to 100 ppm Cs was about 99%; it decreased with increasing Cs concentration in the solution. Dependency of Cs adsorption behavior on the degree of weathering of biotite was clearly observed in the Cs concentration range of 300 to 1000 ppm. With increasing degree of weathering, the rate of decrease in Cs adsorption ratio with increasing initial Cs concentration in the solution became slower and the maximum amount of Cs adsorbed by the sample increased. These results confirm that weathered phyllosilicates, vermiculite, interstratified biotite-vermiculite, and distorted biotite play important roles in Cs adsorption.

View full abstract

Development of Cs selective adsorbents and stable solidification method contributes to the advancement of decontamination system and environmental remediation. This study deals with the preparation of Cs selective composites (insoluble ferrocyanide-loaded zeolites), uptake properties of Cs, stable solidification of composites, and evaluation of Cs leachability. The Cs immobilization (%) for the Cs-saturated composites (Cs-NiFC-SA-5, Cs-CoFC-MC) was above 99% and 96% even after calcination at 1,000℃ and 1,100℃, respectively, indicating that nearly all Cs ions are immobilized in the sintered products. On the other hand, the Cs immobilization (%) for the Cs-saturated composites (Cs-NiFC-A (A51, A51J), Cs-NiFC-LSX) tended to decrease with calcining temperature; for example, the Cs immobilization (%) for NiFC-X at 1,000℃ and 1,100℃ was estimated to be 74.9% and 55.4%, respectively, and many spots concentrating Cs were observed on the surface. The difference in immobilization behavior between natural zeolites and synthetic ones is probably due to the phase transformation and surface morphology at higher temperature above 1,000℃. The increasing order of Cs leaching rate for the sintered products at 1,000℃ was CsNiFC-SA-5(1.60×10⁻⁴ g/(cm²·day)<CsNiFC-A-51J<CsNiFC-LSX. The sintered products of CsNiFC-LSX consisting of CsAlSiO₄ phase at 1,100℃ had a relatively low leaching rate of about 10⁻⁵ g/(cm²· day). The stable solidification of insoluble ferrocyanides was thus accomplished by using the excellent Cs immobilization abilities of zeolite matrices (Cs trapping and self-sintering abilities).

View full abstract

The uptake behavior of Cs, Pd, Mo, Re and Tc on highly functional xerogels (microcapsules: MCs), the characterization of MCs and the chromatographic separation for the simulated HLLW (28 components) and the spent fuel solution were examined by batch and column methods. Granular MCs of ammonium tungstophosphate (AWP) encapsulated with calcium alginate (CaALG) matrices exhibited a high selectivity towards Cs⁺, and a relatively large separation factor (α) of Cs⁺/Rb⁺ above 10 was obtained. The mutual separation of Cs⁺/Rb⁺ was thus accomplished through the packed column. The novel MCs of insoluble ferrocyanides (CuFC) prepared by direct method had an excellent selectivity towards Pd²⁺; relatively large K_d values above 10⁵ cm³/g were obtained. The chromatographic separation of Pd²⁺/Rh³⁺/RuNO³⁺ in simulated HLLW was accomplished using thiourea-HNO₃ eluent. The extractants (LIX63, MIDOA and TOA) can be encapsulated with the alginate polymer gels. The MCs enclosing the above extractants exhibited high selectivity towards Mo(VI), Re(VII) and Tc(VII) ions, and the chromatographic separation for simulated HLLW and spent fuel solutions was accomplished by using stepwise elution methods. The precise separation system combined the above processes is effective for the recovery of nuclear rare metals from HLLWs.

View full abstract

The adsorption behavior of neptunium ions on the synthesized pyridine-type resin (Abbreviated as PYAER) in hydrochloric acid solutions whose concentrations are in the 0.10-11.5 M region has been studied at room temperature. Neptunium has many kinds of valence states of ions; mainly tetravalent, pentavalent, and heptavalent ions. We have controlled the neptunium valence states by using redox reactions and confirmed the valence states in hydrochloric acid solutions using an ultraviolet visible nearinfrared absorption photospectrometry at room temperature before the adsorption experiments described above. After adjusting the valence states of neptunium ions, the adsorption mechanisms on the neptunium ions with PYAER was studied by batch-wise adsorption experiments and the estimated mechanisms were compared with those of heptavalent uranium, trivalent lanthanides, and tetravalent plutonium against PYAER. As a result, it was found that the obtained distribution coefficients (Abbreviated as K_d) of neptunium with PYAER increase with increasing of the concentrations of hydrochloric acid solutions and their order was heptavalent > tetravalent ≒ pentavalent. The K_d values of tetravalent plutonium were found to be between the K_d values of neptunium. On the other hand, it was also revealed that trivalent lanthanides show little adsorption ability for PYAER in the examined hydrochloric acid concentration ranges and PYAER was able to adsorb strongly heptavalent uranium ions with increasing concentrations of hydrochloric acid. In brief, the obtained K_d values increased in order of lanthanides, neptunium (≒ plutonium), and uranium. These results support the positive possibility of the mutual separation of uranium, plutonium containing neptunium, minor actinides (Am, Cm), and lanthanides and were therefore found to be valuable data for our proposed reprocessing process.

View full abstract

The liquid-phase acetic acid esterification kinetics with methanol to methyl acetate and water catalyzed by gel (Lewatit K1221) and macroporous (Lewatit K2629) ion exchange resins have been investigated and compared with literature reported data acquired on Amberlyst 15. The effects of the resin swelling, the initial molar methanol to acetic acid ratio (1:1 – 10:1) and the temperature (303 – 333 K) on the reaction kinetics were investigated. The gel type resin exhibits a remarkably higher catalytic activity compared to the macroporous resins, despite its similar number of sulfonic acid groups. This can be attributed to the differences in active site accessibility during reaction and, hence, in resin swelling, especially when it is in contact with polar components, such as water and methanol. The differences in catalytic behavior between the considered resins have been assessed using an exchange based Eley-Rideal model in which it is assumed that (1) all the active sites are occupied, (2) the acid undergoes a proton exchange with the protonated methanol and (3) the reaction occurs according to an Eley-Rideal mechanism with the surface reaction between protonated acetic acid and methanol from the bulk as ratedetermining step. This model, which implicitly accounts for resin swelling, could describe the observed differences between the various resins. The activation energy was determined at 47 kJ mol⁻¹, irrespective of the resin used.

View full abstract

A novel series of Dion-Jacobson type layered perovskite RbLaNb_2−2xTi_xW_xO₇ (x=0, 0.1, and 0.2) and KCa₂Nb_3−2xTi_xW_xO₁₀ (x=0, 0.15, and 0.3) have been synthesized. The XRD patterns confirm that the optimum conditions for synthesis of RbLaNb_2−2xTi_xW_xO₇ and KCa₂Nb_3−2xTi_xW_xO₁₀ are 1000 and 1100 degree for 6 h, respectively. The estimated optical band gap energies of RbLaNb₂O₇, RbLaNb_1.8Ti_0.1W_0.1O₇ and RbLaNb_1.6Ti_0.2 W_0.2O₇ are 3.21, 3.18 and 3.11, respectively. The influence of the partial substitution of Ti and W on the photo-catalytic activity of pure RbLaNb₂O₇ was evaluated by using the degradation of phenol for 4 hours. At the end of experiment, the normalized concentration of phenol is 0.9, 0.8, 0.5 by RbLaNb₂O₇, RbLaNb_1.8Ti_0.1W_0.1O₇ and RbLaNb_1.6Ti_0.2W_0.2O₇ respectively, which indicates that the substitution of Ti and W for Nb in RbLaNb₂O₇ layered perovskites could increase the photocatalytic efficiency. The photocatalytic activities of KCa₂Nb_3−2xTi_xW_xO₁₀ were also tested and the result has been shown that the phenol degradation by RbLaNb_2−2xTi_xW_xO₇ is better than KCa₂ Nb_3−2xTi_xW_xO₁₀.

View full abstract

Scandium (Sc) which is a kind of rare-earth element has dissolved at a low concentration into the Kusatsu Hot Spring, located in Gunma prefecture, Japan. If Sc can be recovered from hot spring water, it is possible to ensure a stable supply of Sc as a future resource. Therefore, an adsorbent for Sc recovery was developed with radiation-induced graft polymerization of phosphoric acids that have a high affinity for Sc onto a polyethylene fabric. Hot spring water in Kusatsu Town flows into the Yukawa River, so Sc is contained at the concentration of 17 μg dm⁻³ in the Yukawa River. The adsorption performance of Sc was evaluated with the Sc recovery equipment, consisting of 155 mm internal diameter columns and a pump that were set up near Yukawa River. The adsorbent (1.5 dm³) was packed into a column and water from the Yukawa River was pumped through the column at a space velocity of 250 h⁻¹. As a result of the adsorption test, approximately 60 mg of Sc was collected per column. In addition, to achieve a practical use of Sc recovery, the adsorbent needs to be able to be used repeatedly while maintaining its efficiency in terms of cost reduction. So, the reusability of the adsorbent was investigated by repeating adsorption and elution. The breakthrough curves of Sc adsorption showed similar behavior in all tests. The adsorbed Sc from the 19th adsorption test was 56 mg, which was a comparable capacity relative to the average. These results indicated that the adsorbent was used more than 19 times while maintaining high adsorption performance of Sc.

View full abstract

Irreversible swelling of strongly acidic cation exchange resins (SAC) had been observed when ground water in a volcanic zone was used as raw water for ion-exchange pure water production facilities. Vanadium has been presumed to act as an oxidative substance to the SAC resin, with the analysis of the ground water. It was confirmed that hydroxyl radicals were generated when the metavanadate anions were present in strong a sulfuric acidic solution, and the amount of generated radicals changed with the molar ratio of metavanadate to sulfuric acid. When an ammonium vanadate solution was passed through a resin layer of normal cross-linked type SAC, eluted polystyrene sulfonic acids were detected in the treated water. However, highly cross-linked SAC resin is resistive to oxidative degradation in vanadate containing water.

View full abstract

Permeable reactive barriers (PRBs) are a technology for remediating groundwater contaminated with hazardous substances. Fluoride compounds are specified as hazardous substances by Japanese environmental standards. Currently there are no suitable materials applicable to PRB for removing fluoride; hence, we present an adsorbent prepared inexpensively from volcanic ash soil (VAS) as a PRB material. The purpose of this work was to clarify whether VAS is an applicable PRB material to remove fluoride from groundwater. VAS consists of aluminum oxide, silicon oxide, and iron oxide. Previous reports have suggested that the mechanism of fluoride adsorption onto VAS involves an ion-exchange reaction with the active hydroxyl groups of the metal oxides. The present study successfully confirmed the ion-exchange mechanism through batch-wise adsorption experiments. We also confirmed that VAS has a higher adsorption selectivity for fluoride than for the common components in groundwater. Because of the ion-exchange mechanism, the ordinary Langmuir equation cannot be applied to describe the adsorption behavior when the pH differs between batch-wise and column experiments. Therefore, we introduced the modified Langmuir adsorption isotherm, which considers the pH of the aqueous solution at equilibrium to predict the amount of fluoride adsorbed in the column experiment. Column experiments were also conducted to obtain the rate of fluoride adsorption onto VAS. The overall mass transfer coefficient was estimated from experimental breakthrough data by numerical analysis. We obtained both the equilibrium and the kinetic parameters of fluoride adsorption onto VAS for the design of a PRB for removing fluoride from groundwater.

View full abstract