Palladium (Pd) is used in various fields and is a highly rare resource in nature. Recovery of Pd from domestic wastes called “urban mines” is desired in Japan. Bamboo is an abundant biomass resource in Japan, and the promotion of its utilization is desired. In our previous studies, sulfur-impregnated carbonaceous adsorbent with high heavy metal removal has been prepared from biomass resources using sulfur with a high affinity for heavy metals. In this study, sulfur-impregnated carbonaceous bamboo was prepared from bamboo powder by pyrolyzing at 800 °C with sulfur under nitrogen atmosphere for recovering Pd from strong acidic solution. Sulfur-impregnated carbonaceous bamboo had porous structure, high specific surface areas and sulfur content. Palladium could be recovered from strong acidic solution by precipitation of Pd metals on the surface of sulfur-impregnated carbonaceous bamboo, while little amount of Pd was recovered using raw bamboo powder and non-sulfur-impregnated carbonaceous bamboo. The Pd adsorption capacity of sulfur-impregnated carbonaceous bamboo was about 120 mg-Pd/g-carbon, which was about twice as that of a commercially available activated carbon. The adsorption and reduction reaction of Pd on the surface of sulfur-impregnated carbonaceous bamboo occurred rapidly, and it was observed that Pd particles were larger as the reaction time increased. Palladium was precipitated as smaller particles on the surface of sulfur-impregnated carbonaceous bamboo than those on the surface of commercially activated carbon.

Fluorine is used in industrial fields such as electronics, glass processing and so on, and has a large impact on human body. The treatment of fluorine-containing wastewater with lower than Japanese effluent standard of fluoride (8 mg/L) is needed. The adsorption method is attracting attention, and titanium hydroxide (Ti(OH)₄) has high adsorption capacity and high selectivity for fluoride ion due to the hydroxy group (Ti-OH) on the surface. However, production of titanium hydroxide requires high energy. In this study, we aim to prepare a highly selective fluorine adsorbent from ilmenite by mechanochemical treatment to remove low-concentration fluorine in wastewater selectively. Fluorine adsorption of the products from ilmenite by mechanochemical treatment increased for 60 min regardless of the ball diameter used in mechanochemical treatment, and fluorine adsorption of the product from ilmenite was 4.5 times higher than that of raw material after 60 min mechanochemical treatment. Fluorine adsorption on product increased to the maximum at pH 2-3, and the product can remove fluoride ion in seawater at pH 2, selectively. The fluorine adsorption behavior followed Langmuir model and Freundlich model, and maximum adsorption amount of fluoride ion by product from ilmenite was 0.050 mmol/g. Regardless of the temperature the adsorption rates of product from ilmenite follow the pseudo-second order kinetic model than the pseudo-first order kinetics model. The adsorption on the product from ilmenite is the endothermic nature of the adsorption process and spontaneous reaction.

Novel inorganic ion exchangers, tungsten molybdophosphate (WMP) and its silica-supported type (WMP-Si) were synthesized for the removal and recovery of elements from spent nuclear fuel. Both of ion exchangers were synthesized by vacuum impregnation method using a vacuum evaporator from phosphomolybdic acid and ammonium tungstate. The adsorption properties were evaluated by batch experiment in both HNO₃ and HCl, as well as small-scale column test which carried out using Muromac® S-size column, and simulated high-level nuclear waste as feed in HNO₃. The element concentrations before and after batch experiment and column test were evaluated using ICP-MS. In batch experiment results, it was confirmed that both WMP and WMP-Si had high selectivity towards ruthenium in low concentration of HNO₃ and HCl, also strongly adsorbed cesium regardless of the acid concentrations. Small-scale column test also confirmed the adsorption of ruthenium and cesium at low concentrations of HNO₃. On this test, it was confirmed that ruthenium was eluted and cesium remained in WMP-Si after washing with high concentration of HNO₃, which means removal of cesium and recovery of ruthenium is possible by using WMP-Si. Furthermore, the adsorption capacity of ruthenium and cesium in were 0.65 mg Ru/g WMP and 2.38 mg Cs/g WMP respectively.

In order to extract reasonably rare-earth elements (REEs) as deep-sea resources, the effect of ozone (O₃) on REEs on hydroxyapatite (Abbreviated as Ca₃(PO₄)₂) selected as a simulated REEs mud was comprehensively examined in aqueous solutions including alkali metal salts (MCl or CH₃COOM, M = Li, Na, and K) and alkaline earth metal salts (MCl₂ or (CH₃COO)₂M, M = Mg, Ca, Sr, and Ba) ranging in temperature from 278 to 333 K. As a result, it was found that Ca₃(PO₄)₂ exists as a solid state and REEs except Ce maintain their dissolved morphologies during O₃ treatment. Moreover, it was confirmed that the leaching ratios of REEs from Ca₃(PO₄)₂ increase with an increase in the concentrations of alkali metal salts and alkaline earth metal salts in aqueous solutions. This phenomenon implies that their adsorption-desorption mechanisms are chemically controlled through cation exchange reactions between REEs on Ca₃(PO₄)₂ and other metal cations. In addition, the most effective cation to extract REEs from Ca₃(PO₄)₂ into an aqueous solution was found to be Ca ion among these additives. It was considered that the constant increase of the ΔH and ΔS values from La to Lu in the adsorption equilibrium reactions results from the increase in the hydration number of REEs due to the lanthanide contraction. On the basis of these results, the leaching experiments of REEs on Ca₃(PO₄)₂ were carried out to check whether the leaching promoting effect was accomplished by the combined use of O₃ and Ca ion or not. Only when used in conjunction with O₃ and Ca ion, it was found that the synergetic effect results in an almost fourfold increase in their leaching ratios. This promising result shows that it is possible to develop an innovative, modern, and eco-friendly extraction technology to separate REEs from Ca₃(PO₄)₂.

Endotoxin (lipopolysaccharide: LPS) is a cell wall component of Gram-negative bacteria. A rapid detection technique for LPS, a potent immune stimulant, is highly desired as the current detection method using the limulus amebocyte lysate (LAL) assay is time-consuming. Against this backdrop, we developed a novel analytical method to detect LPS using cadmium complexed with a dipicolylamine (dpa)-type pyrene probe (Cd-dpa-C4Py). This probe showed greater fluorescence enhancement at 474 nm in response to LPS compared with a previously reported zinc-type probe (Zn-dpa-C4Py). Moreover, the selectivity of Cd-dpa-C4Py for LPS over other phosphate derivatives, i.e., biomolecules that often coexist with LPS, was further improved; no phosphate derivatives other than LPS gave a substantial fluorescence response. It was demonstrated that the one-point replacement of the central metal complexed with dpa-C4Py played an important role in changing the fluorescence properties, including sensitivity and selectivity, possibly because the ionic radius of Cd²⁺ is larger than that of Zn²⁺, and because the two differ in hardness as Lewis acids according to the hard and soft acids and bases (HSAB) theory. Cd-dpa-C4Py is a promising chemical sensor especially for use in the rapid detection of LPS in water samples that may contain other phosphate derivatives, given its prominent selectivity.

The detection of boron down to ppt order in ultrapure water is required to ensure high-quality and stable semiconductor manufacturing. To realize a simple yet sensitive method for the detection of boron (=boric acid), we designed a ruthenium complex possessing a stable ligand with boric acid sensing function. Gallacetophenone (2’,3’,4’-trihydroxyacetophenone) ligand has a β-diketone moiety that can coordinate to a metal and a cis-diol moiety that shows reactivity with boric acid. Comparison of UV-vis absorption spectra measured in the presence and absence of boric acid at various pH revealed that gallacetophenone showed the greatest response to boric acid at pH 8.58. From the spectral changes in the absorbance of gallacetophenone aqueous solution in various concentrations of boric acid at pH 8.58, decreases in the absorbance at the wavelength of 330 nm were observed with increasing boric acid concentration. On the basis of the relationship between the absorption spectra and the boric acid concentration, the binding constant (assuming a 1:1 binding model) for the interaction between gallacetophenone and boric acid was estimated to be 420.7 ± 28.0 mol^-1 dm³. The electrochemical detection of boric acid was also conducted.

The Aⁿ⁻/CoAl LDH_x precursors with various interlayer anions (Aⁿ⁻) and Co²⁺ to Al³⁺ ratios (x) were successfully synthesized using the co-precipitation method under alkaline conditions. The XRD profiles of the as-prepared Aⁿ⁻/CoAl LDH_x resembles the typical pattern of hydrotalcite materials without any presence of impurities. The TG-DTA analysis revealed that different types of interlayer anions led to the formation of LDH with different thermal behavior. The cobalt aluminum oxide nanocomposite, Aⁿ⁻/CoAl_x_T, was obtained after calcination of Aⁿ⁻/CoAl LDH_x at T K for 2 h, and it was applied as a heterogeneous catalyst for aerobic oxidation of 1-phenyl ethanol to acetophenone using molecular oxygen as a sole oxidant. The Aⁿ⁻/CoAl_x_T acted as efficient catalyst for aerobic oxidation of 1-phenyl ethanol. Among The Aⁿ⁻/CoAl_x_T catalysts tested, CO₃²⁻/CoAl_3_573 gave the most outstanding catalytic performance with the acetophenone yield of 89%.

A layered silicate, KHSi₂O₅, was synthesized via a hydrothermal method using an amorphous silicon dioxide (SiO₂) block, which is industrial waste. This layered silicate was used as a host compound for ion-exchange reactions with Ag⁺ and Cu²⁺ ions, and the antibacterial properties of the ion-exchanged compounds were investigated. The crystal structures of the compounds were retained during the ion-exchange reaction; however, in the case of Cu²⁺, a small amount of Cu(OH)₂ coexisted. The M/Si (where M is Ag or Cu) ratios of the ion-exchanged compounds were 0.03 - 0.50 and 0.01 - 0.32 for M = Ag and Cu, respectively. The antibacterial activity was analyzed by the inhibition zone method using two standard model bacteria: Staphylococcus aureus (S. aureus,gram-positive) and Escherichia coli (E. coli, gram-negative). The Ag-KHSi₂O₅ and Cu-KHSi₂O₅ samples showed good antibacterial activity owing to the release of Ag⁺ and Cu²⁺ ions from their host silicates. Here, the antibacterial activity of each sample were compared by relative antibacterial activity which was calculated based on the bacterial inhibition zone area. The antibacterial activity of Ag-KHSi₂O₅ against S. aureus was higher than that against E. coli, whereas the antibacterial activity of Cu-KHSi₂O₅ against S. aureus was lower than that against E. coli.

The pyrrolidone resin based on styrene-divinylbenzene copolymer was synthesized with the varying ratios of monomers. The proportion of divinylbenzene determines the cross-linkage degree of pyrrolidone resin. We investigated the uranyl ion adsorption on the pyrrolidone resin with varying the cross-linkage in nitric acid solution. We found that the distribution coefficients of uranyl ion depend on the cross-linkage, however, the distribution coefficients are not exactly high in the case of high proportion of pyrrolidone in resin. The cross-linkage effects in the case of constant pyrrolidone concentration were also observed. We explained the cross-linkage effects by permittivity, hydrophobicity, and surface potential of resin.

During the accident at the Fukushima Dai-ichi Nuclear Power Plant at March 2011, radioactive cesium (¹³⁷Cs), which has a long half-life of about 30 years, was released into the environment around the plant. Therefore, methods for the recovery and fixation of ¹³⁷Cs are required. The CHA-type zeolite, chabazite, has high Cs⁺ selectivity; Cs⁺ ions have a diameter of approximately 0.36 nm and can thus enter into and be adsorbed by chabazite, which contains pores with diameters of 0.38 nm. However, some Cs⁺ ions in the large pores may be released by cation exchange in solutions with a high cation concentration. The ANA-type zeolite (ANA) has pores with 0.28 nm diameters, which are smaller than the diameter of Cs⁺ ions. ANA is synthesized by an alkaline hydrothermal treatment of natural zeolites such as clinoptilolite, mordenite, and chabazite. This hydrothermal modification may be useful for the fixation of Cs⁺. In the present study, the modification of chabazite exchanged with Cs⁺ to produce ANA by hydrothermal treatment was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX), and the solution stability of Cs⁺ in the ANA was also evaluated using inductively coupled plasma-mass spectrometry (ICP-MS). Modification of chabazite exchanged with Cs⁺ to produce single-phase ANA was confirmed in a 1.0 mol/L NaOH solution held at 200 °C for 3 to 144 h. The intensity of XRD peaks corresponding to (211) and (220) planes decreased with increasing Cs⁺ concentration. SEM observations showed that the ANA crystals had a trapezohedral shape and a size of about 5 µm. EDX analysis of ANA crystals confirmed the presence of Cs⁺. The amount of Cs⁺ eluted from ANA in a 0.6 mol/L NaCl solution was less than 1.7%.

In this study, to separate Pd(II) and other metal ions from high-level liquid waste (HLLW) for the effective use of limited resources, the applicability of a functionalized silica-based adsorbent was evaluated via batch-adsorption and chromatographic separation experiments using simulated HLLW containing 15 metal ions. The functionalized silica-based adsorbents used were 3-mercaptopropyl-functionalized silica gel (MP-Si), 2,4,6-trimercaptotriazine-functionalized silica gel (DMT-Si) triaminetetraacetate, sodium salt-functionalized silica gel (TAAcONa-Si), and 3-aminopropyl-functionalized silica gel (AP-Si) with different structures. Among them, MP-Si, DMT-Si, and TAAcONa-Si showed an adsorption capacity for Pd(II). In addition, the adsorption of Pd(II) onto TAAcONa-Si had relatively high adsorption stability for HNO₃ concentration and contact time. Moreover, regarding the maximum adsorption amount of Pd(II), adsorption onto MP-Si and DMT-Si with thiol had a larger amount than that of TAAcONa-Si with polydentate ligand. The adsorption of Pd(II) onto TAAcONa-Si was preferable under low-temperature conditions, indicated by thermodynamic analysis. The chromatographic results showed the complete separation of Pd(II) from simulated HLLW using TAAcONa-Si by 0.1-M thiourea–0.01-M HNO₃ solution. On the basis of these results, it is possible to change metal ion selectivity using a functionalized silica-based adsorbent having a different structure, and the separation of Pd(II) and other useful metal ions from HLLW is applicable.

Investigation of absorption behavior of trivalent actinides (An(III)) and Trivalent lanthanides (Ln(III)) on tertiary pyridine resin in sodium nitrate (NaNO₃) aqueous solution has been conducted. Am was used as trivalent actinides element and stable Europium (Eu) and Neodymium (Nd) represented Ln (III) elements. Separation of An (III) and Ln (III) was carried out by conducting chromatography experiment on pyridine resin column in high pH 11 of 4M NaNO₃. High pH was adjusted in order to suppress the protonation and supports tertiary pyridine resin to work as N soft donor ligand during separation. Gamma spectrometry was performed for detection of ²⁴¹Am and ICP-MS was used for measurement of Eu and Nd as stable isotopes.

In this paper, a method to deodorize ammonia and formaldehyde generated in a foundry using an aqueous solution of hypochlorous acid is reported. Air containing ammonia or formaldehyde was absorbed by an aqueous solution of hypochlorous acid, and the concentration of ammonia and formaldehyde before and after absorption, the type of ions in the solution, and the concentration of residual chlorine were measured. The results revealed that ammonia and formaldehyde deodorized upon oxidation in an aqueous solution of hypochlorous acid. However, the oxidation of formaldehyde with hypochlorous acid was only efficient in the presence of an adsorbent. The results have revealed the possibility of reducing foundry odors using a hypochlorous acid solution.

The dissolution behavior of ferrous ions from a pure iron wire in contact with highly-concentrated salt solutions co-existing with ice was visually analyzed. The dissolved ferrous ions complexed with 1,10-phenanthroline doped in the solution, and the resultant coloration was quantitatively evaluated employing a combination of microscopy and image processing. To provide a dimension-controlled solution area, a microchannel was fabricated in bulk ice, and the highly concentrated solutions were filled therein. The effects of various ionic species on the dissolution behavior were studied. We found that dissolution was significant when the wire was in contact with metal chloride solutions, whereas dissolution was not observed with iodide or bromide salt solutions.