Hideaki Shiwaku

Efficient arsenic(V) removal from water by ligand exchange fibrous adsorbent

This study is an efficient arsenic(V) removal from contaminated waters used as drinking water in adsorption process by zirconium(IV) loaded ligand exchange fibrous adsorbent. The bifunctional fibers contained both phosphonate and sulfonate groups. The bifunctional fiber was synthesised by graft polymerization of chloromethylstyrene onto polyethylene coated polypropylene fiber by means of electron irradiation graft polymerization technique and then desired phosphonate and sulfonate groups were introduced by Arbusov reaction followed by phosphorylation and sulfonation. Arsenic(V) adsorption was clarified in column methods with continuous flow operation in order to assess the arsenic(V) removal capacity in various conditions. The adsorption efficiency was evaluated in several parameters such as competing ions (chloride and sulfate), feed solution acidity, feed flow rate, feed concentration and kinetic performances at high feed flow rate of trace concentration arsenic(V). Arsenic(V) adsorption was not greatly changed when feed solutions pH at 3.0-7.0 and high breakthrough capacity was observed in strong acidic area below pH 2.2. Increasing the flow rate brings a decrease both breakthrough capacity and total adsorption. Trace level of arsenic(V) (0.015xa0mM) in presence of competing ions was also removed at high flow rate (750xa0h(-1)) with high removal efficiency. Therefore, the adsorbent is highly selective to arsenic(V) even in the presence of high concentration competing ions. The adsorbent is reversible and reusable in many cycles without any deterioration in its original performances. Therefore, Zr(IV) loaded ligand exchange adsorbent is to be an effective means to treat arsenic(V) contaminated water efficiently and able to safeguard the human health.

Selective cesium removal from radioactive liquid waste by crown ether immobilized new class conjugate adsorbent.

Conjugate materials can provide chemical functionality, enabling an assembly of the ligand complexation ability to metal ions that are important for applications, such as separation and removal devices. In this study, we developed ligand immobilized conjugate adsorbent for selective cesium (Cs) removal from wastewater. The adsorbent was synthesized by direct immobilization of dibenzo-24-crown-8 ether onto inorganic mesoporous silica. The effective parameters such as solution pH, contact time, initial Cs concentration and ionic strength of Na and K ion concentrations were evaluated and optimized systematically. This adsorbent was exhibited the high surface area-to-volume ratios and uniformly shaped pores in case cavities, and its active sites kept open functionality to taking up Cs. The obtained results revealed that adsorbent had higher selectivity toward Cs even in the presence of a high concentration of Na and K and this is probably due to the Cs-π interaction of the benzene ring. The proposed adsorbent was successfully applied for radioactive Cs removal to be used as the potential candidate in Fukushima nuclear wastewater treatment. The adsorbed Cs was eluted with suitable eluent and simultaneously regenerated into the initial form for the next removal operation after rinsing with water. The adsorbent retained functionality despite several cycles during sorption-elution-regeneration operations.

Selective lanthanide sorption and mechanism using novel hybrid Lewis base (N-methyl-N-phenyl-1,10-phenanthroline-2-carboxamide) ligand modified adsorbent

This study aims to develop a highly selective Lewis base adsorbent to investigate the selective sorption and recovery of Eu(III) and Sm(III) from wastewater. The oxygen and nitrogen donor atoms containing Lewis base N-methyl-N-phenyl-1,10-phenanthroline-2-carboxamide (MePhPTA) ligand was synthesized and subsequently an adsorbent was prepared by direct immobilization onto mesoporous silica. Determined maximum adsorption capacities were 125.63 and 124.38 mg/g for Eu(III) and Sm(III), respectively. Experiments with mixed-cations solutions showed that the sequence of preferential adsorption was Eu(III)>Sm(III). The lanthanide sorption by hybrid Lewis base adsorbent (HyLBA) was not adversely affected by the presence of sodium, potassium, calcium, magnesium, chloride, sulfate and nitrate ions due to strong affinity between hard Lewis acid lanthanide and hard Lewis base adsorbent. The crystallography for the Sm-MePhPTA complex suggested that MePhPTA was strongly coordinated to Sm(III) with oxygen and nitrogen by forming a stable complex with two 5-membered rings. The data clarified that bond lengths between Sm(III) and amide oxygen (2.475Å) were shorter than SmN (2.662Å) in phenanthroline moiety indicating strong oxygen driven HyLBA. The results suggested that HyLBA has a good prospect of promising applications for separation/sorption of lanthanide ions from effluents.

Ultimate selenium(IV) monitoring and removal from water using a new class of organic ligand based composite adsorbent.

This work reports the selenium (Se(IV)) detection and removal from water by ligand functionalized organic-inorganic based novel composite adsorbent. The composite adsorbent was prepared by direct immobilization of N,N-di(3-carboxysalicylidene)-3,4-diamino-5-hydroxypyrazole onto the mesoporous silica monolith. The adsorbent exhibited distinct color change in the presence of various concentrations of Se(IV). This was characterized by UV-vis spectroscopy, and the color change was observed by naked-eye observation. The detection limit was determined to be 1.14 μg/L. The effect of solution pH, interferential metal ions, contact time, initial Se(IV) concentration, and adsorbent regeneration were evaluated. The maximum sorption capacity was determined based on the initial concentration. The data fitted well to the Langmuir isotherm model, and the maximum Se(IV) sorption capacity was 111.12 mg/g. The presence of diverse competing ions did not affect the Se(IV) sorption capacity, and the adsorbent had almost no sorption capacity for these coexisting ions, which suggests the high selectivity to Se(IV) ions. The adsorbed Se(IV) was eluted with suitable eluent (0.10 M NaOH) and simultaneously regenerated into the initial form for the next operation. The excellent reusability of the adsorbent was justified after eight consecutive sorption-elution-regeneration cycles. The proposed adsorbent is cost-effective and environmentally friendly and a potential candidate for treatment of water containing Se(IV).

Effect of the Introduction of Amide Oxygen into 1,10-Phenanthroline on the Extraction and Complexation of Trivalent Lanthanide in Acidic Condition

The extractability and complexation properties of lanthanides with N-alkyl-N-phenyl-1,10-phenanthroline-2-carboxamide were investigated. These ligands, which contain two aza-aromatic donors and an oxygen donor in a molecule, are newly developed extractants for actinides and lanthanides. N-Octyl-N-tolyl-1,10-phenanthroline-2-carboxamide exhibited high extractability of Eu3+ even under acidic conditions. In addition, strong complexation in acidic media was confirmed by spectroscopic titration experiments. Investigation of the complexation equilibrium revealed that the presence of an oxygen donor promotes ligand coordination with lanthanides over the competing protonation reaction in acidic solution.

Mechanisms of Se(IV) Co-precipitation with Ferrihydrite at Acidic and Alkaline Conditions and Its Behavior during Aging

Understanding the form of Se(IV) co-precipitated with ferrihydrite and its subsequent behavior during phase transformation is critical to predicting its long-term fate in a range of natural and engineered settings. In this work, Se(IV)-ferrihydrite co-precipitates formed at different pH were characterized with chemical extraction, transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS) to determine how Se(IV) is associated with ferrihydrite. Results show that despite efficient removal, the mode and stability of Se(IV) retention in the co-precipitates varied with pH. At pH 5, Se(IV) was removed dominantly as a ferric selenite-like phase intimately associated with ferrihydrite, while at pH 10, it was mostly present as a surface species on ferrihydrite. Similarly, the behavior of Se(IV) and the extent of its retention during phase transformation varied with pH. At pH 5, Se(IV) remained completely associated with the solid phase despite the phase change, whereas it was partially released back into solution at pH 10. Regardless of this difference in behavior, TEM and XAS results show that Se(IV) was retained within the crystalline post-aging products and possibly occluded in nanopore and defect structures. These results demonstrate a potential long-term immobilization pathway for Se(IV) even after phase transformation. This work presents one of the first direct insights on Se(IV) co-precipitation and its behavior in response to iron phase transformations.

Comparison of the Extractabilities of Tetrachloro- and Tetrabromopalladate(II) Ions with a Thiodiglycolamide Compound

Using N,N,N,N-tetra-2-ethylhexyl-thiodiglycolamide (TEHTDGA) in n-dodecane as the extractant, we compared the percentages of Pd(II) extracted from HCl and HBr solutions, and analyzed the structures of the Pd(II)-extractant complexes. For comparison, similar experiments were performed with di-n-hexyl sulfide (DHS), a well-known sulfide-type extractant. TEHTDGA extracted Pd(II) from both HCl and HBr solutions much faster than DHS. The Pd(II)/(TEHTDGA or DHS) stoichiometry in the organic phase was 1:2. For TEHTDGA, the extractability of Pd(II) from HBr solution was inferior to that from HCl solution, whereas the opposite was true for DHS. However, FT-IR spectroscopy and EXAFS measurements indicated that the inner-sphere structure of Pd(II) in the TEHTDGA complex was almost the same as that in the DHS system: in both cases, two of the halide ions in the tetrachloro- or tetrabromopalladate(II) ion were replaced by the sulfur atoms of two extractant molecules.

Structure and Complexation Studies on 2,2′-Bipyridyl and Trivalent Lanthanides

Separation of trivalent lanthanides (Ln) and trivalent actinides (An) is important task in reprocessing high-level liquid waste. In this study, the relationship between structures of complexes of 2,2′-bipyridyl (Bpy) and Ln (Nd, Er) and coordination strengths were investigated by X-ray diffraction and UV titration. With the decrease in ionic radius from Nd to Er, the N(Bpy)-Ln distance and N(Bpy)-Ln-N(Bpy) angle decreased, the dihedral angle of the Bpy pyridines increased, and the stability constant increased. This information about structure and coordination strength is important for designing better ligands for separating Ln and An ions.