High Ion-exchange Selectivity Research Articles

Synergistic integration of ion-exchange and catalytic reduction for complete decomposition of perchlorate in waste water.

Ion-exchange has been frequently used for the treatment of perchlorate (ClO4(-)), but disposal or regeneration of the spent resins has been the major hurdle for field application. Here we demonstrate a synergistic integration of ion-exchange and catalytic decomposition by using Pd-supported ion-exchange resin as an adsorption/catalysis bifunctional material. The ion-exchange capability of the resin did not change after generation of the Pd clusters via mild ethanol reduction, and thus showed very high ion-exchange selectivity and capacity toward ClO4(-). After the resin was saturated with ClO4(-) in an adsorption mode, it was possible to fully decompose the adsorbed ClO4(-) into nontoxic Cl(-) by the catalytic function of the Pd catalysts under H2 atmosphere. It was demonstrated that prewetting the ion-exchange resin with ethanol significantly accelerate the decomposition of ClO4(-) due to the weaker association of ClO4(-) with the ion-exchange sites of the resin, which allows more facile access of ClO4(-) to the catalytically active Pd-resin interface. In the presence of ethanol, >90% of the adsorbed ClO4(-) could be decomposed within 24 h at 10 bar H2 and 373 K. The ClO4(-) adsorption-catalytic decomposition cycle could be repeated up to five times without loss of ClO4(-) adsorption capacity and selectivity.

Cleanup of waste water from inorganic impurities and petroleum by coal-based adsorbents

On the basis of the angrensky coal are received new adsorbents: composite, with the additive in coal of carbonic salts of shchelochno-ground metals for sewage treatment from ions of inorganic impurity and decrease in rigidity of artesian waters; coal heat treatment at 5500С, with waterproof properties (S=150 m2/g) for clearing of a surface of sewage of mineral oil; steam-gas activation at 8000С (S=700 m2/g) for sewage treatment from the dissolved organic impurity; oxidation by air at 180-2000С, preliminary thermo processed coal at 5500С, with high ion-exchange selectivity (capacity 1,8 mg.ekv./g).

Influence of chloride ions on cadmium adsorptions by oxides, hydroxides, oxyhydroxides, and phyllosilicates

The effect of chloride on adsorption of cadmium (Cd) on oxides, hydroxides and oxyhydroxides (silica, gibbsite, and goethite) and phyllosilicates (two montmorillonites and kaolinite) was compared through experiments carried out in 0.1M NaNO3 and 0.1M NaCl solutions. SOILCHEM estimated that in the NaCl solution, CdCl+ comprised 83% of the total Cd content and the free ions constituted only 17% at pH<8.0, whereas approximately 100% existed as free Cd2+ in the NaNO3 solution over the same pH range. No obvious differences in Cd adsorption on the oxides, hydroxides, and oxyhydroxides were found between the NaNO3 and the NaCl background solutions, implying that the adsorption of CdCl+ on the oxide, hydroxide, and oxyhydroxide samples via an inner-sphere complex was similar to that of Cd2+. In contrast, Cd adsorption on phyllosilicates in the NaNO3 solution was greater than in the NaCl solution from acidic to neutral conditions. The greater adsorption of Cd2+ over CdCl+ appears to reflect the high ion-exchange selectivity of the divalent ion, because both ions would be adsorbed on permanent negatively charged sites arising from isomorphous substitution of phyllosilicates in acidic conditions. The result indicates that the influence of abundant Cl− in suspension on Cd adsorption is dependent on the type of adsorbent minerals.

Permeable Layers with Large Windows in [(CH3CH2CH2)2NH2]5In5Sb6S19·1.45 H2O: High Ion-Exchange Capacity, Size Discrimination, and Selectivity for Cs Ions

A layered indium thioantimonate was synthesized that has extra large windows in the inorganic slabs, imparting a 3D character to the compound. High ion-exchange selectivity and high capacity for Cs+ ions were found to be associated with this novel structure.

Use of Natural Clinoptilolite to Improve Water Quality: Sorption and Selectivity Studies of Lead(II), Copper(II), Zinc(II), and Nickel(II)

Natural clinoptilolite can be used as an ion exchanger for removal of heavy metals and treatment of environmental pollution because of its desirable characteristics of high ion exchange selectivity and resistance to different media. In this work, the potential of natural clinoptilolite from Gördes mines (West Anatolia, Turkey) for the uptake of lead(II), nickel(II), copper(II), and zinc(II), from their single and mixed ion solutions, was evaluated using the batch method. The mineralogical and chemical properties of the sorption material were carried out by X-ray diffraction, X-ray fluoremetry, scanning electron microscopy, and wet analysis. Contact time, initial solution pH, solid-to-liquid ratio, and initial metal cation concentration were determined as single ion sorption parameters. The silicon/aluminum ratio and the theoretical and equivalent exchange capacities, both in single and mixed solutions, were established. Corresponding adsorption constants and distribution coefficients have been found.

Ion-Exchange Reaction of Cs+ Selective Layered γ-Titanium and γ-Zirconium Phosphates

Abstract The H+/MA+ ion-exchange reaction of layered γ-titanium and γ-zirconium phosphates, MT(HPO4)2·nH2O, was examined, where MA is an alkali metal and MT is Ti or Zr. They showed remarkably high ion-exchange selectivity for Cs+ and Rb+ in acidic media. The selectivity for Na+ was rather low, and Li+ exchange hardly occurred. The H+ ion exchange of both γ-phosphates with Cs+ and Rb+ apparently occurred in two steps. These ion-exchange reactions occurred first at a pH value of around 2.0 to form a monobasic structure, MTMAH(PO4)2·nH2O, accompanied by dehydration of the water of crystallization. The second step occurred at a pH around 8.0 to form a dibasic structure, MT(MAPO4)2·nH2O, the interlayer space of both γ-phosphates swelled again. The lattice of crystals gradually collapsed corresponding to further progress of the ion-exchange reaction with Cs+ and Rb+, and the amorphous phase finally appeared. According to 133Cs NMR study, Cs+ was found to be rather restricted. The results were compared with those of layered synthetic mica. The high Cs+ and Rb+ selectivity was ascribed to the dehydration property and strong interactions of these ions with the host lamella layers. The high selectivity of two γ-phosphates for Cs+ in acidic media suggested a potentiality as promising materials for the recovery from radioactive waste. The interfering effect of coexisting Fe2+ was scarcely observed upon Cs+ exchange, and was even positive due to the prevention of lattice coagulation.

Crystallization of Sodium Titanium Silicate with Sitinakite Topology: Evolution from the Sodium Nonatitanate Phase

Titanium silicate (TS) with sitinakite topology and composition Na2Ti2O3SiO4·2H2O has received considerable attention because of its high ion-exchange selectivity toward cesium and strontium. In this paper we report the results of the studies of the crystallization process of TS with a combination of ex and in situ experiments. The effects of various parameters, such as gel composition, time, and temperature of the synthesis, on crystallinity and composition of the final product have been investigated. In situ X-ray powder diffraction studies carried out during the synthesis of TS revealed that the process begins with the formation of layered sodium nonatitanate (SNT) with chemical composition Na4Ti9O20·xH2O, which is also an excellent ion exchanger, selective for strontium and actinides. The pathway of transformation of SNT to the final product is sensitive to alkalinity of the starting gels. At high hydroxide concentration the reaction resulted in the formation of sodium titanium oxide silicate, Na2TiSiO5, which has the mineral natisite topology. This study has revealed a pathway for the synthesis of a combined SNT−TS exchanger for removal of Cs, Sr, and actinides by a single-step in-tank process.

Solid NMR Study of the Ion-Exchange Properties on .GAMMA.-Titanium Phosphate with Alkali Metal Ions

Layered γ-titanium phosphate (γ-TiP), Ti (HPO4) 2⋅2H2O, is well known as the host material of intercalation compounds and the inorganic ion-exchanger of H+/metal ion system. It was found to have high ion-exchange selectivity for Rb+ and Cs+ among alkali metal ions. The ionexchange reactions for these ions progressed in two steps according to pH. Part of water molecules in the mterlayer of γ-TiP was taken away during ion-exchange reaction and an amorphous γ-TiP resulted. This phenomenon was first studied by thermal analysis and further investigation was carried out using solid NMR of 1H and 133Cs in detail. Moreover, the interaction between Fe2+ and Cs+ for the ion-exchange reaction was investigated. Despite Fe2+ was hard to adsorb to γ-TiP, the amount of sorbed Fe2+ increased when Cs+ coexisted and the amount of sorbed Cs+ decreased.

Optimisation of the separation of anions by ion chromatography–capillary electrophoresis using indirect UV detection

The separation of a complex mixture of inorganic and organic anions by ion chromatography–capillary electrophoresis using a cationic polymer added to the background electrolyte and indirect UV detection has been studied. The addition of unmodified polymer to an electrolyte suitable for indirect detection resulted in the appearance of a system peak due to the counter-anion on the polymer and while the position of the analytes relative to this system peak could be changed, this was found to be an unacceptable approach for mixtures of large numbers of analytes. Although conversion of the polymer to replace the counter-ion with the indirect UV detection probe ion simplified the system, this approach restricted the flexibility of the system because the probe and polymer concentration were necessarily linked. This limitation could be overcome by selecting the appropriate type of probe ion, with probes having a low ion-exchange selectivity coefficient providing greater retention of analytes than probes with a high ion-exchange selectivity coefficient. Three electrolyte systems with different probes (benzoate, chromate and phthalate) were modelled using a previously derived migration equation and this was used to optimise the electrolyte composition to enable the separation of a mixture of 24 inorganic and organic anions within 7 min. The electrolyte composition was then optimised for the analysis of anions in Bayer liquor with the final separation selectivity being substantially improved for selected key analytes.

Nuclear magnetic resonance study of ion-exchange reaction on cubic ammonium molybdate

Inorganic ion-exchangers generally exhibit high ion-exchange selectivity in comparison with organic ion-exchangers. The high selectivity has been ascribed to the rigid lattice of the crystal structure, e.g. ion-sieving properties of zeolites. Cubic ammonium molybdate prepared by the precipitation method (CAM) has been shown to have an unusual (compared with other inorganic ion-exchangers) selectivity for K+ among alkali-metal ions. The selectivity of K+ was assumed to result from the hydration of ions incorporated in the crystal lattice. The hydration property of alkali-metal ions incorporated in the lattice was revealed from the 1H NMR study and the selectivity for K+ was accounted for by the hydration of K+ by analogy with the well known properties of electrolyte solutions.