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This study was undertaken to investigate the extraction of In3+ and Ga3+ by 7-(4-ethyl-1-methyloctyl)-8-hydroxy-quinoline (Kelex100), which has been found to be a slow extraction process. Homogeneous liquid-liquid extraction utilizing upper critical solution temperature of 4-methyl-1,3-dioxolan-2-one (propylene carbonate, abbreviated as PC) was used to eliminate the interface and speed up the extraction, since distribution between two phases was thought to be the rate-determining step. The effect of contact time on the percentage of metal extraction was examined at 80ºC using Kelex100 dissolved in toluene and PC solutions and the difference between two solvents was evaluated. The results clearly show that the use of homogeneous liquid-liquid extraction using PC with Kelex100 is faster than traditional two phase extraction. [ABSTRACT FROM AUTHOR]

Nano-sized boehmites with different crystallinity were synthesized at the temperature range of 25 to 200°C in order to produce phosphate absorbents with high capacity. The physicochemical property of boehmites was depended on the synthesis temperature: the particle size was increased and the surface area showed the maximum for the boehmite at 50°C. The phosphate sorptions into boehmites were analyzed at room temperature in the phosphoric acid solutions as a model of wastewater at the concentration of 0.1 to 3.0 mmol l-1 and the pH of 3 to 7. The boehmite synthesized at 50°C exhibited the highest amount of phosphate sorption (1.73 mmol g-1 at pH 3.3) compared with Al-bearing materials. The reaction mechanism during phosphate sorption was described by the anion exchange reaction between phosphate ions in sodium phosphate solution and hydroxide ions on boehmite surfaces. Therefore, the variation in the amount of phosphate sorption on the different boehmite samples depends strongly on the surface area in the specimens. In addition, the sample showed high stability in near-neutral-pH solutions, and an increase in pH toward neutral was found to lead to a decrease in phosphate sorption due to a change in the phosphate species and a reduction of the surface sites. [ABSTRACT FROM AUTHOR]

Abstract: Isothermal treatments of the ammonium-exchanged Na–zeolite A were carried out at 400°C for different durations up to 1000min in the air. The products were characterized by XRD, SEM, AFM, FT-IR, DTA and nitrogen adsorption measurement. The results confirmed that the amorphous pseudomorphism occurred, showing the tweed-like patterns on the surface of cubic solid. These characterizations supported the existence of thin surface layer of zeolite crystal as a microvessel, which was consistent with the previous hypothesis. The amorphous transformation was taking place by the mechanism, in which the zeolite framework reacted with hydrogen decomposed from ammonium ions. The obtained micro-cubic glass should be useful as an eco-functional material, such as the fixation of harmful ions. [Copyright &y& Elsevier]

Korean natural zeolite in which clinoptilolite and mordenite coexisted with feldspar and illite as impurities, was treated with 1.0, 3.0, and 5.0 M NaOH solutions at 100, 150, and 200 °C under autogeneous pressure for 17 hours either with or without an air classification as pretreatment. Phillipsite, analcime, and hydroxycancrinite were identified as reaction products depending on the reaction temperature and NaOH concentration. The air classification of the starting material prior to alkali-hydrothermal treatment effectively reduced the amount of feldspar, which hardly reacted to zeolite in the hydrothermal reaction. The ammonium adsorption behavior of the treated and untreated samples were investigated in solutions of between 10−3 M and 10−2 M NH4Cl. The amount of adsorbed ammonium ions in alkalihydrothermally treated product from air-classified material was higher by about two times than was that of corresponding untreated zeolites. The air-classified zeolite treated in 3 M NaOH solution at 100 °C showed the highest adsorption of ammonium ion among samples. It was explained by both the phase change of clinoptilolite and mordenite to phillipsite with higher cation exchange capacity and the reduction in the amount of feldspar that was less reactive under hydrothermal conditions for the formation of phillipsite. The results indicated that the combination of the air classification and alkali-hydrothermal treatment effectively improved the adsorption behavior for ammonium ions on natural zeolites with impurities. [ABSTRACT FROM AUTHOR]

Ammonium ion exchange behavior of synthetic zeolites, i.e., sodalite (SOD), rho zeolite (RHO), Linde type A zeolite (LTA), and faujasite zeolite (FAU), was investigated by changing the initial concentration of ammonium ions and reaction time. Ammonium ion exchange behavior was dependent on the open-window sizes, the pore structures, and the cation exchange capacities of these zeolites. Regarding sodalite with Na+ ions (Na-SOD), ammonium ion exchange did not completely occur at the equilibrium state because the open-window size is smaller than the diameter of ammonium ions. Regarding RHO with Na+ and Cs+ ions (NaCs-RHO), the larger cations, Cs+ ion, in the cages obstructed the ion exchange at the initial stage. However, the amount of exchanged ammonium ions gradually increased with increasing reaction time, finally achieving equilibrium. Regarding LTA with Na+ ions (Na-LTA), the amount of exchanged ammonium ions decreased with increasing reaction time, and then reached plateau. It indicated that both the ion exchange on the α-cages and physical adsorption on the β-cages occurred at the initial stage, which was followed by the equilibrium state of ion exchange on the α-cages. Regarding FAU with Na+ ions (Na-FAU), no dependence on reaction time was observed, because the size of the open-windows is large enough for ion exchange of ammonium ions. The Na-FAU, which has the biggest open-windows among these zeolites, showed the highest exchange capacity for ammonium ions, 3.20 mmol/g. [ABSTRACT FROM AUTHOR]

This study presents basic research on the use of natural zeolites for the removal of ammonium ions from aqueous solutions. Three natural zeolites from Shimane, Japan, used in this study are shown to contain varying amounts of clinoptilolite and mordenite. The chemical behavior of these natural zeolites was investigated in distilled water, hydrochloric acid, and ammonium chloride solution. The amount of ammonium ions adsorbed by these zeolites was measured using an electrode specific to ammonium ion. The results were compared with published adsorption values for other zeolites. Hydrogen ions displaced the exchangeable cations (Na+, K+, Ca2+, and Mg2+) on the natural zeolites in distilled water and hydrochloric acid. With the decrease in equilibrium pH, the amounts of dissolved silica and alumina increased. This behavior indicates that the structures of the zeolites are damaged under this condition. Ammonium ions were preferentially adsorbed on the natural zeolites in ammonium chloride solution. The amount of ammonium ions adsorbed quantitatively corresponded to the theoretically expected amount at high ammonium concentrations. This result indicates that ammonium adsorption occurs by ion exchange of ammonium ions with Na+, K+, Mg2+, and Ca2+ in cation exchange sites on zeolites. The order of selectivity of ammonium ions for other cations on the zeolites was Na+≫K+>Ca2+>Mg2+. Ammonium adsorption was the highest in the zeolite containing the highest proportion of clinoptilolite of the three natural zeolites. The maximum adsorption was 1.28 mmol/g. [ABSTRACT FROM AUTHOR]