Preparation and characterization of chitosan/Fe2O3 nano composite for the adsorption of thorium (IV) ion from aqueous solution.

In this study, novel chitosan/Fe2O3nano composite Ch/Fe-Onc was synthesized and evaluated as an adsorbent for removing thorium (IV) (Th4+) ion from aqueous solution. The Ch/Fe-Onc was characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). Response surface methodology (RSM) was used in the optimization of Th4+ adsorption for parameters such as pH, the initial metal ion concentration (Th4+ concentration) and contact time. The statistical measures (i.e. analysis of variance, R2, the lack of fit test and the P value) specify that the developed model is proper. Furthermore, the adsorption kinetics was well defined by the pseudo-second-order equation, while the adsorption isotherms were better fitted by the Langmuir model. The adsorption capacity of Ch/Fe-Onc was 430 mg Th4+g-1 composite which leads to 99% removal at 25 °C. Moreover, thermodynamic parameters which state the natural and endothermic nature of the reactions were determined. The loaded Th4+ can be easily regenerated with HNO3 and the Ch/Fe-Onc can be used repeatedly without any significant reduction in its adsorption capacity. The desorption level of Th4+ from the Ch/Fe-Onc by using 0.1 M HNO3, was more than 95%.

Evaluation of PAN-based manganese dioxide composite for the sorptive removal of cesium-137 from aqueous solutions.

Hydrous manganese dioxide-polyacrylonitrile (MnO(2)-PAN) was chemically synthesized and evaluated, as an organic-inorganic composite material, for the removal of radio-contaminant cesium-137 from aqueous solutions. The physico-chemical characterization was carried out by Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), CHN elemental analysis, scanning electron microscopy (SEM), nitrogen adsorption-desorption studies and thermogravimetry-differential scanning calorimetry (TGA-DSC). Batch experiments were carried out as a function of contact time, interference of the coexisting ions and initial pH of adsorptive solution applying a radiotracer technique. The effect of temperature on the distribution coefficient of cesium has been utilized in order to evaluate the changes in the standard thermodynamic parameters. The results indicated that Cs(+) ions could be efficiently removed using MnO(2)-PAN composite in the pH range of 4-9 from aqueous solutions and the uptake of cesium is affected to varying degrees by the presence of some diverse co-ions. The equilibrium isotherms have been determined and the sorption data were successfully modeled using Freundlich model.

Studies on the adsorption behavior of trace amounts of 90Sr2+, 140La3+, 60Co2+, Ni2+ and Zr4+ cations on synthesized inorganic ion exchangers.

Three inorganic ion exchangers namely potassium zinc hexacyanoferrate(II) (PZF), magnesium oxide-polyacrylonitrile composite (MgO-PAN) and ammonium molybdophosphate (AMP) were synthesized. The physicochemical properties of these ion exchangers were determined using different techniques including inductively coupled plasma (ICP), CHNSO elemental analysis, infrared spectroscopy (IR), X-ray diffraction (XRD), thermogravimetric (TGA) and pH - titration curve analysis. The solubility of the synthesized ion exchangers in different acidic and alkaline media, their thermal stability and the effect of gamma irradiation were investigated. It was observed that the exchange capacity of the ion exchangers depend upon the pH value of the solution used. Furthermore, the adsorption of (90)Sr(2+), (140)La(3+), (60)Co(2+) and the distribution coefficient of these ion exchangers for Ni(2+)and Zr(4+) were studied. The effect of parameters such as pH and contact time on the adsorption was also investigated and the optimum conditions for separation of these ions were determined.

Preparations of PAN-based adsorbers for separation of cesium and cobalt from radioactive wastes.

Ion-exchange adsorbers are widely used for radioisotope separation, as well as for the removal of hazardous fission products from aqueous waste prior to discharge to the environment. Inorganic exchangers are of particular interest because of their resistance to radiolytic damage and selectivity for specific fission products. Composite inorganic-organic adsorbers represent a group of inorganic ion exchangers modified by using binding organic material, polyacrylonitrile, for preparation of larger size particles with higher granular strength. At the same time, kinetics of ion exchange and sorption capacity of such composite adsorbers are not influenced by the binding polymer. The contents of active component in composite adsorber were varied over a very broad range of 5-95% of the dry weight of the composite adsorber, and tested for separation and concentration of various stimulated wastes. Three different inorganic sorbents, granular hexacyanoferrate-based ion exchanger, were developed for the removal of Cs and Co ions from waste solutions containing different complexing agents as detergents. Radiation and thermal stability studies show that these adsorbents can be used for medium-active waste treatment.

The application and properties of composite sorbents of inorganic ion exchangers and polyacrylonitrile binding matrix.

A description is given of the preparation and properties of potassium hexacyanocobalt (II) ferrate (II) (KCFC) and the composite, potassium hexacyanocobalt (II) ferrate (II)-polyacrylonitrile (KCFC-PAN). The materials were dried at high temperatures and characterized by chemical analysis, scanning electron microscope, X-ray diffraction, inductively coupled plasma and infrared. The ion exchange of alkaline earth metals and molybdenum on a nonstoichiometric compound K(2)[CoFe(CN)(6)] and its PAN based absorber was examined by batch methods. The adsorption of molybdenum from aqueous solutions on KCFC-PAN was investigated and optimized as a function of equilibration time and pH. The materials which were dried at optimum high temperature of 110 degrees C were found to be stable in water, dilute acids, alkaline solutions and relatively high temperature. The distribution coefficient values K(d) for alkaline earth metals, followed the same trend of increase for both sets of absorbers studied, i.e. Ba(2+)>Sr(2+)>Ca(2+)>Mg(2+), which closely resembles to the order of the size of the hydrated cations. However, the K(d) values show a significant increase for PAN based absorbers in comparison to KCFC absorbers.

Ion exchangers in radioactive waste management: natural Iranian zeolites.

Five samples of natural zeolites from different parts of Iran were chosen for this study. In order to characterize and determine their structures, X-ray diffraction and infrared spectrometry were carried out for each sample. The selective absorption properties of each zeolite were found by calculating the distribution coefficient (K(d)) of various simulated wastes which were prepared by spiking the radionuclides with (131)I, (99)Mo, (153)Sm, (140)La and (147)Nd. All the zeolite samples used in this study had extremely high absorption value towards (140)La; clinoptolite from Mianeh and analsite from Ghalehkhargoshi showed good absorption for (147)Nd; clinoptolite from Semnan and clinoptolite from Firozkoh showed high absorption for (153)Sm; mesolite from Arababad Tabas showed good absorption for (99)Mo; and finally mesolite from Arababad Tabas, clinoptolite from Semnan and clinoptolite from Firozkoh could be used to selectively absorb (131)I from the stimulated waste which was prepared. The natural zeolites chosen for these studies show a similar pattern to those synthetic ion exchangers in the literature and in some cases an extremely high selectivity towards certain radioactive elements. Hence the binary separation of radioactive elements could easily be carried out. Furthermore, these zeolites, which are naturally occurring ion exchangers, are viable economically and extremely useful alternatives in this industry.

The importance of cerium substituted phosphates as cation exchanger-some unique properties and related application potentials.

Seven different samples of an inorganic ion exchanger, cerium phosphate, suitable for column use have been prepared under varying conditions. The property of these exchangers has been characterized by Inductively Coupled Plasma Spectroscopy. These exchangers are stable in water, dilute mineral acids, ethanol, methanol, acetone and ether. However, in concentrated HCl and HNO(3) they decompose. They retain about 50% of their exchange value after drying at 80 degrees C, and can be regenerated twice without any decrease in exchange capacity. The distribution coefficient measurements for alkaline earth metals, tellurium, iodine and molybdenum using these seven ion exchangers were studied. This revealed the relative affinity for each exchanger, where the sorption in general was most effective at pH 6-8. The titration curves of cerium phosphate (disodium) with alkaline earth metals showed that the selectivity sequence Ba(2+)>Sr(2+)>Ca(2+)>Mg(2+) is observed. Furthermore, it could be deduced that the adsorption of alkaline earth metal cations greatly depends on the cation. These studies have also shown that cerium phosphates with divalent ions are strongly preferred to monovalent ones. Therefore, as for the cerium phosphates with large monovalent ions, the lack of exchange for Ba(2+), Mg(2+) or other alkali earth metal ions should be essentially due to steric hindrance and this could include any one of the following: the large crystalline radius of metal ions or large hydrated ionic radius and high energy of hydration for other divalent ions. Three binary separations of Te(IV)-Mo(VI), Te(IV)-I(I) and Mo(VI)-I(I) has been developed and the recovery ranging from 90 to 100% has been achieved on cerium phosphate (disodium) columns.