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.     

Investigation of the resistance of some naturally occurring and synthetic inorganic ion exchangers against gamma radiation

The effect of various doses of gamma radiation on the ion-exchange capacity, distribution coefficient values, elution behaviour, physical effect, pH titration and infrared spectra of some synthetic inorganic ion exchangers, namely the cerium substituted phosphates; and naturally occurring inorganic ion exchangers, zeolites from different parts of Iran, have been studied systematically.No significant change has been observed in the ion-exchange capacity (with the exception of CeP(Na), CeP(Di·Na) and zeolite 5 (deposits of arababad talas)), elution behaviour, physical effect, chemical stability and the infrared spectra of the synthetic ion exchangers irradiated upto a total dose of 200 kGy, while a change has been observed in the pH-titration and distribution behaviour. The increase in pH is sharper for irradiated samples with divalent cations than for the normal samples. Furthermore, the K_d values, and hence the selectivity towards certain cations increase with the total dose absorbed, reaching its optimum selectivity with the dose of 50–100 kGy. The natural zeolites chosen for these studies, show, similar pattern to those of synthetic ion exchangers, and in some cases an extremely high selectivity toward certain cations, like Be^II. These make, zeolites, which are naturally occurring ion exchangers more viable economically, and extremely useful alternative in this industry.     

Inorganic Ion Exchangers for Cesium Removal from Radioactive Wastewater

Ion exchange is a proven process for radioactive wastewater decontamination, where inorganic sorbents are ideal due to their thermal, chemical and radiation stability. This review focuses on the removal of Cs⁺ by inorganic exchangers, viz. zeolites, titanosilicates, hexacyanoferrates metal oxides and hydrous metal oxides, bentonite/clays and the key family of ammonium phosphomolybdates (AMPs). The design of new selective composites is also addressed focusing on those based on AMPs, hexacyanoferrates and titanosilicates/zeolites. Future inorganic Cs⁺ exchangers will encompass promising solids, like lanthanide silicates, sodium titanates and metal sulfides. The sensing ability derived from the photoluminescence properties of lanthanide silicates and the efficiency of layered gallium-antimony-sulfide materials in acidic and basic solutions disclose considerable potential for real applications. The ion exchange systems are discussed in terms of sorbent capacity and selectivity (with competitors), pH, temperature and solution salinity. The microscopic features of the exchangers and the associated mechanisms (e.g., pore size, counterions radii, dehydration energy of the ions, coordination environments in the solid exchanger, and site accessibility) are always used for interpreting the ion exchange behavior. On the whole, more than 250 publications were reviewed and a large compilation of data is provided in Supplemental Material.     

Structural studies on some inorganic ion exchangers

Ferrocyanides of zirconium(IV) and tin(IV), antimonates of cerium(IV) and titanium(IV), and cerium(IV) tungstate, has been shown to be useful materials as inorganic ion exchangers in radio- and analytical chemistry. These materials are sufficiently stable towards high dose of γ-radiations. Attempt is made to study some structural aspects and possible exchange sites of these materials using different techniques like thermal, Mössbauer and infrared spectroscopy.     

H+-Ca2+ Equilibrium Exchange on Polyacrylic Cationites

Potentiometric titration curves of carboxyl-containing polyacrylic cation exchangers (Amberlite IRC 86, Dowex MAC 3, Lewatit CNP 80, Purolite C 104, and Relite CNS) in the H form with calcium ions were measured. It was found that the apparent equilibrium constant strongly depended on the composition of resinate solutions, which was indicative of significant deviations of solutions in the cation exchanger gel phase from the ideal behavior. The largest deviations were observed for Dowex MAC 3 ion exchanger, and the smallest, for Amberlite IRC 86. For the other sorbents, the dependences coincided to within measurement errors. The experimental data were treated in terms of six models of the theory of exchange equilibria. The best approximation to titration curves was obtained in terms of the model that suggested the presence of two types of exchange centers in ion exchangers and took into account the influence of the state of three neighboring fixed groups on each spatially separated center. The amounts of centers of all types in the ion exchangers were determined. Differences in the selectivity of the cation exchangers with respect to calcium ions were explained.     

Iranian natural clinoptilolite and its synthetic zeolite P for removal of cerium and thorium from nuclear wastewaters

The ion-exchange behaviors of an Iranian natural clinoptilolite and its modified forms as well as a relevant synthetic zeolite P were investigated toward cerium and thorium from nuclear wastewaters. Column experiments were performed on different exchangers in various conditions and the effect of parameters such as particle size, pH, temperature, and time were considered. The distribution coefficient, cation exchange capacity and some thermodynamic parameters were calculated. Ion-exchange isotherms and break-through curves were plotted. As a result, the selectivity of synthetic zeolite P from Iranian natural clinoptilolite toward cerium and thorium was compared with that of natural and cationic forms of clinoptilolite     

The influence of the natures of the solvent and coion on the properties of ion-exchange systems

The influence of the coion and the ratio between the water-acetone binary solvent components on cation and anion exchange on sulfo-and aminostyrene ion exchangers with a medium degree of cross-linking were studied. The dependence of selectivity coefficients on the degree of ionite filling by the desired component was found to vary substantially as the composition of the solvent and the radius of the cation changed.     

A comparative study on textural characterization: cation-exchange and sorption properties of crystalline alpha-zirconium(IV), tin(IV), and titanium(IV) phosphates

Tetravalent metal phosphates (M=Zr, Ti, and Sn) were prepared and characterized by XRD, surface properties, and TG-DTA. The cation exchange and sorption behavior of these metal phosphates toward transition metal ions such as Cu(2+), Co(2+), and Ni(2+) have been studied comparatively as a function of temperature and concentration. The adsorption process was found to increases with increase in temperature and concentration. The selectivity order for alpha-titanium and alpha-tin phosphates is Cu(2+)>Co(2+)>Ni(2+), whereas for alpha-zirconium phosphate it is Cu(2+)>Ni(2+)>Co(2+). The ion exchange capacity of alpha-titanium phosphate is greater than those of other phosphates, which is explained on the basis of the surface behavior, disorderness of the system, degree of hydrolysis of incoming guest adsorbate metal ions, and structural steric hindrance of the exchangers during adsorption and sorption. The distribution coefficient, Gibbs free energy, enthalpy, and entropy values indicate that the ion-exchange processes are spontaneous.     

Comparison of Reversed Stationary Phases for the Chromatographic Separation of Inorganic Analytes Using Hydrophobic Ion Mobile Phase Additives

Abstract

Alkyl-modified silica (RSi) and polystyrenedivinylbenzene (PRP-1) stationary phases are compared for the chromatographic separation of inorganic analyte anions and cations using hydro-phobic ions of opposite charge as mobile phase additives. Tetra-alkylammonium salts were used for anion separations and alkyl sulfonate salts for cation separations. Two major equilibria influence the retention of analyte ions on PRP-1. These are: retention of the hydrophobic ion on PRP-1 and an ion exchange selectivity between the hydrophobic counterion and the analyte ion. When using RSi retention is also influenced by ion exchange at residual silanol groups, which act as weak cation exchange sites. Mobile and stationary phase variables that influence analyte retention are identified. Optimization of these provides favorable eluting conditions for the separation of inorganic ionic analytes. Of particular interest is the potential use of PRP-1 and RSi columns for the separation of inorganic cations; conditions for the separation of alkali metals and alkaline earths are discussed.     

Superior Ion‐exchange Property of Amorphous Aluminosilicates Prepared by a Co‐precipitation Method

The development of inexpensive inorganic ion‐exchangers for the purification of environmental pollutants is a social demand. Amorphous aluminosilicates with a relatively high homogeneous Al environment are prepared by a feasible co‐precipitation method, i. e., mixing an acidic aluminum sulfate solution and basic sodium silicate solution, which exhibit excellent ion‐exchange selectivity for Cs⁺ and Sr²⁺. The K_d value for Sr²⁺ was comparable with that of zeolite 4A. The local structures and ion‐exchange behavior of the amorphous aluminosilicates are systematically investigated. The ion‐exchange property of the amorphous aluminosilicates can be tuned by changing the interaction between the exchangeable cation and the amorphous aluminosilicates. Also, the amorphous aluminosilicates can adsorb bulky cations that zeolites hardly adsorb due to the limitation of the miropore size of zeolites.     

Synthesis and ion exchange behaviour of polyaniline Sn(IV) arsenophosphate: a polymeric inorganic ion exchanger

Incorporation of a polymer material into an inorganic ion exchanger provides a class of hybrid ion exchangers with a good ion exchange capacity, high stability, reproducibility and selectivity for heavy metals. Such a type of ion exchanger ‘polyaniline Sn(IV) arsenophosphate’ has been synthesized by mixing polyaniline into inorganic material. This material is characterized using X-ray, IR, TGA studies in addition to ion exchange capacity, pH-titration, elution and distribution behaviour. On the basis of distribution studies, the material has been found to be highly selective for Pb(II). Kinetic study of exchange for the metal ions has been performed and some physical parameters such as self diffusion coefficient D₀, energy E_a and entropy ΔS* of activation have been determined.     

Polystyrene immobilized ionenes as novel stationary phase for ion chromatography

Several aliphatic ionenes (2-6-, 6-6-, 10-6-ionene) have been prepared as ion exchangers for the development of novel high-performance stationary phases for anion chromatography (IC). A macroporous polystyrene/divinylbenzene (PS/DVB) resin with adjusted cation exchange capacity was used as support. Therefore the immobilization of ionenes to polystyrene carriers with remaining positive surface charge became possible for the first time. Strong ion-exchange interactions, resulting in high retention times, between the stationary phase and inorganic as well as organic anionic analytes have been observed. The influence of different ionenes on the retention behaviour during the ion chromatographic separation was investigated. Additionally, partly aromatic and polar ionene backbones were prepared and their retention behaviour as anion exchanger was investigated. The highest number of theoretical plates obtained was about 90.000 per meter. The signal asymmetries were generally lower than obtained for surface functionalized anion exchangers.     

Effect of the porous structure of polymer on the kinetics of Ni<Superscript>2+</Superscript> exchange on hybrid inorganic-organic ionites

Hybrid organic-inorganic ion exchangers are obtained by incorporating amorphous zirconium hydrophosphate into the gel of strong acidic cation exchange resin. Hybrid organic-inorganic ion exchangers are obtained by modifying strong acidic cation exchange resin with amorphous zirconium hydrophosphate. The synthesized materials are studied by standard porometry contact. It is found that raising the inorganic component content to 34 wt % diminishes the microporosity of the samples and simultaneously enhances the of meso- and macropore volume. Experiments establish that modification of a polymer matrix lowers the self-diffusion coefficient of Ni²⁺ from 8.1 × 10⁻¹² to 2.4 × 10⁻¹²–4.1 × 10⁻¹² m² s⁻¹; nevertheless, an inorganic ion exchanger minimizes the inhibitory effect of co-ions on the Ni²⁺ → H⁺ exchange rate. One possible mechanism for of filling of the matrix by with particles of zirconium hydrophosphate is discussed.     

The influence of temperature on the ion exchange properties of phenolformaldehyde sorbents

The influence of temperature on cation exchange on phenol groups of macroporous materials based on phenolformaldehyde resins (PFRs) was studied for Amberlit XAD 761 with irregularly shaped grains obtained by breaking up polycondensation resin blocks and FFS-1.4/0.7 with spherical granules. An increase in temperature caused some decrease in the sorption capacity of PFRs in the alkaline region, but almost did not influence the selectivity of alkali metal ion exchange. The sorption capacity and selectivity of PFRs did not change after multiple (dozens of cycles) transfer of phenol groups from the hydrogen to salt form and back. Ion exchangers of this type can effectively be used for separating mixtures of alkali metal ions containing cesium and rubidium.     

Differential elution of sodium or potassium dihydrogen- and hydrogenphosphate ions from a sephadex G-15 column with sodium or potassium chloride solution

When a mixed solution of sodium or potassium dihydrogenphosphate and disodium or dipotassium hydrogenphosphate was eluted from a Sephadex G-15 column with either a sodium or potassium chloride solution, the elution profiles of ions showed that the hydrogenphosphate ion was eluted more rapidly than the dihydrogenphosphate ion. When the sample solutions containing potassium dihydrogenphosphate and/or dipotassium hydrogenphosphate, all of which were supplemented with phosphorus-32-labelled potassium dihydrogenphosphate, were eluted with sodium chloride solution, the elution profiles of radioactivity showed that the dihydrogenphosphate ion changed to hydrogenphosphate ion and vice versa, depending on the pH values of the sample solution and the availability of the cation of the eluent during elution for the phosphate ion to pair with.     

Sorption Behaviour of Molybdenum on Different Antimonates Ion Exchangers

Various antimonate compounds are well known as important inorganic ion exchangers, since they resist radiation and chemical degradation and also exhibit selectivities towards different cations. Ceric, silicon, titanium and ferric antimonates were prepared as inorganic ion exchangers. Characterization of these materials has been described using different techniques, including thermal analysis, surface area measurements, X-ray diffraction and IR-spectroscopy. In batch distribution experiments the influence of HNO₃ molarity and Mo concentration for Mo sorption on different matrices is described in terms of their retention capacities and distribution coefficients.The selectivities of these exchangers towards molybdenum are in the order: CeSb > SiSb > FeSb > TiSb.     

Investigations on some inorganic ion-exchangers after irradiation

The changes in the ion exchange properties of crystalline zirconium phosphate, cerium phosphate and cerium arsenate after irradiation have been investigated. The absorbed gamma dose was 10⁹ rad in all cases, the experiments were carried out before and immediately after irradiation with the same samples. Besides the investigations of structural change, the ion exchange behaviour of the above mentioned materials was studied in detail. The ion exchange capacities were determined using a tracer technique for the alkali metal ions, and some relations between ion exchange and structure were revealed.     

除Cs用无机离子交换剂的筛选

本文对用于酸性高放废液除Ｃｓｗ的五大类,２０余种无机离子交换剂的Ｃｓ性能进行了研究和比较,确定凝胶－溶胶法制备的亚铁氰化钾钛为我国酸性高放废液除Ｃｓ的首选无机离子交换剂。     

Separation of -amino acids using a series of zwitterionic sulfobetaine exchangers

A set of five new covalently bond sulfobetaine exchangers with inner quaternary amines and outer sulfonic acids have been prepared by attachment of a series of zwitterionic precursors to hyperporous divinylbenzene polymers using a grafting reaction. The series of zwitterionic exchangers have the same backbone and identical spacers to the polymeric backbone, as well as comparable capacities. The only difference is the chain length for one to five methylene groups between the charged functional groups. Chromatographic properties are examined by separation of α-amino acids using sodium acetate and nitric acid eluents. The separation mechanism is explored by varying eluent ionic strength and eluent pH, resulting in the conclusion that amino acids are separated due to cation exchange interactions. This is a behavior never before observed using zwitterionic exchangers. It contradicts the fact that sulfobetaine-type materials used in zwitterionic ion chromatography (ZIC) usually are well suited for anion separation and only poorly for cation separation. Contrary to anion separations using the identical set of exchangers, the materials with three and four methylene groups between the charges give the highest retention factors. Materials showing the high potential in ZIC separations of inorganic anions give low retention factors for amino acids and vice versa.     

Ce离子对苯在Y分子筛上吸附扩散行为的影响

采用液相离子交换法制备了不同稀土含量的Y型分子筛(HY、USY和NaY),研究了稀土铈(Ce)阳离子在Y型分子筛上吸附-脱附烃类分子(苯)过程中的作用机理与影响。通过X射线荧光光谱仪(XRF)、智能质量分析仪(IGA)、脱附指数的计算和巨正则蒙特卡罗模拟计算等多种表征计算方法,对引入稀土物种后,Y型分子筛对苯的饱和吸附量、吸附作用力、脱附热力学参数、苯在Y分子筛上的吸附势能分布及扩散行为等方面进行了研究。结果表明,Ce离子对苯在Y分子筛上脱附活化能的降低、吸附作用力的减弱以及吸附态由团聚态向分散态转变等方面具有显著影响,该作用构成了CeY分子筛催化剂在流化催化裂化(FCC)过程中能够优化轻质产品选择性的重要因素。