High Sorption and Selective Extraction of Actinides from Aqueous Solutions

The selective elimination of long-lived radioactive actinides from complicated solutions is crucial for pollution management of the environment. Knowledge about the species, structures and interaction mechanism of actinides at solid–water interfaces is helpful to understand and to evaluate physicochemical behavior in the natural environment. In this review, we summarize recent works about the sorption and interaction mechanism of actinides (using U, Np, Pu, Cm and Am as representative actinides) on natural clay minerals and man-made nanomaterials. The species and microstructures of actinides on solid particles were investigated by advanced spectroscopy techniques and computational theoretical calculations. The reduction and solidification of actinides on solid particles is the most effective way to immobilize actinides in the natural environment. The contents of this review may be helpful in evaluating the migration of actinides in near-field nuclear waste repositories and the mobilization properties of radionuclides in the environment.     

Synthesis of novel nanomaterials and their application in efficient removal of radionuclides

With the development of nuclear energy, large amounts of radionuclides are inevitably released into the natural environment. It is necessary to eliminate radionuclides from wastewater for the protection of environment. Nanomaterials have been considered as the potential candidates for the effective and selective removal of radionuclides from aqueous solutions under complicated conditions because of their high specific surface area, large amounts of binding sites, abundant functional groups, pore-size controllable and easily surface modification. This review mainly summarized the recent studies for the synthesis, fabrication and surface modification of novel nanomaterials and their applications in the efficient elimination and solidification of radionuclides,and discussed the interaction mechanisms from batch experiments, spectroscopy analysis and theoretical calculations. The sorption capacities with other materials, advantages and disadvantages of different nanomaterials are compared, and at last the perspective of the novel nanomaterials is summarized.     

Microstructures and speciation of radionuclides in natural environment studied by advanced spectroscopy and theoretical calculation

The environmental behavior of radionuclides is mainly dependent on their speciation and microstructures at solid particles.The speciation and microstructures of radionuclides at molecular level can be achieved from advanced spectroscopy techniques and theoretical calculations.In this perspective,we give a brief introduction of the advanced X-ray absorption fine structure(XAFS) technique and theoretical calculation in the analysis of the speciation and microstructures of radionuclides in the natural environment,which is crucial to evaluate the physicochemical behavior of radionuclides in the environment.     

Comparison studies adsorption of thorium and uranium on pure clay minerals and local Malaysian soil sediments

Adsorption studies of thorium and uranium radionuclides on 9 different pure clay minerals and 4 local Malaysian soil sediments were conducted. Solution containing dissolved thorium and uranium at pH 4.90 was prepared from concentrate sludges from a long term storage facility at a local mineral processing plant. The sludges are considered as low level radioactive wastes. The results indicated that the 9 clay minerals adsorbed more uranium than thorium at pH ranges from 3.74 to 5.74. Two local Malaysian soils were observed to adsorb relatively high concentration of both radionuclides at pH 3.79 to 3.91. The adsorption value 23.27 to 27.04 ppm for uranium and 33.1 to 50.18 ppm for thorium indicated that both soil sediments can be considered as potential enhanced barrier material for sites disposing conditioned wastes containing uranium and thorium.     

Analytical techniques for determining radionuclides associated with colloids in waters

Colloids play a major role in the transport of trace metals as well as radionuclides in natural waters. These species are of importance for passive take in biota.Radionuclides may form colloids and pseudocolloids during hydrolysis or through interaction with other components present in the water phase, such as clay minerals or humic substances. Furthermore, aggregation and dispersion and other transformation processes, will influence the colloidal fraction, for instance during storage of samples. Fractionation of radionuclides associated with colloids in natural waters should, therefore, take place in situ or shortly after sampling.Different analytical techniques are useful for the fractionation of colloids, pseudocolloids, and particles. In the present paper, the application of hollow fiber ultrafiltration and dialysis is demonstrated for radionuclides in waste waters from the Oscarshamn nuclear installation in Sweden.The results illustrate that hollow fiber ultrafiltration is a more powerful technique than dialysis. The fractionation is rapid, sorption is of minor significance, the pore size distribution is rather narrow, and the filtering capacity is high.     

Formation of Layered Single- and Double-Metal Hydroxide Precipitates at the Mineral/Water Interface: A Multiple-Scattering XAFS Analysis

Spectroscopic and microscopic studies have shown that Ni and Co sorption by clay minerals may proceed via formation of surface precipitates. Several studies employing X-ray absorption fine structure (XAFS) spectroscopy suggested the formation of turbostratic, alpha-type metal hydroxides, of layered double hydroxides (LDH) with Al-for-metal substitution, and of 1:1 or 2:1 phyllosilicates. Distinction of these phases is difficult because they have low crystallinity and/or a small mass compared to the sorbents, and because they have similar metal-metal distances in their hydroxide layers/sheets. Distinction of these phases is crucial, however, because they have substantially differing solubilities. In this paper we show that an XAFS beat pattern at about 8 ?(-1) can be used as a fingerprint to unequivocally distinguish LDH from the alpha-type hydroxides and phyllosilicates. Full multiple-scattering simulations and experimental spectra of model compounds indicate that the beat pattern is due to focused multiple scattering at Me/Al ratios between 1 and 4 (Me=Ni, Co). By applying the fingerprint method to new and to already published XAFS data on Ni and Co surface precipitates, we found that LDH preferentially forms in the presence of the Al-containing sorbents pyrophyllite, illite, kaolinite, gibbsite, and alumina above pH 7.0. However, alpha-type metal hydroxides form in the presence of the Al-free sorbents talc, silica, and rutile, and in the presence of the Al-containing clay minerals montmorillonite and vermiculite. We believe that the high permanent charge of these latter minerals prevents or retards the release of Al. When Al is available, the formation of LDH seems to be thermodynamically and/or kinetically favored over the formation of alpha-type hydroxides. Copyright 2000 Academic Press.     

Ultrathin hybrid films of clay minerals

Smectites or swelling clay minerals are naturally occurring nanomaterials that can be fully delaminated to elementary clay mineral platelets in dilute aqueous dispersion. This review article gives an overview of the recent progress on how the elementary clay mineral platelets can be reorganized in monolayered or multilayered hybrid nanofilms by layer-by-layer assembly or the Langmuir-Blodgett technique. In the latter case one hybrid layer consists of one layer of elementary clay mineral platelets with a theoretical thickness of 0.96 nm, covered on one side by amphiphilic cations. The organization of the elementary clay mineral platelets and that of the adsorbed amphiphilic cations in the nanofilms has been studied in great detail by ATR-FTIR, UV-Vis and fluorescence spectroscopy, XRD and AFM. The nanofilms carry functional properties, such as chirality, optical nonlinearity and magnetism, which are due to the nature of the amphiphilic cations and to the organization of both the amphiphilic molecules and the elementary clay mineral platelets.     

Sorption speciation of lanthanides/actinides on minerals by TRLFS, EXAFS and DFT studies: a review

Lanthanides/actinides sorption speciation on minerals and oxides by means of time resolved laser fluorescence spectroscopy (TRLFS), extended X-ray absorption fine structure spectroscopy (EXAFS) and density functional theory (DFT) is reviewed in the field of nuclear disposal safety research. The theoretical aspects of the methods are concisely presented. Examples of recent research results of lanthanide/actinide speciation and local atomic structures using TRLFS, EXAFS and DFT are discussed. The interaction of lanthanides/actinides with oxides and minerals as well as their uptake are also of common interest in radionuclide chemistry. Especially the sorption and inclusion of radionuclides into several minerals lead to an improvement in knowledge of minor components in solids. In the solid-liquid interface, the speciation and local atomic structures of Eu(III), Cm(III), U(VI), and Np(IV/VI) in several natural and synthetic minerals and oxides are also reviewed and discussed. The review is important to understand the physicochemical behavior of lanthanides/actinides at a molecular level in the natural environment.     

A review of the migration of radioactive elements in clay minerals in the context of nuclear waste storage

Journal of Radioanalytical and Nuclear Chemistry - Clay is a widespread natural mineral. The review considers physical and chemical properties of clay minerals which are important in terms of...     

Nickel Sorption Mechanisms in a Pyrophyllite-Montmorillonite Mixture

Nickel sorption on pyrophyllite, montmorillonite and a 1:1 pyrophyllite-montmorillonite mixture was studied at pH 7.5 and a reaction time of 40 min. The main modes of Ni uptake under these reaction conditions are adsorption on montmorillonite and surface precipitation on pyrophyllite. For the clay mixture, where adsorption on the montmorillonite component and surface precipitation on the pyrophyllite component compete for Ni uptake, X-ray absorption fine structure spectroscopy (XAFS) was used to estimate the distribution of Ni over the mixture components. This was done by comparison to pyrophyllite-montmorillonite mixtures with known Ni distributions over the mixture components. Nickel uptake on singly reacted pyrophyllite was slightly higher than on singly reacted montmorillonite. This was consistent with the XAFS results for the clay mixture, which suggested that the pyrophyllite component sorbed slightly more Ni than the montmorillonite component. Our findings suggested that both adsorption and surface precipitation were important mechanisms in the overall Ni uptake in the clay mixture, and that neither sorption mechanism truly out-competed the other in the reaction time of 40 min employed. Therefore, both mechanisms should be considered when modeling Ni sorption in similar systems. Copyright 1999 Academic Press.     

Radionuclide‐Activated Nanomaterials and Their Biomedical Applications

Radio‐nanomedicine, or the use of radiolabeled nanoparticles in nuclear medicine, has attracted much attention in the last few decades. Since the discovery of Cerenkov radiation and its employment in Cerenkov luminescence imaging, the combination of nanomaterials and Cerenkov radiation emitters has been revolutionizing the way nanomaterials are perceived in the field: from simple inert carriers of radioactivity to activatable nanomaterials for both diagnostic and therapeutic applications. Herein, we provide a comprehensive review on the types of nanomaterials that have been used to interact with Cerenkov radiation and the gamma and beta scintillation of radionuclides, as well as on their biological applications.     

Radionuclide migration experiments in the laboratory: Some radioanalytical aspects

Radionuclide transport studies in consolidated and unconsolidated geological media are being performed in the laboratory as part of the Canadian Nuclear Fuel Waste Management Program. These studies present an interesting challenge to radiochemists because many of the radionuclides are either not eluted or only partially eluted from fractures or from columns. Therefore, non-invasive radiometric analyses have been applied to determine the location of radionuclides along a flow path during a migration experiment, and invasive analyses have been developed to determine the transport behaviour of these radionuclides at the termination of a migration experiment. Linear gamma scanning has been used in migration experiments with^95mTc and¹³¹I through columns of crushed fracture-infilling material to follow their movement through the columns. Two-dimensional gamma scanning has been used to determine the distribution of¹⁴⁴Ce on fracture surfaces at the termination of migration experiments through natural fractures in granite. In addition, information on the interaction of radionuclides with specific minerals can often be obtained by separating minerals on the basis of density, or by a combination of density and magnetic properties, followed by radiometric assay of the separated fractions.     

XAFS技术在单原子电催化中的应用

X射线吸收精细谱学(XAFS)技术是从20世纪80年代开始逐渐发展起来的一种材料表征技术, 具有对中心吸收原子的局域结构和化学环境敏感的特征, 非常适合表征单原子催化剂. 本文从XAFS技术的原理和特点出发, 深入探讨了该技术在电催化水分解、 燃料电池阴极反应和二氧化碳电化学还原等多个单原子催化应用场景下的独特作用, 并展望了XAFS技术在单原子电催化领域的未来发展与应用前景, 以期为更深入明确的单原子催化剂结构表征和电催化机理描述提供指导.     

Recent Developments in the In Situ XAFS and Related Work for the Characterization of Catalysts in Japan

This short review deals with some recent XAFS (X-ray absorption fine structure) applications to catalysts in Japan. The high transmission ability of X rays makes it possible to carry out in situ work on catalysts. First, in situ XAFS works under flow and high-pressure reaction conditions will be described. The time-resolved XAFS work will be another important topic because it can provide the possibility of observing the change of the reaction active site and the reaction intermediate. Finally, PTRF-XAFS will be described, which is a unique technique and provides three-dimensional local structures of highly dispersed surface species.     

Review: Natural oxalates and their analogous synthetic complexes

Metal oxalates, commonly classified as organic minerals, are widely distributed in Nature, occurring in mineral deposits or as biominerals in plants, fungi, and lichens or in the form of deposits, of different kinds, in animal tissues. Eighteen natural species of this type have so far been reported and investigated. In the first part of this review we give an overview on the general characteristics of these minerals, including also some comments on their environmental effects. The central part of the review is devoted to the discussion of synthetic oxalates, analogous to the natural species, including the usual procedures employed for their synthesis and the thorough analysis of their crystallographic and structural peculiarities. The thermal, spectroscopic, and magnetic properties of these complexes are also discussed in detail. Some comparisons with related coordination compounds are also made along the text.     

Characterization and quantification of Sm(III)/ and Cm(III)/clay mineral outer-sphere species by TRLFS in D2O and EXAFS studies

In order to assess the long-term safety of deep radioactive waste repositories, a precise characterization of the different sorption processes on a molecular basis and the exact definition of geochemical boundary conditions for their relevance are of immense importance. Through sorption on various minerals the migration of radionuclides will be hindered and their retention will be ensured. Using time-resolved laser fluorescence spectroscopy (TRLFS) and extended X-ray absorption fine structure (EXAFS) spectroscopy, it was possible to identify outer-sphere sorbed trivalent lanthanides and actinides onto different montmorillonites and illite. Furthermore, the quantification of Cm(III)/clay outer-sphere sorption in D(2)O at different ionic strengths was shown. The results were confirmed by ion exchange model calculations. Finally, the structural parameters of a Sm(III)/clay outer-sphere complex were obtained by EXAFS measurements.     

Adsorption study of cationic dyes having a trimethylammonium anchor group on hectorite using electrooptic and spectroscopic methods

Clay minerals are natural or synthetic material of colloidal dimensions. Due to the sheetlike structure clay minerals offer a huge specific surface area and hence optimal properties for modification through adsorption. The current work studies the adsorption of five cationic dyes on the synthetic clay mineral hectorite. All dyes have a trimethylammonium anchoring group in common. The adsorbed dye molecules are characterized by means of pulsed electric linear dichroism and UV-VIS spectroscopy. With increasing dye loading a continuous shift in the absorption spectra is observed. But there is no occurrence of a new absorption band. Therefore we conclude that the dyes preferentially adsorb as amorphous aggregates on the clay surface. At low dye loadings the dye molecules lie flat on the clay mineral surface. Increasing dye concentration leads to a continuous increase in average tilt angle. However the orientation of the dye molecules is very sensitive to functional groups. The introduction of a nitro group to a particular dye increases significantly the tendency to lie flat on the surface whereas the introduction of a methoxy group at the same position has the opposite effect.     

Determination of anisotropic surface characteristics of different phyllosilicates by direct force measurements

To fundamentally understand the electrokinetic behavior of clay minerals, it is necessary to study the anisotropic surface charge properties of clay surfaces. In this study, two 2:1 layer natural minerals, talc and muscovite, were chosen as representatives of magnesium and aluminum phyllosilicate minerals, respectively. The molecularly smooth basal planes of both platy minerals were obtained by cleavage along the basal planes, while suitable edge surfaces were prepared by an ultramicrotome cutting technique. Silicon nitride atomic force microscopy tip was used as a probe to study the interaction forces between the tip and clay basal/edge surfaces in aqueous solutions of various pH values. The measured interaction force profiles between the tip and clay basal/edge surfaces were fitted with the classical DLVO (Derjaguin-Landau-Verwey-Overbeek) theory, which allows direct determination of electrical surface potential of talc and muscovite surfaces. The surface potential of muscovite basal planes was found to be significantly more negative than the basal plane of talc, both being pH insensitive. In contrast, the surface potential of edge surfaces was highly pH-dependent, exhibiting a point of zero charge (PZC) at pH 7.5 and 8.1 for edges of muscovite and talc, respectively. The observed differences in surface potential of basal planes and edge surfaces for both talc and muscovite are closely related to their crystal structure and ionization characteristics. The protonation reactivity and the contribution of each surface group to the surface charging behavior are modeled using their protonation constants.     

Sorption of Tc(VII) and Am(III) by carbon materials: effect of oxidation

In this work we studied the effect of oxidation on the sorption properties of carbon materials, produced on the basic of activated carbons FAS and VSK in relation to radionuclides Am(III) and Tc(VII). It has been found that the oxidation increases the distribution coefficients for the extraction of radionuclides of sorption nitric acid raising agents. As to identify the mechanism of the oxidation influence on the sorption properties the physical and chemical properties of the synthesized samples (porous surface structure, IR-spectrums etc.) were studied. The possibility of removal of radionuclides from the real industrial solutions of complex composition using of the obtained carbon nanomaterials was investigated.