Influence of Ionic Strength on Curium(III and Europium(III) Sorption on Halomonas elongata

For long-term safety analysis of a potential radioactive waste disposal site it is, amongst others, a prerequisite to characterize transport and retardation processes of relevant radionuclides to adequately describe hypothetical release scenarios and to assess the barrier capacity of the contaminant providing rock zone, the geological formation, and the overburden. To simulate migration processes of radionuclides a sound understanding of solid-solution interface reactions is necessary to determine the influence of the geochemical environment on sorption, precipitation, speciation, and dissolution processes. For long-term safety assessments of nuclear waste disposal sites, the behavior of activation and fission products as well as radionuclides from decay chains are of major interest. The trivalent lanthanide europium(III) is a chemical homologue for trivalent actinides such as curium(III) and americium(III). In the field of safety assessments there is still a need for sound data concerning the interaction of minerals with the surrounding solution even for well-known surfaces such as quartz, muscovite, and orthoclase. Up to now only some studies have taken the approach to study the interaction and interrelation of surface charge, surface complexation, and transport processes for trivalent lanthanides and actinides for orthoclase, muscovite, and quartz; and so far only few studies tried to describe all processes under varying geochemical conditions with one set of mineral-specific parameters as it had been done in this study. A vast amount of experiments was carried out and evaluated with mechanistic thermodynamic sorption models; surface complexation parameters of Eu were derived and subsequently used to simulate Eu reactive transport under varying experimental boundary conditions with reactive transport models. It was shown that the approach to simulate different geochemical conditions with one surface complexation parameter set yielded adequate predictions of Eu transport under laboratory and close to nature conditions for quartz systems; for orthoclase Eu transport under the influence of complexing ligands was also satisfyingly represented. This study contributed to fill the gap of sorption and transport data of Eu and, thus, trivalent actinides for ubiquitously present minerals. Expertise in the development of reactive transport models was gained and results offered insight into the transport of trivalent lanthanides and actinides.

In many concepts for geological disposal of radioactive waste will be disposed in underground repositories. The long term isolation of radionuolides from the biosphere will be ensured by the presence of several technical and natural barriers. A common technical barrier for radionuclides remaining from reprocessing of spent fuel is high-level nuclear waste glass (HLW-glass). Glass is stable for millions of years under dry conditions, but aqueous solutions may penetrate the near-field confinement and initiate alteration/dissolution of the HLW-glass. During alteration/dissolution processes the contained radionuclides may be mobilized, and various secondary phases form. Some of these new mineral phases represent a significant retention potential for mobilized radionuclides. The trioctahedral smectite hectorite Na 0 . 7 [Li 0 . 7 Mg 5 . 3 Si 8 O 2 0 (OH) 4 ] is one of these secondary phases identified within the alteration layer of corroded HLW glass. Numerous studies have dearly shown that many radionuclides are associated with clay minerals and the migration of radionuclides is strongly reduced by complexation. Due to the structural complexity and chemical variability of smectites, sorption of radionuclides involves several sorption mechanisms: (1) adsorption via inner-sphere and outer-sphere complexation (2) cation exchange in the interlayer and (3) formation of new secondary clay minerals opens the possibility to even incorporate radionuclides into the clay structure. In contrast to adsorbed species, incorporated species are associated with a more independent retention potential regarding changing geochemical conditions. Therefore, they are relevant to many issues in environmental and geochemical sciences. Until recently, it was not known whether the high radio toxic actinides become incorporated into the crystal structure of clay minerals like hectorite. Due to the potential importance in controlling actinide mobility, it is necessary to understand the mechanism of f-element incorporation into the clay structure in detail. Americium is one of the abundant actinides in HLW-glass, and may be mobilized during corrosion. Its chemical homologue, Curium, is present In lesser waste amount, but sensitive for speciation based on time-resolved laser spectroscopy. The lanthanide Europium also exhibits favorable spectroscopic characteristics and has been used as a non radioactive chemical homolog to identify the sorption mechanism. Therefore, using Eu(lll) and Cm(III) is a convenient way to study the chemical behavior of trivalent f-elements during formation of clay minerals. This study focuses on the multi-step synthesis of organo-hectorite as a model system for f-element coprecipitation with clay minerals. The new method was modified to synthesize an Eu- as well as a Cm-containing hectorite. The Eu-containing reaction products were identified unambiguously as hectorite by X-ray diffraction, FTIR-spectroscopy, and atomic force microscopy. After formation of hectorite in the presence of f-elements was assured, the sorption mechanisms of the associated Eu-species were investigated by time-resolved laser fluorescence spectroscopy (TRLFS) and extended X-ray absorption fine structure spectroscopy (EXAFS). An unhydrated Eu-species and a partly hydrated Eu-species could be identified by TRLFS. The unhydrated Eu-species can be interpreted as incorporated Eu(III) into the hectorite structure, or a remaining amorphous silica phase. The TRLFS-spectra of Eu-hectorite and the Eu-silica complexation are too similar to differentiate between these species, but dialysis experiments demonstrate the close association of the unhydrated Eu-species with the crystalline hectorite phase. Samples for TRLFS-measurements were taken during the dialysis process, and the same incorporated Eu-species was identified in the solid phases, as long as the Eu-hectorite was stable under acidic conditions.

Sorption behavior of Eu(Ⅲ) on Tamusu clay under strong ionic strength: Batch experiments and BSE/EDS analysis

KEYWORDS: ionic strengthbacteriacurium(III)europium(III)adsorptionHalomonas elongatecell surfacehydrophobicity

Enantioselectivity has always been a key feature of enzymatic synthesis. In some cases, when enzymes are not strictly enantioselective, by tuning the reaction conditions it is possible to induce an enantioselective switch. A transaminase from Halomonas elongata (ω-HeWT), while generally S-selective, could be shifted towards generating the R-enantiomer at higher concentrations of amino acceptor or ionic strength, for example. Other enzymes are reported to have a similar behavior, and here we discuss some of them and their potential applications.

مصرف بی‌رویه و نادرست آفت‌کش‌ها سبب آلودگی محیط زیست شده است. به منظور کاهش تحرک این ترکیبات در خاک و آلودگی محیط زیست، لزوم کمی نمودن سرنوشت علف‌کش‌هایی با مصرف خاکی وجود دارد. در این تحقیق جذب ماده آلی محلول با غلظت‌های 0، 10، 20، 40، 80 و 160 میلی‌گرم کربن آلی در لیتر در دو خاک در شرایط آزمایشگاهی و در دمای ثابت مورد بررسی قرار گرفت. همچنین تأثیر pH و ماده آلی محلول با غلظت‌های مختلف (0، 10، 40 و 160 میلی‌گرم در لیتر) بر جذب علف‌کش متری‌بیوزین (با مقادیر 5/1، 2، 3، 4، 5 و 6 میلی‌گرم در کیلوگرم) مورد مطالعه قرار گرفت. نتایج نشان داد که ماده آلی محلول بر روی خاک‌ها جذب سطحی شده و هم‌دماهای آن‌ها با مدل فروندلیچ مطابقت داشت. جذب سطحی علف‌کش متری‌بیوزین در هر دو خاک 1 و 2 در حضور ماده آلی محلول کاهش نشان داد. به‌طوری که بیشترین مقدار جذب متری‌بیوزین در هر دو خاک 1 و 2 در تیمار بدون حضور ماده آلی محلول به ترتیب 19/38 و 71/29 میلی‌گرم در کیلوگرم و کمترین میزان در تیمار 160 میلی‌گرم ماده آلی محلول در لیتر به ترتیب 75/7 و 42/5 میلی‌گرم در کیلوگرم بدست آمد. جذب متری‌بیوزین در دامنه pH 5/5-4 در خاک 1 و 2، در تیمار عدم حضور ماده آلی محلول به ترتیب 54/8 و 23/6 درصد بیشتر از تیمار حضور ماده آلی محلول محاسبه گردید. به‌طور کلی افزایش غلظت ماده آلی محلول، سبب کاهش جذب متری‌بیورزین بر روی دو خاک گردید.

This dataset shows the capacity for Europium of media #1 and media #2 in a shakertable experiment. The experimental conditions were 150mL of 500ppm Eu solution, 2g of media, pH of 3.2, at ambient temperature.

Ionic Strength Effects on Cation Sorption to Oxides: Macroscopic Observations and Their Significance in Microscopic Interpretation

It has been firmly established that organic osmolytes (compatible solutes) of halophilic Bacteria and Archaea have positive effects on conformation and activity of proteins, and may therefore improve their functional production. In particular, the amino acid derivative ectoine is known for its conformational stabilization, aggregation suppression, and radical protection properties. The natural producer and industrial production strain Halomonas elongata accumulates ectoine in the cytoplasm, and as a result offers a unique stabilizing environment for recombinant proteins. For the construction of broad hoast range vector systems with fluorescent reporter proteins, we chose the salt-inducible promoter region of the ectoine gene cluster (promA). A closer inspection of the genetic background revealed that its combination of sigma 38 (σ38) and sigma 70 (σ70) promoters was followed by a weak ribosomal binding site (RBS). This inspired a systematic approach for the construction of a promA-based vector series with a synthetic RBS region using the RBS Calculator v2.0, which resulted in a greatly improved salt-dependent expression—even in a deletion construct lacking the σ38 promoter. To expand the application range of this expression system, we looked further into the possible export of recombinant proteins into the periplasm. Both sec and tat leader sequences from H. elongata proved to be suitable for directed periplasmic transport into an extreme environment of freely selectable ionic strength.

Enzymatic enantiopreference is one of the key advantages of biocatalysis. While exploring the synthesis of small cyclic (chiral amines) such as 3‐aminotetrahydrofuran (THF‐amine), using the (S)‐selective transaminase from Halomonas elongata (HEwT), inversion of the enantiopreference was observed at increasing substrate loadings. In addition, the enantiopreference could be altered by variation of the ionic strength, or of the co‐solvent content in the reaction mixture. For example, using otherwise identical reaction conditions, the presence of 2 M sodium chloride gave (R)‐THF‐amine (14 % ee), while the addition of 2.2 M isopropyl alcohol gave the (S)‐enantiomer in 30 % ee. While the underlying cause is not currently understood, it appears likely that subtle changes in the structure of the enzyme cause the shift in enantiopreference and are worth exploring further.

There was synthesized a new sorbent on the basis of maleic anhydride’s copolymer with styrene, modified by dithiocarbamide. There was examined influence of pH on concentrating of lead(II) with chelating sorbent. There was plotted isotherm of lead(II) sorption with synthesized sorbent and investigated optimal conditions of concentration. There was established that with increasing concentration of lead in solution increases quantity of sorptive metal. There was examined influence of ionic strength on sorption. The increasing of ionic strength to 0, 4 mole/l marginally influence on sorption. There was examined influence of different inorganic acids (HClO4, H2SO4, HNO3, HCl) with identical concentration on desorption of lead(II) from sorbent. Maximal desorption of lead(II) is occurred in perchlorate acid. The rate of extraction of lead(II) at optimal conditions was not exceeds 95 %. There was developed procedure of sorption photometric determination of lead(II) in standard specimen ST-IA (519-84 P).

Effect of humic acid on sorption of trace metal ions by sodium aluminosilicate

Revealing chemical speciation behaviors in aqueous solutions for uranium (VI) and europium (III) adsorption on zeolite

The sorption of europium, Eu(III), on suspended silica was studied in perchlorate media under varying concentrations of Eu(III) and silica, at pH 4 to 8, and ionic strength from 0.20 to 1.40 M NaClO4at 298 K. The complexing anions, carbonate, acetate, citrate, oxalate, phosphate and EDTA, affected the sorption of Eu(III). A synergistic enhancement in the sorption of Eu(III) was observed for oxalate and phosphate ligands. Other anions suppressed the sorption in the order: acetate < carbonate < citrate < EDTA. The results of TRLFS studies were consistent with ternary Eu/silica/ligand complexation for oxalate and phosphate anions.

Sorption of Eu(III) onto titanium dioxide: Measurements and modeling