Revisiting the Complexation of Cm(III) with Aqueous Phosphates: What Can We Learn from the Complex Structures Using Luminescence Spectroscopy and Ab Initio Simulations?

The coordination chemistry of Cm(III) with aqueous phosphates was investigated by means of laser-induced luminescence spectroscopy and ab initio simulations. For the first time, in addition to the presence of Cm(H2PO4)2+, the formation of Cm(H2PO4)2+ was unambiguously established from the luminescence spectroscopic data collected at various H+ concentrations (-log10 [H+] = 2.52, 3.44, and 3.65), ionic strengths (0.5-3.0 mol·L-1 NaClO4), and temperatures (25-90 °C). Complexation constants for both species were derived and extrapolated to standard conditions using the specific ion interaction theory. The molal enthalpy ΔRHm0 and molal entropy ΔRSm0 of both complexation reactions were derived using the integrated van't Hoff equation and indicated an endothermic and entropy-driven complexation. For the Cm(H2PO4)2+ complex, a more satisfactory description could be obtained when including the molal heat capacity term. While monodentate binding of the H2PO4- ligand(s) to the central curium ion was found to be the most stable configuration for both complexes in our ab initio simulations and luminescence lifetime analyses, a different temperature-dependent coordination to hydration water molecules could be deduced from the electronic structure of the Cm(III)-phosphate complexes. More precisely, where the Cm(H2PO4)2+ complex could be shown to retain an overall coordination number of 9 over the entire investigated temperature range, a coordination change from 9 to 8 was established for the Cm(H2PO4)2+ species with increasing temperature.

Impact of the Microbial Origin and Active Microenvironment on the Shape of Biogenic Elemental Selenium Nanomaterials.

The shape of nanomaterials affects their colloidal properties, cellular uptake, and fate in the environment. The microbial origin and microenvironment can play a role in altering the shape of the nanomaterial. However, such studies have never been conducted. Here, we demonstrate that the selenium nanomaterials produced by Escherichia coli K-12 are stable and remain as BioSe-Nanospheres under thermophilic conditions, while those produced by anaerobic granular sludge transform to BioSe-Nanorods, due to a lower quantity of proteins coating these nanoparticles, which has been verified by proteomics analysis as well as using chemically synthesized selenium nanomaterials. Furthermore, the presence of Bacillus safensis JG-B5T transform the purified BioSe-Nanospheres produced by E. coli K-12 to BioSe-Nanorods, though they are not transformed in the absence of B. safensis JG-B5T. This is due to the production of peptidases by B. safensis JG-B5T that cleaves the protein coating the BioSe-Nanospheres produced by E. coli K-12, leading to their transformation to trigonal BioSe-Nanorods, which is the thermodynamically more stable state. These findings suggest that the fate of selenium and probably other redox-active elements released from the biological wastewater treatment units needs to be reevaluated and improved by including microbial criteria for better accuracy.

Magnetic properties of biogenic selenium nanomaterials.

Bioreduction of selenium oxyanions to elemental selenium is ubiquitous; elucidating the properties of this biogenic elemental selenium (BioSe) is thus important to understand its environmental fate. In this study, the magnetic properties of biogenic elemental selenium nanospheres (BioSe-Nanospheres) and nanorods (BioSe-Nanorods) obtained via the reduction of selenium(IV) using anaerobic granular sludge taken from an upflow anaerobic sludge blanket (UASB) reactor treating paper and pulp wastewater were investigated. The study indicated that the BioSe nanomaterials have a strong paramagnetic contribution with some ferromagnetic component due to the incorporation of Fe(III) (high-spin and low-spin species) as indicated by electron paramagnetic resonance (EPR). The paramagnetism did not saturate up to 50,000 Oe at 5 K, and the hysteresis curve showed the coercivity of 100 Oe and magnetic moment saturation around 10 emu. X-ray photoelectron spectroscopy (XPS) and EPR evidenced the presence of Fe(III) in the nanomaterial. Signals for Fe(II) were observed neither in EPR nor in XPS ruling out its presence in the BioSe nanoparticles. Fe(III) being abundantly present in the sludge likely got entrapped in the extracellular polymeric substances (EPS) coating the biogenic nanomaterials. The presence of Fe(III) in BioSe nanomaterial increases the mobility of Fe(III) and may have an effect on phytoplankton growth in the environment. Furthermore, as supported by the literature, there is a potential to exploit the magnetic properties of BioSe nanomaterials in drug delivery systems as well as in space refrigeration.

Temperature-dependent luminescence spectroscopic and mass spectrometric investigations of U(VI) complexation with aqueous silicates in the acidic pH-range.

In this study the complexation of U(VI) with orthosilicic acid (H4SiO4) was investigated between pH 3.5 and 5 by combining electrospray ionization mass spectrometry (ESI-MS) and laser-induced luminescence spectroscopy. The ESI-MS experiments performed at a total silicon concentration of 5 · 10-3M (exceeding the solubility of amorphous silica at both pH-values) revealed the formation of oligomeric sodium-silicates in addition to the UO2OSi(OH)3+ species. For the luminescence spectroscopic experiments (25 °C), the U(VI) concentration was fixed at 5 · 10-6M, the silicon concentration was varied between 1.3 · 10-4-1.3 · 10-3M (reducing the formation of silicon oligomers) and the ionic strength was kept constant at 0.2 M NaClO4. The results confirmed the formation of the aqueous UO2OSi(OH)3+ complex. The conditional complexation constant at 25 °C, log *ß = -(0.31 ± 0.24), was extrapolated to infinite dilution using the Davies equation, which led to log *ß0 = -(0.06 ± 0.24). Further experiments at different temperatures (1-25 °C) allowed the calculation of the molal enthalpy of reaction ΔrHm0 = 45.8 ± 22.5 kJ·mol-1 and molal entropy of reaction ΔrSm0 = 152.5 ± 78.8 J·K-1·mol-1 using the integrated van't Hoff equation, corroborating an endothermic and entropy driven complexation process.

Bacillus safensis JG-B5T affects the fate of selenium by extracellular production of colloidally less stable selenium nanoparticles.

Understanding the impact of microorganisms on the mobility of selenium (Se) is important for predicting the fate of toxic Se in the environment and improving wastewater treatment technologies. The bacteria strain Bacillus safensis JG-B5T, isolated from soil in a uranium mining waste pile, can influence the Se speciation in the environment and engineered systems. However, the mechanism and conditions of this process remain unknown. This study found that the B. safensis JG-B5T is an obligate aerobic microorganism with an ability to reduce 70% of 2.5 mM selenite to produce red spherical biogenic elemental selenium nanoparticles (BioSeNPs). Only extracellular production of BioSeNPs was observed using transmission electron microscopy. The two-chamber reactor experiments, genome analysis and corona proteins identified on BioSeNPs suggested that the selenite reduction process was primarily mediated through membrane-associated proteins, like succinate dehydrogenase. Extracellular presence and low colloidal stability of BioSeNPs as indicated by ζ-potential measurements, render B. safensis JG-B5T an attractive candidate in wastewater treatment as it provides easy way of recovering Se while maintaining low Se discharge. As this microorganism decreases Se mobility, it will affect Se bioavailability in the environment and decreases its toxicity.

Draft Genome Sequence of Bacillus safensis Strain JG-B5T, Isolated from a Uranium Mining Waste Pile.

Bacillus safensis strain JG-B5T was isolated from soil of the uranium mining waste pile Haberland located near Johanngeorgenstadt, Saxony, Germany. We report here a draft genome sequence (3.7 Mb) of this bacterial strain. The high metal resistance abilities of B. safensis strain JG-B5T can be exploited for bioremediation of metal and metalloid-contaminated environments.

Removal and recovery of uranium(VI) by waste digested activated sludge in fed-batch stirred tank reactor.

This study demonstrated the removal and recovery of uranium(VI) in a fed-batch stirred tank reactor (STR) using waste digested activated sludge (WDAS). The batch adsorption experiments showed that WDAS can adsorb 200 (±9.0) mg of uranium(VI) per g of WDAS. The maximum adsorption of uranium(VI) was achieved even at an acidic initial pH of 2.7 which increased to a pH of 4.0 in the equilibrium state. Desorption of uranium(VI) from WDAS was successfully demonstrated from the release of more than 95% of uranium(VI) using both acidic (0.5 M HCl) and alkaline (1.0 M Na2CO3) eluents. Due to the fast kinetics of uranium(VI) adsorption onto WDAS, the fed-batch STR was successfully operated at a mixing time of 15 min. Twelve consecutive uranium(VI) adsorption steps with an average adsorption efficiency of 91.5% required only two desorption steps to elute more than 95% of uranium(VI) from WDAS. Uranium(VI) was shown to interact predominantly with the phosphoryl and carboxyl groups of the WDAS, as revealed by in situ infrared spectroscopy and time-resolved laser-induced fluorescence spectroscopy studies. This study provides a proof-of-concept of the use of fed-batch STR process based on WDAS for the removal and recovery of uranium(VI).

Selenium(IV) Sorption Onto γ-Al2O3: A Consistent Description of the Surface Speciation by Spectroscopy and Thermodynamic Modeling.

The sorption processes of Se(IV) onto γ-Al2O3 were studied by in situ Infrared spectroscopy, batch sorption studies, zeta potential measurements and surface complexation modeling (SCM) in the pH range from 5 to 10. In situ attenuated total reflection fourier-transform infrared (ATR FT-IR) spectroscopy revealed the predominant formation of a single inner-sphere surface species at the alumina surface, supporting previously reported EXAFS results, irrespective of the presence or absence of atmospherically derived carbonate. The adsorption of Se(IV) decreased with increasing pH, and no impact of the ionic strength was observed in the range from 0.01 to 0.1 mol L-1 NaCl. Inner-sphere surface complexation was also suggested from the shift of the isoelectric point of γ-Al2O3 observed during zeta potential measurements when Se(IV) concentration was 10-4 mol L-1. Based on these qualitative findings, the acid-base surface properties of γ-Al2O3 and the Se(IV) adsorption edges were successfully described using a 1-pK CD-MUSIC model, considering one bidentate surface complex based on previous EXAFS results. The results of competitive sorption experiments suggested that the surface affinity of Se(IV) toward γ-Al2O3 is higher than that of dissolved inorganic carbon (DIC). Nevertheless, from the in situ experiments, we suggest that the presence of DIC might transiently impact the migration of Se(IV) by reducing the number of available sorption sites on mineral surfaces. Consequently, this should be taken into account in predicting the environmental fate of Se(IV).

Sediment-bound trace metals in Golfe-Juan Bay, northwestern Mediterranean: Distribution, availability and toxicity.

The concentration, potential mobility, cation exchange capacity and toxicity of eight sediment-bound metals in Golfe-Juan Bay, France were examined. Results revealed significant spatial gradient of metal contamination along Golfe-Juan coast. The distribution and concentration of the metals appear to be influenced by the geochemical properties of the sediment, proximity to anthropogenic sources and general water circulation in the bay. The portion of trace metals found in the exchangeable, carbonate, oxidizable and reducible fractions of the sediment constitute 31%-58% of the total sediment-bound trace metal content, suggesting significant potential for remobilization of metals into the water column. Pb and Ni content of the sediment exceed the limits of the French marine sediment quality. Whole sediment extracts showed acute toxicity to marine rotifers. This study concludes that monitoring and management of sediment-bound trace metals in Golfe-Juan Bay are important so as not to underestimate their availability and risk to the marine ecosystems.

Entrapped elemental selenium nanoparticles affect physicochemical properties of selenium fed activated sludge.

Selenite containing wastewaters can be treated in activated sludge systems, where the total selenium is removed from the wastewater by the formation of elemental selenium nanoparticles, which are trapped in the biomass. No studies have been carried out so far on the characterization of selenium fed activated sludge flocs, which is important for the development of this novel selenium removal process. This study showed that more than 94% of the trapped selenium in activated sludge flocs is in the form of elemental selenium, both as amorphous/monoclinic selenium nanospheres and trigonal selenium nanorods. The entrapment of the elemental selenium nanoparticles in the selenium fed activated sludge flocs leads to faster settling rates, higher hydrophilicity and poorer dewaterability compared to the control activated sludge (i.e., not fed with selenite). The selenium fed activated sludge showed a less negative surface charge density as compared to the control activated sludge. The presence of trapped elemental selenium nanoparticles further affected the spatial distribution of Al and Mg in the activated sludge flocs. This study demonstrated that the formation and subsequent trapping of elemental selenium nanoparticles in the activated sludge flocs affects their physicochemical properties.

Extracellular polymeric substances govern the surface charge of biogenic elemental selenium nanoparticles.

The origin of the organic layer covering colloidal biogenic elemental selenium nanoparticles (BioSeNPs) is not known, particularly in the case when they are synthesized by complex microbial communities. This study investigated the presence of extracellular polymeric substances (EPS) on BioSeNPs. The role of EPS in capping the extracellularly available BioSeNPs was also examined. Fourier transform infrared (FT-IR) spectroscopy and colorimetric measurements confirmed the presence of functional groups characteristic of proteins and carbohydrates on the BioSeNPs, suggesting the presence of EPS. Chemical synthesis of elemental selenium nanoparticles in the presence of EPS, extracted from selenite fed anaerobic granular sludge, yielded stable colloidal spherical selenium nanoparticles. Furthermore, extracted EPS, BioSeNPs, and chemically synthesized EPS-capped selenium nanoparticles had similar surface properties, as shown by ζ-potential versus pH profiles and isoelectric point measurements. This study shows that the EPS of anaerobic granular sludge form the organic layer present on the BioSeNPs synthesized by these granules. The EPS also govern the surface charge of these BioSeNPs, thereby contributing to their colloidal properties, hence affecting their fate in the environment and the efficiency of bioremediation technologies.

Selenium(IV) uptake by maghemite (γ-Fe2O3).

The mechanism of selenium(IV) uptake by maghemite was investigated on both the macroscopic and the molecular level. Maghemite nanoparticles exhibited fast adsorption kinetics toward selenium(IV). Batch experiments showed a decreased sorption with increasing pH (3.5-11). Ionic strength variations (0.01 to 0.1 M NaCl) had no significant influence on selenium(IV) uptake. Electrophoretic mobility measurements revealed a significant shift toward lower values of the isoelectric point of maghemite upon selenium(IV) uptake, suggesting the formation of inner-sphere surface complexes. At the molecular level, using X-ray Absorption Fine-Structure Spectroscopy (EXAFS), the formation of both bidentate binuclear corner-sharing ((2)C) and bidentate mononuclear edge-sharing ((1)E) inner-sphere surface complexes was observed, with a trend toward solely (1)E complexes at high pH. The absence of a tridentate surface complex as observed for arsenic(III) and antimonite(III) might be due to the relatively small size of the Se(IV)O3 unit. These new spectroscopic results can be implemented in reactive transport models to improve the prediction of selenium migration behavior in the environment as well as its monitoring through its interaction with maghemite or maghemite layers at the surface of magnetite. Due to its chemical stability even at low pH and its magnetization properties allowing magnetic separation, maghemite is a promising sorbing phase for the treatment of Se polluted waters.

Temperature impact on the sorption of selenium(VI) onto anatase.

The impact of temperature (298 K, 313 K, and 333 K) on the sorption of selenium(VI) onto anatase was investigated for the first time. At a macroscopic level, batch experiments showed a decrease of selenium(VI) retention with both increasing pH (3.5-7.0) and temperature. The thermodynamic parameters of the sorption reaction, i.e. the enthalpy Δ(R)H, entropy Δ(R)S, and the Gibbs free energy Δ(R)G, were determined from the temperature dependence sorption data using the van't Hoff equation. The sorption process was found to be exothermic. Neither significant phase transformation nor a significant increase of anatase solubility could be detected with increasing temperature by XRD and ICP-MS. However, electrophoretic mobility measurements showed that both the zeta potential as well as the isoelectric point (pH(IEP)) of anatase were shifted to lower values with increasing temperature, leading to a decreased selenium(VI) sorption. At a microscopic level, the sorption mechanism of selenium(VI) onto anatase was elucidated at the three investigated temperatures by means of in situ Attenuated Total Reflection Fourier-Transform Infrared spectroscopy (ATR FT-IR). Results evidenced the formation of outer-sphere surface complexes, with no significant structural changes within the investigated temperature range.

Sorption of selenium(IV) onto magnetite in the presence of silicic acid.

Sorption of selenium(IV) and silicic acid onto magnetite (Fe(3)O(4)) was investigated in binary systems, with concentrations of silicic acid under the solubility limit of amorphous silica. Using the double diffuse layer model (DDLM), surface complexation constants of selenium(IV) and H(4)SiO(4) onto magnetite were extracted using Fiteql 4.0. Then, prediction curves of the sorption of selenium(IV) in the presence of silicic acid onto magnetite were obtained, using the calculated surface complexation constants. Finally, laboratory experiments were performed and showed a competition between selenium(IV) and silicic acid for the surface sites of magnetite. Experimental results matched the model predictions, confirming its ability to model qualitatively and quantitatively the ternary system.

Competition between selenium (IV) and silicic acid on the hematite surface.

Competition between selenium (IV) and silicic acid for the hematite (alpha-Fe(2)O(3)) surface has been studied during this work. Single batch experiments have been performed to study separately the sorption of selenium (IV) and silicic acid as a function of the pH. With the help of the 2-pK surface complexation model, experimental data have been fitted using the FITEQL 4.0 program. Two monodentate inner-sphere surface complexes have been used to fit selenite ions retention, triple bond FeSeO(3)(-) and triple bond FeHSeO(3). In order to fit sorption of silicic acid, the two following surface complexes, namely triple bond FeH(3)SiO(4), and triple bond FeH(2)SiO(4)(-), have been used. Using the surface complexation constants coming from these two binary systems, prediction curves of the effect of silicic acid on the retention of selenium (IV) onto hematite have been obtained. Finally, performed experiments showed a competition between selenium (IV) and silicic acid for the surface sites of hematite. Experimental data matched DDLM predictions, confirming the ability of the surface complexation model to predict quantitatively and qualitatively the ternary system selenium (IV)/H(4)SiO(4)/hematite.

Sorption of silicates on goethite, hematite, and magnetite: experiments and modelling.

Sorption of H(4)SiO(4) (including experiments as a function of time, K(d) measurement with different m/v ratios and sorption edges) onto different iron (hydro)oxides as goethite (alpha-FeOOH), hematite (alpha-Fe(2)O(3)), and magnetite (Fe(3)O(4)) has been studied with concentration of silicates under solubility limit. A surface complexation model has been used to account for sorption edge of silicates onto these iron oxide surfaces. It reveals that two types of surface complex namely FeH(3)SiO(4) and FeH(2)SiO(4)(-), are needed to describe properly the experimental observations.