Determination of in situ speciation of manganese in treated acid mine drainage water by using multiple diffusive gradients in thin films devices

Acid mine drainage (AMD) is a serious environmental problem that creates acidic solution with high Mn concentrations. The speciation of residual Mn from AMD after an active treatment involving the addition of a neutralizing agent can reliably evaluate the treatment efficiency and provide knowledge of the Mn species being inputted into the environment. The aim of this study was to evaluate the in situ lability and speciation of Mn using the diffusive gradients in thin films (DGT) technique with treated drainage water from a uranium mine (TAMD). DGT devices with different binding phases (Chelex-100 and P81 and DE81membranes) were used to perform the in situ speciation of Mn.     

TRLFS study on the speciation of uranium in seepage water and pore water of heavy metal contaminated soil

In situ leaching of uranium ores with sulfuric acid during active uranium mining activity on the Gessenheap has caused longstanding environmental problems of acid mine drainage and elevated concentrations of uranium. To study there remediation measures the test site Gessenwiese, a recultivated former uranium mining heap near Ronnenburg/East Thuringia/Germany, was installed as a part of a research program of the Friedrich-Schiller University Jena to study, among other techniques, the phytoremediation capacity of native and selected plants towards uranium. In the first step the uranium speciation in surface seepage and soil pore waters from Gessenwiese, ranging in pH from 3.2 to 4.0, were studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Both types of water samples showed mono-exponential luminescence decay, indicating the presence of only one major species. The detected emission bands were found at 477.5, 491.8, 513.0, 537.2, 562.3, and 590.7 nm in case of the surface water samples, and were found at 477.2, 493.2, 513.8, 537.0, 562.4, and 590.0 nm in case of the soil water samples. These characteristic peak maxima together with the observed mono-exponential decay indicated that the uranium speciation in the seepage and soil pore waters is dominated by the uranium (VI) sulfate species UO₂SO_4(aq). Due to the presence of luminescence quenchers in the natural water samples the measured luminescence lifetimes of the UO₂SO_4(aq) species of 1.0–2.6 μs were reduced in comparison to pure uranium sulfate solutions, which show a luminescence lifetime of 4.7 μs. These results convincingly show that in the pH range of 3.2–4.0 TRLFS is a suitable and very useful technique to study the uranium speciation in naturally occurring water samples.     

Complexation of uranium(VI) with protocatechuic acid—application of iterative transformation factor analysis to EXAFS spectroscopy

The speciation of 1 mM uranium(VI) in carbonate-free aqueous solutions of 50 mM protocatechuic acid (PCA, 3,4-dihydroxybenzoic acid) was studied in the pH range of 4.0 to 6.8 using EXAFS spectroscopy. The uranium L_III-edge EXAFS spectra were analyzed using a newly developed computer algorithm for iterative transformation factor analysis (FA). Two structural different uranium(VI) complexes were observed. The speciation in the pH range of 4.0 to 4.8 is dominated by a 1:2 or 1:3 uranium(VI)/PCA complex with bidentate coordination of the carboxyl group to the uranium(VI) moiety. Already at pH 4.6 significant amounts of a second species are formed. This uranium(VI) species contains two PCA ligands that are bound to the uranium via their neighboring phenolic hydroxyl groups under formation of five-member rings.     

Electrospray ionization of alkali and alkaline earth metal species. Electrochemical oxidation and pH effects

The utility of electrospray ionization mass spectrometry (ESI-MS) for characterizing dissolved metal species has generated considerable interest in the use of this technique for metal speciation. However, the development of accurate speciation methods based on ESI-MS requires a detailed understanding of the mechanisms by which dissolved metal species are ionized during electrospray. We report how the analysis of alkali and alkaline earth metal species provides new information about some of the processes that affect electrospray ion yield. Selected metal ions and organic ligands were combined in 50 : 50 water-acetonitrile buffered with acetic acid or ammonium acetate and analyzed by flow injection ESI-MS using mild electrospray conditions. Species formed by alkali metal ions with thiol and oxygen-donating ligands were detected in acidic and neutral pH solutions. Electrochemical oxidation of N, N-diethyldithiocarbamate and glutathione during electrospray was indicated by detection of the corresponding disulfides as protonated or alkali metal species. The extent of ligand oxidation depended on solution pH and the dissociation constant of the thiol group. Tandem mass spectrometric experiments suggested that radical cations such as [NaL](+.) (where L=N,N-diethyldithiocarbamate) can be generated by in-source fragmentation of disulfide species. Greater complexation of alkali metals at neutral pH was indicated by a corresponding decrease in the relative abundance of the free metal ion. The number of alkali metal ions bound by glutathione and phthalic acid also increased with increasing pH, in accordance with thermodynamic equilibrium theory. Alkaline earth metal species were detected only in acidic solutions, the absence of 8-hydroxyquinoline complexes being attributed to their relative instability and subsequent dissociation during electrospray. Hence, accurate speciation by ESI-MS depends on experimental conditions and the intrinsic properties of each analyte. Copyright 2000 John Wiley & Sons, Ltd.     

Fe(III)-coordination properties of neuromelanin components: 5,6-dihydroxyindole and 5,6-dihydroxyindole-2-carboxylic acid

The Fe(III)-coordination chemistry of neuromelanin building-block compounds, 5,6-dihydroxyindole (DHI), 5,6-dihydroxyindole-2-carboxylic acid (DHICA), and 5,6-dihydroxy-N-methyl-indole (Me-DHI), and the neurotransmitter dopamine were explored in aqueous solution by anaerobic pH-dependent spectrophotometric titrations. The Fe(III)-binding constants and pH-dependent speciation parallel those of catechol in that mono, bis, and tris FeLx species are present at concentrations dependent on the pH. The bis FeL2 dihydroxyindole species are favorable for L = DHI and DHICA under neutral to mildly acidic conditions. DHI and DHICA are stronger Fe(III) chelates than catechol, dopamine, and Me-DHI at pH values from 3 to 10. Oxidation studies reveal that iron accelerates the air oxidation of DHI and DHICA.     

Extraction studies of uranium(VI) and thorium(IV) with tributylphosphine oxide

Clay minerals occur widely in nature and play a very important role in agriculture, mineral recovery and chemical manufacturing. Among the many properties which affect clay behaviour, water binding and ion exchanging appear to be the most important. The study of the cation exchange capacity of soils is of great theoretical and practical importance since the CEC determines in many ways the behavior of nutrients, chemical amendments, and many toxic compounds entering the sols. Sorption interactions with montmorillonite and other clay minerals in soils are potantially important mechanisms for attenuating the mobility of heavy metal cations through the subsurface environment. In this work the cation exchange capacity (CEC) of montmorillonite from west Anatolia, and sorptions with montmorillonite for attenuating the mobility of uranium were studied. The CEC value was found to be 77 meq/100 g montmorillonite. The relative importance of test parameters e.g., contact time, particle size, pH and U(+6) aqueous speciation was determined. The results show that sorption on montmorillonite is a funtion of pH depending strongly on the aqueous U(+6) species. It reaches a maximum at near neutral pH(pH}7). At low and at high pH solutions the sorption values of uranium are poor. These sorption values were attributed to the formation of aqueous U(+6) carbonate complexes in alkaline conditions and the ionexchange process between UO₂ ⁺² species and interlayer cations on montmorillonite in acidic solutions.     

Sequestering agents for uranyl chelation: new calixarene ligands

Synthesis of sulfocatecholamide (CAMS) and hydroxypyridinone (HOPO) calixarene ligands and determination of their binding abilities for the uranyl cation were described. Chelating properties were determined by UV spectrophotometry in aqueous media under various pH conditions and further studied by ¹H NMR analysis of the resonance signals of both aromatics' protons of the chelating groups. Each ligand shows a more or less pronounced affinity for uranium. HOPO calixarenes exhibit significant affinity towards uranyl ion at acidic and neutral pH while CAMS calixarene is more efficient at basic pH.     

ABSORPTION AND PHOTOCHEMISTRY OF SENSORY RHODOPSIN—I: pH EFFECTS

Pyranine (8-hydroxyl-1,3,6-pyrene-trisulfonate) was used as a pH-probe to test whether there is a light-induced proton release to the bulk phase during the photochemical reaction cycle of sensory rhodopsin-I (SR-I). We conclude that the retinylidene Schiff-base proton is retained by SR-I-containing envelope vesicles during the SR-I photocycle under the conditions described here. Bacteriorhodopsin containing vesicles were used as a control to show that light-induced proton release can be observed under identical data acquisition parameters as those used for SR-I-containing vesicles. In addition, the effects of extravesicular pH on the absorption maximum (lambda max) and the SR-I photocycle were studied. SR-I properties are insensitive to pH in the range approximately 3 to approximately 8 with lambda max remaining at 587 nm. The lambda max shifts to 565 nm below pH 3.0 and to 552 nm at pH 10.8 with an apparent pKa of 8.5. Flash-induced absorbance changes of SR-I are described under neutral, alkaline and acidic conditions. The neutral, alkaline and acid SR-I forms each undergo similar photoreactions producing long-lived (> 500 ms decay half-time) blue-shifted intermediates. The UV/near-UV absorption of the photoproducts from neutral and alkaline SR-I indicate a deprotonated Schiff base, whereas acid SR-I produces a species with lambda max > 460 nm indicative of a protonated Schiff base.     

Colloidal Regularities of the Interaction between Uranium(VI) and the Cells of Metal-Resistant Bacillus cereus AUMC 4368 Bacterial Culture

Sorption of uranium(VI) by the cells of metal-resistant Bacillus cereus AUMC 4368 bacterium was studied in aqueous solutions as a function of pH, equilibrium concentration of metal, and the presence of co-ions with account of the changes in phase state of metals and biocolloids. Experimental data indicate that the sorption of uranium(VI) by negatively charged biocolloids is maximal at pH 4.2–4.5 (1.2 mM per 1g of dry biomass), when metal is present in the form of positively charged hydroxocomplexes. At pH 8, the interaction between uranium(VI) and the cells is inhibited due to the formation of negatively charged water-soluble hydroxocarbonate complexes and uranate ions. Co, Sr, Cu, Ca, Mg, and Zn ions do not influence the efficiency of sorption of uranium(VI) in a weakly acidic medium, but can cause inhibiting effect in neutral pH region. The most pronounced effect expressed in broadening of sorption range and in the heterocoagulation of uranyl is observed in the presence of Fe³⁺ ions. It was established that the binding of uranium(VI) occurs by the carboxyl surface groups of Bacillus cereuscell surface. Uranium(VI) is irreversibly bound by the carboxyl groups of cell surface and its efficient desorption is possible only during the interaction with citric acid or sodium hydrocarbonate with the formation of water-soluble complexes transferred to aqueous phase. It was shown that uranyl in the form of organocomplexes (citric, humatic, and fulvatic) is not sorbed by biocolloids.     

Kinetic study of uranium speciation in model solutions and in natural waters using Competitive Ligand Exchange Method

Kinetic speciation of uranium in model solutions containing uranium and humic acid (HA) and in natural waters has been investigated by Competitive Ligand Exchange Method (CLEM). In alkaline freshwaters, most of uranium species were uranium-carbonate species, which were labile in the CLEM experiment. The uranium speciation of every sample was characterized either as “labile” or “non-labile” uranium complexes depending on the dissociation rate coefficients of the complexes. The results showed that as the U(VI)/HA ratio was decreased, the dissociation rate coefficients decreased and the labile fraction decreased as well. When the U(VI)/HA ratio was 0.1, the labile fraction of the U(VI)-HA increased with increasing pH; however, there was no pH effect on the dissociation of U(VI)-HA complexes at lower U(VI)/HA ratios. Chelex-100 had some limitations in its use for the study of dissociation of U(VI)-HA complex at very low U(VI)/HA ratios. By developing an analytical method and procedure for quantitative determination of kinetic parameters for the dissociation of uranium-HA complexes in model solutions and natural waters, this work has made a substantial contribution to analytical chemistry.     

Characterization of isopoly metal oxyanions using electrospray time-of-flight mass spectrometry

Electrospray time-of-flight mass spectrometry was used to study dilute (10(-3) M) solutions of tungstate, vanadate and perrhenate oxyanions under acidic and basic conditions. The electrospray mass spectra of tungstate and vanadate solutions indicate the presence of protonated monomeric oxyanions in basic solution (pH approximately 10) and protonated polymeric species in acidic solutions (pH approximately 4). Monomeric perrhenate was the only species detected in both acidic and basic perrhenate solutions. For all three systems, the core metalate species detected by electrospray were consistent with reported speciation in aqueous solutions. Copyright 2000 John Wiley & Sons, Ltd.     

Anthocyanin Color Stabilization by Host-Guest Complexation with p-Sulfonatocalix[n]arenes

Flavylium-based compounds in their acidic and cationic form bring color to aqueous solutions, while under slightly acidic or neutral conditions they commonly bring discoloration. Selective host-guest complexation between water-soluble p-sulfonatocalix[n]arenes (SCn) macrocycles and the flavylium cationic species can increase the stability of the colored form, expanding its domain over the pH scale. The association constants between SCn and the cationic (acid) and neutral basic forms of flavylium-based compounds were determined through UV-Vis host-guest titrations at different pH values. The affinity of the hosts for synthetic chromophore was found to be higher than for a natural anthocyanin (Oenin). The higher affinity of SC4 for the synthetic flavylium was confirmed by ¹H NMR showing a preferential interaction of the flavylium phenyl ring with the host cavity. In contrast with its synthetic counterpart, the flavylium substitution pattern in the anthocyanin seems to limit the inclusion of the guest in the host’s binding pocket. In this case, the higher affinity was observed for the octamer (SC8) likely due to its larger cavity and higher number of negatively charged sulfonate groups.     

Aqueous uranium(VI) hydrolysis species characterized by attenuated total reflection Fourier-transform infrared spectroscopy

The speciation of uranium(VI) in micromolar aqueous solutions at ambient atmosphere was studied by attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy and by speciation modeling applying the updated NEA thermodynamic database. It can be shown that reliable infrared spectra of micromolar U(VI) solutions are obtained abolishing the restrictions of previous spectroscopic investigations to millimolar concentrations and, consequently, to the acidic pH range. A significant change of the U(VI) speciation can be derived from the spectral alterations of the absorption band representing the antisymmetric stretching mode (nu3) of the UO2(2+) ion observed upon lowering the U(VI) concentration from the milli- to the micromolar range at a constant pH 4 value. The acquisition of spectra of diluted U(VI) solutions allows the increase of the pH up to 8.5 without the risk of formation of colloidal or solid phases. The infrared spectra are compared to the results of the computed speciation patterns. Although a complete interpretation of the spectra can not be given at this state of knowledge, the spectral data strongly suggest the presence of monomeric U(VI) hydroxo species already showing up at a pH value > or = 2.5 and dominating the speciation at pH 3. This is in contradiction to the predicted speciation where the fully hydrated UO2(2+) is expected to represent the main species at pH values below 4. At ambient pH, a more complex speciation is suggested compared to the results of the computational modeling technique. The predicted dominance of the UO2(CO3)3(4-) complex at pH > or = 8 was not confirmed by the infrared data. However, the infrared spectra indicate the formation of hydroxo complexes obviously containing carbonate ligands.     

Structural photodynamics of camptothecin, an anticancer drug in aqueous solutions

Steady-state and time-resolved picosecond emission studies were carried out to study the role of the proton concentration in the acid-base properties of the anticancer drug camptothecin (CPT) in its ground and electronically first excited states. The results show that, under acidic conditions, the excited-state proton-transfer (ESPT) reaction is irreversible, in contrast to previous literature data. We found that the prototropic species are equilibrated at the excited state (pK(a)* = 1.85) only in a restricted range of pH (1.5 < pH < 3), whereas only one species, either the neutral form (τ(N) = 3.76 ns) or the protonated form (τ(C) = 2.83 ns), can be detected at pH > 3 and pH < 1.5, respectively. The proton motion from the acidic solution to the neutral form in the pH 1-2 domain is diffusion-controlled. Within the range of pH 1-2, the reaction rate constant for the formation (k(d)) of the encounter complex between the proton and the neutral form ranges from 1.17 × 10(10) to 7.33 × 10(10) M(-1) s(-1), respectively. Under more acidic conditions (pH 0.9-0.95), the protonation of CPT does not depend on the diffusive step, because of the large amount of protons. The direct proton-transfer rate constant (k(DPT)*) increases with the proton concentration (time constants change from 24 ps to ～1 ns at pH 0.9 and 2, respectively). The number of protons involved in the proton transfer changes from approximately one, for the diffusive regime, to approximately four, for the static regime. We found good agreement between the Birks model for equilibrated flourophores and the Debye-Smoluchowski equation (DSE) to accurately explain the ESPT reaction of CPT with acidic water in the reversible range. The proton motion at pH 2 (equilibrium range) exhibits diffusion-controlled behavior and can be explained using the Smoluchowski model. Our results show that the interaction of CPT with acidic water depends on the concentration of the acid, which changes the nature of both the structure and dynamics.     

Thermal behaviour and the cone calorimetric analysis of the jute fabric treated in different pH condition

In this paper, the effect of pH, i.e. acid and alkali was investigated on thermal stability of ligno-cellulosic polymeric fibrous (jute) material. The jute fabric was subjected to treatment under different pH, namely 4.5, 7, 10, 12, i.e. in acidic, neutral and alkaline conditions followed by drying prior to any thermal and physical characterization. The improvement in the thermal stability of jute to flame was measured in terms of limiting oxygen index value, vertical flammability and temperature profile of burning zone. Likewise thermo-gravimetry, differential scanning calorimetry and cone calorimeter analysis were also used to elucidate the improvement in thermal stability of the treated fabric. The changes in heat release rate, mass loss rate, heat of combustion, smoke production, etc., in the untreated and treated sample were measured in detail in cone calorimeter. Only the alkali-treated jute fabric samples showed profound improvement in thermal stability.

     

Gross alpha,gross beta and activity concentration of 226Ra in some fertilizers commonly used in the south of Vietnam and health risk due to radionuclides transferred from fertilizers to food crops

Twelve types of chemical fertilizers commonly used in the south of Vietnam were collected for analysis. It was found that the activity concentration of ²²⁶Ra was in the range from below detectable level (BDL) to 139 Bq kg^?1 while gross alpha and gross beta activities were in the ranges from BDL—691 Bq kg^?1 and BDL—18753 Bq kg^?1 respectively. The correlation was found between gross alpha activity and activity concentration of ²²⁶Ra in most of fertilizers. The radiological hazard due to application of fertilizers is insignificantly under the agricultural conditions.

     

New preservation method for inorganic arsenic speciation in acid mine drainage samples

A new preservation method has been proposed for the speciation of As(III) and As(V) in acid mine drainage (AMD) samples, characterised by low pH and high metallic content. Samples were taken from a polymetallic sulphides mining area in the province of Huelva (SW Spain), under exploitation until the 1960s for its Cu, Pb and Zn sulphides. The abandoned mine works and the numerous waste rocks heaps produce AMD with high As content, an aqueous pollution source for the nearby streams. Short-term (from few hours to 1 week) preservation of the two inorganic arsenic species was studied, trying different containers (polyethylene, glass), presence or absence of light, temperatures (ambient, refrigerated, frozen), preserving agents and procedures (EDTA, HCl or AcH acids, cation-exchange resin). The speciation results obtained by liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) indicated a rapid conversion of the samples with most of the preservation procedures reported in the literature after 3 h after sample collection. A promising method for arsenic preservation has been developed in this work, which maintains the arsenic species distribution in the original samples for a longer time. It consists in the use of opaque glass containers, acidification of the samples with HCl and in situ cleanup with cationic exchange resin, which allowed to preserve the samples for As speciation for at least 48 h.     

Release and speciation of uranium in low-ionic-strength groundwaters at an abandoned uranium mine in Val Vedello (Orobic Alp—Italy) by adsorptive cathodic stripping voltammetry

Adsorptive cathodic stripping voltammetry (AdCSV) with HDME and a chloranilic acid ligand was used in the trace analysis of uranyl ions at pH?=?2 in low-ionic-strength groundwaters around mining areas. Upon optimization, the limit of detection around 0.10?µg?L^?1 was found with linearity up to 10?µg?L^?1. In the abandoned mining area of Val Vedello (Orobic Alps, Italy), measured uranium concentrations in water ranged from 0.3?µg?L^?1 above the uranium mineralization levels to 145?µg?L^?1 in groundwaters percolating from mine galleries. Such uranium concentrations are related to natural weathering effects of CO₂ and/or hydrogen carbonate ion on uranium mineralizations under oxic conditions. A marked seasonal dependence was then found, in agreement with literature data on a pre-operational survey dating back to 1980–1981. No significant chemical impact of the abandoned mining activity on groundwater quality could be found. Accordingly, no significant increase in contaminants derived from the heat-burn of explosives, such as chloride and nitrate, in groundwaters from mine galleries was found.     

Speciation of particulate uranium in seawater: Mass balance analysis of sequential leaching experiments

A sequential leaching experiment for chemical speciation of particulate uranium in seawater was carried out using solution chemistry techniques. Mass action analysis on the leaching processes reveals that the major species of particulate uranium in seawater is an organic complex of uranium(VI), which is dissociated completely in the leaching solution of pH 1.0. Inert uranium, which is not dissolved in the leaching solution of pH 1.0, exists is suspended matter although it is a minor constituent. The result suggests that this species in an organic complex of uranium(IV). The analysis of the experimenmt deduces that an organic binding site in suspended matter reacts as a polydentate ligand, which has more than two stepwise protonation constants within the pH range of 2.0 to 8.2. The conditiona stability constant of the organic uranium complex in suspended matter under the conditions of seawater is within the following range: 12<log K_c,U<16. These findings suggest stronglt that the organic binding site in suspended matter can form stable chelates with metallic elements.     

Spectrophotometric determination of uranium(VI) with 7-chloro-8-hydroxyquinoline-5-sulphonic acid

Uranium(VI) and 7-chloro-8-hydroxyquinoline-5-sulphonic acid form a 1:2 complex with λ_max at 355 nm, in aqueous medium at pH 6.6. A procedure for accurate spectrophotometric determination of hexavalent uranium with 7-chloro-8-hydroxyquinoline-5-sulphonic acid has been described. Optimum conditions, including the effect of pH, time, temperature, order of addition of the reagents, and excess of the reagent have been studied. Range for adherance to Beer's law, effective photometric range, molar absorptivity, and Sandell sensitivity have also been reported as 1–38 ppm, 5.7–28.5 ppm, 6575 and 0.036 μg of uranium/cm² respectively. The method has been compared with some other methods for determination of uranium spectrophotometrically, with regard to their sensitivities. Interferences of various ions in the measurement of the color have been investigated, and the tentative structure of the colored species in solution has been proposed.