Addition Of Hydrofluoric Acid Research Articles

Influence of Pressure and Temperature on the Flexible Behavior of Iron-Based MIL-53 with the CO2 Host: A Comprehensive Experimental and DFT Study.

This research focuses on developing MIL-53-type compounds with Fe obtained with ligands derived from PET waste, followed by the controlled addition of hydrofluoric acid (HF). Incorporating HF into the MOF structure induced substantial changes in the material textural properties, resulting in a significant change in CO2 adsorption. Furthermore, a distinctive structural alteration (breathing effect) was observed in the CO2 isotherms at different temperatures; these structural changes have not been observed by X-ray diffraction (XRD) because this characterization has been performed at room temperature, whereas the adsorption experiments were conducted at 260, 273, and 303 K and different pressures. Subsequently, DFT studies were performed to investigate the CO2-filling mechanisms and elucidate the material respiration effect. This approach offers promising opportunities for sustainable materials with improved gas adsorption properties.

Development of Wet Chemical Analysis Technique for Tramp Elements (M = As, Pb, Sb, and Sn) in Silver-M Alloys

Wet chemical analysis techniques for four elements (M = As, Pb, Sb, and Sn) in Ag – M binary alloys were investigated with emphasis on the choice of solvent acid and the characteristic wavelength used in the ICP-AES (Inductively-Coupled Plasma Atomic Emission Spectrometer) analysis. The elements are representative tramp elements in ferrous scrap. The activity of these elements needs to be increased to remove them efficiently during the molten scrap refining process. The activity of these elements in the molten scrap (molten iron alloy) is usually measured by a chemical equilibration technique with molten Ag. Therefore, performing an accurate and reliable chemical analysis of these elements in the molten iron alloy and the molten Ag alloy is important. Preliminary tests using conventional acids (hydrochloric acid, nitric acid) resulted in unreliable results. In the present study, the proper choice of acids as solvents was investigated for each element M in the Ag-M alloys. Several synthesized Ag-M alloys of known compositions were analyzed using two ICP-AES systems independently, for cross-checking. As and Pb in Ag alloys could be successfully dissolved in the nitric acid-based solution. On the other hand, Sb and Sn in Ag alloys did not dissolve in the nitric acid-based solution completely, leaving some precipitates. It was found that the addition of hydrofluoric acid could resolve this problem. In addition to this, the effect of the mass of the Ag-M alloy and wavelength selection during ICP-AES analysis on the accuracy and the reproducibility were investigated. An optimized procedure for the wet chemical analysis of these elements in Ag-M alloys is reported.

Green-synthesized MIL-100(Fe) modified with palladium as a selective catalyst in the hydrogenation of citronellal to citronellol

The influence of palladium embedded into green-synthesized MIL-100(Fe) and its role as a selective catalyst in the hydrogenation of citronellal into citronellol were investigated. MIL-100(Fe) was synthesized in water at 95 °C without addition of hydrofluoric acid (HF). The loading of Pd was carried out using wet impregnation method with Pd loadings of 1 and 3 wt%. The obtained materials were then tested as catalyst in hydrogenation of citronellal in a batch reactor. XRD analysis confirmed the high crystallinity of the synthesized MIL-100(Fe). FTIR analysis indicated the deprotonation of carboxylic ligand and its coordination with Fe3+ metal ions. The materials had thermal stability up to 287 °C according to TG/DTA analysis. The modification with palladium changed the morphology and decreased the crystallinity, surface area, and porosity as shown by XRD, SEM, TEM and nitrogen sorption isotherm analysis. The presence of Pd successfully increased the catalytic performance and selectivity to convert the citronellal into citronellol through a hydrogenation reaction, and an optimum 63.7% conversion and 22.2% selectivity to citronellol was attained over 3% Pd/MIL-100(Fe).

Determination of inorganic elements in geopropolis samples by inductively coupled plasma optical emission spectrometry

Information on the mineral composition of geopropolis produced by bees native to the Amazon region is of great importance for the chemical characterization of this product. This study aimed to determine the Ca, Cu, Fe, K, Mg, Mn, P, and Zn contents in 22 samples of geopropolis from northern Brazil by inductively coupled plasma optical emission spectrometry (ICP OES). Geopropolis samples were digested in a microwave oven using concentrated nitric acid and hydrogen peroxide and subsequent addition of hydrofluoric acid. The accuracy of the analytical procedures was assessed by elemental determination using certified reference material Poplar Leaves (GBW 07604). Analyte recoveries ranged between 88% and 99%, and there was no statistical difference (p < 0.05) between the determined and certified values. The accuracy of the measurements was evaluated by the addition and recovery test, and the recoveries ranged between 93% and 118%. The results showed high levels of Fe, Ca, Mg, K, and P in the samples. Principal component analysis (PCA) was performed and the results showed that there was better separation and grouping of the samples in relation to the geographic region, indicating that the mineral composition of geopropolis can vary according to the characteristics of the region. Thus, this study reported for the first time information about the mineral composition of geopropolis produced in northern Brazil, which can serve as a database for the characterization of the product in this region.

A methodological proposal for the analysis of Cladocera (Crustacea, Branchiopoda) subfossils from sediments of temporary aquatic ecosystems.

The main objective of the present study was to promote some adaptations to the standard methodology used in the analysis of Cladocera subfossils. The samples used in this study were collected at Lagoa dos Coutos, a temporary lake located on an outcrop with iron-rich duricrust in the Serra do Gandarela (Minas Gerais, Brazil). The sediment from this pond, typical of temporary ecosystems in the region, is characterized by rigid concretions that are difficult to dissolve in aqueous media, making it difficult to visualize and analyze subfossils taxa. Sediment samples were prepared according to the standard methodology used in paleolimological studies and the methodological adaptations proposed in the present study, which included the addition of 1 mg of Kochia scoparia, a palynological marker used to estimate subfossil density, as well as the addition of hydrofluoric acid (HF) to oxidize silicate materials. The samples prepared according to the new methodological procedure improved Cladocera subfossil visualization, facilitating the taxonomic analysis of the species. The samples submitted to the standard methodological procedure had a significantly higher mean of sediment particles (mean of 84.2 sediment particles) and 70% more residues compared to the samples prepared with the newly proposed methodology (mean of 22.1 sediment particles). Absolute data on the temporal variation of the density of Cladocera subfossils was obtained by using the palinological marker K. scoparia, which showed higher densities of subfossils in more recent, humid periods (112,000 subfossils/cm3 at 5 cm, equivalent to 3,500 years BP). The results indicate that the new methodology can contribute to advances in paleolimnological studies of temporary aquatic ecosystems, whose lake histories are rarely investigated, despite their ecological relevance as ecosystems that indicate environmental and climatic changes.

Unusual Mineral Diversity in a Hydrothermal Vein-type Deposit: the Clara Mine, SW Germany, as a Type Example

AbstractThe Clara baryte-fluorite-(Ag-Cu) mine exploits a polyphase, mainly Jurassic to Cretaceous, hydrothermal unconformity vein-type deposit in the Schwarzwald, SW Germany. It is the type locality for 13 minerals, and more than 400 different mineral species have been described from this occurrence, making it one of the top five localities for mineral diversity on Earth.The unusual mineral diversity is mainly related to the large number and diversity of secondary, supergene, and low-temperature hydrothermal phases formed from nine different primary ore-gangue associations observed over the last 40 years; these are: chert/quartz-hematite-pyrite-ferberite-scheelite with secondary W-bearing phases; fluorite-arsenide-selenide-uraninite-pyrite with secondary selenides and U-bearing phases (arsenates, oxides, vanadates, sulfates, and others); fluorite-sellaite with secondary Sr- and Mg-bearing phases; baryte-tennantite/tetrahedrite ss-chalcopyrite with secondary Cu arsenates, carbonates, and sulfates; baryte-tennantite/tetrahedrite ss-polybasite/pearceite-chalcopyrite, occasionally accompanied by Ag±Bi±Pb-bearing sulfides with secondary Sb oxides, Cu arsenates, carbonates, and sulfates; baryte-chalcopyrite with secondary Fe- and Cu-phosphates; baryte-pyrite-marcasite-chalcopyrite with secondary Fe- and Cu-sulfates; quartz-galena-gersdorffite-matildite with secondary Pb-, Bi-, Co-, and Ni-bearing phases; and siderite-dolomite-calcite-gypsum/anhydrite-quartz associations.The first eight associations are of Jurassic to Cretaceous age and are related to at least eight different pulses of hydrothermal fluids (plus the meteoric fluids responsible for supergene oxidation); the last association is of Neogene age. Spatial juxtaposition of the various primary associations produces overlaps of the secondary associations. In addition to natural oxidation processes, two anthropogenic additions led to specific mineral associations: (1) lining of the adit walls with concrete resulted in high-pH assemblages of mainly Ca-rich phases, including arsenates and sulfates; and (2) the addition of hydrofluoric acid to counterbalance the high-pH fluids produced by power plant ashes introduced into the exploited parts of the mine resulted in fluoride assemblages of alkali and alkaline earth metals.This contribution describes for the first time all types of assemblages and associations observed and physicochemical considerations and models of formation for some of the supergene associations. The meteoric fluids responsible for element mobilization and redistribution, and for the formation of new, secondary phases, interacted with wall rocks prior to and during percolation through the actual hydrothermal associations. Depending on the amount of reaction with ore, gangue, and host rock phases, the chemical composition of the meteoric fluids and its redox potential may vary over short distances. Hence different mineral assemblages and zoned associations record fluid compositional changes, even on the millimeter to centimeter scale. Unusual mineral diversity at the Clara mine therefore develops from a combination of diverse primary hydrothermal mineralization stages, an unusual number of fluid flow events involving compositionally different fluids, and local equilibrium conditions that change within centimeters during supergene processes involving meteoric fluids and anthropogenic additions.

A comparison of two digestion methods for assessing heavy metals level in urban soils influenced by mining and industrial activities

A comparison between two digestion methods of hot plate Hossner (total-total) and USEPA method 3051 (total-recoverable) was carried out to suggest a proper method for determining nine heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) content of three urban soils affected by mining (Mahd AD'Dahab) or industrial activities (Riyadh and Jubail) at Saudi Arabia. The results showed no significant differences between two digestion methods for Cd, Cu, Pb and Zn in soils affected by mining and for Cr, Cu, Pb and Zn in soils affected by industrial activities. Additionally, lower biases were obtained between two methods for metals Cd, Cu, Zn and Pb in the urban soil samples from mining area with the percent biases of −16.5%, +6.24%, −12.4% and +24.1%, respectively. The results also revealed that only Cu and Zn in the soil samples from Riyadh were extracted satisfactorily using USEPA 3051 with low biases of +5.69% and −9.61%, respectively. Meanwhile, only Pb in soil samples from Jubail showed lower baise between two methods with satisfactory biase of −8.07%. The correlation coefficients were significant between total-recoverable and total-total concentrations for Cu (r = 0.66), Pb (r = 0.72) and Cd (r = 0.65) in soil samples from mining area. Overall, concentrations of Co, Cr, Fe, Mn, and Ni that may show soil background concentrations were found higher by Hossner method than by USEPA 3051; thus, this suggests the addition of hydrofluoric acid (HF) is necessary for the determination of lithogenic metal concentrations. It could be concluded that the USEPA 3051 may be recommended and applied for total Cd, Cu, Pb and Zn originated from anthropogenic source in mining and industrial areas.

Influence of Digestion Procedure and Residual Carbon on Manganese, Copper, and Zinc Determination in Herbal Matrices by Atomic Absorption Spectrometry.

Mineralization to the complete oxidation of sample carbon component does not always assure the best analyte recovery. Particular attention should be paid to the presence of silicon in the investigated plant sample and especially in the certified reference material for which Si content is scarcely given by the providers. During mineralization without addition of the hydrofluoric acid, the residual carbon may block silica surfaces and increase availability of an analyte for its spectral determination in the solution. This issue is of particular relevance because standard protocols for digestion of plant matrices often do not support hydrofluoric acid addition. Several procedures recommended for decomposition of herbal plants were applied for the respective certified reference material and examined in detail. Manganese, copper, and zinc contents were analyzed in all samples by the flame atomic absorption spectrometry. Additionally, the residual carbon was determined in all mineralizates. Silicon content was analyzed by the X-ray fluorescence method. The best recoveries were observed for samples characterized by relatively high residual carbon.

Control synthesis and formation mechanism of sphere‐like titanium dioxide

Using a simple hydrothermal method without surfactants and templates, different morphologies of titanium dioxide (TiO2) have been synthesised such as nanocubes, nanosheets and microspheres. The effects of the addition of hydrofluoric acid (HF) and hydrogen peroxide (H2O2) in the preparation of TiO2 were studied. It was found that more H2O2 may accelerate the formation of a spherical morphology and that HF has three roles: dissolving Ti powder, retarding the hydrolysis of titanium precursor and reducing surface energy. Reaction time has a significant effect on morphological transformation. The aggregation of microstructures is described, the effects of the addition of HF and H2O2 on the condition of aggregation have been studied. Photocatalysis measurements showed that sphere-like TiO2 consisting of nanocubes exhibited the highest activity for degrading rhodamine B under UV light.

Electroless Displacement Deposition of Noble Metal on Silicon Powder for Recovering from Urban Mines

Noble metal is not only precious but also crucial for such industries as electronics, catalysts, and jewelry. Recycling noble metals from scrap electronics and industrial wastes, which are called urban mines, is important to preserve natural resources and the environment. In the conventional recycling process, scraps and wastes are dissolved in an aqueous solution and refined chemically. To recover noble metals from a low concentration solution, an ion-exchange resin, activated carbon, electrolysis, or cementation is used. We have been studying electroless displacement deposition of noble metal nanoparticles on silicon (Si) substrates (1) for efficient solar cell production (2) and metal film formation (3). This deposition is a local galvanic reaction expressed by followings:Mn+ → M + nh+ (h+: hole)Si + 4HF2 - + 2h+ → SiF6 2- + 2HF + H2 and/or Si + 6F- + 4h+ → SiF6 2-.Recently, we applied this deposition for recovering noble metals from aqueous solutions (4). Figure 1 shows outline of this recovering process. The first step of the process is addition of hydrofluoric acid (HF) and Si powder into an aqueous solution of noble metal ions. Noble metal particles are deposited on Si powder. The second step of the process is addition of oxidizing agent, such as nitric acid into the solution. Only Si is dissolved into the solution, and only noble metal particles remain in the solid-state. This method is classified into cementation. Features of this recovering are simplicity of process, high efficiency of recovering noble metal, and availability of using waste Si powder and HF provided by electronics industries. Furthermore, this recovering can selectively recover noble metal and copper unlike conventional cementation. In this study, we have investigated recover of noble metal using sawdust Si powder, and replacement of toxic HF by non-toxic agent such as ammonium fluoride (NH4F). 0.2 M (M: mol dm-3) Si powder was added in a mixture solution of metals and 0.15 M HF. The initial concentration of each metal salt in the solution was 1.0 mM. After stirring at 200 rpm at a solution temperature of 298 K, the solution was filtered. The recovery was determined by measurement of change in metal ion concentration of the solution with inductively coupled plasma-atomic emission spectrometry (ICP-AES). Figure 2 shows the recovery plots of noble metals versus treatment time. These recovering uses 350 mesh Si powder or slicing slurry including sawdust Si after using for industrial wefering. Mean diameter of 350 mesh Si powder is 25 μm, and of slicing slurry is 10 μm. Slicing slurry is result in higher efficiency than Si powder. This efficiency of recovery is explained by specific surface area of Si. Figure 3 shows recovery plots of noble metals using 350 mesh Si powder and 0.15 M NH4F instead of HF. Au and Pt were recovered using non-toxic agent under lower rate than that for using HF.ACKNOWLEDGEMENTSThe authors thank Dong Rong Electronics Co., Ltd. for supplying used silicon slurry. The present work was partly supported by Exploratory Research of A-STEP from JST, Grant-in-Aid from Kawanishi Memorial ShinMaywa Education Foundation, and JSPS KAKENHI Grant Number 23560875.REFERENCESS. Yae, N. Nasu, K. Matsumoto, T. Hagihara, N. Fukumuro, and H. Matsuda, Electrochim. Acta, 53, 35 (2007).S. Yae, in: L.A. Kosyachenko (Ed.), Solar Cells - New Aspects and Solutions, InTech, Ch. 11, p. 321, Available from: http://www.intechopen.com (2011).S. Yae, K. Sakabe, N. Fukumuro, S. Sakamoto, and H. Matsuda, J. Electrochem. Soc ., 158(9), D573 (2011).K. Fukuda, S. Yae, N. Fukumuro, S. Sakamoto, and H. Matsuda, ECS Trans., 53(19), 69 (2013).

Purification process of coal-based coke powder as anode for Li-ion batteries

A process of purification of coal-based coke powder as anode for Li-ion batteries was attempted. The process started with the treatment of coke powder with dilute hydrofluoric acid solution, followed by united-acid-leaching using sulfuric acid and hydrochloric acid. The effects of altering the hydrofluoric acid addition, hydrofluoric acid concentration, contact time, temperature and acid type were investigated. A minimum ash content of 0.35% was obtained when proper conditions were applied. The electrochemical performance of purified coke powder shows greatly improved electrochemical performance. The as-purified coke powder presented an initial reversible capacity of 257.4 mAh/g and a retention rate of 95% after 50 cycles. The proposed purification process paves a way to prepare a promising anode material with good performance with low cost of coke powder for Li-ion batteries.

The effect of photoanode thickness on the performance of dye-sensitized solar cells containing TiO2 nanosheets with exposed reactive {001} facets

Abstract

Determination of the total and extractable mass fractions of cadmium and lead in mineral feed by using isotope dilution inductively coupled plasma mass spectrometry

This paper describes the determination of the total and extractable mass fractions of Cd and Pb in mineral feed test sample distributed by the Community Reference Laboratory for Heavy Metals in Feed and Food (CRL-HM), in the frame of the fifth interlaboratory comparison for the European Union National Reference Laboratories (NRL). The developed in this study protocol for the total and extractable mass fractions of Pb and Cd in mineral feed sample is based on isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS). The applied dual spiking approach reduced by 50% the number of analytical steps. The addition of hydrofluoric acid in the digestion step was found necessary to ensure a full decomposition and complete isotope equilibration. Quadrupole inductively coupled plasma mass spectrometer equipped with collision reaction interface (CRI) was employed for the measurements of Cd and Pb. Two methods for the determination of Cd were applied and compared. In the first one the high molybdenum content was reduced by introduction of matrix separation step followed by standard ICP-MS mode measurement, whereas in the second one CRI mode was used for the determination of Cd without preliminary matrix separation. The estimation of the combined uncertainty was performed according to the ISO guidelines. Uncertainty propagation was used as a tool for validation of proposed analytical procedure. Contributions from the correction for moisture content, sample homogeneity, procedural blank, instrumental background and dead time effects were evaluated in both cases. The largest uncertainty contributors for Cd and Pb is due to the within bottle homogeneity of the mineral feed sample – 50.3% and 90% respectively. The IUPAC data for isotope composition are the second major contributor to the combined uncertainty of the result for the total mass fraction of Cd in mineral feed – 43.3%. However, the ID ICP-MS results achieved from the two series of samples (partial and total extraction) were in excellent agreement within uncertainty, irrespective of the method used for extraction. The ID ICP-MS results for the total and extractable mass fractions of Cd and Pb in feed sample were compared with the results obtained with external calibration approach and routinely applied in the daily analytical practice of the Belgium National Reference Laboratory for trace elements in food and feed.

Extending wipe sampling methodologies to elements other than lead

Wipe sampling is the USA regulatory protocol for determination of "dust lead loadings" in residential environments. Few studies have applied the wipe sampling method to metals other than lead (Pb) for the purpose of residential exposure assessments. This study was undertaken to develop and expand the wipe method for quantifying additional metal(loid)s including arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), and antimony (Sb); and to provide information on typical background loadings for these metals in urban Canadian homes. A total of 932 wipe samples, 220 field blanks, and 220 duplicate wipes were collected from 222 homes located in three cities in Ontario, Canada using the ASTM 1728 standard. The wipes were digested using a modified version of the ASTM 1644 standard for Pb, which prescribes a hot nitric acid/hydrogen peroxide digestion. The key modification was the addition of hydrofluoric acid to improve recoveries of the target elements, and determination using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Generally, a large proportion of the results fell below the limits of detection (LOD) and quantification (LOQ). To distinguish "elevated" metal loadings from loadings characterized as "urban background", an upper background threshold for each element was derived using a normality (Q-Q) plot. LOQ was determined to be the appropriate minimum threshold based on quality assurance criteria. It is concluded that wipes are a useful sampling option to investigate multi-element loadings in residential environments.

Anodic oxidation of tungsten in sulphuric acid solution—Influence of hydrofluoric acid addition

The anodic oxidation of tungsten has been studied in 1 M H 2SO 4 solutions containing 0–0.25 M HF. The active-to-passive transition is observed in the potential range 0.4–1.0 V vs. SCE, indicating coupling between film formation and metal dissolution reactions. Steady-state currents measured in the passivation and passivity ranges increase significantly with increasing fluoride concentration, indicating enhanced dissolution of the oxide film. The electrochemical impedance response is dominated by the processes in the barrier sublayer and at its interface with the electrolyte. The presence of a pseudo-inductive loop in the impedance spectra at intermediate frequencies indicates point defect interaction during the film growth and dissolution processes. A kinetic model including the recombination reaction between positively and negatively charged point defects at the film/solution interface as well as an elaborate kinetic scheme for the tungsten dissolution through the film mediated by cation vacancies is proposed. It is found to reproduce satisfactorily the steady-state currents and the impedance spectra as depending on potential in the range 0.4–5 V. Such a model for the conduction mechanism in the barrier sublayer is believed to be an essential part of a modelling approach to the formation of a nanoporous overlayer on tungsten in fluoride-containing solutions.

Electrodeposition of metal molybdenum from electrolytes containing hydrofluoric acid

The effect of hydrofluoric acid on the cathodic reduction of molybdate ions is studied. It is shown that the mechanism of this process is determined by the acid concentration: in a concentration range below 25 g/l the intermediate products of molybdate-ion reduction, namely, black or colored deposits containing molybdenum with the average valence of 3.6–4 are formed on the cathode. For the concentration above 50 g/l, molybdate ions are completely reduced and form at the cathode dense light metallic coatings with a thickness of 3–5 μm and good adhesion to the substrate. The addition of hydrofluoric acid prevents polymerization of molybdate ions.

ELECTRODEPOSITION OF METALLIC MOLYBDENUM FROM AQUEOUS ELECTROLYTES CONTAINING HYDROFLUORIC ACID

The influence of hydrofluoric acid on the cathodic reduction of molybdate ions has been investigated. It is shown that the mechanism of the process is determined by the acid concentration: in the range of concentrations less than 25 g·l–1 black or colored deposits are formed on the cathodic intermediate products of reduction of the molybdate ions the average valency of molybdenum in which is 3.6–4. At concentrations higher than 50 g·l–1 molybdate ions are completely reduced, forming on the cathode dense lustrous metal coatings 3–5 mm of thickness with good adhesion to the substrate. Addition of hydrofluoric acid prevents polymerization of molybdate ions. On the basis of Arrhenius equations, the effective activation energy of electroreduction of molybdate ions is determined, the ion size predetermining diffusion limitations of the processes proceeding at the film formed on the electrode surface.

The role of the fluorine concentration and substrate temperature on the electrical, optical, morphological and structural properties of chemically sprayed ZnO:F thin films

The effect of both the fluorine/zinc ratio, [F]/[Zn], in the starting solution and the substrate temperature ( T S) on the transport, structural and optical properties of chemically sprayed fluorine-doped zinc oxide (ZnO:F) thin films is reported. An important decrease in the resistivity (on the order of 1.2×10 −2 Ωcm) is observed in films deposited at 500 °C, from a starting solution with a [F]/[Zn] ratio as low as 10 at.%. In order to obtain such decrease, an adequate combination of, an excess in acetic acid, the addition of hydrofluoric acid and an aging process of 9 days of the solution were required. A minimum resistivity was obtained in films deposited with a [F]/[Zn] of 20 at.%, beyond this value the films obtained show higher resistivity values. As the [F]/[Zn] ratio in the solution increases, the grain size decreases, as observed by scanning electron microscopy. A (002) preferential growth is observed in films deposited with [F]/[Zn] ratios in solution lower than 20 at.%, whereas a switching from (002) to (101) is observed in the films deposited with the highest [F]/[Zn] ratio. A typical transmittance higher than 85% and a band gap ( E g) of 3.3 eV were obtained in the films deposited at the optimum conditions.

The effects of hydrofluoric acid addition on the hydrothermal synthesis of templated uranium sulfates

The effect of employing hydrofluoric acid as a mineraliser in the formation of organically templated uranium sulfate materials has been studied. Variable amounts of HF((aq)) were added to a series of reaction gels in which all other reactant concentrations were invariant, resulting in the formation of three different phases, depending upon the fluoride concentration. Two of these phases are novel; [N(2)C(4)H(14)][UO(2)(H(2)O)(SO(4))(2)] is a new templated uranium sulfate, containing anionic [UO(2)(H(2)O)(SO(4))(2)](2-) chains that hydrogen bond to one-another forming pseudo-layers, and [N(2)C(4)H(14)][UO(2)F(SO(4))](2) is the first example of a templated uranium sulfate fluoride, which consists of uranium fluoride chains linked by sulfate groups to form [UO(2)F(SO(4))](-) layers. The role of F(-) in these reactions is two-fold; it acts as a mineraliser when present in small concentrations, while it is incorporated into the reaction product when present in larger mole fractions. Both of the new materials have been characterised using a range of physical techniques including single crystal X-ray structure analysis.

Online element determination in biological and environmental samples by flame AAS coupled with a high-temperature/high-pressure flow digestion system

The coupling of a high temperature/high pressure flow digestion system (Tmax >300 °C, pmax >30 MPa) to a flame AAS instrument enables an effective and rapid online element determination in biological and environmental matrices. An electrically heated Pt–Ir capillary acts as a digestion tube at a temperature of 320 °C. The reliability of the method is demonstrated by the determination of element traces in various standard reference-materials. The pure digestion time of various matrices (wheat flour, spinach, orchard leaves, tomato leaves, bovine liver, pig kidney, sewage sludge, coal fly ash), as 2% suspensions in 2.5 M HNO3, is about 1 min, and the time needed for the whole procedure is between 3 and 8 min. Detection limits, based on 2% slurry concentrations, are about 0.25 µg g−1 (Cd), 4.5 µg g−1 (Pb), 2.2 µg g−1 (Cu), 1.4 µg g−1 (Mn) and 0.8 µg g−1 (Zn). Standard deviations were found to be in a range of 2 to 10%. Due to the totally glass-free equipment, samples with a high silicate content can be digested by the addition of hydrofluoric acid.