HF HCl Research Articles

Ion Exchange Separation Techniques for NAA of Refractory Metals

Radiochemical separation methods have been applied for the neutron activation analysis of impurities in four high-purity refractory metals, Ta, Nb, W and Mo. Impurities in the metals of Ta, Nb and W can be separated into groups using anion exchange resin with HF and/or a mixture of HF acid and HCl, but those in Mo is done using both anion and cation exchange resins. The coprecipitation of U with Th in HF media is also investigated.

Influence of selective logging and sedimentological process on geochemistry of tropical rainforest streams

Stream sediment geochemical surveys are well-suited to mineral exploration in tropical rainforests. However, there is evidence that watershed disturbance can increase sediment loads and thereby dilute or even eliminate geochemical anomalies that, under natural conditions, result from the preferential concentration of heavy minerals by streams. To investigate this and other factors influencing background and threshold values in rainforest streams, sediments have been collected from disturbed and undisturbed watersheds on the Kuamut Formation in the Danum Valley, Sabah, Malaysia. In the laboratory a <2 mm portion was wet-screened to obtain the abundance of the 0.424–2 mm, 0.212–0.424 mm, 0.053–0.212 mm and −0.053 mm size fractions, and the magnetic 0.053–0.212 mm fraction. Another portion was wet-sieved to obtain the −0.212 mm fraction for analysis by ICP–ES after a total decomposition using HF–HCl–HNO 3. Mineralogy of the sediments and heavy mineral concentrates was determined by X-ray diffraction. Results show that although average concentrations of many elements are significantly higher in sediments from unlogged versus logged watersheds, the differences do not simply relate to the effects of logging. Correlation coefficients for the complete data set show two main trends: (1) concentrations of Ca–Mg–Ti–Co–Cr–Sr–V increase with increasing abundance of magnetite; and (2) K–Ba correlate with abundance of fine (<53 μm) sediment. However, a scatterplot of Ti vs K (as geochemical surrogates for magnetite vs fines) shows much more complex relations than indicated by the overall correlations. Most importantly, the Ti–K correlations can be negative or positive depending on which drainage basin the sediments are from. Furthermore, trends in concentration of many trace elements follow the Ti–K trends within individual drainage basins. Insofar as all the streams are on a single geological unit, the presence of distinct linear trends in the scatterplots implies that the composition of the sediments is being systematically modified in a variety of ways. The association between magnetite and Ca–Mg–Ti–Co–Cr–Sr–V (and negative correlation with K–Ba) is best developed in the two largest streams and most likely results from fluvial processes that concentrate heavy minerals and eliminate fines from the stream bed. Conversely, field observations suggest that a trend for Ti–K, together with many other elements, to be positively correlated at low concentrations of Ti depends on whether the sediment source is dominated by bedrock or by regolith supplied from recent mass-wasting events, the frequency of which is increased by logging. It is concluded that selective logging of lowland tropical rainforest does not cause major changes in stream sediment geochemistry except in the vicinity of recent landslides where input of deeply weathered tropical regolith lowers geochemical background. The combined effects of sediment source (landslide regolith versus bedrock) and sedimentological processes on sediment geochemistry can be visualized in X– Y– Z `process' plots, where X– Y are suitable index elements and Z is the element of interest.

Measurement of fixed ammonium and nitrogen isotope ratios using dry combustion

Clay‐fixed NH4–N can represent up to 18 percent of the total soil N for Canadian agricultural soils. A modification of the Silva and Bremner's method for determining clay‐fixed NH4 was developed. The Silva and Bremner procedure incorporates dissolution of mineral residues by a HF–HCl digestion in order to release bound NH4, following removal of exchangeable NH4 and organic N. Steam distillation is used to recover NH4 from the soil digest. The procedure presented in this paper substitutes combustion in an automated elemental analyzer for the HF–HCl digestion step. Combustion with an elemental analyzer follows removal of exchangeable NH4 with 0.5 M KCl and organic N with wet digestion using KOBr. The elimination of the HF–HCl digestion and steam distillation steps shortens the time required for analysis and avoids the use of strong reagents. The procedure is also suitable for 15N studies when combined with a mass spectrometer. The two techniques gave virtually the same results for 17 soils with the slope of the regression of 1.03 and a coefficient of determination of 0.97. Simultaneous measurements of fixed NH4 and N isotope ratios using continuous flow mass spectrometry can be carried out.

Is selective preservation of nitrogenous organic matter reflected in the δ[formula omitted] signal of lacustrine sediments?

The δ 13 C and C/N ratios of organic matter in core from a lake near Kalamazoo, SW Michigan, representing ∼12 k years were measured. The δ 13 C values of two fractions, one obtained by demineralization using dilute hydrochloric acid ( δ 13 C HCl ) and the other a fraction obtained by HF–HCl digestion ( δ 13 C HF–HCl ), ranged from −24 to −12‰ with the δ 13 C HF–HCl being generally more negative. Both fractions showed a similar pattern of variation with depth. The δ 13 C values are less negative when compared to sediment organic δ 13 C values from other Midwestern lakes, but are consistent with a dissolved inorganic carbon (DIC) source. The C/N ratios of the HCl fraction ranged from 11 to 12, typical of organic carbon in midwestern lakes. However, the C/N ratios of the HF–HCl residue varied from 13 to 25 suggesting that this fraction had lost components enriched in nitrogen. Because compounds such as proteins and amino acids (hereafter referred to as NC for `nitrogenous compounds') in sediments are more labile, enriched in δ 13 C and lower in C/N ratios, compared to more stable lignin and cellulose, it is interpreted that the HF–HCl digestion removed these compounds. A Δ 13 C parameter defined as: Δ 13 C=δ 13 C HCl −δ 13 C HF–HCl should, in principle, be controlled by fluctuations in the preservation of NC in the water column. Previous studies have linked preservation of nitrogenous compounds in sediments to existing climate. This hypothesis is supported by a good correlation between the Δ 13 C parameter and the previously demonstrated climate-sensitive organic δD record in this lake core. Moreover, the δ 13 C correlated strongly with percentage organic carbon content in this core. This behavior is consistent with a process where increased organic carbon production and burial depletes the DIC in 12 C , thereby reducing the fractionation between the organic and inorganic reservoirs.

Comparison of basis set superposition error corrected perturbation theories for calculating intermolecular interaction energies

Recently, two different but conceptually similar basis set superposition error (BSSE) free second-order perturbation theoretical schemes were developed by us that are being based on the chemical Hamiltonian approach (CHA). Using these CHA-MP2 and CHA-PT2 methods, a comparison is made between the a posteriori and a priori BSSE correction schemes at the correlated level. Sample calculations are presented for four hydrogen bonded complexes (HFH3N, HFH2O, H2SHF, and H2OHCl) in nine different basis sets (from 6–31G to TZV**++). The results show that the BSSE content is very significant in the interaction energy if electron correlation is accounted for, so removing the BSSE is very important. The differences of the two perturbational theories discussed are connected solely with the different one electron orbital sets used for building up the unperturbed single determinant wave function. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 274–283, 1999

Determination of scandium in geological materials, rare earth minerals and niobate/tantalate-type of samples by inductively coupled plasma atomic emission spectrometry after solvent extraction/acid hydrolysis separation

Solvent extraction of scandium from 1.5 M HCl medium using di(2-ethyl hexyl) phosphoric acid in hexane or benzene selectively separates Sc from the accompanying elements in rare-earth minerals (like monazite, xenotime, gadolinite) and also in geological materials. Acid hydrolysis separation of Nb/Ta-type samples separates Sc from the major matrix elements and the remaining elements do not influence the Sc signal in inductively coupled plasma atomic emission spectrometry or flame atomic absorption spectrometry. To avoid the matrix effect due to sodium that accompanies the analyte using the reported backstripping of Sc from the organic extract by 2 M NaOH, the organic extract was evaporated off leaving the Sc in the residue which in turn was treated with a mixture of HNO 3–HClO 4, dissolved in HCl (10%, v/v) and made up to a known volume before aspiration in the plasma for estimation. The silica-rich geological materials were dissolved by HF–HCl–H 2SO 4 treatment and the rare-earth minerals (monazite/xenotime) were digested by H 2SO 4–HCl followed by dissolution in 1.5 M HCl before applying the solvent extraction procedure. In Nb/Ta-type of samples, Sc was separated from Nb and Ta by acid hydrolysis, involving fusion with Na 2O 2, dissolution in HCl followed by NH 3 precipitation and hydrolysis in HCl. The oxychloride precipitates of Nb and Ta are filtered off and the filtrates assayed for Sc. The proposed methods have been applied to some international geological reference standards (SY-2, SY-3, MRG-1, Mica-Fe, G-2, GH and ASK-2), rare-earth minerals like monazite, xenotime and gadolinite and also to some Nb/Ta-type samples including reference standards IGS-33 and IGS-34, and the results are compared. Both methods are simple, rapid and accurate, showing a relative standard deviation of less than 1% at the 55 μg g −1 level and 9.0% (at the 1.0 μg g −1).

Behaviour of Zr, Hf, Nb, Ta and Pa on macroporous anion exchanger in chloride–fluoride media

Sorption properties of Zr, Hf, Nb, Ta and Pa at trace level towards a macroporous anion exchanger in HF–HCl media were investigated with two ion exchange methods: static (batch technique) and dynamic (column chromatography using the elution mode). Variations of the distribution coefficients as a function of HCl and HF concentration in the range 0.02–0.8 M for both acids are presented in the form of contour plots. Some of the most promising separation possibilities are pointed out.

Altered pharmacokinetics of halofantrine by an antacid, magnesium carbonate

This study investigated the in vitro adsorption of halofantrine (Hf) by some antacids. Magnesium carbonate showed the highest adsorptive effect, the extent of adsorption being up to 83%. Only 4% of Hf adsorbed by the antacid could be eluted with 0.1 M HCl while no detectable elution occurred with water. Other antacids investigated were magnesium trisilicate and aluminium hydroxide and these had Hf-adsorption capacities of 23 and 43%, respectively. The effect of magnesium carbonate on the bioavailability of Hf was evaluated in seven healthy volunteers. The subjects were administered with 500 mg oral dose of Hf–HCl or the same dose of the drug in combination with 1 g of magnesium carbonate, in a crossover fashion. Blood samples were collected at predetermined time intervals and were analysed for Hf and its major metabolite, desbutylhalofantrine (Hfm), using high-performance liquid chromatography method. The results showed that magnesium carbonate significantly prolonged ( P<0.05) the time to reach maximum plasma concentration ( T max) of Hf. Also the maximum plasma concentrations ( C max) of Hf and Hfm were significantly reduced ( P<0.05). Furthermore, there was a reduction in the area under the curve (AUC) values of Hf and this was as high as 56% (range 1–56%). Results of this study suggest that it may not be advisable to concomitantly administer Hf with an antacid like magnesium carbonate.

The effect of acid treatment of coal on H 2S evolution during pyrolysis in hydrogen

The amount of H 2S evolved during pyrolysis was analyzed by g.c.-m.s. for four types of raw coal samples, Taiheiyo, Datong, Wandoan and Mequinenza. These coals were treated with HNO 3 or HF HCl solution, in which inorganic sulfur was eliminated by the acid treatment. In the case of HNO 3-treated samples, the evolution of H 2S in the low temperature region, below 500°C, was reduced by the chemical oxidation. At high temperatures, the amount of H 2S evolution from acid-treated coal was markedly increased compared to the raw coals, especially Taiheiyo and Wandoan, through the elimination of minerals. From X-ray fluorescence analysis and X-ray powder diffraction of coal and char, it was confirmed that calcium in the raw coal has an important role for the fixation of sulfur during pyrolysis.

Studies of chemical hardness and chemical potential on isomers and hardness profiles of hydrogen-bonded systems

In the present investigation, chemical hardness and electronic chemical potential for isomers of different molecules were studied by taking into account the principle of maximum hardness. Different isomers of the molecules, XC(O)OX (X=F, Cl), C2H3NO, C2H2, and HCNC, were considered for the above investigation. In most of the cases, the chemical hardness was found to be a good indicator for predicting the most stable isomer and not the chemical potential. The hardness profiles of different configurations of the interacting systems, HF(DOTTED BOND)HCN, HF(DOTTED BOND)HCl, and CH3OH(DOTTED BOND)H2O hydrogen-bonded complexes, were studied. The extrema of the hardness profiles does not coincide well with the energy, but in some cases, the hardness profile follows the interaction path. The higher hardness–higher stability concept among different configurations of the hydrogen-bonded complexes are discussed. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 231–242, 1997

Combining ab initio computations, neural networks, and diffusion Monte Carlo: An efficient method to treat weakly bound molecules

We describe a new method to calculate the vibrational ground state properties of weakly bound molecular systems and apply it to (HF)2 and HF–HCl. A Bayesian Inference neural network is used to fit an analytic function to a set of ab initio data points, which may then be employed by the quantum diffusion Monte Carlo method to produce ground state vibrational wave functions and properties. The method is general and relatively simple to implement and will be attractive for calculations on systems for which no analytic potential energy surface exists.

Faceted Etch Pits Formed on Surfaces of an Icosahedral Al&lt;SUB&gt;70&lt;/SUB&gt;Pd&lt;SUB&gt;20&lt;/SUB&gt;Mn&lt;SUB&gt;10&lt;/SUB&gt; Quasicrystal

An icosahedral Al 70 Pd 20 Mn 10 quasicrystal was etched under several etching conditions with solutions composed of HF and H2O plus HCl and/or HNO 3 . The formation of etch pits was examined closely by scanning electron microscopy and replica electron microscopy. When etched for 5 s at 293 K with the etchants of different compositions, the faceted pits were often observed except for a few exceptions. All those pits revealed the similar shape of pentagonal dodecahedron where the pentagonal faces were curved slightly near their corners and edges. By etching for 5 s with a solution of HF+HCl+H 2 O (1:3:5 in volume ratio), the average size of the pits decreased from 4.5 to 2.5 μm with an increase of etching temperature from 273 to 333 K, and the pentagonal faces tended to be flattened above 313 K. The pentagonal faces near the corners and edges of the pits became more curved and the average size remained unchanged (∼4.5 μm) with increasing etching time in the range of I and 20 s at a temperature of 293 K. By comparing the surfaces before and after etching at the same areas, it was concluded that the faceted pits originated from irregular small holes which pre-existed on the polished surface.

Detection of noble metal depletion in layered mafic intrusions: a potential aid to exploration for platinum-group element deposits

In layered mafic intrusions, economically important platinum-group element (PGE) mineralisation can result from collection of PGE and Au from the silicate melt by Ni ( ± Cu) S droplets, which settle to form PGE- and Au-enriched layers. An important consequence is that the PGE and Au are depleted in the remaining silicate fraction. The ability to recognise PGE and Au depletion in rocks crystallised from a depleted melt would be useful in exploration for discriminating between favourable (containing PGE- and Au-depleted silicates) and unfavourable layers (those that had not experienced NiS collection of PGE and Au). Drychlorination was applied to drill core samples of the Fox River Sill (Manitoba, Canada) in order to remove metallic minerals. The remaining silicate fractions were digested by microwave heating in a mixture of HFHClHNO 3, evaporated to near dryness, re-digested in aqua regia, and re-constituted in distilled de-ionized water. The solutions were analysed by ICP-MS for PGE and Au. The PGE and Au contents of the silicate fractions of samples collected from mineralised layers were significantly depleted relative to the PGE and Au contents of silicate fractions of samples collected from a non-mineralised layer. Verification of the ICP-MS method for the determination of Pd was carried out by means of DCP-AES. Instrumental neutron activation analysis (INAA) was used to verify the method for Au and Ir.

Determination of impurities in tantalum by a radiochemical neutron activation analysis

A radiochemical separation method using Dowex 1×8 (200–400 mesh) has been applied to two tantalum metals of 99.9% purity. While tantalum was still retained on the resin, the elements Na, K, Cr, Mn, Fe, Co and Zn were separated with 2M HF and subsequently the elements Sc, As, Zr, Mo, Eu, W and Hf with a mixture of 0.5M HF and 3M HCl. The separation yields for all impurities was 98–100%. Elemental contents were calculated by a single comparator method using two monitors.

Microwave and infrared electric-resonance optothermal spectroscopy of HF–HCl and HCl–HF

Microwave and infrared spectra of HF–HCl and HCl–HF have been obtained using a molecular-beam electric-resonance optothermal spectrometer, which operates by quadrupole-field focusing of polar molecules onto a bolometer detector. The HF–HCl microwave measurements extend to Ka=1, the previous Ka=0 results of Janda, Steed, Novick, and Klemperer, allowing the determination of the Ka dependence and asymmetry of the Cl quadrupole coupling constant. For the metastable HCl–HF isomer no previous spectroscopic measurements have been reported. Here, microwave spectra are observed for the Ka=0 and 1 states and interpreted in terms of an L-shaped hydrogen-bonded structure for the complex, with a 3.235 Å center-of-mass separation between the HF and HCl subunits. The DJ distortion constant indicates that the harmonic stretching force constant for HCl–HF is ∼35% larger than that of HF–HCl. Infrared spectra of the Ka=0–0 and 1–0 subbands of the H–F stretching band for HF–HCl and of the Ka=0–0 subband of the H–F stretch for HCl–HF are also reported. The vibrational predissociation linewidths depend on vibration, Ka state, isotopic species, and isomer excited.

Heavy carbon in individual oxide grains from the Murchison meteorite

The carbon isotopic composition of individual oxide grains from Murchison HF—HCl acid residue CFOc has been measured in the ion microprobe. Many grains (Mg-spinel, Cr-spinel, and Fe-oxide) contain carbon with large 13C excesses ranging to 7000‰ (corresponding to 12C/ 13C= 11). In most cases the carbon is present as micron-sized subgrains. The association of silicon with the anomalous carbon points towards SiC as carrier. If this tentative identification is correct then the SiC grains most likely originated in the circumstellar atmospheres of red giants. Oxide grains in which the 18O/ 16O ratio has also been measured show variable 16O excesses which are not correlated with the 13C excesses. This indicates that the sources of the anomalous carbon and oxygen isotopic compositions of the oxide grains are unrelated.

Relations between chemical species distribution and the fluctuating activity of Vulcano (Italy)

Abstract Five years of systematic observation of the fumaroles of Vulcano have allowed us to detect some compositional trends coincident with a fluctuation in temperature. A gradual decrease of CO2, H2S+SO2, HF is observed with the lowering of temperature, while HCl slightly increases. These physical-chemical characters of the system are not readily explained as simply produced by different stages in magma degassing, and the previous hypothesis of the significant influence of a brackish aquifer on the fumaroles still appears a reliable working model. R-mode factor analysis allowed to distinguish the differentiated role of chemical species for which different genetic processes can be derived. The ratios HF HCl and SO 2 H 2 S are taken as indicators of the changing activity of the system, and also the available data for Usu (Japan) and Mount St. Helens (USA) are considered.

Colloidally separated samples from Allende residues: Noble gases, carbon and an ESCA-study

A non-colloidal fraction separated by physical means from an HF HCl -resistant residue of the Allende carbonaceous meteorite exhibits a ratio of isotopically “normal” ( Q-type) xenon to “anomalous” xenon ( X-type) that is ~4 times larger than usually observed. Coincidentally this fraction contains carbon that is isotopically heavier by ~10%. than bulk Allende residue samples. ESCA analyses of companion colloidal separates show that the major portion of the S contained in our HF HCl -residues is elemental rather than a sulfide. They also confirm earlier observations that no elementally distinct surface coating is present, in accord with the absence of a surface-sited sulfur-bearing gas carrier, and that the oxygen content is increased after etching with nitric acid. For these separates noble gas data coupled with the ESCA data for nitrogen and the isotopic data for carbon point to the existence of heterogeneities among the noble gas-, carbon- and nitrogen-bearing phases and, thus, preservation of discrete components from the variety of source regions (or production mechanisms, or both) sampled by the Allende parent body. In sharp contrast to the success of physical and chemical methods in yielding samples in which one of the major noble gas components predominates to an extraordinary degree over the other, carbon isotopic compositions that have been inferred for the respective carrier phases in these same samples are strongly contradictory. Mass and isotope balance considerations lead us to conclude that a major fraction of the carbonaceous matter in Allende is noble-gas-poor, a result that could be confirmed by direct isolation of a sample, the carbon in which is dominated by this variety; and for that reason no simple relationship is discernable yet between observed isotopic compositions and either major noble gas component. Similar ambiguities may exist for nitrogen. The possible relationship between carbon-rich phases in ureilites and carbonaceous chondrites is considered.

Numerical analysis of a chain-excited self-contained cw HF–HCl chemical laser utilizing an F–H2–CIF–He mixture

Using a two-dimensional boundary-layer model, an investigation is made of a self-contained cw HF–HCl chemical laser with simultaneous stimulated emission from HF and HCl. It is proposed that a mechanism involving a cold reaction between fluorine and hydrogen F + H2→HF + H and a mechanism involving a chain reaction between chlorine monofluoride ClF and H2 (by introducing ClF into the secondary stream) should be used to produce vibrationally excited HF and HCl molecules in the active medium of the laser. Calculations show that a total laser energy of ~250 J/g (per 1 g of mixture) may be achieved using this design of HF–HCl laser, the ratio of the energies emitted by HF and HCl being approximately 3:1. Results of an investigation of the amplifying properties of the active medium of a cw HF–HCl laser are presented and dependences of the energy characteristics on various parameters of the system are given for planar and cylindrical geometries of the nozzle array.

A comparative study of standards for determinations of trace wear metals in jet engine oils

The feasibility of using acid-treated metal powder standards for the determination of trace wear metals in spent jet engine oils is evaluated. The addition of 2:3:3 (v/v/v) HF—HCl—HNO 3 mixture to used lubricating oils did not cause any statistically reliable differences from results obtained with organometallic standards. Two sets of six correlation samples, one set being acid-treated, were analyzed for Cu, Cr, Mg, Fe, Mo and V by flame atomic absorption and flame atomic fluorescence spectrometry against each set of standards.