Multielement trace analysis of high purity aluminium by neutron activation

Instrumental neutron activation analysis was applied to multielement trace analysis of high purity aluminium samples. In order to reduce the production of²⁴Na from the matrix, samples were activated by thermal neutron flux of high cadmium ratio. Detection limits of various impurity elements were evaluated. So called “five nine” class standard aluminium samples were analyzed and concentrations of various impurity elements were determined. The analytical results obtained on zone refined aluminium samples showed that zone refining is effective against many elements, such as Na, Cr, Fe, Co, Cu, Ga, As, Br, Ba, La, Ce, Sm, Yb, Lu, Hf, W, Th and U, but not very effective against the element Sc.     

Speciation of trace amounts of aluminium in percolating water of forest soil by online coupling HPLC-ICP-MS

Procedures were developed for the speciation of trace amounts of aluminium present in percolating water of forest soil by online coupling of different chromatographic separation methods to an ICP-MS detection system. Inorganic and organic aluminium species were fractionated on a cation exchange column IONPAC CG12 (10-32). Phytotoxic polymeric aluminium hydroxides, as e.g. Al₁₃ (AlO₄Al₁₂(OH)₂₄(H₂O)₁₂ ⁷⁺), were determined using pyrocatechol violet (PCV) as a species dependant complexing reagent prior to the cation exchange step. Size fractionation of the organic aluminium species was obtained by size exclusion chromatography using the columns Superdex-75-HR 10/30 and Superdex-Peptide-HR 10/30. Validation of the speciation procedures proved that online coupling HPLC to the element selective and sensitive ICP-MS detection system leads to low detection limits of 0.3–0.6 μg/L and high precision and reproducibility (1.2–3.5%) of the speciation procedures. Speciation data determined for aluminium in a percolating water of the Zierenberg catchment are given.     

Speciation of trace amounts of aluminium in percolating water of forest soil by online coupling HPLC-ICP-MS

Procedures were developed for the speciation of trace amounts of aluminium present in percolating water of forest soil by online coupling of different chromatographic separation methods to an ICP-MS detection system. Inorganic and organic aluminium species were fractionated on a cation exchange column IONPAC CG12 (10-32). Phytotoxic polymeric aluminium hydroxides, as e.g. Al₁₃ (AlO₄Al₁₂(OH)₂₄(H₂O)₁₂ ⁷⁺), were determined using pyrocatechol violet (PCV) as a species dependant complexing reagent prior to the cation exchange step. Size fractionation of the organic aluminium species was obtained by size exclusion chromatography using the columns Superdex-75-HR 10/30 and Superdex-Peptide-HR 10/30. Validation of the speciation procedures proved that online coupling HPLC to the element selective and sensitive ICP-MS detection system leads to low detection limits of 0.3–0.6 μg/L and high precision and reproducibility (1.2–3.5%) of the speciation procedures. Speciation data determined for aluminium in a percolating water of the Zierenberg catchment are given. Received: 20 November 1998 / Revised: 28 January 1999 / Accepted: 3 February 1999     

The surface chemistry of Bayer process solids: a review

The Bayer process is used for refining bauxite to smelting grade alumina (Al₂O₃), the precursor to aluminium. The process was developed and patented by Karl Josef Bayer 110 years ago, and has become the cornerstone of the aluminium production industry worldwide. Production of alumina reached 46.8 megatonnes (Mt) worldwide by the end of 1997, with Australia the worlds largest producer of bauxite and refiner of alumina with just under 30% of world production. Although the refining process is well established and the basic theories underpinning it are well defined, the fundamental chemistry of the Bayer process is not well understood. Of particular interest to industrial and academic researchers alike, is the chemistry of the Bayer process solids—aluminium trihydroxide, ‘red mud’ and sodium oxalate. The surface chemistry of these solids is of great industrial importance as the refining industry experiences significant restrictions due to limitations imposed on the process by surface chemical reactions. Of scientific interest is the conceptual advancement of our knowledge and understanding of the nature of surfaces under extreme (non-ideal) conditions. A review of the current literature relating to these important Bayer process solids is thus presented. While not exhaustive, the review is thorough and aims to familiarise the reader with current levels of understanding regarding the nature of Bayer process solids surfaces under Bayer process conditions, and the significant roles these solids play in the overall efficiency of the refining process. It is hoped that this review will provide a useful starting point for researchers new to the area of Bayer process research, whilst also stimulating further fundamental research in this economically and scientifically significant area.     

Preconcentration of trace metals from acidic solutions by coprecipitation with dithizone

Traces of Ag, Bi, Cd, Cu, Hg, Pb, Pd and Zn are separated by carrier precipitation with dithizone from diluted HNO₃ and HCl solutions. The separated trace elements are determined by flame AAS and/or by spectrophotometry. The preconcentration recovery is dependent on the acid concentration of the sample solution. The amount of dithizone precipitated is optimized. The detection limits (ng/ml) are 15.0 (Pb, Zn), 12.0 (Pd), 10.0 (Bi), 6.0 (Ag), 5.0 (Hg), 2.0 (Cu) and 1.0 (Cd). Aluminium, aluminium sulfate and gallium are analyzed with the method. The accuracy of the results was checked by differential pulse voltammetry.     

Adsorption of SO2 on alumina

The adsorption of SO₂ on alumina used in the aluminium industry, the so-called smelter-grade alumina, was studied in the temperature range 15–120°C. It was found that at temperatures lower than 40°C, sulphur dioxide was bonded to alumina reversibly by physical forces, and the adsorption could be described satisfactorily by the Langmuir adsorption isotherm. The heat of adsorption was estimated to be −33 kJ mol⁻¹. At temperatures ranging from 80°C to 120°C, which prevail in dry scrubbers in the aluminium industry, the heat of adsorption was determined to be −56 kJ mol⁻¹. When SO₂ was adsorbed at temperatures higher than 80°C, about 30 % of the SO₂ could not be desorbed even if the samples were heated up to 250°C. In the presence of SO₂ and oxygen, the formation of sulphate was observed at temperatures above 90°C.     

Genesis and activity of mo-based hydrotreating catalysts prepared by a sol-gel method

Molybdenum oxide-alumina catalysts used in hydrodesulfurization (HDS) with a wide range of Mo loadings (1–25% Mo) were prepared by the sol-gel process. Two different methods of adding the molybdenum oxide precursor to the support were used.In the first route, alumina is prepared by hydrolysis of aluminium tri sec-butylate in butanol and butanediol, and molybdenum is deposited by a classical dry impregnation with ammonium heptamolybdate (AHM). In the second route, the molybdenum oxospecies are dispersed in butanediol and added to the aluminium alkoxide before hydrolysis. The solids were calcined to obtain the oxide precursors which are then sulfided to give the active phase in hydrodesulfurization.The effect of preparation on the structural properties of alumina as well as on the state and dispersion of molybdenum in the dried, calcined and sulfided form was studied by various characterization techniques (XRD, XPS, Raman spectroscopy). Molybdenum appears to be present as well dispersed oxomolybdenum species in the oxide form even at high loadings. This good dispersion of molybdenum is preserved after sulfidation which induces the formation of MoS₂ crystallites whose morphology has been determined by HREM.The catalyst activities were evaluated in thiophene hydrodesulfurization and compared with that of catalysts prepared by dry impregnation of a commercial alumina. The observed performances are in agreement with the good dispersion of molybdenum at high loadings we were able to obtain owing to the sol-gel process.     

Comparative study of bulk and partial digestion methods for airborne PM10-bound elements in a high mineral dust urban site in Constantine,Algeria

When high mineral loads in atmospheric particulate matter (PM) are present, particular attention should be paid to the selection of appropriate acidic digestion protocols for wet chemical analysis. We report on a comparative study of elemental recovery yields from five different pre-analytical acid digestion procedures for mineral-rich urban background PM₁₀ samples collected in the city of Constantine (Northeastern Algeria). Five reference materials (NIST 1633b, UPM 1648, NAT-7, SO-2 and SO-4) were also digested according to the same protocols. The selected acidic digestion/extraction procedures are widely used for PM chemical analysis and comprise P1 (HNO₃/HF/HCl), P2 (HCl/HNO₃), P3 (HCl/H₂O₂/HNO₃), P4 (HNO₃/HF/HClO₄) and P5 (HNO₃/H₂O₂); the latter assisted with microwave digestion. Elemental recovery yields were compared for major and trace elements typically determined in PM for source apportionment analysis and the results evidenced large differences. For most elements, the bulk extraction procedures (requiring the use of HF) allowed a full elemental recovery, particularly for elements that are associated with aluminium silicate species and oxides that are resistant to mild acid attack. In contrast, in the extraction protocols without HF low recovery yields were obtained for elements such as Al, Ti, Zr, Sc and other aluminium silicate-related elements in PM₁₀ samples with high mineral dust load. We highlight that the European standard digestion method EN-14902:2005 should be applied specifically for the metals for which this method was developed, but caution should be taken when the analysis of other elements in PM is required, especially in urban areas where road and vehicle wear dust is likely to be a major component of ambient PM. When using wet chemistry analysis for PM source apportionment studies, we strongly recommend HF bulk dissolution of samples to ensure the reliability of the geochemical information when coupled with an appropriate analytical tool.     

Determination of about thirty elements in aluminium and its alloys by means of neutron activation analysis

Neutron activation analysis and radiochemical separations in HCl, HF media are used to determine 30 elements in aluminium and alloys. Amounts lower than 1 μg of element may be determined. A good agreement is found with the results of atomic absorption spectrometry. This procedure is applied routinely for determinations of trace elements or major components.     

Determination of traces of calcium, magnesium, iron and nickel in aluminium salts by atomic-absorption spectrophotometry with a microwave-excited source and hollow-cathode lamps

The determination of trace amounts of calcium and magnesium in solutions containing large concentrations of aluminium salts may be accomplished by co-precipitating their hydroxides on iron(III) hydroxide, dissolving the precipitate, and extracting the 8-hydroxyquinolates of calcium and magnesium into methyl isobutyl ketone at about pH 11. The extract may be sprayed into the airpropane flame of a simple unmodulated spectrophotometer and atomic-absorption measurements for calcium and magnesium made at 4227 and 2852 A respectively. The limits of determination correspond to 10 and 1 ppm of calcium and magnesium in solid alumina. Iron and nickel may be co-precipitated on hydrated manganese(IV) oxide and their 8-hydroxyquinolates extracted at pH 4.5. Measurements of atomic absorption for these elements at 2483 and 2320 A respectively yield limits of determination corresponding to 10 ppm in alumina. Hollow-cathode lamps may be used for calcium, magnesium and nickel, but a simple microwave-excited discharge tube gives much better sensitivity than a hollow-cathode lamp for iron.     

Studies in heavy ion activation analysis

¹⁵N induced radioactivation was used to study the possible trace determination of light elements with 1Z17. 55 nuclear reactions were investigated with ion beam energies ranging from E_1ab=10 MeV to E_1ab=30 MeV. Three elements were found to be determinable non-destructively, selectively and sensitively: Li, Be and Mg. Nuclear interferences have also been defined and quantified. The technique has been tested by analyzing NBS standards. Finally, Li and Be have been determined in glass samples and Mg in various types of alumina.     

Microwave assisted sample preparation for determining water-soluble fraction of trace elements in urban airborne particulate matter: evaluation of bioavailability

The feasibility of using two different microwave-based sample preparation methods was investigated to determine the total and water-soluble trace metal fraction in airborne particulate matter. The extraction techniques were then applied to urban particulate matter of different sizes in order to evaluate their bioavailability of associated trace metals. While a combination of HNO₃-HF-H₂O₂ was used for the total trace metal fraction of particulate matter, water was employed for the microwave-assisted extraction of water-soluble trace metal fractions. Inductively coupled plasma-mass spectrometry (ICP-MS) was used for the analysis of trace elements. The experimental protocol for the microwave assisted digestion was established using two different SRMs (1648, urban particulate matter and 1649a, urban dust). In the case of water-soluble trace metal fraction, the quantities extracted from the SRMs were compared between ultrasonic and microwave-assisted extractions, and there was a good agreement between the two extraction methods. Blanks values and limits of detection (LODs) for total and water-soluble trace metal concentrations were determined for three different filter substrates (Teflon, Zeflour, and Quartz). Subsequently, the proposed digestion method was evaluated for its extraction efficiency with these filter substrates. Finally, the real-world application of the proposed microwave-based sample preparation methods was demonstrated by analyzing trace elements in airborne particulate samples collected from different outdoor environments in Singapore. The solubility of 11 trace elements detected in the particulate samples is quantified.     

Determination of trace elements in uranium oxide by Total Reflection X-ray Fluorescence spectrometry

A study on the applicability of Total Reflection X-ray Fluorescence for the determination of multielements in trace amounts in U₃O₈ matrix has been made. The calibration of the Total Reflection X-ray Fluorescence spectrometer and the validation of the method were done using multielement standards. The trace elements present in U₃O₈ standards and samples were determined after separating the U matrix by solvent extraction using tri-n-butyl phosphate and trioctyl phosphine oxide as extractants. From the aqueous phase the elements K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Sr, Y, Zr, Pb and Ba, etc., were determined by Total Reflection X-ray Fluorescence using Ga as an internal standard. An intercomparison of the Total Reflection X-ray Fluorescence determined concentrations of the trace elements specific to nuclear fuel, e.g. Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn in U₃O₈ standards/samples with certified concentrations for these elements in U₃O₈ standards and Inductively Coupled Plasma Atomic Emission Spectroscopy determined concentrations in real U₃O₈ samples was also made. The method shows a precision and accuracy better than 5% (1σ) for most elements in concentration range of ng/mL with a sample size of 10 μL.     

PIXE analysis of the hydrothermal leaching of trace elements in coal

The minor and trace element content in coal is of great interest due to the potential impact on the environment from the release of these elements during combustion. Reducing the concentrations of potentially hazardous elements in coal prior to combustion is one way of dealing with this issue. In this research particle induced X-ray emission (PIXE) was used to investigate a hydrothermal leaching process for the removal of trace elements from a bituminous coal. The leaching agents HNO₃ and NaOH were evaluated along with the effects of process parameters (temperature, pressure, and time) on the method's effectiveness. The variable with the greatest influence was the leaching agent itself. HNO₃ was determined to be more effective than NaOH in reducing elemental concentrations for nearly all the elements determined. Increasing the temperature did result in greater reductions for some elements (Cl, Br, Zn) whereas increasing the pressure and duration of the leaching process had minimal impact on reductions, in elemental concentrations.     

Determination of Trace Elements in Arsenic and Antimony Minerals by Atomic Absorption Spectrometry and k0-Instrumental Neutron Activation Analysis After Removal of As and Sb

The content of trace elements in arsenic and antimony minerals from the Allchar mine, Macedonia, was determined by electrothermal atomic absorption spectrometry (ETAAS) and k₀-instrumental neutron activation analysis (k₀-INAA) after removal of arsenic and antimony. Their direct determination by ETAAS or k₀-INAA in arsenic (realgar and orpiment) and antimony (stibnite) minerals is limited by strong matrix interferences from As and Sb. Successful elimination of both elements was realized by the extraction of their iodide complexes into toluene. It was found that the optimal conditions were triple extraction of arsenic into toluene from 6mol·L^–1 HCl with addition of KI. Triple extraction of antimony was most successful in the system 4.5mol·L^–1 H₂SO₄ and KI into toluene. In both cases, trace elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) were then detected in the aqueous phase by ETAAS. The proposed procedures with ETAAS were checked by the method of standard additions and Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn determined in realgar, orpiment and stibnite. Using k₀-INAA the trace elements Ba, Ce, Co, Cr, Cs, Fe, Hg, Sc, Tb, Th, U and Zn in realgar and orpiment were determined before and after As and Sb removal from the same aliquot of sample. The removal of both elements with KI into toluene was higher than 99.8% and no losses of trace elements were observed.     

Cr6+-containing phases in the system CaO−Al2O3−CrO42−−H2O at 23 °C

Synthesis and investigation of lamellar calcium aluminium hydroxy salts was performed to study the incorporation of chromate ions in the interlayer of lamellar calcium aluminium hydroxy salts. Different AFm-phases (calcium aluminate hydrate with alumina, ferric oxide, mono-anion phase) containing chromate were synthesized. These AFm-phases belong to the group of layered double hydroxides (LDHs).3CaO·Al₂O₃·CaCrO₄·nH₂O and C₃A·1/2Ca(OH)₂·1/2CaCrO₄·12H₂O were obtained as pure phases and their different distinct interlayer water contents and properties determined. Solid solution of chromate-containing phases and tetracalcium-aluminate-hydrate (TCAH) were studied. The uptake of chromate into TCAH from solutions was proven. Chromate contents in solution decrease to <0.2 mg/l.     

Determination of trace elements in human gallstone and bile by k0-INAA

Summary The trace elements composition of gallbladder stones samples of the types cholesterol, pigment and mixed stones in addition to bile have been investigated by k₀-instrumental neutron activation analysis (k₀-INAA). The samples were obtained from several individuals of adult subjects of the Libyan population who undergone open surgery of gallbladder (cholecystectomy) at Al-khadra University Hospital in Tripoli. The samples were lyophilized, irradiated together with Au wire and Zr foil, which serve as flux ratio monitor and a parameter at TNRC. Concentrations of 24 elements in gallstone and 23 elements in bile were determined. The levels of the trace elements in the various samples investigated are measured and discussed. The reliability of the analysis was checked with several biological standard reference materials.     

PIGE and PIXE analyses of pentasil type boroaluminosilicates

The elemental composition of various synthetic crystalline sodium-boroaluminosilicates, especially the Al content and the silicon to aluminium bulk ratio, were determined by means of the combination of PIGE (Proton-Induced Gamma-Ray Emission Spectrometry) and PIXE (Proton-Induced X-Ray Emission Spectrometry). Light elements (B, O, Na, Al) were determined by means of gamma-ray emission. Proton-induced X-ray emission provided information on heavy elements present down to impurities. The Si/Al ratios, which mainly determine the catalytic and adsorptive properties of the zeolites, are compared with those obtained with other methods (EPMA, H₂O sorption capacity) and show good agreement.     

Hierarchical Structure of NiMo Hydrodesulfurization Catalysts Determined by Ptychographic X-Ray Computed Tomography

Hydrodesulphurization, the removal of sulphur from crude oils, is an essential catalytic process in the petroleum industry safeguarding the production of clean hydrocarbons. Sulphur removal is critical for the functionality of downstream processes and vital to the elimination of environmental pollutants. The effectiveness of such an endeavour is among other factors determined by the structural arrangement of the heterogeneous catalyst. Namely, the accessibility of the catalytically active molybdenum disulphide (MoS₂) slabs located on the surfaces of a porous alumina carrier. Here, we examined a series of pristine sulfided Mo and NiMo hydrodesulphurization catalysts of increasing metal loading prepared on commercial alumina carriers using ptychographic X-ray computed nanotomography. Structural analysis revealed a build consisting of two interwoven support matrix elements differing in nanoporosity. With increasing metal loading, approaching that of industrial catalysts, these matrix elements exhibit a progressively dissimilar MoS₂ surface coverage as well as MoS₂ cluster formation at the matrix element boundaries. This is suggestive of metal deposition limitations and/ or catalyst activation and following prohibitive of optimal catalytic utilization. These results will allow for diffusivity calculations, a better rationale of current generation catalyst performance as well as a better distribution of the active phase in next-generation hydrodesulphurization catalysts.     

有序介孔Al2O3∶RE3+的制备及Gd3+对Eu3+的能量传递

以P123为表面活性剂,异丙醇铝为铝源,用简易溶胶-凝胶法,获得了单掺和双掺Gd3+,Eu3+的介孔氧化铝组装体。用广角X-射线衍射仪(WAXD)进行了物相分析;小角X-射线衍射仪(SAXD)、比表面仪进行了孔结构分析和形貌表征;研究了组装体的发光性能并发现Gd3+对Eu3+有能量传递作用,并分析了能量传递过程。