Showing papers by "Ray L. Frost published in 2006"

XPS study of the major minerals in bauxite: gibbsite, bayerite and (pseudo-)boehmite.

Abstract: Synthetic corundum (Al2O3), gibbsite (Al(OH)3), bayerite (Al(OH)3), boehmite (AlO(OH)) and pseudoboehmite (AlO(OH)) have been studied by high resolution XPS. The chemical compositions based on the XPS survey scans were in good agreement with the expected composition. High resolution Al2p scans showed no significant changes in binding energy, with all values between 73.9 and 74.4 eV. Only bayerite showed two transitions, associated with the presence of amorphous material in the sample. More information about the chemical and crystallographic environment was obtained from the O1s high resolution spectra. Here a clear distinction could be made between oxygen in the crystal structure, hydroxyl groups and adsorbed water. Oxygen in the crystal structure was characterised by a binding energy of about 530.6 eV in all minerals. Hydroxyl groups, present either in the crystal structure or on the surface, exhibited binding energies around 531.9 eV, while water on the surface showed binding energies around 533.0 eV. A distinction could be made between boehmite and pseudoboehmite based on the slightly lower ratio of oxygen to hydroxyl groups and water in pseudoboehmite.

Raman spectroscopy of three polymorphs of BiVO4: clinobisvanite, dreyerite and pucherite, with comparisons to (VO4)3-bearing minerals: namibite, pottsite and schumacherite

Abstract: Both Raman and infrared spectroscopy have been used to characterise the three phase related minerals dreyerite (tetragonal BiVO4 ), pucherite (orthorhombic BiVO4) and clinobisvanite (monoclinic BiVO4 ) and a comparison of the spectra is made with that of the minerals namibite (Cu(BiO2)VO4(OH)), schumacherite ((Bi3O(OH)(VO4)2) and pottsite (PbBiH(VO4)2.2H2O). Pucherite, clinobisvanite and namibite are characterised by VO4 stretching vibrations at 872, 824 and 846 cm-1. The Raman spectrum of dreyerite shows complexity in the 750 to 950 cm-1 region with two intense bands at 836 and 790 cm-1 assigned to the symmetric and antisymmetric VO4 modes. The minerals schumacherite and pottsite are characterised by bands at 846 and 874 cm-1. In both the infrared and Raman spectra bands are observed in the 1000- 1100 cm-1 region which are attributed to the antisymmetric stretching modes. The Raman spectra of the low wavenumber region are complex. Bands are identified in the 328 to 370 cm-1 region and in the 404 to 498 cm-1 region and are assigned to the ν2 and ν4 bending modes. The minerals namibite and schumacherite are characterised by intense bands at 3514 and 3589 cm-1 assigned to the symmetric stretching vibrations of the OH units. Importantly Raman spectroscopy enables new insights into the chemistry of these bismuth vanadate minerals. Raman spectroscopy enables the identification of the bismuth vanadate minerals in mineral matrices where paragenetic relationships exist between the minerals.

Structural evolution in a hydrothermal reaction between Nb2O5 and NaOH solution: from Nb2O5 grains to microporous Na2Nb2O6.2/3H2O fibers and NaNbO3 cubes.

Abstract: Niobium pentoxide reacts actively with concentrate NaOH solution under hydrothermal conditions at as low as 120 degrees C. The reaction ruptures the corner-sharing of NbO7 decahedra and NbO6 octahedra in the reactant Nb2O5, yielding various niobates, and the structure and composition of the niobates depend on the reaction temperature and time. The morphological evolution of the solid products in the reaction at 180 degrees C is monitored via SEM: the fine Nb2O5 powder aggregates first to irregular bars, and then niobate fibers with an aspect ratio of hundreds form. The fibers are microporous molecular sieve with a monoclinic lattice, Na2Nb2O6 center dot(2)/3H2O. The fibers are a metastable intermediate of this reaction, and they completely convert to the final product NaNbO3 Cubes in the prolonged reaction of 1 h. This study demonstrates that by carefully optimizing the reaction condition, we can selectively fabricate niobate structures of high purity, including the delicate microporous fibers, through a direct reaction between concentrated NaOH solution and Nb2O5. This synthesis route is simple and suitable for the large-scale production of the fibers. The reaction first yields poorly crystallized niobates consisting of edge-sharing NbO6 octahedra, and then the microporous fibers crystallize and grow by assembling NbO6 octahedra or clusters of NbO6 octahedra and NaO6 units. Thus, the selection of the fibril or cubic product is achieved by control of reaction kinetics. Finally, niobates with different structures exhibit remarkable differences in light absorption and photoluminescence properties. Therefore, this study is of importance for developing new functional materials by the wet-chemistry process.

Microstructure of hdtma+-modified montmorillonite and its influence on sorption characteristics

Abstract: A series of organoclays with monolayer, bilayer, pseudotrilayer, paraffin monolayer and paraffin bilayer were prepared by ion exchange. The microstructural parameters, including BET-N2 surface area, pore volume, pore size, surfactant loading and distribution, were deter-mined by X-ray diffraction (XRD), N2 adsorption-desorption and high-resolution thermogra-vimetric analysis (HRTG). The results show that both BET-N2 surface area and pore volume decrease from low to high surfactant loading as the average pore size increases. After modify-ing montmorillonite with hexadecyltrimethylammonium bromide (HDTMAB), two basic or-ganoclay models were proposed on the basis of HRTG results: 1) the surfactant mainly occu-pied the clay interlayer and 2) both the clay interlayer space and external surface were modi-fied by surfactant. In the former case, the sorption mechanism of p-nitrophenol to the organo-clay at relative low concentration involves both surface adsorption and partition whereas the latter mainly involves partition. This study demonstrates that the distribution of adsorbed sur-factant and the arrangement of adsorbed HDTMA+ within the clay interlayer control the effi-ciency and mechanism of sorption by the organoclay rather than BET-N2 surface area, pore volume, and pore diameter.

A novel organoclay with antibacterial activity prepared from montmorillonite and Chlorhexidini Acetas

Abstract: A series of novel organoclays with antibacterial activity were synthesized using Ca-montmorillonite and Chlorhexidini Acetas (CA) by ion-exchange. The resultant organoclays were characterized using X-ray diffraction (XRD), high-resolution thermogravimetric analysis (HRTG) and Fourier transform infrared spectroscopy (FTIR). Their antibacterial activity was assayed by so-called halo method. In the organoclay prepared at low CA concentration, CA ions within the clay interlayer adopt a lateral monolayer while a ‘kink’ state or a special state with partial overlapping of the intercalated CA in the organoclays prepared at 1.0 – 4.0 CEC. HRTG analysis demonstrates that CA located outside the clay interlayer exists in all synthesised organoclays, resulting from the complex molecular configuration of CA. The dramatic decrease of the surface adsorbed water and interlayer water is caused by the surface property transformation and the replacement of hydrated cations by cationic surfactant. These observations are supported by the results of FTIR. Antibacterial activity test against E. coli demonstrates that the antibacterial activity of the resultant organoclays strongly depends on the content of CA. Meanwhile, the resultant organoclay shows a long-term antibacterial activity that can last for at least one year. These novel organoclays are of potential use in synthesis of organoclay-based materials with antibacterial activity.

Raman spectroscopy of hydrotalcites with phosphate in the interlayer: implications for the removal of phosphate from water

Abstract: Hydrotalcites with phosphate in the interlayer were prepared at different pH values. At pH >11.0 (PO4)(3-) was the intercalated ionic species, whereas at pH < 11.0 a mixture of (PO4)(3-) and (HPO4)(2-) ions was intercalated. Powder X-ray diffraction shows that the hydrotalcite formed at pH 9.5 is poorly diffracting with a d-spacing of 11.9 angstrom; whereas the d(003) spacing for the phosphate interlayered hydrotalcite formed at pH 11.9 and 12.5 was 8.0 and 7.9 angstrom respectively. The addition of a thermally activated ZnAl-HT to a phosphate solution resulted in the uptake of the phosphate and the reformation of the hydrotalcite. Raman spectroscopy of the phosphate interlayered hydrotalcites shows that the interlayered anion is pH dependent and only above pH 11.9 is the orthophosphate anion intercalated. At lower pH, the monohydrogen phosphate anion is intercalated. Raman spectroscopy shows that upon addition of the thermally activated hydrotalcite to an aqueous phosphate solution, results in the uptake of phosphate anion from the solution. Copyright (C) 2006 John Wiley & Sons, Ltd.

Molecular structure of the uranyl silicates : a Raman spectroscopic study

Abstract: Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals including uranophane, sklodowskite, cuprosklodowskite, boltwoodite and kasolite. Raman spectra clearly show well resolved bands in the 750 to 800 cm-1 region and in the 950 to 1000 cm-1 region assigned to the ν1 modes of the (UO2)2+ units and to the (SiO4)4- tetrahedra. Sets of Raman bands in the 200 to 300 cm-1 region are assigned to ν2 δ (UO2)2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of ν2 δ (UO2)2+ vibrations. The (SiO4)4- tetrahedral are characterized by bands in the 470 to 550 cm-1 and in the 390 to 420 cm-1 region. These bands are attributed to the ν4 and ν2 (SiO4)4- bending modes. The minerals show characteristic OH stretching bands in the 2900 to 3500 cm-1 and 3600 to 3700 cm-1 region ascribed to water stretching and SiOH stretching vibrations. The high wavenumber position of the δH2O bands indicate strong hydrogen bonding of water in these uranyl silicates. Bands in the 1400 to 1550 cm-1 region are attributed to δSiOH modes. The Raman spectroscopy of uranyl silicate minerals enabled separation of the bands attributed to distinct vibrational units. This enabled definitive assignment of the bands. The spectra are analysed in terms of the molecular structure of the minerals.

A Raman spectroscopic study of selected minerals of the rosasite group

Abstract: Minerals in the rosasite mineral group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite, nullaginite and pokrovskite have been studied by Raman spectroscopy at 298 and 77 K and complimented with infrared spectroscopy. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the structure is the same as malachite i.e. monoclinic. A comparison is made with the spectra of malachite. The symmetry of the carbonate anion in the rosasite mineral group is C2v or Cs and is composition dependent. Two (CO3)2- symmetric stretching modes are observed for the rosasite minerals at 1060 and 1090 cm-1. Two hydroxyl stretching modes are observed for the rosasite mineral group. The position of these bands is determined to be a function of the hydrogen bond lengths. Hydrogen bond distances for rosasite are calculated as 2.867, 2.799 and 2.780 A whereas for pokrovskite the distances are 3.280 and 2.999 A. The effect of lowering the temperature from ambient to 77 K results in a decrease of the hydrogen bond distances by 5%. Multiple Raman bands are observed in the 800 to 850 cm-1 and the 720 to 750 cm-1 regions and are attributed to ν2 and ν4 bending modes confirming the reduction of the carbonate anion in the rosasite structure.

A Raman Spectroscopic Study of the Uranyl Selenite Mineral Haynesite

Abstract: The mineral haynesite, a uranyl selenite, has been characterised by Raman spectroscopy at 298 and 77 K. Two bands at 811.5 and 800.2 cm-1 are assigned to the symmetric stretching modes of the (UO2)2+ and (SeO3)2- units respectively. These values give calculated U-O bond lengths of 1.799 and/or 1.801 A. The broad band at 861.8 cm-1 is assigned to the ν3 antisymmetric stretching mode of the (UO2)2+ (calculated U-O bond length 1.813 A). Additional bands are observed in the 77 K spectrum. In the spectroscopy of selenite compounds the position of the antisymmetric stretching vibration occurs at lower wavenumbers than the symmetric stretching mode and thus the band at 746.6 cm-1 is attributed to the ν3 antisymmetric stretching vibration of the (SeO3)2- units. The ν4 and the ν2 vibrational modes of the (SeO3)2- units are observed at 418.5 cm-1 and 472.1 cm-1. Bands observed at 278.3, 257.3 and 218.8 cm-1 are assigned to OUO bending vibrations.

A Raman spectroscopic study of the uranyl phosphate mineral parsonsite

Abstract: The mineral parsonsite, with samples from The Ranger Uranium Mine, Australia, and the La Faye Mine, Grury, Saone-et-Loire, Burgundy, France, has been characterised by Raman spectroscopy at 298 and 77 K and complemented with infrared spectroscopy. Two Raman bands close to 807 and 796 cm−1 are attributed to the ν1(UO2)2+ symmetric stretching modes, while two bands close to 953 or 945 cm−1 and 863–873 cm−1 are assigned to the ν3(UO2)2+ anti-symmetric stretching vibrations. Four or five bands (953, 926, 910, 883 cm−1) are observed in the infrared spectrum in this region. Bands at 965–967 and 972 cm−1 are assigned to the ν1(PO4)3− symmetric stretching modes and bands that are observed in the 987 to 1078 cm−1region to the ν3(PO4)3− anti-symmetric stretching modes. Bands at 465, 439, 406, 394 cm−1 (298 K) and 466, 442, 405, 395 cm−1(77 K) are assigned to the split, doubly degenerate ν2(PO4)−3bending vibrations. Bands of very low intensity at 609, 595, 591, 582, 560 and 540 cm−1are attributed to the split, triply degenerate ν4(PO4)−3bending modes. Bands observed at wavenumbers lower than 300 cm−1are connected with the split ν2(δ) (UO2)2+ bending, ν(UOligand), δ(UOligand) and lattice vibrations. UO bond lengths in uranyl were calculated from the Raman and infrared spectra, which are in agreement with those from the available X-ray single crystal structure analysis of parsonsite. A short comment is given on the water content and the possibility of a hydrogen-bonding network in the parsonsite crystal structure. Copyright © 2006 John Wiley & Sons, Ltd.

Characterization of Intercalated Ni/Al Hydrotalcites Prepared by the Partial Decomposition of Urea

Abstract: Layered double hydroxides containing Ni2+ and Al3+ have been synthetized by homogeneous precipitation through urea hydrolysis. The nature of the interlayer species changes according to the treatment of the samples, formation of interlayer (NH2)COO- species being observed immediately after precipitation, which undergo transformation to carbonate after hydrothermal treatment. Simultaneously, liberation of ammonia during decomposition under hydrothermal conditions gives rise to formation of [Ni(NH3)6]2+ species in solution.

Raman Spectroscopy of Walpurgite

Abstract: Raman spectra of walpurgite, (UO2)Bi4O4(AsO4)2. 2 H2O, recorded at 298 K and 77 K are presented and compared with infrared spectra of walpurgite and phosphowalpurgite. Bands connected with (UO2)2+, (AsO4)3- and H2O stretch and bend, and Bi-O stretch are tentatively assigned. Hydrogen bond lengths are calculated from the wavenumbers of the H2O stretching vibrations and compared with those from crystal structure analysis of walpurgite.

Thermal decomposition of ammonium jarosite (NH4)Fe3(SO4)2(OH)6

Abstract: Thermogravimetry combined with mass spectrometry has been used to study the thermal decomposition of a synthetic ammonium jarosite. Five mass loss steps are observed at 120, 260, 389, 510 and 541°C. Mass spectrometry through evolved gases confirms these steps as loss of water, dehydroxylation, loss of ammonia and loss of sulphate in two steps. Changes in the molecular structure of the ammonium jarosite were followed by infrared emission spectroscopy (IES). This technique allows the infrared spectrum at the elevated temperatures to be obtained. IES confirms the dehydroxylation to have taken place by 300°C and the ammonia loss by 450°C. Loss of the sulphate is observed by changes in band position and intensity after 500°C.

Thermal decomposition of hydronium jarosite (H3O)Fe3 (SO4)2 (OH)6

Abstract: Thermogravimetry combined with mass spectrometry has been used to study the thermal decomposition of a synthetic hydronium jarosite. Five mass loss steps are observed at 262, 294, 385, 557 and 619°C. The mass loss step at 557°C is sharp and marks a sharp loss of sulphate as SO3 from the hydronium jarosite. Mass spectrometry through evolved gases confirms the first three mass loss steps to dehydroxylation, the fourth to a mass loss of the hydrated proton and a sulphate and the final step to the loss of the remaining sulphate. Changes in the molecular structure of the hydronium jarosite were followed by infrared emission spectroscopy. This technique allows the infrared spectrum at the elevated temperatures to be obtained. Infrared emission spectroscopy confirms the dehydroxylation has taken place by 400 and the sulphate loss by 650°C. Jarosites are a group of minerals formed in evaporite deposits and form a component of the efflorescence. The minerals can function as cation and heavy metal collectors. Hydronium jarosite has the potential to act as a cation collector by the replacement of the proton with a heavy metal cation.

Integrated Risk Framework for Onsite Wastewater Treatment Systems

Abstract: Onsite wastewater treatment systems (OWTS) are becoming increasingly important for the treatment and dispersal of effluent in new urbanised developments that are not serviced by centralised wastewater collection and treatment systems. However, the current standards and guidelines adopted by many local authorities for assessing suitable site and soil conditions for OWTS are increasingly coming under scrutiny due to the public health and environmental impacts caused by poorly performing systems, in particular septic tank-soil adsorption systems. In order to achieve sustainable onsite wastewater treatment with minimal impacts on the environment and public health, more appropriate means of assessment are required. This paper highlights an integrated risk based approach for assessing the inherent hazards associated with OWTS in order to manage and mitigate the environmental and public health risks inherent with onsite wastewater treatment. In developing a sound and cohesive integrated risk framework for OWTS, several key issues must be recognised. These include the inclusion of relevant stakeholders throughout framework development, the integration of scientific knowledge, data and analysis with risk assessment and management ideals, and identification of the appropriate performance goals for successful management and mitigation of associated risks. These issues were addressed in the development of the risk framework to provide a generic approach to assessing risk from OWTS. The utilisation of the developed risk framework for achieving more appropriate assessment and management techniques for OWTS is presented in a case study for the Gold Coast region, Queensland State, Australia.

Integrated risk framework for onsite wastewater treatment systems

Abstract: Onsite wastewater treatment systems (OWTS) are becoming increasingly important for the treatment and dispersal of effluent in new urbanised developments that are not serviced by centralised wastewater collection and treatment systems. However, the current standards and guidelines adopted by many local authorities for assessing suitable site and soil conditions for OWTS are increasingly coming under scrutiny due to the public health and environmental impacts caused by poorly performing systems, in particular septic tank-soil adsorption systems. In order to achieve sustainable onsite wastewater treatment with minimal impacts on the environment and public health, more appropriate means of assessment are required. This paper highlights an integrated risk based approach for assessing the inherent hazards associated with OWTS in order to manage and mitigate the environmental and public health risks inherent with onsite wastewater treatment. In developing a sound and cohesive integrated risk framework for OWTS , several key issues must be recognised. These include the inclusion of relevant stakeholders throughout framework development, the integration of scientific knowledge, data and analysis with risk assessment and management ideals, and identification of the appropriate performance goals for successful management and mitigation of associated risks. These issues were addressed in the development of the risk framework to provide a generic approach to assessing risk from OWTS . The utilisation of the developed risk framework for achieving more appropriate assessment and management techniques for OWTS is presented in a case study for the Gold Coast region, Queensland State, Australia.

Raman spectroscopic study of the uranyl phosphate mineral dewindtite

Abstract: Raman spectra of two uranyl mineral dewindtite samples are presented and interpreted. Observed bands are attributed to the stretching and bending vibrations of (UO2)2+ and (PO4)3- units and water molecules. Hydrogen bonding network in dewindtite crystal structure is shortly mentioned. U-O bond lengths in uranyls are calculated with empirical relations and wavenumbers of the (UO2)2+ stretching vibrations. These calculations are in agreement with the X-ray single crystal structure data.

Thermal decomposition of the synthetic hydrotalcite iowaite

Abstract: The thermal stability and thermal decomposition pathways for synthetic iowaite have been determined using thermogravimetry in conjunction with evolved gas mass spectrometry. Chemical analysis showed the formula of the synthesised iowaite to be Mg6.27Fe1.73(Cl)1.07(OH)16(CO3)0.336.1H2O and X-ray diffraction confirms the layered structure. Dehydration of the iowaite occurred at 35 and 79°C. Dehydroxylation occurred at 254 and 291°C. Both steps were associated with the loss of CO2. Hydrogen chloride gas was evolved in two steps at 368 and 434°C. The products of the thermal decomposition were MgO and a spinel MgFe2O4. Experimentally it was found to be difficult to eliminate CO2 from inclusion in the interlayer during the synthesis of the iowaite compound and in this way the synthesised iowaite resembled the natural mineral.