Thermal analysis and infrared emission spectroscopic study of kaolinite-potassium acetate intercalate complex

The thermal behavior and decomposition of kaolinite-potassium acetate intercalation complex was investigated through a combination of thermogravimetric analysis and infrared emission spectroscopy. Three main changes were observed at 48, 280, 323 and 460 °C which were attributed to (a) the loss of adsorbed water (b) loss of the water coordinated to acetate ion in the layer of kaolinite (c) loss of potassium acetate in the complex and (d) water through dehydroxylation. It is proposed that the KAc intercalation complex is stability except heating at above 300 °C. The infrared emission spectra clearly show the decomposition and dehydroxylation of the kaolinite intercalation complex when the temperature is raised. The dehydration of the intercalation complex is followed by the loss of intensity of the stretching vibration bands at region 3600-3200 cm-1. Dehydroxylation is followed by the decrease in intensity in the bands between 3695 and 3620 cm-1. Dehydration is completed by 400 °C and partial dehydroxylation by 650 °C. The inner hydroxyl group remained until around 700 °C.

A Raman spectroscopic study of M2+M3+ sulfate minerals, römerite Fe2+Fe23+ (SO4)4· 14H2O and botryogen Mg2+Fe3+ (SO4)2(OH)·7H2O

The mixed valency (M2+M3+) sulphate minerals, römerite Fe2+Fe23+(SO4)4•14H2O and botryogen Mg2+Fe3+(SO4)2(OH).7H2O have been studied by Raman spectroscopy. The Raman spectra of the two types of crystals proved very similar but not identical. The observation of two symmetric stretching modes confirmed the presence of the two non-equivalent sulphate units in the römerite structure. The observation of multiple bands in the antisymmetric stretching region and in the bending regions proves the symmetry of the sulphate anion is significantly reduced in the römerite structure. The number of Raman bands related to the (SO4)2- symmetric and antisymmetric vibrations support the X-ray single crystal structure conclusion that two symmetrically distinct S6+ are present in the structure of botryogen. Römerite is a mineral of environmental significance as it is commonly found in tailings and dumps.

Raman spectroscopic study of the uranyl titanate mineral brannerite (U,Ca,Y,Ce)2(Ti,Fe)2O6 –Effect of Metamictization

Raman spectra of the uranyl titanate mineral brannerite were analysed and related to the mineral structure. A comparison is made with the Raman spectra of uranyl oxyhydroxide hydrates. Observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, U-OH bending vibrations, H2O and (OH)- stretching, bending and libration modes. U-O bond lengths in uranyls and O-H…O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of brannerite are in harmony with those of the uranyl oxyhydroxides. The mineral brannerite is metamict as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and with bands that are significantly broader.

Raman spectroscopy of gallium- and zinc-based hydrotalcites

Insight into the unique structure of hydrotalcites (HTs) has been obtained using Raman spectroscopy. Gallium-contg. HTs of formula Zn4 Ga2(CO3)(OH)12 · xH2O (2:1 ZnGa-HT), Zn6 Ga2(CO3)(OH)16 · xH2O (3:1 ZnGa-HT) and Zn8 Ga2(CO3)(OH)18 · xH2O (4:1 ZnGa-HT) have been successfully synthesized and characterised by X-ray diffraction (XRD) and Raman spectroscopy. The d(003) spacing varies from 7.62 Å for the 2:1 ZnGa-HT to 7.64 Å for the 3:1 ZnGa-HT. The 4:1 ZnGa-HT showed a decrease in the d(003) spacing, compared to the 2:1 and 3:1 compds. Raman spectroscopy complemented with selected IR data has been used to characterize the synthesized gallium-contg. HTs. Raman bands obsd. at around 1050, 1060 and 1067 cm-1 are attributed to the sym. stretching modes of the (CO32-) units. Multiple ν3 (CO32-) antisym. stretching modes are found between 1350 and 1520 cm-1, confirming multiple carbonate species in the HT structure. The splitting of this mode indicates that the carbonate anion is in a perturbed state. Raman bands obsd. at 710 and 717 cm-1 and assigned to the ν4 (CO32-) modes support the concept of multiple carbonate species in the interlayer.

A Raman spectroscopic study of copiapites Fe2+Fe3+(SO4)6(OH)2 · 20H2O: environmental implications

Raman spectroscopy has been used to study selected mineral samples of the copiapite group. Copiapite (Fe2+Fe3+(SO4)6(OH)2 · 20H2O) is a secondary mineral formed through the oxidn. of pyrite. Minerals of the copiapite group have the general formula AFe4(SO4)6(OH)2 · 20H2O, where A has a + 2 charge and can be either magnesium, iron, copper, calcium and/or zinc. The formula can also be B2/3Fe4(SO4)6(OH)2 · 20H2O, where B has a + 3 charge and may be either aluminum or iron. For each mineral, two Raman bands are obsd. at around 992 and 1029 cm-1, assigned to the (SO4)2-ν1 sym. stretching mode. The observation of two bands provides evidence for the existence of two non-equiv. sulfate anions in the mineral structure. Three Raman bands at 1112, 1142 and 1161 cm-1 are obsd. in the Raman spectrum of copiapites, indicating a redn. of symmetry of the sulfate anion in the copiapite structure. This redn. in symmetry is supported by multiple bands in the ν2 and ν4(SO4)2- spectral regions.

Raman spectroscopic study of the uranyl titanate mineral euxenite (Y,Ca,U,Ce,Th) (Nb,Ta,Ti)2O6

Raman spectra of the uranyl titanate mineral euxenite were analyzed and related to the mineral structure. A comparison is made with the Raman spectra of uranyl oxyhydroxide hydrates. The obsd. bands are attributed to the Ti[n.63743]O and (UO2)2+ stretching and bending vibrations, as well as lattice vibrations of rare-earth ions. The Raman bands of euxenite are in harmony with those of the uranyl oxyhydroxides. The mineral euxenite is metamict as is evidenced by the intensity of the U[n.63743]O stretching and bending modes, which are of lower intensity than expected, and with bands that are significantly broader.

Synthesis and Raman spectroscopic characterisation of hydrotalcites based on the formula Ca6Al2(CO3)(OH)16· 4H2O

We have successfully synthesized hydrotalcites (HTs) contg. calcium, which are naturally occurring minerals. Insight into the unique structure of HTs has been obtained using a combination of X-ray diffraction (XRD) as well as IR and Raman spectroscopies. Calcium-contg. hydrotalcites (Ca-HTs) of the formula Ca4Al2(CO3)(OH)12·4H2O (2:1 Ca-HT) to Ca8Al2(CO3)(OH)20· 4H2O (4:1 Ca-HT) have been successfully synthesized and characterised by XRD and Raman spectroscopy. XRD has shown that 3:1 calcium HTs have the largest interlayer distance. Raman spectroscopy complemented with selected IR data has been used to characterize the synthesized Ca-HTs. The Raman bands obsd. at around 1086 and 1077 cm-1 were attributed to the ν1 sym. stretching modes of the (CO32-) units of calcite and carbonate intercalated into the HT interlayer. The corresponding ν3 CO32- antisym. stretching modes are found at around 1410 and 1475 cm-1.

Vibrational spectroscopic study of the antimonate mineral bindheimite Pb2Sb2O6(O,OH)

Raman spectroscopy complimented with infrared spectroscopy has been used to characterise the antimonate mineral bindheimite Pb2Sb2O6(O,OH). The mineral is characterised by an intense Raman band at 656 cm-1 assigned to SbO stretching vibrations. Other lower intensity bands at 664, 749 and 814 cm-1 are also assigned to stretching vibrations. This observation suggests the non-equivalence of SbO units in the structure. Low intensity Raman bands at 293, 312 and 328 cm-1 are assigned to the OSbO bending vibrations. Infrared bands at 979, 1008, 1037 and 1058 cm-1 may be assigned to δ OH deformation modes of SbOH units. Infrared bands at 1603 and 1640 cm-1 are assigned to water bending vibrations, suggesting that water is involved in the bindheimite structure. Broad infrared bands centred upon 3250 cm-1 supports this concept. Thus the true formula of bindheimite is questioned and probably should be written as Pb2Sb2O6(O,OH,H2O)

An infrared study of adsorption of paranitrophenol on mono, di and trialkyl surfactant intercalated organoclays

Infrared spectroscopy has been used to study the adsorption of paranitrophenol on mono, di and tri alkyl surfactant intercalated montmorillonite. Organoclays were obtained by the cationic exchange of mono, di and tri alkyl chain surfactants for sodium ions [hexadecyltrimethylammonium bromide (HDTMAB), dimethyldioctadecylammonium bromide (DDOAB), methyltrioctadecylammonium bromide (MTOAB)] in an aqueous solution with Na-montmorillonite. Upon formation of the organoclay, the properties change from strongly hydrophilic to strongly hydrophobic. This change in surface properties is observed by a decrease in intensity of the OH stretching vibrations assigned to water in the cation hydration sphere of the montmorillonite. As the cation is replaced by the surfactant molecules the paranitrophenol replaces the surfactant molecules in the clay interlayer. Bands attributed to CH stretching and bending vibrations change for the surfactant intercalated montmorillonite. Strong changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surface. This study demonstrates that paranitrophenol will penetrate into the untreated clay interlayer and replace the intercalated surfactant in surfactant modified clay, resulting in the change of the arrangement of the intercalated surfactant.

A Raman spectroscopic study of the ‘cave’ mineral ardealite Ca2(HPO4)(SO4)•4H2O

The mineral ardealite Ca2(HPO4)(SO4)•4H2O is a ‘cave’ mineral and is formed through the reaction of calcite with bat guano. The mineral shows disorder and the composition varies depending on the origin of the mineral. Raman spectroscopy complimented with infrared spectroscopy has been used to characterise the mineral ardealite. The Raman spectrum is very different from that of gypsum. Bands are assigned to SO42- and HPO42- stretching and bending modes.

The application of Raman spectroscopy to the study of the uranyl mineral coconinoite Fe2Al2(UO2)2(PO4)4(SO4)(OH)2•20H2O

Raman spectra of the uranyl containing mineral coconinoite, Fe2Al2(UO2)2(PO4)4(SO4)(OH)2•20H2O, are presented and compared with the mineral’s infrared spectra. Bands connected with (UO2)2+, (PO4)3- , (SO4)2-, (OH)- and H2O stretching and bending vibrations, are assigned. Approximate U-O bond lengths in uranyl, (UO2)2+, and O-H...O hydrogen bond lengths are calculated from the wavenumbers of the U-O stretching vibrations and (OH)- and H2O stretching vibrations, respectively, and compared with published data for similar natural and synthetic compounds.

A vibrational spectroscopic study of hydrated Fe3+ hydroxyl-sulphates; polymorphic minerals butlerite and parabutlerite

Raman and infrared spectra of two polymorphous minerals with the chemical formula Fe3+(SO4)(OH)•2H2O, monoclinic butlerite and orthorhombic parabutlerite, are studied and the spectra assigned. Observed bands are attributed to the (SO4)2- stretching and bending vibrations, hydrogen bonded water molecules, stretching and bending vibrations of hydroxyl ions, water librational modes, Fe-O and Fe-OH stretching vibrations, Fe-OH bending vibrations and lattice vibrations. The O-H...O hydrogen bond lengths in the structures of both minerals are calculated from the wavenumbers of the stretching vibrations. One symmetrically distinct (SO4)2- unit in the structure of butlerite and two symmetrically distinct (SO4)2- units in the structure of parabutlerite are inferred from the Raman and infrared spectra. This conclusion agrees with the published crystal structures of both mineral phases.

Vibrational spectroscopic study of the mineral tsumebite Pb2Cu(PO4,SO4) (OH)

The mineral tsumebite Pb2Cu(PO4)(SO4)(OH), a copper phosphate-sulfate hydroxide of the brackebuschite group has been characterised by Raman and infrared spectroscopy. The brackebuschite mineral group are a series of monoclinic arsenates, phosphates and vanadates of the general formula A2B(XO4)(OH,H2O), where A may be Ba, Ca, Pb, Sr, while B may be Al, Cu2+,Fe2+, Fe3+, Mn2+, Mn3+, Zn and XO4 may be AsO4, PO4, SO4,VO4. Bands are assigned to the stretching and bending modes of PO43- and HOPO3 units. Hydrogen bond distances are calculated based upon the position of the OH stretching vibrations and range from 2.759 Å to 3.205 Å. This range of hydrogen bonding contributes to the stability of the mineral.

Raman spectroscopy of newberyite Mg(PO3OH)•3H2O – a cave mineral

Newberyite Mg(PO3OH)•3H2O is a mineral found in caves such as from Moorba cave, Jurien Bay, Western Australia, the Skipton Lava tubes (SW of Ballarat, Victoria, Australia) and in the Petrogale Cave (Madura , Eucla, Western Australia). Because these minerals contain oxyanions, hydroxyl units and water, the minerals lend themselves to spectroscopic analysis. Raman spectroscopy can investigate the complex paragenetic relationships existing between a number of ‘cave’ minerals. The intense sharp band at 982 cm-1 is assigned to the PO43- ν1 symmetric stretching mode. Low intensity Raman bands at 1152, 1263 and 1277 cm-1 are assigned to the PO43- ν3 antisymmetric stretching vibrations. Raman bands at 497 and 552 cm-1 are attributed to the PO43- ν4 bending modes. An intense Raman band for newberyite at 398 cm-1 with a shoulder band at 413 cm-1 is assigned to the PO43- ν2 bending modes. The values for the OH stretching vibrations provide hydrogen bond distances of 2.728Å (3267 cm-1), 2.781Å (3374cm-1), 2.868Å (3479 cm-1), and 2.918Å (3515 cm-1). Such hydrogen bond distances are typical of secondary minerals. Estimates of the hydrogen-bond distances have been made from the position of the OH stretching vibrations and show a wide range in both strong and weak bonds.

Raman spectroscopy of stercorite H(NH4)Na(PO4)•4H2O – a cave mineral from Petrogale Cave, Madura, Eucla, Western Australia

Raman spectroscopy complimented with infrared spectroscopy has been used to characterise the mineral stercorite H(NH4)Na(PO4)·4H2O. The mineral stercorite originated from the Petrogale Cave, Madura, Eucla, Western Australia. This cave is one of many caves in the Nullarbor Plain in the South of Western Australia. These caves have been in existence for eons of time and have been dated at more than 550 million years old. The mineral is formed by the reaction of bat guano chemicals on calcite substrates. A single Raman band at 920 cm−1 defines the presence of phosphate in the mineral. Antisymmetric stretching bands are observed in the infrared spectrum at 1052, 1097, 1135 and 1173 cm−1. Raman spectroscopy shows the mineral is based upon the phosphate anion and not the hydrogen phosphate anion. Raman and infrared bands are found and assigned to PO43−, H2O, OH and NH stretching vibrations. The detection of stercorite by Raman spectroscopy shows that the mineral can be readily determined; as such the application of a portable Raman spectrometer in a ‘cave’ situation enables the detection of minerals, some of which may remain to be identified.