116,066 research outputs found

    A revised scheme for the reactivity of iron (oxyhydr)oxide minerals towards dissolved sulfide

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    The reaction between dissolved sulfide and synthetic iron (oxyhydr)oxide minerals was studied in artificial seawater and 0.1 M NaCl at pH 7.5 and 25°C. Electron transfer between surface-complexed sulfide and solid phase Fe(III) results in the oxidation of dissolved sulfide to elemental sulfur, and the subsequent dissolution of the surface-reduced Fe. Sulfide oxidation and Fe(II) dissolution kinetics were evaluated for freshly precipitated hydrous ferric oxide (HFO), lepidocrocite, goethite, magnetite, hematite, and Al-substituted lepidocrocite. Reaction kinetics were expressed in terms of an empirical rate equation of the form: R-i = k(i)(H2S)(t=0)(0.5)A where Ri is the rate of Fe(II) dissolution (RFe) or the rate of sulfide oxidation (RS), ki is the appropriate rate constant (kFe or kS), (H2S)t=0 is the initial dissolved sulfide concentration, and A is the initial mineral surface area. The rate constants derived from the above equation suggest that the reactivity of Fe (oxyhydr)oxide minerals varies over two orders of magnitude, with increasing reactivity in the order, goethite < hematite < magnetite << lepidocrocite ≈ HFO. Competitive adsorption of major seawater solutes has little effect on reaction kinetics for the most reactive minerals, but results in rates which are reduced by 65-80% for goethite, magnetite, and hematite. This decrease in reaction rates likely arises from the blocking of surface sites for sulfide complexation by the adsorption of seawater solutes during the later, slower stages of adsorption (possibly attributable to diffusion into micropores or aggregates). The derivation of half lives for the sulfide-promoted reductive dissolution of Fe (oxyhydr)oxides in seawater, suggests that mineral reactivity can broadly be considered in terms of two mineral groups. Minerals with a lower degree of crystal order (hydrous ferric oxides and lepidocrocite) are reactive on a time-scale of minutes to hours. The more ordered minerals (goethite, magnetite, and hematite) are reactive on a time-scale of tens of days. Substitution of impurities within the mineral structure (as is likely in nature) has an effect on mineral reactivity. However, these effects are unlikely to have a significant impact on the relative reactivities of the two mineral groups

    Sulphidizing of Cerussite

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    The oxide minerals, such as cerussite, are not as amen­able to flotation as the sulphide minerals. Sulphidization is the usual means used today to increase the recovery of an oxide flotation; however, sulphidization under the most ad­vantageous conditions does not yield very satisfactory re­coveries

    Modification of bauxite residue with oxalic acid for improved performance in intumescent coatings

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    Valorization of bauxite residue (BR) enhances the dynamics of its application in intumescent coating for fire retarding systems. This BR, an alumina production waste could contain up to 45% ferrous oxide along with residual aluminous minerals. In an attempt to optimize the fire retardant properties of these minerals in intumescent systems, BR was treated in oxalic acid, varying the heating temperature between 50 °C and 100 °C at a constant pH of 2.65. X-ray florescence spectrometry revealed up to 80% reduction in iron content and total dissolution of desilication products (DSPs). The process temperature was found to affect the efficiency with which iron oxide was removed and with which the dissolved DSPs were precipitated as aluminum hydrates. X-ray diffraction revealed increased crystallinity and a gibbsite-dominated compound. Incorporation of the modified bauxite residues into a control intumescing formulation resulted in improved endothermic cooling, increased char expansion and char reinforcement. An inverse relationship appeared to exist between aluminum hydrates and iron as removal of iron led to enhanced intumescence and increased char expansion while higher iron content led to a compact, less expanded char. A balance of the fire retarding minerals occurred at a leaching temperature of 75 °C in oxalic acid. Best heat shielding performance thus occurred at XBR75-IC5 as char expansion increased by 12% and the substrate temperature reduced by 31% over the control IC system. Thus, BR may act as alternative fire retardant filler for intumescing systems

    Fingerprinting Paleo-Groundwater Sources Using Stable Oxygen and Iron Isotopes of Iron Oxide Concretions from the Boiler Room , Moab Area, Utah

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    Isotopes are naturally occurring atoms of an element that vary in the number of neutrons present in their nuclei, resulting in different atomic masses. The most common stable isotopes of oxygen are oxygen-18 (18O) and oxygen-16 (16O). Geochemical processes, such as the formation of a solid mineral from dissolved elements in a fluid, can result in preferential concentration of one isotope over the other in a process known as fractionation. By measuring the ratio of 18O and 16O in solid minerals and using known fractionation values, the isotopic ratio of the fluid from which those minerals formed can be determined. Calculated values can then be compared to known isotopic ranges for different fluids (e.g., surface vs groundwaters). In this study, we use the measured oxygen isotope ratios of iron oxide minerals (i.e., hematite) in rocks from the Boiler Room near Moab, Utah to determine the fluid(s) from which they formed and compare various proposed formation models. Ratios of stable isotopes for oxygen and iron, measurement of elemental concentrations, and textural observations of the rocks suggest that iron oxide minerals in the Boiler Room formed from a three-step process. First, a rock unit composed of carbonate minerals was deposited in a surface pond during the Jurassic period. After this unit was buried, an upward flowing acidic fluid dissolved the carbonate minerals within this layer. Changing geochemical conditions during this process caused iron dissolved in the acidic fluid to precipitate as hematite. Dissolution and replacement of the initially formed carbonate minerals resulted in the unique iron oxide rocks observed in the Boiler Room location where feeder pipes terminate into a horizontal layer of concentrated iron oxide. Understanding the formation processes of iron oxide minerals is important for reconstructing the history of fluid flow and mineral alteration in diverse geologic environments

    Microstructural analysis and magnetic characterization of native and magnetically modified montmorillonite and vermiculite

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    Two clay minerals of the similar 2 : 1 layer structure and chemical composition, vermiculite and montmorillonite, were studied using a wide spectrum of experimental methods in their original states and the magnetically modified states after mixing with microwave-synthesized iron oxide particles. This magnetic modification led to different microstructural morphology influencing magnetic behaviour at room and more pronounced at low temperatures.Web of Scienceart. no. 373810

    Thermal Stability of Azurite and Malachite in Relation to the Formation of Mediaeval Glass and Glazes

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    Azurite and malachite have been extensively used as pigments in ancient and medieval manuscripts, glasses and glazes. The thermal stability of naturally occurring azurite and malachite was determined using a combination of controlled rate thermal analysis combined with mass spectrometry and infrared emission spectroscopy. Both azurite and malachite thermally decompose in six overlapping stages but the behaviour is different for the two minerals. These stages occur around 282, 328, 350, 369, 384 and 840 degrees Celsius for azurite and 250, 321, 332, 345, 362 and 842 degrees Celsius for malachite. The first two stages are associated with the loss of water, whereas stages 3 and 4 result from the simultaneous loss of water and carbon dioxide. The sixth stage is associated with reduction of cupric oxide to cuprous oxide and finally to copper. Infrared emission spectroscopy shows that dehydroxylation occurs before the loss of carbonate and that the thermal decomposition is complete by 375 degrees Celsius. The implication of this research is that in the preparation of glass or glazes using these two hydroxy-carbonate minerals of copper the samples will decompose at low temperatures and any colour formation in the glass is not due to azurite or malachite

    Impact of grain-coating iron minerals on dielectric response of quartz sand and implications for ground-penetrating radar

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    An unexpected result of ground-penetrating radar (GPR) surveys in the Great Victoria Desert (South Australia) was the lack of returning signal in what appeared to be a favorable environment for GPR, with dry silica sand and calcrete aggregates in the near surface. We found that the dielectric response of the dry sand samples had much higher dielectric losses than comparable sands from Western Australia and that the dielectric losses are controlled by the presence of iron oxide minerals, although iron concentrations themselves are only around 0.4%. The samples contained over 90% quartz, with subsidiary amounts of carbonates, kaolin, and smectite occurring with the iron oxide minerals as a coating on the quartz grains. An acid washing procedure removed the reducible iron oxide minerals from the clay coating but left the clays substantially unaltered. Subsequent dielectric and magnetic analysis of the samples indicates that the iron oxide minerals removed during the washing process are responsible for the reduction of GPR penetration at 250 MHz from approximately 10 m to only 1 m

    Pemetaan Endapan Mineral Teralterasi Hidrotermal Menggunakan Analisis Citra Landsat 8 di Sekitar Gunung Api Bur Ni Geureudong, Kabupaten Bener Meriah, Aceh

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    Vegetation area and altered mineral by hydrothermal mapping using Landsat 8 satellite data has been done at Bur Ni Geurudong Volcano, Bener Meriah Regency, Aceh Province. Bands 5 and 4 data were used for Normalized Different Vegetation Index (NDVI) transformation technique. Band composition ratio of 6/5 and 6/7 were used for band ratio technique to interprete ferric oxide and clay minerals. The results show moderate (0.2-0.5) distribution of vegetation density found at Wih Pesam and Pante Raya Barat. The high density (0.50-0.88) vegetation areas are found at Silih Nara and Pinto Rime Gayo. The maximum distribution (1.98-2.23) of ferric oxide minerals found at Bur Ni Telong and few at Pinto Rime Gayo with sulfur content manifestation. This mineral is also founded on Silinara manifestation area. Maximum (2.33-8.88) distribution of clay mineral was found at Bur Ni Geureudong Volcano, few seen at Bur Ni Telong area. Based on the results, the Landsat 8 satellite imagery is effectively used for mapping of ferric oxide and clay minerals. Mapping of ferric oxide and clay minerals rovide information about the types of minerals that exist in Bur Ni Geurudong Volcano as a preliminary information about the types of geothermal reservoir rocks in the region

    COMPLEX PROCESSING OF POLYMETALLIC LEAD-ZINC ORE

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    It is known that oxide minerals of useful components are presented by complex oxidized forms and are not practically floatable. The paper gives the opportunity for complex oxide lead-zinc ore to be prepared effectively to flotation beneficiation based on pyrosulphidization of oxide minerals while roasting. The process of roasting is held in the atmosphere of overheated steam using sub-quality pyrite concentrates as sulphidizer. Using such pyrite concentrates make it possible to solve the problem of utilization and treatment of pyrite concentrates
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