[Show abstract][Hide abstract] ABSTRACT: The chemical and physical properties of carbonaceous matter (CM) were studied in Paleoproterozoic metasediment-hosted, orogenic-type gold deposits in Burkina Faso (the Inata deposit), in Mali (the Syama deposit), and in Ghana (the Obuashi and Bogoso deposits). Two types of CM occur in all the studied deposits: metamorphosed and hydrothermal. Metamorphosed CM prevails in all the deposits. Hydrothermal CM occurs in small veinlets in hydrothermally altered rocks and in quartz veins or forms irregular accumulations parallel or sub-parallel to C-type cleavage within the shear zones. The origin of hydrothermal CM, which occurs in paragenesis with Au-bearing arsenopyrite or pyrite, seems to have been due to supersaturation of hydrothermal fluids with carbon at the deeper or middle crustal levels. The isotopic composition of carbon in bulk CM (-33.1 to -26.2‰, VPDB) indicates its biogenic origin. The isotopic composition of carbon in hydrothermal carbonates ranges from -14.5 to -4.4‰ (VPDB), which suggest mixing of carbon derived from a deep-seated source with carbon derived from an organic source. The interaction of hydrothermal fluids with metamorphosed CM could be one of the causes of the reduction of hydrothermal fluids and formation of the respective mineralization. The optical properties and Raman spectra of the metamorphosed CM particles in the individual studied mineral deposits differ considerably. The temperatures calculated on the basis of the Raman spectra of metamorphosed CM vary between 280 and 440. °C, depending on the thermometer used, and correspond to temperatures of metamorphism of upper sub-grenschist and greenschist facies. The temperatures calculated for hydrothermal CM at the individual deposits, are only slightly lower compared to the metamorphosed CM at the same deposits, which indicates approximately the same temperature of the metamorphic and hydrothermal processes.
No preview · Article · Sep 2015 · Precambrian Research
[Show abstract][Hide abstract] ABSTRACT: High pressure sorption experiments with carbon dioxide and methane were carried out at a temperature of 45 °C and at pressures up to 15 MPa with three samples of methane-bearing, medium-rank coals in a moisture-equilibrated state using a manometric method. The samples were taken from selected positions of drill cores from exploration boreholes in the Bohemian part of the Upper Silesian Basin, and were characterized by a narrow range of degree of coalification and markedly different petrographic compositions, including a different mineral matter content. The total porosity of the coal samples was between 9% and 10%. A positive correlation was found between the equilibrium moisture in the coal samples and the total abundance of oxygen functional groups determined by FTIR. The excess sorption capacities ranged from 0.78 to 0.91 mmol g−1 for CO2 and from 0.45 to 0.52 mmol g−1 for CH4, and after recalculation to coal organic matter, the excess sorption capacities increased by up to 14% in the coal with the highest mineral fraction. The highest CO2/CH4 ratio was found in the sample that had the highest inertinite and liptinite content. The experimental isotherm data was fitted by modified Langmuir and Dubinin–Radushkevich sorption isotherms. The parameters obtained by these two methods were in good agreement for carbon dioxide. It was found that the sorption capacity of the organic matter in a coal sample with prevalence of inertinite (63.0 vol.%) was lower only by 14% for CO2 and by 18% for CH4 than the sorption capacity of the organic matter in a coal sample with prevalence of vitrinite (65.3 vol.%). This provided confirmation that the petrographic composition of a coal has an ambiguous effect.
[Show abstract][Hide abstract] ABSTRACT: A few non-conventional humate sorbents, i.e. iron humate (FeH), aluminium humate (AlH), calcium humate (CaH), magnesium humate (MgH), and zinc humate (ZnH), were prepared from a commercial product Fortehum L/K (Humatex, Bílina, Czech Republic). The metal content in humates was determined by X-ray fluorescence analysis, the organic elements (C, H, N, and S) were analysed by an Elementar Vario III and the functional groups were determined by classical methods using KBr pellets and diffuse reflection infrared spectroscopy (DRIFTS). FeH, AlH, and ZnH were tested as sorbents for the removal of inorganic or organic pollutants (metals, inorganic ions, dyes, and chlorophenols) from waste water. Sorption properties decreased in order: ZnH, AlH, FeH. CaH and MgH are partly soluble and therefore they are not usable as sorbents. However, their ion-exchange abilities for heavy metals are excellent which makes them usable for phytoremediation and bioremediation.
No preview · Article · Nov 2014 · Chemical Papers- Slovak Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Contents of uranium in coals from Odeř in the northernmost part of the Sokolov Basin, Czech Republic, in the vicinity of the well known St. Joachimsthal uranium ore deposits, reach extremely high values. In the present work, coal samples with contents of uranium ranging from 0.02 to 6 wt.% were studied. The study employing a whole complex of analytical techniques has been aimed at identification of changes in the structure of coal organic matter, which are associated with the high contents of uranium in coal. The study includes proximate and ultimate analyses, multielement analysis by instrumental neutron and photon activation analyses, micropetrographic analysis by optical microscopy, ESEM/EDX analysis of mineral matter, infrared and Raman spectroscopies, solvent extraction followed by gas chromatography with mass spectroscopy (GC/MS), and analytical pyrolysis (Py-GC/MS). The study has confirmed previously proposed explanation of uraniferous mineralization in sedimentary carboniferous substances by the mechanism of reduction and fixation of soluble U(VI) (uranyl, UO2(2+)) species (e.g., humic, carbonate/hydroxo/phosphate complexes) by sedimentary organic matter under diagenetic or hydrothermal conditions, and formation of insoluble U(IV) species as phosphate minerals and uraninite. The process is accompanied with alteration and destruction of the coal organic matter. The changes in the structure of coal organic matter involve dehydrogenation and oxidation mainly in the aliphatic, aromatic and hydroxyl structures, and an increase in aromaticity, content of ether bonds, and the degree of coalification.
[Show abstract][Hide abstract] ABSTRACT: The base sand layers of the aeolian Great Dune of Pilat, which stretches along the coast of Arcachon Bay, have been locally impregnated with a dark brown to black amorphous organic substance of humate composition. The humate-cemented sand forms a well-indurated horizon 40–50 cm in thickness that developed immediately beneath the Holocene peaty layer (P1“paleosoil”). The humate, identified by means of FT-IR and Raman micro-spectroscopy, acted both as a cementing agent and as a coloring agent; it formed thin coats and meniscus cements between individual sandstone grains which, in turn, caused the dark, asphaltic-like appearance of the sandstone. Field observations, combined with geochemical analyses, and the presence of identical geochemical compounds recognized in the peat and sandstone humate cement, suggest that the peat-containing low-coalified (Rr = 0.2%) fragments of higher, submerged and floating plants and marine algae deposited in a saline and reducing environment served as an obvious source rock for the humate. The humate derived from decaying organic remains that descended from the peat into the permeable sand, where it indurated irreversibly over a period shorter than 3500 years.The present-day actions of waves and tides contribute to the erosion of the frontal parts of the humate-impregnated sandstone horizon, resulting in the formation of the dark rounded sandstone slabs and pebbles that are deposited on nearby beaches. This process provides a fine example of recent black pebble formation that derived from pre-existing organic matter-impregnated source rocks. In contrast to their tropical carbonate counterparts, however, the humate-induced blackening of the sandstone pebbles appears to be relatively unstable, as the impregnated fragments bleach when exposed to air and seawater for a few seasons.
Full-text · Article · Jul 2013 · International Journal of Coal Geology
[Show abstract][Hide abstract] ABSTRACT: Se is a trace element and an important micronutrient. At higher concentrations it may become a serious threat for the environment and human health. Se occurs in nature in organic or inorganic compounds (SeO 32-, SeO 42-). The toxic compounds can be removed from water by adsorption on aluminosilicates (kaolins, bentonites, zeolites). The aim of this work was the preparation of new low-cost sorbents based on kaolins and determination of their stability. The adsorbents were prepared by treatment of kaolin with Fe 2+ or Al 3+ solution yielding mesoporous amorphous Fe III or Al III oxides/hydroxides. The obtained materials were selective adsorbents of Se IV in water. The batch sorption was performed with 10-1500 mg l -1 aqueous Se solutions and evaluated using a Langmuir model. The removal of Se using the Al-treated kaolin was more effective than its Fe analog.
[Show abstract][Hide abstract] ABSTRACT: Ni2Si, NiSi and NiSi2 contacts were prepared on n-type 4H– and 6H–SiC(0001) by deposition of Ni and Si multilayers in the respective stoichiometry after high-temperature annealing, as well as pure Ni contacts. After annealing, the individual contacts were analyzed by Raman spectroscopy and electrical property measurements. Contact structures were then etched-off and subsequently observed by means of AFM (Atomic Force Microscopy). Ni reacted with SiC, forming Ni2Si and carbon. At NixSiy/SiC contact structures the respective silicides were already formed at low annealing temperatures, when only Schottky behavior of the structures was observed. The intended silicides, once formed, did not change any further with increasing annealing temperature. All contact structures provided good ohmic behavior after being annealed at 960 °C. By means of combined AFM and Raman analysis of the etched-off contacts we found that the silicide contact structures very probably did not react with SiC which is in accordance with the thermodynamic assumptions. After annealing the silicide contact structures at such temperature, when Schottky behavior changed to ohmic, a certain form of interaction between the SiC substrate and the silicide contact structures must have occurred.
No preview · Article · Apr 2012 · Thin Solid Films
[Show abstract][Hide abstract] ABSTRACT: Carbonate reef talus facies of the Koněprusy Limestone (Pragian, Lower Devonian, Barrandian) locally exhibit widespread impregnation by organic matter resulting in a partial to complete blackening of the limestones. Two contrasting types of impregnation are recognized: blackening of individual carbonate fossils and bioclastic layers within the limestone originated very early during diagenesis. The blackening is due to finely dispersed organic matter and possibly some iron sulphides and clay minerals that selectively adhered to the outer layers of corals, bryozoans, and crinoid fragments, leaving other fossils unaltered. These darkened fossils are similar to black pebbles—i.e., reworked, dark to black limestone clasts and bioclasts that are known to occur exclusively in shallow-water zones of both ancient and modern carbonates. The alteration of fossil fragments may have taken place in very shallow-water environments, possibly those of saline and reducing back-reef lagoons or supratidal-intertidal zones, with organic matter being derived from decayed algae and microbes, or early vascular terrestrial plant material. Following the coloration, the blackened fossils were removed from their original position by waves or storms and transported into relatively deeper-water reef slope settings to form graded, “salt-and-pepper”-colored bioclastic beds. The presence of blackened fossils in the carbonate succession may point to episodic emergence and indicates a vanished vegetated siliciclastic hinterland that may once have existed to the west or south from the present-day erosive edge of the Barrandian Devonian strata. Subvertical veins cutting the Koněprusy Limestone and filled with black solid bitumen and blackened calcite resulted from a subsequent but substantially later diagenetic event, which is a testament of aqueous and petroleum fluid migration through the succession during deeper burial. Microthermometric characteristics of the aqueous inclusions embedded in vein calcite indicate that the veins were precipitated by brines of low to moderate salinity (0.5–9.5 wt% NaCl equiv.) with temperatures in the range of 87–116°C. The bitumen in the veins is epi-impsonite (Rr = 0.70–1.90%), which is interpreted as degraded petroleum residuum that experienced thermal alteration at around 120°C. The AFT modeling combined with fluid inclusion microthermometry and wider geological considerations indicate that the veins originated during the Variscan orogeny, most probably upon deep burial of the Lower Paleozoic strata in Carboniferous time.
[Show abstract][Hide abstract] ABSTRACT: The aim of this paper has been to characterize the relation between the pyrolysis temperature of phenol-formaldehyde resin, the development of a porous structure, and the mechanical properties for the application of semipermeable membranes for gas separation. No previous study has dealt with this problem in its entirety. Phenol-formaldehyde resin showed an increasing trend toward micropore porosity in the temperature range from 500 till 1000°C, together with closure of mesopores and macropores. Samples cured and pyrolyzed at 1000°C pronounced hysteresis of desorption branch. The ultimate bending strength was measured using a four-point arrangement that is more suitable for measuring of brittle materials. The chevron notch technique was used for determination the fracture toughness. The results for mechanical properties indicated that phenol-formaldehyde resin pyrolyzates behaved similarly to ceramic materials. The data obtained for the material can be used for calculating the technical design of gas separation membranes.
Full-text · Article · Jan 2012 · Ceramics Silikaty
[Show abstract][Hide abstract] ABSTRACT: Inexpensive regenerable natural sorbents of toxic metals and radionuclides with high capacity, good mechanical properties and stability have been developed. They are used in waste water treatment, groundwater remediation and in construction of active geochemical barriers. The review deals with sorption properties of humic substances and chitosan as sorbents, which can be used either separately or combined, with enhanced sorption capacity and operation conditions. Sorption studies on chitosan-doped lignite and oxihumolite sorbents are presented.
[Show abstract][Hide abstract] ABSTRACT: The use of clays as effective arsenic sorbents has been strongly limited due to their low pHZPC and cation active behaviour in aqueous systems at pH>3.5. A simple Fe/Al/Mn pre-treatment can significantly improve their sorption affinity to oxyanions, including arsenites and arsenates. The dynamics of arsenic adsorption from groundwater is also controlled by dissolved Fe/Mn ions, which behave as promoters of As adsorption, or competitors to adsorption sites. Low grade calcinated kaolin (MT) and bentonite (BT) were used as clay sorbents. Arsenic adsorption on raw clays without presence of Fe/Mn ions is very slow and limited. During co-adsorption the Fe/Mn ions and As oxyanions were adsorbed together onto a sorbent surface. Both Mn and Fe particles demonstrated a good sorption affinity to the clay surface, but only Fe particles supported As adsorption considerably (80% of As were removed in Fe/As system, while
No preview · Article · Nov 2011 · Applied Clay Science
[Show abstract][Hide abstract] ABSTRACT: Ni, Ni2Si and Pd contacts were prepared on n-type 4H-SiC and annealed in the temperature range of 750–1150 °C. The annealed contacts were analyzed before and after acid etching, and different features were found in unetched and etched contacts. Carbon left on the SiC surface after the acid etching of Ni2Si contacts annealed at 960 °C was highly graphitized. In nickel contacts, the graphitization of interface carbon began at 960 °C and increased after annealing at higher temperatures. In palladium contacts, the onset of the interface carbon graphitization was observed after annealing at 1150 °C. For all three types of metallization, the minimal values of contact resistivity were achieved only when the sharp first-order peak at 1585 cm−1 and distinct second-order peak at ∼2700 cm−1 related to the presence of graphitized carbon were detected by Raman spectroscopy after the acid etching of contacts. The properties of unannealed secondary contacts deposited onto etched primary contacts were similar to the properties of the primary contacts unless carbon was selectively etched. The results show that ohmic behavior of Ni-based and Pd contacts on n-type SiC originates from the formation of graphitic carbon at the interface with SiC.
Full-text · Article · Nov 2010 · Applied Surface Science
[Show abstract][Hide abstract] ABSTRACT: a b s t r a c t Voltammetry of immobilized microparticles (VMP), diffuse reflectance UV–vis spectroscopy (DRS), X-ray powder diffraction (XRD), and Raman spectroscopy were used to identify V(V) oxidic species in vanadia catalysts supported on titania, alumina, mesoporous silicas, and composites of Al 2 O 3 and TiO 2 with mont-morillonite (MMT). V 2 O 5 was detected by VMP irrespective of its crystallinity at concentrations close to the detection limit of crystalline V 2 O 5 by XRD. The interpretation of DRS was re-evaluated after VMP anal-yses, because detection of lower concentrations of V 2 O 5 by DRS is complicated by partial overlap of their absorption bands with rather intense absorption bands of major oligomeric vanadate species, while sen-sitivity of VMP to V 2 O 5 is much better than to less condensed vanadates. VMP selectively identified poly-vanadates prevailing on TiO 2 supports and oligomeric vanadate species prevailing on alumina at medium V-loadings. XRD-nanocrystalline V 2 O 5 was found as major species on impregnated mesoporous silicas with V loading above 4 wt.%. Al-and Ti-chemically modified MMTs disperse V(V) oxide species preferen-tially either on the Al 2 O 3 or TiO 2 components, or on the aluminosilicate components; these cases are eas-ily distinguished by VMP. VMP, especially if combined with spectral and XRD analyses, can produce detailed information about V(V) oxidic forms at V-loading close to or slightly above the critical monomer monolayer concentration, where 2-D and 3-D condensation of [VO 4 ] units is initiated. These forms play an important role in functionality of heterogeneous catalysts in oxidative dehydrogenation of ethane.
Full-text · Article · Aug 2009 · Journal of electroanalytical chemistry
[Show abstract][Hide abstract] ABSTRACT: In this paper, we demonstrate that combined application of X-ray diffraction (XRD), electron microscope/microprobe analysis (EMPA), and Raman microspectroscopy is an available and powerful approach for identification and characterization of iron arsenate minerals in complex environmental samples. Arsenic-rich material from the medieval mining dump close to the Giftkies mine in the Jáchymov ore district (Czech Republic) has been studied. Scorodite, kankite, amorphous iron arsenate (pitticite), and, to a lesser extent, native sulfur were determined in the studied samples as products of low-temperature arsenopyrite weathering. Scorodite and kankite form mixed nodules and crusts, which are locally coated by hardened gel-like amorphous pitticite. Pitticite also borders fractures in the mineralized rock fragments in the dump. Native sulfur, in microscopic crystals and grainy aggregates, originates directly in places with dissolved arsenopyrite and forms pseudomorphs. The Raman spectra presented in the paper can serve as comparative data for phase identification in other contaminated areas. New Raman data for the hydroxyl stretching region of scorodite (important bands: 3514, 3427, and 3600 cm(-1)) and the whole Raman spectrum for pitticite (important bands: 472, 831, 884, 2935, 3091, 3213, 3400, and 3533 cm(-1)) are a valuable output of this paper.
[Show abstract][Hide abstract] ABSTRACT: Arsenic, antimony and selenium belong to toxic contaminants with high environmental risk. In contrast to metal cationic contaminants (Be, Zn, Cd, Hg Pb, etc.) the metalloids and nonmetals of groups 5 and 6 of periodic system generally form the oxyanions in two oxidizing states (i.e. arsenates and arsenites, antimonates and antimonites, as well as selenates and selenites) in dependence on redox potential and pH value. It is well known that above mentioned oxyanions have a strong adsorption affinity to hydrated oxides and/or oxides hydroxides of Fe, Al and Mn, preferably Fe forming stable surface complexes. In fact, commercially produced Fe oxides-based sorbents are too expensive for strongly contaminated aqueous systems. Aluminosilicates have opened new possibilities in sorption technology due to favourable surface properties, availability, environmental and economical reasons, but they are not selective sorbents of anionic contaminants thanks to a low pHZPC. A simple Fe/Al/Mn pre-treatment of raw aluminosilicates can significantly improve their sorption affinity to oxyanionic contaminants, including arsenites and arsenates, selenites and selenates and antimonites and antimonates, respectively. Different types of natural and/or second-rate clays (metakaolines with the large content of Fe, raw bentonites and natural clinoptilolite-rich tuff, ) from Central European localities were used for FeII, Fe , AlIII and MnII pre-treatment.
No preview · Article · Jan 2009 · Acta Geodynamica et Geomaterialia
[Show abstract][Hide abstract] ABSTRACT: The utilization of low-grade clay materials as selective sorbents represents one of the most effective possibilities of As removal from contaminated water reservoirs. The simple pre-treatment of these materials with Fe (Al, Mn) salts can significantly improve their sorption affinity to As oxyanions. The natural kaolin calcined at 550 degrees C (mostly metakaolin) and raw bentonite (mostly montmorillonite) pre-treated with Fe(II), Fe(III), Al(III) and Mn(II) salts were used to remove of As from the model anoxic groundwater with As(III) concentration about 0.5 and 10 mg L(-1). All the pre-treating methods were appropriate for bentonite; the efficiency of As(III) sorption varied from 92 to >99%, by the sorption capacity higher than 4.5 mg g(-1). In the case of metakaolin, Fe(II)- and Mn(II)-treatments proved the high sorption efficiency (>97%), while only <50% of As was removed after Fe(III) and Al(III) pre-treatment. The sorption capacities of treated metakaolin ranged from 0.1 to 2.0 mg g(-1).
No preview · Article · Oct 2008 · Journal of hazardous materials
[Show abstract][Hide abstract] ABSTRACT: Marine black shales of the Lower Cambrian Niutitang Formation in southern China host Mo–Ni–platinum group elements (PGE) mineralization confined to a phosphate- and pyrite-rich stratiform body (max. 20-cm thick). The H/C atomic ratio, carbon isotopic composition, FTIR spectra of bulk organic matter, and spectra of extractable part of organic matter indicate similar sources and thermal evolution of organic matter in barren and mineralized black shales.The morphology and relative abundance of organic particles in barren and mineralized shales are different. In barren black shales, organic particles comprise only elongated bodies and laminae 2–10 μm across or elongated larger bodies (> 10 μm) with Rmax = 2.96–5.21% (Type I particles). Mineralized black shales contain Type I particles in rock matrix (90–95 vol%), small veinlets or irregular organic accumulations (Type II particles, 1–5 vol%) that display weak to well developed mosaic texture and a variable reflectance (Rmax = 3.55–8.65%), and small (< 1 to 5 μm) rounded or irregular Type III organic particles (1–4 vol%) distributed within phosphate nodules and sulphide rip-up clasts. Type III particles show similar reflectance as particles of Type I in rock matrix. Type I particles are interpreted as remnants of in situ bacterially reworked organic matter of cyanobacteria/algal type, Type II as solidified products or oil-derived material (migrabitumen), and Type III particles as remnants of original organic matter in phosphatized or sulphidized algal/microbial oncolite-like bodies. Equivalent vitrinite reflectances of Type I and III particles in barren and mineralized rocks are similar and correspond to semi-anthracite and anthracite. Micro-Raman spectra of organic particles in rocks display a wide belt in the area of 1600 cm− 1 (G belt) and approximately the same belt in the area of 1350 cm− 1 (D belt). The ratio of integrated areas of the two belts correlate with Rmax values.The Mo–Ni–PGE mineralized body is interpreted as to represent a remnant of phosphate- and sulphide-rich subaquatic hardground supplied with organic material derived from plankton and benthic communities as well as with algal/microbial oncolite-like bodies that originated in wave-agitated, shallow-water, nearshore environment.
No preview · Article · Nov 2007 · International Journal of Coal Geology
[Show abstract][Hide abstract] ABSTRACT: Natural soil profiles strongly contaminated by arsenic (As) have been studied. Soils were characterised by its pH, chemical composition, carbonate, humus, exchangeable cations and H+, and oxalate extractable Fe contents. Mineralogical and chemical speciation of the As was studied by mineralogical methods and sequential extraction. Results were compared and discussed regarding the two different types of soil environment: i) soil developed above the flat unforested granodiorite bedrock and ii) soil developed above the volcanosedimentary bedrock in a sloping forested area. As-bearing minerals were concentrated from soils using heavy liquid and determined using XRD, SEM-EDS/WDS, and Raman spectroscopy. Iron (III) oxyhydroxides (FOHs); K(-Ba) pharmacosiderite, arseniosiderite, scorodite, and jarosite were identified as products of arsenopyrite and/or pyrite oxidation. Arsenates of varying chemical compositions dominate the soil above the granodiorite, while goethite, minor hematite and other indistinguishable FOHs are observed in the soil above the volcanosediments. The diversity and stability of the As secondary minerals in the studied soils are influenced partly by variation in the bedrock composition and mainly by the presence/absence of vegetation cover which mirrors in various contents of exchangeable Ca2+, content of Fe oxalate, and pH. The results of the sequential extraction show an average to high As retention by these soils, when As was extracted during the third and fourth extraction steps (NH4-oxalate buffer, ascorbic acid) in most samples. This finding indicates that As is more mobile in soils where arsenates dominate over well crystallized FOHs.