Anthracite Samples Research Articles

Rare earth and radioactive elements in some coals from the Sofia, Svoge and Pernik Basins, Bulgaria

Coal samples from three Bulgarian basins were investigated for their rare earth and radioactive element concentrations. The samples ranged in rank from lignite to anthracite. All the samples contained La, Ce, Sm, Eu, Tb, Yb, Th and U. Lu occurs in sub-bituminous coal samples from the Pernik Basin and in a lignite sample from the Sofia Basin. The concentrations of most elements are lower than or close to data reported in the literature from other coal basins or the Clarke values determined by Yudovich et al. (1985). The elements Tb and Lu are exceptions to this, together with Th in the Svoge Basin anthracites. The lowest concentrations of most elements are found in lignite samples from the Sofia Basin; the highest concentrations occur in anthracite samples from the Svoge Basin. In this study the Sofia and Svoge coals display inorganic affinities for the elements. Sub-bituminous coal samples from the Pernik Basin, however, show a more widespread organic affinity for the elements. The trace elements were also grouped in geochemical associations by cluster analysis. In the lignite samples from the Sofia Basin and the sub-bituminous coal from the Pernik Basin, this grouping is almost identical. U, Tb and Yb are grouped in an association; the other elements are grouped separately. Ce, Th and Sm correlate well in a separate association. The anthracites from the Svoge Basin display two associations: one including U, Th and Sm, and the other composed of the remaining elements, which correlate well with one another and with the coal ash.

The role of shear strain in the graphitization of a high-volatile bituminous and an anthracitic coal

A ‘soft’ carbon-based high-volatile bituminous ( R o max=0.68%) coal and a ‘hard’ carbon-based Pennsylvania anthracite ( R o max=5.27%) were deformed in the steady state at high temperatures and pressures in a series of coaxial and simple shear deformation experiments designed to constrain the role of shear strain and strain energy in the graphitization process. Tests were carried out in a Griggs-t type solid (NaCl) medium apparatus at T=400–900°C, constant displacement rates of 10 -5−10 -6 s −1, at confining pressures of 0.6 GPa (coaxial) or 0.8 and 1.0 GPa (simple shear). Coaxial samples were shortened up to 50%, whereas shear strains up to 4.9 were attained in simple shear tests. Experiments lasted up to 118 h. Deformed, high-volatile bituminous coal was extensively coked and no correlation between strain and R o max, bireflectance or coal texture was observed in any samples. With increasing temperature, R o max and bireflectance increase in highly anisotropic, coarse mosaic units, but remain essentially constant in the fine granular mosaic, which becomes more abundant at higher temperatures. Graphite-like reflectances are observed locally only in highly reactive macerals and in pyrolytic carbon veins. The degree of molecular ordering attained in deformed bituminous coal samples appears to be determined by the heating-pressurization path rather than by subsequent deformation. Graphitization did not occur in coaxially deformed anthracite. Nonetheless, dramatic molecular ordering occurs at T>700°C, with average bireflectance values increasing from 1.68% at 700°C to 6.36% at 900°C. Anisotropy is greatest in zones of high strain at all temperatures. In anthracite samples deformed in simple shear over the 600–900°C range at 1.0 GPa, the average R o max values increase up to 11.9%, whereas average bireflectance values increase up to 10.7%. Bireflectance increases with progressive bedding rotation and, thus, with increasing shear strain. Graphitization occurs in several anthracite samples deformed in simple shear at 900°C. X-ray diffraction and transmission electron microscopy of highly anisotropic material in one sample confirms the presence of graphite with d 002=0.3363 nm. These data strongly suggest that shear strain, through its tendency to align basic structural units, is the factor responsible for the natural transformation of anthracite to graphite at temperatures far below the 2200°C required in hydrostatic heating experiments at ambient pressure.

Chemical and petrographic characterization and liquefaction yields of Spanish coals

A preliminary screening of spanish coals including samples of Anthracite from 19 mines, of Bituminous and Subbituminous coal from 32 mines and Hard and Soft brown coal (Lignites) from 32 mines was made based on their proximate and ultimate analysis, looking for the most promising ones as raw materials for liquefaction processes. Relationships between different coal characteristics were established. Ergun correlation between gross calorific value and moisture content seems not to be acceptable for spanish coals. Some of the coals selected (Lignites) were studied via petrographic characterization, and finally tested in a laboratory autoclave reactor of 400 c.c. under standarized operating conditions. Correlations between coal characteristics and the liquefaction yields obtained are compared with other data from the Technical Literature. The results obtained for subbituminous coals about the influence of rank in liquefaction has been verified for our lignites.

Macromolecular structure of coals. V. Molecular weight distribution of extracted coal chains

AbstractSeven coal samples with carbon contents ranging from 69.95% to 94.17% on a dry mineral matter‐free (dmmf) basis were extracted with pyridine at reflux temperature for two weeks. The liquids obtained (coal extracts) were analyzed for molecular weight distribution by gel permeation chromatography at 35°C using a solution of 10% pyridine and 90% tetrahydrofuran as the mobile phase. Calibration was done by use of anionically‐prepared monodisperse polystyrene and by a series of polynuclear low molecular weight compounds. The number average (M̄Mn) and weight average (M̄w) molecular weights of the coal extracts were found to depend on the carbon content of the initial coal samples. As the carbon content increased, M̄n and M̄w decreased from original values of 640 and 1120 for the lignite sample, passing through a minimum of 600 and 895 respectively and reaching a maximum of M̄n = 725 and M̄w = 1 445 for the anthracite sample with 94.17% C. Previously extracted coal matrices were alkylated by the Sternberg alkylation technique which causes degradation of the macromolecular chains of the coal matrix. Gel permeation chromatographic analysis of pyridine‐extracted liquids of the solid alkylated coal showed average molecular weights smaller than those of the original coal extracts (M̄n = 440–470, M̄w = 445–590).

Effect of anthracite properties and formulation on properties of bench scale cathode blocks for aluminum smelting

Bench scale cathode blocks for aluminum smelting having an aggregate of 70 pct anthracite calcined at 1135°C—30 pct ball milled graphite and a coal tar pitch binder were fabricated, baked at 1135°C, and tested for electrical resistivity and expansion during electrolysis in a test cell. Twelve anthracite samples, for which a number of chemical and physical properties were determined, were used in cathode fabrication so that relationships among anthracite properties and cathode properties could be determined. Cathode expansion during electrolysis increased with increasing sulfur content of the anthracite but appeared to decrease with increasing silicon content. Electrical resistivity decreased with an increase in the fraction of green anthracite exhibiting a conchoidal rather than laminar fracture. With the finer of two anthracite aggregate sizings used, both cathode expansion during electrolysis and electrical resistivity decreased sharply as binder content was increased from 16 to 22 pct. Baked apparent density also increased at the same time but was not,per se, a valid indicator of either electrical resistivity or expansion during electrolysis; cathodes produced using a coarser anthracite sizing, which resulted in higher baked apparent densities, had higher electrical resistivities and expansions during electrolysis. Electrical resistance of all cathodes increased during electrolysis in the test cell by an amount proportional to the amount of expansion.

Enrichment of Radiocarbon for Dating Samples up to 75,000 Years

Abstract The range of the radiocarbon dating method can be extended by about 20,000 years by means of thermal diffusion isotopic enrichment. A description of the Clusius-Dickel type enrichment columns and their operation is given. Prior to enrichment the carbonaceous sample material is combusted to CO2 and then reduced to CO. The enriched sample is re-oxidized to CO2 . The combustion-, reduction-and oxidation-apparatus and their operation are described. The performance of the thermal diffusion columns has been tested and an empirical, volume independent relation between the isotope separation factors of 14C 16O and all molecules with mass 〈30〉 is given q14 - 1 = (1.13 ± 0.05) (q30 - 1) + (0.035 ± 0.005) (q30 - 1)2 . The influence of contaminations on the reability of 14C dates obtained with this method is discussed. Laboratory contaminations can be kept below the detection limit as is shown by the preparation of two anthracite samples. Still there may be some influence on dates obtained for very old samples. As far as laboratory contaminations are concerned, dates up to 75,000 years can be obtained.

Experimental studies of anthracite coals at high pressures and temperatures

Three samples of anthracite, Middle Mammoth, Lykens Valley, and St. Nicholas have been subjected to temperatures in the range of 400-900 degrees C and pressures of 2,000 to 20,000 psi in hydrothermal pressure vessels. Selected runs were taken to 30 Kb in an opposed anvil device.The altered materials were studied primarily to determine differences in morphology of the grains, their reflectance values and degree of anisotropy. X-ray diffraction analyses were run to determine the mineral assemblages present before and after treatment.The reflectance values of the altered materials increase with temperature while pressure alone appears to have little effect. When temperature and pressure are held constant, reflectance increases with increasing time of the experimental runs. The rate of increase of reflectance is greatest in the temperature range where evolution of volatile matter is also the greatest. As might be expected the highest coal showed the least change in reflectance under the conditions applied.It was possible to fuse the anthracite particles with temperatures and pressures as low as 400 degrees C and 2,000 psi. Increased retention time at constant temperature and pressure causes an increase in the degree to which the grains are fused. The extreme temperature and pressure conditions to which the anthracites were subjected have caused them to behave in a fashion similar to bituminous coals at much lower pressures and somewhat lower temperatures.Observations made during this investigation correlate with existing theories on coal metamorphosis, pyrolysis and structure, extended from lower rank coals.