The present state of the methods commonly used for inorganic and mineral matter characterization in coal is described and summarized. The application of various separation procedures, macroscopic observations, reflected and transmitted optical microscopy, scanning and transmission electron microscopy, X-ray diffraction, differential thermal and thermogravimetric analyses, Mossbauer spectroscopy, infrared spectroscopy, and chemical analyses are briefly discussed. A short critical overview on the advantages and limitations of the above listed methods as well as some recommendations during their utilization are also presented.

Methods for characterization of inorganic and mineral matter in coal: A critical overview

Characterization of electrooxidized Pittsburgh No. 8 Coal

Distribution of inorganic and organic substances in the hydrocyclone separated Slovak sub-bituminous coal

Although Fe-sulfate minerals occur only rarely on Earth as alteration products of sulfidic basalts or in hydrothermal systems, multiple lines of evidence point to the importance of Fe- (and other) sulfate minerals on the surface of Mars. One such martian data set comes from the MIMOS II Mossbauer spectrometers on the Mars Exploration Rovers, which acquired hundreds of spectra from the martian surface at two locations. Interpretation of those spectra has been limited by the lack of a comprehensive set of laboratory analog spectra of the broad range of naturally occurring sulfate minerals. Accordingly, this study reports Mossbauer data of 98 samples representing 47 different sulfate mineral species, all containing six- or higher-coordinated Fe. The resultant Mossbauer parameters are related to the local polyhedral environment around the Fe cation in each mineral to explain variations in spectral characteristics. Results show that the size of the coordination polyhedron is the best predictor of quadrupole splitting, which increases with both octahedral volume and mean bond length. Species within groups of structurally similar minerals are shown to have comparable spectral peaks that generally fall within small ranges. Although coordination polyhedron geometry is not necessarily unique to any particular mineral species or group, Mossbauer data can be used to help constrain mineral identifications from martian spectra. The number of mineral species is large, but the range of crystal structures and hyperfine parameters may be small, so that in many cases, individual minerals cannot be uniquely fingerprinted. Examples would include quenstedtite, coquimbite, kornelite, and lausenite, which have indistinguishable spectra, as do apjohnite, bilinite, dietrichite, and romerite. Overlap of Mossbauer parameters is a particular complication for identification of Fe 3+ -rich phases because the range of Mossbauer parameters for Fe 3+ in any coordination number is so small. Previous analyses of martian Mossbauer spectra reported the presence of jarosite (Klingelhofer et al. 2004; Morris et al. 2004) and an unspecific ferric sulfate (Morris et al. 2008). New data presented here indicate that botryogen, metasideronatrite, and slavikite exhibit Mossbauer spectra similar to those attributed to jarosite at Meridiani Planum. Fibroferrite and rhomboclase have parameters similar to those observed at Arad Samra, and copiapite and parabutlerite could be present at Tyrone Mount Darwin and Berkner Island. Unique mineral identifications are generally not possible from Mossbauer data alone, particularly for paramagnetic phases, although combining Mossbauer results with other data sets enables a greater level of confidence in constraining mineralogy. This study provides a new expansive data set for future interpretation of iron sulfates on Mars.

Mössbauer parameters of iron in sulfate minerals

Coal is one of the main sources of energy in many parts of the world and has one of the largest reserves/production ratios amongst all the non-renewable energy sources. Gasification of coal is one among the advanced technologies that has potential to be used in a carbon constrained economy. However, gasification availability at several commercial demonstrations had run into problems associated with fouling of syngas coolers due to unpredictable flyash formation and unburnt carbon losses. Computer models of gasifiers are emerging as a powerful tool to predict gasifier performance and reliability, without expensive testing. Most computer models used to simulate gasifiers tend to model coal as a homogenous entity based on bulk properties. However, coal is a heterogeneous material and comminution during feedstock preparation produces particle classes with different physical and chemical properties. It is crucial to characterize the heterogeneity of the feedstocks used by entrained flow gasifiers. To this end, a low ash US bituminous coal that could be used as a gasifier feedstock was segregated into density and size fractions to represent the major mineral matter distributions in the coal. Float and sink method and sieving were employed to partition the ground coal. The organic and inorganic content of all density fractions was characterized for particle size distribution, heating value, ultimate analysis, proximate analysis, mineral matter composition, ash composition, and petrographic components, while size fractions were characterized for heating value, ash composition, ultimate and proximate analysis. The proximate, ultimate and high heating value analysis showed that variation in these values is limited across the range of size fractions, while the heterogeneity is significant over the range of density fractions. With respect to inorganics, the mineral matter in the heavy density fractions contribute significantly to the ash yield in the coal while contributing very little to its heating value. The ash yield across the size fractions exhibits a bimodal distribution. The heterogeneity is also significant with respect to the base-to-acid ratio across the size and density fractions. The results indicate that the variations in organic and inorganic content over a range of density and size classes are significant, even in the low ash, vitrinite rich coal sample characterized here. Incorporating this information appropriately into particle population models used in gasifier simulations will significantly enhance their accuracy of performance predictions.

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Characterization of Size and Density Separated Fractions of a Bituminous Coal as a Feedstock for Entrained Slagging Gasification

Minerals were identified in three Colombian coal samples from the Southwest of the country using Mossbauer spectroscopy and X-ray diffraction Original and sink separated coal fractions of specific gravity 140 and 160 with particle size less than 600 µm were used in the study Using Mossbauer spectroscopy, the minerals identified in the original coal samples were pyrite jarosite, ankerite, illite and ferrous sulfate, whereas by means of X-ray diffraction, minerals identified were kaolinite, quartz, pyrite, and jarosite Differences in mineral composition were found in the original and sink separated fractions using both techniques Mossbauer spectra show that the mineral phases in low concentrations such as illite, ankerite and ferrous sulfate do not always appear in the spectra of sink coals, despite of those minerals occurring in the original coal, due to the fact that they are associated with the organic matter and not liberated in the grinding process X-ray results show that the peak intensity grows as the specific gravity is increased indicating that the density separation method could be an effective process to clean coal

Mineral identification in Colombian coals using Mössbauer spectroscopy and X-ray diffraction

In this work a study on gold mineral samples is reported, using optical microscopy, X-ray diffraction (XRD) and Mossbauer spectroscopy (MS). The auriferous samples are from the El Diamante mine, located in Guachavez-Narinno (Colombia) and were prepared by means of polished thin sections. The petrography analysis registered the presence, in different percentages that depend on the sample, of pyrite, quartz, arsenopyirite, sphalerite, chalcopyrite and galena. The XRD analysis confirmed these findings through the calculated cell parameters. One typical Rietveld analysis showed the following weight percent of phases: 85.0% quartz, 14.5% pyrite and 0.5% sphalerite. In this sample, MS demonstrated the presence of two types of pyrite whose hyperfine parameters are δ 1 = 0.280 ± 0.002 mm/s and δ 1 = 0.642 ± 0.002 mm/s, Δ 2 = 0.379 ± 0.002 mm/s and Δ 2 = 0.613 ± 0.002 mm/s.

Structural and Electronic Properties Study of Colombian Aurifer Soils by Mössbauer Spectroscopy and X-ray Diffraction

En este trabajo se propone la tecnica Mossbauer como una herramienta util para realizar una caracterizacion de muestras como suelos y arcillas, y ademas, se pretende mostrar como llevar una muestra de suelo (o arcilla comun) a una arcilla especial. Las muestras de suelo se tomaron de cuatro zonas diferentes del pais, se les hizo un estudio por difraccion de rayos X y posteriormente espectroscopia Mossbauer, obteniendo por esta ultima tecnica resultados mas confiables al cualificar y cuantificar las muestras. Luego de identificar los minerales de arcillas presentes, se obtuvo la fraccion arcilla y se trataron para extraer los oxidos e hidroxidos de hierro, obteniendo al aplicar Mossbauer una muestra compuesta por esmectita y otros minerales de arcilla en bajas proporciones.

J. Mojica

Papers

Mineral identification in Colombian coals using Mössbauer spectroscopy and X-ray diffraction

Structural and Electronic Properties Study of Colombian Aurifer Soils by Mössbauer Spectroscopy and X-ray Diffraction

Caracterización de arcillas colombianas por espectroscopia mössbauer y difracción de rayos-x