Curtis A. Palmer

The geology, botany and chemistry of selected peat-forming environments from temperate and tropical latitudes

Abstract Peat has been studied in several geologic settings: (1) glaciated terrain in cold temperate Maine and Minnesota, U.S.A.; (2) an island in the Atlantic Ocean off the coast of Maine, where sea level is rising; (3) the warm temperate U.S. Atlantic and Gulf Coastal Plains, where sea level has changed often; and (4) the tropical coast of Sarawak, Malaysia, and the tropical delta of the Batang Hari River, Sumatra, Indonesia. Most of these deposits are domed (ombrotrophic or partly ombrotrophic) bogs in which peat accumulation continued above the surface of the surrounding soil. However, the bogs of the U.S. Atlantic and Gulf Coastal Plains are comparatively not as domed, and many have almost level surfaces. In some bogs, aquatic or semi-aquatic plant materials accumulated, replaced water in the depressions, and formed a surface on which marsh or swamp vegetation could subsequently live, die, and accumulate. In others, the plant materials accumulated initially on level silt or sand surfaces supporting marshes or swamps. As the peat dome formed, plants growing on it changed from luxuriant ones near the base of the dome, where nutrients were brought into the bog by surface and ground water, to stunted ones at the top of the dome, where the raised bogs are fed by nutrient-poor precipitation. The physical and chemical changes that take place in the sequence of environments from the pond stage of deposit development, through the grassy marsh stage, through the forested swamp stage, and finally through the heath dome stage can be measured in terms of acidity and ash, volatile matter, carbon, hydrogen, nitrogen, sulfur and oxygen contents, as well as in the kind and distribution of trace elements. The organic and inorganic contents of the deposits relate to geomorphology, and geomorphology relates to their settings. As models of coal formation, some domed peat deposits may help in solving problems of distribution and character of ancient coal beds. But clearly not all peat deposits are precursors of coal. Most Holocene peat deposits are subject to destruction by erosion, fire and decomposition through microbial and chemical oxidation before burial. The best environments for coal precursors have biomass accumulation, a continuously rising water table within the mass, and minimum influx of clay and silt until preservation by burial. The most suitable settings for future economic coal deposits are domed bogs that accumulate thick, widespread peat having low ash and low sulfur contents. The ombrotrophic peat deposits of tropical Sarawak and Sumatra are thick and extensive, contain low-ash and low-sulfur peat, and have high heating values. They are considered to be the best tropical coal analogs because of their extent and chances of preservation; the base of the peat is below adjacent river levels, and chemical and structural conditions are favorable for accumulation.

Mode of occurrence of arsenic in four US coals

An integrated analytical approach has been used to determine the mode of occurrence of arsenic in samples of four widely used US coals: the Pittsburgh, Illinois #6, Elkhorn/Hazard, and Wyodak. Results from selective leaching, X-ray absorption fine structure (XAFS) spectroscopy, and electron microprobe analysis show that pyrite is the principal source of arsenic in the three bituminous coals, but the concentration of As in pyrite varies widely. The Wyodak sample contains very little pyrite; its arsenic appears to be primarily associated with organics, as As3+, or as arsenate. Significant (10–40%) fractions of arsenate, derived from pyrite oxidation, are also present in the three bituminous coal samples. This information is essential in developing predictive models for arsenic behavior during coal combustion and in other environmental settings.

Distribution of trace elements in selected pulverized coals as a function of particle size and density

Abstract Trace elements in coal have diverse modes of occurrence that will greatly influence their behavior in many coal utilization processes. Mode of occurrence is important in determining the partitioning during coal cleaning by conventional processes, the susceptibility to oxidation upon exposure to air, as well as the changes in physical properties upon heating. In this study, three complementary methods were used to determine the concentrations and chemical states of trace elements in pulverized samples of four US coals: Pittsburgh, Illinois No. 6, Elkhorn and Hazard, and Wyodak coals. Neutron Activation Analysis (NAA) was used to measure the absolute concentration of elements in the parent coals and in the size- and density-fractionated samples. Chemical leaching and X-ray absorption fine structure (XAFS) spectroscopy were used to provide information on the form of occurrence of an element in the parent coals. The composition differences between size-segregated coal samples of different density mainly reflect the large density difference between minerals, especially pyrite, and the organic portion of the coal. The heavy density fractions are therefore enriched in pyrite and the elements associated with pyrite, as also shown by the leaching and XAFS methods. Nearly all the As is associated with pyrite in the three bituminous coals studied. The sub-bituminous coal has a very low content of pyrite and arsenic; in this coal arsenic appears to be primarily organically associated. Selenium is mainly associated with pyrite in the bituminous coal samples. In two bituminous coal samples, zinc is mostly in the form of ZnS or associated with pyrite, whereas it appears to be associated with other minerals in the other two coals. Zinc is also the only trace element studied that is significantly more concentrated in the smaller (45 to 63 μm) coal particles.

Mode of occurrence of chromium in four US coals

The mode of occurrence of chromium in three US bituminous coals and one US subbituminous coal has been examined using both X-ray absorption fine structure (XAFS) spectroscopy and a selective leaching protocol supplemented by scanning electron microscopy (SEM) and electron microprobe measurements. A synthesis of results from both methods indicates that chromium occurs principally in two forms in the bituminous coals: the major occurrence of chromium is associated with the macerals and is not readily leached by any reagent, whereas a second, lesser occurrence, which is leachable in hydrofluoric acid (HF), is associated with the clay mineral, illite. The former occurrence is believed to be a small particle oxyhydroxide phase (CrO(OH)). One coal also contained a small fraction (<5%) of the chromium in the form of a chromian magnetite, and the leaching protocol indicated the possibility of a similar small fraction of chromium in sulfide form in all three coals. There was little agreement between the two techniques on the mode of occurrence of chromium in the subbituminous coal; however, only a limited number of subbituminous coals have been analyzed by either technique. The chromium in all four coals was trivalent as no evidence was found for the Cr6+ oxidation state in any coal.

Chemistry and origin of minor and trace elements in vitrinite concentrates from a rank series from the eastern United States, England, and Australia

Abstract A rank series consisting of twelve vitrinite concentrates and companion whole-coal samples from mined coal beds in the eastern United States, England, and Australia were analyzed for C, H, N, O, ash, and 47 trace and minor elements by standard elemental, instrumental neutron activation analysis (INAA), and direct-current-arc spectrographic (DCAS) techniques. The reflectance of vitrinite, atomic H:C and O:C, and ash-free carbon data were used to determine ranks that range from high-volatile C bituminous coal to meta-anthracite. A van Krevelen (atomic H:C vs. O:C) diagram of the vitrinite concentrates shows a smooth curve having its lowest point at H:C = 0.18 and O:C = 0.01. This improves the van Krevelen diagram by the addition of our vitrinite concentrate from meta-anthracite from the Narragansett basin of New England. Boron content (400–450 ppm) in two Illinois basin vitrinite concentrates was about an order of magnitude higher than B contents in other concentrates analyzed. We attribute this to marine origin or hydrothermal activity. The alkaline-earth elements Ca, Mg and Ba (DCAS) have higher concentrations in our vitrinite concentrates from bituminous coals of the Appalachian basin, than they do in vitrinite concentrates from the marine-roofed bituminous coals of the Illinois basin; therefore, a nonmarine origin for these alkaline-earth elements is postulated for the Appalachian basin coals. An ion-exchange mechanism due to high concentrations of these elements as ions in diagenetic water, but probably not recent ground water, may be responsible for the relatively high values of these elements in Appalachian concentrates. Higher concentrations of Ni and Cr in one of the English vitrinite concentrates and of Zr in the Australian concentrate probably indicate organic association and detrital influence, respectively.

Selected elements in major minerals from bituminous coal as determined by INAA: Implications for removing environmentally sensitive elements from coal

Copyright (c) 1996 Elsevier Science B.V. All rights reserved. The four most abundant minerals generally found in Euramerican bituminous coals are quartz, kaolinite, illite and pyrite. These four minerals were isolated by density separation and handpicking from bituminous coal samples collected in the Ruhr Basin, Germany and the Appalachian basin, U.S.A. Trace-element concentrations of relatively pure (s99 + %r separates of major minerals from these coals were determined directly by using instrumental neutron activation analysis (INAAr. As expected, quartz contributes little to the trace-element mass balance. Illite generally has higher trace-element concentrations than kaolinite, but, for the concentrates analyzed in this study, Hf, Ta, W, Th and U are in lower concentrations in illite than in kaolinite. Pyrite has higher concentrations of chalcophile elements (e.g., As and Ser and is considerably lower in lithophile elements as compared to kaolinite and illite. Our study provides a direct and sensitive method of determining trace-element relations with minerals in coal. Mass-balance calculations suggest that the trace-element content of coal can be explained mainly by three major minerals: pyrite, kaolinite and illite. This conclusion indicates that the size and textural relationships of these major coal minerals may be a more important consideration as to whether coal cleaning can effectively remove the most environmentally sensitive trace elements in coal than what trace minerals are present.

Distribution of trace elements in coal from the Powhatan No. 6 mine, Ohio

Abstract Size and density separates of low-temperature-ashed coal from the Powhatan No. 6 mine, Ohio, have been used to determine the mode of occurrence of 28 minor and trace elements in coal. The size distribution of the major minerals has been determined, and correlations of trace elements with major minerals have been made. The role of minor minerals in the mode of occurrence of trace elements is also discussed. Instrumental-neutron-activation analysis was used to determine elemental concentrations, and X-ray diffraction and scanning electron microscopy were used for mineral identification.

Toxic substances from coal combustion -- A comprehensive assessment

The Clean Air Act Amendments of 1990 identify a number of hazardous air pollutants (HAPs) as candidates for regulation. Should regulations be imposed on HAP emissions from coal-fired power plants, a sound understanding of the fundamental principles controlling the formation and partitioning of toxic species during coal combustion will be needed. With support from the Federal Energy Technology Center (FETC), the Electric Power Research Institute, and VTT (Finland), Physical Sciences Inc. (PSI) has teamed with researchers from USGS, the Massachusetts Institute of Technology (MIT), the University of Arizona (UA), the University of Kentucky (UK), the University of Connecticut (UC), the University of Utah (W) and the University of North Dakota Energy and Environmental Research Center (EERC) to develop a broadly applicable emissions model useful to regulators and utility planners. The new Toxics Partitioning Engineering Model (ToPEM) will be applicable to all combustion conditions including new fuels and coal blends, low-NO{sub x} combustion systems, and new power generation plants. Development of ToPEM will be based on PSIs existing Engineering Model for Ash Formation (EMAF). This report covers the reporting period from the submission of the draft Phase 1 Final Report through the end of June, 1998. During this period two of the three Phase 2 coals were procured and pulverized samples were distributed to team members. Analysis of Phase 1 X-Ray Absorption Fine Structure (XAFS) data, particularly of mercury in sorbent samples, continued. An improved method for identifying mercury compounds on sorbents was developed, leading to a clearer understanding of forms of mercury in char and sorbents exposed to flue gas. Additional analysis of Phase 1 large scale combustion data was performed to investigate mechanistic information related to the fate of the radionuclides Cs, Th, and Co. Modeling work for this period was focused on building and testing a sub-model for vaporization of major elements during combustion.

Using laser micro mass spectrometry with the LAMMA-1000 instrument for monitoring relative elemental concentrations in vitrinite

The variation in relative elemental concentrations among a series of coal macerals belonging to the vitrinite maceral group was determined using laser micro mass spectrometry (LAMMS). Variations in Ba, Cr, Ga, Sr, Ti, and V concentrations among the coals were determined using the LAMM A-1000 instrument. LAMMS analysis is not limited to these elements; their selection illustrates the application of the technique. Ba, Cr, Ga, Sr, Ti, and V have minimal site-to-site variance in the vitrinite macerals of the studied coals as measured by LAMMS. The LAMMS data were compared with bulk elemental data obtained by instrumental neutron activation analysis (INAA) and D. C. arc optical emission spectroscopy (DCAS) in order to determine the reliability of the LAMMS data. The complex nature of the ionization phenomena in LAMMS and the lack of standards characterized on a microscale makes obtaining quantitative elemental data within the ionization microvolume difficult; however, we demonstrate that the relative variation of an element among vitrinites from different coal beds in the eastern United States can be observed using LAMMS in a “bulk” mode by accumulating signal intensities over several microareas of each vitrinite. Our studies indicate gross changes (greater than a factor of 2 to 5 depending on the element) can be monitored when the elemental concentration is significantly above the detection limit.“Bulk” mode analysis was conducted to evaluate the accuracy of future elemental LAMMS microanalyses. The primary advantage of LAMMS is the inherent spatial resolution, ~ 20μm for coal. Two different vitrite bands in the Lower Bakerstown coal bed (CLB-1) were analyzed. The analysis did not establish any certain concentration differences in Ba, Cr, Ga, Sr, Ti, and V between the two bands.

Chemistry and origin of minor and trace elements in selected vitrinite concentrates from bituminous and anthracitic coals

Abstract Twelve hand-picked vitrinite concentrates and companion whole-coal samples were analyzed for trace and minor elements by instrumental neutron activation analysis (INAA) and direct-current-arc spectrographic techniques (DCAS). The vitrinite concentrates contained 94 to nearly 100 vol.% vitrinite compared to 71–95 vol.% in the companion whole coals. The ash contents of the vitrinite concentrates were 2 to more than 190 times less than the ash contents of the companion whole coals. Organic and inorganic affinities were determined by comparing the elemental concentrations in the vitrinite concentrates to the concentrations in the companion whole coals. The ratios of these concentrations for 33 selected elements are shown in Figure 1. Ratios greater than 1 indicate organic affinity, and ratios less than 1 indicate inorganic affinity. Br and W generally showed organic affinity in all samples in this study. In the nine samples from the eastern United States (Fig. 1A-C) less than one-fourth of the trace elements show organic affinity compared to nearly one-half for the three English and Australian samples (Fig. 1D). The elements that generally show organic affinity in the non-U.S.A. samples studied include As, Cs, Hf, and Ni, which have generally inorganic affinities in the U.S.A. samples, and Cr, Sb, Se, and U, which have mixed (both organic and inorganic) affinities, in the U.S.A. coals studied, has an inorganic affinity in the English coals studied. B shows organic affinity in the samples from the Illinois basin (Fig. 1C). For the samples studied, Ba shows organic affinity in the Appalachian basin bituminous coals (Fig. 1B), inorganic affinity in the Illinois basin coals, and overall mixed affinities. In all the samples studied, Cu, Mn, Na, Sr, Ta, V, and Zn show mixed affinities, and A1, Co, Eu, Fe, Ga, K, La, Mg, Sc, Si, Th, Ti, and Ub have generally inorganic affinity.