Illinois Basin Coals Research Articles

Resources from coal beneficiation waste: Chemistry and petrology of the Ayrshire coal tailings ponds, Chandler, Indiana

Tailings (refuse) material, a mixture of fine coal and rock from the beneficiation of high volatile C bituminous Pennsylvanian Illinois Basin coals, was recovered from the tailings pond near the site of the former preparation plant. The material has widely varying concentrations of some elements, such as Sn, which might reflect non-coal contamination of the product stream at any point from mining and beneficiation of the coal to disposal of the waste product. The rare earth elements have a strong M-type enrichment. Concentration of the rare earths is below what would normally be considered to be an economic grade. The mix of coal and REE-lean rock, though, implies that the resource must be examined with an eye towards the recovery of critical elements, not just for the reconnaissance bulk characterization, as was done here. Despite the low concentration of REE and other critical elements, factors such as the ease of moving the comminuted, near-surface material and its proximity to highway, rail, and river transport implies that such resources must be carefully examined; not simply dismissed because the grade is below a cutoff level developed for coal, not mixed rock + coal.

Trace element partitioning during coal preparation: Insights from U.S. Illinois Basin coals

A suite of 72 samples of Illinois Basin coal was collected from 2015 to 2018, from 14 active coal mining and preparation operations in Illinois and Indiana. The goals of the study were to investigate the behavior of trace elements during coal preparation and provide current coal quality data for active mining operations in the Illinois Basin, which has become one of the most important suppliers of U.S. coal. Samples include raw coal, cleaned coal, and waste (refuse) coal. The efficiency of cleaning is shown by reduction of ash yield, increase in heating values, and a pronounced shift in the proportion of sulfur forms. In most raw coals, pyritic sulfur (Py S) exceeds organic sulfur (Org S; Org S/Py S ≤ 1.0), whereas in prepared coals, organic sulfur is the predominant sulfur form (Org S/Py S ≥ 1.0). In waste (refuse) coals, Org S/Py S is substantially reduced, or almost entirely in the pyritic form (Org S/Py S near zero). Trends in the distribution of inorganically-associated lithophile and chalcophile elements are shown, as well those for elements having mixed organic-inorganic associations and those that are primarily organic-hosted. Lithophile elements, including Li, Al, P, Ti, Sc, Rb, Y, Zr, Nb, Cs, Ba, the lanthanides, Hf, Th, and U, are partitioned into waste coals with corresponding reduction in cleaned coals. At the same time, chalcophile elements hosted by pyrite, such as As, Sb, Hg, and Pb, are also partitioned into waste coals. Rare earth elements (REEs), including Sc, Y, and the lanthanides, are enriched in waste coals at levels that approximate their content in the upper continental crust (UCC). Several other critical elements, defined as mineral commodities deemed critical to the economy and security of the United States, including V, Cr, As, Rb, Sb, and Cs, show enrichment in waste coals, that may facilitate their co-extraction with the REEs. Concentrations for elements of environmental concern in cleaned coals are similar to or below those for world average coals with the exception of Pb in coals from Illinois. Laser-ablation ICP-MS (LA-ICP-MS) for pyrite in a subset of 21 samples of raw and cleaned coal provided direct determinations of V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, Sb, Au, Hg, Tl, Pb, and Bi. LA-ICP-MS was used together with bulk sample pyritic sulfur and trace element concentrations to estimate the elemental proportion of bulk Cu, As, Hg, and Pb in pyrite, indicating that Hg and Pb are hosted almost entirely by pyrite, whereas the proportion of Cu and As in pyrite accounts for about half of the bulk content. With growing interest in recovering critical elements from coal, partitioning of a large range of elements into waste coals presents a possible opportunity, but also a potential hazard, due to enrichment in harmful elements such as Hg, As, and Pb.

Role of VES-based fracturing fluid on gas sorption and diffusion of coal: An experimental study of Illinois basin coal

As a kind of environmentally friendly and non-polluting fracturing fluid, the VES-based fracturing fluid is gradually promoted in the field coalbed methane (CBM) stimulation in recent year. However, the fracturing fluid residue trapped in the reservoir may have a potential negative impact on gas flow in CBM reservoirs. In this study, the fracturing fluid based on surfactant was selected to treat the coal sample. The lab experiments have been conducted including the isothermal methane sorption, the low-temperature nitrogen sorption and the 13C nuclear magnetic resonance (NMR) measurements. The results showed that the methane sorption capacity was modified with cleaning fluid treatment and residuals. It was found that the sorption capacity can be recovered through water washing. It is important to point out that the diffusivity of coal has been significantly damaged indicated by the paramount decrease of diffusion coefficient even after the water washing. Additionally, no significant chemical coal molecular structure changes were observed with VES-based fracturing fluid treatment based on the NMR data. The fracturing fluid changes the coal pore structure mainly because the residue of the fracturing fluid enters the coal pore system, thereby adhering on the pore wall or blocking the pore throat. Most residues entered into the coal seam will be trapped in mesopores and macropores, cause serious damage to the CBM diffusivity in the coal matrix, thereby posing an adverse effect to the CBM production.

Distribution of rare earth elements in fly ash derived from the combustion of Illinois Basin coals

This study examined rare earth element (REE) trends for Illinois Basin coal-sourced fly ashes, with the goal of understanding the elemental composition and resource potential for various fly ash fractions. Illinois Basin coals have a high volatile C through A bituminous rank with a moderate ash content (slightly>12% ash (dry basis)), about 3% sulfur, and, in general, lower concentrations of hazardous and other trace elements than many Central Appalachian coals. Fly ash from the combustion of Illinois Basin coals tends to have a high Fe2O3 content owing to the amount of pyrite in the feed coals. The rare earth element (REE) concentrations in Illinois Basin coal-sourced fly ashes are less than that for fly ashes from the combustion of Central Appalachian coals. The Upper continental crust-corrected fly ashes show an H-type enrichment, a positive EuN/EuN*, and, in some cases, a sharp Gd peak. For comparison, a suite of fly ashes from the combustion of a blend of eastern Kentucky coals had an H-type enrichment, a positive EuN/EuN*, but only a minimal Gd peak. In contrast, fly ash from the combustion of the Fire Clay coal, a REE-rich coal, had a negative EuN/EuN* and a sharp Gd peak. These results highlight the importance of feed coal composition on trace element contents of respective combustion fly ash fractions and also the unique REE enrichment patterns of the Illinois Basin fly ashes relative to the better studied fly ashes of eastern Kentucky and Central Appalachia.

Evaluating the changes of sorption and diffusion behaviors of Illinois coal with various water-based fracturing fluid treatments

The water-based fracturing stimulation is commonly used for low permeability coalbed methane (CBM) reservoirs. The influence of various fracturing fluids on the gas sorption and diffusion behaviors were experimentally studied in the work. The Illinois basin coal was selected for the experimental measurements. We used slickwater, guar gel and viscoelastic surfactant (VES) fracturing fluids to treat the coal. The sorption and diffusion behaviors were measured and quantified by the volumetric sorption experiments. The microscope was employed for the coal sample surface observation to qualitatively characterize the coating and residue behavior of fracturing fluids. It was found that all types of fracturing fluids can significantly influence the gas sorption capacity of coal. Apart from the low concentration of polyacrylamide (0.1% and 0.3%) slickwater, all other fracking fluids damage the gas sorption capacity. For most fracturing fluids, the sorption capacity can be recovered closely back to its virgin coal condition with extensive water washing. For the coal samples treated by the VES fracturing fluid, both the Langmuir volume and Langmuir pressure were dramatically increased. The adverse effect of fracturing fluids on coal is apparent and all diffusion coefficients decrease with the treatment. Even with extensive washing, the diffusion coefficient cannot recover for slickwater and VES fluids. But guar gel fluid has the best diffusion recovery because of the easy removal of the guar gel. This study provides a preliminary data set for fracturing fluid selection for Illinois coal in terms of sorption and diffusion.

Distribution of Rare Earth Elements in the Illinois Basin Coals

Distribution of Rare Earth Elements in the Illinois Basin Coals

Distinction of strontium isotope ratios between water-soluble and bulk coal fly ash from the United States

Coal ash is one of the largest industrial waste streams in the United States and contains elevated concentrations of hazardous elements that could pose environmental and human health risks. Due to the relatively high strontium concentrations in coal ash and the distinctive 87Sr/86Sr ratios, strontium isotopes have been utilized to trace coal ash contaminants in impacted water resources. While previous studies have characterized the Sr isotope ratios for the water-soluble Sr derived from coal ash, the strontium isotopic composition of the bulk coal ash has not been systematically evaluated. In the current study, we report the 87Sr/86Sr ratios of bulk and water-soluble Sr in fly ash derived from coals of the three major coal-producing basins in the U.S., the Appalachian Basin, Illinois Basin, and Powder River Basin. The data show a wide range of 87Sr/86Sr ratios in the bulk fly ash samples (0.710788–0.722311), with the most radiogenic 87Sr/86Sr ratios in fly ash originating from Illinois Basin coals (0.718029 ± 0.003365; n = 16), followed by those from Appalachian Basin coals (0.712641 ± 0.000860; n = 16), and those from Powder River Basin coals (0.711663 ± 0.000489; n = 7). The 87Sr/86Sr ratios in the water leachates are significantly lower than the 87Sr/86Sr ratios of the bulk fly ash for Illinois Basin and Appalachian Basin (0.711660 ± 0.001172 and 0.710694 ± 0.000317, respectively, p-value < 0.01), whereas there is no significant difference for the Powder River Basin fly ash (0.711666 ± 0.000456, p-value = 0.13). These isotopic differences most likely reflect the different mineralogical compositions of the studied fly ash and the differential solubility of carbonate phases with low 87Sr/86Sr ratios relative to more radiogenic silicate phases. Overall, the distinction between the strontium isotope ratios of bulk fly ash versus water-soluble fly ash is important, as it refines the application of strontium isotopes as a forensic tracer for tracking coal ash spills and contamination in the environment.

Leaching of rare Earth elements from an Illinois basin coal source

The existence of rare earth elements (REEs) in coal sources at elevated concentrations has been the focus of several studies over the past decade. However, limited research has been conducted on methods to recover and refine the REEs. This paper reports the results of a detailed study into the potential of selectively recovering REEs in an Illinois basin coal source by leaching. Leaching characteristics are obtained for several segments obtained from a core sample as well as three different reject materials collected at a coal processing plant. Using a 1.2 mol/L sulfuric acid solution at 75 °C, over 60% REE recovery is achieved from the direct floor and an inner parting material as well as the coal-rich core segments that are pretreated by low-temperature plasma oxidation to obtain access to the micro-dispersed mineral matter. In the leachable parting material, fluorapatite is detected by XRD analysis, which is one of the more soluble phosphate minerals with a documented association with REEs. For the three plant reject samples, the leaching recovery values obtained for the heavy REEs are higher than those obtained for the light REEs under the standard leaching conditions and when 0.1 mol/L (NH4)2SO4 was used to extract REEs by an ion exchange mechanism. Thermal activation by roasting or chemical activation by pretreatment using 8 mol/L NaOH solution increases the total REE recovery with significantly higher gains obtained for the light REEs. Leaching kinetics are relatively fast within the first 2 h and then slow to provide relatively low overall recovery values under the standard test conditions for the coarse and fine reject samples. However, significantly higher recovery values are realized when treating mixed-phase (middling) particles existing within the coarse reject material.

Aqueous acid and alkaline extraction of rare earth elements from coal combustion ash

The recovery of rare earth elements (REEs) from coal combustion fly ash has recently gained attention as a possible beneficial reuse application that could provide an alternative, low-grade source of REEs in an unstable global supply market. To economically recover REEs, an efficient process needs to be developed to remove them from the ash. This study investigated different methods of leaching REEs from fly ash and other coal combustion ashes. Aqueous acid and alkaline leaching were employed on multiple types of coal fly ash samples (representing coals from three major U.S. coal basin sources) with variable leaching parameters that include extractant type (HCl, NaOH), extractant concentration, leachate-to-ash ratio, and addition of CaO during the leaching process. Acid leaching of high calcium-containing fly ashes such as samples derived from Powder River Basin coals had the highest recoveries of REEs (near 100% of total REE contents), while leaching efficiencies were much lower (<40%) for low calcium fly ashes from Appalachian and Illinois Basin coals. If the fly ashes were subjected to aqueous NaOH (to decompose alumunosilicates) and followed with dilute acid to maintain solubility of metal cations, recoveries of the REEs was up to 85% for Appalachian ashes. Overall, these results demonstrate that REEs in the Powder River Basin-based coal fly ashes are more easily leached into acidic solution than the other ashes tested. While the Appalachian Basin-based coal ashes contained the highest total REEs concentrations out of all regional coal ash sources, these ashes required more complex leaching methods that first decompose the aluminosilicate glassy matrix of the ash (e.g. alkaline digestion) prior to acid leaching.

Influence of varying bedding thickness of underclay on floor stability

The variation in bedding thickness of the weak immediate floor has long been a challenge in the Illinois basin coal mines when it comes to floor stability. The vertical thickness of the immediate floor is not constant throughout the mines and can vary over short horizontal distances. The biggest misconception from a design standpoint is to use the maximum or average thickness found from core logs taken from various locations on the mine property. The result of this practice is oversized pillars in the areas where the weak immediate floor has thinned vertically. This over-design leaves coal in situ which could have otherwise been extracted. This paper presents a plane strain numerical model to illustrate the effect of a change in bedding thickness of a weak immediate floor across one or two coal pillars. The floor bearing capacity of the variable floor below each pillar where then compared to the consistent floor. The results show that the varying bedding thickness of weak underclay has an impact on the bearing capacity of the floor. Geometrically with the decrease in bedding thickness for constant pillar width, the B/H ratio increases exponentially. The influence of varying bedding thickness on the floor bearing capacity is apparent at higher B/H ratios. The floor bearing capacity under a single pillar is in variable floor model if the average thickness remains constant. For single pillar, the average of the bedding thickness can be considered and for pillars in a panel, and a safety factor has been proposed to take into account this change in bedding thickness.

Geochemical and petrographic alteration of rapidly heated coals from the Herrin (No. 6) Coal Seam, Illinois Basin

Coals altered by rapid heating events (i.e., those intruded by dikes and sills) are thought to follow a different geochemical maturation pathway than coals altered through diagenesis. If an igneous intrusion alters the petrographic and geochemical properties of a coal, the effect should also be observable in the coal's molecular structure. In this study, we evaluate whether coals altered by rapid heating follow distinct maturation trends from coals that were altered by slower heating (burial maturation). Petrographic, geochemical, and micro-FTIR analyses were performed on a series of Pennsylvanian Illinois Basin coal samples, collected at various distances from a Permian igneous dike. Standard coal characterization techniques including vitrinite reflectance and proximate and ultimate analyses provide valuable insights on the maturation pathways experienced by rapidly heated coals. These techniques were coupled with reflectance micro-FTIR to provide a better understanding of the molecular changes that occur in the coal structure during relatively short-lived, intensive heating events.With decreasing distance to the intrusion, coals have higher mean random vitrinite reflectance values (Rr) within the dike alteration zone. Coking textures similar to those observed in industrial cokes are observed within 2m of the intrusion. Geochemical data for HCl-treated coals indicate an overall loss of H, O, and N and an increase in C approaching the dike. Intruded coals have higher volatile matter (VM) yields at high rank than coals of similar rank that result from normal burial maturation. When plotted on a van Krevelen diagram or Seyler chart, intruded coals follow different coalification trends than coals matured through normal burial diagenesis.Reflectance micro-FTIR analysis of collotelinite shows increased aromaticity with rank: both the ratio of the aromatic CH stretching band at ~3100–3000cm−1 versus the aliphatic CHx stretching bands between 3000 and 2800cm−1 (AR1), and the ratio of the aromatic out-of-plane deformation bands between ~900–700cm−1 versus the aliphatic CHx band (AR2) increase with increasing Rr. Within the 3000–2800cm−1 region, there is an increase in the area under the asymmetric CH3 peak at ~2960cm−1 relative to the asymmetric CH2 peak at ~2920cm−1 with increased rank. Within the 900–700cm−1 region, the overall intensity of the ~750cm−1 peak (aromatic rings with four adjacent H atoms) relative to the ~870cm−1 peak (aromatic rings with one isolated H atom) increases up to 2.5% Rr, likely reflecting a lower degree of substitution (DOS) of alkyl groups on aromatic ring sites. The prevalence of the 750cm−1 peak at high rank may represent a lower degree of condensation of aromatic rings in the structure of intruded coals compared to normally matured coals.

Organic petrology, geochemistry, gas content and gas composition of Middle Pennsylvanian age coal beds in the Eastern Interior (Illinois) Basin: Implications for CBM development and carbon sequestration

Fifty four samples of coal and organic-rich roof shale strata were collected as part of a coal bed methane exploration program. Following canister desorption to document gas contents, the samples were analyzed by geochemical and petrographic methods. Coal samples were found to have moderate ash yields (avg. 13.5%, dry basis), and high total sulfur contents (avg. 4.3%, dry basis). The average gas content was 1.91m3/ton. Petrographically, the coals were dominated by vitrinite macerals (avg. 81.6%, mmf), especially telovitrinite. By comparison, liptinite (avg. 7.1%, mmf) and inertinite macerals (avg. 11.3%, mmf), were minor in occurrence. Coal samples ranged from high volatile C to high volatile A bituminous in rank (avg. Ro maximum, 0.76%).Shale samples had higher ash yields (avg. 76.1, dry basis), though total sulfur contents were comparable to the coal samples (avg. 4.2%, dry basis). Gas contents were lower than the corresponding coal samples (avg. 0.65m3/ton). Petrographically, the shale samples contained decreased amounts of vitrinite (avg. 25.6%, mmf), and higher amounts of liptinite (avg. 45.4%, mmf) and inertinite (avg. 29.0%, mmf) macerals, relative to the coal samples.Gas obtained from coal and shale beds in the Illinois Basin was relatively pure (high CH4 content). Limited data also indicated that Illinois Basin coals have the ability to adsorb fairly significant amounts of CO2. This suggests that CO2 injection to enhance methane production (ECBM), and/or to sequester CO2 may have some potential. Mineralization in the coals could negatively impact CBM production, but it was found that the majority of the mineralization was present in the roof strata.

Gas diffusion behavior of coal and its impact on production from coalbed methane reservoirs

This paper discusses the results of an experimental study carried out to study and evaluate the sorption and diffusion properties of methane in Illinois basin coals. As a first step, sorption results were modeled using the Langmuir isotherm model and the Langmuir Constants were estimated. Next, the diffusion coefficient, D, was estimated by modeling experimental data using the unipore diffusion theory and Fick's law of diffusion. The results clearly indicated a negative correlation between D and pressure for pressures below 3.5 MPa. The overall trend of the variation was found to be bi-modal, its value remaining constant at high pressures, followed by a sharp increase below this critical pressure. Finally, a comparison of the sorption and diffusion results revealed that D depended on the surface coverage, which exhibits a positive relationship with pressure. The trend of diffusion variation with pressure appeared to be in good agreement with the results reported in the past studies using the bi-disperse diffusion model. The practical implication of the results is that the movement of methane is eased significantly at low pressures. Given the low in situ pressure typically encountered in the Illinois basin, this is a positive finding. Finally, this behavior may be responsible, at least in part, for the increased gas production rates encountered in the San Juan basin after several years of production.

Elemental modes of occurrence in an Illinois #6 coal and fractions prepared by physical separation techniques at a coal preparation plant

Abstract In order to gain better insight into elemental partitioning between clean coal and tailings, modes of occurrence have been determined for a number of major and trace elements (S, K, Ca, V, Cr, Mn, Fe, Zn, As, Se, Pb) in an Illinois #6 coal and fractions prepared by physical separation methods at a commercial coal preparation plant. Elemental modes of occurrence were largely determined directly by XAFS or Mossbauer spectroscopic methods because the concentrations of major minerals and wt.% ash were found to be highly correlated for this coal and derived fractions, rendering correlations between individual elements and minerals ambiguous for inferring elemental modes of occurrence. Of the major elements investigated, iron and potassium are shown to be entirely inorganic in occurrence. Most (90%) of the iron is present as pyrite, with minor fractions in the form of clays and sulfates. All potassium is present in illitic clays. Calcium in the original coal is 80–90% inorganic and is divided between calcite, gypsum, and illite, with the remainder of the calcium present as carboxyl-bound calcium. In the clean coal fraction, organically associated Ca exceeds 50% of the total calcium. This organically-associated form of Ca explains the poorer separation of Ca relative to both K and ash. Among the trace elements, V and Cr are predominantly inorganically associated with illite, but minor amounts (5–15% Cr, 20–30% V) of these elements are also organically associated. Estimates of the V and Cr contents of illite are 420 ppm and 630 ppm, respectively, whereas these elements average 20 and 8 ppm in the macerals. Arsenic in the coal is almost entirely associated with pyrite, with an average As content of about 150 ppm, but some As (~ 10%) is present as arsenate due to minor oxidation of the pyrite. The mode of occurrence of Zn, although entirely inorganic, is more complex than normally noted for Illinois basin coals; about 2/3 is present in sphalerite, with lesser amounts associated with illite and a third form yet to be conclusively identified. The non-sulfide zinc forms are removed predominantly by the first stage of separation (rotary breaker), whereas the sphalerite is removed by the second stage (heavy media). Germanium is the only trace element determined to have a predominantly organic association.

Maceral/ microlithotype partitioning with particle size of pulverized coal: Examples from power plants burning Central Appalachian and Illinois basin coals

Pulverized coals from eleven power plants burning Central Appalachian coal blends and eight power plants burning Illinois Basin coal blends were studied in order to assess the petrographic nature of industrial-scale coal grinding. All coals were high volatile bituminous. Coals were wet screened at 100 (150 μ), 200 (75 μ), 325 (about 40 μ), and 500 (about 25 μ) mesh. Petrographic analysis of the whole coals and size fractions consisted of a combined maceral and microlithotype analysis. Microlithotype analysis, in particular, provides a reasonable approximation of the whole-particle composition at the scale of utility coal pulverization. In the size fractions, duroclarite, the most abundant trimaceral microlithotype, is most abundant in the coarsest fraction and least abundant in the finest fraction. Vitrite, the most abundant monomaceral microlithotype, exhibits the opposite trend. Duroclarite becomes more enriched in vitrinite towards the finer sizes. The partitioning of microlithotypes and the partitioning of macerals within the microlithotypes is indicative of the relative brittle nature of vitrite compared to the hard-to-grind trimaceral microlithotypes. Increased vitrinite in duroclarite is an indication that the microlithotype within the particular size fraction is more brittle than relatively vitrinite-depleted duroclarite in coarser fractions. The relative grindability of microlithotypes will, in turn, impact combustion efficiency.

Impact of co-combustion of petroleum coke and coal on fly ash quality: Case study of a Western Kentucky power plant

Petroleum coke has been used as a supplement or replacement for coal in pulverized-fuel combustion. At a 444-MW western Kentucky power station, the combustion of nearly 60% petroleum coke with moderate- to high-sulfur Illinois Basin coal produces fly ash with nearly 50% uncombusted petroleum coke and large amounts of V and Ni when compared to fly ash from strictly pulverized coal burns. Partitioning of the V and Ni, known from other studies to be concentrated in petroleum coke, was noted. However, the distribution of V and Ni does not directly correspond to the amount of uncombusted petroleum coke in the fly ash. Vanadium and Ni are preferentially associated with the finer, higher surface area fly ash fractions captured at lower flue gas temperatures. The presence of uncombusted petroleum coke in the fly ash doubles the amount of ash to be disposed, makes the fly ash unmarketable because of the high C content, and would lead to higher than typical (compared to other fly ashes in the region) concentrations of V and Ni in the fly ash even if the petroleum coke C could be beneficiated from the fly ash. Further studies of co-combustion ashes are necessary in order to understand their behavior in disposal.

Mercury content of the Springfield coal, Indiana and Kentucky

With pending regulation of mercury emissions in United States power plants, its control at every step of the combustion process is important. An understanding of the amount of mercury in coal at the mine is the first step in this process. The Springfield coal (Middle Pennsylvanian) is one of the most important coal resources in the Illinois Basin. In Indiana and western Kentucky, Hg contents range from 0.02 to 0.55 ppm. The variation within small areas is comparable to the variation on a basin basis. Considerable variation also exists within the coal column, ranging from 0.04 to 0.224 ppm at one Kentucky site. Larger variations likely exist, since that site does not represent the highest whole-seam Hg nor was the collection of samples done with optimization of trace element variations in mind. Estimates of Hg capture by currently installed pollution control equipment range from 9–53% capture by cold-side electrostatic precipitators (ESP) and 47–81% Hg capture for ESP + flue-gas desulfurization (FGD). The high Cl content of many Illinois basin coals and the installation of Selective Catalytic Reduction of NO x enhances the oxidation of Hg species, improving the ability of ESPs and FGDs to capture Hg.

Environmental and tectonic influences on the formation and distribution of carbonate nodules above the Springfield coal seam, southern Illinois Basin

Carbonate nodules have been encountered for many years in the southern Illinois Basin, in parts of southern Illinois, southern Indiana, and southwestern Kentucky. The nodules occur as oblate spheroids of calcium carbonate that are isolated in the shale immediate roof of coal mines. They are common in the Springfield coal seam, known as the No. 5 seam in Illinois, and as the No. 9 seam in western Kentucky. Several different mechanisms have been proposed for the formation of various semi-spherical objects in coal measure rocks. The distribution and association with rooted horizons suggest that carbonate nodules in black fossiliferous shale observed in the roof of a studied mine in the Springfield seam represent pedogenic carbonate paleosols, which formed in a caliche-favoring environment subsequent to Springfield mire deposition. This interpretation is supported by 87Sr/ 86Sr isotope ratios of 0.710893 ± 13 to 0.711035 ± 12, which indicate a freshwater rather than seawater source. Petrographic examination of rock textures and mineral grains indicates that nodules collected from two Illinois Basin coal mines are composed of subangular grains of fine-grained, crystalline microspar. Although the carbonate is not ferroan, iron hydroxide stains interstices between microspar grains. The rounded, commonly pinched boundaries of nodules truncate commonly imbricated microspar grains. In contrast, concentric growth patterns are not observed except as defined by secondary, subhedral to euhedral pyrite crystals that form a diffuse, concentric replacement zone around the nodule's outer rind. Polished slickensides, with well-developed radial slickenlines, are developed at highly compacted margins in black shale or mudstone that commonly encases the carbonate nodules. Of the 450 carbonate nodules documented at a study mine in the southern Illinois Basin, the long axes of 36% are preferentially aligned parallel to regional structures such as anticline axes and drag folds that are interpreted to have formed in response to compression during the Late Pennsylvanian-Permian Alleghanian orogeny. Mapping also suggests that clusters of carbonate nodules are spatially associated with the trends of low-angle drag folds in the immediate roof of the Springfield seam at the study mine. The preferential elongation and distribution with respect to tectonic structures suggest that regional compression influenced the shape and distribution of carbonate nodules, and that nodule lithification may have been approximately contemporaneous with regional deformation.

Micro- and nanochemistry of fly ash from a coal-fired power plant

Fly ash from a coal-fired power plant was investigated to obtain detailed information on its physical and chemical properties, and to gain an understanding of potential environmental and health impacts associated with itsdisposal in landfills. The studied material was produced through combustion of Illinois Basin coal and trapped within the power plant by an electrostatic precipitator. It is a fine-grained, low-Ca fly ash containing primarily SiO 2 , Al 2 O 3 , and Fe 2 O 3 , and is enriched in many toxic elements (e,g., Be, Zn, As, Cd, Tl, Pb, and U) by a factor of up to 30 relative to coal. The ash consists of mainly hematite, magnetite, mullite, quartz, and amorphous material. These constituents occur mostly as spherical particles with diameters of less than 13 μm. We examined the physical, chemical, and structural characteristics of individual fly ash particles by scanning and transmission electron microscopy and electron probe microanalysis. The results demonstrate that, with the exception of complex plerospheres, individual particles are chemically fairly homogeneous, but a pronounced compositional variation exists among particles with similar physical and structural attributes. Electron microprobe data document that several trace elements, including U, are partitioned into the Fe-rich particles. Transmission electron microscopy revealed that various types of small (<1 μm) crystalline Ca-rich phases, including lime, are attached to the glass spheres, particularly the nonmagnetic glass. These crystals may contain substantial amounts of S. Even though only a few of these crystals were analyzed quantitatively, our data indicate that the Ca-rich and S-rich phases may be important hosts for trace elements such as V and Zn. The observed element partitioning and the existence of surface-attached crystals enriched in certain trace elements suggest that fly ash from coal-fired power plants might have a more deleterious environmental impact than is inferred from bulk analytical data.

Desulfurization of Hot Syngas Containing Hydrogen Chloride Vapors Using Zinc Titanate Sorbents

There is a primary need to increase the use of Illinois coal resources by developing new methods of converting the coal into electricity with highly efficient and environmentally acceptable systems. New coal gasification processes that can generate electricity with high thermal efficiency either in a combined gas-turbine, a steam-turbine cycle (IGCC), or in a fuel cell (MCFC) are being developed. Both of these new coal-to-electricity pathways require that the coal-derived fuel gas be at a high temperature and free of potential pollutants, such as sulfur compounds. Unfortunately, some high-sulfur Illinois coals also contain a significant amount of chlorine, which converts into hydrogen chloride (HCl) in the coal gas. In this study, two simulated gasifier-product streams were contacted with the zinc titanate desulfurization sorbent in a bench-scale atmospheric fluidized-bed reactor at temperatures ranging from 538 to 750 °C (1000−1382 °F). The first set of experiments involved treating a medium-Btu fuel gas (simulating that of a “Texaco” oxygen-blown, entrained-bed gasifier) containing 1.4% H2S and HCl concentrations of 0, 200, and 1500 ppmv. The second set of experiments evaluated the hot-gas desulfurization of a low-Btu fuel gas (simulating the product of the “U-Gas” air-blown gasifier), which had a 0.5% H2S content and with HCl concentrations of 0, 200, and 800 ppmv. These operating conditions were typical of the gas-treatment requirements of gasifier systems fueled by Illinois basin coals containing up to 0.6% chlorine. The results of the experiments at 538 and 650 °C at all the HCl concentrations revealed no deleterious effects on the capability of the sorbent to remove H2S from the fuel-gas mixtures. In most cases, the presence of the HCl significantly enhanced the desulfurization reaction rate. Some zinc loss, however, was encountered in certain situations at 750 °C when low-steam operating conditions were present. Also of interest, a portion of the incoming HCl was removed from the gas stream and was retained permanently by the sorbent.