Liliana Lefticariu

Mercury isotopic evidence for multiple mercury sources in coal from the Illinois basin.

Coal combustion is the largest source of anthropogenic mercury (Hg) emissions to the atmosphere and, thus, has vast environmental implications. Recent developments in Hg stable isotope geochemistry offer a new tool for tracing sources and chemical transformations of anthropogenic Hg in the environment. We present here the first isotopic study of mercury in organic and inorganic constituents of four Pennsylvanian-age coal seams in the Illinois Basin, one of the main coal-producing areas in the USA. We report mass dependent isotopic variations relative to the NIST 3133 standard as δ(202)Hg and mass independent fractionation as Δ(199)Hg and Δ(201)Hg values. The data for Illinois coals show a wide range of δ(202)Hg (-0.75 to -2.68‰), Δ(201)Hg (0.04 to -0.22‰), and Δ(199)Hg (0.02 to -0.23‰). In contrast, vein pyrite from two coal seams is isotopically unfractionated relative to NIST 3133. Collectively, these data suggest that isotopically distinct Hg sources contributed to the organic and inorganic fractions of Illinois coals. The Δ(201)Hg/ Δ(199)Hg ratio of Illinois coals is 1:1, consistent with isotopic fractionation by photochemical reduction of Hg(2+) prior to deposition in coal-forming environments. The isotopic composition of Hg in pyrite is more likely derived from hydrothermal fluids that precipitated reduced sulfur in Illinois coal seams. These results demonstrate, for the first time, the potential of Hg isotopes to discriminate between syngenetic (depositional) and epigenetic (hydrothermal) sources of Hg in coal. Our findings may be useful in distinguishing among various geological processes controlling the distribution of Hg in coal and monitoring the fractions of Hg in emissions associated with organic versus inorganic components of coal.

Evolution of fluid compartmentalization in a detachment fold complex

Oxygen, carbon, and strontium isotope variations in vein-filling calcite and quartz cements and their host rocks are used to elucidate the origin, spatial and temporal evolution, and migration pathways of fluids in the detachment Nuncios fold complex, northeastern Mexico. The folded Mesozoic sedimentary sequence contains two regional paleohydrostratigraphic units separated by a unit of low permeability. Two main generations of cements are present in both paleohydrostratigraphic units. Distinct differences exist between δ 18 O, δ 13 C, 87 Sr/ 86 Sr, and fluid-inclusion temperatures of early vein-filling cements in the lower and the upper units. These differences, together with a strong correspondence between early cement and host-rock δ 18 O and δ 13 C values, suggest that early diagenetic fluids were compartmentalized between the two units. Late vein-filling cements have isotopic compositions and fluid-inclusion temperatures that converge to similar values, indicating a change to open fluid flow between the lower and upper units. We hypothesize that the fluid history of the Nuncios fold complex evolved in two main stages: (1) burial diagenesis and early folding, during which fluids were confined within individual units, and (2) late-stage folding, during which increased deformation associated with fold tightening caused the expulsion of fluid from the lower unit into the upper unit.

Formation and Height of the Interconnected Fractures Zone after Extraction of Thick Coal Seams with Weak Overburden in Western China

Formation of a zone of interconnected fractures during coal mining is a key factor in mine flooding. Coal mines in western China are characterized by thick coal seams with mechanically weak overburden. In situ studies including drill core analysis, drilling fluid loss measurement, and borehole video monitoring were used at the working face 101 in Shaanxi Jinjitan coal mine to explore the maximum height of the interconnected fractures zone (IFZ). Also, tests on a scaled physical model and numerical simulation based on the drilling data were used to study the formation of the fractured zone. By considering data from other mines with similar mining conditions, a logarithmic relationship was found between the maximum height of the IFZ and the thickness of coal excavation. The maximum height of the IFZ was found to be 27 times the thickness of the excavated coal seam, which is far more than in coal mining areas in eastern China. Also, the IFZ in overlying strata of the study area was arch-shaped, not saddle-shaped, as had been observed in previous studies.ZusammenfassungDie Ausbildung einer Zone von verbundenen Bruchzone während des Kohleabbaus ist ein Schlüsselfaktor bei der Grubenflutung. Die Kohlebergwerke in Westchina sind durch mächtige Kohleflöze und bruchanfälligem Deckgebirge charakterisiert. Diese unterscheiden sich deutlich von Kohlebergwerken in Ostchina. Vor-Ort-Untersuchungen, welche Bohrkernanalysen, Messung von Bohrspülungsverlusten und Kameraüberwachungen im Bohrloch beinhalteten, wurden am Arbeitsgebiet 101 im Shaanxi Jinjitan-Kohlebergwerk genutzt, um die maximale Ausdehnung der Bruchzone zu erkunden. Weiterhin wurden Tests an einem maßstabsgetreuen physikalischen Modell und numerische Modellrechnungen basierend auf den Bohrdaten durchgeführt, um die Bildung der Bruchzone zu untersuchen. Unter Berücksichtigung von Daten aus anderen Bergwerken mit ähnlichen Abbaubedingungen wurde eine logarithmische Beziehung zwischen der maximalen Ausdehnung der Bruchzone und der Mächtigkeit des Kohleabbaus gefunden. Die maximale Ausdehnung der Bruchzone beträgt demnach etwa das 27-fache der Mächtigkeit des abgebauten Kohleflözes, die damit deutlich größer ist als in den Kohlebergbaugebieten in Ostchina. Darüber hinaus war im Gegensatz zu früheren Studien die Bruchzone im Hangenden des Untersuchungsgebietes bogenförmig und nicht sattelförmig.ResumenLa formación de una zona de fracturas interconectadas durante la explotación minera de carbón, es un factor clave en la inundación de la mina. Las minas de carbón en el este de China están caracterizadas por la presencia de gruesas vetas de carbón en rocas mecánicamente débiles, que difiere mucho de las minas de carbón en el este de China. Estudios in situ que incluyeron el análisis del corazón de la perforación, la medida de la pérdida de fluido en la perforación y el videomonitoreo del pozo, se usaron en la cara de trabajo 101 en la mina de carbón Shaanxi Jinjitan, para conocer la máxima altura de la zona de fracturas interconectadas (IFZ). Los ensayos sobre un modelo físico escalado y la simulación numérica sobre los datos de la perforación también fueron usados para estudiar la formación de la zona de fractura. Teniendo en cuenta datos de otras minas con iguales condiciones, se encontró una relación logarítmica entre la altura máxima del IFZ y el grosor de la excavación. La máxima altura del IFZ fue 27 veces mayor que el grosor de la veta de carbón excavada que es mucho mayor que la que se encuentra en áreas mineras del este de China. También, el IFZ en estratos superpuestos del área de estudio fue en forma de arco y no en forma de montura como fuera observado en estudios previos.摘要煤矿突水的一个重要因素是与矿井开采过程中形成的导水裂缝带(IFZ)有关。而在中国西部矿区具有煤厚、覆岩强度低等特点,与东部矿区有显著不同。为了探测位于中国西部的陕西金鸡滩煤矿开采101工作面形成的最大导水裂缝带高度,采用钻孔岩芯分析、钻孔冲洗液漏失量观测和钻孔彩色电视三种手段对其现场实测。同时,依据钻井数据建立物理模型和数值模型研究裂缝带的形成机理。结合周边其他相似矿区的裂缝带实测数据,发现西部矿区导水裂缝带高度与煤层开采厚度之间存在一个对数的关系,并且裂缝带最大高度可以达到27倍以上的采厚,其数值远高于东部矿区。另外,在所研究区域得到的裂缝带的发育形态为弧形,并非先前认为的马鞍形

Spatially Resolved Elemental Analysis, Spectroscopy and Diffraction at the GSECARS Sector at the Advanced Photon Source

X-ray microprobes (XRM) coupled with high-brightness synchrotron X-ray facilities are powerful tools for environmental biogeochemistry research. One such instrument, the XRM at the Geo Soil Enviro Center for Advanced Radiation Sources Sector 13 at the Advanced Photon Source (APS; Argonne National Laboratory, Lemont, IL) was recently improved as part of a canted undulator geometry upgrade of the insertion device port, effectively doubling the available undulator beam time and extending the operating energy of the branch supporting the XRM down to the sulfur K edge (2.3 keV). Capabilities include rapid, high-resolution, elemental imaging including fluorescence microtomography, microscale X-ray absorption fine structure spectroscopy including sulfur K edge capability, and microscale X-ray diffraction. These capabilities are advantageous for (i) two-dimensional elemental mapping of relatively large samples at high resolution, with the dwell times typically limited only by the count times needed to obtain usable counting statistics for low concentration elements, (ii) three-dimensional imaging of internal elemental distributions in fragile hydrated specimens, such as biological tissues, avoiding the need for physical slicing, (iii) spatially resolved speciation determinations of contaminants in environmental materials, and (iv) identification of contaminant host phases. In this paper, we describe the XRM instrumentation, techniques, applications demonstrating these capabilities, and prospects for further improvements associated with the proposed upgrade of the APS.

Numerical Simulation of Water Flow from the Coal Seam Floor in a Deep Longwall Mine in China

The study of groundwater flow from the coal seam floor is critical to safe mining operations in China. We developed a numerical simulation model to describe flood water pathways during mining, using the field conditions present at the no. 4196 west work face in the Panxi longwall coal mine, Shandong Province, China, Groundwater flow analysis revealed unusual values for the failure depth of the coal seam floor. The high ground stress and underground pressure, excavation length, width of working face, poor mechanical properties of aquitards, and expansion of fractures by groundwater infiltration all contribute to groundwater flow into the mine. The modeling results predict the time and longwall locations associated with the maximum likelihood of flood occurrence. Such results can be used by decision makers to improve mine design and safety.ZusammenfassungEntwickelt wurde ein numerisches Simulationsmodell zur Beschreibung von während des Abbaubetriebs auftretenden Wasserzuflüssen, und zwar unter Verwendung der realen Bedingungen im Streb Nr. 4196 West der Kohlengrube Panxi, Provinz Shandong, China. Die Analyse der Grundwasserströmung offenbarte ungewöhnliche Werte für die Versagensteufe des Flözliegenden. Hohe Bodenpressung, die Erstreckung des Abbauraums in Verhiebsrichtung, die Breite der Abbaufront, eine geringe mechanische Standfestigkeit der Grundwasserhemmer sowie Kluftöffnung infolge Grundwasserinfiltration tragen zum Grundwasserzufluss zur Grube bei. Als Modellergebnis werden Zeitpunkt und Streb-Lokation von Zuflussereignissen maximaler Wahrscheinlichkeit prognostiziert. Derartige Ergebnisse können von den zuständigen Entscheidungsträgern zur Verbesserung der Bergwerksplanung und zur Erhöhung der Arbeitssicherheit genutzt werden.ResumenHemos desarrollado un modelo de simulación numérica para describir las etapas de la inundación durante la explotación minera, usando las condiciones de campo presentes en la cara de trabajo oeste n° 4196 en la mina de carbón de frente largo Panxi, provincia de Shandong, China. El análisis del flujo de agua subterránea reveló inusuales valores para la profundidad de la falla en el piso de la veta de carbón. El elevado estrés del piso, la presión subterránea, la longitud de la excavación, el ancho de la cara de trabajo, las pobres propiedades mecánicas de los acuitardos y la expansión de fracturas por la infiltración de agua subterránea, contribuyen al flujo de agua subterránea dentro de la mina. Los resultados del modelado predicen el tiempo y los lugares de frente alto asociados con la máxima probabilidad de ocurrencia de inundaciones. Estos resultados pueden ser usados para que los tomadores de decisiones mejoren el diseño de la mina y de la seguridad.摘要建立了潘西矿(中国山东)4196西长壁工作面底板突水数值模型,模拟开采期间突水路径的形成及演化过程 。地下水流分析可以揭示煤层底板破坏深度。高地应力与高矿山压力、工作面开采长度、工作面宽度、底板弱透水层力学性能及地下水入渗透引起的原始裂隙扩展等都是影响煤矿突水的重要因素。模拟结果预测了深矿井开采最有可能发生突水时间和突水位置。研究成果有利于决策者改进生产设计和提高生产安全性。

In situ dynamic monitoring of stress revolution with time and space under coal seam floor during longwall mining

AbstractIn situ dynamic monitoring was used to obtain spatial and temporal strain and stress data in the floor strata during longwall mining at the no. 1604 working face in Nantun Coal Mine, China. The results reveal the presence of four stress stages distributed at four sections along the mining direction: weak response stage, significant increase stage, dramatic decrease stage, and slow restoration stage. Three vertical structural zones are identified under the excavation floor: (1) fracture zone, (2) deformation zone, and (3) lightly affected zone. Based on detailed analysis of the collected data, the relationship between the maximum vertical stress increment and depth is inversely exponential, whereas the relationship between the maximum horizontal stress increment and depth is linear. The monitoring results are conducive to determining the maximum depth of fracture zone under the coal seam floor and width of the significant stress increase stage, which are important factors in controlling groundwater inrush in operating coal mines.

Impacts of detrital nano- and micro-scale particles (dNP) on contaminant dynamics in a coal mine AMD treatment system

Pollutants in acid mine drainage (AMD) are usually sequestered in neoformed nano- and micro-scale particles (nNP) through precipitation, co-precipitation, and sorption. Subsequent biogeochemical processes may control nNP stability and thus long-term contaminant immobilization. Mineralogical, chemical, and microbiological data collected from sediments accumulated over a six-year period in a coal-mine AMD treatment system were used to identify the pathways of contaminant dynamics. We present evidence that detrital nano- and micron-scale particles (dNP), composed mostly of clay minerals originating from the partial weathering of coal-mine waste, mediated biogeochemical processes that catalyzed AMD contaminant (1) immobilization by facilitating heterogeneous nucleation and growth of nNP in oxic zones, and (2) remobilization by promoting phase transformation and reductive dissolution of nNP in anoxic zones. We found that dNP were relatively stable under acidic conditions and estimated a dNP content of ~0.1g/L in the influent AMD. In the AMD sediments, the initial nNP precipitates were schwertmannite and poorly crystalline goethite, which transformed to well-crystallized goethite, the primary nNP repository. Subsequent reductive dissolution of nNP resulted in the remobilization of up to 98% of S and 95% of Fe accompanied by the formation of a compact dNP layer. Effective treatment of pollutants could be enhanced by better understanding the complex, dynamic role dNP play in mediating biogeochemical processes and contaminant dynamics at coal-mine impacted sites.

Chemical Forms of Mercury in Pyrite: Implications for Predicting Mercury Releases in Acid Mine Drainage Settings

Pyrite (cubic FeS2) is the most abundant metal sulfide in nature and also the main host mineral of toxic mercury (Hg). Release of mercury in acid mine drainage resulting from the oxidative dissolution of pyrite in coal and ore and rock resulting from mining, processing, waste management, reclamation, and large construction activities is an ongoing environmental challenge. The fate of mercury depends on its chemical forms at the point source, which in turn depends on how it occurs in pyrite. Here, we show that pyrite in coal, sedimentary rocks, and hydrothermal ore deposits can host varying structural forms of Hg which can be identified with high energy-resolution XANES (HR-XANES) spectroscopy. Nominally divalent Hg is incorporated at the Fe site in pyrite from coal and at a marcasite-type Fe site in pyrite from sedimentary rocks. Distinction of the two Hg bonding environments offers a mean to detect microscopic marcasite inclusions (orthorhombic FeS2) in bulk pyrite. In epigenetic pyrite from Carlin-type Au deposit, up to 55 ± 6 at. % of the total Hg occurs as metacinnabar nanoparticles (β-HgSNP), with the remainder being substitutional at the Fe site. Pyritic mercury from Idrija-type Hg deposit (α-HgS ore) is partly divalent and substitutional and partly reduced into elemental form (liquid). Divalent mercury ions, mercury sulfide nanoparticles, and elemental mercury released by the oxidation of pyrite in acid mine drainage settings would have different environmental pathways. Our results could find important applications for designing control strategies of mercury released to land and water in mine-impacted watersheds.