Coal Fragments Research Articles

Application of fractal theory to top-coal caving

The experiences of underground coal mining in China show that coal in a thick hard coal seam with a hard roof, the so-called “double hard coal seam”, is difficult to be excavated by top-coal caving technique. In order to solve the problem, a top-coal weakening technique is proposed in this paper. In the present study, fractal geometry provides a new description of the fracture mechanism for blasting. By means of theoretical analysis of the relationship between the fractal dimension of blasting fragments and the dynamite specific energy, a mechanical model for describing the size distribution of top-coal and the dissipation of blasting energy is proposed. The theoretical results are in agreement with laboratory and in situ test results. Moreover, it is shown that the fractal dimension of coal fragments can be used as an index for optimizing the blasting parameters for a top-coal weakening technique.

COMMENT ON MELLUSO ET AL. (2003): The Ricetto and Colle Fabbri wollastonite and melilite-bearing rocks of the central Apennines, Italy

The bimodal rock of Ricetto consists of a felsic glassy component, which prevails volumetrically at the top of the rock, and mafic spherules of acicular diopside + anorthite + wollastonite pseudomorph after melilite, which are concentrated at the bottom of the rock. This texture clearly indicates liquid immiscibility, which can be modeled in the compositional space SiO 2 - Al 2 O 3 -MgO-CaO and Al 2 O 3 -CaO-(FeO T + MgO). The spinifex and dendritic forms are due to quenching from a melt at temperature of 1000-1100 °C: melilite was the first phase to crystallize and the subsequent rapid cooling caused its breakdown to a more stable assemblage. The strict chemical similarity between the rock under study and the surrounding siliciclastic sandstones, together with the results of 14 C radiometric analysis on coal fragments found at bottom of the convex central part of the body, demonstrate that the rock of Ricetto is a man-made pyrometamorphic product. The genetic attribution of the Colle Fabbri occurrence to pyrometamorphic phenomena somewhat similar to Ricetto is difficult to be asserted, as the crystallization history at Colle Fabbri has been much more complicated than at Ricetto. The common presence of melilite and wollastonite cannot account for a direct comparison between the Ricetto and Colle Fabbri rocks, as conspicuous mineralogic, petrologic, and geologic differences exist between these two occurrences.

Petrographic and geochemical characteristics of organic matter associated with stream sediments in Trail area British Columbia, Canada

Abstract Fifty-six samples of stream sediments from 12 creeks in the vicinity of Trail, British Columbia, Canada were examined to determine their origin, characterize their organic matter and their relation to natural/geogenic and anthropogenic sources. The samples were initially screened by Rock-Eval® 6 pyrolysis for their TOC, HI, and OI contents and then examined by both reflected (polarized) and fluorescent light microscopy. It was found that organic matter in stream sediments is mostly from natural/biological sources from local vegetation, such as woody tissue, suberin, spores, and pollen, as well as altered natural/biological input from char formed due to forest fires. Anthropogenic organic matter, mostly coke particles, was also found in the stream sediments. The coke particles have anisotropic properties with medium grained texture formed from medium volatile bituminous coal. The occurrence of coke particles is limited to Ryan Creek located close to an area were some small gold, nickel, and lead smelting operations previously occurred. There is no evidence to indicate that the coke particles found in the creek are emitted from the lead and zinc smelter currently in operation in the area. There are no coal-bearing strata in the area that may have a direct input of coal fragments in any of the creeks.

04/01470 Fuel combustion in the fluidized bed of an inert material equipped with an unmovable catalytic small-volume package: Yazykov, N. A. et al. Khimiya v Interesakh Ustoichivogo Razvitiya, 2003, 11, (1), 321–326

Coal devolatilization studies to maximize the yield of condensable products by operating at elevated temperatures and heating rates have been published. The objectives of this study were to investigate the influences of relatively mild operating conditions (e.g. relatively low temperature and pressure) on product quality, by comparing devolatilized products obtained at various temperatures and heating rates. Fixed bed, fluid bed, and entrained flow reactor units were used to obtain pyrolysis products. In addition, literature data on tar yields in various reactor units at a range of temperatures and residence times were surveyed and compared with experimental data. The liquids were characterized by a number of techniques, including field ionization mass spectroscopy (f.i.m.s.), sequential elution solvent chromatography (s.e.s.c.) and elemental analysis. The results demonstrate that the quality and yield of liquids obtained at a rapid heating rate are functions of peak pyrolysis temperature. It was shown that at a rapid heating rate, the yields of heavier polyfunctional groups (i.e. hydrocarbons with greater mean molecular weight) are greater than those obtained in the fixed bed slow heating rate reactor. The liquids generated at a slow heating rate are of lower molecular weight, viscosity, and sulphur content, and of higher HC atomic ratios compared with the liquids obtained in a rapid heating rate unit. The effect of increasing the maximum pyrolysis temperature (at a constant slow heating rate) was to increase the yield of light gases (mainly H) at the expense of char hydrogen content and char reactivity. The tar yield is not markedly influenced when the peak devolatilization temperature is increased at a relatively slow heating rate. However, the quality (as defined by the HC (atomic) ratio) of the liquids, and the reactivity (in air) of char, was reduced when the peak pyrolysis temperature was increased. At a rapid heating rate, the primary products, which have many structural characteristics of the parent coal, are devolatilized. The quality of the liquids obtained at a rapid heating rate is, therefore, determined by the devolatilized primary coal fragments evolved at the devolatilization temperature. In a slow heating rate fixed bed unit, however, the primary coal fragments undergo additional cracking reactions which involve stabilization of free radicals by donatable hydrogen. This leads to the formation of low molecular weight hydrocarbons of relatively higher quality. In-situ (both intraparticle or extraparticle) stabilization of reactive coal fragments by donatable hydrogen may lead to a significant improvement in the overall quality of the pyrolysis liquids in a fixed bed system in which time-temperature history is conducive for such reactions.

Flash Pyrolysis of Lakhara Lignite Utilizing Effective Radical Transfer

AbstractFlash pyrolysis of raw and tetralin treated coal samples were carried out in nitrogen atmosphere. Two representative coal samples from Lakhra coalmines labeled Lakhra‐3 (L3) and Lakhra‐6B (L6B) were pyrolyzed in their raw state and after treatment with tetralin. Initial experiments were carried out at 700 °C with 2 milligrams of 80 mesh size samples. The main hydrocarbon products detected from both samples were methane, ethylene, ethane, propane, butane, pentane, benzene, toluene and xylene (BTX). The ratio of the total hydrocarbon yield from L3 and L6B raw samples is 1:1.49, respectively, while the relative yield of aliphatic C1‐C5 straight chain products to BTX are 7.65:5.49. Theses differences in product yields clearly indicate the compositional variation between the two samples. The total hydrocarbon yield (C1‐C5 +BTX) of tetralin swollen L3 coal and L6B coal was larger than the raw coal at all temperatures, and larger by 50.6% and 32.6%, respectively, at 700 °C. The treatment of coal samples has a more pronounced effect on BTX yield than C1‐C5 aliphatic hydrocarbons. BTX yield of tetralin treated L3 coals at 700 °C was 3.5 times higher while for L6B coal the BTX yield was 2.1 times higher than the raw samples. These significant increases in hydrocarbons yields can be explain in terms of the suppression of the cross‐linking reactions of coal fragments due to the penetration of tetralin in to the micropores of coal, as well as the effective H radicals transfer from tetralin to coal fragments during pyrolysis.

Initiation of turbidity currents: outcrop evidence for Eocene hyperpycnal flow turbidites

The most widely used, although not as widely documented, explanation for initiation of turbidites is the conversion of catastrophic sediment failures into turbidites. Such instantaneous sediment failures generate short-lived surge-type flows that deposit turbidite beds described as Bouma sequences. In this communication, we present data from the Eocene Central Basin of Spitsbergen that shows turbidite systems that are volumetrically dominated by thick ungraded and laminated sandy turbidite beds, deposited by gradual aggradation from sustained flows. Sustained flows are long-lived and more or less continuous. They can be generated by a variety of mechanisms, e.g.: (1) instability during volcanic eruptions and the consequent remobilisation of unconsolidated material; (2) seismically triggered subaerial sliding within the drainage; (3) storm surges; (4) retrogressive slope failure; (5) breaching; and (6) hyperpycnal flows. Our database shows that in the Eocene Central Basin, the sustained flows were generated by hyperpycnal flows, i.e., by direct river effluent. The hyperpycnal flow turbidites have been recognized on the basis of (1) physical connection between fluvial and turbidite channels at the shelf edge, (2) abundance of thick turbidite sandstone beds, (3) sand-prone nature of the turbidite systems, (4) downslope changes of individual thick, sandy turbidite beds, and their collapsed pinch-out segments, (5) great abundance of continental material (leaves, coal fragments) in turbidite beds, (6) low abundance of associated slumped or debris-flow beds, and (7) the occurrence of turbidites in systematically accreted shelf-margins. These features strongly suggest that hyperpycnal flow, generated by direct river effluent, deposited significant number of turbidite beds in the documented slope and basin-floor turbidite successions. We also argue that the hyperpycnal flows are preferentially fed into the deepwater slopes beyond the shelf edge during the falling stage and lowstand of relative sea level. The turbidite beds were studied in the context of seismic-scale (1×15 km), dip-oriented outcrops by measuring detailed vertical sections, following individual beds and packages of beds downslope for distances over 5 km, lateral mapping, and helicopter-taken photomosaics.

High-temperature rapid pyrometamorphism induced by a charcoal pit burning: The case of Ricetto, central Italy

Bulk chemistry and mineralogy of the peculiar rock of Ricetto (Carseolani Mts., Central Apennines, Italy) was studied to resolve its controversial origin: igneous dyke or anthropic product. This hybrid rock consists of a colorless, felsic component made up of glass plus quartz, and a brown, femic component made up of fans and spherulites of diopside, calcic plagioclase, wollastonite, and melilite. Textural relationships indicate very rapid cooling and immiscibility phenomena. The bulk chemistry of the rock is the same as that of the surrounding siliciclastic sandstone. The 14C analysis of a coal fragment from bottom of the body yields the conventional age of 227(±50) years. The Ricetto occurrence is an example of pyrometamorphism of a siliceous limestone induced by a charcoal pit burning. The small size of the heat source at Ricetto caused an intense but short-lived melting of the country rock. Prograde metamorphism caused a temperature increase up to 1,000–1,100 °C when melilite crystallization conditions were reached at appreciable P(CO2) and high f(O2). Melting occurred in a close system represented by the simplified equation: 3Cal+16.5Qtz+Ms+Bt→Mel+Melt+2H2O+3CO2+0.5O2. Diopside+calcic plagioclase+wollastonite formed by melilite breakdown during rapid cooling, through the reaction: 6Mel+6Qtz+0.5O2→3Di+2An+7Wo. Liquid immiscibility caused the separation between the felsic melt component and the femic melilite-bearing component. Immiscibility was characterized by different fractionation of alumina and alkalies between these two phases. Differences in bulk, glass, and mineral chemistry between the Ricetto and other melilite-bearing pyrometamorphic rocks can be attributed mainly to different protoliths.

Model Tests and Field Experiments for Fragmentation Assessment During Ringhole Blasting in BG Panels

Experimental blasts were conducted in concrete blocks of known strengths to correlate field results in Blasting Gallery (BG) panels of GDK-10 Incline for improving fragmentation of coal to an optimum level so that blasted coal could easily be lifted totally by remote controlled LHDs and thereby mitigating the possibility of occurrence of spontaneous heating in BG districts before exhaustion of the panel. Various charge loading parameters and consequent breakage results were critically analyzed to arrive at a constructive conclusion, which could satisfactory improve the blast results.

Coal inclusions in sedimentary rocks: a geochemical phenomenon. A review

In many coal-bearing basins, there are numerous coalified fragments of ancient plants (coal-precursors) enclosed in host rocks. Such fragments occur in isolated positions out of the coal beds. In the Russian literature, these coal fragments are named coal inclusions. Coal inclusions are mostly the remains of stems, trunks, and branches, as well as the roots of trees. The review presented covers: (a) definition and classification of fossil woods; (b) relations between coalification and mineralization of fossil woods; (c) some special topics dealing with different and even zonal coalification degree of coal inclusions embedded different host rocks; (d) some historical data on geochemistry of coal inclusions; (e) basic empirical regularities in geochemistry, observed world-wide; (f) some data about chemical nature of humin substance—a precursor of lignite and vitrain matter in coalified wood; (g) results of calculations modelling the Ge enrichment in coal inclusions; (h) economic importance of Ge in coal inclusions; and (j) use of coal inclusion geochemistry for indication of some diagenetic and catagenetic processes, and as a tool for stratigraphic correlation. The most part of the above studies performed during 1934–1972 were outlined in the monograph “Geochemistry of coal inclusions in sedimentary rocks” [Yudovich, Ya.E., 1972. Geochemistry of coal inclusions in sedimentary rocks. L.: Nauka [Leningrad: “Science” Pub. House], 84 pp.]. These materials are added to some recent work by Bulgarian and Russian geologists, performed with use of modern analytical methods. It has been shown that: (a) coalified wood may contain very exotic micro-mineral phases, sometimes far unexpected; (b) apart from Ge, coalified wood may contain high concentrations of some other trace elements, which were earlier not detected because of analytical limitations (REE, As, etc.). These special peculiarities can be partly contributed by epigenetic hydrothermal processes. As a summary, the review shows that coal inclusions are unique geochemical phenomenon, sharply different from even neighboring coal beds in trace element content. Among the most extreme elements is germanium, its mean concentration in the ash of coal inclusions being up to 220 times higher than in the ash of coal beds. The most important peculiarity of the coalified wood is the good preservation of the original lignin structures, which may effectively scavenge Ge from solutions, whereas peat-born coals (in beds) contained such structures in far fewer amounts. In addition, a reservoir of dissolved germanium in peat bog waters was of lower concentration than in sediments, which buried the coal inclusions. Finally, the peat bog acidic environment may act as an unfavorable factor. Ge-enrichment can be completed in a time ranging from a few thousand years up to tens of million years. However, if the waters are enriched in Ge, the process can proceed more rapidly and would be completed even under the most unfavorable parameters (compared to the model conditions). This implies that enrichment can take place during the early diagenetic stage. Such a scenario was supported by geologic considerations. Some Canadian and Soviet works performed from 1950 to 1960 along with some recent Russian studies show that Ge in coal inclusions can be of economic interest. Geochemistry and mineralogy of coal inclusions are of great interest and need further detailed study.

Secondary mineral phases associated with a historic arsenic calciner identified using automated scanning electron microscopy; a pilot study from Cornwall, UK

Historical polymetallic mining in Cornwall, UK has resulted in significant soil contamination. In particular the processing and refinement of arsenic in purpose built calciners has resulted in areas of localised, but extremely high contamination of soils with arsenic. Consequently, there is concern regarding the impact of this historic arsenic contamination on the local population. In this study automated scanning electron microscopy has been carried out to identify the phase distribution of arsenic within soil samples from: (a) adjacent to a calciner chimney, (b) adjacent to the calciner works and (c) for comparison, a sample of residue from the calciner dumps. Whilst the soil samples contain between 200 and 3325 ppm arsenic, the calciner residue contains approximately 12% arsenic. Although arsenopyrite is present in all the samples examined it is rare. Instead, the dominant arsenic mineral species present are As–Fe oxides which occur in a range of textural settings including: rims around coal, coke and fly ash particles; secondary phases infilling porosity with coal and coke particles; rims around silicate minerals and as a secondary phase cementing silicate grains and coal fragments together. In addition, in the sub 20 μm size fraction from the calciner residue samples up to 15% of the grains present are As–Fe oxides, and of these many of the grains are less than 10 μm in size and are potentially inhalable. These new data are significant in our understanding of the long-term dispersal of arsenic in the environment and its potential bioavailability.

AREIAS E LAGOAS DO PANTANAL, BRASIL: HERANÇA PALEOCLIMÁTICA?

The Pantanal basin, in the central-western South America, presents many surprising features such as the giant Taquari alluvial fan; the great number of ponds, many of them with alkaline brine waters, mainly in the southwest part of the Taquari fan; the countless fossil geomorphic features preserved in the surface of the fan. A mantle of white sands is associated with these features extending to the adjacent source areas. The main doubts that these characteristics pose may be summarized in one question: would the Taquari and other fans be a sedimentary construction of the current semi-humid climate, or would it represent one geohistoric moment of a semi-arid climate? In this case, the unstability of these constructions may be meaningful and relevant to environmental occupation and management. Several researchers have already investigated some aspects, such as geomorphic characteristic in radar images, grain size distributions properties, current sediment dynamics etc., lasting without answer the central subject on the recent past dynamics. The characterization of the geomorphic features in aerial panchromatic photographs, Landsat images, with field support, comparatively to radar images, allowed a progress in its characterization. The sediment properties associated with these geomorphic features as well as to correlative deposits in the source area, brought a new understanding of its paleoenvironmental meaning. Dating of coal fragments and shells by C14 method helped historical development. The white sands, generalized at the Pantanal, is typical of the last pre-current event of sedimentation; frequently show granulometric characteristic of eolic deposition although the analysis of geoforms does not allow the recognition of dunes. An important characteristic is the textural inversion, evidencing the mixture of population with different inherited attributes from the source area. However, the mixture of population does not explain the characteristics of distribution such as very selective grain size. For its time, the several types of ponds, incorporate an older group of selected features: deflation hollows, later flooded, forming salted pans, surrounded by eolian constructions (lunetes, spurs) and small terraced ridges (“cordilheiras”). These constructions are made up of white fine sands, with good sorting, that represent a testimony of eolian action. The remobilization of these sands previously worked, had been done by hidrologic flows in braided channels or in sheet floods, where the sediments were dispersed by crevasses and avulsion lobes, interfingering in the previous landscape, destroying it partially and building the lobes of the Taquari fan. The mantle of eolian white sands, that covers red paleolatosoils, either in the Taquari fan or in the adjacent areas, is interpreted as the record of an arid and cold paleoclimate, contemporary to the last glacial event in terminal Pleistocene. The eolian forms are relicts and they are largely obliterated by the restoration of alluvial fan systems. Because of high sedimentary charge due to the change in the pluviometric regime, the construction of depositional lobes was dominated by alluvial processes (braided channels, crevasses, avulsion lobes and sheet flows). This event, attributed to the climatic changes in the beginning of Holocene, has caused elevation of the regional phreatic level and formation of ponds in the remaining depressions of eolian deflation due to its isolation their waters became progressively brine. Great part of this landscape is progressively being destroyed by the current processes of tributary drainage (“vazantes “), established on the old lobes with partial reutilization of the previous distributary channel valleys.

Paleoenvironment and sea-level change in the early Cretaceous Barents Sea?implications from near-shore marine sapropels

The late Volgian (early Boreal Berriasian) sapropels of the Hekkingen Formation of the central Barents Sea show total organic carbon (TOC) contents from 3 to 36 wt%. The relationship between TOC content and sedimentation rate (SR), and the high Mo/Al ratios indicate deposition under oxygen-free bottom-water conditions, and suggest that preservation under anoxic conditions has largely contributed to the high accumulation of organic carbon. Hydrogen index values obtained from Rock-Eval pyrolysis are exceptionally high, and the organic matter is characterized by well-preserved type II kerogen. However, the occurrence of spores, freshwater algae, coal fragments, and charred land-plant remains strongly suggests proximity to land. Short-term oscillations, probably reflecting Milankovitch-type cyclicity, are superimposed on the long-term trend of constantly changing depositional conditions during most of the late Volgian. Progressively smaller amounts of terrestrial organic matter and larger amounts of marine organic matter upwards in the core section may have been caused by a continuous sea-level rise.

Anatomy of shelf deltas at the edge of a prograding Eocene shelf margin, Spitsbergen

Abstract Although shelf‐edge deltas are well‐imaged seismic features of Holocene and Pleistocene shelf margins, documented outcrop analogues of these important sand‐prone reservoirs are rare. The facies and stratigraphic architecture of an outcropping shelf‐edge delta system in the Eocene Battfjellet Formation, Spitsbergen, is presented here, as well as the implications of this delta system for the generation of sand‐prone, shelf‐margin clinoforms. The shelf‐edge deltas of the Battfjellet Formation on Litledalsfjellet and Høgsnyta produced a 3–5 × 15 km, shelf edge‐attached, slope apron (70 m of sandstones proximally, tapering to zero on the lower slope). The slope apron consists of distributary channel and mouth‐bar deposits in its shelf‐edge reaches, passing downslope to slope channels/chutes that fed turbiditic lobes and spillover sheets. In the transgressive phase of the slope apron, estuaries developed at the shelf edge, and these also produced minor lobes on the slope. The short‐headed mountainous rivers that drained the adjacent orogenic belt and fed the narrow shelf, and the shelf‐edge position of the discharging deltas, made an appropriate setting for the generation of hyperpycnal turbidity currents on the slope of the shelf margin. The abundance of organic matter and of coal fragments in the slope turbidites is consistent with this notion. Evidence that many of the slope turbidites were generated by sustained turbidity currents that waxed then waned includes the presence of scour surfaces and thick intervals of plane‐parallel laminae within turbidite beds in the slope channels, and thick spillover lobes with repetitive alternations of massive and flat‐laminated intervals. The examined shelf‐edge to slope system, now preserved mainly below the shelf break and dominated by sediment gravity‐flow deposits, has a threefold stratigraphic architecture: a lower, progradational part, in which the clinoforms have a slight downward‐directed trajectory; a thin aggradational zone; and an upper part in which clinoforms backstep up onto the shelf edge. A greatly increased density of erosional channels and chutes marks the regressive‐to‐transgressive turnaround within the slope apron, and this zone becomes an angular unconformity up near the shelf edge. This unconformity, with both subaerial and subaqueous components, is interpreted as a sequence boundary and developed by vigorous sand delivery and bypass across the shelf edge during the time interval of falling relative sea level. The studied shelf‐margin clinoforms accreted mostly during falling stage (sea level below the shelf edge), but the outer shelf later became estuarine as sea level became re‐established above the shelf edge.

A statistical evaluation on the correlations between thermal fragmentation of South African coal and coal characteristics

A statistical evaluation on the correlations between thermal fragmentation of South African coal and coal characteristics

Granulation of weak rock as a precursor to peperite formation: coal peperite, Coombs Hills, Antarctica

Peperite formed by mingling of magma with coal, and with fragmented coal plus other country rock, is exposed at Coombs Hills, Antarctica, in rocks of the Mawson Formation, where Ferrar Supergroup basalt encountered the Beacon Supergroup continental sedimentary succession. An internally laminated, 0.5-m-thick coal bed passes gradationally through a coal-fragment-dominated peperite into a glass-rich, basalt-dominated coal fragment–matrix peperite, and then into coherent basalt. Initial interaction of magma with water-saturated coal and host sediments locally brecciated the coal. Subsequent mingling of basalt with a slurry of coal fragments and water, driven by viscosity and density contrasts between the basalt and the slurry and by flow inhomogeneities in intruding magma, led to increasingly complex mingling of the two fluids via bifurcation of fingering viscous flows. This mingling was complicated by the participation of phases with time- and space-dependent thermal properties and viscosity (coal fragments, coal–water slurry, and basaltic magma), and the generation of multiple (?) gas phases through devolatilisation of heated coal. The initial elastic response of the coal fragments to stress resulted in: (a) fluidal mingling of coal and basalt facilitated by softening of coal during heating associated with intrusion; and (b) localised formation of blocky coal clasts during high stress events associated with passage of a liquid, and/or a gas phase(s), through the coal. The presence of fluidal- and blocky-shaped coal fragments in the coal peperite, with both curved and planar surfaces bounding single coal clasts, suggests that clast morphology in the magma–sediment dispersion was controlled at very small scales by the time-, temperature-, and stress-dependent qualities of the coal. Fluidal and blocky clast shapes in the coal peperite, coupled with vesicles in the coal clasts, suggest that transient properties of either the host or intrusion during non-explosive magma–sediment interaction may exert a strong control on clast morphology and mingling characteristics.

Development of an alternative laboratory method to determine thermal fragmentation of coal sources during pyrolysis in the gasification process

Lump coal may undergo fragmentation when exposed to high temperatures thus changing the particle size distribution of the coal [1]. Primary fragmentation occurs during devolatilization. In fixed-bed gasification, fragmentation may lead to a change in permeability of the coal bed resulting in non-ideal reaction conditions, where unstable gasifier conditions arise. The aims of this study were to quantify the degree of size degradation (primary fragmentation) and to use the data to optimize coal blends with respect to thermal fragmentation. It was found to be possible to quantify the degree of size degradation for a given coal source. The current experimental procedure was changed to achieve a substantial reduction in the time it takes for analysis; this alternative method taking only 2–3 h. Different coals gave significant differences in the amount of fragmentation they undergo. The amount of thermal fragmentation of non-caking coal under 2.6 MPa pressure can be predicted from the thermal fragmentation values obtained under atmospheric conditions.

フライアッシュ人工骨材の発泡機構 フライアッシュ人工骨材 （第２報）

To produce an artificial aggregate of stable quality, investigations of the expansion / sinter mechanism of coal fly ash are required. The purpose of this study is to clarify the influence of carbonecious substances on pellet expansion by firing, especially related to the atmospheric conditions. The study revealed two types of expansion. One relates to unburned coal fragments which exist separately from ash particles. In this case, large pores are formed around an oxidization front in the expanded pellet, accompanied by a macroscopic double - core structure in the sintered zone proceeding from outside. The other relates to very small coal fragment trapped in glassy spheres. Because the spheres in the pellet are distributed homogeneously, small pores are also inflated homogeneously with producing CO2 and CO. These gasses are generated by a reaction of the unburned coal fragments and oxygen in the glassy structure.

Lake sediment coring in South Greenland in 1999

The transition from the last ice age to the Holocene was a period of extremely rapid and large climatic changes (Björck et al. 1998). Because of this, the period has attracted much attention by Quaternary workers since these fluctuations were first demonstrated by Danish scientists (Hartz & Milthers 1901; Iversen 1934, 1954). In the ice-free parts of Greenland, many attempts have been made over the past few decades to find sediments from this transitional period. Some radiocarbon dates on marine molluscs from the late-glacial have been published, but most are based on conventional dating of several shells that might represent a mixture of Holocene and interglacial material. Conventional radiocarbon dating of lake sediments has also produced a number of ‘late-glacial’ dates, but where checked by accelerator mass spectrometry (AMS) radiocarbon dating, the sediments have proved to be Holocene (Björck et al. 1994a, b). These sediments contain ‘old carbon’ in the form of coal fragments and reworked interglacial organic detritus. In 1999 we tried a new approach to locate late-glacial lake sediments in Greenland. In southernmost Greenland, the shelf is narrow and the land area relatively small. Therefore the amount of glacierization during the Quaternary glacial stages must have been limited. In addition, this region is situated so far south in the North Atlantic that it must have been much influenced by the warming at 14,700 GRIP years BP (Björck et al. 1998). The southern location also means that the temperature conditions would allow a fairly rich plant and animal life to have become established rather early after recession of the ice. Sediment records from lakes located near sea-level at some distance from the outer coast extend back to the earliest Holocene (Fredskild 1973). Lakes situated at higher elevations might have become deglaciated earlier, when the Inland Ice thinned over the coast towards the end of the last ice age. Thus, in the 1999 programme we have sampled high-elevation basins, situated at 350–720 m above sea level (see Table 1). Basins situated in cirque valleys were avoided because it is possible that glaciers would have been present in such basins during the Little Ice Age. However, it turned out that most of the high-elevation basins investigated were devoid of sediments. Even at water depths over several tens of metres, the bottom consisted of stones and boulders and a good sedimentary sequence was only found in a single lake. For this reason, low-elevation basins as far away as possible from the present ice margin were also cored. In addition, it was decided to core a series of isolation basins at different elevations below the marine limit in order to establish a securely constrained curve for the relative shore-level change after the last deglaciation. Many such curves have been published from different parts of Greenland, but they are mainly based on mollusc shell dates which are much more uncertain than dates from isolation basins. The dated molluscs lived at various depths below sea-level and their relationship to the former sea-level is always uncertain. The locations of the cored basins are shown in Fig. 1 and short notes on the lakes are given in Table 1. This work is a continuation of the studies of recent years on lake sediments in South and West Greenland by the Geological Survey of Denmark and Greenland (Anderson & Bennike 1997; Overpeck et al. 1998; Anderson et al. 1999; 2000, this volume; Bennike 2000; Brodersen & Anderson 2000, this volume).

Influence of petrographic composition/organic matter distribution of fluvial aquifer sediments on the sorption of hydrophobic contaminants

Quaternary fluvial valley deposits form major groundwater reservoirs for the drinking water supply, which are at the same time favorable urban and industrialized areas where contamination of the aquifers and their sediments occurs frequently. The transport behavior of dissolved hydrophobic organic contaminants (HOC) depends on the sorptive interactions (sorption isotherms, sorption kinetics) with the sediment grains and therefore on the sediment history in terms of source rocks (lithocomponents), petrographic composition, and depositional processes (lithofacies, e.g. grain-size distribution). The geological formations present in the source rock area already determine the variability of lithocomponents and thus the sorption capacities for organic contaminants in the valley (aquifer) sediments since they show distinct differences in organic carbon content (Corg) and nature of organic matter (both influence the sorption behavior of hydrophobic organic compounds). In general, lithocomponents originating from sedimentary rock have higher Corg contents and thus higher sorption capacities compared to metamorphic and magmatic components, and the quartz and feldspar minerals. The petrographic composition of the samples is grain-size-dependent but very similar within a specific lithofacies. Higher fractions of sedimentary rock fragments occur in the gravel-dominated lithofacies, which therefore have higher sorption capacities. In contrast to this, the sand grain-size fractions (sand facies) are, due to decay and transport processes (sediment maturity), enriched in stable lithocomponents such as quartz minerals which consequently lead to lower sorption capacities for HOC. Attention has to be drawn to the impact of strongly sorbing constituents such as Tertiary coal fragments (local source rock area) present in some of the sand samples.

IMPACT OF COAL MASS STRUCTURE ON FRAGMENTATION DURING MINING AND PROCESSING

Coal fragmentation is a function of the material strength, lithotype bedding and banding, and fracture of a given seam and is induced through the application of energy during the mining and handling process. A large field and laboratory based project was designed to measure, model and understand this process so that tools can be developed to optimise fragmentation in the mining process. Field audits were conducted during which coal seams were characterised in situ and discrete parcels were mined blasted and free dug and then tracked through the handling and crushing stations. Samples of ROM, crusher product and breaker product and reject were sized and analysed for washability. The results show that the results of fragmentation can be linked to the inherent band size distribution of the coal. Band thickness distributions can also be used as an input to blast fragmentation models. The results also show that mining method does not significantly impact on the final size distribution of the ROM. However, it does impact significantly on downstream processing behaviour. Although size distributions of breaker product were similar for the blasted and free dug coals from the same block, the washability of the coarse and fine coal from each trial were significantly different.