Distribution Of Mineral Matter Research Articles

Effect of Sedimentary Facies Characteristics on Deep Shale Gas Desserts: A Case from the Longmaxi Formation, South Sichuan Basin, China

Shale gas is one of the hot spots of energy development. Due to the strong heterogeneity and low physical properties of shale gas reservoirs, and the complex influencing factors of pore development, it is necessary to conduct a comprehensive analysis of the control factors of high-quality reservoirs. The sedimentary characteristics, mineral composition, pore structure and controlling factors of high quality reservoir development are studied on the basis of thin section, scanning electron microscopy (SEM) and QEMSCAN analysis, X-ray diffraction (XRD), total organic carbon (TOC), Nano-CT scanning and Low-pressure N2 adsorption (N2GA) analysis on shale samples from the Longmaxi Formation in South Sichuan Basin. The results show the following: (1) According to lithology, sedimentary structure, organic carbon content and mineral composition, six sedimentary microfacies can be divided. (2) Organic matter pores are developed in organic-rich siliceous shale and organic-rich silty shale at the bottom of the first member of the Longmaxi formation, with average porosity of more than 5% and permeability of more than 2 × 10−3 μm2, which is conducive to the formation of high-quality shale gas reservoirs. (3) The contents of siliceous and TOC are positively correlated with porosity and specific surface area, while the contents of carbonate and clay minerals are negatively correlated with reservoir quality. (4) In the first member of the Longmaxi formation, the sedimentary water depth becomes shallower from bottom to top, and the sedimentary environment changes from a reduction to an oxidation environment. The contents of siliceous and organic matter decrease, while the contents of clay minerals and carbonate minerals show the opposite trend. The difference in sedimentary microfacies affects the distribution of mineral and organic matter and controls the heterogeneity of the shale reservoir.

Nano-scale physicochemical attributes and their impact on pore heterogeneity in shale

Heterogeneity in shale due to distribution of mineral and organic matter controls the disposition of pores in them. While the effect of vertical anisotropy is accounted for most cases of porosity estimation, the effect of bedding parallel heterogeneity is often ignored. This study dives deep into the shale fabric using bedding parallel sections, and the pore volume distribution is estimated in shales of varying thermal maturity and organic carbon content (2.6% − 38.2 %). Three among the five shales used in this study are early mature (Tmax: 439–444 °C), whereas the remaining two are over-mature, signified by very high S4Tpeak (670–685 °C). The higher thermal maturity indicates thermal alteration induced by igneous intrusion. The pore volume, functional groups, and organic matter distribution are systematically derived in different positions of the bedding parallel section using a combination of 3D imaging, spectroscopy, small-angle scattering and low-pressure gas adsorption techniques. These spot-specific properties are further compared with bulk properties to quantify the extent of heterogeneity. It is observed that the over-mature shales with higher aromaticity contain 150–200% more bulk accessible pore volume than the lesser-mature shales. It is also evident that the smaller mesopores (∼10 nm pore width) are more inaccessible compared to their coarser (∼20 nm pore width) counterparts. Higher matured shales show increased inaccessibility of mesopores up to 228 % due to bitumen deposition in pores during thermal maturation, resulting in a sharp decline in mesopore surface fractal dimension. The uniformity of the functional group and organic matter distribution in different parts of the shale depends on the maturity, and reflects the extent of variation in pore volume across the specimen. The 3D tomography-derived spatial abundance of organic matter in over-mature shales show higher deviation (±15-20%) from the average than lesser-mature shales (5–10%). This study proposes a multiscale methodology which can evolve and develop as a protocol for systematic, reservoir-scale maturity-dependent heterogeneity quantification in gas-shales.

Late Pleistocene cryogenesis features of a loess-paleosol sequence in the Srednyaya Akhtuba reference section, Lower Volga river valley, Russia

Permafrost is considered to be one of the important sources of additional water for the vast Late Quaternary Caspian Sea transgressions. The insufficiency of proxy evidence on landscape and climate dynamics during the long Atelian regression (MIS 4 – MIS 3) complicates the analysis of changes in the Caspian water balance. Traces of Late Pleistocene cryogenesis structures were catalogued in the alluvial and loess-soil deposits of the Srednyaya Akhtuba reference section. Four stages of permafrost development were described for the first time in the Lower Volga region. Under conditions of seasonal and longer-term freezing in the Late Pleistocene, cryogenic transformation of the deposits took place; this determined the composition, structure and properties of the loess-paleosol complex at the site. Cryolithological, micromorphological analyzes and particle size distribution of mineral matter were carried out for each horizon, and traces of cryogenic processes were described in order to evaluate the regional paleoclimatic conditions that prevailed during their formation. Optically stimulated luminescence dating was used to establish a chronological framework for the main phases of the development of cryogenic modification in the Lower Volga region. The fourth stage of formation involved deep cracking of the substrate, which occurred during freezing in MIS 4, coincident with the Atelian regression of the Caspian Sea. The third stage is expressed as large wedge-shaped structures (pseudomorphs) on the border of loess and alluvial packages, with their formation known to be associated with the degradation of ice wedges. During the second and first stages of freezing, plastic deformation of deposits occurred.

Characterization of Chemical Structure with Relative Density of Three Different Ranks of Coal from India

A comparative study of coals of different ranks having different chemical structure and petrography would be desirable to gain an in-depth knowledge of Indian coals. Here, we report structural and petrographic analyses of three different coals: Coal A (coking coal), Coal B (semi-coking coal) and Coal C (non-coking coal) of Indian origin. The vitrinite reflectances of the three coals were measured to be 1.26, 1.38 and 0.46 for Coal A, Coal B and Coal C, respectively. Size fractionation (− 3.0 + 1.0 mm, − 1.0 + 0.5 mm and − 0.5 mm) followed by density gradient separation (1.2, 1.3, 1.4, 1.6, 1.8 g/cm3) were performed for all the coal samples to study mineral matter liberation and distribution of macerals in different density fractions. Petrographic analysis of different density fractions revealed a direct proportionality of vitrinite content to swelling properties. The highest free-swelling indices (7.5 and 6.5) were observed for 1.2 density fraction of Coal A and Coal B, respectively. Fourier transform infrared spectroscopy revealed crucial information relating the degree of aromaticity and aliphaticity with observed coking properties. Specifically, aromaticity (AR1) (CHar stretching/CHal stretching, (3000–3100 cm−1)/(2800–3000 cm−1) and mean reflectance (Ro in %) were found to have a strong positive linear correlation with each other, indicative of an increase in aromaticity with coal rank.

Mineralogical Study of Beneficiated and Carbonized Indian Coking Coal for Better Utilization: A Case Study

Coking/metallurgical coal is one of the essential raw materials for steel industries. The metallurgical coal in India contains high ash content (mineral matters), is rich in inertinite, and requires optimization before its proper utilization. Distribution of mineral matter in coking coal plays a significant role in achieving the desired product for blast furnace and coke-making operations. The present paper reports a case study on the distribution and nature of mineral matter in Indian coking coals at varying densities with respect to the coal’s beneficiation behavior. The maceral analysis indicated the maximum liberation of reactives at the relative density (RD) of 1.2–1.3 g/cm3 while maximum inerts concentrated at the highest density (RD > 1.8 g/cm3). The most dominating mineral matter found in the coal is argillaceous minerals containing substantial amounts of quartz followed by carbonate and sulfides existing as cavity fillings or in disseminated form. X-ray diffraction (XRD), X-ray fluorescence (XRF), and electron-probe microanalysis (EPMA) techniques were used to study the mineral distribution and transformation behavior of coke produced from the coking coal during carbonization process. A case study on the reactivity of dispersed mineral matter in coke and the implication of mineral transformation behavior on coke is also discussed in this paper.

Mineral matter and trace elements in ashes from a high-arsenic lignite fired power plant in Inner Mongolia, China

The distribution, enrichment, and environmental influence of trace elements and mineral matter in fly ash (FA), bottom ash (BA), and flue gas desulfurization gypsum (FGDG) from a high arsenic coal-fired power plant in Inner Mongolia, China were studied by X-ray diffraction spectrometry (XRD), X-ray fluorescence spectrometry (XRF), field scanning electron microscopy equipped with energy dispersive X-ray spectrometry (FSEM-EDX), atomic fluorescence spectroscopy (AFS), and inductively coupled plasma-mass spectrometry (ICP-MS).The results showed that mineral matter in FA included quartz, mullite, and gypsum, and that in BA included quartz, enstatite, magnetite, and hematite. The arsenic content in the lignites reached 44.4 μg/g, which was much higher than the global average content of lignite. Most of the trace elements in lignite, except for Mo, Sb, and W, had enrichment trends in the fine grade samples. Arsenic is a toxic element enriched in FA compared with the world lignite ash, while there are several elements of environmental concern are depleted elements (Mo, Cd, Ba, and U). The Cs and Hf are also enriched elements in FA, where Hf showed a significant enrichment. The contents of most trace elements in the smaller particles of FA were higher than those in the larger particles, except for Y and Re. The arsenic content in BA was evidently lower than that in FA, which was 24.4 μg/g, and the trace elements enriched in the smaller particles of BA included Li, Zn, Ga, Rb, Mo, Cd, In, Sb, Cs, Nd, Tl, Pb, Bi, and Th. With the exceptions of As, Sr, Cd, and Sb, the amount of trace elements in flue gas desulfurization gypsum was much lower than that in average Chinese soil. Because the fly ash was stacked for a long time, arsenic and several other trace elements leached into soil surrounding the fly ash dump. As a results the elemental content of old fly ash is less than those collected in this study, which indicates the soil in vicinity need to be monitored continuously for their possible environmental effect.

Study of microstructure, maceral and mineral matter in two different coals of the Nepal Himalaya

The Eocene coals from the western (Tosh coalfield) and central regions (Jhadewa coalfield) of the Nepal Himalaya have been studied under the petrological and the Scanning Electron Microscopes to explain the mode of occurrence of mineral matter and their microstructural relations with organic constituents. As shown by the results of the coal samples, three kinds of coals in diminishing abundance are moderately dull coal, moderately bright coal and bright coal. Distribution of mineral matter in the Eocene coals shows that the bright coal is rare in western Nepal and the moderately bright coal is abundant in central Nepal. Mineral matter in moderately dull coals contains superficial impregnating and cavity filling. Mineral matter in bright coals contains superficial mounting and pore fillings, but in moderately bright coals contains superficial impregnating, cavity filling, and intimate intergrowth. Mineral matters in
 moderately dull coals, moderately bright coals and bright coals respectively range from 38.27 to 47.12 vol%, 12.31 and 15.73 vol%, and 12.31 and 15.73 vol%. The Jhadewa coalfield (central Nepal) contains more macerels than the Tosh coalfield (western Nepal), whereas the Tosh coalfield contains more mineral matter than the Jhadewa coalfield. The results indicate two different origins for coal deposits from two different regions.

Mineral occurrence and its impact on fracture generation in selected Qinshui Basin coals: An experimental perspective

The effect of mineral matter on the fracture evolution was investigated for Lower Permian and Upper Pennsylvanian coal samples from the Qinshui Basin of China. Optical microscopy, scanning electron microscopy with energy dispersive X-ray spectrometry (SEM–EDS), and X-ray computed tomography (X-ray CT) were used to investigate the composition and modes of occurrence of minerals within the coals and to characterize the natural and induced fractures present within the samples. The spatial distribution of mineral matter investigated by X-ray CT demonstrates that the variation of mineralization within the cleats/fractures occurred at fine scales, and most of minerals were scattered in coal core samples. The original fractures normally were present as two sets: one set was almost parallel to the bedding plane, and the other was almost perpendicular to the bedding plane. For created fractures, the difference in density between the matrix and mineral matter may weaken the cohesion of coals, and it could explain why the created fractures propagate along the junction of minerals and organic coal matrix. The internal fracture porosities varied from 0.06% to 20.69%, which indicates a strong internal heterogeneity of the coals after a stress is applied. The inclination of the main shear fractures ranges from 55° to 95°. Using energy analysis, the fracture energy appears to represent nearly half of the total dissipated energy, which can be correlated with the fracture density and orientation. The formation and distribution of shear fractures is related to the spatial distribution of mineral matter and the overall mineral content. These investigations serve to characterize hydro-fracturing and pulverized coal generation during coalbed methane development.

Microstructural Relation of Macerals with Mineral Matter in Eocene Coal

Scanning electron micrography of unpolished lithotype of coal samples from coalfields of Meghalaya shows a wide variation in distribution of mineral matter in them. It is abundant in moderately dull coal, less abundant in moderately bright coal, and rare to very rare in bright coals. Its order of abundance in individual lithotypes may be put as: ‘moderately dull coal’ > ‘moderately bright coal’ > ‘bright coal’. There exists a specific micro-structural relation between mineral matter and the coaly substance. In the moderately dull coal, mineral matter occurs as superficial impregnation and cavity filling; in moderately bright coal as superficial impregnation, cavity filling, and intimate intergrowth; and in bright coals as superficial mounting and pore fillings.

Quantitative chemical profiling of coal using core-scanning X-ray fluorescence techniques

A study has been carried out to test the possibility of measuring detailed quantitative profiles of the abundance of different inorganic elements through exploration cores of coal seams using automated energy-dispersive X-ray fluorescence (ED-XRF) core scanning instrumentation. Such an approach has potential application for rapidly determining the distribution of mineral matter in a coal seam, identifying horizons at which particular elements (such as phosphorus) may be concentrated, evaluating in detail the relationships between different elements in the coal, and maximising the data available to guide broader-scale sampling for conventional analysis programmes.Profiling was carried out on a series of segments from a 60mm diameter core of the Goonyella Middle seam in the northern Bowen Basin of Queensland, using an Itrax core scanner (Cox Analytical, Sweden). The scanning process included high resolution optical imaging, X-radiography, and ED-XRF spectroscopy covering the principal major elements, with XRF spectra being obtained at intervals of 200μm along the axis of each core. A series of calibration curves derived from separately-scanned pressed pellets of reference coals was used to determine the concentration of each element for each step in each sample, allowing a set of quantitative element profiles to be created for each core segment. These were evaluated in conjunction with the relevant X-radiographs and optical images to provide an integrated basis for assessing the variations in inorganic element characteristics through the core sections. The results were also compared to conventionally-determined chemical and mineralogical data for a representative core, to confirm the validity of the quantifications developed.

Seasonal dynamics of suspended matter in waters of Lake Khanka

Outline maps of the distribution of suspended mineral matter in the waters of Lake Khanka are constructed from the summer, spring, autumn, and winter observation results. The analysis allows distinguishing seasonal variations in the distribution of suspended mineral matter over the lake water area and shows that the lake ecosystem functions under conditions of an uninterrupted annual cycle of suspended matter concentration.

Comparative evaluation of the mineralogical composition of Sphagnum peat and their corresponding humic acids, and implications for understanding past dust depositions

With 6.5 m of peat accumulated during the past ca. 15,000 years, Etang de la Gruère (EGr) represents the longest continuous record of atmospheric dust deposition in northern hemisphere. This paper presents a comparative study of the mineralogical composition of Sphagnum peat samples and their corresponding humic acids (HA) from a peat core collected at EGr bog. The purpose of this study was to better understand the dominant process responsible for the amount and distribution of mineral matter in ombrotrophic (i.e., rain-fed) peat. Specifically, the goal was to separate the relative importance of the changing rates of atmospheric mineral dust deposition (during the past two millennia) from the mineralization of organic matter (OM), for the distribution of the ash fraction of the peat profile.The results suggest that variations in ash content at EGr are mainly the result of an increase in the rate of supply of dust particles and cannot be attributed simply, or exclusively, to differences in the degree of OM decay: evidence is provided by both acid insoluble ash (AIA) profiles and the correlations among lithogenic elements (Al, Si, Ti, Y, and Zr), total ash content and AIA. Moreover, our findings suggest that part of the AIA occurring in peat extremely is stable, and is unaffected by the extreme chemical conditions used to extract the HA fraction: this may be partly due to the inherent stability of quartz and “heavy minerals” such as zircon and rutile, but organic coatings developed on mineral surfaces during peat diagenesis, or the formation of some other kind of organo-mineral complex, might also play a role. Consequently, testimonies of past dust depositions can be observed also into the recalcitrant HA fraction of the peat.

Physical and Chemical Characterization of Coal Particles Used as Entrained Flow Gasifier Feedstock: Heterogeneity in Mineral Matter Distribution

Several challenges still exist in successful and reliable operation of entrained flow slagging gasifiers (EFG) using coal as a fuel. The formation of flyash and its carryover with the gas stream causes fouling and plugging of syngas coolers, leading to reduction in heat rate and overwhelming of the solids handling systems. In order to predict flyash formation as well as carbon loss in an EFG, a thorough understanding of the effect of feedstock properties on fuel conversion rates during gasification is required. Current state of the art in gasification modeling treats coal as a homogenous material although it well known that coal is heterogeneous. Different classes of particles, when fed into an EFG, behave differently in terms of carbon conversion and mineral transformations. Therefore, it is critical to develop modeling tools that can incorporate physical and chemical characteristics of the feedstock and the effect of the operating conditions on particle transformations, in order to predict fate of the char/ash particles generated in the gasifier. During the grinding of coal, macerals and minerals separate due to mineral liberation. When subjected to gravity fractionation, the liberated minerals tend to accumulate in heavier density particles. Various physical and chemical characterizations are performed on size separated particle classes of the four gravity fractions with an aim to bring out the heterogeneity in the coal and its impact on conversion. Characterization indicated that almost all of the gasifiable matter is present in the two lighter gravity fractions and bulks of the minerals are present in the two heavier gravity fractions. The mineral matter was characterized and quantified using ash yield measurements, X-ray fluorescence, X-ray diffraction, Computer Controlled Scanning Electron Microscopy (CCSEM) and the iron minerals were measured using Mossbauer spectroscopy. Characterization results show the heterogeneity across the coal in multiple chemical components and prompt the need to account for heterogeneity in models.

Processing of fine particles using closely spaced inclined channels

A Reflux Classifier consists of a set of parallel inclined channels above a conventional fluidised bed. Recently Galvin et al. (2009, 2010) [3,2] discovered a new and powerful separation mechanism for elutriating particles on the basis of density, utilising closely spaced channels. This arrangement suppresses the effects of particle size, thus promoting the effect of particle density. A series of particle fractionation experiments was conducted in this study to examine the effects of the channel spacing. Inclined channel spacings of 1.77, 4.2, 7, 9, and 18 mm were used in the work. A continuous distribution of coal and mineral matter, consisting of particles in the size ranges from 0.25 to 2.0 mm and 0.038 to 0.25 mm were used, with the particle density ranging from 1275 to 2600 kg/m 3. The results demonstrate the benefits of the new separation mechanism, with greatly improved fractionation achieved using the more closely spaced channels.

Unburnt carbon from coal fly ashes as a precursor of activated carbon for nitric oxide removal

The aim of this work is to evaluate the characteristics of an activated carbon obtained from unburnt carbon in coal fly ashes to be used in the removal of NO. Carbon-rich fraction was obtained by mechanical sieving of fly ashes. The mineral matter was removed by conventional HCl and HF demineralization procedure. Activation was carried out with steam at 900 °C in order to develop porosity onto the sample. Characterization of samples was performed by several techniques with a main objective: to follow the mineral matter content, composition and distribution on the samples in order to better understand how to remove it from unburnt carbon in fly ashes. To study the use of this unburnt carbon as a precursor for the preparation of activated carbons for gas cleaning, the NO removal by ammonia using activated carbon as a catalyst at low temperature was performed. Results show a good performance of activated carbon in this reaction that is in relationship with BET surface area.

Influence of petrographic and mineral matter composition of coal particles on their combustion reactivity ☆

Combustion at programmed temperature in a thermobalance is a rapid technique, which monitors coal burning characteristics and has shown its utility to classify coals according to their combustion performance. However, combustion profiles are affected by different coal properties and characteristics such as particle size, rank, maceral composition and mineral matter content, whose separate effects are difficult to determine. The objective of this work was to ascertain the influence of coaly and mineral matter composition and distribution on burning profiles as determined by thermogravimetric analysis, by using coals of different rank, and fractions of these coals obtained by density separation. Five coals ranging in rank from lignite to anthracite and with variable mineral matter content and composition were used in this study. Density fractions were separated from each coal to obtain samples with different organic/mineral matter proportions. Some of the factors influencing coal combustion profiles are widely recognised as the negative effect of increasing both rank and inertinite content on the reactivity. The favorable effect of mineral matter content on the reactivity has shown to be related to the maceral size within the density fractions and the intimate association organic/mineral matter that favors the diffusion of the reacting gas. Catalytic effects of the mineral matter could not be demonstrated.

Mineral Matter Distribution on Coal Surface and Its Effect on Coal Wettability

Coal is an organic sedimentary rock composed of organic macerals and mineral matter. As it is demonstrated in this paper the discrete mineralogical nature of coal largely influences the wetting of the coal surface by water. Both advancing and receding contact angles were measured using the captive-bubble technique with an automatic bubble shape analysis software. The distribution and amount of mineral inclusions on the coal surface were determined by scanning electron microscopy and examined using the image analysis system. To determine the amount and size distribution of mineral grains, the coal surface layer, on which the contact angles were measured, was separated from the larger piece used in the measurements by microslicing. The separated surface layer was subjected to a low-temperature ashing followed by particle size analysis. As expected, a significant scatter of contact angle values was obtained for the same coal samples. Increasing the amount of mineral matter on the coal surface reduced the value of both advancing and receding contact angles. Also, the scatter of contact angle values increased with the increasing mineral matter content from about 1 to 50 wt%. The results reveal that an important factor in analysis of contact angle variation on coal surfaces is the size of the hydrophilic mineral inclusions. Both the advancing and the receding contact angles decrease with increasing size of the mineral grains. Additionally, the scatter of contact angle values increase with increasing size of the mineral matter grains. Finally, the results of fractal dimension analysis of mineral matter grains distributed over the coal surface indicate that there is no significant effect from the shape of hydrophilic mineral inclusions on both advancing and receding contact angles.

Geochemistry, mineralogy, and technological properties of the main Stephanian (Carboniferous) coal seams from the Puertollano Basin, Spain

This study is focused on the occurrence and distribution of mineral matter and major and trace elements in the high volatile bituminous coal from Puertollano (south-central Spain). The relationship between ash behaviour and inorganic composition, as well as the possible formation of fouling and slagging deposits in boilers during the conversion process, were investigated. The Puertollano coals do not exhibit plastic properties, despite their rank, probably because of their high ash and inertinite contents. The Puertollano coal has medium to low total S content (0.48% to 1.63% db, with a mean of 1.0% db) and is characterised by relatively high contents of Si, Pb, Sb, and Cs. Some elements such as As, Cd, Co, Cr, Cu, Ge, Li, Mn, Ni, W, and Zn are also present in relatively high contents. The enrichment in a number of heavy metals could be attributed to the common sulphide ores occurring near the Puertollano coal deposit. The following trace elements affinities are deduced: (a) sulphide affinity: As, Co, Cd, Cu, Ni, Sb, Tl, and Zn; (b) aluminum–silicate affinity: K, Ti, B, Co, Cr, Cs, Cu Ga, Hf, Li, Nb, Rb, Sn, Ta, Th, V, Zr, and LREE; (c) Carbonate affinity: Ca, Mg, Mn, and B; (d) organic affinity: B. The very high Si levels and the anomalous enrichment in Cs, Ge, Pb, Sb, and Zn shown by the Puertollano coals account for the high contents of these elements in the Puertollano fly ash when compared with the other Spanish coal fly ashes. The chemical composition of the high temperature ash (HTA) is consistent with the trend shown by the ash fusion temperatures (AFT) and also with the predictive indices related to slagging and fouling propensities. Thus, the ash fusion temperatures increase with high values of Al 2O 3 as well as with the decrease in Fe 2O 3, CaO, and MgO.

529 Relationship of Soil Temperature, pH, and Organic Carbon Content to Nitrogen Release in Cranberry Soils

Soluble nitrogen (ammonium and nitrate) is released when soil organic matter is mineralized. The amount of N released by this process depends on the amount of organic matter present and soil temperature. Cranberry (Vaccinium macrocarpon Ait.) grows in acidic soils with a wide range in organic matter content. To evaluate how soil N release is affected by soil temperature, intact soil cores were collected from sites that had received no fertilizer and placed in PVC columns. Four different soil types, representing the range of cranberry soils (sand, sanded organic soil, peat, and muck), were used. Each column was incubated sequentially at six different temperatures from 10 to 24 °C (2.8 °C temperature intervals) for 3 weeks at each temperature, with the soils leached twice weekly to determine the amount of N release. The total amount of N in leachate was highest in organic soils, intermediate in the sanded organic soil, and lowest in the sands. The degree of decomposition in the organic soils was important in determining which form of N predominated. In the more highly decomposed organic soil (muck), most of the N was converted to nitrate. The data from this study resulted in the development of two models—one predicting the N mineralization and the other predicting the proportion of N in each of the two forms. Key factors for N release rate were soil temperature, percentage of clay, and organic carbon content. For predicting the proportion of N as ammonium vs. nitrate, key factors were soil temperature, soil pH, and the distribution of mineral matter in the silt and sand fractions.

98/02638 Mineral matter and trace elements distribution in Mesozoic coals from Peru: Carrascal Miranda, E. R. et al. DGMK Tagungsber., 1997, 9702, (Proceedings ICCS '97, Volume 1), 413–416.

98/02638 Mineral matter and trace elements distribution in Mesozoic coals from Peru: Carrascal Miranda, E. R. et al. DGMK Tagungsber., 1997, 9702, (Proceedings ICCS '97, Volume 1), 413–416.