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Silicic, mafic and alkali intra-seam tonsteins have been known from SW China for a number of years. This paper reports on the geochemical compositions of coals and tonsteins from three seam sections of the Songzao Coalfield, SW China, and evaluates the geological factors responsible for the chemical characteristics of the coal seams, with emphasis on the influence from different types of volcanic ashes. The roof and floor samples of the Songzao coal seams mostly have high TiO2 contents, consistent with a high TiO2 content in the detrital sediment input from the source region, namely mafic basalts from the Kangdian Upland on the western margin of the coal basin. The coals from the Songzao Coalfield generally have high ash yields and are highly enriched in trace elements including Nb, Ta, Zr, Hf, rare earth elements (REE), Y, Hg and Se; some variation occurs among different seam sections due to input of geochemically different volcanic ash materials. The geochemistry of the Songzao coals has also been affected by the adjacent tonstein/K-bentonite bands. The relatively immobile elements that are enriched in the altered volcanic ashes also tend to be enriched in the adjacent coal plies, possibly due to leaching by groundwaters. The coals near the alkali tonstein bands in the Tonghua and Yuyang sections of the Songzao Coalfield are mostly high in Nb, Ta, Zr, Hf, Th, U, REE and Y. Coal samples overlying the mafic K-bentonite in the Tonghua section are high in V, Cr, Zn and Cu. The Datong coal, which has neither visible tonstein layers nor obvious volcanogenic minerals, has high TiO2, V, Cr, Ni, Cu and Zn concentrations in the intervals between the coal plies affected by mafic and alkaline volcanic ashes. This is consistent with the suggestion that a common source material was supplied to the coal basin, derived from the erosion of mafic basaltic rocks of the Kangdian Upland. Although the Songzao coal is generally a high-sulfur coal, most of the chalcophile trace elements show either poor or negative correlations with total iron sulfide contents. The absence of traditional pyrite-metal associations may reflect wide variations in the concentrations of these elements in individual pyrite/marcasite components, or simply poor retention of these elements in the pyrite/marcasite of the relevant coals. [ABSTRACT FROM AUTHOR]

This paper reports the mineralogy and geochemistry of the Late Permian C1 Coal from Bole and Laibin mines in eastern Yunnan, Southwestern China (C1 Coal in Laibin mine is composed of three layers termed B1, B2, and B3). The coals are characterized by medium-high ash yields and very low sulfur contents. Compared with average values of trace element concentrations in hard coals worldwide, the Bole and Laibin coals are enriched in V, Co, Cu, Zn, and Se, which were mainly derived from the sediment-source region of the Kangdian Upland. Major minerals in the coal samples and roof and floor strata include quartz, interstratified berthierine/chamosite (B/C), as well as kaolinite, mixed layer illite/smectite, calcite, pyrite, and anatase. Unlike a pure chamosite, the 7 Å peak of interstratified B/C is sharp and narrow, while the 14 Å peak is broad and weak, or absent in some coal samples. Interstratified B/C was largely precipitated from low-temperature Fe-rich and Mg-rich hydrothermal fluids or, in some cases, is an alteration product of kaolinite. Secondary phases of quartz, calcite, pyrite, kaolinite, chalcopyrite, gypsum, and REE-phosphates in the coal samples are the dominant authigenic minerals formed at syngenetic and early diagenetic stages. Four intra-seam partings in C1 Coal, B1, and B3 layers are identified as tonsteins derived from felsic volcanic ashes. These tonsteins consist mainly of cryptocrystalline kaolinite with graupen and vermicular textures, and minor amounts of high-temperature quartz, zircon, apatite, monazite, and anatase. The floor of the C1 Coal in the Bole mine is a tuffaceous claystone and consists of altered high-Ti basalt volcaniclastics, characterized by high concentrations of Zr, Nb, V, Co, Cu, and Zn, low Al2O3/TiO2 ratio (~4.62), high Ti/Y ratio (~900), enrichment of middle rare earth elements, and positive Eu anomalies. [ABSTRACT FROM AUTHOR]

Plant growth requires a complex network of arbuscular mycorrhizal (AM) fungi and bacteria to supply organic compounds and major (C, N, P, etc.) and trace nutrients to the roots. Hyperaccumulation by certain plant species is based on the threshold 'maxima' a plant can safely ingest/absorb an element from soils without tissue damage. The latter criteria for hyperaccumulation vary between elements. The amount of an element a plant can absorb depends both on the ability of the species to uptake the element and on the element concentrations and bioavailability in the substrate. A plant growing directly on a mineral-rich substrate or a short height above the soil should be able to access inorganic matter via the roots. In contrast, a plant capable of accumulating inorganic elements, but growing on a peat without direct root contact with the inorganic soil fraction, would suffer a dearth of mineral nutrients. Partitioning of elements occurs within hyperaccumulators. For example, the preferential binding of heavy rare earth elements (HREE) to organic ligands leads to the relative enrichment of HREE in aerial plant structures. The presence of hyperaccumulators in a wide range of present-day plant species suggests that this mechanism was present among peat-forming plants in the fossil record. Examples from peats through low-rank coals to high volatile A bituminous coals show that hyperaccumulation provides a viable hypothesis for the consequent enrichment of certain elements. Complications from the depositional history and diagenetic alteration of the peat; metamorphism and mineralization through the history of the coal; and, not the least, the problems implicit in sampling suitable intervals in working mines, cores, natural exposures, etc., present problems in the extrapolation of the modern plant mechanisms to coals. Coal represents natural settings and, apart from Miocene and younger coals produced from vegetation with known relatives in modern setting, we cannot experiment on the ancient plants. The analogies between the geochemical appearance of coals and the element uptake and partitioning behavior of modern plants, however, does offer hope that hyperaccumulation might have been a mechanism, potentially one of many mechanisms, for the organic associations of inorganic elements in coals. • Hyperaccumulation varies between elements and between plant species. • Certain plants are known to be accumulators of rare earths and other elements. • Partitioning of REE occurs in the transfer from the roots to shoots to leaves. • Low-rank and high volatile bituminous coals exhibit complex element associations. • Certain REE patterns in coals resemble those seen in translocations in modern plants. • Uncertainties in modern plants and coals comparisons are challenges in studies. [ABSTRACT FROM AUTHOR]

A ternary Ce/Rb – (Tb/La)*100 – (Ba/Nb)/5 plot proposed here for classifying ocean island basalts (OIB) is considered as a reliable and robust approach not only for identifying the geochemical affinities of their mantle source regions, but also for appraisal of their source region lithologies. Sr-Nd-Pb-Hf-He isotopic ratios are traditionally regarded as the most reliable means for the classification of OIBs. However, these are not as easily nor quickly obtained as trace elements analyses. Therefore, the ternary plot proposed here is regarded as a suitable equivalent for the classification of OIB end-members using trace elements alone. The ternary Ce/Rb – (Tb/La)*100 – (Ba/Nb)/5 plot was tested by a screened OIB global data set for which the geodynamic settings were recognized based on their isotopic data. It provided precise, sharp boundaries for HIMU, EMI, EMII, and DMM affinities of OIB that correspond with their isotopic counterparts, indicating that these trace element ratios are controlled by their source regions and settings. The ternary plots also identify the geochemical affinity of the source mantle regions for intraplate continental basalts. Mantle geochemical affinity and lithology of source region suggested by the present ternary model are also comparable with the mantle source characteristics and lithology based on the studies of olivine phenocrysts hosted by unmodified OIB. [Display omitted] • Ce/Rb, Tb/La and Ba/Nb furnish a reliable classification for OIB mantle endmembers. • The OIB systematics based on trace element ratios evaluates source lithologies. • OIB classification using the trace elements is as accurate as the isotopic scheme. • The proposed model revive discussion in the trace elements behavior in the mantle. • The OIB systematics is a venue to investigate crustal trace element contribution. [ABSTRACT FROM AUTHOR]

The leaching behavior of trace elements in five fly ashes from five Chinese coal-fired power plants were obtained by conducting the new US EPA leaching test methods (LEAF) and the conventional EPA Toxicity Characteristic Leaching Procedure (TCLP) test method. These were done under a range of pH values and liquid to solid ratios. Despite different elemental and mineralogical compositions of the ashes and different ranks of the respective feed coals, the majority of elements show similar liquid/solid partitioning (LSP) curve trends among the different ash samples in the pH-dependent leaching tests. This indicates that most elements are sensitive to changes in pH. Different LSP curves exist for Cr from pH-dependent tests, probably due to different valence states of this element in the unleached fly ashes. Although most elements show similar LSP curves for different fly ash samples from the liquid/solid (L/S) dependent tests, variation exists for LSP curves of some individual elements among different ash samples. Caution should be taken when generating general L/S dependent leaching characteristics for individual elements. The leachate concentrations of the highly soluble elements such as B and Se, as well as oxyanions under alkaline conditions, are dependent on their initial concentrations in the fly ashes. The conventional EPA method TCLP overestimates the leachability of most hazardous elements, such as Be, B, Co, Ni, Cu, Zn, Cd, Sb, and U, at least in the studied alkaline fly ashes. LEAF tests have the advantage of being a comprehensive evaluation of the leaching characteristics, with a range of pH and L/S allowing for the examination of leachability under various conditions at different disposal or beneficial use scenarios. • the US EPA LEAF and TCLP test methods were conducted on five Chinese fly ashes. • pH plays the most important role in controlling element leaching activities. • The leachate con-cen-tra-tions of highly soluble elements are controlled by the concentrations in the fly ashes. • The rank of feed coals does not obviously affect the leachability of the fly ashes. • Caution should be paid to some elements (e.g., Se, Mo and Sr) that showed their maximum leaching under alkaline conditions. [ABSTRACT FROM AUTHOR]

Coal, one of the most complex geological materials, consists of organic and mineral matter, the latter including crystalline minerals, non-crystalline mineraloids, and elements with non-mineral associations. Overall, the modes of occurrence of elements in coal are classified into organic, mineral, and intimate organic associations, the latter including those adsorbed on to the surface of organics, dissolved in pore waters, and hosted in very fine-grained minerals (sub-micro- or nano-minerals) encased in or shielded by the organic matter of coal. Mineral associations, defined as elements associated with minerals are straightforward; however, confusion about organic and intimate organic associations of elements usually arise in the literature. Understanding organic, mineral, and intimate organic associations of elements is important not only because non-mineral elements and, to a lesser extent, elements associated with fine-grained minerals, play a significant role in affecting the utilization of coal, but also such modes of occurrence of elements provide useful geochemical information on coal formation and coal-bearing basin evolution. With a few exceptions (such as Cd, Nb, Ta, Zr, and Hf), most elements determined in coal, particularly in low-rank coal, have varying-degrees of organic association. In this paper, we review the definition of associations of non-mineral elements in coal, as well as their methods of determination, and then review the associations of selected elements including environmentally-sensitive (e.g., S, As, U, and Hg) and critical elements, the latter of which drive some of the significant advancements in technology and energy efficiency in the world today (e.g., rare earth elements and Y, Ge, and U), and some major elements (e.g., Ca, Mg, Fe, Al, and Ti) that largely occur in non-mineral forms in low-rank coals. • The modes of occurrence of elements in coal are classified into organic, mineral, and intimate organic associations • The intimate organic associations include those adsorbed on to the surface of organics, dissolved in pore waters, and hosted in very fine-grained minerals. • Most elements determined in coal have varying-degrees of organic association. [ABSTRACT FROM AUTHOR]

• Element geochemistry in coals varies notably in a laterally correlated coal seam. • Various geological factors are responsible for the difference in the elemental geochemistry of the coals. • Some critical metals including REY are redeposited within the coal section as a result of acidic leaching. • The Datanhao coal seam has potential in industrial utilization of certain critical metals. This paper discusses the modes of occurrence of critical elements and their origins in the studied coal and associated rock samples (partings and roof strata) from the Datanhao coal mine, Daqingshan Coalfield, Inner Mongolia, northern China. The studied coals are enriched in trace elements including Zr, Hf, Th, Be, F, Zn, Ga, Nb, Mo, Cd, In, Sn, Ta, Hg, W, Pb, and rare earth elements and Y (REY). Zirconium, Nb, Ta, and Hf are largely associated with anatase in the studied coal and non-coal samples. The main carriers of REY, Th, and U in both coal and non-coal samples are Ca-bearing REE-phosphate minerals, most likely monazite, although U is partly associated with organic matter. Fluorine in the Datanhao coals is mainly associated with kaolinite. Most partings identified as volcanic ash-derived tonsteins from the Datanhao Mine exhibit negative Eu anomalies that, along with the common presence of equant-shaped euhedral volcanic quartz (beta-quartz), indicate a felsic volcanic source located in the Xing'an-Mongolia Orogenic Belt. Other probable sources of clastic material into the basin include the pre-Cambrian granites from the adjacent uplands, which may be responsible for the light rare earth element enrichment of the studied deposits, and associated metamorphic rocks from the adjacent uplands. Owing to acidic hydrothermal fluids, which are most likely related to the Yanshanian (Jurassic to Early Cretaceous) intrusive activity and/or low-temperature basinal waters circulating within the coal-bearing unit during the epigenetic stage, most of the coal benches from the Datanhao mine are also relatively enriched in middle rare earth elements. On the other hand, some coal and non-coal bench samples from the middle Datanhao section are enriched in heavy REE. This, along with the presence of abundant syngenetic or early diagenetic carbonate minerals, indicates deposition in an episodic alkaline environment, the origin of which is mostly probably attributed to evaporation and/or saline water inputs resembling a playa lake environment. As the concentrations of Zr, Hf, Nb, and Ta are all close to or higher than the respective industry cut-off grades or standards for these critical elements, the Datanhao coal seam has potential economic significance for these as an important by-product of the coal mining. [ABSTRACT FROM AUTHOR]