Greta M. Eskenazy

Rare earth elements in a sampled coal from the Pirin deposit, Bulgaria

Abstract Rare earth elements (La, Ce, Sm, Eu, Tb, Yb, and Lu) in a columnar section of the coal of the Pirin deposit, Bulgaria, have been determined by neutron activation analyses. The REE content in the coals is lower than the average REE content of shales from North America, Europe, and the Soviet Union. The REE abundances increase with the increasing ash content of the coals. The bottom of the seam is slightly enriched in REE, the trend being more pronounced in HREE (Tb, Yb, Lu). The REE content depends on the thickness of the coal layers: the thin coal layers are enriched in REE as compared to the thick ones. The chondrite-normalized distribution patterns are very uniform. They are characterized by a negative Eu anomaly whose mean value is 0.30 (varying in the individual samples from 0.21 to 0.49) and a positive Lu anomaly. It is supposed that the Eu anomaly is inherited from the source rocks. The shale-normalized distribution patterns show a distinct relative enrichment in HREE and a negative Eu anomaly. The relative enrichment in HREE is a specific feature of the REE geochemistry in the Pirin deposit. The LREE/HREE ratio is lower than that of composite shale; it increases with the increasing ash content of the coals and from the bottom to the top of the coal bed. REE are bound predominantly to the aluminosilicates of the mineral matter in the coals. All REE are positively correlated to the ash, Si, Al, Fe, and Na. The source of REE in coals is mainly the suspended terrigenous material. The specific enrichment of REE in the ash of low-ash coals is a result of the interaction between the dissolved REE and the products of disintegration and decay of organic substances, mainly the humic acids.

Behaviour of elements and minerals during preparation and combustion of the Pernik coal, Bulgaria

The chemical and mineral composition, including major (Al, Ca, Fe, K, Mg, S, Si, Ti), minor (Na, P) and trace (Br, Cl, Co, Cr, Cu, Li, Mn, Ni, Pb, Rb, Sr, Zn) elements and different minerals, of the Pernik subbituminous coals and their preparation and combustion solid waste products were studied. Feed coals, upgraded coals (high-grade and low-grade coals) and their waste products, namely coal slimes and host rocks generated from the Pernik coal preparation plant, as well as combustion waste products such as bottom ashes, fly ashes and lagooned ashes resulted from the Republica coal-fired thermoelectric power station were characterized. The occurrence and behaviour (partitioning, volatilization, condensation, capture and retention) of the above-mentioned elements and various minerals during coal preparation and combustion are described. The results indicate some technological problems and possible environmental pollution of the air, water, soil and vegetation with certain elements in the areas surrounding both thermoelectric power station and coal preparation plant.

Contents, modes of occurrence and origin of chlorine and bromine in coal

Contents, modes of occurrence and origin of Cl and Br in individual coal samples from 34 deposits worldwide (Bulgaria, Australia, the United States, Japan, Canada, South Africa, China, and Ukraine) were studied. Some relationships of Cl and Br contents with chemical and mineral composition, rank, age, ash yield and geographic location of coals are described. Despite of similar chemical and geochemical properties of Cl and Br some distinct differences in the association, behaviour and occurrence of both elements in coal were found and discussed. Chlorine and Br in coal may occur, in decreasing order of significance, as organic compounds, as impurity components in the crystalline and amorphous inorganic constituents, in the fluid constituents and as discrete minerals. Both elements could have an organic occurrence and association with water-soluble (mainly ionic) and water-insoluble (ionic and covalent) organic combinations. Chlorine was identified as an impurity in minerals and inorganic phases such as clay minerals, mica, feldspars, polyhalite, gypsum, siderite, volcanic glass, phosphates and other carbonates and sulphates. A characteristic Br association with illite and to a lesser extent with mica, kaolinite and Fe-bearing minerals was also found. Water molecules, hydroxyl groups and exchangeable cations in various minerals play a leading role for the inorganic occurrence and distribution of both elements. Discrete Cl minerals such as sylvite, halite, chlorapatite and probably carnallite were also identified. Significant amounts of Cl ions may associate with solutions in the inherent moisture of the coal mesoporosity. Limited proportions of both elements may also occur in gas–liquid inclusions of different solid phases. The favourable conditions for Cl and Br enrichments in coal are also discussed.

Rare earth elements and yttrium in lithotypes of Bulgarian coals

Abstract Rare earth element and yttrium abundances in vitrain, xylain, liptain, fusain and whole coal samples from Bulgarian coal deposits have been studied. Vitrain, xylain, and liptain are depleted, while fusain is enriched in REE and Y as compared to the whole coal samples from which they were selected. Chondrite-normalized patterns show relative enrichment of light (LREE) against heavy (HREE) rare earth elements, negative Eu anomaly, and positive Lu anomaly. The shale-normalized patterns of the lithotypes reveal an increase from LREE to HREE, while those of the whole coal samples and mineral interlayers are less fractionated. The petrographic composition of the coals is of secondary importance for the concentration of the REE and Y. The main factors are the source area and the input of dissolved REE and Y into the coal depositional sites.

Aspects of the geochemistry of rare earth elements in coal : an experimental approach

Abstract Many coals worldwide are slightly enriched in heavy rare earth elements (HREE) relative to light rare earth elements (LREE) as compared with chondrites and shales. A factor contributing to this fractionation could be the ability of the HREE to form complexes with organic compounds which are more stable than those of the LREE. In order to test this hypothesis, experiments on the sorption of several light and heavy rare earth elements (La, Ce, Sm, Eu, Gd, Ho, Er, Lu) on xylain and humic acids were performed. The sorption on xylain was found to be pH and time dependent. Maximum quantity was sorbed in the range of pH 3 to 5. Sorption equilibrium was reached in 5 to 7 days. The shape of the sorption isotherms for all REE studied were similar. The maximum content sorbed for each REE was about 0.2 mEq/0.5 g xylain. When all REE were present in equal concentration in the initial solution, the quantity sorbed was also 0.2 mEqv/0.5 g xylain. Nearly the same quantity of Na, K, Ca and Mg were displaced from the sorbent. These results suggest a cation-exchange mechanism in which Na, K, Ca and Mg bound to –COOH and –OH groups were replaced by the REE cations. The capacity of humic acids leached from xylain was found to be about 0.05 mEq REE on 0.250 mg humic acids (HA). The individual REE were sorbed in nearly equal quantities.

Contents, modes of occurrence and behaviour of chlorine and bromine in combustion wastes from coal-fired power stations

Abstract Contents, modes of occurrence and behaviour of Cl and Br in combustion wastes from eleven Bulgarian coal-fired thermoelectric power stations (TPS) were studied. Despite some differences, there are indicative close relationships between the contents, redistributions, modes of occurrence and behaviour of Cl and Br in fly ash (FA), bottom ash (BA) and stack emissions during coal combustion. Chlorine and Br occur in inorganic and organic combinations in FA and BA. Both elements are normally present, in decreasing order of significance, as: (1) impurities in the glass phases (dominantly for Br); (2) impurities in the various crystalline components (dominantly for Cl) such as surface-bound Ca–Na–K–Mg sulphates and phosphates; (3) organic compounds in char; (4) impurities in the fluid constituents; (5) probable discrete inorganic phases. Dominant proportions (up to 96%) of the initial Cl and Br in coal are normally emitted during combustion process in TPS. The main reasons for Cl and Br volatilisation, condensation, capture and retention during coal combustion are described. The results also indicate some possible environmental pollution of the air, water and soil with Cl and Br in the areas surrounding the large TPS.

Geochemistry of boron in Bulgarian coals

A set of 466 individual full channel samples (coals, coaly shales and partings) of thirteen Bulgarian coal deposits, as well as vitrain lenses, gagatite and coalified woods embedded in sedimentary rocks have been analyzed by atomic emission spectroscopy. The deposits consist of lignites, subbituminous and bituminous coals. The average boron content ranges from 15 to 164 ppm in the coals. The boron content of the individual coal samples ranges from 2 to 164 ppm. About 86% of the samples have a B content from 2 to 110 ppm, which corresponds to the most probable interval of concentration for coals worldwide. The boron content is not related to rank. The lignites have the lowest boron content. Some of the vitrain and xylain samples studied are enriched in boron in comparison with the whole-coal samples. Boron occurs in both organic (Borg) and inorganic (Binorg) forms. Excluding one deposit, the boron content in the ash correlates negatively with the ash content, whereas in coals it usually slightly increases with increasing ash content. Organically associated B dominates in the low-ash coals and in the deposits enriched in boron. The coals of the Burgas deposit have the highest B content, which is in agreement with the geological evidence for marine influence during the early stages of coalification. The distribution of B is also independent of other geological factors.

Geochemistry of arsenic and antimony in Bulgarian coals

Abstract Arsenic and Sb were quantified by instrumental neutron activation analysis in ∼400 individual full channel samples comprising coals, coaly shales and partings from 14 Bulgarian coal deposits. The mean values for As in the coal deposits range from 2 to 58 ppm, while mean values for Sb range from 0.2 to 16 ppm. The As means by coal rank are: lignites, 11 ppm; subbituminous, 19 ppm; bituminous, 37 ppm. The values for Sb are: lignites, 0.5 ppm; subbituminous, 4.2 ppm; bituminous, 1.1 ppm. Regional geological factors have more important influence on As and Sb content than does the rank of the coal. The highest As and Sb contents were found in single vitrain lenses hosted in sediments: 4011 ppm As and 137 ppm Sb. Arsenic is present mainly in pyrite, which was demonstrated by analysis of pyrite hand-picked from coals and microprobe analysis of pyrite grains in coal samples. Presence of organically associated As is supposed as well. Indirect evidence shows that Sb in Bulgarian coals has a dominant organic affinity. There is no correlation between As and Sb. The enhanced Sb and As content of the Vulce pole, Pcelarovo and Meden buk deposits is related to hydrothermal and volcanic activity in the region. The deposits are located in a Paleogene mollasse formation with Sb mineralization (stibnite containing >1000 ppm As). One factor controlling enrichment of coals in As and Sb could be paleothermal solutions penetrating coal beds. The source for background levels of As and Sb in coals could be detrital material containing Fe-oxides which are hosts of both elements. In a peat-forming environment (low pH, reducing conditions, abundant H2S) some As and Sb bound to Fe-oxides could be redistributed, partly coprecipitated with pyrite and partly accumulated by the organic matter.

Zirconium and hafnium in Bulgarian coals

A study of the geochemical behaviour of zirconium (Zr) and afnium (Hf) in several Bulgarian coal deposits has shown that the content of these elements varies considerably, the highest concentrations being found in fragments of coalified woods included in sandstones. Zr and Hf content of the lithotypes of the coals is lower than that of the corresponding whole coal samples. The ZrHf ratio for xylain and vitrain is always lower than that for whole coal samples. Zr and Hf are mainly associated with the inorganic matter of the coals and Zrorg and Hforg dominate only in the low ash coals of some deposits. It is assumed that Zrorg and Hforg were leached from the terrigenous minerals supplied to the peat swamp and fixed by the organic matter. These processes result in a slight separation of both elements.

On the geochemistry of indium in coal-forming process

Abstract The content and distribution of In in 168 samples from 7 coal deposits in Bulgaria were studied, using a spectrochemical method with a detection limit of 0.002 ppm. Indium is present in all samples, its content varying from 0.002 to 0.167 ppm in the coal and from 0.005 to 0.57 ppm in the ash. The mean contents for individual deposits do not differ statistically, and for all the deposits the In concentration (ppm) can be expressed generally by the equation In = 0.00068 A (A is the coal ash content in %). Of the petrographic constituents of coal, vitrain, xylene and liptain are enriched in In. In is associated with both the organic and with the inorganic matter of the coal. Inorganic matter and clay minerals in particular, act only as carriers of Indium. In contrast, organic matter concentrates In only to a small degree relative to other trace elements.