Selenium In Coal Research Articles

Chemical association of copper and selenium in coals of Sindh by time saving single step strategy and their impact on groundwater.

The aim of the present study is to estimate the different chemical fractionations of copper (Cu) and selenium (Se) in coal samples of different coal mining areas. The Cu and Se bound to various chemical fractions of coal collected from two mining fields of Sindh, Pakistan, have been determined by BCR sequential extraction scheme (BCR-SES). The long duration of the BCR sequential scheme (51h) was reduced by a time-saving shaking device (ultrasonic bath) termed as ultrasonic-assisted extraction (USE) depending on the same operating conditions and extracting solutions used for BCR sequential extraction scheme. The both trace elements were determined in aquifer water, sampled from different depth of both coal mining fields. In addition, the groundwater of dug well in the vicinity of coal mining areas were also analyzed for Cu and Se using reported extraction methodologies. The partitioning of Cu and Se bound with different chemical fractions of coal was successfully made by proposed USE, within 2h as compared to long duration of BCR-SES (51h). The Cu and Se concentrations in acid-soluble fractions of coal samples were > 10%, enhanced by USE extraction procedure than those values gained via BCR-SES (p < 0.01). About 67 to 69% of Cu were found in the first three fractions, whereas their remaining amount corresponding to 31 to 33%, respectively bound with crystalline/residual fraction, while up to 66.1 to 71.1% of total Se contents extracted in three extractable phases, followed up to 28.9 to 33.8% of it was bound with residual phase. The concentrations of Cu and Se in groundwater of different aquifers were found in decreasing order as AQ1 > AQII > AQIII; the same trend was observed for two aquifers of Lakhra coal mining, whereas the groundwater samples have two to three folds higher levels of Se than WHO limit. The Cu levels in water samples were significantly lower than the recommended limit of WHO for drinking water (p < 0.01).

Coal mining‐derived ochres in the UK: a potential selenium trap

Thanks to the pioneering research of Paul Younger over the past 20 years, acid mine drainage in the UK has been recognized as a major environmental issue. Acid mine drainage and hydrous ferric oxide deposition are environmental hazards resulting from centuries of extensive coal mining activities across the UK. Oxidative weathering of pyrite in coal from spoil heaps and exposed bedrock can liberate trace elements, releasing them into local water systems. In addition to posing an environmental threat through water and ground contamination, ochres can also act as a remediation material, trapping elements such as selenium. Trace elements with a close association to iron oxides, such as selenium, may fix to the fine‐grained ochre materials, resulting in hyper‐enriched ochres. Selenium in coals has been known to cause an environmental issue in areas of North America but is also an important commodity for solar cells and nanotechnologies. Coal‐bearing areas of the UK, such as Northumberland, are known to contain a high selenium content, and coal‐derived ochres in these regions also contain significant selenium. The widespread occurrence of ochres in UK coal‐mining regions may therefore present a unique ‘E tech’ trace element source and prevent a toxicity problem for which they were once thought to be responsible.

Concentration, distribution, and modes of occurrence of selenium in Huaibei coalfield, Anhui province, China

Selenium, a toxic element, is highly enriched in the coals of the Huaibei coal deposit, China. For this study, Se content along with rock-forming and trace element abundances was determined in 123 coal and 19 rock samples collected from the main coal seams in seven coal mines in the Huaibei coalfield. This was done to investigate the Se geochemistry in the Huaibei coals. Compared with average Chinese coal and other coals around the world, the Huaibei coals are enriched in Se by a factor of five. Differences in the boron content in the sequence of Huaibei coal seams show that the depositional environment of the formations hosting the coal seams evolved from a delta front to a prodelta setting and then to a delta plain environment. Selenium is distributed unevenly both horizontally and vertically in the Huaibei coal deposit. Pearson correlation coefficients between Se with several elements (Ca, Fe, and S) indicate that iron-bearing clay minerals and carbonates are the dominant carriers of Se in coals of the Lower Shihezi Formation. Selenium in coals from No. 3 and No. 10 coal seams are mainly associated with sulfide minerals. The well-developed faults in Huaibei coalfield may have contributed to the enrichment of Se in Huaibei coals.

Determination of As and Se in coal and coal combustion products using closed vessel microwave digestion and collision/reaction cell technology (CCT) of inductively coupled plasma mass spectrometry (ICP-MS)

Toxic elements arsenic and selenium in coal are of great concern mainly because of their adverse effects on human health during coal combustion. This paper describes the concentration determination of As and Se in coal and coal combustion products (CCPs), performed by collision/reaction cell technology (CCT) of inductively coupled plasma mass spectrometry (ICP-MS; collectively ICP-CCT-MS) after closed vessel microwave digestion. The reagents for 50-mg coal sample digestion are 2-ml 40% (v/v) HF and 5-ml 65% (v/v) HNO3 but for the CCP samples, the reagents include 5-ml 40% HF and 2-ml 65% HNO3. To significantly diminish the argon-based interferences at mass to charge ratios (m/z) 75 (40Ar35Cl) and 78 (40Ar38Ar), a helium and hydrogen mixture was used in the optimized hexapole collision cell. The results showed that CCT technology can effectively diminish the spectral interferences of the Ar-based polyatomic ions 40Ar35Cl and 40Ar38Ar to 75As and 78Se, respectively. The method detection limit of As and Se is 0.024 and 0.095μg/l, respectively, and their linearity of the calibration curves in the range 0–100μg/l has a determination coefficient r2>0.9999. The determination of As and Se in NIST standard reference materials of coal and fly ash samples showed that ICP-CCT-MS plus closed vessel microwave digestion is a reliable method for concentration determination of the two elements in coal and CCPs.

Environmental impacts of coal combustion: A risk approach to assessment of emissions

This paper summarises some of the work performed in the Cooperative Research Centre for Coal in Sustainable Development (CCSD) on emissions from current power generation. A comprehensive approach was taken in the CCSD program to assessing environmental issues of concern for the power, and by implication the coal, industries. Here results of sampling on full scale operating plants are described, and detailed data on emission fluxes, particle size distributions, trace element concentrations as a function of particle size, and speciation of the trace elements are illustrated. The results show that particle capture in electrostatic precipitators (ESPs) is significantly less efficient than in fabric filters (FFs), particularly for submicron material, and that significant enrichment is observed in the finer particle sizes emitted from both ESPs and FFs. Results for the speciation of chromium, arsenic and selenium in coals, bottom ash and fly ash are also presented. The majority of chromium in fly ash is present in the less toxic Cr 3+ form. Speciation of arsenic in feed coals is variable but the dominant form of As in fly ash is the less toxic As 5+.

Sequential solvent extraction for the modes of occurrence of selenium in coals of different ranks from the Huaibei Coalfield, China

Forms of selenium in bituminous coal, anthracite, and cokeite (natural coke) from Huaibei Coalfield, Anhui, China, have been determined by sequential solvent extraction. The selenium content in bulk samples is 4.0, 2.4, and 2.0 μg/g in bituminous coal, anthracite, and cokeite, respectively. The six forms of selenium determined by six-step solvent extraction are water-leachable, ion-exchangeable, organic matter-associated, carbonate-associated, silicate-associated, and sulfide-associated. The predominant forms of selenium in bituminous coal are organic matter-associated (39.0%), sulfide-associated (21.1%), and silicate bound (31.8%); these three forms account for 92% of the total. The organic matter bound-selenium decrease dramatically from bituminous coal (39.0%) to anthracite (11.6%) and to cokeite (0%), indicating that organic matter bound selenium is converted to other forms during metamorphism of the coal, most likely sulfide-form. The sulfide-associated form increased remarkably from bituminous coal (21.1%) to anthracite (50.4%) and cokeite (54.5%), indicating the formation of selenium sulfide, possibly in pyrite during the transformation of bituminous coal to anthracite and cokeite. The silicate-associated selenium in bituminous coal (31.8%) is much higher than that in anthracite (16.4%) and cokeite (15.8%), indicating that silicate-associated selenium is partly converted to sulfide during metamorphism.

Selenium in coal: A review

Abstract The World average Se content in coals (coal Clarke of Se) for hard coals and brown coals are respectively 1.6 ± 0.1 and 1.0 ± 0.15 ppm. On an ash basis, these contents are greatly increased and are 9.9 ± 0.7 and 7.6 ± 0.6 ppm, respectively. Therefore, Se is a very coalphile element: it has strong affinity to coal matter — organic and (or) inorganic but is certainly authigenic. The “coal affinity” of Se is like that for Ge and S. Both organic (Seorg) and inorganic selenium (Semin) can exist in coal. In addition, Se can occur not only as a chemical-bound form, but also in sorbed (acid leachable) selenate form in the oxidized coals. The sulfidic form of Se is represented by isomorph Se in pyrite and some more rare sulfides, and the selenidic form by clausthalite PbSe. “Organic” Se may be present as both Se-organic compounds and elemental Se° dissiminated through organic matter. There are some preliminary data that cleaning of high-sulfur coals, very effective for S, is less effective for Se due to enhanced contribution of the Seorg form (vs. Sorg). There are two genetic types of the Se-accumulations in coal: “reducing” and “oxidizing”. In the first type, Se is enriched in high-sulfur coals, concentrating in sulfide phases. These accumulations are, in general, syngenetic, and may be epigenetic only if there are abundant hydrothermal sulfides of Fe, Cu, As, Pb. In coals of the second type, Se is enriched in the bed oxidation zones. Such coals are (or were) located in the areas with arid climate and enhanced Se content in water. Se concentrates in coal as a reduction or sorption geochemical barrier, probably, mostly as Se° in oxidized organic matter and partly pyrite. This type is characterized by oxidizing zonality and close paragenesis of Se with U, Fe, Mo, V, and Pb. These Se accumulations are mostly epigenetic. A study of Se in coal is evidently insufficient, and further detailed studies are needed, especially regarding Se forms (modes of occurrence).

Geochemistry of selenium in coals: ecological aspect

Experiments were performed to compare intermediate-scale (1 m3) and laboratory-scale (20 l) coal dust inerting results. Intermediate-scale inerting levels appear to be lower than laboratory-scale values. This can possibly be attributed to the use of a strong ignition source to initiate the test, which may have overdriven the explosions in the smaller test vessel. Previously reported agreement between the smaller test vessel and full-scale experiments may be due to overdriving in the 20 l chamber, leading to high inerting levels similar to those encountered in full-scale tests due to flame acceleration. Additionally, a reduction in the particle size of the rock dust used for inerting has been found to influence the quantity required to prevent an explosion in the 1 m3 chamber. This agrees with previous work conducted in smaller chambers.

Distribution and mode of occurrence of selenium in US coals

Selenium excess and deficiency have been established as the cause of various health problems in man and animals. Combustion of fossil fuels, especially coal, may be a major source of the anthropogenic introduction of selenium in the environment. Coal is enriched in selenium relative to selenium's concentration in most other rocks and relative to selenium in the Earth's crust.Data from almost 9,000 coal samples have been used to determine the concentration and distribution of selenium in US coals. The geometric mean concentration of selenium in US coal is 1.7 ppm. The highest mean selenium value (geometric mean 4.7 ppm) is in the Texas Region. Atlantic Coast (Virginia and North Carolina) and Alaska coals have the lowest geometric means (0.2 and 0.42 ppm, respectively). All western coal regions have mean selenium concentrations of less than 2.0 ppm. In contrast, all coal basins east of the Rocky Mountains (except for several small basins in Rhode Island, Virginia, and North Carolina) have mean selenium values of 1.9 or greater.Generally, variations in selenium concentration do not correlate with variations in ash yield, pyritic sulphur, or organic sulphur concentrations. This may be the result of multiple sources of selenium; however, in some non-marine basins with restricted sources of selenium, selenium has positive correlations with other coal quality parameters.Selenium occurs in several forms in coal but appears to be chiefly associated with the organic fraction, probably substituting for organic sulphur. Other important forms of selenium in coal are selenium-bearing pyrite, selenium-bearing galena, and lead selenide (clausthalite). Water-soluble and ion-exchangeable selenium also have been reported.

High-performance liquid chromatographic determination of selenium in coal after derivatization to 2,1,3-benzoselenadiazoles

High-performance liquid chromatography was examined for the determination of selenium after derivatization to 2,1,3-benzoselenadiazoles using 1,2-diaminobenzene, 1,2-diamino-4-nitrobenzene (NDAB), 2,3-diaminonaphthalene and 3,3′-diaminobenzidine as derivatizing agents. Elution was carried out using a mixture of chloroform and hexane, with ultraviolet spectrophotometric detection. The 2,1,3-benzoselenadiazoles were extracted into toluene. Linear calibrations were obtained for 0–4 µg of selenium in 10 cm3 of solution and the detection limits were 20–50 ng of selenium in 10 cm3 of solution. The method was applied to the determination of selenium in coal samples and a shampoo using NDAB as the derivatizing reagent in acidic solution.

Direct atomic spectrometric analysis by slurry atomisation. Part 4. Determination of selenium in coal by electrothermal atomisation atomic absorption spectrometry

The determination of selenium in whole powdered coal without sample dissolution is described. The sample was introduced into a graphite furnace as a slurry for analysis by atomic absorption spectrometry. The coal was slurried in nickel nitrate (matrix modifier), nitric acid and ethanol (wetting agent). The effects of the type of background correction (continuum source or Smith-Hieftje), the furnace programme, the various matrix modifiers and air ashing, particularly on a spectral interference from iron, were investigated. Method calibration was achieved using aqueous standards and sample destruction was carried out in situ in the furnace. The preferred method used Smith-Hieftje background correction, the 196.0-nm resonance line and in situ air ashing. Selenium was successfully determined in four certified reference material coals with a typical relative standard deviation of 5% at the 1 µg g–1 level. The limit of detection (2σ) of the method is 0.05 µg g–1.

The determination of arsenic and selenium in coal by continuous flow hydride-generation atomic absorption spectrometry and atomic fluorescence spectrometry

Concentrated perchloric acid is used to digest coal for subsequent determination of arsenic and selenium by hydride-generation atomic absorption and fluorescence spectrometry. Arsenic and selenium are removed from potentially interfering metal ions by coprecipitation with lanthanum hydroxide. The detection limits, 58 and 36 ng g −1 by atomic absorption and 25 and 10 ng g −1 by atomic fluorescence, for arsenic and selenium in coal, respectively, are adequate for the normal levels of these metals.

Mineral matter and elemental concentrations in selected western canadian coals

Major and trace element analyses were performed on coals from various locations in western Canada, and on low-temperature (150 °C) and high-temperature (1000 °C) coal ash produced from these coals. Elemental analyses were carried out by X-ray fluorescence spectroscopy and intense neutron activation analyses. Based on their trace elements, the coals in this study fall into two groups: 1. low-rank coals (lignite-subbituminous) of late Cretaceous and Tertiary age; and 2. high-rank coal (bituminous-semianthracite) of Jurassic-Cretaceous age. The elemental analyses of the coals and coal ash indicate that the local conditions had considerable influence on the concentrations of certain trace elements. Antimony and selenium in coals are the only elements which are enriched relative to concentrations in the earth's crust; arsenic is concentrated in lignite to subbituminous coal, but is depleted in bituminous-anthracite coals; as expected the ash of these coals showed many more instances of enrichment.

Determination of selenium in coal using graphite furnace atomic absorption spectrometry after chemical separation.

Determination of selenium in coal using graphite furnace atomic absorption spectrometry after chemical separation.

Arsenic and Selenium in Texas Lignite

Abstract Texas lignite samples were analyzed for arsenic and selenium utilizing hydride generation-dc helium emission spectrometry and gas chromatography-microwave plasma emission spectrometry. Arsenic and selenium were present in the samples at levels ranging from 1.0 to 5.5ppm and 3.9 to 22.9 ppm, respectively. The arsenic concentrations vary slightly whereas the selenium levels fluctuate strongly as a function of depth in the lignite deposit. Analysis of specific gravity fractions of mined lignite indicated that arsenic and selenium are primarily associated with the lower density fractions and therefore probably in organic combination. Knowledge of the chemical nature of the arsenic and selenium in coals is necessary in order to select the most appropriate chemical and physical treatment methods to control emission of these toxic elements to the atmosphere during direct combustion and to prevent catalyst deactivation during fuel conversion processes. Elements associated with the heavier mineral fractio...

Determination of mercury and selenium in coal by neutron activation analysis

Determination of mercury and selenium in coal by neutron activation analysis