Elements in coal and fly ash

Zielinski, R. A. Finkelman, R. B. 1997. Radioactive Elements in Coal and Fly Ash Abundance, Forms and Environmental Significance. USGS, Central Region Energy Resources Team, Fact Sheet FS-163-97. U.S. Geological Survey National Center, Reston, VA. 

Battelle has developed instrumental neutron activation analysis (INAA) techniques which permit very sensitive and accurate multielement analysis of approximately 40 elements in coal and fly ash. These techniques, which will be described in this work, form the basis for extensive environmental studies of the effluent from coal-powered generating facilities and other pollution sources. 

Table II-A. Nuclear Data Relating to the Measurement of the Elements in Coal and Fly Ash...

The precision for a single determination is 5-10% for most of the 40 elements in coal and fly ash. Battelles technique of INAA has been shown to have 5-10% accuracy by the replicate analyses of well characterized standards such as U.S.G.S. Basalt Standard BCR-1 and NBS-Orchard Leaves (SRM 1571) (32). 

Birge, W.J. 1978. Aquatic toxicology of trace elements of coal and fly ash. Pages 219-240 in J.H. Thorp and J.W. Gibbons (eds.). Energy and Environmental Stress in Aquatic Systems. U.S. Dep. Energy, Sympos. Ser. 48, CONF-771114. 

Spark source (SSMS) and thermal emission (TEMS) mass spectrometry are used to determine ppb to ppm quantities of elements in energy sources such as coal, fuel oil, and gasoline. Toxic metals—cadmium, mercury, lead, and zinc— may be determined by SSMS with an estimated precision of 5%, and metals which ionize thermally may be determined by TEMS with an estimated precision of 1% using the isotope dilution technique. An environmental study of the trace element balance from a coal-fired steam plant was done by SSMS using isotope dilution to determine the toxic metals and a general scan technique for 15 other elements using chemically determined iron as an internal standard. In addition, isotope dilution procedures for the analysis of lead in gasoline and uranium in coal and fly ash by TEMS are presented. 

Preliminary studies have shown that it is possible to remove over half of the potentially toxic trace elements present in coal when the mineral matter is reduced by coal washing. When coal is burned in a power plant, about 13% of the mercury and about 50% of the lead and cadmium may remain with the fly ash. Analytical chemical techniques have been developed to determine Hg, Cu, Cr, Mn, Ni, Cd, Pb, and F in coal and fly ash. These techniques produce accurate and precise results despite the fact that there are no coals with established trace element content, except for mercury. 

INAA has been used for routine determination of about 30-48 elements in coal., soils, fly ash with excellent accuracy and precision proved by analysis of NIST and IAEA standard reference materials (Germani et al., 1980 Allan and Sansoni, 1990 Shtangeeva, 1994). Combination of pile and epithermal irradiations inereases the precision and accuracy and detection limits for a number of elements (Kostadinov and Djingova, 1980, 1981a). Detection limits are in the low mg/kg and xg/kg range and the precision is 1-8%. Analysis of soil EDTA and acetic acid extracts has been performed in (Bajo et al., 1989) and the content of 29 elements is determined with a precision of 4-10%. For some of the elements however (Tb, Ti and Zn) accuracy was not good (20-40%). 

The significance of these two elements in coal or fly ash is from the point of view of their recovery from coal ashes or fly ashes. The concentration levels of these two technologically valuable elements in other mineral sources (principally zinc and aluminum ores) is about the same level as in coal or fly ashes (Table VI). Both of these elements are difficult to determine by most analytical techniques. We have chosen to use two sensitive and relatively selective reagents to extract these elements into organic solvents and then spectrophoto-metrically measure them. The flow scheme of analysis is given in Table VII. 

Ondov JM, Zoller WH, Olmez I, et al. 1975. Elemental concentrations in the National Bureau of Standards environmental coal and fly ash standard reference materials. Anal Chem 47 1102-1109. 

If a solid-state Ge(Li) detector and a 1000- to 4000-channel analyzer are available, instrumental NAA can be extended to many elements. For example, Rancitelli (6) has analyzed coal and fly ash for 25 major, minor, and trace elements by using instrumental NAA with computer data reduction. Block and Dams (7) used similar analysis and reported on 43 elements in coal. Clearly, this is a good method for rapidly monitoring the composition of many coal samples. 

Coal and fly ash are currently monitored to control air and ground water pollution, to evaluate mass balance in coal production and as indirect control of emission (based on the differences in contents between coal and fly ash). Some areas sufTer from a severe pollution by emission of fluorine to the atmosphere and its consequent transport into the ground water. Chlorine is responsible for burner corrosion and has to be determined to assess the risk monitoring of these elements under good quality control implies that CRMs of coal and fly ash should be available. A new coal reference material (CRM 460) has hence been prepared with the objective to certify both F and Cl [13,14] as described below, only fluorine could be certified, owing to an in-homogeneity detected for Cl. 

All major ash elements and some trace elements are determined in coal or fly ash by inductively coupled plasma emission spectrometry. Parr oxygen bomb combustion followed by ion selective electrode. X-ray fluorescence or atomic absorption spectrom-etric measurements are used to determine halogens, sulfur, nitrogen, mercury, arsenic, selenium, and phosphorus. Hydride generation-atomic absorption spectrometry is used to determine traces of As,... 

Von Lehmden DJ, Jungers RH, and Lee Jr RE (1974) Determination of trace elements in coal, fly ash, fuel oil, and gasoline - a preliminary comparison of selected analytical techniques. 

Mullite is almost twice as abundant in low-Ca fly ash when compared to high-Ca fly ash, mainly due to differences in the Al content of the clay minerals associated with the coal (McCarthy et al. 1990). Using atomic absorption spectroscopy (AAS) and scanning electron microscopy /electron microprobe analyses (SEM/ EMPA) Stevenson Huber (1987) found a correlation between the elemental composition of ash particles and the clay mineral species in the raw coal. They concluded that the geologic origin of the coal had a significant impact on the microchemical composition of the ash. 

As was previously mentioned, trace elements that sublime at temperatures below those attained during coal combustion (e.g., As, Se, Hg, Zn), and are associated with thermally unstable solid phases (in particular organic matter and sulphide minerals), are subject to vaporization into furnace gases. Once these gases, and fly ash particles entrained in the gases, are vented from the combustion furnace they quickly cool, leading to the condensation of volatilized elements onto the... 

Overall, the Kentucky and Purdue studies show similar trends. The most important change resulting from the addition of TDF to coal is the increase in the Zn content of the fly ash. In contrast, most other trace elements have lower concentrations in the fly ash resulting from the combustion of the blend. Despite many similarities, two notable differences between the two test bums are observed. S03 and Pb showed opposite trends in the Purdue fly ash compared to the Kentucky fly ash. In both studies, enrichments of many trace elements... 

Combustion of coal and other fossil fuels is a major source in the envi- ronment of trace elements that are hazards to human health. Toxic elements such as Hg, As, Sb, F, Se, and T1 are volatilized during coal combustion and are emitted directly into the atmosphere or concentrated in the fly ash (1, 2, 3). Most elements in coal occur at only parts per million levels, but large tonnages of coal are consumed each year in the United States. In addition, coal conversion processes, which could vastly increase coal use are now being considered seriously. The fate of trace elements during these processes is largely unknown. 

Methods and technology were developed to analyze 1000 samples/yr of coal and other pollution-related samples. The complete trace element analysis of 20-24 samples/wk averaged 3-3.5 man-hours/sample. The computerized data reduction scheme could identify and report data on as many as 56 elements. In addition to coal, samples of fly ash, bottom ash, crude oil, fuel oil, residual oil, gasoline, jet fuel, kerosene, filtered air particulates, ore, stack scrubber water, clam tissue, crab shells, river sediment and water, and corn were analyzed. Precision of the method was 25% based on all elements reported in coal and other sample matrices. Overall accuracy was estimated at 50%. 

Mass balance measurements for 41 elements have been made around the Thomas A. Allen Steam Plant in Memphis, Tenn. For one of the three independent cyclone boilers at the plant, the concentration and flow rates of each element were determined for coal, slag tank effluent, fly ash in the precipitator inlet and outlet (collected isokinetically), and fly ash in the stack gases (collected isokinetically). Measurements by neutron activation analysis, spark source mass spectroscopy (with isotope dilution for some elements), and atomic adsorption spectroscopy yielded an approximate balance (closure to within 30% or less) for many elements. Exceptions were those elements such as mercury, which form volatile compounds. For most elements in the fly ash, the newly installed electrostatic precipitator was extremely efficient. 

Spark-source mass spectrometry (SSMS) has been used extensively in the determination of trace elements in coal. Whole coal samples as well as ash residues, fly ash, and coal dust have been analyzed using this technique. 

The sorbent and leaching characteristics of fly ash can be related to operating temperatures in the boiler and to coal ash compositions that provide low ash fusion temperatures. Boiler temperatures that favor the fusion of the ash and maintain the ash in the fused state reduce the amount of trace elements leached from the fly ash and improve the sorbent characteristics of the fly ash for removal of these elements from ash pond effluents. In addition, the leachable amounts of each of the elements analyzed in this study can be correlated with the fly ash particle area and with their bulk compositions in the original coal. No correlation could be identified between the sorbent characteristics of fly ashes and their particle size and bulk, major, minor and trace elemental compositions, with the exception of the carbon content. Only organic removals, as measured by COD from ash pond effluent could be correlated with the carbon content of the fly ash particles. 

F, Hg, Mo, Ni, Pb, S, Sb, Se, and Zn. The comparison of partitioning data previously developed for bituminous and subbitum-inous coals with samples of lignite, bottom ash, and fly ash from two Texas lignite-fired power plants showed great variability in results. Therefore few conclusions regarding trace element partitioning as a function of coal rank can be drawn at this time,... 

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