The Chemical Analysis of Argonne Premium Coal Samples
Edited by Curtis A. Palmer
U.S. Geological Survey Bulletin 2144
Determination of Selected Elements in Coal Ash from Eight Argonne Premium Coal Samples by Atomic Absorption Spectrometry and Atomic Emission Spectrometry
By Michael W. Doughten
Methods for the determination of 22 elements in coal ash from Argonne Premium Coals by inductively coupled argon plasma-atomic emission spectrometry and flame and graphite furnace atomic absorption spectrometry are described. Coal ashes were analyzed in triplicate to determine the precision of the methods. Results of the analyses of National Institute of Standards and Technology (NIST) standard reference materials 1633 and 1633a are reported. Accuracy of the methods was determined by comparing element concentrations in standard reference materials determined in this study with their certified values and literature values.
Procedures are described and results are presented for the determination of 22 elements in the coal ashes from 8 Argonne Premium Coal samples by inductively coupled argon plasma-atomic emission spectrometry (ICAP-AES) and atomic absorption spectrometry (AAS). Results of the ICAP-AES and AAS analyses of two standard reference materials from the National Institute of Standards and Technology (formerly the National Bureau of Standards, NBS), NIST 1633 and 1633a (coal fly ashes), are included and are compared with their certified values as well as with other values reported in the literature. Cadmium and lead were determined by graphite furnace atomic absorption spectrometry (GFAAS); cobalt and lithium were determined by flame atomic absorption spectrometry (FAAS). All other elements were determined by ICAP-AES. All the analyses described in this paper were performed in the U.S. Geological Survey laboratory in Reston, Va.
SAMPLE PREPARATION
Raw coal samples were ashed by weighing 70 g of coal into a previously weighed porcelain crucible. The crucible was placed in an electric furnace, which was slowly heated to 200°C. After 1.5 hours at 200°C, the temperature was increased to 350°C and was held at that temperature for 2 hours. The temperature was then increased to 525°C and maintained for about 36 hours. After the sample cooled for 1 to 2 hours, the weight of the ash was determined by subtracting the weight of the crucible from the weight of the crucible plus ash. Ash yield was reported as percent ash and was calculated by:
Percent ash = (weight ash)/(weight coal) x 100
Percent ash data are listed in table 1.
Sample solutions for analysis by ICAP-AES and AAS were prepared by weighing 100 mg of the coal ash and placing it in a 75-mL Teflon screwcap bomb, then adding 7 mL of concentrated nitric acid. The bomb was capped and heated on a hotplate overnight at 200°C. After cooling, the bomb was uncapped, and 2 mL of concentrated nitric acid, 2 mL of concentrated perchloric acid, and 10 mL of hydrofluoric acid were added. All acids used were reagent grade. The bomb was then recapped and again heated on a hotplate at 200°C for 4 hours. The bomb was uncapped, and the solution evaporated to dryness. The sample was allowed to cool, and 10 mL of 2N hydrochloric acid was added. The bomb was recapped once again and gently heated until the solution was clear, indicating complete dissolution. The solution was then transferred to a 15-mL polyethylene tube. This digestion procedure was used to determine that the concentration of the coal ash in solution was 1 percent.
SAMPLE ANALYSIS
The determinations of Ba, Be, Cr, Cu, Mn, Ni, Sr, V, Y, Zn, K, P, and Ti were made directly on this solution by ICAP-AES using a Jarrell-Ash model 1160 Atomcomp ICP system. Cobalt and lithium were determined on this solution by FAAS using a Perkin-Elmer model 5000 atomic absorption spectrometer. A deuterium arc lamp background corrector was used for Co. Lithium requires no background correction. Concentrations for Co and Li were calculated from a calibration curve established by analyzing a set of cobalt and lithium standard solutions.
The sample solution was diluted 1 to 10 with 2N hydrochloric acid and analyzed for sodium and magnesium by ICAP-AES. Cadmium was determined on this solution by using a Perkin-Elmer atomic absorption spectrometer with a graphite furnace assembly (model HGA 500) and a Zeeman background correction system. Lead was determined on this solution by using a Perkin-Elmer model 603 atomic absorption spectrometer with a graphite furnace assembly (model HGA 2100) and a deuterium arc lamp background correction system. A 2 percent solution of ammonium phosphate (NH4 H2 PO4 ) (see table 2) was used as a matrix modifier for both Cd and Pb. Concentrations for Cd and Pb were calculated from a calibration curve (absorbance versus concentration (µg/g)) established from analyzing a set of Cd and Pb standard solutions. This diluted solution was further diluted to 1 to 100 with 2N hydrochloric acid and analyzed for aluminum, calcium, and iron by ICAP-AES.
All calibration solutions for AAS and AES were prepared in 2N hydrochloric acid. Instrumental operating parameters for GFAAS and FAAS are listed in tables 2 and 3. ICAP-AES wavelengths and concentration ranges are listed in table 4. Trace- and major-element concentrations are listed in tables 5 and 6.
NIST standard reference materials 1633 and 1633a were used as control standards for each determination. Each Argonne Premium Coal sample was run in triplicate (labeled 1, 2, and 3) with the exception of UT PC-6, which was run in duplicate due to a lack of available sample. Data for these analyses are shown in tables 5 and 6. The replicate analyses show the precision of the methods used. The relative percent standard deviation was generally about ±5 percent. Comparison of the analyses of these control standards with NIST certified values (NBS, 1975, 1979), with AAS values (Kane, 1989), and with values determined by instrumental neutron activation analysis (Ondov and others, 1975; Rowe and Steinnes, 1977) shows the accuracy of the methods (tables 7 and 8). ICAP-AES in Reston of samples WY PC-2 and POC PC-5 determined lower concentrations of barium and strontium than other methods of analysis (see table 2 in paper by Palmer and Klizas, this volume). They were probably caused by incomplete dissolution of barium sulfate present in the sample. Low Sr results may have been caused by Sr co-precipitating with Ba.
Sample IL PC-3 showed a wide concentration range for Ba (420-540 µg/g). Sample ND PC-8 showed low concentrations of potassium. These values were close to the detection limit, and that may account for the error. This also could be due to sampling error or incomplete digestion of barite that may be present in the sample.
Beryllium values determined by ICAP-AES were corrected for vanadium and titanium interferences, and zinc values determined by ICAP-AES were corrected for interferences by manganese, iron, and vanadium. Interference corrections vary depending on the instrument operating conditions used and should be determined before the start of the analysis.
Gladney, E.S., O'Malley, B.T., Roelandts, J., and Gills, T.E., 1987, Compilation of elemental concentration data for NBS clinical, biological, geological, and environmental standard reference materials: National Bureau of Standards Special Publication 260-111, p. 1633-1-1633-26, 1633a-1-1633a-14.
Kane, J.S., 1989, The determination of selected elements in coal ash by atomic absorption spectrometry in Golightly, D.W., and Simon, F.O., eds., Methods for sampling and inorganic analysis of coal: U.S. Geological Survey Bulletin 1823, p. 47-53.
National Bureau of Standards, 1975, National Bureau of Standards certificate of analysis, standard reference material 1633, trace elements in coal fly ash: Washington, D.C., National Bureau of Standards, 2 p.
------1979, National Bureau of Standards certificate of analysis, standard reference material 1633a, trace elements in coal fly ash: Washington, D.C., National Bureau of Standards, 2 p.
Ondov, J.M., Zoller, W.H., Olmez, Ilham, Aras, N.K., Gordon, G.E., Rancitelli, L.A., Abel, K.H., Filby, R.H., Shah, K.R., and Ragaini, R.C., 1975, Elemental concentrations in the National Bureau of Standards' environmental coal and fly ash standard reference materials: Analytical Chemistry, v. 47, no. 7, p. 11020-1109.
Rowe, J.J., and Steinnes, E., 1977, Instrumental activation analysis of coal and fly ash with thermal and epithermal neutrons: Journal of Radioanalytical Chemistry, v. 37, no. 2, p. 849-856
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