Progress XAFS spectroscopy, sequential extraction-ASV, and CPEV measurements indicate that soluble NiSO4 and not the more toxic Ni3S2 ,species predominate in low- and high-S residual oil ashes produced experimentally at excess 0, concentrations of 5 1% and 2 or 3 mol%. As indicated in the following table, the sequential extraction-ASV method detected the presence of significant proportions of NiO that was not detected using XAFS spectroscopy, even though the spectra of NiO are very distinctive from those for the dominant NiSO4 species. In future research, residue from the first step of the extraction procedure in the table on p. 44 will be analyzed using XAFS spectroscopy to corroborate the existence of NiO in residual oil ash. Fuel S content did not significantly affect Ni speciation; however, increasing excess 02 concentrations promoted Ni sulfation. The sequential extraction-ASV method also indicated the presence of very small proportions, <2%, of nickel sulfide. Analyses of a high-sulfur oil ash sample and the extraction residues from this ash by CPEV suggest that the nickel sulfide is present as NiS and not Ni3S2. The proportions of sulfidic nickel (NixSy) and NiO measured in these ash samples produced experimentally are much lower, while the relative proportions of soluble Ni are much greater than previous sequential extraction-ASV measurements of oil ashes collected from utility-scale boilers. Potential sources of these differences in Ni speciation include the sampling methods employed and the actual physicochemical properties of the ashes produced in a laboratory-scale versus utility-scale com bustion system. Research is currently under way to identify the cause(s) of disagreement in Ni speciation results. Supplemental Keywords: Toxics, Air, Scientific Discipline, Engineering, Chemistry, & Physics, Chemical Engineering, HAPS, Environmental Engineering, Environmental Chemistry, Environmental Monitoring, 33/50, heavy metals, oil fired utility boiler, nickel speciation, Nickel Compounds, residual oil ash, nickel & nickel compounds, residual oil-fired utility boilerProgress and Final Reports: 2002 Progress Report The speciation of Ni emitted from residual-oil-fired utility boilers requires investigation because the possible presence of small respirable particles containing nickel subsulfide (Ni3S2) is a health concern. An experimental approach was used to investigate the Ni speciation of residual oil combustion ash. Ash from a low- and high-sulfur (0.33 and 1.80 wt%, respectively) residual oil was produced using a laboratory-scale combustion system at excess O2 concentrations of I 1 and 2 or 3 mol%. Ni speciation analyses were performed using XAFS spectroscopy, sequential extraction-ASV, and CPEV. Research goals are threefold: Identify and quantify the chemical forms of Ni in No. 6 fuel oil combustion ash Investigate the effects of fuel sulfur (S) and excess 0, concentrations on Ni speciation Evaluate the comparability of Ni speciation analysis results obtained by sequential extraction-ASV, CPEV, and XAFS spectroscopy The speciation of Ni emitted from residual-oil-fired utility boilers requires investigation because the possible presence of small respirable particles containing nickel subsulfide (Ni3S2) is a health concern. An experimental approach was used to investigate the Ni speciation of residual oil combustion ash. Ash from a low- and high-sulfur (0.33 and 1.80 wt%, respectively) residual oil was produced using a laboratory-scale combustion system at excess O2 concentrations of I 1 and 2 or 3 mol%. Ni speciation analyses were performed using XAFS spectroscopy, sequential extraction-ASV, and CPEV. Research goals are threefold: Identify and quantify the chemical forms of Ni in No. 6 fuel oil combustion ash Investigate the effects of fuel sulfur (S) and excess 0, concentrations on Ni speciation Evaluate the comparability of Ni speciation analysis results obtained by sequential extraction-ASV, CPEV, and XAFS spectroscopy" /> NICKEL SPECIATION OF RESIDUAL OIL ASH | Science Inventory | US EPA

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NICKEL SPECIATION OF RESIDUAL OIL ASH

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Impact/Purpose:

The speciation of Ni emitted from residual-oil-fired utility boilers requires investigation because the possible presence of small respirable particles containing nickel subsulfide (Ni3S2) is a health concern. An experimental approach was used to investigate the Ni speciation of residual oil combustion ash. Ash from a low- and high-sulfur (0.33 and 1.80 wt%, respectively) residual oil was produced using a laboratory-scale combustion system at excess O2 concentrations of I 1 and 2 or 3 mol%. Ni speciation analyses were performed using XAFS spectroscopy, sequential extraction-ASV, and CPEV.

Research goals are threefold:

  • Identify and quantify the chemical forms of Ni in No. 6 fuel oil combustion ash
  • Investigate the effects of fuel sulfur (S) and excess 0, concentrations on Ni speciation
  • Evaluate the comparability of Ni speciation analysis results obtained by sequential extraction-ASV, CPEV, and XAFS spectroscopy

The speciation of Ni emitted from residual-oil-fired utility boilers requires investigation because the possible presence of small respirable particles containing nickel subsulfide (Ni3S2) is a health concern. An experimental approach was used to investigate the Ni speciation of residual oil combustion ash. Ash from a low- and high-sulfur (0.33 and 1.80 wt%, respectively) residual oil was produced using a laboratory-scale combustion system at excess O2 concentrations of I 1 and 2 or 3 mol%. Ni speciation analyses were performed using XAFS spectroscopy, sequential extraction-ASV, and CPEV.

Research goals are threefold:

  • Identify and quantify the chemical forms of Ni in No. 6 fuel oil combustion ash
  • Investigate the effects of fuel sulfur (S) and excess 0, concentrations on Ni speciation
  • Evaluate the comparability of Ni speciation analysis results obtained by sequential extraction-ASV, CPEV, and XAFS spectroscopy

Description:

EPA GRANT NUMBER: R827649C002
Title: Nickel Speciation Of Residual Oil Ash
Investigators: Kevin C. Galbreath, John Won, Frank E. Huggins, Gerald P. Huffman, Christopher J. Zygarlicke, Donald L. Toman
Institution: University of North Dakota
EPA Project Officer: Bill Stelz
Project Period: October 15, 1999 - October 14, 2002
Project Amount: $10,000
RFA: Center for Air Toxic Metals (CATM)
Research Category: Targeted Research

Description

Objective:

The speciation of Ni emitted from residual-oil-fired utility boilers requires investigation because the possible presence of small respirable particles containing nickel subsulfide (Ni3S2) is a health concern. An experimental approach was used to investigate the Ni speciation of residual oil combustion ash. Ash from a low- and high-sulfur (0.33 and 1.80 wt%, respectively) residual oil was produced using a laboratory-scale combustion system at excess O2 concentrations of I 1 and 2 or 3 mol%. Ni speciation analyses were performed using XAFS spectroscopy, sequential extraction-ASV, and CPEV.

Research goals are threefold:

  • Identify and quantify the chemical forms of Ni in No. 6 fuel oil combustion ash
  • Investigate the effects of fuel sulfur (S) and excess 0, concentrations on Ni speciation
  • Evaluate the comparability of Ni speciation analysis results obtained by sequential extraction-ASV, CPEV, and XAFS spectroscopy






Approach:

Combustion tests were conducted using a CEPS, a 42-MJ/hr combustion system, to elucidate differences in the Ni speciation of ashes produced from low- and high-S fuel oils at excess O2 concentrations of I 1 and 2 or 3 mol%. Detailed descriptions of the CEPS are provided in the CATM 1994-1995 Annual Report [l] and in a previous CATM Newsletter [2]. Bulk ash samples were collected at the inlet of the convection pass section of the CEPS using glass-fiber filters. The ash samples were analyzed first using XAFS spectroscopy because it is a nondestructive technique. Ni K-edge XAFS spectroscopy measurements were conducted on beam line X-19A of the National Synchrotron Light Source, Brookhaven National Laboratory, New York. XAFS spectra of reagent-grade Ni compounds were acquired and used essentially as "fingerprints" for identifying different Ni species. The five-step extraction procedure in the table below was also used for determining Ni speciation. Ni in each extract was quantified by ASV of nickel dimethylglyoxime collected on a hanging mercury drop electrode with a CH-620 electroanalytical system in square-wave voltammetry mode. Ni concentration was obtained by the method of standard additions. In addition to analyzing the Ni extraction fractions, total Ni was determined. Although this method currently cannot be used to discriminate between nickel sulfide and subsulfide species, CPEV was used to distinguish between Ni3S2 and NiS. Mineral and synthetic standards of Ni3S2 and NiS as well as ash and extraction residues were mixed with microcrystalline graphite powder and fashioned into CPEs. Cyclic voltammetry and linear sweep voltammetry were performed using a CH-620 electroanalyzer to identify Ni3S2 and NiS.


RONG>Progress

XAFS spectroscopy, sequential extraction-ASV, and CPEV measurements indicate that soluble NiSO4 and not the more toxic Ni3S2 ,species predominate in low- and high-S residual oil ashes produced experimentally at excess 0, concentrations of 5 1% and 2 or 3 mol%. As indicated in the following table, the sequential extraction-ASV method detected the presence of significant proportions of NiO that was not detected using XAFS spectroscopy, even though the spectra of NiO are very distinctive from those for the dominant NiSO4 species. In future research, residue from the first step of the extraction procedure in the table on p. 44 will be analyzed using XAFS spectroscopy to corroborate the existence of NiO in residual oil ash. Fuel S content did not significantly affect Ni speciation; however, increasing excess 02 concentrations promoted Ni sulfation. The sequential extraction-ASV method also indicated the presence of very small proportions, <2%, of nickel sulfide. Analyses of a high-sulfur oil ash sample and the extraction residues from this ash by CPEV suggest that the nickel sulfide is present as NiS and not Ni3S2. The proportions of sulfidic nickel (NixSy) and NiO measured in these ash samples produced experimentally are much lower, while the relative proportions of soluble Ni are much greater than previous sequential extraction-ASV measurements of oil ashes collected from utility-scale boilers. Potential sources of these differences in Ni speciation include the sampling methods employed and the actual physicochemical properties of the ashes produced in a laboratory-scale versus utility-scale com

bustion system. Research is currently under way to identify the cause(s) of disagreement in Ni speciation results.

Supplemental Keywords: Toxics, Air, Scientific Discipline, Engineering, Chemistry, & Physics, Chemical Engineering, HAPS, Environmental Engineering, Environmental Chemistry, Environmental Monitoring, 33/50, heavy metals, oil fired utility boiler, nickel speciation, Nickel Compounds, residual oil ash, nickel & nickel compounds, residual oil-fired utility boiler

Progress and Final Reports:
2002 Progress Report

Record Details:

Record Type:PROJECT( ABSTRACT )
Start Date:10/15/1999
Completion Date:10/14/2002
Record ID: 53857