Final Report: Nickel, Chromium, and Arsenic Speciation of Ambient Particulate Matter in the Vicinity of an Oil-Fired Utility Boiler

EPA Grant Number: R827649C010
Subproject: this is subproject number 010 , established and managed by the Center Director under grant R827649
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Center for Air Toxic Metals® (CATM®)
Center Director: Groenewold, Gerald
Title: Nickel, Chromium, and Arsenic Speciation of Ambient Particulate Matter in the Vicinity of an Oil-Fired Utility Boiler
Investigators: Pavlish, John H. , Benson, Steven A. , Galbreath, Kevin C. , Timpe, Ronald C. , Zygarlicke, Christopher J. , Hassett, David J. , Holmes, Michael J. , Miller, Stanley J. , Laudal, Dennis L. , Olson, Edwin S. , Thompson, Jeffrey S. , Heebink, Loreal V. , Ralston, Nicholas V.C. , Mibeck, Blaise , Kong, Lingbu
Institution: University of North Dakota
EPA Project Officer: Chung, Serena
Project Period: October 15, 1999 through October 14, 2004
RFA: Center for Air Toxic Metals (CATM) (1998) RFA Text |  Recipients Lists
Research Category: Targeted Research


The objective of this research project was to address air toxic trace element emissions, which have become a matter of worldwide concern as well as a regulatory issue in the United States. The specific objective of this research project was to develop and disseminate critical information on air toxic metal compounds to support development and implementation of pollution prevention and control strategies that will reduce effectively air toxic metal emissions and releases to the environment.

Summary/Accomplishments (Outputs/Outcomes):

Uncertainties in the chemical speciation of nickel, chromium, and arsenic in ambient particulate matter (PM) associated with oil-fired boilers greatly affect inhalation health risk estimates, primarily because of the great variability in cancer potencies for different chemical species. Nickel subsulfide and hexavalent chromium were of primary concern because of their carcinogenicity.

Both thermodynamic modeling and experimental results indicate that NiSO4·H2O and Cr2(SO4)3 are the predominant low-temperature species in both low- and high-sulfur residual oil ashes. Competing reactions of alkali- and alkaline-earth metals with SOx(g) and H2SO4(l,g) are expected to limit nickel sulfation. To evaluate the amount of sulfation, several samples were analyzed using many different techniques. Discrete phases of nickel or chromium were not detected using scanning electron microscopy and X-ray diffraction, which suggests that nickel and chromium forms are submicron and, perhaps, amorphous. K-edge X-ray absorption fine-structure (XAFS) spectroscopy analyses indicated that NiSO4 and Cr2(SO4)3, and not the more toxic Ni3S2 and Cr6+ forms, were predominant (> 95%) in the residual oil ashes that were analyzed. No detectable Ni3S2 was observed in ash samples from either the conversion and environmental process simulator (CEPS) or full-scale tests. More than 99 percent of the nickel in fly ashes produced in CEPS tests was NiSO4·xH2O, and greater than 95 percent of the nickel in fly ashes from two different residual oils burned in a full-scale boiler was identified as a combination of NiSO4·xH2O and nickel-bearing spinel. The same forms of nickel were analyzed by XAFS in ambient total suspended particulate (TSP) matter collected from the plant, but the ratio of sulfate to spinel was greater in ambient TSP. Further studies on urban TSP, PM10, and PM2.5 samples collected from an air-monitoring site in Davie, Florida, indicated the presence of NiSO4·xH2O, a spinel-type mineral, and a very small amount of NiS.

These overall findings suggest that the carcinogenic properties of nickel emissions from residual oil-fired boilers are overestimated in the U.S. Environmental Protection Agency’s nickel inhalation cancer risk assessment, which assumed that the nickel emitted would have 50 percent of the carcinogenic potency of Ni3S2, whereas the sulfate and spinel forms identified in this study are not known to present a cancer risk—albeit other health risks may be a concern.

Supplemental Keywords:

air, air quality, analysis, control, emissions, environment, hazardous, measurement, mercury, metals, modeling, pollutants, pollution, sampling, species, toxic, transformations,, Scientific Discipline, Air, Toxics, Chemical Engineering, Environmental Chemistry, HAPS, 33/50, Engineering, Chemistry, & Physics, Environmental Engineering, residual oil-fired utility boiler, Chromium, nickel speciation, chemical composition, chemical detection techniques, oil fired utility boiler, nickel & nickel compounds, Nickel Compounds, arsenic speciation, residual oil ash

Relevant Websites: Exit Exit

Progress and Final Reports:

Original Abstract
  • 2000
  • 2001
  • 2002
  • 2003 Progress Report

  • Main Center Abstract and Reports:

    R827649    Center for Air Toxic Metals® (CATM®)

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R827649C001 Development And Demonstration Of Trace Metals Database
    R827649C002 Nickel Speciation Of Residual Oil Ash
    R827649C003 Atmospheric Deposition: Air Toxics At Lake Superior
    R827649C004 Novel Approaches For Prevention And Control For Trace Metals
    R827649C005 Wet Scrubber System
    R827649C006 Technology Commercialization And Education
    R827649C007 Development Of Speciation And Sampling Tools For Mercury In Flue Gas
    R827649C008 Process Impacts On Trace Element Speciation
    R827649C009 Mercury Transformations in Coal Combustion Flue Gas
    R827649C010 Nickel, Chromium, and Arsenic Speciation of Ambient Particulate Matter in the Vicinity of an Oil-Fired Utility Boiler
    R827649C011 Transition Metal Speciation of Fossil Fuel Combustion Flue Gases
    R827649C012 Fundamental Study of the Impact of SCR on Mercury Speciation
    R827649C013 Development of Mercury Sampling and Analytical Techniques
    R827649C014 Longer-Term Testing of Continuous Mercury Monitors
    R827649C015 Long-Term Mercury Monitoring at North Dakota Power Plants
    R827649C016 Development of a Laser Absorption Continuous Mercury Monitor
    R827649C017 Development of Mercury Control Technologies
    R827649C018 Developing SCR Technology Options for Mercury Oxidation in Western Fuels
    R827649C019 Modeling Mercury Speciation in Coal Combustion Systems
    R827649C020 Stability of Mercury in Coal Combustion By-Products and Sorbents
    R827649C021 Mercury in Alternative Fuels
    R827649C022 Studies of Mercury Metabolism and Selenium Physiology