SCIENCE: Surface Enrichment of Trace Elements in Electric Steel Furnace Dust

Article in Environmental Science & Technology (1983) 17, 435-439 by Marc J. Van Craen, Erlc A. Denoyer, David F. S. Natusch, and F. Adams (Department of Chemistry, University of Antwerp, Belgium).

Secondary ion mass spectrometry (SIMS) and laser microprobe mass analysis (LAMMA) have been used to study the surface enrichment of trace elements in dusts emitted from an electric steel making furnace. It is demonstrated that the elements Na, P, S, C1, K, Cr, Mn, Co, Cu, Zn, and Pb are preferentially enriched on the particle surfaces and that several of these elements are appreciably leachable by water. In several cases the chemical forms of the elements are indicated.

Introduction
A number of workers have reported the observation that certain trace elements increase in specific concentration (micrograms per gram) with decreasing particle size in particles emitted to the atmosphere from high-temperature combustion or conversion processes (1-5). The mechanism that gives rise to this phenomenon has not been fully established; however it has been suggested (1,6) that certain trace elements, or their compounds, are volatilized at the elevated temperatures encountered during particle formation and then condense onto the surfaces of coentrained particles during emission. Such a mechanism would give rise to surface enrichment of the volatilized elements, and this has been observed for coal fly ash and for automobile exhaust particles (7, 8).

The environmental significance of surface enrichment of potentially toxic species is several fold. First, if it occurs as a result of the proposed volatilization-condensation mechanism, small particles will contain higher concentrations of trace elements than large particles, and this will promote emission to the atmosphere, atmospheric enrichment, and pulmonary deposition following inhalation (1, 9). Second, surface enrichment results in enhanced concentrations of potentially toxic species being in immediate contact with the external environment (e.g., body fluids). Finally, if the surface-enriched species are soluble, as is the case for coal fly ash and automobile exhaust particles, then they can be readily mobilized to produce possibly adverse environmental or toxicological effects.

In order to explore further the universality of the surface- enrichment phenomenon, we have chosen to study dust derived from an electric steel making furnace. The trace elements present are derived from the original ore used, and the high temperatures (1500 “C) involved in the furnace operation are sufficient to volatilize several of the elements known to be present. The techniques employed include secondary ion mass spectrometric (SIMS) determination of elemental depth profiles in particle conglomerates, laser microprobe mass analysis (LAMMA) of individual particles, and X-ray fluorescence spectrometry (XRF) of the bulk particulate sample. In all cases analyses are performed before and after the particles have been leached with water to determine the extent of solubility of surface-enriched species. …

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