The chemical speciation of Ni in fly ash produced from approximately 0.85 wt % S residual (no. 6 fuel) oils in laboratory (7 kW)- and utility (400 MW)-scale combustion systems was investigated using X-ray absorption fine structure (XAFS) spectroscopy, X-ray diffraction (XRD), and acetate extraction [1 M NaOAc-0.5 M HOAc (pH 5) at 25 degrees C]-anodic stripping voltammetry (ASV). XAFS was also used to determine the Ni speciation of ambient particulate matter (PM) sampled near the 400-MW system. Based on XAFS analyses of bulk fly ash and their corresponding acetate extraction residue, it is estimated that > 99% of the total Ni (0.38 wt %) in the experimentally produced fly ash occurs as NiSO4.xH2O, whereas > 95% of the total Ni (1.70 and 2.25 wt %) in two fly ash samples from the 400-MW system occurs as NiSO4.xH2O and Ni-bearing spinel, possibly NiFe2O4. Spinel was also detected using XRD. Acetate extracts most of the NiSO4.xH2O and concentrates insoluble NiFe2O4 in extraction residue. Similar to fly ash, ambient PM contains NiSO4.xH2O and NiFe2O4; however, the proportion of NiSO4.xH2O relative to NiFe2O4 is much greater in the PM. Results from this and previous investigations indicate that residual oil ash produced in the 7-kW combustion system lack insoluble Ni (e.g., NiFe2O4) but are enriched in soluble NiSO4.xH2O relative to fly ash from utility-scale systems. This difference in Ni speciation is most likely related to the lack of additive [e.g., Mg(OH)2] injection and residence time in the 7-kW combustion system.

Volz and W. D. Mayer, ibid., 4249 (1966). (6) Attempts to prepare 1-halocyclopropyl and -cyclobutyl cations were so far unsuccessful. Further efforts to generate these ions are underway. (7) (a) G. A. Olah and P. E.

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The speciation of Ni emissions from residual oil-fired utility boilers requires investigation because the possible presence of small respirable particles containing Ni 3 S 2 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-S (0.33 and 1.80 wt %, respectively) residual oil was produced using a 42-MJ/h combustion system at excess O 2 concentrations of e1 and 2 or 3 mol %. Ni speciation analyses were performed using X-ray absorption fine-structure (XAFS) spectroscopy and sequential extraction-anodic stripping voltammetry (ASV). XAFS measurements indicate that >95% of the total Ni (3-9 wt %) present in the ashes occurs as Ni 2+ coordinated to O 2-. Both methods indicate that NiSO 4 is the dominant form, although significant proportions of NiO (5-24%) were measured by sequential extraction-ASV. The sequential extraction-ASV method also indicated the presence of very small proportions, <2%, of Ni sulfide (Ni x S y ). Fuel S content did not significantly affect Ni speciation; however, increasing excess O 2 concentrations promoted Ni sulfation. The predominance of NiSO 4 and relatively low proportions of Ni x S y in the experimentally produced ashes are inconsistent with sequential extraction-ASV determinations of Ni speciation in ashes collected from full-scale utility boilers. Differences in sampling procedures and combustion conditions are being investigated to explain this inconsistency.