Browsing by Subject "Fly ash - Analysis"

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    Direct determination of cadmium and beryllium in coal and fly ash slurries using graphite furnace atomic absorption spectrometry
    (1990) Haraldsen, Lana Celeste; Pougnet, M A Bruno
    Graphite Furnace Atomic Absorption Spectrometry (GFAAS) was used for the determination of cadmium and beryllium in coal and fly ash slurries. Sample preparation involved grinding the sample to a fine powder and slurrying it in a suitable solvent. Stable slurries were maintained by magnetic stirring during sampling. Pyrolytically coated graphite tubes were used for cadmium determinations, while beryllium was determined with platform atomisation. Ammonium dihydrogen orthophosphate and magnesium nitrate matrix modifiers were used for cadmium and beryllium determinations respectively. Calibration graphs constructed with aqueous standards containing the appropriate matrix modifier were rectilinear to at least 100 pg cadmium and 45 pg beryllium. Results were calculated with integrated peak area measurements. The detection limits were 2.9 pg for cadmium and 0.7pg for beryllium. Beryllium determinations were performed with semi-automatic sample introduction. The novel semi-automatic sampling unit utilised magnetic stirring for· the maintenance of stable slurries and operated with the standard Perkin-Elmer AS-40 autosampler. The principles of this unit were extended to the development of a fully automatic auto-sampling unit. The design and operation of both units are described. The accuracy of the methods was evaluated by analysing standard reference materials and in some cases, comparisons with acid digestion procedures. Data are presented for the analysis of South African coal and fly ash samples. The slurry methods had acceptable accuracy and precision. In comparison with the conventional acid digestion procedures using high pressure bombs, a time-saving advantage was realised.
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    The mineralogy and chemistry of pulverised fuel ash produced by three South African coal-burning power stations
    (1990) Bosch, Gordon L
    The chemical and mineral compositions are presented for 63 pulverized fuel ash (PFA) and 16 input coal samples collected from Lethabo, Duvha and Matla power stations over the period 1987-1988. Bulk chemical composition was determined by X-ray fluorescence spectrometry. The mineral concentrations were determined by semi-quantitative X-ray diffraction based on integrated counts over peak areas, with silicon used as an internal standard. The particle size distributions were determined for two sample sets from each power station with a Malvern Instruments Particle Sizer. The major phases present in the ash are glass ( 45-75% ), mullite (16-39%) and quartz (1.5-16% ). The quartz concentration decreases in PF A from fields 1 to 4 in all the stations, and is positively correlated with the SiO₂ concentration. The concentrations of glass, mullite and quartz in PFA generally vary within well defined limits which remain constant with time. An exception is the glass concentration in Duvha PFA. Spinel concentration generally decreases in concentration in PFA from fields 1 to 4, and is positively correlated with the Fe₂O₃ concentration. Of the trace elements determined, Zr, Rb and Mn generally have no or very low enrichment in concentration in PFA from fields 1 to 4. The highest enrichment factors ( > 5) were found for As, Ge and Se in Duvha PF A. The composition of the glass and ferrite spinel phases were determined by electron microprobe analysis. The glass consists of SiO₂ (21-100%) and Al₂ O₃ (0.1-49%), with significant proportions of CaO, TiO₂, Fe₂O₃ and MgO. Al₂O₃ , MgO and TiO₂ substitute for FeO in the spinel structure, with MgO substitution dominant in Duvha spinels. Chemical mass balance calculations suggest that of the elements determined for Lethabo PFA, the only one released in a significant proportion to the atmosphere is S(92% ).