Environ. Sci. Technoi. 1084, 18, 124-126
Identification of V02+ in Particles from the Flue Lines of Oil-Fired Power Plantst Delbert J. Eatough," Norman L. Eatough, Max W. Hill, Nolan F. Mangelson, and Lee D. Hansen
Thermochemical Institute and Departments of Chemistry and Physics, Brigham Young University, Provo, Utah 84602 Fly ash samples were collected from the flue lines of two different oil-fired power plants and analyzed by a variety of analytical procedures designed to determine the V cations extractable from the samples. Both V02+ and V02+were shown to be present in the samples. The V(V) cation, V02+,was the principal species extracted from these samples.
Introduction Vanadium is a major constituent of the fly ash resulting from the combustion of oil. However, little information is available on the chemical nature of V in such ashes. Henry and Knapp ( I ) have reported X-ray diffraction, XRD, and fourier transform infrared spectroscopy, FTIR, data indicating that Vz05and VOS04.3Hz0 were present in the oil fly ash samples studied by them. The VzO, was insoluble in water whereas the V02+cation was readily extracted by water. An additional V species was extracted from some samples, but the identity could not be established from the available data. The FTIR spectrum for this unidentified vanadium salt was similar to but not identical with that for VS04.2Hz0. The possible presence of VS04.2Hz0was not supported by the XRD data. They conclude that a VS04 salt of a different hydration state may account for the observed spectra. On the basis of valence state analysis, Henry and Knapp (1)could find no evidence for soluble V(V> cations in the oil fly ashes studied by them. Allegrini and Mattogno (2) have reported on the surface analysis of collected oil fly ash using photoelectron spectroscopy. They demonstrated the presence of at least three chemical forms of vanadium in the samples studied. The exact chemical species present were not established, but the observed binding energies were consistent with those expected for V(1V) or V(V) oxides. It would seem probable that some soluble V(V) could be present in oil fly ash samples. In acidic ( 1 , 3 )oil fly ashes it would be expected that soluble V(V) would be present as the V02+ cation ( 4 ) , presumably as (VO2)MSO4or (VOz)zS04salts, where M is some other monovalent cation. The presence of soluble VOz+ salts can be expected to affect both the toxicity and chemistry associated with oil fly ash. It is known that V02+has a low toxicity, but the VOz+ cation is highly toxic (5, 6 ) . We report here the results of analytical procedures designed to determine the possible presence of V02+ in aqueous extracts of flue line collected oil fly ash samples. Experimental Section Fly ash samples were obtained by isokinetic sampling from the flue lines, near the stack header, of two different oil-fired power plants located near Greenville, MS, and Morro Bay, CA. The plant in Mississippi (MS) is a 770MW plant burning domestic gulf coast oil. The details of sample collection have been previously published (7). The plant in California (CA) is a 1030-MW plant burning Venezuelan oil, nominally containing 0.5% S. Samples at the CA plant were obtained from the flue line by sampling isokinetically onto 47-mm acid-washed quartz fiber filters Thermochemical Institute ContribuGonNo. 257. 124
Environ. Sci. Technol., Vol. 18, No. 2, 1984
(Pallflex,Inc.). The sample flow rate was about 10 L/min, and the filter was maintained at the flue line gas temperature (150 "C) during sampling. Two samples were collected, each during a 60-min sampling period. Samples were stored in sealed containers filled with Ar and kept at -80 "C until analyzed. The sample from the plant in MS was split in half for the various analysis procedures. Half of the sample was extracted with HzO for 20 min in an ultrasonic bath. The resulting solution was filtered and analyzed by ion chromatography, IC, proton-induced X-ray emission analysis, PIXE (€9,and a combined pH-calorimetric procedure (9) to determine anions, elemental content, and acid-base titratable species, respectively. The remaining half of the sample was extracted with 0.1 M HC1/2.5 mM FeC13for 20 min in an ultrasonic bath and filtered. The acid-extracted material was analyzed for Crz072--oxidizable species, S042-,and NOz-by calorimetric procedures (10-12) and by PIXE for elemental content. AS substantially less material was obtained in the samples collected at the oil-fired power plant in CA, the sample analysis scheme was altered slightly. Each collected sample from this plant was extracted with H20, and the analysis procedures described above were carried out. A fraction of the HzO extract was mixed with a 0.5 M HC1/12.5 mM FeC13solution to give a 0.1 M HC1/2.5 mM FeC1, solution which was analyzed calorimetrically as described above.
Results The results of the analyses are summarized in Table I and in Figures 1 and 2. The NO3-, and C1- concentrations given in Table I were determined by IC analysis of the aqueous extracts. The concentration of S042-in the acidic extract of the MS sample was also determined calorimetrically. The IC and calorimetric determinations of sulfate were in agreement. The concentrations of H+, VOz+,and V02+were determined from the results of the combined pH-calorimetric titrations of aqueous extracts as discussed below. The concentrations of K+, Ca2+,Vbt, Fe3+,Ni2+,Zn2+,and Pb2+were determined by PIXE analysis of the aqueous extracts and also by PIXE analysis of the acidic extract of the MS sample. The concentrations of elements determined by PIXE analysis of the aqueous and acidic extracts of the MS sample were in agreement except for the concentrations of Ca2+and Fe3+as noted in Table I. The Fe3+oxidation state is assigned to iron because the calorimetric redox titrations all indicated no Fe2+was present in the samples analyzed. No Fe(II), S(1V) (12),or NO, ( I O ) was detected in any of the samples by the analytical procedures used. Discussion The combined calorimetric, IC, and PIXE data allowed the identification of the extractable V cations in the oil fly ash samples studied. The data indicated that V02+and V02+cations were both present. No soluble V2+or V3+ was seen. The evidence for these conclusions follows for each cation. V2+and V3+Cation. That no soluble V(I1) or V(II1) compounds were present in the samples was established by both the acid-base and the calorimetric redox titration
0013-936X/84/0918-0124$01.50/0
0 1984 American Chemical Society
Table I. Species Determined to be Present in H,O Extracts of the Oil Fly Ash Samples. Given as the Mole Ratio to Sulfate' sample SO,zNO,c1H+ K+ Caz+
MS
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