Journal ofRadioanalytical Chemistry, VoL 31 (1976) 495-502

I N S T R U M E N T A L N E U T R O N A C T I V A T I O N ANALYSIS

OF F L Y ASHES AND EMISSIONS

I. OBRUSNI'K,* ]3. STARKOVA,** J. BLA~EK**

*Nuclear Research Institute, 250 68 ~e~ near Prague (Czechoslovakia)

**Research Institute o f A ir Engineering, Prague (Czechoslovakia)

(Received November 12, 1975)

Instrumental neutron activation analysis (INAA) has been utilized for the analysis of 19 dif- ferent fly ashes, 1 sample of coal and 3 samples of industrial emissions. Both short and long ir- radiations in a nuclear reactor have been used. The irradiated samples have been measured by means of a computer-based Ge(Li)gamma-ray spectrometer. The concentrations of 27 elements have been determined in the samples.

Introduction

Over the past several years there has been increasing concern about environmental pollution problems. A great interest has been devoted to air pollution analysis. Many analyses of pol- lution aerosols have been made all over the world. One of the analytical methods suitable for such kind of analyses is instrumental activation analysis 0NAA).

The main sources of aerosols in air are: stationary industrial fossil fuel combustion (coal based power plants, thermal power plants etc.), various industrial processes (cement works, iron works, chemical industry etc.), automobile fuel combustion and, finally, the natural dust originating from soils.

Solid particles originating from fly ashes produced by the combustion of solid fuels (coal) contribute rather seriously to the air pollution in Czechoslovakia. Fine particles of the fly ashes penetrate through current separating devices of large combustion sources (e. g. particles with the size below 30tam penetrate through mechanical separation devices while particles smaller than 5/~m penetrate through two-step separating devices).

Then, aerosols can be created by the dispersion of such f'me particles in the surroundings of the combustion sources. The fly ashes emitted from the combustion sources are harmful and dangerous because they are carriers of a number of harmful and toxic elements.

INAA as a very sensitive multielemental analytical method, has been used most often for the complete analysis of aerosols (e.g. Refs l-l 0). However, the papers dealing with an

I. RadioanaL Chem. 31 (1976) 495

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INAA of fly ashes and other emissions are rather rare I 1-17 in comparison with the INAA of aerosols, even though these materials can seriously contribute to air contamination. Re- cently, the National Bureau of Standards (NBS) produced a standard reference material SRM 1633 made from fly ash, l i-is which seems to be a very promising standard reference material.

In this work, we have tried to analyze the samples of fly ashes and some other emissions taken from various sources by INAA. We have determined concentration ranges of some major, minor and trace elements in these samples. The next step in our work will be a comparative INAA of fly ashes and aerosols taken simultaneously from the area close to the large source of fly ash emission.

Experimental

Sampling procedure

Fly ashes or emissions were taken from a smoke duct by a sampling isokinetic tube either prior to or after passing through a separating device. 19 samples of different fly ashes from power stations and steam generating stations were analyzed. The samples of emissions were taken from cement works and fluorite mills. All samples were homogenized prior to analysis.

Non-destructive neutron activation analysis

A procedure for non-destructive NAA of fly ashes and emissions consisted of two ir- radiations: a short (10 rain) irradiation and a long one (6 hrs).

(a)Short irradiation (10 min) was used for the determination of elements giving rise to short-lived isotopes. Samples and standards packed in polyethylene vials were placed in a rabbit which carried them through a pneumatic tube (35 sec) to a position in the core of the nuclear reactor in l~,e~ with a neutron flux of I �9 1013 n-cm "2 �9 sec q . Each irradiated sample was then counted twice with a Plurimat 20 computer-based Ge(Li) 4096 channel gamma-ray spectrometer system. Two samples and one neutron flux monitor were irradi- ated simultaneously. The following schedule of counting was used:

First counting: The first sample-counting was started I0 min after the end of irradiation; counting geometry G~ (21 cm), counting interval 5 min, energy range up to 3200keV. The second sample-counting was started 20 rain after the end of irradiation; geometry G2 (8 cm), counting time 10 min, energy range up to 2000 keV. The isotopes 28A1, S2v, Sl Ti, S6Mn, 49Ca and lZSI were predominant in the spectra from the first counting. The irradiation of the next samples was carried out during the counting of the second sample.

496 J. Radioanal. Chem. 31 (1976)

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Second counting:All samples were counted 12-36 hrs after the end of irradiation; geometry G3 (2 cm), counting interval 10 min, energy range 2000 keV. The photopeaks of 24Na, a2 K, 76As, 7:Ga and ~4~ were predominant in the spectra.

The same procedure was used for the irradiation and counting of multielement standards) 6 1 O0/~g of copper was used as a neutron flux monitor.

(b) Long irradiation (6 hrs) was used for the determination of elements giving rise to long-lived radionuclides. 20 mg samples of fly ash or emission were packed in a thick (1 mm) polyethylene foil and irradiated together with multielement standards and Co/Au neutron flux monitor. The samples and corresponding standards were then counted 24-36 hrs after the irradiation. The elements As, La, K, Na, Br, Sm, Ga etc. were determined by this measurement. By the second counting, after 14-21 days cooling time, we determined all the remaining elements (Fe, Sc, Sb, Co, Zn, Th, Ce, Se, Cs, Cr, Eu, Rb, Hf etc.).

Gamma-ray spectrometry

The gamma-ray spectra of each sample were taken several times after each irradiation. A block diagram of the counting system is shown in Fig. 1. Two coaxial Ge(Li) detectors (UJV) of different efficiency were used: one detector with 3% relative efficiency and 2.5 keV

Dead time Detector Preomp. An~ol i f~" Converter stabilizer

Fast reader Tel et ,.jpe

Fig. 1. Block diagram of gamma-my spectrometry system used

resolution (FWHM) for the 1332 keV photons of 6~ and a larger detector with 9.5% relative efficiency and 3.0 keV resolution. Pulses from the detectors were passed through an Ortec preamplifier, linear amplifier and base-line restorer to maintain a better resolution of the pulses at higher counting rates. The pulses from the base-line restorer were fed to a 100 MHz ADC CT 102 (lntertechnique) and the digital information was stored in a Plurimat 20 0ntertechnique) analyzing unit containing a small computer Multi-8 (24K of 8 bits memory). The acquisited spectra were processed on-line by a PRM OIC program written in a PAL assembler.

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1. OBRUSN~K et al.: INSTRUMENTAL NEUTRON ACTIVATION ANALYSIS

The peak areas and energies obtained from this program together with other necessary data (half-life, weights o f samples and standards etc.) were used for an off-line calculation of the final results by means o f a special program writ ten in LEM computer language.

Possible losses by coincidence summing and pile-up effect were corrected by the pulse generator method. 18 A dead-time stabilizer (Geophysics, Brno)has been used to avoid counting errors caused by a variable dead-time in the case of short irradiation measurements. 19

Results and discussion

The properties of radionuclides used for non-destructive NAA of fly ashes and emissions are summarized in Table 1. The concentrations o f elements found in the analyzed samples of fly ashes, industrial emissions and in one sample o f coal (for comparison), are given in

Table 1 Production and properties of nuclides observable with Ge(Li) detection in neutron irradiated fly ashes

and emissions

Element Isotope Half-life Cooling time Gamma-rays used, keV

AI V Ca Ti I Ba Mn Na K Ga Br As La Sm Th Ce Cs Se Fe Co Sb Eu Rb Cr Zn Se Hf

28A1 2.31 m S2V 3.76 m 49Ca 8.8 m SlTi 5.79m

1281 25 m 139Ba 83 m S6Mn 2.58 h 24Na 15 h ~2K 12.52 h 72Ga 14.3 h 82Br 35.9 h ?6As 26.3 h

140La 40.3 h lS3Sm 47.1 h 23Spa 27.0 d 131Ce 32.5 d ; 34Cs 2.07 y 46Sc 83.9 d 59Fe 45.1 d 6~ 5.2 y

124Sb 60.9 d IS2Eu 12.2 y

86Rb 18.7 d SlCr 27.8 d 6s Zn 245 d 7SSe 121 d

181Hf 44.6 d

10-20m 10-20 m 10-20 m 10-20 m 10-20 m 10-20 m 10-20 m 24-36 h 24-36 h 24-36 h 24-36 h 24-36 h 24-36 h 24-36 h 20-30 d 20-30 d 20-30 d 20-30 d 20-30 d 20-30 d 20-30 d 20-30 d 20-30 d 20-30 d 20-30 d 20-30 d 20-30 d

1778.9 1434.4 3083.0 320.0 442.7 165.8 1810.7,846.9 1368.4 1524.7 834.1,630.1 776.6, 619.0 657.0,559.2 1595.4,486.8 103.2 311.8 145.4 795.8 889.4 1098.6, 1291.5 1173.1, 1332.4 1690.7,602.6 1407.5 1076.6 320.0 1115.4 264.6, 136.0 482.2

498 I. RadioanaL Chem. 31 (1976)

I. OBRUSNI'K et al.: INSTRUMENTAL NEUTRON ACTIVATION ANALYSIS

Table 2

Elemental composition of fly ashes and emissions (ppm except as noted)

Element

AI, % Ca,% K,% Fe, %

V Mn Na As La Br Sc Sb Co Zn Sm Th Ce Cs Cz Eu Ga Ti Se Rb I Ba Hf

Conc. range

7 .5-14.4 0.8-4.3 0 .2-3 .2 2.4-7.1 180-650 190-1550

1310-5800 20-4800 16-80

8 - 2 0 0 12 -40

5 - 2 8 0 20-130

100-1300 11 -36

2 - 2 2 0 5 8 - 1 2 0 11-36 6 5 - 2 4 0

1 .3 -4 .2 4 2 - 5 3

5900-8300 15 -110

3350-4600 2 0 - 1 1 0

470 - 650 4 .9-6 .3

NA NA 0.5 2.0 NA 253

1220 5~

13.4 41

6.5 < 3

9.8 <.100 10.3

25 25

2.8 25

</).5 NA NA

( 1 5 ND NA NA 1.0

* l - fluorite mills, 2 , 3 - different cement works, N A - no analysis, N D - not detected.

J. Radioanal. Chem. 31/1976] 499

I. OBRIJSNIKet al.: INSTRUMENTAL NEUTRON ACTIVATION ANALYSIS

Table 2. One sample of fly ash was divided into two fractions: one fraction with particles smaller than 7 tam in diameter and a second one with particles with diameter greater than 7/am. By means of this sorting an investigation of the distribution of some elements could be made as a function of the particle size. The results from this experiment can be used only for a tough estimation as we have analyzed only one sample. This experiment will be repeated once more in a greater extent. The examples of fly ash spectra from long irradiation taken after 36 hrs and 3 weeks cooling are shown in Fig. 2 and 3.

In terferences

Some correction for the presence of 46Sc had to be done in the calculation of results for 6s Zn (1120 keV - a6Sc, 1115 keV - ~SZn). The possibilities of contributions from (n, p) and (n, t~) reactions were taken into account. This contribution was rather serious in the case of the determination of magnesium (27Mg), because the same nuclide 27Mg was formed by the reaction 27AI (n, p)27Mg and the content of aluminium in the samples was rather high (about 10%). For this reason, we have omitted the results for Mg in Table 2.

Precision

The precision of the determination varied from 2-5% for the determination of Sc, Mn, As, Ce, to 5 - 10% for Na, Cs, La, Cr, Sm, Th, V, Fe, Co. Ga. The precision of the determination of the other elements was 10 - 25%.

Conclusions

From the results summarized in the Table 2 as well as from the previous workr 6,t7 it follows that:

(1) the elements Fe, AI, Na, K, Ca and Ti occur in fly ashes and emissions in the highest concentrations (0.1-20%).

(2) a further group of elements (V, Mn, La, Sc, Sm, Ce, Cs and Cr) occurs in these materials in lower concentrations and the concentration fluctuations in the dependence on the origin of the sample and time of sampling are rather small.

(3) the highest differences in concentration can be found in the third group of elements: As, Sb, Co, Zn, Th, Eu and Se. These elements are promising for an identification of sources of emissions (and consequently imissions).

We have determined up to 27 elements in one sample by INAA of fly ashes and other emissions. Some other elements have been identified in several samples as well (Hg, C1, Cu, Au and Ta) but have not been determined quantitatively.

500 Z Radioanal. Chem. 31 (1976)

I. OBRUSNIK et al.: INSTRUMENTAL NEUTRON ACTIVATION ANALYSIS

#

J,j L I

o~

~m o

2000 3000 t.000-- Ci'~nnel number

Fig. 2. Gamma-ray spectrum of power plant fly ash. Irradiation time: 6 hrs, neutron flux: 1013n "cm "2 "sec "1 , decay time: 36 hrs, counting time: 10 rain

I,,~il ~ ~F~ ,~ ~ .~ ~.# II ~l

o IOOO 2000

I , , ,

, o

3000�84

Cl*w3nn el nun'wDer

i

�9 iii ii -

Fig. 3. Gamma-ray spectrum o f power plant fly ash. Irradiation time: 6 hrs, neutron flux: 1013 n "em "z -sec "1 , decay time: 21 days, counting time: 15 rain

J. RadioanaL Chem. 31 (1976) 501

1. OBRUSNfK et al.: INSTRUMENTAL NEUTRON ACTIVATION ANALYSIS

INAA is a very promising method for such kind o f complex elemental analysis. We have found that, for the identification o f sources o f air pollution produced by solid fuel com- bustion, the determination of La, Cs, Cr, Sm, As, Sb, Co, Zn, Th, Eu and Se can be used.

This work will continue by the analysis of samples of emissions from the large sources of air pollution and the samples o f aerosols taken in the surroundings of these sources. Both types o f samples will be analyzed by INAA mainly for the above ment ioned group of elements. The evaluation of these results will show whether the identification o f sources o f air contaminat ion can be really done from the elemental analyses of atmospheric aerosols.

References

1. R. DAMS, J. A. ROBBINS, K. A. RAHN, J. W. WINCHESTER, Anal. Chem., 42 (1970) 861. 2. W.H. ZOLLER, G. E. GORDON, Anal. Chem., 42 (1970) 257. 3. G.F. CLEMENTE, La Chimica e l'lndustria, 54 (1972) 805. 4. E.S. GLADNEY, W. H. ZOLLER, A. G. JONES, G. E. GORDON, Environ. Sci. Technol.,

8 (1974)551. 5. I.M. DALE, H. J. DUNCAN, C. McDONALD, Radiochem. Radioanal. Letters, 15 (1973) 77. 6. H. VOGG, R. HARTEL, Z. Anal. Chem., 267 (1973) 257. 7. K.K.S. PILLAY, C. C. THOMAS, Jr., C. M. HYCKE, Nucl. Technol., 10 (1971) 224. 8. K. RAHN, J. J. WESOLOWSKI, W. JOHN, H. R. RALSTON, J. Air Pollut. Contr. Ass., 21 (1971)

406. 9. R.H. FILBY, K. R. SHAH, Toxic. Environ. Chem. Rev., 2 (1974) 1.

10. Proc. IAEA Symp. Nuclear Techniques in Environmental Pollution, Salzburg, 26-30 Oct. 1970. 11. L.A. RANCITELLI, BNWL - 1751PT 2, p. 56-57. 12. D.J. VON LEHMDEN, R. H. JUNGERS, R. E. LEE, Jr., Anal. Chem., 46 (1974) 239. 13. J.M. ONDOV, W. H. ZOLLER, 1. OLMEZ, G. E. GORDON, Anal. Chem., 47 (1975) 1102. 14. R.A. NADKARNI, Radiochem. Radioanal. Letters, 21 (1975) 161. 15. E. ORVINI, T. E. GILLS, P. D. LA FLEUR, Anal. Chem., 46 (1974) 1294. 16. I. OBRUSNfK, B. ST/~RKOV/~, Radioizotopy, 14 (1973) 437. 17. B. STARKOVA, J. BLA2EK, I. OBRUSN|K, Ochrana ovzdusi, 7 (1975) 37. 18. O.U. ANDERS, Nucl. Instr. Methods, 68 (1969) 205. 19. J. BARTO~EK, G. WlNDELS, J. HOSTE, Nucl. Instr. Methods, 103 (1972) 43.

502 J. Radioanal Chem. 31 (1976)