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X-ray powder diffractometry of emissions from the cement industry
Atmospheric Printed
Environment
in Great
Vol. 23, No. 10. pp. 20X5-2091,
1989. Q
Britain.
Oc@&6981/89 $3.00+0.00 1989 Pergamon Press plc
X-RAY POWDER DIFFRACTOMETRY OF EMISSIONS FROM THE CEMENT INDUSTRY P. P. PAREKH*T,A.
R. KHAN*
and M. T. DAVIN$
*Wadsworth Center for Laboratories and Research, New York State Department of Health, Empire State Plaza, PG. Box 509, Albany, NY 12201-0509, USA., TDepartment of Environmental Health and Toxicology, School of Public Health Sciences, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, NY 12201-0509, U.S.A. and $New York State Geological Survey, New York State Education Department, Albany, NY U.S.A. (First received 13 February 1989 and infinalform
27 March 1989)
Abstract-X-ray powder diffractometry has been found capable of identifying and distinguishing limestone and cement particles, the two important emissions of the cement industry. The limestone shows strong reflections p~ncipally at 1.87,1.91,~2.09,2.28,2.49,3.03 and 3.83 A from its main constituent, calcite, whereas cement shows reflections at 1.76.2.18.2.60.2.64. a doublet at 2.73-2.77 and 3.02 8, from its main phases, the di-, and tri-calcium silicates. X-ray diffraction analysis of airborne particles collected on glass fib-mfilters in the vicinity of cement factories in Karachi, Pakistan and Ravena, New York State, revealed limestone but no cement particles, This observation was consistent with our earlier inference drawn from chemical and statistical methods for Karachi’s ambient aerosols. The method can complement the selective leaching technique suggested earlier by us for source identification. On the basis of model calculations, a methodology has been worked out that would make the present technique adaptable to plant conditions. Key word index: X-ray powder diffractometry, limestone, cement dust, atmospheric aerosols, cement factory, emissions, model estimates, analytical application.
1NTRODUCTION non-specific lung disease and reduction in ventilatory lung function have been observed amongst cement workers (Kalacic, 1973a,b). Occupational related symptoms were cough and phlegm production, catarrh, chronic bronchitis and chest tightness. Cement dust is also a skin and eye irritant (conjunctivitis) and is a threat to the g~troint~tinal tract (Pimental and Menezes, 1978; Oleru, 1984). Cement and limestone (raw material) are the two types of dusts that are primarily emitted in a cement plant. Since cement dust is a potential health hazard, a knowledge of its concentration in the environs of the plant is essential. This may also be true of limestone dust; however, no studies have been conducted to investigate its adverse health effects. To identify these two dust types, Parekh and Husain (1988) developed a chemical method utilizing the aqueous solubilities of the various limestone- and cement-forming Ca (Mg) compounds. The sample under study is leached with water and the leachate analyzed for the marker elements (Ca, Mg, Al and Si) from whose concentrations, the individual concentrations of the two dust types are determined. The method was proven applicable to ambient air aerosols collected at a downwind receptor which contain these Ca compounds at concentration levels of few pg me3 of air-i.e. below their maximum solubilities in water. The dust levels in a cement factory are expected to be several orders of magnitude higher (mg mm3 of air) as shown later in our model calculations; and hence Chronic
exceed their solubihty limits. The method of Parekh and Husain (1988) is unsuited for the measurement of cement/limestone dusts in a plant’s environs. Besides, for routine monitoring of these dusts in a plant, a simple non-destructive and rapid instrumental method would be preferred to chemical methods, which are in general laborious and time consuming In this article we report a simple X-ray powder diffra~tomet~c (XRD) method to identify and quantify limestone and cement dusts. Our main premise for the XRD method was based on the fact that limestone and cement have different chemical compositions. The former is composed largely of carbonate miner~s while the latter contains two alkaline earth (mainly Ca) silicates (Parekh and Husain, 1988). The method was applied to their analysis in ambient aerosols collected at receptors downwind from two cement factories. A procedure adaptable to plant conditions (involving sample collection, instrument calibration and application to field samples) has been worked out.
The X-ray diffractometer used was either a Noreico-Philips water-cooled diffraction unit Type 12045 B/3 or Diano Diffraction unit with a graphite monochromator. The diffracted X-rays were recorded by a scintillation detector with a pulse height selector, The detector output was registered by a bunting-rate meter and recorded on a chart at a speed of 2” 20 min-‘. Intensity measurements were made over the range 20 = Y-60” under the following experimental conditions: CuK, radiation (45 kV and
2086
P. P. PAREKHet al.
60”
50”
40”
300
20”
100
5O
20 Fig 1. X-ray diffraction patterns of(a) portland cement NBS SRM 634, and (b) limestone ZGI-KH. C=calcite, Q=quartz, P=pyrite, TCS = tricalcium silicate, DCS = dicalcium silicate. (ReE Joint Committee on Powder Diffraction Standards: Powder Diffraction Files, 1972 and
1980.)
25 mA); divergence slit: 1”; scatter slit: 1”; receiving slit: 0.006 inches (0.15 mm). The filters were mounted on 27 x 46 mm microscope slides with the help of doublecoated transparent tapes. Powders (limestones, cements, and Karachi’s composite sample) were slurried with melted petroleum jelly (a binder) on slides in a manner to approach randomness. The dilfractometer yielded highly reproducible patterns. The precision in the measurement of d-spacing was better than f 0.02 A.
DIFFRACTION PA’M’ERNS
A. Limestone and Portland cement Figure 1 shows the XRD patterns for the standard reference samples of limestone, ZGI-KH, and a portland cement, NBS SRM PC-634. The former is a reference limestone standard supplied by the Zentrales Geologisches Institut of the G.D.R. These are finely ground (< 40 pm) homogenous standards also used in our previous study (Parekh and Husain, 1988). Table 1 gives the prominent calcite peaks in the KH and the di-, and tri-calcium silicate peaks in the PC-634 samples. These have been tabulated in the decreasing order of their intensities. The most intense 3.03 A peak of KH lies close to the 3.02 A peak of PC-634. However there are many other characteristic peaks that do not overlap (1.60,1.87,1.91,2.09,2.28,2.49 and 3.83 A for the calcite in the limestone and the 1.762.18, 2.60, 2.64 and the doublet at 2.73-2.77 A for the di-, and the t&calcium silicate phases of the PC). The patterns for three additional portland cements were studied (NBS SRM PC-635, PC-639 and a sample of cement manufactured by the Atlantic Cement Co., Ravena, NY) and a limestone sample from
Table 1. The d-spacings for the prominent peaks in the XRD patterns of limestone and portland cement Limestone 3.03 (C) 2.28 (C) 1.87 (C) 1.91 (C)
2.09CC) 2.49 (C) 3.83 (C) 1.60 (C) 3.34 fQ) 1.63 (P)
d (A) Portland cement 2.77 (TCS) 2.73 (TCS) 2.60 (TCS) 2.18 (TCS) 3.02 (TCS) 1.76 (DCS) 2.95 (DCS) 2.64 (DCS) 1.62 (DCS) 2.88 (Des) 1.97 (TCS)
C = calcite; Q = quartz, P = pyrite, TCS = tricalcium silicate, DCS =dicalcium silicate. The values are arranged in decreasing order of peak heights. These are the
same for the bracketed ones.
Coeymans, NY. (The Coeymans limestone is the raw material used by the Atlantic cement plant in Ravena.) These three portland cements and the limestone sample yielded patterns almost identical to those shown in Fig, 1 for SRM PC-634 and KH, respectively. As expected, the two most important mineral phases in KH are the calcite and the quartz. A small but well-de~ned peak at d= 1.63 A suggested the presence of iron pyrite, FeS,. This peak was also noted in the XRD pattern of limestone from Coeymans, NY. Association of sulfide minerals (pyrite, galena, sphalerite) with limestones is a common geochemical feature (e.g. Moeller et al., 1979). The high S content in KH (0.09%, Flanagan, 1973) also supports the presence of
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Emissions from the Cement industry
pyrite in its XRD pattern. The portland cement is predominantly a mixture of di-, and t&calcium silicates (DCS and TCS, respectively) with very small amounts of tricalcium aluminate and tetracalcium aluminoferrite. The DCS and TCS peaks can be seen in its XRD pattern; the peak intensities of the latter two phases are very weak for obvious reasons. B. Ambient aerosols Preliminary investigations showed that glass fibre filter had the most amorphous pattern; and was thus best suited for XRD analysis. Ambient aerosols were collected on glass fibre filters using high volume samplers placed approximately 7 km downwind from a cement factory in Karachi, Pakistan and 1 km from that in Ravena, NY. The Karachi site was used in the earlier study (Parekh et al., 1987). Figure 2 gives the XRD patterns for the Ravena and Karachi aerosols (b and c, respectively). The patterns showed two distinct aks corresponding to d spacings of 3.34 and 3.03 8”. The first peak is that of quartz while the second one may be from limestone (calcite) and/or cement (tricalcium silicate). This peak, however, could not be assigned to cement because it is not supported by other peaks of portland cement (listed in Table 1) which are more or less equal in their iniensities. The peak at d = 3.03 A suggests the presence of limestone and not cement aerosols. An additional calcite peak (d
60'
500
40'
=2.28 A) in Karachi sample further supports this observation. Other calcite peaks (listed in Table 1) are missing because of their very low relative intensities. To ensure that the 3.03 %nd 2.28 A peaks were indeed from calcite, we obtained an XRD pattern on a preconcentrated sample of Karachi aerosols (henceforth referred to as composite sample). The preconcentration was achieved by folding the filter paper into two halves with the loaded side inside and then gently rubbing the inside of the filters and collecting the loose particles on a clean glassine paper. About 30 mg of the aerosol powder was collected from eight filters. Figure 2a shows the pattern for this composite sample. (Since only one sample was collected at Ravena site, preconcentration could not be done.) Several well-defined peaks become visible. The cement peaks are missing. The principal limestone (calcite) peak at d = 3.03 A is clearly supported by all the calcite peaks listed in Table 1. Other identifiable mineral phases in the composite sample were NaCl (1.63, 1.99 and 2.81 A) and two aluminosilicates, chlorite (4.7,7.1 and 14.3 A) and plagioclase (3.2, 4.0 and 6.4-6.5 A). The 1.63 A peak could also result from the presence of a pyritic phase in these aerosols since it was observed both in the KH and the Coeymans limestone samples. In their source apportionment of Karachi aerosols, Parekh et al. (1987) found that marine and soil aeros-
30"
209
IO0 5'
28 Fig. 2. X-ray diffraction patterns of atmospheric aerosols collected on glass fibre filters at distant downwind receptors at Karachi, Pakistan (a and c) and Ravena, NY State (b). Pattern (a) is for the composite (prezoncentrated) aerosol sample of Karachi. PL = plagioclaae, CHL =chlorite. (Ref: same as in Fig. 1 caption) For the remaining abbreviations, see Fig. 1 caption.
P. P. PAREKHet al.
2088
01s formed about 12% and 28% of the total aerosol mass, respectively. The appearances of NaCl (seasalt) and the chlorite-plagioclase (soil) phases in the pattern (Fig. 2a) are reasonable. The quartz phase in this pattern suggests that it should be an important constituent of the Karachi aerosols and should form a substantial part of the component undetermined by Parekh et al. (1987). APPLICATTON AT THE PLANT
The main objective of this work was to determine the feasibility of applying the XRD technique to plant environment. The method should therefore be tested on the samples collected within the plant. Since it was difficult to procure samples from within the Karachi plant, we had to work out the methodology based on model calculations. Model estimates
The following procedure was used for the conversion of the observed ambient concentrations 1 of limestone-cement aerosols at a downwind receptor into the emission rate Q of the cement plant in Karachi. This procedure was essentially based on the dispersion model calculations of Turner (Turner, 1967). From the estimate of the source strength so derived, the concentrations of these aerosols that could be expected within the plant’s premises were calculated. The concentration, x, of aerosols at a downwind receptor having x, y and z coordinate axes from a
point source with an effective emission height, H, is given by
x (exp[-
l/2(2--H/a,)‘]
t exp[ - l/2 (z+H/oJ2]j
where x-axis extends in the direction of the mean wind (it is essentially the source-receptor distance) y and z axes are the horizontal and vertical planes perpendicular to the x- axis, respectively. The plume travels along or parallel to the x - axis Q = strength of the emission source in g s- ’ u = wind speed in m s-l by and u, are the horizontal and vertical dispersion coefficients (in m), respectively. During the entire study period, the receptor was essentially in the direction of the prevailing winds from the cement factory (see wind rose in Fig. 3). Hence the observed aerosols (with concentration x) derived from this plant may be assumed, as a first approximation, to have arrived along the center line of the plume, thus y =O. Also, because the emissions were shown to be fugitive in nature, i.e. ground level source (Parekh et al., 1987; Parekh and Husain, 1988) and the concentrations were recorded at ground level (the receptor was only 1.3 m above ground), H and z are each = 0. Hence Equation 1 reduces to
1 km
60
METROPOLITAN
A’
/’
AREA
\ \
/
-/
’ __,-
I
A i
/ / /
/
”
(1)
SUBURBAN AREA
Fig. 3. Map of Karachi showing the source S (the cement factory) and the receptor R. The source-reoeptor distance = 7 km. The wind+rost &et&ted for the study period (22-27 July 1985)shows the receptor was always directly downwind from the cement plant; numbers indicate % frorjucncyofthewind d&&ion. The circk around the source signifies the plant’s periphery (fOOm)for which model estimates of its ambient dust contents were made. &shed line demarcWs the city’sindustrial/commercial area from its suburbia.
Emissions from the cement industry
The estimations given below are only quasi-quantitative and were meant to determine only the order of magnitude of the concentrations of pollution aerosols within the plant’s premises. Such estimates were needed to construct working calibration curves for the XRD analysis of limestone and cement dusts that would reasonably represent the concentration levels at the plant. The source-receptor distance is 7 km. The surface wind speeds, u, varied between -4 and 9 m s-l, with mean values of u = 6.5 + 1.8 m s- ’ during days and 5.3 f 1.4 ms-r during nights. During daytime, the incoming solar radiation was moderate to strong. Temperatures were constant within + 2°C; 30°C (days) and 28°C (nights). Under these meteorological conditions, the atmospheric stabilities were generally categorized under class ‘c’ during days and class ‘D’ during nights (Turner, 1967). The horizontal and vertical dispersion coefficients, cry and gZ, were obtained from Turner (1967) for the two pertinent stability classes. The Q values estimated using Equation 2 were plotted for the 1985 study period (Fig. 4). Mean Q=24Of lSOgs-’ during days and only 20 f 10 g s- 1 during nights. The product of CT~. 0,. u in Equation 2 is only a factor of about 6 higher for day than for night (this is mainly attributable to convectional currents generated by diurnal heating during daylight hours). The much higher difference in the Q value (12 times) presumably arises from a more intense plant operation during daytime. Aerosol concentration, xl, at the plant
In the manufacturing operations of the plant, i.e. at the emission points, the cement workers do wear protective devices such as respirators, goggles, gloves and boots. It would therefore be more appropriate to determine the dust contents in the ambient air at a
2089
distance from the emission points, where no protective devices are worn. The evaluation is essential in the cause-effect study of these dusts on the plant’s employees. For simplicity, source-recipient distance of 1OOm was arbitrarily chosen. We prefer using ‘recipient’ to ‘receptor’ since the subject here is the cement worker. Using the mean values of Q and II given above and Turner’s values for uY and 6, (for 100 m), the concentration of the limestoneement dusts, x’, expected at 100 m distance were calculated. x’= w 140mgmm3 during the day and N 35 mgmv3 at night. The measured dust level in the cement depot of a Nigerian cement plant was -31 mgmm3 (Oleru, 1984). Our model estimates of 35-140 mgmd3 are in the right order of magnitude. Sampling and calibration Due to practical difficulties, no ‘on-site’ cement plant sampling could be done. We, therefore, had to resort to the above model estimates for evolving a working methodology. Based on our model calculations, the following procedure is recommended for sampling and instrumental calibration that is easily adaptable to plant conditions. Samplers suitable for plant operation are the Sierra Andersen’s Series 280 ‘Cyclade’ cascade cyclone sampler or the six stage Mark V high-capacity stack sampler. Both these samplers are capable of sampling in areas of high mass loading (mg mm3); both can collect particles in different size fractions (15-0.3 pm; an important feature to study respirable fraction and health effects) and need minimal manpower for their operation. No filter substrate is needed for sample collection; samples get collected in various stainless steel thimbles, each corresponding to a particular size range. For subsequent XRD analysis, these samples could then be weighed out in desired quantities and
500 -
250 -
JULY
1985
Fig. 4. Histogram of Q, the emission rate from the cement plant based on model calculations. Q values for nights are shaded.
P. P.
2090
PAREKH et al.
prepared in a manner identical to the one described below for the calibration standards. Both the samples and the standards would thus exhibit identical (preferred) orientation in their XRD analysis. A set of calibration standards were prepared using NBS-SRM-634 Portland Cement standard and ZGIKH Limestone standard. In addition to the two standards, three synthetic mixtures of portland cement and limestone were prepared in different weight ratios (in percentage) of 90: 10, 50: 50 and 10:90. After the mixtures were homogenized, approximately 90 mg each of the two standards and the three synthetic mixtures were weighed and transferred to 10 ml capacity Teflon beaker. This weight was the mean of the day and night time concentrations obtained in our model calculations. The powder was slurried in 5-6 ml of absolute ethanol and poured into a Millipore demountable filter holder having a Whatman 934-AH glass microfibre filter (4.25 cm) with _ 50 ml column of ethanol above it. A uniform suspension of the powder was thus achieved. Filtration was carried out without applying vacuum. This resulted in a welldistributed deposit of the sample on the filter. The last drops of the alcohol was removed by applying a low suction. The filter was dried overnight in a vacuum desiccator and then accurately weighed. The surface densities were quite comparable for all the five calibration standards (8.4 + 0.2 mg cm - 2). The four reflections of cement at 2.18,2.60,2.73 and 2.95 A and of limestone at 1.87, 2.09, 2.28 and 2.49 A
0
(Fig. 1) could be used to characterize and quantify these two dusts in their mixture. However, the XRD patterns of their synthetic mixtures showed that only the 2.60 A line of cement and the 2.28 A line of limestone were sensitive enough to give positive signals at the concentration ranges considered. No interference from other mineral phases are conceivable at these two reflections. The d-spacings for the aluminosilicates, like clays and shales (also used as raw materials in cement production) are mostly 3.0 A and greater (20 = 34” to 6”, see, for example, Fig. 2a). Using these lines, calibration curves were constructed based on their peak heights (Fig. 5). Peak widths were 0.3“ to 0.4” 20. The detection limits were comparable for both limestone and cement, -5 mg per filter (14.2 cm?) for each under the experimental conditions employed. This concentration corresponded to the smallest peak height that could be measured with a precision of + 50%. Peak heights obtained on duplicate runs of the standards were reproducible within f 20%. CONCLUSION
The present study shows that XRD analysis is capable of identifying and distinguishing limestone and cement aerosols. In so far as the analysis of ambient aerosols at a downwind receptor is concerned, it can complement the selective leaching technique suggested earlier by us. It is particularly useful
80
60
40
20
CONCENTRATION
1uu
(mg)
Fig. 5. Peak height, PH (in mm) vs concentration C (in mg per filter deposit of 11 cm’) of portland cement, PC, or lirnestooe, L, in the calibration standards. The least squares fits are defined by the following linear regressions.
For PC C= -0.45(
+0.27)+0.53
(+O.lO) x PH (r=0.99).
For L C = 0.45 ( + 0.29) + 0.43 ( + 0.08) x PH (r= 0.99).
Emissions from the cement industry
for monitoring plant’s environs where the concentration levels of these dusts are bound to be relatively high (several tens of mg m- ’ of air). The technique is not restricted to the cement industry. Diverse industries use diverse types of rocks, ores and minerals. XRD can identify their airborne particles through their mineral constituents. Since most of these emissions are fugitive, the method may prove useful only for the study of local emissions; i.e. for short-range transported pollutants. Acknowledgement-The
authors are thankful to Liaquat Husain, N.Y. State Department of Health and Philip Whitney, N.Y. State Geological Survey for their interest and encouragement, to Kenneth Steele, Univ. of Arkansas, Fayetteville, for carrying out XRD analysis in his laboratory. The assistance of Jeanine Bowen, Badar Ghauri, William Knox, Edward LeGere and Zikrur Rehman Siddiqi in sample collection is gratefully acknowledged. Contribution # 545 of the New York State Science Service (M. T. Davin). REFERENCES
Flanagan F. J. (1973) 1972 values for international geochemical reference samples. Geochim. Cosmochim. Acta 37, 1189-1200.
2091
Kalacic I. (1973a) Chronic nonspecific lung disease in cement workers. Arch. Envir. Health Za, 76-83. Kalacic I. (1973b) Ventilatory lung function in cement workers. Arch. Enuir. Health 26, 84-85. Moeller P., Morteani G., Hoefs J. and Parekh P. P. (1979) The origin of the ore bearing solution in the Pb-Zn veins of the western Han, Germany, as deduced from rare earth elements and isotope distributions in calcites. Chem. Geol. 26, 197-215. Parekh P. P., Ghauri B., Siddiqi Z. R. and Husain L. (1987) The use of chemical and statistical methods to identify sources of selected elements in ambient air aerosols in Karachi, Pakistan. Atmospheric Environment 21, 1267-1274.
Parekh P. P. and Husain L. (1988) Selective leaching of atmospheric aerosols: resolution of limestone and cement. Atmospheric
Environment 22, 707-713.
Pimental J. C. and Menezes A. P. (1978) Pulmonary and hepatic granulomatous disorders due to inhalation of cement and mica dusts. Thorax 33,219-227. Oleru U. G. (1984) Pulmonary function and symptoms of Nigerian workers exposed to cement dust. Envir. Res. 33, 379-385.
Turner D. B. (1967) Workbook of Atmospheric Dispersion Estimates. Envir. Health Ser.: Air pollution; Public Health Service Publ. No. 999-AP-26. U.S. Dept. Health, Education and Welfare, Cincinnati, Ohio.
Environment
in Great
Vol. 23, No. 10. pp. 20X5-2091,
1989. Q
Britain.
Oc@&6981/89 $3.00+0.00 1989 Pergamon Press plc
X-RAY POWDER DIFFRACTOMETRY OF EMISSIONS FROM THE CEMENT INDUSTRY P. P. PAREKH*T,A.
R. KHAN*
and M. T. DAVIN$
*Wadsworth Center for Laboratories and Research, New York State Department of Health, Empire State Plaza, PG. Box 509, Albany, NY 12201-0509, USA., TDepartment of Environmental Health and Toxicology, School of Public Health Sciences, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, NY 12201-0509, U.S.A. and $New York State Geological Survey, New York State Education Department, Albany, NY U.S.A. (First received 13 February 1989 and infinalform
27 March 1989)
Abstract-X-ray powder diffractometry has been found capable of identifying and distinguishing limestone and cement particles, the two important emissions of the cement industry. The limestone shows strong reflections p~ncipally at 1.87,1.91,~2.09,2.28,2.49,3.03 and 3.83 A from its main constituent, calcite, whereas cement shows reflections at 1.76.2.18.2.60.2.64. a doublet at 2.73-2.77 and 3.02 8, from its main phases, the di-, and tri-calcium silicates. X-ray diffraction analysis of airborne particles collected on glass fib-mfilters in the vicinity of cement factories in Karachi, Pakistan and Ravena, New York State, revealed limestone but no cement particles, This observation was consistent with our earlier inference drawn from chemical and statistical methods for Karachi’s ambient aerosols. The method can complement the selective leaching technique suggested earlier by us for source identification. On the basis of model calculations, a methodology has been worked out that would make the present technique adaptable to plant conditions. Key word index: X-ray powder diffractometry, limestone, cement dust, atmospheric aerosols, cement factory, emissions, model estimates, analytical application.
1NTRODUCTION non-specific lung disease and reduction in ventilatory lung function have been observed amongst cement workers (Kalacic, 1973a,b). Occupational related symptoms were cough and phlegm production, catarrh, chronic bronchitis and chest tightness. Cement dust is also a skin and eye irritant (conjunctivitis) and is a threat to the g~troint~tinal tract (Pimental and Menezes, 1978; Oleru, 1984). Cement and limestone (raw material) are the two types of dusts that are primarily emitted in a cement plant. Since cement dust is a potential health hazard, a knowledge of its concentration in the environs of the plant is essential. This may also be true of limestone dust; however, no studies have been conducted to investigate its adverse health effects. To identify these two dust types, Parekh and Husain (1988) developed a chemical method utilizing the aqueous solubilities of the various limestone- and cement-forming Ca (Mg) compounds. The sample under study is leached with water and the leachate analyzed for the marker elements (Ca, Mg, Al and Si) from whose concentrations, the individual concentrations of the two dust types are determined. The method was proven applicable to ambient air aerosols collected at a downwind receptor which contain these Ca compounds at concentration levels of few pg me3 of air-i.e. below their maximum solubilities in water. The dust levels in a cement factory are expected to be several orders of magnitude higher (mg mm3 of air) as shown later in our model calculations; and hence Chronic
exceed their solubihty limits. The method of Parekh and Husain (1988) is unsuited for the measurement of cement/limestone dusts in a plant’s environs. Besides, for routine monitoring of these dusts in a plant, a simple non-destructive and rapid instrumental method would be preferred to chemical methods, which are in general laborious and time consuming In this article we report a simple X-ray powder diffra~tomet~c (XRD) method to identify and quantify limestone and cement dusts. Our main premise for the XRD method was based on the fact that limestone and cement have different chemical compositions. The former is composed largely of carbonate miner~s while the latter contains two alkaline earth (mainly Ca) silicates (Parekh and Husain, 1988). The method was applied to their analysis in ambient aerosols collected at receptors downwind from two cement factories. A procedure adaptable to plant conditions (involving sample collection, instrument calibration and application to field samples) has been worked out.
The X-ray diffractometer used was either a Noreico-Philips water-cooled diffraction unit Type 12045 B/3 or Diano Diffraction unit with a graphite monochromator. The diffracted X-rays were recorded by a scintillation detector with a pulse height selector, The detector output was registered by a bunting-rate meter and recorded on a chart at a speed of 2” 20 min-‘. Intensity measurements were made over the range 20 = Y-60” under the following experimental conditions: CuK, radiation (45 kV and
2086
P. P. PAREKHet al.
60”
50”
40”
300
20”
100
5O
20 Fig 1. X-ray diffraction patterns of(a) portland cement NBS SRM 634, and (b) limestone ZGI-KH. C=calcite, Q=quartz, P=pyrite, TCS = tricalcium silicate, DCS = dicalcium silicate. (ReE Joint Committee on Powder Diffraction Standards: Powder Diffraction Files, 1972 and
1980.)
25 mA); divergence slit: 1”; scatter slit: 1”; receiving slit: 0.006 inches (0.15 mm). The filters were mounted on 27 x 46 mm microscope slides with the help of doublecoated transparent tapes. Powders (limestones, cements, and Karachi’s composite sample) were slurried with melted petroleum jelly (a binder) on slides in a manner to approach randomness. The dilfractometer yielded highly reproducible patterns. The precision in the measurement of d-spacing was better than f 0.02 A.
DIFFRACTION PA’M’ERNS
A. Limestone and Portland cement Figure 1 shows the XRD patterns for the standard reference samples of limestone, ZGI-KH, and a portland cement, NBS SRM PC-634. The former is a reference limestone standard supplied by the Zentrales Geologisches Institut of the G.D.R. These are finely ground (< 40 pm) homogenous standards also used in our previous study (Parekh and Husain, 1988). Table 1 gives the prominent calcite peaks in the KH and the di-, and tri-calcium silicate peaks in the PC-634 samples. These have been tabulated in the decreasing order of their intensities. The most intense 3.03 A peak of KH lies close to the 3.02 A peak of PC-634. However there are many other characteristic peaks that do not overlap (1.60,1.87,1.91,2.09,2.28,2.49 and 3.83 A for the calcite in the limestone and the 1.762.18, 2.60, 2.64 and the doublet at 2.73-2.77 A for the di-, and the t&calcium silicate phases of the PC). The patterns for three additional portland cements were studied (NBS SRM PC-635, PC-639 and a sample of cement manufactured by the Atlantic Cement Co., Ravena, NY) and a limestone sample from
Table 1. The d-spacings for the prominent peaks in the XRD patterns of limestone and portland cement Limestone 3.03 (C) 2.28 (C) 1.87 (C) 1.91 (C)
2.09CC) 2.49 (C) 3.83 (C) 1.60 (C) 3.34 fQ) 1.63 (P)
d (A) Portland cement 2.77 (TCS) 2.73 (TCS) 2.60 (TCS) 2.18 (TCS) 3.02 (TCS) 1.76 (DCS) 2.95 (DCS) 2.64 (DCS) 1.62 (DCS) 2.88 (Des) 1.97 (TCS)
C = calcite; Q = quartz, P = pyrite, TCS = tricalcium silicate, DCS =dicalcium silicate. The values are arranged in decreasing order of peak heights. These are the
same for the bracketed ones.
Coeymans, NY. (The Coeymans limestone is the raw material used by the Atlantic cement plant in Ravena.) These three portland cements and the limestone sample yielded patterns almost identical to those shown in Fig, 1 for SRM PC-634 and KH, respectively. As expected, the two most important mineral phases in KH are the calcite and the quartz. A small but well-de~ned peak at d= 1.63 A suggested the presence of iron pyrite, FeS,. This peak was also noted in the XRD pattern of limestone from Coeymans, NY. Association of sulfide minerals (pyrite, galena, sphalerite) with limestones is a common geochemical feature (e.g. Moeller et al., 1979). The high S content in KH (0.09%, Flanagan, 1973) also supports the presence of
2087
Emissions from the Cement industry
pyrite in its XRD pattern. The portland cement is predominantly a mixture of di-, and t&calcium silicates (DCS and TCS, respectively) with very small amounts of tricalcium aluminate and tetracalcium aluminoferrite. The DCS and TCS peaks can be seen in its XRD pattern; the peak intensities of the latter two phases are very weak for obvious reasons. B. Ambient aerosols Preliminary investigations showed that glass fibre filter had the most amorphous pattern; and was thus best suited for XRD analysis. Ambient aerosols were collected on glass fibre filters using high volume samplers placed approximately 7 km downwind from a cement factory in Karachi, Pakistan and 1 km from that in Ravena, NY. The Karachi site was used in the earlier study (Parekh et al., 1987). Figure 2 gives the XRD patterns for the Ravena and Karachi aerosols (b and c, respectively). The patterns showed two distinct aks corresponding to d spacings of 3.34 and 3.03 8”. The first peak is that of quartz while the second one may be from limestone (calcite) and/or cement (tricalcium silicate). This peak, however, could not be assigned to cement because it is not supported by other peaks of portland cement (listed in Table 1) which are more or less equal in their iniensities. The peak at d = 3.03 A suggests the presence of limestone and not cement aerosols. An additional calcite peak (d
60'
500
40'
=2.28 A) in Karachi sample further supports this observation. Other calcite peaks (listed in Table 1) are missing because of their very low relative intensities. To ensure that the 3.03 %nd 2.28 A peaks were indeed from calcite, we obtained an XRD pattern on a preconcentrated sample of Karachi aerosols (henceforth referred to as composite sample). The preconcentration was achieved by folding the filter paper into two halves with the loaded side inside and then gently rubbing the inside of the filters and collecting the loose particles on a clean glassine paper. About 30 mg of the aerosol powder was collected from eight filters. Figure 2a shows the pattern for this composite sample. (Since only one sample was collected at Ravena site, preconcentration could not be done.) Several well-defined peaks become visible. The cement peaks are missing. The principal limestone (calcite) peak at d = 3.03 A is clearly supported by all the calcite peaks listed in Table 1. Other identifiable mineral phases in the composite sample were NaCl (1.63, 1.99 and 2.81 A) and two aluminosilicates, chlorite (4.7,7.1 and 14.3 A) and plagioclase (3.2, 4.0 and 6.4-6.5 A). The 1.63 A peak could also result from the presence of a pyritic phase in these aerosols since it was observed both in the KH and the Coeymans limestone samples. In their source apportionment of Karachi aerosols, Parekh et al. (1987) found that marine and soil aeros-
30"
209
IO0 5'
28 Fig. 2. X-ray diffraction patterns of atmospheric aerosols collected on glass fibre filters at distant downwind receptors at Karachi, Pakistan (a and c) and Ravena, NY State (b). Pattern (a) is for the composite (prezoncentrated) aerosol sample of Karachi. PL = plagioclaae, CHL =chlorite. (Ref: same as in Fig. 1 caption) For the remaining abbreviations, see Fig. 1 caption.
P. P. PAREKHet al.
2088
01s formed about 12% and 28% of the total aerosol mass, respectively. The appearances of NaCl (seasalt) and the chlorite-plagioclase (soil) phases in the pattern (Fig. 2a) are reasonable. The quartz phase in this pattern suggests that it should be an important constituent of the Karachi aerosols and should form a substantial part of the component undetermined by Parekh et al. (1987). APPLICATTON AT THE PLANT
The main objective of this work was to determine the feasibility of applying the XRD technique to plant environment. The method should therefore be tested on the samples collected within the plant. Since it was difficult to procure samples from within the Karachi plant, we had to work out the methodology based on model calculations. Model estimates
The following procedure was used for the conversion of the observed ambient concentrations 1 of limestone-cement aerosols at a downwind receptor into the emission rate Q of the cement plant in Karachi. This procedure was essentially based on the dispersion model calculations of Turner (Turner, 1967). From the estimate of the source strength so derived, the concentrations of these aerosols that could be expected within the plant’s premises were calculated. The concentration, x, of aerosols at a downwind receptor having x, y and z coordinate axes from a
point source with an effective emission height, H, is given by
x (exp[-
l/2(2--H/a,)‘]
t exp[ - l/2 (z+H/oJ2]j
where x-axis extends in the direction of the mean wind (it is essentially the source-receptor distance) y and z axes are the horizontal and vertical planes perpendicular to the x- axis, respectively. The plume travels along or parallel to the x - axis Q = strength of the emission source in g s- ’ u = wind speed in m s-l by and u, are the horizontal and vertical dispersion coefficients (in m), respectively. During the entire study period, the receptor was essentially in the direction of the prevailing winds from the cement factory (see wind rose in Fig. 3). Hence the observed aerosols (with concentration x) derived from this plant may be assumed, as a first approximation, to have arrived along the center line of the plume, thus y =O. Also, because the emissions were shown to be fugitive in nature, i.e. ground level source (Parekh et al., 1987; Parekh and Husain, 1988) and the concentrations were recorded at ground level (the receptor was only 1.3 m above ground), H and z are each = 0. Hence Equation 1 reduces to
1 km
60
METROPOLITAN
A’
/’
AREA
\ \
/
-/
’ __,-
I
A i
/ / /
/
”
(1)
SUBURBAN AREA
Fig. 3. Map of Karachi showing the source S (the cement factory) and the receptor R. The source-reoeptor distance = 7 km. The wind+rost &et&ted for the study period (22-27 July 1985)shows the receptor was always directly downwind from the cement plant; numbers indicate % frorjucncyofthewind d&&ion. The circk around the source signifies the plant’s periphery (fOOm)for which model estimates of its ambient dust contents were made. &shed line demarcWs the city’sindustrial/commercial area from its suburbia.
Emissions from the cement industry
The estimations given below are only quasi-quantitative and were meant to determine only the order of magnitude of the concentrations of pollution aerosols within the plant’s premises. Such estimates were needed to construct working calibration curves for the XRD analysis of limestone and cement dusts that would reasonably represent the concentration levels at the plant. The source-receptor distance is 7 km. The surface wind speeds, u, varied between -4 and 9 m s-l, with mean values of u = 6.5 + 1.8 m s- ’ during days and 5.3 f 1.4 ms-r during nights. During daytime, the incoming solar radiation was moderate to strong. Temperatures were constant within + 2°C; 30°C (days) and 28°C (nights). Under these meteorological conditions, the atmospheric stabilities were generally categorized under class ‘c’ during days and class ‘D’ during nights (Turner, 1967). The horizontal and vertical dispersion coefficients, cry and gZ, were obtained from Turner (1967) for the two pertinent stability classes. The Q values estimated using Equation 2 were plotted for the 1985 study period (Fig. 4). Mean Q=24Of lSOgs-’ during days and only 20 f 10 g s- 1 during nights. The product of CT~. 0,. u in Equation 2 is only a factor of about 6 higher for day than for night (this is mainly attributable to convectional currents generated by diurnal heating during daylight hours). The much higher difference in the Q value (12 times) presumably arises from a more intense plant operation during daytime. Aerosol concentration, xl, at the plant
In the manufacturing operations of the plant, i.e. at the emission points, the cement workers do wear protective devices such as respirators, goggles, gloves and boots. It would therefore be more appropriate to determine the dust contents in the ambient air at a
2089
distance from the emission points, where no protective devices are worn. The evaluation is essential in the cause-effect study of these dusts on the plant’s employees. For simplicity, source-recipient distance of 1OOm was arbitrarily chosen. We prefer using ‘recipient’ to ‘receptor’ since the subject here is the cement worker. Using the mean values of Q and II given above and Turner’s values for uY and 6, (for 100 m), the concentration of the limestoneement dusts, x’, expected at 100 m distance were calculated. x’= w 140mgmm3 during the day and N 35 mgmv3 at night. The measured dust level in the cement depot of a Nigerian cement plant was -31 mgmm3 (Oleru, 1984). Our model estimates of 35-140 mgmd3 are in the right order of magnitude. Sampling and calibration Due to practical difficulties, no ‘on-site’ cement plant sampling could be done. We, therefore, had to resort to the above model estimates for evolving a working methodology. Based on our model calculations, the following procedure is recommended for sampling and instrumental calibration that is easily adaptable to plant conditions. Samplers suitable for plant operation are the Sierra Andersen’s Series 280 ‘Cyclade’ cascade cyclone sampler or the six stage Mark V high-capacity stack sampler. Both these samplers are capable of sampling in areas of high mass loading (mg mm3); both can collect particles in different size fractions (15-0.3 pm; an important feature to study respirable fraction and health effects) and need minimal manpower for their operation. No filter substrate is needed for sample collection; samples get collected in various stainless steel thimbles, each corresponding to a particular size range. For subsequent XRD analysis, these samples could then be weighed out in desired quantities and
500 -
250 -
JULY
1985
Fig. 4. Histogram of Q, the emission rate from the cement plant based on model calculations. Q values for nights are shaded.
P. P.
2090
PAREKH et al.
prepared in a manner identical to the one described below for the calibration standards. Both the samples and the standards would thus exhibit identical (preferred) orientation in their XRD analysis. A set of calibration standards were prepared using NBS-SRM-634 Portland Cement standard and ZGIKH Limestone standard. In addition to the two standards, three synthetic mixtures of portland cement and limestone were prepared in different weight ratios (in percentage) of 90: 10, 50: 50 and 10:90. After the mixtures were homogenized, approximately 90 mg each of the two standards and the three synthetic mixtures were weighed and transferred to 10 ml capacity Teflon beaker. This weight was the mean of the day and night time concentrations obtained in our model calculations. The powder was slurried in 5-6 ml of absolute ethanol and poured into a Millipore demountable filter holder having a Whatman 934-AH glass microfibre filter (4.25 cm) with _ 50 ml column of ethanol above it. A uniform suspension of the powder was thus achieved. Filtration was carried out without applying vacuum. This resulted in a welldistributed deposit of the sample on the filter. The last drops of the alcohol was removed by applying a low suction. The filter was dried overnight in a vacuum desiccator and then accurately weighed. The surface densities were quite comparable for all the five calibration standards (8.4 + 0.2 mg cm - 2). The four reflections of cement at 2.18,2.60,2.73 and 2.95 A and of limestone at 1.87, 2.09, 2.28 and 2.49 A
0
(Fig. 1) could be used to characterize and quantify these two dusts in their mixture. However, the XRD patterns of their synthetic mixtures showed that only the 2.60 A line of cement and the 2.28 A line of limestone were sensitive enough to give positive signals at the concentration ranges considered. No interference from other mineral phases are conceivable at these two reflections. The d-spacings for the aluminosilicates, like clays and shales (also used as raw materials in cement production) are mostly 3.0 A and greater (20 = 34” to 6”, see, for example, Fig. 2a). Using these lines, calibration curves were constructed based on their peak heights (Fig. 5). Peak widths were 0.3“ to 0.4” 20. The detection limits were comparable for both limestone and cement, -5 mg per filter (14.2 cm?) for each under the experimental conditions employed. This concentration corresponded to the smallest peak height that could be measured with a precision of + 50%. Peak heights obtained on duplicate runs of the standards were reproducible within f 20%. CONCLUSION
The present study shows that XRD analysis is capable of identifying and distinguishing limestone and cement aerosols. In so far as the analysis of ambient aerosols at a downwind receptor is concerned, it can complement the selective leaching technique suggested earlier by us. It is particularly useful
80
60
40
20
CONCENTRATION
1uu
(mg)
Fig. 5. Peak height, PH (in mm) vs concentration C (in mg per filter deposit of 11 cm’) of portland cement, PC, or lirnestooe, L, in the calibration standards. The least squares fits are defined by the following linear regressions.
For PC C= -0.45(
+0.27)+0.53
(+O.lO) x PH (r=0.99).
For L C = 0.45 ( + 0.29) + 0.43 ( + 0.08) x PH (r= 0.99).
Emissions from the cement industry
for monitoring plant’s environs where the concentration levels of these dusts are bound to be relatively high (several tens of mg m- ’ of air). The technique is not restricted to the cement industry. Diverse industries use diverse types of rocks, ores and minerals. XRD can identify their airborne particles through their mineral constituents. Since most of these emissions are fugitive, the method may prove useful only for the study of local emissions; i.e. for short-range transported pollutants. Acknowledgement-The
authors are thankful to Liaquat Husain, N.Y. State Department of Health and Philip Whitney, N.Y. State Geological Survey for their interest and encouragement, to Kenneth Steele, Univ. of Arkansas, Fayetteville, for carrying out XRD analysis in his laboratory. The assistance of Jeanine Bowen, Badar Ghauri, William Knox, Edward LeGere and Zikrur Rehman Siddiqi in sample collection is gratefully acknowledged. Contribution # 545 of the New York State Science Service (M. T. Davin). REFERENCES
Flanagan F. J. (1973) 1972 values for international geochemical reference samples. Geochim. Cosmochim. Acta 37, 1189-1200.
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Kalacic I. (1973a) Chronic nonspecific lung disease in cement workers. Arch. Envir. Health Za, 76-83. Kalacic I. (1973b) Ventilatory lung function in cement workers. Arch. Enuir. Health 26, 84-85. Moeller P., Morteani G., Hoefs J. and Parekh P. P. (1979) The origin of the ore bearing solution in the Pb-Zn veins of the western Han, Germany, as deduced from rare earth elements and isotope distributions in calcites. Chem. Geol. 26, 197-215. Parekh P. P., Ghauri B., Siddiqi Z. R. and Husain L. (1987) The use of chemical and statistical methods to identify sources of selected elements in ambient air aerosols in Karachi, Pakistan. Atmospheric Environment 21, 1267-1274.
Parekh P. P. and Husain L. (1988) Selective leaching of atmospheric aerosols: resolution of limestone and cement. Atmospheric
Environment 22, 707-713.
Pimental J. C. and Menezes A. P. (1978) Pulmonary and hepatic granulomatous disorders due to inhalation of cement and mica dusts. Thorax 33,219-227. Oleru U. G. (1984) Pulmonary function and symptoms of Nigerian workers exposed to cement dust. Envir. Res. 33, 379-385.
Turner D. B. (1967) Workbook of Atmospheric Dispersion Estimates. Envir. Health Ser.: Air pollution; Public Health Service Publ. No. 999-AP-26. U.S. Dept. Health, Education and Welfare, Cincinnati, Ohio.