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Quantitative determination of the mordenite content of natural zeolite rocks by infrared spectroscopy
Spectrochim~ca Acta, Vol. 4lA. Printed in Gnat Britain.
No.
12, pp. 1457-1458.
Quantitative
1985.
0584&8539,85 53.00 + 0 00 Pergamon PressLtd.
determination of the mordenite content of natural zeolite rocks by infrared spectroscopy J. HLAVAY,* I. VAssPiNYIt and J.
INCZI?DY*
*Institute for Analytical Chemistry and TDepartment of Mineralogy, University of Chemical Engineering, P. 0. Box 158, Veszprbm 8201, Hungary (Received 1 July 1985)
Abstract-A method has been developed for the quantitative determination of mordenite in different zeolite rocks. Standards and natural samples were pretreated by intensive grinding and pellets were prepared using an alcoholic technique. Absorbances at 1220 cm- ’ were calculated and the calibration curve was derived by means of standard samnles of mordenite-auartz mixtures. The results were compared with those from X-ray powder diffraction. a
Among the most widely investigated varieties of crystalline solids are the zeolites. X-Ray powder diffraction and, more recently, electron diffraction have been applied extensively to them. However, during the last 15 years it has been increasingly recognized that i.r. spectroscopy can yield extra information and can serve as a very rapid and useful structural analytical technique. Infrared spectroscopy based structural studies of zeolites were discussed in great detail by FLANIGEN et al. [l, 21. Mostly synthetic zeolites were investigated and characteristic bands were assigned to various zeolite structures and groups, and to structural subunits such as double rings and large pore openings. Hydrogen and ion exchanged forms of synthetic mordenite-like zeolites have also been studied by the i.r. technique [3]. JOSHI et al. [4] examined some natural and synthetic zeolites and correlated the observed absorption bands with their framework structure and the B/AI ratios in the aluminosilicate framework. No work has been done on the estimation of the zeolite content of natural rocks. In the present study, an attempt was made to determine the mordenite content of natural Hungarian zeolites by i.r. spectroscopy. EXPERIMENTAL Samples were obtained from the Tokaj mountain in north Hungary from drill-cores. Along with mordenite, the zeolite rocks contain mainly quartz and feldspar. A synthetic mordenite, Zeosorb VlOOP, was used as standard material both for the i.r. and the X-ray powder diffraction measurements. Infrared spectra were recorded on a UR-10 i.r. spectrophotometer (Carl Zeiss, Jena, G.D.R.). X-Ray powder diffractograms were obtained by a Model 1051 Philips diffractometer at 154 pm wavelength (CuK,). The particle size distribution in the pellet was measured by a VIDIMAT image analyser (Research Institute for Ferrous Metallurgy, Hungary). Samples and standards were ground in a vibration mill with agate balls for 2 h. Pellets were prepared using an alcoholic treatment as described earlier [S]. An internal standard method was used to determine the mordenite
content of the zeolite rocks by X-ray powder diffraction [6]. The base-line technique was applied for the calculation of the characteristic absorbances. Infrared spectra and particle size distributions were obtained on the same area of the pellets [5]. RESULTS AND DISCUSSION
The i.r. spectrum of natural zeolite rock is shown in Fig. 1. Absorption band assignments are as follows: 1220 cm- ’ : asymmetric stretching vibration of external linkage in mordenite; 1070 cm- ’ : Si-0 asymmetric stretching vibration; 800 and 780 cm- 1: Si-0 symmetric stretching vibration. The absorption band at 1220 cm- ’ was chosen for the quantitative analyses. Standard samples were prepared by mixing the synthetic mordenite and pure quartz. The mordenite content of the pellet ranged from 20 to 100 %. The dilution method was used and 1.00 mg of the mordenite-quartz mixture was weighed in all cases. It is well-known that the intensity of an i.r. absorption band is greatly affected by changing the particle size of the solid sample [7]. To prevent or decrease the effect of particle size on the absorbances, both the standards and the natural rocks were thoroughly ground. Then, during pellet preparation, the samples were further treated in an agate mortar with ethanol. The aggregates formed on grinding were broken up and the particle size decreased. For reliable quantitative measurement, the average particle size distribution of the standards and the unknown samples has to be identical. With 2 h grinding and the pellet preparation technique described above the two averages were identical within experimental error. The equation of the calibration line for the determination of mordenite is: Y= 1.87x lo-‘+151
x lo-‘X
where Y = absorbances at 1220 cm- 1 and X = mass of the mordenite in standards (m/m %). The standard error of regression, S,, is f 2.9 x 10e3, while the standard deviation of the slope, S,, is &-3.0 x lo- 5 1457
J. HLAVAY et al
1458
Table 1. Mordenite content of some natural zeolite rocks
1600
1400
1200
1M)O
800 cm-’
Fig. 1. Infrared spectrum of natural Hungarian zeolite rock. and that of the intercept, St,, is + 1.8 x 10e3. The regression coefficient, r, is 0.998. The average particle diameter of the standards in the pellet, d,,, = 3.28 f 0.139 pm at Student t (N, 0.95) = 2.262. Standard deviation of the mean, Sd = f 0.196 and the 95 % confidence limit, c.1. = f 4.24 %. The mordenite content found in the drill cores is shown in Table 1. The values were calculated by means of the calibration line. As can be seen in Table 1, the particle size of the pellets is about 3.2 pm for both the standards and the natural samples. This means that the effect of the differences in particle sizes on the intensity of the absorption band is negligible. The correlation between the i.r. and X-ray results is fairly good. In a very complex matrix, such as natural zeolites, the absorption band of mordenite at 1220 cm- ’ includes a small absorption due to a shoulder of the Si-G asymmetric stretch in silicates. Therefore, the intensity measured is not purely that of other silicates make a minor the mordenite, contribution.
Sample
d,, Olm)
1 2 3 4 5 6
3.43 3.13 3.27 3.33 3.34 3.18
Amount of mordenite Infrared spectrum X-Ray diffraction (%) (%) 15&3 26f3 46*3 50*3 54*3 42f4
14 28 42 48 53 39
Gibbsite as an internal standard was used for the estimation of the mordenite concentration of zeolite by X-ray powder diffraction. The reflection peak at d = 920 pm was chosen and the samples were shaken to avoid orientation effects. A relative standard deviation of 4-5 y0 was achieved for the measurements. In the quantitative phase analysis of the silicates, soils or natural rocks the difference between the results of the i.r. and X-ray methods is acceptable. In conclusion, it is evident that a quantitative determination of the mordenite content in zeolites may be reliably carried out by i.r. spectroscopy using proper pretreatment of the samples and pellet preparation. The method can be applied in geology or in environmental research where zeolite rocks or dust are of importance. REFERENCES [l] E. M. FLANIGEN,ACS Monograph No. 171,80 (1976). [2] E. M. FLANIGEN,H. KHATAMIand H. A. SZYMANSKI, Advances in Chemistry Series No. 101, 201 (1971). [3] H. G. KARGE, ACS Symposium Series 40, 584 (1977). [4] M. S. JOSHIand B. T. BHOSKAR,Ind. J. pure oppl. Phys. 19, 560 (1981). [5] J. HLAVAY and J. INCZ~DY, Spectrcchim. Acto 4lA, 783 (1985). [6] H. P. KLUG and L. E. ALEXANDER,X-Ray Dtfiacrion Procedures. Wiley, New York (1954). [I] G. DUYCKAERTS,Analyst 84, 201 (1959).
No.
12, pp. 1457-1458.
Quantitative
1985.
0584&8539,85 53.00 + 0 00 Pergamon PressLtd.
determination of the mordenite content of natural zeolite rocks by infrared spectroscopy J. HLAVAY,* I. VAssPiNYIt and J.
INCZI?DY*
*Institute for Analytical Chemistry and TDepartment of Mineralogy, University of Chemical Engineering, P. 0. Box 158, Veszprbm 8201, Hungary (Received 1 July 1985)
Abstract-A method has been developed for the quantitative determination of mordenite in different zeolite rocks. Standards and natural samples were pretreated by intensive grinding and pellets were prepared using an alcoholic technique. Absorbances at 1220 cm- ’ were calculated and the calibration curve was derived by means of standard samnles of mordenite-auartz mixtures. The results were compared with those from X-ray powder diffraction. a
Among the most widely investigated varieties of crystalline solids are the zeolites. X-Ray powder diffraction and, more recently, electron diffraction have been applied extensively to them. However, during the last 15 years it has been increasingly recognized that i.r. spectroscopy can yield extra information and can serve as a very rapid and useful structural analytical technique. Infrared spectroscopy based structural studies of zeolites were discussed in great detail by FLANIGEN et al. [l, 21. Mostly synthetic zeolites were investigated and characteristic bands were assigned to various zeolite structures and groups, and to structural subunits such as double rings and large pore openings. Hydrogen and ion exchanged forms of synthetic mordenite-like zeolites have also been studied by the i.r. technique [3]. JOSHI et al. [4] examined some natural and synthetic zeolites and correlated the observed absorption bands with their framework structure and the B/AI ratios in the aluminosilicate framework. No work has been done on the estimation of the zeolite content of natural rocks. In the present study, an attempt was made to determine the mordenite content of natural Hungarian zeolites by i.r. spectroscopy. EXPERIMENTAL Samples were obtained from the Tokaj mountain in north Hungary from drill-cores. Along with mordenite, the zeolite rocks contain mainly quartz and feldspar. A synthetic mordenite, Zeosorb VlOOP, was used as standard material both for the i.r. and the X-ray powder diffraction measurements. Infrared spectra were recorded on a UR-10 i.r. spectrophotometer (Carl Zeiss, Jena, G.D.R.). X-Ray powder diffractograms were obtained by a Model 1051 Philips diffractometer at 154 pm wavelength (CuK,). The particle size distribution in the pellet was measured by a VIDIMAT image analyser (Research Institute for Ferrous Metallurgy, Hungary). Samples and standards were ground in a vibration mill with agate balls for 2 h. Pellets were prepared using an alcoholic treatment as described earlier [S]. An internal standard method was used to determine the mordenite
content of the zeolite rocks by X-ray powder diffraction [6]. The base-line technique was applied for the calculation of the characteristic absorbances. Infrared spectra and particle size distributions were obtained on the same area of the pellets [5]. RESULTS AND DISCUSSION
The i.r. spectrum of natural zeolite rock is shown in Fig. 1. Absorption band assignments are as follows: 1220 cm- ’ : asymmetric stretching vibration of external linkage in mordenite; 1070 cm- ’ : Si-0 asymmetric stretching vibration; 800 and 780 cm- 1: Si-0 symmetric stretching vibration. The absorption band at 1220 cm- ’ was chosen for the quantitative analyses. Standard samples were prepared by mixing the synthetic mordenite and pure quartz. The mordenite content of the pellet ranged from 20 to 100 %. The dilution method was used and 1.00 mg of the mordenite-quartz mixture was weighed in all cases. It is well-known that the intensity of an i.r. absorption band is greatly affected by changing the particle size of the solid sample [7]. To prevent or decrease the effect of particle size on the absorbances, both the standards and the natural rocks were thoroughly ground. Then, during pellet preparation, the samples were further treated in an agate mortar with ethanol. The aggregates formed on grinding were broken up and the particle size decreased. For reliable quantitative measurement, the average particle size distribution of the standards and the unknown samples has to be identical. With 2 h grinding and the pellet preparation technique described above the two averages were identical within experimental error. The equation of the calibration line for the determination of mordenite is: Y= 1.87x lo-‘+151
x lo-‘X
where Y = absorbances at 1220 cm- 1 and X = mass of the mordenite in standards (m/m %). The standard error of regression, S,, is f 2.9 x 10e3, while the standard deviation of the slope, S,, is &-3.0 x lo- 5 1457
J. HLAVAY et al
1458
Table 1. Mordenite content of some natural zeolite rocks
1600
1400
1200
1M)O
800 cm-’
Fig. 1. Infrared spectrum of natural Hungarian zeolite rock. and that of the intercept, St,, is + 1.8 x 10e3. The regression coefficient, r, is 0.998. The average particle diameter of the standards in the pellet, d,,, = 3.28 f 0.139 pm at Student t (N, 0.95) = 2.262. Standard deviation of the mean, Sd = f 0.196 and the 95 % confidence limit, c.1. = f 4.24 %. The mordenite content found in the drill cores is shown in Table 1. The values were calculated by means of the calibration line. As can be seen in Table 1, the particle size of the pellets is about 3.2 pm for both the standards and the natural samples. This means that the effect of the differences in particle sizes on the intensity of the absorption band is negligible. The correlation between the i.r. and X-ray results is fairly good. In a very complex matrix, such as natural zeolites, the absorption band of mordenite at 1220 cm- ’ includes a small absorption due to a shoulder of the Si-G asymmetric stretch in silicates. Therefore, the intensity measured is not purely that of other silicates make a minor the mordenite, contribution.
Sample
d,, Olm)
1 2 3 4 5 6
3.43 3.13 3.27 3.33 3.34 3.18
Amount of mordenite Infrared spectrum X-Ray diffraction (%) (%) 15&3 26f3 46*3 50*3 54*3 42f4
14 28 42 48 53 39
Gibbsite as an internal standard was used for the estimation of the mordenite concentration of zeolite by X-ray powder diffraction. The reflection peak at d = 920 pm was chosen and the samples were shaken to avoid orientation effects. A relative standard deviation of 4-5 y0 was achieved for the measurements. In the quantitative phase analysis of the silicates, soils or natural rocks the difference between the results of the i.r. and X-ray methods is acceptable. In conclusion, it is evident that a quantitative determination of the mordenite content in zeolites may be reliably carried out by i.r. spectroscopy using proper pretreatment of the samples and pellet preparation. The method can be applied in geology or in environmental research where zeolite rocks or dust are of importance. REFERENCES [l] E. M. FLANIGEN,ACS Monograph No. 171,80 (1976). [2] E. M. FLANIGEN,H. KHATAMIand H. A. SZYMANSKI, Advances in Chemistry Series No. 101, 201 (1971). [3] H. G. KARGE, ACS Symposium Series 40, 584 (1977). [4] M. S. JOSHIand B. T. BHOSKAR,Ind. J. pure oppl. Phys. 19, 560 (1981). [5] J. HLAVAY and J. INCZ~DY, Spectrcchim. Acto 4lA, 783 (1985). [6] H. P. KLUG and L. E. ALEXANDER,X-Ray Dtfiacrion Procedures. Wiley, New York (1954). [I] G. DUYCKAERTS,Analyst 84, 201 (1959).