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Raman spectroscopy of some complex arsenate minerals—implications for soil remediation
Spectrochimica Acta Part A 59 (2003) 2797 /2804 www.elsevier.com/locate/saa
Raman spectroscopy of some complex arsenate minerals* implications for soil remediation
/
Ray L. Frost *, J. Theo Kloprogge Centre for Instrumental and Developmental Chemistry, Queensland University of Technology, 2 George Street, GPO Box 2434, Brisbane, Qld. 4001, Australia Received 11 December 2002; accepted 6 February 2003
Abstract The application of spectroscopy to the study of contaminants in soils is important. Among the many contaminants is arsenic, which is highly labile and may leach to non-contaminated areas. Minerals of arsenate may form depending upon the availability of specific cations for example calcium and iron. Such minerals include carminite, pharmacosiderite and talmessite. Each of these arsenate minerals can be identified by its characteristic Raman spectrum enabling identification. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Carminite; Clinotyrolite; Kankite; Pharmacosiderite; Picropharmacolite; Talmessite; Raman spectroscopy
1. Introduction The formation of secondary minerals is important. Arsenate mineral formation is quite common and such minerals may form as leachates in soils [1 /6]. The presence of arsenic in soils is a widespread and common phenomena [7 /9]. The arsenate may have originated from old mine sites [10 / 13]. The arsenate in the soils is commonly mobile and can contaminate adjacent areas either through ground water or other mechanisms such as
* Corresponding author. Tel.: /61-7-3864-2407; fax: /61-73864-1804. E-mail address: [email protected] (R.L. Frost).
through plant growth [2,9,14,15]. Arsenates in soils may originate from old munition dumps and from munition wastes such as from ‘Mustard gas’ [16,17]. The effect of contamination of soils by arsenates can lead to phytotoxicity [12,18,19]. Arsenic compounds in conjunction with copper and chromium have been used extensively as a biocide to prevent borer attach in timber. This also is a cause of contamination of soils [20 /22]. In Australia, arsenic compounds of an inorganic nature were used as the principal chemical ingredient in cattle dips [11,23,24]. The pH of the soil and post-contaminant treatment such as with lime or fertilisers containing phosphate can effect the speciation of the arsenic compounds [6,25]. No matter what the origin of the arsenic/arsenates in
1386-1425/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S1386-1425(03)00103-3
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R.L. Frost, J.T. Kloprogge / Spectrochimica Acta Part A 59 (2003) 2797 /2804
the soils, the identification of its presence is imperative. Secondary minerals, which may form in soils, are often dependent upon the availability of cations in the soils. Often the cations of iron, calcium and magnesium are the most likely available cations. It is important, therefore, to study potential arsenates of these minerals. Carminite and Kankite are two possible minerals. Carminite (Pb(Fe3)2(AsO4)2(OH)2) is an alteration product of arsenopyrite and is orthorhombic (point group 2/m , 2/m , 2/m ) [26 /29]. The carminite structure contains stepped chains edge-sharing pairs of Fe(O,OH)6 octahedral; these chains are linked by AsO4 tetrahedra and Pb atoms in distorted square antiprismatic coordination [29]. Kankite ((Fe3)2(AsO4) ×/3H2O) is monoclinic and of not well defined point group [30]. Another iron bearing arsenate mineral is pharmacosiderite (K(Fe3)4(AsO4)3(OH)4 ×/6/7H2O). This mineral is cubic with point group 4 3m [31,32]. Three calcium bearing arseno-minerals are picropharmacolite, talmessite and tilasite. Picropharmacolite H2Ca4Mg(AsO4)4 ×/11H2O is a triclinic mineral with point group 1: This mineral is common in mine workings. A related mineral is talmessite (Ca2Mg(AsO4)×/2H2O) also triclinic of point group 1 [33 /35]. Tilasite (CaMg(AsO4)F) is monoclinic of point group 2/m [36]. In this research we present the Raman spectra of selected arsenate minerals of iron and calcium.
2. Experimental 2.1. Minerals Minerals were obtained from the South Australian museum. The samples were phase analysed using X-ray diffraction and the compositions checked using EDX measurements. 2.2. Raman microprobe spectroscopy The crystals of the minerals were placed and orientated on a polished metal surface on the stage of an Olympus BHSM microscope, which is equipped with 10 and 50 / objectives. The micro-
scope is part of a Renishaw 1000 Raman microscope system, which also includes a monochromator, a filter system and a Charge Coupled Device (CCD). Raman spectra were excited by a Spectra-Physics model 127 He /Ne laser (633 nm) at a resolution of 2 cm 1 in the range between 100 and 4000 cm 1. Repeated acquisitions using the highest magnification were accumulated to improve the signal to noise ratio in the spectra. Spectra were calibrated using the 520.5 cm 1 line of a silicon wafer. Spectroscopic manipulation such as baseline adjustment, smoothing and normalisation were performed using the Spectracalc software package GRAMS (Galactic Industries Corporation, NH, USA). Band component analysis was undertaken using the Jandel ‘PEAKFIT’ software package, which enabled the type of fitting, function to be selected and allows specific parameters to be fixed or varied accordingly. Band fitting was done using a Gauss / Lorentz cross-product function with the minimum number of component bands used for the fitting process. The Gauss /Lorentz ratio was maintained at values greater than 0.7 and fitting was undertaken until reproducible results were obtained with squared correlations of r2 greater than 0.995.
3. Results and discussion 3.1. Hydroxyl stretching vibrations The Raman spectra of the hydroxyl stretching region of the arsenates studied in this work are shown in Fig. 1. The results of the spectroscopic analysis are reported in Table 1. The spectra display a considerable amount of noise. This is a result of the low intensity of the bands and the need to use low power (B/0.1 mW) as the samples may decompose under the power of the incident radiation. Particularly susceptible are the blue to green minerals when using the 633 nm radiation. The Raman spectrum of the hydroxyl stretching region of carminite shows a broad profile centred upon 3250 cm 1, which may be resolved into two components at 3254 and 3217 cm 1. The Raman spectrum of kankite also displays broad bands at 3408 and 3221 cm 1. A broad band is also
R.L. Frost, J.T. Kloprogge / Spectrochimica Acta Part A 59 (2003) 2797 /2804
Fig. 1. Raman spectra of the hydroxyl stretching region of: (a) carminite, (b) kankite, (c) pharmacosiderite, (d) clinotyrolite, (e) picropharmacolite, (f) talmessite.
observed at 3112 cm 1. The Raman spectrum of the other Fe3 bearing mineral pharmacosiderite has bands centred at 3498, 3378, 3358 and 3138 cm 1. The mineral clinotyrolite has two bands at 3489 and 3403 cm 1. The position and number of bands depends on the structure of the mineral and the symmetry of the elements within that structure. Studies have shown a strong correlation between OH stretching frequencies and both the O O bond distances and with the H O hydrogen bond distances [37 /40]. The elegant work of Libowitzky (1999) showed that a regression function could be employed relating the above correlations with regression coefficients better than 0.96 [41]. The function is n1 /3592/304/109exp(/
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d(O /O)/0.1321) cm 1. Two types of OH units are identified in the structure and the known hydrogen bond distances used to predict the hydroxyl stretching frequencies. In this work we have used the Libowitzky function to predict hydrogen bond distances for the OH units in the crystal structure. In this way we calculate the hydrogen bond distances by the use of the Raman hydroxyl stretching bands. The data for the hydroxyl stretching region in Table 2 fundamentally distinguishes between types of OH units according to the hydrogen bond distances, namely strongly hydrogen bonded and weakly hydrogen bonded [42]. To the best of our knowledge, no neutron diffraction studies of these minerals have been forthcoming and hence no hydrogen bond distances are known. In this set of data, the hydroxyl stretching frequencies of the Raman spectra have been used to predict the hydrogen bond distances for these minerals and by using the band width of the hydroxyl stretching frequencies estimates of the variation in the hydrogen bond distances predicted. The two hydroxyl vibrations for carminite at 3254 and 3217 cm 1 lead to estimated hydrogen ˚ . These bond distances of 2.724 and 2.710 A distances represent the distance between the hydrogen of the hydroxyl unit and the adjacent oxygen of the arsenate group. Two hydrogen ˚ are deterbond distances of 2.804 and 2.711 A mined for kankite. For pharmacosiderite four hydroxyl Raman bands are observed. This results in four hydrogen bond distances of 2.893, 2.784, ˚ . The first hydrogen bond 2.772 and 2.685 A distance is long and represents weak hydrogen bonding whereas the hydrogen bond distances of ˚ may be considered as short and represents B/2.7 A strong hydrogen bonding. The width of the OH ˚ and is stretching bands varies from 96.3 to 614.3 A a measure of the variation of hydrogen bond distances in the structure. In contrast, the hydrogen bond distances for the two hydroxyl units for ˚ and the width clinotyrolite are 2.880 and 2.800 A of the two bands are 60.0 and 41.0 cm 1. The significance of these narrow bands means that the variation in the hydrogen bond distance is small. The variation for the two bands is estimated as 9/ ˚ , respectively. The hydrogen 0.068 and 9/0.015 A
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Table 1 Raman spectroscopic analysis of some complex arsenate minerals Kankite (Fe3 )2(AsO4) ×/ 3H2O
Pharmacosiderite K(Fe3 )4(AsO4)3(OH)4 ×/6 / 7H2O
Clinotyrolite Ca2Cu9[(As,S)O4](O,OH)10 ×/ 10H2O
Picropharmacolite H2Ca4Mg(AsO4)4 ×/ 11H2O
Talmessite Ca2Mg(AsO4) ×/ 2H2O
3254 3217
3408 3221 3112
3498 3378 3358 3138
3489 3403
3448 3212 2922?
2882 2376
1629 1469 1065 849 835 822 738 543 497 467
881 832 808 790 733 564 492
1061 1012 880 862 810 789
475
350 324
398 373 290
395 302 275
259 210
240 228 198 179
262 238 195 166
1136 1007 883 841 802
980 866 750
931 905 877 836 814 783
669 618 505 493 462 414 385 359 314
530 460
455 445
397 325 230
388 363 357 305 276 212 196 173
260 210 179
Tilasite CaMg(AsO4)F
1518 1318 1107 1056 820
659 611 493 410
297 245
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Carminite Pb(Fe3 )2(AsO4)2(OH)2
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Table 2 Correlation between hydroxyl stretching frequencies and estimated hydrogen bond distances Mineral
Suggested hydrogen bond origin
Carminite
OH1 OH2 Kankite H2O 1 H2O 2 Pharmacosiderite OH1 OH2 H2O 1 H2O 2 Clinotyrolite OH1 OH2 Picropharmacolite H2O 1 H2O 2 Talmessite H2O 1 H2O 2
Observed Raman band posi- Estimated hydrogen bond ˚) tions (cm1) distance (A
Observed Raman band width (cm1)
3254 3217 3408 3221 3498 3378 3358 3138 3489 3403 3448 3212 3250 2882
277.0 288.0 207.0 104.0 147.4 96.3 358.8 614.3 60.0 41.0 218.6 350.7 105.0 307.0
bond distances for picropharmacolite are esti˚ and for talmessite mated at 2.836 and 2.708 A ˚ 2.722 and 2.625 A. The mineral tilasite does not contain any hydroxyl groups but does contain fluorine. Fluorine (AW /17) can function like a hydroxyl group and may replace the OH units in structures. 3.2. Vibrations of the AsO4 unit The Raman spectra of the AsO4 stretching region are shown in Fig. 2. Perhaps apart from tilasite, the spectra show complexity with multiple bands observed in this 750/950 cm 1 region. The free arsenate ion has tetrahedral symmetry and thus should have four bands of which two are infrared active with theoretical values of n3 (F2) 887 cm1 and n4 (F2) 463 cm 1. The Raman active modes are observed at 837 (A1) and 349 (E) cm 1. Upon coordination of the arsenate ion to the copper atom, the symmetry of the arsenate ion reduces to C3v and may further reduce to Cs . The implication is that all bands will be both infrared and Raman active. For carminite, bands are observed in the AsO stretching region at 849, 835, 822 and 738 cm 1. The first band is the most intense and is assigned
2.724 2.710 2.804 2.711 2.893 2.784 2.772 2.685 2.880 2.800 2.836 2.708 2.722 2.625
to the n1 symmetric stretching mode. The next two bands are assigned to the n3 antisymmetric stretching modes. The band at 738 cm 1 may be attributed to the hydroxyl deformation mode. For the mineral kankite broad bands are observed at 883 {n3 (F2)}, 832 {n1 (A1)} and 808 cm 1. Component bands are also observed at 790 and 733 cm 1. The latter two bands may be assigned to hydroxyl deformation modes. The Raman spectrum of pharmacosiderite shows two intense bands at 880 and 862 cm 1, attributed to the {n3 (F2)} and 832 {n1 (A1)} vibrational modes. The band at 789 cm 1 may be assigned to the OH deformation vibration. For clinotyrolite, AsO4 stretching bands are observed at 841 and 802 cm 1. For picropharmacolite, only broad bands are observed centred upon 866 and 750 cm 1. Talmessite shows well defined Raman bands at 877 and 836 cm1 whereas tilasite displays only a broad band at 820 cm 1. The Raman spectra of the minerals under discussion of the low wavenumber region are shown in Fig. 3. The widths of many of the bands observed in the AsO stretching region are also observed in the low wavenumber region. The bands in the 400 /500 cm1 region are assignable to the bending n4 (F2) mode. The most intense
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band is observed at 497 cm 1 with other bands at 543 and 467 cm 1. The observation of multiple bands is characteristic of reduced symmetry of the AsO4 unit in the crystal. The Raman spectra of kankite in this region shows an intense band at 492 cm 1 and similarly pharmacosiderite shows an intense band at 475 cm 1. For clinotyrolite, an intense band is observed at 493 cm 1 with shoulders at 462 and 505 cm 1. The Raman spectrum of picropharmacolite seems ill-defined in this region. In contrast, the two minerals tilasite and talmessite have well defined spectra. Talmessite shows two bands at 455 and 445 cm 1. Tilasite shows a sharp band at 410 cm 1 with a low intensity band at 493 cm 1. The n2 bending mode is normally found at around 349 cm1. The Fe bearing arsenates of
Fig. 3. Raman spectra of the low wavenumber region of: (a) carminite, (b) kankite, (c) pharmacosiderite, (d) clinotyrolite, (e) picropharmacolite, (f) talmessite, (g) tilasite.
Fig. 2. Raman spectra of the AsO4 stretching region of: (a) carminite, (b) kankite, (c) pharmacosiderite, (d) clinotyrolite, (e) picropharmacolite, (f) talmessite, (g) tilasite.
carminite, kankite and pharmacosiderite display a complex set of bands. For carminite bands are observed at 324 and 350 cm 1 and are assigned to the n2 in-plane bending mode. Strong bands are observed at 210 and 259 cm 1 and one possibility for their designation is FeO stretching vibrations. The n2 bands for kankite are observed at 398 and 373 cm 1 and for pharmacosiderite at 395 and 302 cm 1. These later bands are of comparatively low intensity. For the mineral clinotyrolite, bands in this region are observed at 385, 359 and 314 cm 1. The bands for picropharmacolite are ill defined. For talmessite, strong bands are observed at 363 and 357 cm 1. Strong bands are also observed at 305 and 276 cm 1. One possibility for their
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assignation is to CaO and MgO stretching vibrations. The Raman spectrum of tilasite appears different and strong bands are observed at 297 and 245 cm 1. The position of both of these bands appears too low for the assignment to the n2 bending vibration.
4. Conclusions The application of Raman spectroscopy to the study of selected Fe and Ca bearing mineral phases of arsenate has shown that the minerals can be identified by their Raman spectra. Selected secondary minerals of Ferric iron and calcium were analysed. The implication is that a Raman spectrum of a contaminated soil may be used in attempt to identify mineral components in that soil. Such identification may then lead to recommendations for the removal of such contamination [43,44].
Acknowledgements The infra-structure support of the Queensland University of Technology School of Physical and Chemical Sciences is gratefully acknowledged. Professor Allan Pring of the South Australian Museum is thanked for the loan of the arsenate minerals.
References [1] H. Akhter, F.K. Cartledge, J. Miller, M. Mclearn, J. Environ. Eng. (Reston, VA) 126 (2000) 999. [2] D.K. Bhumbla, R.F. Keefer, Adv. Environ. Sci. Technol. 26 (1994) 51. [3] G. Bombach, A. Pierra, W. Klemm, Fresenius’ J. Anal. Chem. 350 (1994) 49. [4] V. Dutre, C. Kestens, J. Schaep, C. Vandecasteele, Sci. Total Environ. 220 (1998) 185. [5] K.H. Karstensen, O. Ringstad, I. Rustad, K. Kalevi, K. Jorgensen, K. Nylund, T. Alsberg, K. Olafsdottir, O. Heidenstam, H. Solberg, Talanta 46 (1998) 423. [6] M. Pantsar-Kallio, P.K.G. Manninen, Sci. Total Environ. 204 (1997) 193.
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[7] W.W. Wenzel, A. Brandstetter, H. Wutte, E. Lombi, T. Prohaska, G. Stingeder, D.C. Adriano, J. Plant Nutr. Soil Sci. 165 (2002) 221. [8] P.S. Yarlagadda, M.R. Matsumoto, J.E. Vanbenschoten, A. Kathuria, J. Environ. Eng. (New York) 121 (1995) 276. [9] P.W. Abrahams, I. Thornton, Agric. Ecosyst. Environ. 48 (1994) 125. [10] E.H. Amonoo-Neizer, D. Nyamah, S.B. Bakiamoh, Water Air Soil Pollut. 91 (1996) 363. [11] P.M. Ashley, B.G. Lottermoser, Aust. J. Earth Sci. 46 (1999) 861. [12] J. Bech, C. Poschenrieder, M. Llugany, J. Barcelo, P. Tume, F.J. Tobias, J.L. Barranzuela, E.R. Vasquez, Sci. Total Environ. 203 (1997) 83. [13] M. Chen, L.Q. Ma, C.G. Hoogeweg, W.G. Harris, Environ. Forensics 2 (2001) 117. [14] A. Brandstetter, E. Lombi, W.W. Wenzel, D.C. Adriano, Environ. Sci. Pollut. Control Ser. 23 (2000) 715. [15] J. Christova, C. Stanchev, K. Rekalov, Dokl. Bulg. Akad. Nauk. 46 (1993) 81. [16] Beletskaya, Bilger, Boronin, Bunnett, Costantino, Cullen, Dominas, Goessler, Haiduc, Maeda, Martens, NATO ASI Series, Series 1: Disarmament Technologies, vol. 19, 1998, pp. 177. [17] F. Juillot, P. Ildefonse, G. Morin, G. Calas, A.M.D. Kersabiec, M. Benedetti, Appl. Geochem. 14 (1999) 1031. [18] M.B. Mcbride, C.E. Martinez, Environ. Sci. Technol. 34 (2000) 4386. [19] H. Helgesen, E.H. Larsen, Analyst (Cambridge, UK) 123 (1998) 791. [20] J. Rajander, L. Harju, J.O. Lill, K.E. Saarela, A. Lindroos, S.J. Heselius, Nucl. Instrum. Methods Phys. Res. Sect. B: Beam Interact. Mater. Atoms. 150 (1999) 510. [21] D.E. Stilwell, K.D. Gorny, Bull. Environ. Contam. Toxicol. 58 (1997) 22. [22] M.F. Azizian, K. Osathaphan, P.O. Nelson, Preprints of Extended Abstracts presented at the ACS National Meeting, American Chemical Society, Division of Environmental Chemistry, vol. 40, 2000, pp. 16. [23] Q. Zhou, Z. Gao, J. Environ. Sci. (China) 6 (1994) 330. [24] R.G. Mclaren, R. Naidu, J. Smith, K.G. Tiller, J. Environ. Qual. 27 (1998) 348. [25] F.J. Peryea, R. Kammereck, Water Air Soil Pollut. 93 (1997) 243. [26] J.J. Finney, 1962. [27] J.J. Finney, Am. Mineral. 48 (1963) 1. [28] Kharisun, M.R. Taylor, D.J.M. Bevan, A.D. Rae, A. Pring, Mineral. Mag. 61 (1997) 685. [29] Kharisun, M.R. Taylor, D.J.M. Bevan, A. Pring, Mineral. Mag. 60 (1996) 805. [30] F. Cech, J. Jansa, F. Novak, Neues Jahrb. Mineral. Monatsh. (1976) 426. [31] J. Zemann, Experientia 3 (1947) 452. [32] C. Rewitzer, R. Hochleitner, Rivista Mineral. Ital. (1989) 83. [33] M. Catti, G. Ferraris, G. Ivaldi, Bull. Soc. Fr. Mineral Cristallogr. 100 (1977) 230.
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[34] R. Brasse, P. Mattrat, H. Guerin, Bull. Soc. Chim. Fr. (1968) 2686. [35] I.V. Pekov, R.A. Vinogradova, N.V. Chukanov, I.M. Kulikova, Zapiski Vserossiiskogo Mineralogicheskogo Obshchestva 130 (2001) 10. [36] V. Bermanec, Neues Jahrbuch fuer Mineralogie, Monatshefte (1994) 289. [37] J. Emsley, Chem. Soc. Rev. 9 (1980) 91. [38] H. Lutz, Struct. Bonding (Berlin, Germany) 82 (1995) 85.
[39] [40] [41] [42]
W. Mikenda, J. Mol. Struct. 147 (1986) 1. A. Novak, Struct. Bonding (Berlin) 18 (1974) 177. E. Libowitsky, Monatschefte Chem. 130 (1999) 1047. J. Miller, H. Akhter, F.K. Cartledge, M. Mclearn, J. Environ. Eng. (Reston, VA) 126 (2000) 1004. [43] E. Lombi, W.W. Wenzel, D.C. Adriano, Environ. Sci. Pollut. Control Ser. 23 (2000) 739. [44] N. Papassiopi, S. Tambouris, A. Kontopoulos, Water Air Soil Pollut. 109 (1999) 1.
Raman spectroscopy of some complex arsenate minerals* implications for soil remediation
/
Ray L. Frost *, J. Theo Kloprogge Centre for Instrumental and Developmental Chemistry, Queensland University of Technology, 2 George Street, GPO Box 2434, Brisbane, Qld. 4001, Australia Received 11 December 2002; accepted 6 February 2003
Abstract The application of spectroscopy to the study of contaminants in soils is important. Among the many contaminants is arsenic, which is highly labile and may leach to non-contaminated areas. Minerals of arsenate may form depending upon the availability of specific cations for example calcium and iron. Such minerals include carminite, pharmacosiderite and talmessite. Each of these arsenate minerals can be identified by its characteristic Raman spectrum enabling identification. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Carminite; Clinotyrolite; Kankite; Pharmacosiderite; Picropharmacolite; Talmessite; Raman spectroscopy
1. Introduction The formation of secondary minerals is important. Arsenate mineral formation is quite common and such minerals may form as leachates in soils [1 /6]. The presence of arsenic in soils is a widespread and common phenomena [7 /9]. The arsenate may have originated from old mine sites [10 / 13]. The arsenate in the soils is commonly mobile and can contaminate adjacent areas either through ground water or other mechanisms such as
* Corresponding author. Tel.: /61-7-3864-2407; fax: /61-73864-1804. E-mail address: [email protected] (R.L. Frost).
through plant growth [2,9,14,15]. Arsenates in soils may originate from old munition dumps and from munition wastes such as from ‘Mustard gas’ [16,17]. The effect of contamination of soils by arsenates can lead to phytotoxicity [12,18,19]. Arsenic compounds in conjunction with copper and chromium have been used extensively as a biocide to prevent borer attach in timber. This also is a cause of contamination of soils [20 /22]. In Australia, arsenic compounds of an inorganic nature were used as the principal chemical ingredient in cattle dips [11,23,24]. The pH of the soil and post-contaminant treatment such as with lime or fertilisers containing phosphate can effect the speciation of the arsenic compounds [6,25]. No matter what the origin of the arsenic/arsenates in
1386-1425/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S1386-1425(03)00103-3
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the soils, the identification of its presence is imperative. Secondary minerals, which may form in soils, are often dependent upon the availability of cations in the soils. Often the cations of iron, calcium and magnesium are the most likely available cations. It is important, therefore, to study potential arsenates of these minerals. Carminite and Kankite are two possible minerals. Carminite (Pb(Fe3)2(AsO4)2(OH)2) is an alteration product of arsenopyrite and is orthorhombic (point group 2/m , 2/m , 2/m ) [26 /29]. The carminite structure contains stepped chains edge-sharing pairs of Fe(O,OH)6 octahedral; these chains are linked by AsO4 tetrahedra and Pb atoms in distorted square antiprismatic coordination [29]. Kankite ((Fe3)2(AsO4) ×/3H2O) is monoclinic and of not well defined point group [30]. Another iron bearing arsenate mineral is pharmacosiderite (K(Fe3)4(AsO4)3(OH)4 ×/6/7H2O). This mineral is cubic with point group 4 3m [31,32]. Three calcium bearing arseno-minerals are picropharmacolite, talmessite and tilasite. Picropharmacolite H2Ca4Mg(AsO4)4 ×/11H2O is a triclinic mineral with point group 1: This mineral is common in mine workings. A related mineral is talmessite (Ca2Mg(AsO4)×/2H2O) also triclinic of point group 1 [33 /35]. Tilasite (CaMg(AsO4)F) is monoclinic of point group 2/m [36]. In this research we present the Raman spectra of selected arsenate minerals of iron and calcium.
2. Experimental 2.1. Minerals Minerals were obtained from the South Australian museum. The samples were phase analysed using X-ray diffraction and the compositions checked using EDX measurements. 2.2. Raman microprobe spectroscopy The crystals of the minerals were placed and orientated on a polished metal surface on the stage of an Olympus BHSM microscope, which is equipped with 10 and 50 / objectives. The micro-
scope is part of a Renishaw 1000 Raman microscope system, which also includes a monochromator, a filter system and a Charge Coupled Device (CCD). Raman spectra were excited by a Spectra-Physics model 127 He /Ne laser (633 nm) at a resolution of 2 cm 1 in the range between 100 and 4000 cm 1. Repeated acquisitions using the highest magnification were accumulated to improve the signal to noise ratio in the spectra. Spectra were calibrated using the 520.5 cm 1 line of a silicon wafer. Spectroscopic manipulation such as baseline adjustment, smoothing and normalisation were performed using the Spectracalc software package GRAMS (Galactic Industries Corporation, NH, USA). Band component analysis was undertaken using the Jandel ‘PEAKFIT’ software package, which enabled the type of fitting, function to be selected and allows specific parameters to be fixed or varied accordingly. Band fitting was done using a Gauss / Lorentz cross-product function with the minimum number of component bands used for the fitting process. The Gauss /Lorentz ratio was maintained at values greater than 0.7 and fitting was undertaken until reproducible results were obtained with squared correlations of r2 greater than 0.995.
3. Results and discussion 3.1. Hydroxyl stretching vibrations The Raman spectra of the hydroxyl stretching region of the arsenates studied in this work are shown in Fig. 1. The results of the spectroscopic analysis are reported in Table 1. The spectra display a considerable amount of noise. This is a result of the low intensity of the bands and the need to use low power (B/0.1 mW) as the samples may decompose under the power of the incident radiation. Particularly susceptible are the blue to green minerals when using the 633 nm radiation. The Raman spectrum of the hydroxyl stretching region of carminite shows a broad profile centred upon 3250 cm 1, which may be resolved into two components at 3254 and 3217 cm 1. The Raman spectrum of kankite also displays broad bands at 3408 and 3221 cm 1. A broad band is also
R.L. Frost, J.T. Kloprogge / Spectrochimica Acta Part A 59 (2003) 2797 /2804
Fig. 1. Raman spectra of the hydroxyl stretching region of: (a) carminite, (b) kankite, (c) pharmacosiderite, (d) clinotyrolite, (e) picropharmacolite, (f) talmessite.
observed at 3112 cm 1. The Raman spectrum of the other Fe3 bearing mineral pharmacosiderite has bands centred at 3498, 3378, 3358 and 3138 cm 1. The mineral clinotyrolite has two bands at 3489 and 3403 cm 1. The position and number of bands depends on the structure of the mineral and the symmetry of the elements within that structure. Studies have shown a strong correlation between OH stretching frequencies and both the O O bond distances and with the H O hydrogen bond distances [37 /40]. The elegant work of Libowitzky (1999) showed that a regression function could be employed relating the above correlations with regression coefficients better than 0.96 [41]. The function is n1 /3592/304/109exp(/
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d(O /O)/0.1321) cm 1. Two types of OH units are identified in the structure and the known hydrogen bond distances used to predict the hydroxyl stretching frequencies. In this work we have used the Libowitzky function to predict hydrogen bond distances for the OH units in the crystal structure. In this way we calculate the hydrogen bond distances by the use of the Raman hydroxyl stretching bands. The data for the hydroxyl stretching region in Table 2 fundamentally distinguishes between types of OH units according to the hydrogen bond distances, namely strongly hydrogen bonded and weakly hydrogen bonded [42]. To the best of our knowledge, no neutron diffraction studies of these minerals have been forthcoming and hence no hydrogen bond distances are known. In this set of data, the hydroxyl stretching frequencies of the Raman spectra have been used to predict the hydrogen bond distances for these minerals and by using the band width of the hydroxyl stretching frequencies estimates of the variation in the hydrogen bond distances predicted. The two hydroxyl vibrations for carminite at 3254 and 3217 cm 1 lead to estimated hydrogen ˚ . These bond distances of 2.724 and 2.710 A distances represent the distance between the hydrogen of the hydroxyl unit and the adjacent oxygen of the arsenate group. Two hydrogen ˚ are deterbond distances of 2.804 and 2.711 A mined for kankite. For pharmacosiderite four hydroxyl Raman bands are observed. This results in four hydrogen bond distances of 2.893, 2.784, ˚ . The first hydrogen bond 2.772 and 2.685 A distance is long and represents weak hydrogen bonding whereas the hydrogen bond distances of ˚ may be considered as short and represents B/2.7 A strong hydrogen bonding. The width of the OH ˚ and is stretching bands varies from 96.3 to 614.3 A a measure of the variation of hydrogen bond distances in the structure. In contrast, the hydrogen bond distances for the two hydroxyl units for ˚ and the width clinotyrolite are 2.880 and 2.800 A of the two bands are 60.0 and 41.0 cm 1. The significance of these narrow bands means that the variation in the hydrogen bond distance is small. The variation for the two bands is estimated as 9/ ˚ , respectively. The hydrogen 0.068 and 9/0.015 A
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Table 1 Raman spectroscopic analysis of some complex arsenate minerals Kankite (Fe3 )2(AsO4) ×/ 3H2O
Pharmacosiderite K(Fe3 )4(AsO4)3(OH)4 ×/6 / 7H2O
Clinotyrolite Ca2Cu9[(As,S)O4](O,OH)10 ×/ 10H2O
Picropharmacolite H2Ca4Mg(AsO4)4 ×/ 11H2O
Talmessite Ca2Mg(AsO4) ×/ 2H2O
3254 3217
3408 3221 3112
3498 3378 3358 3138
3489 3403
3448 3212 2922?
2882 2376
1629 1469 1065 849 835 822 738 543 497 467
881 832 808 790 733 564 492
1061 1012 880 862 810 789
475
350 324
398 373 290
395 302 275
259 210
240 228 198 179
262 238 195 166
1136 1007 883 841 802
980 866 750
931 905 877 836 814 783
669 618 505 493 462 414 385 359 314
530 460
455 445
397 325 230
388 363 357 305 276 212 196 173
260 210 179
Tilasite CaMg(AsO4)F
1518 1318 1107 1056 820
659 611 493 410
297 245
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Carminite Pb(Fe3 )2(AsO4)2(OH)2
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Table 2 Correlation between hydroxyl stretching frequencies and estimated hydrogen bond distances Mineral
Suggested hydrogen bond origin
Carminite
OH1 OH2 Kankite H2O 1 H2O 2 Pharmacosiderite OH1 OH2 H2O 1 H2O 2 Clinotyrolite OH1 OH2 Picropharmacolite H2O 1 H2O 2 Talmessite H2O 1 H2O 2
Observed Raman band posi- Estimated hydrogen bond ˚) tions (cm1) distance (A
Observed Raman band width (cm1)
3254 3217 3408 3221 3498 3378 3358 3138 3489 3403 3448 3212 3250 2882
277.0 288.0 207.0 104.0 147.4 96.3 358.8 614.3 60.0 41.0 218.6 350.7 105.0 307.0
bond distances for picropharmacolite are esti˚ and for talmessite mated at 2.836 and 2.708 A ˚ 2.722 and 2.625 A. The mineral tilasite does not contain any hydroxyl groups but does contain fluorine. Fluorine (AW /17) can function like a hydroxyl group and may replace the OH units in structures. 3.2. Vibrations of the AsO4 unit The Raman spectra of the AsO4 stretching region are shown in Fig. 2. Perhaps apart from tilasite, the spectra show complexity with multiple bands observed in this 750/950 cm 1 region. The free arsenate ion has tetrahedral symmetry and thus should have four bands of which two are infrared active with theoretical values of n3 (F2) 887 cm1 and n4 (F2) 463 cm 1. The Raman active modes are observed at 837 (A1) and 349 (E) cm 1. Upon coordination of the arsenate ion to the copper atom, the symmetry of the arsenate ion reduces to C3v and may further reduce to Cs . The implication is that all bands will be both infrared and Raman active. For carminite, bands are observed in the AsO stretching region at 849, 835, 822 and 738 cm 1. The first band is the most intense and is assigned
2.724 2.710 2.804 2.711 2.893 2.784 2.772 2.685 2.880 2.800 2.836 2.708 2.722 2.625
to the n1 symmetric stretching mode. The next two bands are assigned to the n3 antisymmetric stretching modes. The band at 738 cm 1 may be attributed to the hydroxyl deformation mode. For the mineral kankite broad bands are observed at 883 {n3 (F2)}, 832 {n1 (A1)} and 808 cm 1. Component bands are also observed at 790 and 733 cm 1. The latter two bands may be assigned to hydroxyl deformation modes. The Raman spectrum of pharmacosiderite shows two intense bands at 880 and 862 cm 1, attributed to the {n3 (F2)} and 832 {n1 (A1)} vibrational modes. The band at 789 cm 1 may be assigned to the OH deformation vibration. For clinotyrolite, AsO4 stretching bands are observed at 841 and 802 cm 1. For picropharmacolite, only broad bands are observed centred upon 866 and 750 cm 1. Talmessite shows well defined Raman bands at 877 and 836 cm1 whereas tilasite displays only a broad band at 820 cm 1. The Raman spectra of the minerals under discussion of the low wavenumber region are shown in Fig. 3. The widths of many of the bands observed in the AsO stretching region are also observed in the low wavenumber region. The bands in the 400 /500 cm1 region are assignable to the bending n4 (F2) mode. The most intense
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band is observed at 497 cm 1 with other bands at 543 and 467 cm 1. The observation of multiple bands is characteristic of reduced symmetry of the AsO4 unit in the crystal. The Raman spectra of kankite in this region shows an intense band at 492 cm 1 and similarly pharmacosiderite shows an intense band at 475 cm 1. For clinotyrolite, an intense band is observed at 493 cm 1 with shoulders at 462 and 505 cm 1. The Raman spectrum of picropharmacolite seems ill-defined in this region. In contrast, the two minerals tilasite and talmessite have well defined spectra. Talmessite shows two bands at 455 and 445 cm 1. Tilasite shows a sharp band at 410 cm 1 with a low intensity band at 493 cm 1. The n2 bending mode is normally found at around 349 cm1. The Fe bearing arsenates of
Fig. 3. Raman spectra of the low wavenumber region of: (a) carminite, (b) kankite, (c) pharmacosiderite, (d) clinotyrolite, (e) picropharmacolite, (f) talmessite, (g) tilasite.
Fig. 2. Raman spectra of the AsO4 stretching region of: (a) carminite, (b) kankite, (c) pharmacosiderite, (d) clinotyrolite, (e) picropharmacolite, (f) talmessite, (g) tilasite.
carminite, kankite and pharmacosiderite display a complex set of bands. For carminite bands are observed at 324 and 350 cm 1 and are assigned to the n2 in-plane bending mode. Strong bands are observed at 210 and 259 cm 1 and one possibility for their designation is FeO stretching vibrations. The n2 bands for kankite are observed at 398 and 373 cm 1 and for pharmacosiderite at 395 and 302 cm 1. These later bands are of comparatively low intensity. For the mineral clinotyrolite, bands in this region are observed at 385, 359 and 314 cm 1. The bands for picropharmacolite are ill defined. For talmessite, strong bands are observed at 363 and 357 cm 1. Strong bands are also observed at 305 and 276 cm 1. One possibility for their
R.L. Frost, J.T. Kloprogge / Spectrochimica Acta Part A 59 (2003) 2797 /2804
assignation is to CaO and MgO stretching vibrations. The Raman spectrum of tilasite appears different and strong bands are observed at 297 and 245 cm 1. The position of both of these bands appears too low for the assignment to the n2 bending vibration.
4. Conclusions The application of Raman spectroscopy to the study of selected Fe and Ca bearing mineral phases of arsenate has shown that the minerals can be identified by their Raman spectra. Selected secondary minerals of Ferric iron and calcium were analysed. The implication is that a Raman spectrum of a contaminated soil may be used in attempt to identify mineral components in that soil. Such identification may then lead to recommendations for the removal of such contamination [43,44].
Acknowledgements The infra-structure support of the Queensland University of Technology School of Physical and Chemical Sciences is gratefully acknowledged. Professor Allan Pring of the South Australian Museum is thanked for the loan of the arsenate minerals.
References [1] H. Akhter, F.K. Cartledge, J. Miller, M. Mclearn, J. Environ. Eng. (Reston, VA) 126 (2000) 999. [2] D.K. Bhumbla, R.F. Keefer, Adv. Environ. Sci. Technol. 26 (1994) 51. [3] G. Bombach, A. Pierra, W. Klemm, Fresenius’ J. Anal. Chem. 350 (1994) 49. [4] V. Dutre, C. Kestens, J. Schaep, C. Vandecasteele, Sci. Total Environ. 220 (1998) 185. [5] K.H. Karstensen, O. Ringstad, I. Rustad, K. Kalevi, K. Jorgensen, K. Nylund, T. Alsberg, K. Olafsdottir, O. Heidenstam, H. Solberg, Talanta 46 (1998) 423. [6] M. Pantsar-Kallio, P.K.G. Manninen, Sci. Total Environ. 204 (1997) 193.
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[7] W.W. Wenzel, A. Brandstetter, H. Wutte, E. Lombi, T. Prohaska, G. Stingeder, D.C. Adriano, J. Plant Nutr. Soil Sci. 165 (2002) 221. [8] P.S. Yarlagadda, M.R. Matsumoto, J.E. Vanbenschoten, A. Kathuria, J. Environ. Eng. (New York) 121 (1995) 276. [9] P.W. Abrahams, I. Thornton, Agric. Ecosyst. Environ. 48 (1994) 125. [10] E.H. Amonoo-Neizer, D. Nyamah, S.B. Bakiamoh, Water Air Soil Pollut. 91 (1996) 363. [11] P.M. Ashley, B.G. Lottermoser, Aust. J. Earth Sci. 46 (1999) 861. [12] J. Bech, C. Poschenrieder, M. Llugany, J. Barcelo, P. Tume, F.J. Tobias, J.L. Barranzuela, E.R. Vasquez, Sci. Total Environ. 203 (1997) 83. [13] M. Chen, L.Q. Ma, C.G. Hoogeweg, W.G. Harris, Environ. Forensics 2 (2001) 117. [14] A. Brandstetter, E. Lombi, W.W. Wenzel, D.C. Adriano, Environ. Sci. Pollut. Control Ser. 23 (2000) 715. [15] J. Christova, C. Stanchev, K. Rekalov, Dokl. Bulg. Akad. Nauk. 46 (1993) 81. [16] Beletskaya, Bilger, Boronin, Bunnett, Costantino, Cullen, Dominas, Goessler, Haiduc, Maeda, Martens, NATO ASI Series, Series 1: Disarmament Technologies, vol. 19, 1998, pp. 177. [17] F. Juillot, P. Ildefonse, G. Morin, G. Calas, A.M.D. Kersabiec, M. Benedetti, Appl. Geochem. 14 (1999) 1031. [18] M.B. Mcbride, C.E. Martinez, Environ. Sci. Technol. 34 (2000) 4386. [19] H. Helgesen, E.H. Larsen, Analyst (Cambridge, UK) 123 (1998) 791. [20] J. Rajander, L. Harju, J.O. Lill, K.E. Saarela, A. Lindroos, S.J. Heselius, Nucl. Instrum. Methods Phys. Res. Sect. B: Beam Interact. Mater. Atoms. 150 (1999) 510. [21] D.E. Stilwell, K.D. Gorny, Bull. Environ. Contam. Toxicol. 58 (1997) 22. [22] M.F. Azizian, K. Osathaphan, P.O. Nelson, Preprints of Extended Abstracts presented at the ACS National Meeting, American Chemical Society, Division of Environmental Chemistry, vol. 40, 2000, pp. 16. [23] Q. Zhou, Z. Gao, J. Environ. Sci. (China) 6 (1994) 330. [24] R.G. Mclaren, R. Naidu, J. Smith, K.G. Tiller, J. Environ. Qual. 27 (1998) 348. [25] F.J. Peryea, R. Kammereck, Water Air Soil Pollut. 93 (1997) 243. [26] J.J. Finney, 1962. [27] J.J. Finney, Am. Mineral. 48 (1963) 1. [28] Kharisun, M.R. Taylor, D.J.M. Bevan, A.D. Rae, A. Pring, Mineral. Mag. 61 (1997) 685. [29] Kharisun, M.R. Taylor, D.J.M. Bevan, A. Pring, Mineral. Mag. 60 (1996) 805. [30] F. Cech, J. Jansa, F. Novak, Neues Jahrb. Mineral. Monatsh. (1976) 426. [31] J. Zemann, Experientia 3 (1947) 452. [32] C. Rewitzer, R. Hochleitner, Rivista Mineral. Ital. (1989) 83. [33] M. Catti, G. Ferraris, G. Ivaldi, Bull. Soc. Fr. Mineral Cristallogr. 100 (1977) 230.
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R.L. Frost, J.T. Kloprogge / Spectrochimica Acta Part A 59 (2003) 2797 /2804
[34] R. Brasse, P. Mattrat, H. Guerin, Bull. Soc. Chim. Fr. (1968) 2686. [35] I.V. Pekov, R.A. Vinogradova, N.V. Chukanov, I.M. Kulikova, Zapiski Vserossiiskogo Mineralogicheskogo Obshchestva 130 (2001) 10. [36] V. Bermanec, Neues Jahrbuch fuer Mineralogie, Monatshefte (1994) 289. [37] J. Emsley, Chem. Soc. Rev. 9 (1980) 91. [38] H. Lutz, Struct. Bonding (Berlin, Germany) 82 (1995) 85.
[39] [40] [41] [42]
W. Mikenda, J. Mol. Struct. 147 (1986) 1. A. Novak, Struct. Bonding (Berlin) 18 (1974) 177. E. Libowitsky, Monatschefte Chem. 130 (1999) 1047. J. Miller, H. Akhter, F.K. Cartledge, M. Mclearn, J. Environ. Eng. (Reston, VA) 126 (2000) 1004. [43] E. Lombi, W.W. Wenzel, D.C. Adriano, Environ. Sci. Pollut. Control Ser. 23 (2000) 739. [44] N. Papassiopi, S. Tambouris, A. Kontopoulos, Water Air Soil Pollut. 109 (1999) 1.