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Chapter 48 Scandium
Chapter48
Scandium
Scandium (Sc, atomic weight 44.96, melting point 1539°C, d = 3.0 g cm - 3 ) is a soft, silvery-white metal. It occurs in the earth's crust with an average abundance of 25 ppm, usually accompanying uranium ores. The metal reacts readily with water. In aqueous solution, it occurs exclusively in the III oxidation state, primarily as Sc3+ which tends to hydrolyze and to form polymeric species. The hydroxide, Sc(OH)3 , precipitates at pH above 4.8 is amphoteric and dissolves in excess alkali to give the tetrahydroxoscandate anion, Sc(OH) 4 . Scandium forms stable fluoride (ScF6-), sulphate, thiocyanate, ascorbate and oxalate complexes. In some chemical properties, Sc resembles the lanthanides and in others aluminium. 48.1 SEPARATION AND PRECONCENTRATION Extraction
Extraction of Sc as the thiocyanate complex into diethyl ether allows its separation from the REEs. This can also be achieved by extracting Sc and REEs with TOPO and stripping the REEs into the aqueous phase [1]. Scandium can also be extracted as the ascorbato complex with Aliquat 336S [2]. Several extraction reagents (solvents) proposed included 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one (benzene) [3], methyltrioctylammonium chloride (xylene) [4], crown ethers (CH 2Cl 2) [5], acetylacetone [6]. Substoichiometric extraction of Sc with Alizarine into octanol has been proposed [7]. Ion exchange
The anionic Sc sulphate complex is retained by anion exchangers and passes through cation exchangers. Matrix effects in the separation of Sc 645
by cation exchange have been discussed [8]. Scandium can be separated from REEs by ion interaction chromatography of nitriloacetato complexes in the presence of 1-octanesulphonate [9]. 48.2 DETERMINATION TECHNIQUES Spectrophotometry andfluorometry
The colour reaction of Sc with Xylenol Orange in a slightly acidic medium is the basis of the most popular spectrophotometric method (e = 2.9x10 4 at 565 nm). Many anions and cations interfere. Triphenylmethane dyes, e.g. Chrome Azurol S or Eriochromocyanine R in the presence of surfactants, e.g. Zephiramine or cetylpyridinium, offer very high sensitivities (- lx 105) and are selective vs Y and the lanthanides. Fluorometric methods allow DLs down to 0.2 ng ml-1 to be reached and have been reviewed [10]. The example reagents include quinizarine [11] and 1,2,7-trihydroxyanthraquinone [4]. Atomic absorptionspectrometry
Flame AAS offers a sensitivity of 0.3 g ml-l in the recommended N 20-C2 H2 , reducing (rich, red) flame at the most sensitive 391.2 nm line. Ionization should be controlled by the addition of 0.1% or more of KC1. The Sc signal is reduced in the presence of sulphate and fluoride so matrix matching is necessary. Graphite furnace AAS fails for Sc albeit it was reported for its determination as part of a multielement analysis scheme [12]. Electrothermal atomization of Sc from graphite and tantalum surfaces has been discussed [13]. Atomic emission spectrometry
Scandium was determined by flame (N0-C 2 2H 2) AES with a high resolution monochromator with a DL of 10-15 ng ml-1 141. Inductively coupled plasma AES offers DLs down to 1 ng ml-l at the most sensitive 361.38 and 357.25 nm lines. Spectral interferences in the determination of Sc in pure Ce, Nd and La matrices have been discussed [15]. Application of a wall-stabilized plasma arc AES has been reported [16]. Neutron activation analysis
Neutron activation analysis is based on the reaction 4 5Sc(n,y)4 6Sc and
counting the 4 6Sc (tl2 = 85 d, E
=
0.89 and 1.12 MeV) [17,18]. A chemical
separation is required in the presence of long-lived radionuclides (e.g. 59 Fe, 60Co, IlOmAg). A DL down to 0.04 ng was reported [18]. 646
Mass spectrometry
Scandium is monoisotopic (45Sc). The determination by ICP MS is hampered by the interference with CO 2 H [19]. TABLE 48.1 Methods for the determination of scandium Sample (amount)
Decomposition
Separation and/or preconcentration
Determin. technique
DL (pg/g)
Ref.
Mineral water none
cation exchange
ICP AES
0.0005
20
Fly ash
evaporn. with HF, dissoln. in HCI or HNO 3 -H2 02
extrn. with methyltrioctylammonium chloride (xylene)
GF AAS
100a
21
Fly ash, geoCRMs (0.25 g)
HNO3 -HC104-HF (bomb)
none
GF AAS
0.8
22
Fly ash, geoCRMs (0.25 g)
fusion with LiB40 7 , dissoln. in HNO 3
none
ICP AES
0.6
22
GeoCRMs (0.2 g)
fusion with K2 CO3 K2 B4 07
none
ICP MS
0.1
23
GeoCRMs (0.1 g)
n.g.
cation exchange
GFAAS
<0.001
12
GeoCRMs (0.3 g)
HF-HC04-HNO 3, the residue fused with Li2B4 07
none
ICP AES
<1
8
Geo??
HNO3 -HF
extrn. with Alizarine NAA (octanol)
10 b
7
Rocks (0.1 g)
HF-H 2SO4 or fusion none with LiBO 2
FLU
2a
4
W-ores (0.5 g)
fusion with Na 2 02 , dissoln. with HCI
VIS
n.g.
3
Milk, body fluids, soil
dry ashing
INAA
0.0001
18
a
extrn. with 1phenyl-3-methyl-4benzoyl-pyrazol-5one (benzene)
In the solution fed, ng/ml; b absolute detection limit, ng. 647
48.3 ANALYSIS OF REAL SAMPLES The virtual lack of the need of trace determination of Sc is responsible for the scarcity of methods in the literature developed with the objective of solving a real analytical problem. Applications, summarized in Table 48.1, refer primarily to geochemical materials. Scandium is often determined in the multielement array by ICP AES (cf. Part II).
REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
648
D. Weiss, T. Paukert and I. Rubeska, J. Anal. At. Spectrom., 5 (1990) 371. M.A. Karve and S.M. Khopkar, Bull. Chem. Soc. Jpn., 64 (1991) 655. Z.M. Luo and W.M. He, Talanta, 37 (1990) 641. F. Garcia-Sanchez, C. Cruces Blanco and A. Heredia Bayona, Talanta, 34 (1987) 345. N.V. Deorkar and S.M. Khopkar, Bull. Chem. Soc. Jpn., 64 (1991) 1962. S. Katsuta, H. Imura and N. Suzuki, Anal. Sci., 7 (1991) 661. S.D. Jadhav and Z.R. Turel, J. Radioanal.Nucl. Chem., 176 (1993) 443. D.W. Zachman, Anal. Chem., 60 (1988) 420. R. Kuroda, T. Wada, Y. Kokubo and K. Oguma, Talanta, 40 (1993) 237. M.E. Urefia Pozo, A. Garcia de Torres, J.M. Cano Pav6n and F. Sanchez Rojas, Analyst, 116 (1991) 757. F. Garcia-Sdnchez, M. Hernandez Lopez and J.C. Marquez G6mez, Analyst, 112 (1987) 1037. J.G. Sen Gupta, J. Anal. At. Spectrom., 8 (1993) 93. J.G. Sen Gupta, Talanta, 34 (1988) 1043. V. Otruba and L. Sommer, FreseniusZ. Anal. Chem., 335 (1989) 887. N. Daskalova, S. Velickov, N. Krasnobaeva and P. Slavova, Spectrochim. Acta, 14 (1992) E1595. I.M. Kenawy and M.A.H. Hafez, Anal. Sci., 5 (1989) 55. M.Z. Iqbal and M.A. Quadir, J. Radiochem. Nucl. Chem., 145 (1990) 189. D.H. Oughton and J.P. Day, J. Radioanal. Nucl. Chem., 174 (1993) 177. C. Vancasteele, H. Vanhoe and R. Dams, J. Anal. At. Spectrom., 8 (1993) 781. J. Kubova, V. Nevoral and V. StreAko, J. Anal. At. Spectrom., 9 (1994) 241. T. Suzuki, H. Nakagawa and K. Sawada, Anal. Sci., 2 (1986) 309. M. Bettinelli, U. Baroni and N. Pastorelli, Analyst, 112 (1987) 23. A. Rivoldini and S. Fadda, J. Anal. At. Spectrom., 9 (1994) 519.
Scandium
Scandium (Sc, atomic weight 44.96, melting point 1539°C, d = 3.0 g cm - 3 ) is a soft, silvery-white metal. It occurs in the earth's crust with an average abundance of 25 ppm, usually accompanying uranium ores. The metal reacts readily with water. In aqueous solution, it occurs exclusively in the III oxidation state, primarily as Sc3+ which tends to hydrolyze and to form polymeric species. The hydroxide, Sc(OH)3 , precipitates at pH above 4.8 is amphoteric and dissolves in excess alkali to give the tetrahydroxoscandate anion, Sc(OH) 4 . Scandium forms stable fluoride (ScF6-), sulphate, thiocyanate, ascorbate and oxalate complexes. In some chemical properties, Sc resembles the lanthanides and in others aluminium. 48.1 SEPARATION AND PRECONCENTRATION Extraction
Extraction of Sc as the thiocyanate complex into diethyl ether allows its separation from the REEs. This can also be achieved by extracting Sc and REEs with TOPO and stripping the REEs into the aqueous phase [1]. Scandium can also be extracted as the ascorbato complex with Aliquat 336S [2]. Several extraction reagents (solvents) proposed included 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one (benzene) [3], methyltrioctylammonium chloride (xylene) [4], crown ethers (CH 2Cl 2) [5], acetylacetone [6]. Substoichiometric extraction of Sc with Alizarine into octanol has been proposed [7]. Ion exchange
The anionic Sc sulphate complex is retained by anion exchangers and passes through cation exchangers. Matrix effects in the separation of Sc 645
by cation exchange have been discussed [8]. Scandium can be separated from REEs by ion interaction chromatography of nitriloacetato complexes in the presence of 1-octanesulphonate [9]. 48.2 DETERMINATION TECHNIQUES Spectrophotometry andfluorometry
The colour reaction of Sc with Xylenol Orange in a slightly acidic medium is the basis of the most popular spectrophotometric method (e = 2.9x10 4 at 565 nm). Many anions and cations interfere. Triphenylmethane dyes, e.g. Chrome Azurol S or Eriochromocyanine R in the presence of surfactants, e.g. Zephiramine or cetylpyridinium, offer very high sensitivities (- lx 105) and are selective vs Y and the lanthanides. Fluorometric methods allow DLs down to 0.2 ng ml-1 to be reached and have been reviewed [10]. The example reagents include quinizarine [11] and 1,2,7-trihydroxyanthraquinone [4]. Atomic absorptionspectrometry
Flame AAS offers a sensitivity of 0.3 g ml-l in the recommended N 20-C2 H2 , reducing (rich, red) flame at the most sensitive 391.2 nm line. Ionization should be controlled by the addition of 0.1% or more of KC1. The Sc signal is reduced in the presence of sulphate and fluoride so matrix matching is necessary. Graphite furnace AAS fails for Sc albeit it was reported for its determination as part of a multielement analysis scheme [12]. Electrothermal atomization of Sc from graphite and tantalum surfaces has been discussed [13]. Atomic emission spectrometry
Scandium was determined by flame (N0-C 2 2H 2) AES with a high resolution monochromator with a DL of 10-15 ng ml-1 141. Inductively coupled plasma AES offers DLs down to 1 ng ml-l at the most sensitive 361.38 and 357.25 nm lines. Spectral interferences in the determination of Sc in pure Ce, Nd and La matrices have been discussed [15]. Application of a wall-stabilized plasma arc AES has been reported [16]. Neutron activation analysis
Neutron activation analysis is based on the reaction 4 5Sc(n,y)4 6Sc and
counting the 4 6Sc (tl2 = 85 d, E
=
0.89 and 1.12 MeV) [17,18]. A chemical
separation is required in the presence of long-lived radionuclides (e.g. 59 Fe, 60Co, IlOmAg). A DL down to 0.04 ng was reported [18]. 646
Mass spectrometry
Scandium is monoisotopic (45Sc). The determination by ICP MS is hampered by the interference with CO 2 H [19]. TABLE 48.1 Methods for the determination of scandium Sample (amount)
Decomposition
Separation and/or preconcentration
Determin. technique
DL (pg/g)
Ref.
Mineral water none
cation exchange
ICP AES
0.0005
20
Fly ash
evaporn. with HF, dissoln. in HCI or HNO 3 -H2 02
extrn. with methyltrioctylammonium chloride (xylene)
GF AAS
100a
21
Fly ash, geoCRMs (0.25 g)
HNO3 -HC104-HF (bomb)
none
GF AAS
0.8
22
Fly ash, geoCRMs (0.25 g)
fusion with LiB40 7 , dissoln. in HNO 3
none
ICP AES
0.6
22
GeoCRMs (0.2 g)
fusion with K2 CO3 K2 B4 07
none
ICP MS
0.1
23
GeoCRMs (0.1 g)
n.g.
cation exchange
GFAAS
<0.001
12
GeoCRMs (0.3 g)
HF-HC04-HNO 3, the residue fused with Li2B4 07
none
ICP AES
<1
8
Geo??
HNO3 -HF
extrn. with Alizarine NAA (octanol)
10 b
7
Rocks (0.1 g)
HF-H 2SO4 or fusion none with LiBO 2
FLU
2a
4
W-ores (0.5 g)
fusion with Na 2 02 , dissoln. with HCI
VIS
n.g.
3
Milk, body fluids, soil
dry ashing
INAA
0.0001
18
a
extrn. with 1phenyl-3-methyl-4benzoyl-pyrazol-5one (benzene)
In the solution fed, ng/ml; b absolute detection limit, ng. 647
48.3 ANALYSIS OF REAL SAMPLES The virtual lack of the need of trace determination of Sc is responsible for the scarcity of methods in the literature developed with the objective of solving a real analytical problem. Applications, summarized in Table 48.1, refer primarily to geochemical materials. Scandium is often determined in the multielement array by ICP AES (cf. Part II).
REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
648
D. Weiss, T. Paukert and I. Rubeska, J. Anal. At. Spectrom., 5 (1990) 371. M.A. Karve and S.M. Khopkar, Bull. Chem. Soc. Jpn., 64 (1991) 655. Z.M. Luo and W.M. He, Talanta, 37 (1990) 641. F. Garcia-Sanchez, C. Cruces Blanco and A. Heredia Bayona, Talanta, 34 (1987) 345. N.V. Deorkar and S.M. Khopkar, Bull. Chem. Soc. Jpn., 64 (1991) 1962. S. Katsuta, H. Imura and N. Suzuki, Anal. Sci., 7 (1991) 661. S.D. Jadhav and Z.R. Turel, J. Radioanal.Nucl. Chem., 176 (1993) 443. D.W. Zachman, Anal. Chem., 60 (1988) 420. R. Kuroda, T. Wada, Y. Kokubo and K. Oguma, Talanta, 40 (1993) 237. M.E. Urefia Pozo, A. Garcia de Torres, J.M. Cano Pav6n and F. Sanchez Rojas, Analyst, 116 (1991) 757. F. Garcia-Sdnchez, M. Hernandez Lopez and J.C. Marquez G6mez, Analyst, 112 (1987) 1037. J.G. Sen Gupta, J. Anal. At. Spectrom., 8 (1993) 93. J.G. Sen Gupta, Talanta, 34 (1988) 1043. V. Otruba and L. Sommer, FreseniusZ. Anal. Chem., 335 (1989) 887. N. Daskalova, S. Velickov, N. Krasnobaeva and P. Slavova, Spectrochim. Acta, 14 (1992) E1595. I.M. Kenawy and M.A.H. Hafez, Anal. Sci., 5 (1989) 55. M.Z. Iqbal and M.A. Quadir, J. Radiochem. Nucl. Chem., 145 (1990) 189. D.H. Oughton and J.P. Day, J. Radioanal. Nucl. Chem., 174 (1993) 177. C. Vancasteele, H. Vanhoe and R. Dams, J. Anal. At. Spectrom., 8 (1993) 781. J. Kubova, V. Nevoral and V. StreAko, J. Anal. At. Spectrom., 9 (1994) 241. T. Suzuki, H. Nakagawa and K. Sawada, Anal. Sci., 2 (1986) 309. M. Bettinelli, U. Baroni and N. Pastorelli, Analyst, 112 (1987) 23. A. Rivoldini and S. Fadda, J. Anal. At. Spectrom., 9 (1994) 519.