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Analysis of some Nigerian solid mineral ores by energy-dispersive X-ray fluorescence spectroscopy
Nuclear Instruments and Methods in Physics Research B 184 (2001) 437±440
www.elsevier.com/locate/nimb
Analysis of some Nigerian solid mineral ores by energy-dispersive X-ray ¯uorescence spectroscopy E.I. Obiajunwa
*
Centre for Energy Research and Development (CERD), Obafemi Awolowo University, Ile-Ife, Nigeria Received 19 April 2001; received in revised form 25 June 2001
Abstract Determination of major, minor and trace elements in some Nigerian solid mineral ores by energy-dispersive X-ray ¯uorescence (EDXRF) spectroscopy is described. Concentration values of major, minor and trace elements for Z > 18 are reported. The mineral ores studied include (i) tantalite±coloumbite minerals, (ii) bismuth minerals and (iii) lead minerals. The accuracy and precision of the technique for chemical analysis was assured by analysing the geological standards mica±Fe (biotite) and NBS 278 (obsidian). Ó 2001 Published by Elsevier Science B.V.
1. Introduction Accurate and precise determination of major, minor and trace elements in mineral ores is very important in their geochemical studies [1]. Elemental composition of mineral ores is equally of great importance in the classi®cation/grading of the ores. Qualitative and quantitative data on ore samples are also of great interest to mineral prospectors and investors. With a renewed interest in solid minerals prospecting in Nigeria, prospectors and investors in solid minerals want to be sure of the quality/grade of the ores they are dealing with. There is therefore a need for a fast, reliable, nondestructive multi-elemental analytical technique for the analysis of the solid mineral samples. The
energy-dispersive X-ray ¯uorescence (EDXRF) technique is one such technique as it oers fast, non-destructive and reliable analysis for a wide variety of materials [2±4]. The solid samples generally need little preparation; they only should be presented to the spectrometer in a homogeneous and reproducible form. In the present work, we have employed the EDXRF technique in the analysis of solid mineral ores from dierent minerals prospecting sites mainly from the South-West and North Central regions of Nigeria.
2. Experimental 2.1. Sample preparation
*
Tel.: +234-36-233638; fax: +234-36-232975. E-mail address: [email protected] (E.I. Obiajunwa).
All samples were sun-dried and then ground into ®ne powder in an agate mortar. They were
0168-583X/01/$ - see front matter Ó 2001 Published by Elsevier Science B.V. PII: S 0 1 6 8 - 5 8 3 X ( 0 1 ) 0 0 7 6 6 - 2
438
E.I. Obiajunwa / Nucl. Instr. and Meth. in Phys. Res. B 184 (2001) 437±440
then pressed into thick pellets of 13 mm diameter in Spec-Caps [5] without binders. The National Institute of Standards and Technology (NIST) geological standards ± mica±Fe and NBS 278 were equally pressed into pellets in a similar manner as the samples, and these were used for quality assurance. 2.2. Analysis The elemental analysis of the samples/standards was performed using an EDXRF spectrometer. The spectrometer consists of a Siemens FKO-04 tube with Mo anode a Kristallo¯ex 710H X-ray Generator, a Canberra series 7300 Si(Li) detector (resolution of 165 eV at 5.9 keV), with Canberra Model 1510 integrated signal processor, and a Canberra S 100 MCA card interfaced to a 486 IBM/PC. The equipment runs under quantitative X-ray analysis system (QXAS) [6], which includes facilities for data acquisition, spectrum analysis and interpretation and quantitative analysis. Each sample/standard pellet was irradiated for 20 min at ®xed tube operating conditions of 30 kV and 5 mA. The standard was run just before and immediately after running the samples. The un®ltered MoKa;b excitation allows determination of elements with characteristic K- or L-lines in the energy range 3.3±16 keV. A parameterless smooth-®lter
model in the AXIL program of the QXAS package was used for ®tting the spectra over the energy region of interest.
3. Results and discussion The results of EDXRF analysis for the tantalite, bismuth and lead ores are presented in Tables 1±3, respectively. All data are the results of average of two measurements on each sample with a relative standard deviation of less than 10%. In the tantalite ores, Table 1, 10 elements (K, Ca, Ti, V, Mn, Fe, Se, Zr, Nb and Ta) were detected. Concentration ranges of Ta and Nb (the major elements) in the samples are (6.94±10.55%) and (8.34±15.21%), respectively. It is known that tantalite±columbite or tantalite±niobium ores are oxides of tantalum±niobium, iron and manganese (Fe,Mn)(Ta,Nb)O6 [7]. In the bismuth ores, Table 2, 11 elements (Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb and Bi) were detected. Zn was detected in only one sample, BI-4, and Cr was also detected only in sample BI-1. Vanadium was detected in two samples, BI-1 and BI-3. Concentration ranges of the major elements in the samples, Bi and Pb, were (35.10±47.9%) and (0.77±5.45%), respectively. We note that lead was not detected in one of the samples, BI-4.
Table 1 EDXRF results for the tantalite oresa Element
T-C1
T-C2
T-C3
T-C4
K Ca Ti V Mn Fe Se Zr Nb Ta
1095:8 46:5 48:3 1:7 565:8 32:0 134:4 6:6 3176:5 112:3 444:7 12:6 2591:2 54:9 1:4 0:03% 8:3 0:23% 8:5 0:24%
1752:3 86:8 ND 1:3 0:08% 20:5 0:9 4055:2 114:6 1:9 0:06% 71:5 1:5 1:0 0:02% 15:2 0:33% 6:9 0:2%
32:5 1:6 313:1 13:3 6446:8 273:5 358:5 12:7 4585:4 129:7 1:9 0:04% 178:4 3:8 1:6 0:04% 12:3 0:26% 9:5 0:27%
ND 9:9 0:4 758:5 37:6 ND 9401:9 322:4 4408:0 124:7 ND ND 9:1 0:25% 10:6 0:3%
ND: not detected. a Concentrations of elements are given in lg/g except for those of major elements in %.
E.I. Obiajunwa / Nucl. Instr. and Meth. in Phys. Res. B 184 (2001) 437±440
439
Table 2 EDXRF results for the bismuth oresa Element
BI-1
BI-2
BI-3
BI-4
Ca Ti V Cr Mn Fe Ni Cu Zn Pb Bi
139:1 4:9 133:6 7:6 34:0 1:7 13:7 0:5 25:1 0:9 1209:6 34:2 210:3 7:4 434:9 18:5 ND 2:8 0:06% 35:1 0:7%
79:0 2:8 125:7 7:1 ND ND 46:6 1:7 122:6 3:5 258:1 9:1 597:7 25:4 201:4 5:7 0:77 0:01% 39:4 0:8%
73:6 2:6 119:6 6:8 ND ND ND 86:5 2:5 184:3 6:5 425:8 18:1 142:8 4:0 5:5 0:1% 47:9 1:0%
10:6 0:4 370:9 21:0 ND ND 15:5 0:6 1322:4 37:4 157:5 5:6 341:2 37:4 668:9 18:9 ND 36:1 0:7%
ND: not detected. a Concentrations of elements are given in lg/g except for those of major elements in %.
Table 3 EDXRF results for the lead oresa
Table 4 EDXRF results for mica±Fe (biotite) and NBS 278 (obsidian)
Element
PBO-1
PBO-2
PBO-3
Mn Fe Co Ni Cu Zn Sr Pb
1:3 0:05% 14:6 0:4% 1830 64:7 650 23:0 403 17:1 1:0 0:03% 132 2:8 46:7 1:0%
0:9 0:04% 11:4 0:3% 1386 49:0 560 19:8 100:0 4:2 3:1 0:08% 293 6:2 47:2 1:0%
1:1 0:04% 11:6 0:3% 21 0:7 220 7:8 ND 7:9 0:23% ND 35:6 0:8%
ND: not detected. a Concentrations of elements are given in lg/g except for those of major elements in %.
In the lead ores, Table 3, only eight elements (Mn, Fe, Co, Ni, Cu, Zn, Sr and Pb) were detected. The major elements in the ores were Pb (35.6±47.2%), Fe (11.4±14.6%), Zn (1.0±7.9%) and Mn (0.92±1.28%). The other elements occurred only in trace quantities (21±1830 ppm). The presence of zinc in association with lead ores is known to cause diculties in smelting, hence mechanical separation techniques such as ¯otation-processes should be used in the extraction of the lead [7]. The accuracy of the experimental values was assured by the analyses of the geological standards ± mica±Fe (biotite) and NBS 278 (obsidian). The results of these analyses, Table 4, are in good agreement with the certi®ed values [8].
Mica±Fe (biotite)
NBS 278 (obsidian)
Element Certi®ed value*
Analysed value
Certi®ed value*
Analysed value
K Ca Ti Mn Fe Zn Rb Sr Zr Pb
7.263% 3073 1.499% 2711 17.94% 1300 2200
7.22% 3839 1.97% 2905 16.8% 960 2220
800
793
2.763% 5620 1170 322.2 1.141% 44 102 50.8 232 13.13
2.73% 5774 1154 258 1.14% 51 101 56 290 14
Concentrations of elements are give in lg/g except for those of major elements in %.
4. Conclusion The EDXRF technique was employed in the analysis of some Nigerian solid mineral ores. The concentrations of the major, minor and trace elements in the dierent ores were determined. The technique has proved to be quite adequate for the analysis of solid minerals. The EDXRF technique is fast, reliable and non-destructive and can be used on a routine basis.
440
E.I. Obiajunwa / Nucl. Instr. and Meth. in Phys. Res. B 184 (2001) 437±440
References [1] T. Ossaka, K. Kekagawa, T. Oi, M. Mukaida, J. Radioanal. Nucl. Chem. 183 (1994) 235. [2] J.I. Nwachukwu, E.I. Obiajunwa, I.B. Obioh, in: A.K. Garg, V. Banerjie, S.N. Swamy, P. Dwivedi (Eds.), Petroleum Geochemistry and Exploration in the Afro-Asian Region, BRPC, New Delhi, India, 2000, pp. 139±145. [3] A. Johnson, G.C. Lalor, H. Robotham, M.K. Vutchkor, J. Radioanal. Nucl. Chem. 209 (1996) 101.
[4] V. Leenanupan, K. Srichom, J. Radioanal. Nucl. Chem. 207 (1996) 137. [5] R.H. Obenauf (Ed.), SPEX Handbook of Sample Preparation and Handling, 3rd ed., 1991, p. 95. [6] QXAS Users Manual, International Atomic Energy Agency (IAEA), Vienna, 1993. [7] H.H. Read, Rutley's Elements of Mineralogy, George Allen & Unwin, London, 1976, p. 456. [8] K. Govindaraju (Ed.), Geostandards Newsletter, Vol. 18, 1994.
www.elsevier.com/locate/nimb
Analysis of some Nigerian solid mineral ores by energy-dispersive X-ray ¯uorescence spectroscopy E.I. Obiajunwa
*
Centre for Energy Research and Development (CERD), Obafemi Awolowo University, Ile-Ife, Nigeria Received 19 April 2001; received in revised form 25 June 2001
Abstract Determination of major, minor and trace elements in some Nigerian solid mineral ores by energy-dispersive X-ray ¯uorescence (EDXRF) spectroscopy is described. Concentration values of major, minor and trace elements for Z > 18 are reported. The mineral ores studied include (i) tantalite±coloumbite minerals, (ii) bismuth minerals and (iii) lead minerals. The accuracy and precision of the technique for chemical analysis was assured by analysing the geological standards mica±Fe (biotite) and NBS 278 (obsidian). Ó 2001 Published by Elsevier Science B.V.
1. Introduction Accurate and precise determination of major, minor and trace elements in mineral ores is very important in their geochemical studies [1]. Elemental composition of mineral ores is equally of great importance in the classi®cation/grading of the ores. Qualitative and quantitative data on ore samples are also of great interest to mineral prospectors and investors. With a renewed interest in solid minerals prospecting in Nigeria, prospectors and investors in solid minerals want to be sure of the quality/grade of the ores they are dealing with. There is therefore a need for a fast, reliable, nondestructive multi-elemental analytical technique for the analysis of the solid mineral samples. The
energy-dispersive X-ray ¯uorescence (EDXRF) technique is one such technique as it oers fast, non-destructive and reliable analysis for a wide variety of materials [2±4]. The solid samples generally need little preparation; they only should be presented to the spectrometer in a homogeneous and reproducible form. In the present work, we have employed the EDXRF technique in the analysis of solid mineral ores from dierent minerals prospecting sites mainly from the South-West and North Central regions of Nigeria.
2. Experimental 2.1. Sample preparation
*
Tel.: +234-36-233638; fax: +234-36-232975. E-mail address: [email protected] (E.I. Obiajunwa).
All samples were sun-dried and then ground into ®ne powder in an agate mortar. They were
0168-583X/01/$ - see front matter Ó 2001 Published by Elsevier Science B.V. PII: S 0 1 6 8 - 5 8 3 X ( 0 1 ) 0 0 7 6 6 - 2
438
E.I. Obiajunwa / Nucl. Instr. and Meth. in Phys. Res. B 184 (2001) 437±440
then pressed into thick pellets of 13 mm diameter in Spec-Caps [5] without binders. The National Institute of Standards and Technology (NIST) geological standards ± mica±Fe and NBS 278 were equally pressed into pellets in a similar manner as the samples, and these were used for quality assurance. 2.2. Analysis The elemental analysis of the samples/standards was performed using an EDXRF spectrometer. The spectrometer consists of a Siemens FKO-04 tube with Mo anode a Kristallo¯ex 710H X-ray Generator, a Canberra series 7300 Si(Li) detector (resolution of 165 eV at 5.9 keV), with Canberra Model 1510 integrated signal processor, and a Canberra S 100 MCA card interfaced to a 486 IBM/PC. The equipment runs under quantitative X-ray analysis system (QXAS) [6], which includes facilities for data acquisition, spectrum analysis and interpretation and quantitative analysis. Each sample/standard pellet was irradiated for 20 min at ®xed tube operating conditions of 30 kV and 5 mA. The standard was run just before and immediately after running the samples. The un®ltered MoKa;b excitation allows determination of elements with characteristic K- or L-lines in the energy range 3.3±16 keV. A parameterless smooth-®lter
model in the AXIL program of the QXAS package was used for ®tting the spectra over the energy region of interest.
3. Results and discussion The results of EDXRF analysis for the tantalite, bismuth and lead ores are presented in Tables 1±3, respectively. All data are the results of average of two measurements on each sample with a relative standard deviation of less than 10%. In the tantalite ores, Table 1, 10 elements (K, Ca, Ti, V, Mn, Fe, Se, Zr, Nb and Ta) were detected. Concentration ranges of Ta and Nb (the major elements) in the samples are (6.94±10.55%) and (8.34±15.21%), respectively. It is known that tantalite±columbite or tantalite±niobium ores are oxides of tantalum±niobium, iron and manganese (Fe,Mn)(Ta,Nb)O6 [7]. In the bismuth ores, Table 2, 11 elements (Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Pb and Bi) were detected. Zn was detected in only one sample, BI-4, and Cr was also detected only in sample BI-1. Vanadium was detected in two samples, BI-1 and BI-3. Concentration ranges of the major elements in the samples, Bi and Pb, were (35.10±47.9%) and (0.77±5.45%), respectively. We note that lead was not detected in one of the samples, BI-4.
Table 1 EDXRF results for the tantalite oresa Element
T-C1
T-C2
T-C3
T-C4
K Ca Ti V Mn Fe Se Zr Nb Ta
1095:8 46:5 48:3 1:7 565:8 32:0 134:4 6:6 3176:5 112:3 444:7 12:6 2591:2 54:9 1:4 0:03% 8:3 0:23% 8:5 0:24%
1752:3 86:8 ND 1:3 0:08% 20:5 0:9 4055:2 114:6 1:9 0:06% 71:5 1:5 1:0 0:02% 15:2 0:33% 6:9 0:2%
32:5 1:6 313:1 13:3 6446:8 273:5 358:5 12:7 4585:4 129:7 1:9 0:04% 178:4 3:8 1:6 0:04% 12:3 0:26% 9:5 0:27%
ND 9:9 0:4 758:5 37:6 ND 9401:9 322:4 4408:0 124:7 ND ND 9:1 0:25% 10:6 0:3%
ND: not detected. a Concentrations of elements are given in lg/g except for those of major elements in %.
E.I. Obiajunwa / Nucl. Instr. and Meth. in Phys. Res. B 184 (2001) 437±440
439
Table 2 EDXRF results for the bismuth oresa Element
BI-1
BI-2
BI-3
BI-4
Ca Ti V Cr Mn Fe Ni Cu Zn Pb Bi
139:1 4:9 133:6 7:6 34:0 1:7 13:7 0:5 25:1 0:9 1209:6 34:2 210:3 7:4 434:9 18:5 ND 2:8 0:06% 35:1 0:7%
79:0 2:8 125:7 7:1 ND ND 46:6 1:7 122:6 3:5 258:1 9:1 597:7 25:4 201:4 5:7 0:77 0:01% 39:4 0:8%
73:6 2:6 119:6 6:8 ND ND ND 86:5 2:5 184:3 6:5 425:8 18:1 142:8 4:0 5:5 0:1% 47:9 1:0%
10:6 0:4 370:9 21:0 ND ND 15:5 0:6 1322:4 37:4 157:5 5:6 341:2 37:4 668:9 18:9 ND 36:1 0:7%
ND: not detected. a Concentrations of elements are given in lg/g except for those of major elements in %.
Table 3 EDXRF results for the lead oresa
Table 4 EDXRF results for mica±Fe (biotite) and NBS 278 (obsidian)
Element
PBO-1
PBO-2
PBO-3
Mn Fe Co Ni Cu Zn Sr Pb
1:3 0:05% 14:6 0:4% 1830 64:7 650 23:0 403 17:1 1:0 0:03% 132 2:8 46:7 1:0%
0:9 0:04% 11:4 0:3% 1386 49:0 560 19:8 100:0 4:2 3:1 0:08% 293 6:2 47:2 1:0%
1:1 0:04% 11:6 0:3% 21 0:7 220 7:8 ND 7:9 0:23% ND 35:6 0:8%
ND: not detected. a Concentrations of elements are given in lg/g except for those of major elements in %.
In the lead ores, Table 3, only eight elements (Mn, Fe, Co, Ni, Cu, Zn, Sr and Pb) were detected. The major elements in the ores were Pb (35.6±47.2%), Fe (11.4±14.6%), Zn (1.0±7.9%) and Mn (0.92±1.28%). The other elements occurred only in trace quantities (21±1830 ppm). The presence of zinc in association with lead ores is known to cause diculties in smelting, hence mechanical separation techniques such as ¯otation-processes should be used in the extraction of the lead [7]. The accuracy of the experimental values was assured by the analyses of the geological standards ± mica±Fe (biotite) and NBS 278 (obsidian). The results of these analyses, Table 4, are in good agreement with the certi®ed values [8].
Mica±Fe (biotite)
NBS 278 (obsidian)
Element Certi®ed value*
Analysed value
Certi®ed value*
Analysed value
K Ca Ti Mn Fe Zn Rb Sr Zr Pb
7.263% 3073 1.499% 2711 17.94% 1300 2200
7.22% 3839 1.97% 2905 16.8% 960 2220
800
793
2.763% 5620 1170 322.2 1.141% 44 102 50.8 232 13.13
2.73% 5774 1154 258 1.14% 51 101 56 290 14
Concentrations of elements are give in lg/g except for those of major elements in %.
4. Conclusion The EDXRF technique was employed in the analysis of some Nigerian solid mineral ores. The concentrations of the major, minor and trace elements in the dierent ores were determined. The technique has proved to be quite adequate for the analysis of solid minerals. The EDXRF technique is fast, reliable and non-destructive and can be used on a routine basis.
440
E.I. Obiajunwa / Nucl. Instr. and Meth. in Phys. Res. B 184 (2001) 437±440
References [1] T. Ossaka, K. Kekagawa, T. Oi, M. Mukaida, J. Radioanal. Nucl. Chem. 183 (1994) 235. [2] J.I. Nwachukwu, E.I. Obiajunwa, I.B. Obioh, in: A.K. Garg, V. Banerjie, S.N. Swamy, P. Dwivedi (Eds.), Petroleum Geochemistry and Exploration in the Afro-Asian Region, BRPC, New Delhi, India, 2000, pp. 139±145. [3] A. Johnson, G.C. Lalor, H. Robotham, M.K. Vutchkor, J. Radioanal. Nucl. Chem. 209 (1996) 101.
[4] V. Leenanupan, K. Srichom, J. Radioanal. Nucl. Chem. 207 (1996) 137. [5] R.H. Obenauf (Ed.), SPEX Handbook of Sample Preparation and Handling, 3rd ed., 1991, p. 95. [6] QXAS Users Manual, International Atomic Energy Agency (IAEA), Vienna, 1993. [7] H.H. Read, Rutley's Elements of Mineralogy, George Allen & Unwin, London, 1976, p. 456. [8] K. Govindaraju (Ed.), Geostandards Newsletter, Vol. 18, 1994.