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The extraction of 10Be from lake sediments leaching versus total dissolution
Chemical Geology (Isotope Geoscience Section), 52 (1985) 375-373 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
375
THE EXTRACTIONOF “‘BE FROM LAKE SEDIMENTS LEACHING VERSUS TcrrAL DISSOLUTION T.A. BROWN’, D.E. NELSON’, J.R. SOUTHON’ and J.S. VOGEL’ ’ Department of Archaeology, Simon Fraser University, Bumaby, B.C. V5A IS6 (Canada) ‘Department of Archaeology, Simon Fraser University, Bumaby, B.C. WA IS6 and Tandem Accekmtor Laboratory, i&Master University, Hamilton, Ont. L8S 4Kl (Canada) (Received
July 10, 1984; revised and accepted
October
2, 1984)
Abstract Brown, T.A., Nelson, D.E., Southon, J.R. and Vogel, J.S., 1985. The extraction of “Be ments: leaching versus total dissolution. Chem. Geol. (Isot. Geosci. Sect.), 52: 375-378.
from
lake sedi-
loBe concentration measurements of 20 lake sediment samples prepared by leaching with 8 N HCl are compared with measurements of 29 samples prepared by total dissolution in HF. The data provide unambiguous evidence showing the leaching technique to be effective in extracting all of the loBe from the sediments.
The application of accelerator-basedmass spectrometry (AIMS) to the study of natural loBe concentrations in sediments and soils has increased experimental detection sensivities by severalorders of magnitude over standard p-counting methods (Raisbeck et al., 1979; Brown et al., 1981; Southon et al., 1983). The development of loBe AMS has thereby greatly improved the time resolution attainable from sediment cores and has increased interest in the potential use of the radioisotope as a dating technique, as a measure of production variations of similarly produced radioisotopes such as “C and as a measure of erosion rates and other geological processes (Wolfli, 1985). The increased measurement capabilities provided by AA&S require a rapid and quantitative loBe sample preparation method to produce the large numbers of samples which are now measurable. Recent AMS measurements of loBe in deep-sea sediments, continental sediments and soils have, in general, used sample pre-
paration techniques involving total dissolution by HF (Brown et al., 1981; Lundberg et al., 1983; Southon et al., 1983). These techniques, although varying in detail, required loBe extraction times of many hours. In one of the earliest @counting measurements of loBe concentrations in seep-sea sediments (Goel et al., 1957) two methods of “Be extraction from the sediments were used: (1) repeated treatments with a variety of acids and basesand complete dissolution of the residue with HF; (2) leaching of the dry sediment with 12 N HCl followed by repeated washing with HCl. The second method was used to avoid the “laborious and time-consuming” steps of the first method. However, the authors were uncertain as to whether all of the loBe was extracted from the sediment by the leaching technique. A quantitative examination of the leaching method (Amin et al., 1966) showed that w 10% of the loBe in the sediment remained in the residue after repeated
016%9622/85/$03.30
B.V.
1. Introduction
0 1985 Elsevier Science Publishers
376
leaching with 6 N HCl. A secondexamination of the effectiveness of leaching with 6 N HCl (Finkel et al., 1977) showed that - 18% of the loBe was not removed from the sediment. Thus, although claims have been made that leaching with 6 N HCl quantitatively extracts “Be from sediments and soils (Monaghan et al., 1983), direct evidence supporting the claims has not been published. As part of a series of loBe concentration measurements on lake sediment cores from Anderson Pond, White County, Tennessee, U.S.A. (36’02’N lat., 85” 30’W long.) we have compared the effectiveness of the leaching technique vs. the total dissolution technique in the extraction of loBe from the sedimentary material. We find that, for this sediment, an 8 N HCl leaching technique gave loBe concentrations identical to those from total dissolution by HF.
overnight at low temperature to avoid decomposition of the acid. The residues and nitric acid were then evaporated to near dryness. Next, the residues were treated with HF for 2 hr. and again evaporated to near dryness. This two-step procedure was repeated, resulting in the dissolution of the residues. The leachates were then combined with the products of the dissolution steps to compose the total dissolution samples. The loBe was separated from the samples after the addition of 1 mg 9Be carrier, by anion- and cation-exchange resin techniques similar to those of Ku et al. (1979). The AMS measurements were made on the MeMaster University FN Tandem Van de Graaff by a measurement technique which has been described previously (Southon et al., 1983).
2. Materials and methods
A total of 68 “Be measurements on 49 separately prepared samples were made. The leaching technique was used to prepare 20 of the samples; the total dissolution technique was used to prepare the other .29 samples. Each measurement consisted of several determinations of the l”Be19Be ratio of the sample relative to that of a known standard. To determine the long-term reproducibility of our AMS technique, 15 of the 49 prepared Be0 sampleswere remeasured at least once on different occasionsseparated by several months (a total of 34 measurements). A x2 analysis of these repeated measurements on individual samples (expressed as percentage deviations from the mean for each sample) showed that the distribution was most consistent with an experimental uncertainty (lo) of 6% (P = 0.96). The measured loBe concentrations are shown as a function of core depth in Fig. 1. The measured concentitions for samples from equivalent depths in the two cores 76C and 76D showed no systematic difference between the cores; hence, no distinction has been made between data from the two
The Anderson Pond cores, 76C and 76D (Delcourt, 1979; Lund, 1981), are composed predominantly of elastic sediments: the upper 250 cm are dominated by chert-rich limestone residues and the lower 400 cm by Lower Pennsylvanianelastic sediments. Sections of these cores from various depths were prepared for loBe extraction by first drying the sediments at 100°C overnight, then grinding the material to a fine homogeneouspowder. Samplesweighing - 2 g were separated from the powdered depth-sections and baked at 400°C for 3 hr. to remove organic material. For both preparation techniques, the samples were leached with 8 N HCl at 100°C for 1 hr., with frequent agitation. The leachates were separated from the residues by centrifuging and the residues were washed repeatedly with 8 N HCl. The washings,after separation from the residues by centrifuging, were combined with the leachates to form the leached samples. For samples prepared by total dissolution, the residues remaining after leaching were first treated with HN03
3. Results and discussion
377 TABLE
I
Comparison
and total dissolution
Depthsection (cm) (1)
‘OBe g/g sample
71.977.0 128.8-134.7 134.7-140.6 172.5-177.8 199.0-204.3 237.4-286.8 339.1-383.2 431.4-475.4 523.5-571.7
4.56* 0.27 5.25t0.22 4.40* 0.19 4.37*0.19 3.84kO.23 3.90*0.23 3.87* 0.23 3.06kO.18 2.98i0.18
leaching
(X
sample
lo-“) :;:I
dissolution
sample
Leaching efficiency* (4)
(2) 4.39r0.15 4.62kO.28 5.09*0.31 4.38kO.15 3.81i0.23 4.06+ 0.24 3.38t0.20 3.14t0.19 3.47*0.21
1.039i 0.071 1.136iO.084 0.864iO.065 0.998*0.055 1.008t0.086 0.961iO.080 1.145kO.096 0.975*0.0&32 0.859*0.073
Average
0.998
=avg
0.034
*As defined
SO
of leaching
100
in text.
150 200 Core Depth
250 450 (cm)
650
Fig. 1. loBe g/g sample as a function of core depth for the cores 76C and 7.6D. The concentrations for leached samples (0) are compared with those for total-dissolution samples (X ). Error bars indicate 6% (lo) uncertainty in individual loBe measurements.
cores. The “Be concentration data show no evidence of a systematic difference’ between the leached samples and the total dissolution samples. The two extraction techniques are compared in detail in Table I, which lists data
for the nine depth-sections from which samples were prepared by both methods. For cases where the measurement process was carried out only once, the uncertainties given in Table I reflect the 6% lo value as derived above. For samples measured repeatedly on the accelerator, the mean of the “Be concentrations and the uncertainty of the mean (ucl) are given. Taking the total dissolution technique to be 100% effective in extracting ‘OBe from the sediment, we define the leaching efficiency to be the ratio of the “Be concentration of the leached sample to that of the total-dissolution sample (Table I, column 4). The average leaching efficiency is statistically equal to 1.00 with an uncertainty of 0.03. This is strong evidence that leaching with 8 N HCl ‘is as effective as total dissolution for extracting loBe from these Anderson Pond elastic sediments. These results indicate that extracting “Be from sediments by leaching is a quantitative procedure, and suggest that this technique may be more generally applicable. If so, it will provide an effective and relatively simple method for extracting loBe from sedimentary materials.
318
Acknowledgements We thank S. Lund for providing the cores and R. Korteling and T.L. Ku for the use of their laboratory facilities and for their advice. This project was financed in part through grants from the NSERC and the NSF (Grants OCE-7901092 and OCE-8100662 awarded through the MANOP Project). We gratefully acknowledge the assistance and generosity of the Tandem accelerator staff at McMaster University. Reference8 Amin, B.S., Kharkar, D.P. and Lal, D., 1966. Cosmogenic loBe and “Al in marine sediments. Deepsea Res., 13: 805-624. Brown, L., Sacks, I.S., Tera, F., Klein, J. and Middleton, R., 1981. Beryllium-10 in continental sediments. Earth Planet Sci. Lett., 55: 370-376. Delcourt, H.R., 1979. Late Quaternary vegetation history of the Eastern Highland Rim and adjacent Cumberland Plateau of Tennessee. Ecol. Monogr., 49(3): 255-280. Finkel, R., Krishnaswami, S. and Clark, D.G., 1977. loBe in Arctic Ocean sediments. Earth Planet Sci. Lett., 35: 199-204. Goel, P.S., Eharkar, D.P., Lal, D., Narsappaya, N., Peters, B. and Yatirajam, V., 1957. The beryllium10 concentration in deep sea sediments. Deep-Sea Res., 4: 202-210.
Ku, T.L., Omara, A. and Chen, P.S., 1979. “Be and U-series isotopes manganese nodules from the central North Pacific. In: J.L. Bishoff and Z. Piper (Editors), Oceanography of the Pacific Manganese Nodule Province. Plenum, New York, N.Y., pp. 791-314. Lund, S., 1981. Late Quaternary secular variation of the Earth’s magnetic field as recorded in the wet sediments of three North American Lakes. Ph.D. Thesis, University of Minnesota, Minneapolis, Minn., 232 pp. Lundberg, L., Ticich, T., Herzog, G.F., Hughes, T., Ashley, G., Monlot, R.K., Tuniz, C., Kruse, T. and Savin, W., 1983. loBe and Be in the Maurice River-Union Lake system of southern New Jersey. J. Geophys. Res., 88(C7): 4478-4504. Monaghan, M.C., Krishnaswami, S. and Thomas, J.H., 1983. “Be concentrations and the long term fate of particle-reactive nuclides in five soil profiles from California. Earth Planet Sci. Lett., 65: 51-60. Ralsbeck, G.M., Yiou, F., Fruneau, M., Loiseaux, J.M., Lieuvin, M., Ravel, J.C. and Hayes, J.D., 1979. A search in a marine sediment core for “Be concentration variations during a geomagnetic reversal. Geophys. Res. Lett., 6(9): 717-719. Southon, J.R., Vogel, J.S., Nowikow, I., Nelson, D.E. and Korteling, R.G., 1983. The measurement of loBe concentrations with a Tandem accelerator. Nucl. Instrum. Meth., 205: 251-257. Wiilfli, W. (Editor), 1985. Proc. 3rd Int. Symp. on Accelerator Mass Spectrometry, Zurich, Switaerland, Apr. 10-13, 1984. Nucl. Instr. Meth. (In press.)
375
THE EXTRACTIONOF “‘BE FROM LAKE SEDIMENTS LEACHING VERSUS TcrrAL DISSOLUTION T.A. BROWN’, D.E. NELSON’, J.R. SOUTHON’ and J.S. VOGEL’ ’ Department of Archaeology, Simon Fraser University, Bumaby, B.C. V5A IS6 (Canada) ‘Department of Archaeology, Simon Fraser University, Bumaby, B.C. WA IS6 and Tandem Accekmtor Laboratory, i&Master University, Hamilton, Ont. L8S 4Kl (Canada) (Received
July 10, 1984; revised and accepted
October
2, 1984)
Abstract Brown, T.A., Nelson, D.E., Southon, J.R. and Vogel, J.S., 1985. The extraction of “Be ments: leaching versus total dissolution. Chem. Geol. (Isot. Geosci. Sect.), 52: 375-378.
from
lake sedi-
loBe concentration measurements of 20 lake sediment samples prepared by leaching with 8 N HCl are compared with measurements of 29 samples prepared by total dissolution in HF. The data provide unambiguous evidence showing the leaching technique to be effective in extracting all of the loBe from the sediments.
The application of accelerator-basedmass spectrometry (AIMS) to the study of natural loBe concentrations in sediments and soils has increased experimental detection sensivities by severalorders of magnitude over standard p-counting methods (Raisbeck et al., 1979; Brown et al., 1981; Southon et al., 1983). The development of loBe AMS has thereby greatly improved the time resolution attainable from sediment cores and has increased interest in the potential use of the radioisotope as a dating technique, as a measure of production variations of similarly produced radioisotopes such as “C and as a measure of erosion rates and other geological processes (Wolfli, 1985). The increased measurement capabilities provided by AA&S require a rapid and quantitative loBe sample preparation method to produce the large numbers of samples which are now measurable. Recent AMS measurements of loBe in deep-sea sediments, continental sediments and soils have, in general, used sample pre-
paration techniques involving total dissolution by HF (Brown et al., 1981; Lundberg et al., 1983; Southon et al., 1983). These techniques, although varying in detail, required loBe extraction times of many hours. In one of the earliest @counting measurements of loBe concentrations in seep-sea sediments (Goel et al., 1957) two methods of “Be extraction from the sediments were used: (1) repeated treatments with a variety of acids and basesand complete dissolution of the residue with HF; (2) leaching of the dry sediment with 12 N HCl followed by repeated washing with HCl. The second method was used to avoid the “laborious and time-consuming” steps of the first method. However, the authors were uncertain as to whether all of the loBe was extracted from the sediment by the leaching technique. A quantitative examination of the leaching method (Amin et al., 1966) showed that w 10% of the loBe in the sediment remained in the residue after repeated
016%9622/85/$03.30
B.V.
1. Introduction
0 1985 Elsevier Science Publishers
376
leaching with 6 N HCl. A secondexamination of the effectiveness of leaching with 6 N HCl (Finkel et al., 1977) showed that - 18% of the loBe was not removed from the sediment. Thus, although claims have been made that leaching with 6 N HCl quantitatively extracts “Be from sediments and soils (Monaghan et al., 1983), direct evidence supporting the claims has not been published. As part of a series of loBe concentration measurements on lake sediment cores from Anderson Pond, White County, Tennessee, U.S.A. (36’02’N lat., 85” 30’W long.) we have compared the effectiveness of the leaching technique vs. the total dissolution technique in the extraction of loBe from the sedimentary material. We find that, for this sediment, an 8 N HCl leaching technique gave loBe concentrations identical to those from total dissolution by HF.
overnight at low temperature to avoid decomposition of the acid. The residues and nitric acid were then evaporated to near dryness. Next, the residues were treated with HF for 2 hr. and again evaporated to near dryness. This two-step procedure was repeated, resulting in the dissolution of the residues. The leachates were then combined with the products of the dissolution steps to compose the total dissolution samples. The loBe was separated from the samples after the addition of 1 mg 9Be carrier, by anion- and cation-exchange resin techniques similar to those of Ku et al. (1979). The AMS measurements were made on the MeMaster University FN Tandem Van de Graaff by a measurement technique which has been described previously (Southon et al., 1983).
2. Materials and methods
A total of 68 “Be measurements on 49 separately prepared samples were made. The leaching technique was used to prepare 20 of the samples; the total dissolution technique was used to prepare the other .29 samples. Each measurement consisted of several determinations of the l”Be19Be ratio of the sample relative to that of a known standard. To determine the long-term reproducibility of our AMS technique, 15 of the 49 prepared Be0 sampleswere remeasured at least once on different occasionsseparated by several months (a total of 34 measurements). A x2 analysis of these repeated measurements on individual samples (expressed as percentage deviations from the mean for each sample) showed that the distribution was most consistent with an experimental uncertainty (lo) of 6% (P = 0.96). The measured loBe concentrations are shown as a function of core depth in Fig. 1. The measured concentitions for samples from equivalent depths in the two cores 76C and 76D showed no systematic difference between the cores; hence, no distinction has been made between data from the two
The Anderson Pond cores, 76C and 76D (Delcourt, 1979; Lund, 1981), are composed predominantly of elastic sediments: the upper 250 cm are dominated by chert-rich limestone residues and the lower 400 cm by Lower Pennsylvanianelastic sediments. Sections of these cores from various depths were prepared for loBe extraction by first drying the sediments at 100°C overnight, then grinding the material to a fine homogeneouspowder. Samplesweighing - 2 g were separated from the powdered depth-sections and baked at 400°C for 3 hr. to remove organic material. For both preparation techniques, the samples were leached with 8 N HCl at 100°C for 1 hr., with frequent agitation. The leachates were separated from the residues by centrifuging and the residues were washed repeatedly with 8 N HCl. The washings,after separation from the residues by centrifuging, were combined with the leachates to form the leached samples. For samples prepared by total dissolution, the residues remaining after leaching were first treated with HN03
3. Results and discussion
377 TABLE
I
Comparison
and total dissolution
Depthsection (cm) (1)
‘OBe g/g sample
71.977.0 128.8-134.7 134.7-140.6 172.5-177.8 199.0-204.3 237.4-286.8 339.1-383.2 431.4-475.4 523.5-571.7
4.56* 0.27 5.25t0.22 4.40* 0.19 4.37*0.19 3.84kO.23 3.90*0.23 3.87* 0.23 3.06kO.18 2.98i0.18
leaching
(X
sample
lo-“) :;:I
dissolution
sample
Leaching efficiency* (4)
(2) 4.39r0.15 4.62kO.28 5.09*0.31 4.38kO.15 3.81i0.23 4.06+ 0.24 3.38t0.20 3.14t0.19 3.47*0.21
1.039i 0.071 1.136iO.084 0.864iO.065 0.998*0.055 1.008t0.086 0.961iO.080 1.145kO.096 0.975*0.0&32 0.859*0.073
Average
0.998
=avg
0.034
*As defined
SO
of leaching
100
in text.
150 200 Core Depth
250 450 (cm)
650
Fig. 1. loBe g/g sample as a function of core depth for the cores 76C and 7.6D. The concentrations for leached samples (0) are compared with those for total-dissolution samples (X ). Error bars indicate 6% (lo) uncertainty in individual loBe measurements.
cores. The “Be concentration data show no evidence of a systematic difference’ between the leached samples and the total dissolution samples. The two extraction techniques are compared in detail in Table I, which lists data
for the nine depth-sections from which samples were prepared by both methods. For cases where the measurement process was carried out only once, the uncertainties given in Table I reflect the 6% lo value as derived above. For samples measured repeatedly on the accelerator, the mean of the “Be concentrations and the uncertainty of the mean (ucl) are given. Taking the total dissolution technique to be 100% effective in extracting ‘OBe from the sediment, we define the leaching efficiency to be the ratio of the “Be concentration of the leached sample to that of the total-dissolution sample (Table I, column 4). The average leaching efficiency is statistically equal to 1.00 with an uncertainty of 0.03. This is strong evidence that leaching with 8 N HCl ‘is as effective as total dissolution for extracting loBe from these Anderson Pond elastic sediments. These results indicate that extracting “Be from sediments by leaching is a quantitative procedure, and suggest that this technique may be more generally applicable. If so, it will provide an effective and relatively simple method for extracting loBe from sedimentary materials.
318
Acknowledgements We thank S. Lund for providing the cores and R. Korteling and T.L. Ku for the use of their laboratory facilities and for their advice. This project was financed in part through grants from the NSERC and the NSF (Grants OCE-7901092 and OCE-8100662 awarded through the MANOP Project). We gratefully acknowledge the assistance and generosity of the Tandem accelerator staff at McMaster University. Reference8 Amin, B.S., Kharkar, D.P. and Lal, D., 1966. Cosmogenic loBe and “Al in marine sediments. Deepsea Res., 13: 805-624. Brown, L., Sacks, I.S., Tera, F., Klein, J. and Middleton, R., 1981. Beryllium-10 in continental sediments. Earth Planet Sci. Lett., 55: 370-376. Delcourt, H.R., 1979. Late Quaternary vegetation history of the Eastern Highland Rim and adjacent Cumberland Plateau of Tennessee. Ecol. Monogr., 49(3): 255-280. Finkel, R., Krishnaswami, S. and Clark, D.G., 1977. loBe in Arctic Ocean sediments. Earth Planet Sci. Lett., 35: 199-204. Goel, P.S., Eharkar, D.P., Lal, D., Narsappaya, N., Peters, B. and Yatirajam, V., 1957. The beryllium10 concentration in deep sea sediments. Deep-Sea Res., 4: 202-210.
Ku, T.L., Omara, A. and Chen, P.S., 1979. “Be and U-series isotopes manganese nodules from the central North Pacific. In: J.L. Bishoff and Z. Piper (Editors), Oceanography of the Pacific Manganese Nodule Province. Plenum, New York, N.Y., pp. 791-314. Lund, S., 1981. Late Quaternary secular variation of the Earth’s magnetic field as recorded in the wet sediments of three North American Lakes. Ph.D. Thesis, University of Minnesota, Minneapolis, Minn., 232 pp. Lundberg, L., Ticich, T., Herzog, G.F., Hughes, T., Ashley, G., Monlot, R.K., Tuniz, C., Kruse, T. and Savin, W., 1983. loBe and Be in the Maurice River-Union Lake system of southern New Jersey. J. Geophys. Res., 88(C7): 4478-4504. Monaghan, M.C., Krishnaswami, S. and Thomas, J.H., 1983. “Be concentrations and the long term fate of particle-reactive nuclides in five soil profiles from California. Earth Planet Sci. Lett., 65: 51-60. Ralsbeck, G.M., Yiou, F., Fruneau, M., Loiseaux, J.M., Lieuvin, M., Ravel, J.C. and Hayes, J.D., 1979. A search in a marine sediment core for “Be concentration variations during a geomagnetic reversal. Geophys. Res. Lett., 6(9): 717-719. Southon, J.R., Vogel, J.S., Nowikow, I., Nelson, D.E. and Korteling, R.G., 1983. The measurement of loBe concentrations with a Tandem accelerator. Nucl. Instrum. Meth., 205: 251-257. Wiilfli, W. (Editor), 1985. Proc. 3rd Int. Symp. on Accelerator Mass Spectrometry, Zurich, Switaerland, Apr. 10-13, 1984. Nucl. Instr. Meth. (In press.)