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Some data on the marine geochemistry of rhenium
Chemical Geology Elsevier Publishing Company, Amsterdam - Printed in The Netherlands
Short Communication SOME DATA ON THE MARINE GEOCHEMISTRY
OF RHENIUM
J. OLAFSSON~ and J.P. RILEY
Department of Oceanography, University of Liverpool, Liverpool (GreatBritain) (Received October 6,1971)
ABSTRACT Olafsson, J. and Riley, J.P., 1972. Some data on the marine geochemistry of rhenium. Chem. Geol., 9: 227-230. Neutron activation procedures have been used for the determination of rhenium in sea water and sediments. Water from the North Atlantic was found to contain 2.7 -5.8 ng 1-1 of Re (average 4.0 ng 1-I Re). Analyses carried out on 11 samples of deep sea sediments, representative of the principal classes, showed highly significant correlations between Re and Si and between Re and the inverse of the carbonate content. No significant correlation was found between Re and Mn. It is suggested that the Re present in the sediments is associated with the silicate phases and this hypothesis is supported by adsorption studies. INTRODUCTION Probably because of its very low terrestrial abundance Re has been little studied in the marine environment. Its presence in sea water was first reported by Scadden (1969) who found 6 - 1 0 ng 1-1 in the surface waters of the Pacific Ocean. Concentrations in the same range have been observed by Matthews and Riley (1970) for the subsurface waters at a station in the eastern sub-tropical Atlantic. The occurrence of the element in a few species of marine organisms has been investigated by Fukai and Meinke (1962), who found concentrations (expressed on a dry weight basis) varying from 15 p.p.b, in the sea lettuce Ulva sp., to < 3 p.p.b, in the crustacean, Pandalus sp. The present communication presents what are believed to be the first published data on the levels of Re in recent deep sea sediments. In addition, some figures are also given for its concentration at several levels in the water column in the North Atlantic. METHODS OF ANALYSIS Samples were analyzed by neutron activation procedures utilizing the induced 186Re activity. Sea water samples were collected by means of an 8 1 National Institute of Oceanography polypropylene water sampling bottle and filtered through a 0.45/am Present address: Marine Research Institute, Skulagata 4, Reykjavik (Iceland)
228
J. OLAFSSON AND J.P. RILEY
membrane filter. Re was pre-concentrated from them by ion exchange. The concentrate was activated for a total of 24 h in a thermal neutron flux of 3.5 × 1012 n. cm -2 • sec -1 in the Joint Universities Reactor at Risley, Lancs. After cooling for 2 days, 15 mg of inert Re was added as carrier. Subsequent processing and counting of 186 Re activity was carried out as described by Matthews and Riley (1970). Sediment samples (0.5 g) were irradiated directly, along with standards, for a total of 7 days in a thermal neutron flux of 5" t 0 ~2 II" c m - 2 • sec -1 in the Dido Reactor at Harwell. After cooling for 3 days, 15 mg of inert rhenium (as KReO4) was added as carrier and the samples were fused with sodium peroxide. The fused cake was thoroughly leached with water and the insoluble residue was removed by centrifilgation. The clear liquid was diluted to 500 ml and sufficient hydrochloric acid was added to give the solution acidity of 0.1N. The resulting solution was passed through a 10 cm X 6 mm diameter column of Deacidite F F anion exchange resin in its chloride form. The column was washed with water and adsorbed Re was eluted with 60 ml of 4 N nitric acid. The eluate was evaporated to dryness on a hot plate and the residue was taken up in 5M sodium hydroxide. Solvent extraction of Re from this solution, and its subsequent purification by non-aqueous ion exchange was carried out using the radiochemical separation scheme employed for sea water samples. The identity and radiochemical purity of the 186 Re activity separated from the irradiated samples of both sea water and sediments was confirmed by T-spectrometry, and determination of its aluminium absorption curve and half-life. It is estimated that the coefficient of variation of the analytical method for both sea water and sediments is -+ 15% (Matthews and Riley, 1970). The sediments were analyzed colorimetrically for silica (Riley, 1958). Mn was determined in a hydrofluoric acid-perchloric acid digest of the sample using atomic absorption spectrophotometry. An approximate measure of the calcium carbonate content o f the samples was obtained by the determination of the Ca dissolved from them by 2 N a c e t i c acid. RESULTS AND DISCUSSION Re was determined in water samples collected at several depths in the North Atlantic (Table l). The concentrations found were similar to those observed by previous workers (Scadden, 1969; Matthews and Riley, 1970). Analyses were carried out on a total of 11 deep sea sediments (Table II), representative of the principal sediment classes. Correlation coefficients calculated from the results show that, if the obviously anomalous samples Q3 and T3 are neglected, there is a 98% probability of an inverse relationship between Re and the CaCO3 content of the sample. If the same samples are excluded, there is a highly significant probability (r = 0.89) of a direct correlation between Re and Si. In contrast, there is no significant correlation between Re and Mn (r = 0.67). This suggests that the Re present in the deep sea sediments is associated mainly with the silicate minerals (mainly clays), and not with either the carbonate or ferromanganese mineral tractions. In an attempt to test this hypothesis,
MARINE GEOCHEMISTRYOF RHENIUM
229
TABLE I Rhenium in water from the North Atlantic Latitude
Longitude
Sampling depth (m)
Temperature (°C)
Salinity (°/oo)
Rhenium Watermass~ (ng. 1-l)
68°30'N 66°35 'N 66°23'N 62°58 'N 62 °58' N 62°58'N
12°12'W 18°50'W 09°00'W 19°51 'W 19°51 'W 19°51 'W
1000 400 1000 0 900 1250
-0.50 0.41 -0.40 7.8 6.1 4.8
34.91 34.88 34.94 35.20 35.10 35.00
3.7 2.7 3.3 5.8 4.4 4.3
Arctic bottmn water Arctic intermediate water Arctic bottom water Atlantic water Atlantic water Atlantic water
~rAccording to Stefansson (1962). TABLE II Occurrence of rhenium in marine sediments Sample No. ~i"
Latitude
Longitude
Waterdepth (m)
Rhenium (p.p.b.)
Percentage . . . . . . . Si Mn CaC0 3
Q3(11-20) H6(28-30) E1(20-20.5) A2(32-35) J6B(25-26) T3(18-20) J5(25-26) R4(5.0-7.6) N3(3-5) I2 Cusp(290-300)
57°56'N 31°00'N 22°06'N 10°09'N 37°14'N 68°28 'N 37°14'N 61°04'N 48°40'N 33°52'N 37015'N
29°08'W 23°20'W 20°29'W 36°02'W 14°20'W 06°45 'W 27°40'W 32°30'W 24°31'W 19°17 'W 143°07 'W
1274 4947 4195 5068 1977 2337 2240 2200 4096 4700 5220
19.4 4.3 3.3 5.4 1.7 3.7 1.4 4.3 6.8 2.7 11.3
12.3 7.6 7.3 15.2 9.0 32.3 9.5 6.0 19.6 3.2 28.6
0.068 0.079 0.050 0.048 0.(170 0.035 (1.123 0.065 0.051 0.072 0.41
34.8 50.1 53.3 37.6 48.5 0.3 45.9 54.6 26.1 62,5 0.2
~'For core samples the figures in parentheses represent the depth range (in cm) of the core section below the sediment surface.
adsorption studies were carried out radiochemically, using perrhenate labelled with 186 Re. It was found that no detectable adsorption of the element occurred when ferric hydroxide or manganese dioxide were precipitated from sea water at its natural pH. Neither was it carried down with calcium carbonate, either precipitated chemically as aragonite, or biologically in the calcite secreted by a mollusc. On the other hand, the clay minerals illite and kaolinite and an argillaceous deep sea sediment adsorbed the perrhenate ion to a very significant extent from sea water. This suggests that the geochemical balance of Re in sea water may well be maintained by adsorptive processes of this nature, particularly during the formation of authigenic clay minerals. The adsorbed perrhenate ions may subsequently be incorporated into the clay mineral lattice.
230
J. OLAFSSON AND J.P. RILEY
ACKNOWLEDGEMENTS This w o r k was partly s u p p o r t e d by a grant (to J.O.) f r o m the Icelandic Science Foundation.
REFERENCES Fukai, R. and Meinke, W.W., 1962. Activation analyses of vanadium, arsenic, molybdenum, tungsten, rhenium and gold in marine organisms. Limnol. Oceanogr., 7: 186-200. Matthews, A.D. and Riley, J.P., 1970. The determination of rhenium in sea water. Anal 6'him. Acta, 51: 455-462. Riley, J.P., 1958. The rapid analysis of silicate rocks and minerals. Anal. Chirn. Acta, 19: 413-430. Scadden, E.M., 1969. Rhenium: its concentration in Pacific Ocean surface waters. Geochim. Cosmochim. Acta, 35: 633-637. Stefansson, U., 1962. North Icelandic waters. Rit Fiskideildar, 3:1 -269.
Short Communication SOME DATA ON THE MARINE GEOCHEMISTRY
OF RHENIUM
J. OLAFSSON~ and J.P. RILEY
Department of Oceanography, University of Liverpool, Liverpool (GreatBritain) (Received October 6,1971)
ABSTRACT Olafsson, J. and Riley, J.P., 1972. Some data on the marine geochemistry of rhenium. Chem. Geol., 9: 227-230. Neutron activation procedures have been used for the determination of rhenium in sea water and sediments. Water from the North Atlantic was found to contain 2.7 -5.8 ng 1-1 of Re (average 4.0 ng 1-I Re). Analyses carried out on 11 samples of deep sea sediments, representative of the principal classes, showed highly significant correlations between Re and Si and between Re and the inverse of the carbonate content. No significant correlation was found between Re and Mn. It is suggested that the Re present in the sediments is associated with the silicate phases and this hypothesis is supported by adsorption studies. INTRODUCTION Probably because of its very low terrestrial abundance Re has been little studied in the marine environment. Its presence in sea water was first reported by Scadden (1969) who found 6 - 1 0 ng 1-1 in the surface waters of the Pacific Ocean. Concentrations in the same range have been observed by Matthews and Riley (1970) for the subsurface waters at a station in the eastern sub-tropical Atlantic. The occurrence of the element in a few species of marine organisms has been investigated by Fukai and Meinke (1962), who found concentrations (expressed on a dry weight basis) varying from 15 p.p.b, in the sea lettuce Ulva sp., to < 3 p.p.b, in the crustacean, Pandalus sp. The present communication presents what are believed to be the first published data on the levels of Re in recent deep sea sediments. In addition, some figures are also given for its concentration at several levels in the water column in the North Atlantic. METHODS OF ANALYSIS Samples were analyzed by neutron activation procedures utilizing the induced 186Re activity. Sea water samples were collected by means of an 8 1 National Institute of Oceanography polypropylene water sampling bottle and filtered through a 0.45/am Present address: Marine Research Institute, Skulagata 4, Reykjavik (Iceland)
228
J. OLAFSSON AND J.P. RILEY
membrane filter. Re was pre-concentrated from them by ion exchange. The concentrate was activated for a total of 24 h in a thermal neutron flux of 3.5 × 1012 n. cm -2 • sec -1 in the Joint Universities Reactor at Risley, Lancs. After cooling for 2 days, 15 mg of inert Re was added as carrier. Subsequent processing and counting of 186 Re activity was carried out as described by Matthews and Riley (1970). Sediment samples (0.5 g) were irradiated directly, along with standards, for a total of 7 days in a thermal neutron flux of 5" t 0 ~2 II" c m - 2 • sec -1 in the Dido Reactor at Harwell. After cooling for 3 days, 15 mg of inert rhenium (as KReO4) was added as carrier and the samples were fused with sodium peroxide. The fused cake was thoroughly leached with water and the insoluble residue was removed by centrifilgation. The clear liquid was diluted to 500 ml and sufficient hydrochloric acid was added to give the solution acidity of 0.1N. The resulting solution was passed through a 10 cm X 6 mm diameter column of Deacidite F F anion exchange resin in its chloride form. The column was washed with water and adsorbed Re was eluted with 60 ml of 4 N nitric acid. The eluate was evaporated to dryness on a hot plate and the residue was taken up in 5M sodium hydroxide. Solvent extraction of Re from this solution, and its subsequent purification by non-aqueous ion exchange was carried out using the radiochemical separation scheme employed for sea water samples. The identity and radiochemical purity of the 186 Re activity separated from the irradiated samples of both sea water and sediments was confirmed by T-spectrometry, and determination of its aluminium absorption curve and half-life. It is estimated that the coefficient of variation of the analytical method for both sea water and sediments is -+ 15% (Matthews and Riley, 1970). The sediments were analyzed colorimetrically for silica (Riley, 1958). Mn was determined in a hydrofluoric acid-perchloric acid digest of the sample using atomic absorption spectrophotometry. An approximate measure of the calcium carbonate content o f the samples was obtained by the determination of the Ca dissolved from them by 2 N a c e t i c acid. RESULTS AND DISCUSSION Re was determined in water samples collected at several depths in the North Atlantic (Table l). The concentrations found were similar to those observed by previous workers (Scadden, 1969; Matthews and Riley, 1970). Analyses were carried out on a total of 11 deep sea sediments (Table II), representative of the principal sediment classes. Correlation coefficients calculated from the results show that, if the obviously anomalous samples Q3 and T3 are neglected, there is a 98% probability of an inverse relationship between Re and the CaCO3 content of the sample. If the same samples are excluded, there is a highly significant probability (r = 0.89) of a direct correlation between Re and Si. In contrast, there is no significant correlation between Re and Mn (r = 0.67). This suggests that the Re present in the deep sea sediments is associated mainly with the silicate minerals (mainly clays), and not with either the carbonate or ferromanganese mineral tractions. In an attempt to test this hypothesis,
MARINE GEOCHEMISTRYOF RHENIUM
229
TABLE I Rhenium in water from the North Atlantic Latitude
Longitude
Sampling depth (m)
Temperature (°C)
Salinity (°/oo)
Rhenium Watermass~ (ng. 1-l)
68°30'N 66°35 'N 66°23'N 62°58 'N 62 °58' N 62°58'N
12°12'W 18°50'W 09°00'W 19°51 'W 19°51 'W 19°51 'W
1000 400 1000 0 900 1250
-0.50 0.41 -0.40 7.8 6.1 4.8
34.91 34.88 34.94 35.20 35.10 35.00
3.7 2.7 3.3 5.8 4.4 4.3
Arctic bottmn water Arctic intermediate water Arctic bottom water Atlantic water Atlantic water Atlantic water
~rAccording to Stefansson (1962). TABLE II Occurrence of rhenium in marine sediments Sample No. ~i"
Latitude
Longitude
Waterdepth (m)
Rhenium (p.p.b.)
Percentage . . . . . . . Si Mn CaC0 3
Q3(11-20) H6(28-30) E1(20-20.5) A2(32-35) J6B(25-26) T3(18-20) J5(25-26) R4(5.0-7.6) N3(3-5) I2 Cusp(290-300)
57°56'N 31°00'N 22°06'N 10°09'N 37°14'N 68°28 'N 37°14'N 61°04'N 48°40'N 33°52'N 37015'N
29°08'W 23°20'W 20°29'W 36°02'W 14°20'W 06°45 'W 27°40'W 32°30'W 24°31'W 19°17 'W 143°07 'W
1274 4947 4195 5068 1977 2337 2240 2200 4096 4700 5220
19.4 4.3 3.3 5.4 1.7 3.7 1.4 4.3 6.8 2.7 11.3
12.3 7.6 7.3 15.2 9.0 32.3 9.5 6.0 19.6 3.2 28.6
0.068 0.079 0.050 0.048 0.(170 0.035 (1.123 0.065 0.051 0.072 0.41
34.8 50.1 53.3 37.6 48.5 0.3 45.9 54.6 26.1 62,5 0.2
~'For core samples the figures in parentheses represent the depth range (in cm) of the core section below the sediment surface.
adsorption studies were carried out radiochemically, using perrhenate labelled with 186 Re. It was found that no detectable adsorption of the element occurred when ferric hydroxide or manganese dioxide were precipitated from sea water at its natural pH. Neither was it carried down with calcium carbonate, either precipitated chemically as aragonite, or biologically in the calcite secreted by a mollusc. On the other hand, the clay minerals illite and kaolinite and an argillaceous deep sea sediment adsorbed the perrhenate ion to a very significant extent from sea water. This suggests that the geochemical balance of Re in sea water may well be maintained by adsorptive processes of this nature, particularly during the formation of authigenic clay minerals. The adsorbed perrhenate ions may subsequently be incorporated into the clay mineral lattice.
230
J. OLAFSSON AND J.P. RILEY
ACKNOWLEDGEMENTS This w o r k was partly s u p p o r t e d by a grant (to J.O.) f r o m the Icelandic Science Foundation.
REFERENCES Fukai, R. and Meinke, W.W., 1962. Activation analyses of vanadium, arsenic, molybdenum, tungsten, rhenium and gold in marine organisms. Limnol. Oceanogr., 7: 186-200. Matthews, A.D. and Riley, J.P., 1970. The determination of rhenium in sea water. Anal 6'him. Acta, 51: 455-462. Riley, J.P., 1958. The rapid analysis of silicate rocks and minerals. Anal. Chirn. Acta, 19: 413-430. Scadden, E.M., 1969. Rhenium: its concentration in Pacific Ocean surface waters. Geochim. Cosmochim. Acta, 35: 633-637. Stefansson, U., 1962. North Icelandic waters. Rit Fiskideildar, 3:1 -269.