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Behaviour of nickel and cobalt in natural waters of granitic areas: a first approach
Chemical Geology, 107 ( 1993 ) 417-421 Elsevier Science Publishers B.V., Amsterdam
417
Behaviour of nickel and cobalt in natural waters of granitic areas: a first approach N. Gassama a, G. Michard a, C. Beaucaireb and G. Sarazin a aLaboratoire de Gbochimie des Eaux, Universitb de Paris 7, Paris, France bLCASH, CEN de Fontenay aux Roses, Fontenay aux Roses, France
(Received March 17, 1993: revised and accepted March 30, 1993 )
A square-wave voltammetry method based upon the enhancement of Ni and Co adsorption onto a mercury drop electrode by complexation has been used to measure concentrations in natural fresh waters from granitic areas. This method permits determination of 10 - 9 M N i and 10 -1° M C o in a reliable manner. Waters of various saturation indices were collected. Results show that complex formation is the main process which controls the solubility of trace metals. Trace metal complexation is affected by the relative amounts of anions and the redox state of waters.
1. Introduction Behaviour of trace metals in natural waters is of fundamental and environmental interest. Occurring at trace levels in natural conditions, they can be introduced by industrial wastes. So it is important to know their behaviour to quantify and predict the effects of these contributions. On account of the very low amounts of nickel and cobalt in natural fresh waters, there is a lack of knowledge about their concentrations. Graphite-furnace atomic absorption spectrometry (GFAAS) and classic polarographic methods are not sensitive enough to allow precise measurements and therefore need preconcentration steps which increase the contamination risk of the sample. Zhang et al.
(1989) have proposed a square-wave voltammetric method to perform these analyses. It is a reliable technique, faster than differentialpulse voltammetry, and has better sensitivity. As defined by Pihlar et al. (1981), they used dimethylglyoxime as a complexing agent to enhance the adsorption of Ni and Co onto a mercury drop electrode. An electrolytic buffer containing triethanolamine (TEA), NH4C1 and ammonia is added. Waters more or less far from water-rock equilibrium were sampled in French granitic areas. Surface waters (springs, rivers, lake), shallow mine waters of various salinity, and geothermal waters have been studied.
2. Sampling Surface waters are from the Margeride granitic plateau (south Massif Central, France). The Aydat Lake is in the middle part of the Massif Central, on the Hercynian basement. Waters from two uranium mines were sampied, one in Limousin (northeast of the Massif Central), the other one in Vend6e (south of the Brittany peninsula). The geothermal waters are from the French Eastern Pyr6n6es. Water samples were filtered using 450 nm pore size filters and acidified with Suprapur ® grade nitric acid to p H = 2 . They were stored in previously washed polycarbonate or poly-
418
ethylene bottles. Cleanness tests were carried out upon bottles, after storage of a standard solution over increasing times. No tests were made for the filtration step. Results show that polycarbonate and polyethylene bottles do not modify significantly the Ni or Co content of the water, even after two months. Surface water samples were UV-irradiated to prevent dissolved organic matter complexation or redox reaction which can interfere with the electrochemical analysis.
3. Analytical method Previously developed for seawater analysis, this method has been modified for freshwater analysis without difficulties. The supporting electrolyte is used as an ionic strength buffer. All reagents are of Suprapur ® grade except TEA which is of analytical reagent grade. The sample aliquot is weighed into the cell to avoid contamination. The borosilicate polarographic cell contains 10 g of sample, and 0.4 ml and 50/zl of added electrolyte-buffer solution and DMG solution, respectively. The pH is close to 8.0. The adsorption time is 240 s at an adsorption potential of - 0 . 7 0 0 V vs. AgAgC1-KC1 standard electrode. The electrode is a hanging drop used with a medium size mercury drop. Standard addition method has been used. Before measurements a blank was estimated by replacing the sample by deionized water. Protocol analysis consists of measuring a blank then two solutions and so on. The blank is subtracted from the value found for the two following solutions. Each sample was measured three times, and only exceptionally did results differ more than _+ 10%. The detection limit is ~1-10-~1 and 3- 10-~o M for Co and Ni, respectively.
4. Results and discussion We sampled 27 springs and rivers in Mageride. The Co concentrations range from
N. GASSAMA ET AL.
< 1.10 - ~ to 4.47.10 -9 M. The Ni concentrations vary from 7.10 -l° to 7.62-10 -8 M. Ni and Co distributions show no trend, neither with any other element nor with pH. They are mobile cations in such waters. In Aydat Lake, we sampled water column profiles and pore waters in the surficial sediment (from 0 to 52.5 cm depth). The water column was sampled during the time of maximal thermal stratification of the lake. The bottom waters were anoxic because of the oxygen consumption during the organic matter mineralization. The different redox states control the distribution of transition metals like Fe and Mn. As shown by Sarazin and Devaux ( 1991 ) no soluble species of Fe and Mn are present in the oxic waters. They are present as insoluble Fe (III)- and Mn (IV)-oxyhydroxides compounds. In the reduced waters, Fe and Mn concentrations increase from the thermocline to the bottom due to the reduction and dissolution of oxyhydroxide compounds. Ni and Co distributions are not so easy to explain. As traces, they are influenced by local fluctuations more than minor elements. Ni distribution does not roughly vary along the water column profile, and lies around 3.5" 10 -9 M. The Co distribution is quite different. It is almost absent in the upper waters and appears below the thermocline just after Fe and Mn reduction. Its concentration increases till the bottom of the lake to ~3.2-10 -l° M. These results are in good agreement with those presented by Balistrieri et al. (1992) on Lake Sammamish, Washington, U.S.A., only for the Co distribution. The pore water measurements show a Ni amount below the detection limit. Ni should be present in the particulate phase and Co should be concentrated in the dissolved phase. In the studied lake, Co is in the particulate phase in the oxic waters and is removed in the reduced waters. This behaviour can be connected to an adsorption-oxidation reaction taking place at the MnO2 surface. In the surficial sediment, Co remains in the aqueous
419
BEHAVIOUR OF Ni AND Co IN NATURAL WATERS OF GRANITIC AREAS
phase. Ni does not react as a function of the redox state in the water column. In the surficial sediment, it is present in the particulate phase although calculations show that Ni-sulfide or Ni-hydroxide cannot precipitate. In the Limousin mine, the 14 waters sampled at different depths show unequilibrated oxic waters with mean pH around 8.0 and an up-flow temperature around 20°C. The Ni amounts vary from 3" l0 -I° to 2.16- l0 -s M, and the Co amounts from l ' 1 0 -I~ to 4.05-10 -9 M. Two groups of water can be identified using S O ~ - / C 1 - ratio. SO~--rich waters should result from pyrite alteration. They exhibit a log (Co (II) ) vs. log (SO42- ) linear relationship (Fig. 1a) which can be fit by the equation, where R is the correlation coefficient:
l o g ( N i ( I I ) ) = 1.82 l o g ( U ( I V ) ) + 7 . 2 9 ,
log(Co(II) ) =3.03 log(SO~- ) - 1.17,
These results show a different behaviour between Ni-Co and Cu-Cd. The Eastern Pyrenean hot waters are alkaline, reducing and HS--rich. They are equilibrated with rocks at 110°C which is the calculated temperature based upon chalcedony equilibrium. The Ni and Co amounts are very low, close to the limit of detection. Co and SO42- seems to be lightly correlated (Fig. l d), which may be caused by uncertainties due to low level concentrations. We retain the calculated equation:
R=0.843 Ni amounts do not show the same trend. The Vendfe mine waters are quite different. They are C1--rich with amounts ranging from 2.45-10 - 3 to 2.25-10-~ M. They are neutral oxic waters where C1- is the major anion and which are equilibrated with chalcedony at a temperature around 40 ° C. Ni and Co amounts vary from 5- 10- t° to 8.10- 10-7 M a n d 7- 10 -11 to 2.21- 10-7 M, respectively. They show good correlation with each other and l o g ( S O 4 - ) (Fig. lb and c) and l o g ( U ( I V ) ) . The calculated equations are: log(Co(II) ) =0.91 log(Ni(II) ) - 1.96, R=0.947 log(Co(II) ) =3.22 log(SOl- ) +0.38, R=0.907 log(Ni(II) ) = 2.34 log(SOl- ) - 1.16, R=0.899 log(Co(II) ) = 1.78 l o g ( U ( I V ) ) +9.02, R=0.950
R=0.897 Cu and Cd concentrations can be measured by GFAAS in some samples (amounts > 5- 10 - 9 and > 1- 10 -s M of Cd and Cu, respectively). Their concentrations increase with the CI- concentration. With only five points, we find: log(Cu(II) ) =0.33 log(Cl- ) - 7 . 4 6 , R=0.894 log(Cd(II) ) =0.61 log(Cl- ) - 7 . 2 5 , R=0.935 log(Cd(II) ) = 1.21 log(Cu(II) ) + 1.59, R=0.973
log(Co(II) ) = 1.58 log(SO42- ) - 4 . 5 7 , R=0.678 In such waters Ni and Co have different behaviours, but both seem to be reduced by the presence of sulfur. Ni and Co have different behaviours except in C1--rich waters. Since the first evolved stage of water, Co is linked to SO42-, with a typical relation: log(Co(II) ) = K log(SO~- ) +constant with K ranging between 1.6 and 3.2. This relation can be seen as an enhancement of the Co dissolution by way of sulfate corn-
420
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Fig. 1. a. Relationship between Co and SO42- in SO 2--rich waters in the Limousin mine. b. Relationship between Co and SO~- in Vende6 mine waters. c. Relationship between Ni and SO 2- in Vende6 mine waters. d. Relationship between Co and SO~- in geothermal waters.
plexation even if Co 2+ is the major dissolved species o f Co (COSO4° considered as the single sulfate complex). Ni shows no control except in C1--rich waters where it evolves like Co, giving a relation near: l o g ( N i ( I I ) ) = 2 . 3 log(SO 2- ) - 1.2 In these waters, U shows the same behaviour, Cu and Cd are linked to C l - , suggesting
that the formation of chloride complexes enhanced their dissolution. 5. Conclusions These analytical conditions have permitted measurement of solutions containing ~ 1 0 - 9 M Ni and ~ 10-,o M C o in a reliable manner. This first approach shows the importance of complex formation in the solubility o f trace
l
t
BEHAVIOUR OF Ni AND Co IN NATURAL WATERS OF GRANITIC AREAS
metals in natural granitic fresh waters. Nowadays thermodynamic data are lacking so it is difficult to explain more accurately these results. Laboratory experiments must be done to fulfil this study, by separating each influencing parameter. References Balistrieri, L.S., Murray, J.W. and Paul, B., 1992. The biogeochemical cycling of trace metals in the water column of Lake Sammamish, Washington: Response to seasonally anoxic conditions. Limnol. Oceanogr., 37(3): 529-548.
421 Pihlar, B., Valenta, P. and NiJrnberg, H.W., 1981. New high-performance analytical procedure for the voltammetric determination of nickel in routine analysis of waters, biological materials and food. Fresenius Z. Anal. Chem., 307: 337-346. Sarazin, G. and Devaux J., 1991. Diag6n6se prdcoce de la mati~re organique dans la colonne d'eau et le sddimenl d'un lac eutrophe: le lac d'Aydat (Puy-de-D6me). Oc6anis, 17(5): 533-560. Zhang, H., Wollast, R., Vire, J.-C. and Patriarche, G.J., 1989. Simultaneous determination of cobalt and nickel in sea water by adsorptive cathodic stripping squarewave voltammetry. Analyst (London), 114: 15971602.
417
Behaviour of nickel and cobalt in natural waters of granitic areas: a first approach N. Gassama a, G. Michard a, C. Beaucaireb and G. Sarazin a aLaboratoire de Gbochimie des Eaux, Universitb de Paris 7, Paris, France bLCASH, CEN de Fontenay aux Roses, Fontenay aux Roses, France
(Received March 17, 1993: revised and accepted March 30, 1993 )
A square-wave voltammetry method based upon the enhancement of Ni and Co adsorption onto a mercury drop electrode by complexation has been used to measure concentrations in natural fresh waters from granitic areas. This method permits determination of 10 - 9 M N i and 10 -1° M C o in a reliable manner. Waters of various saturation indices were collected. Results show that complex formation is the main process which controls the solubility of trace metals. Trace metal complexation is affected by the relative amounts of anions and the redox state of waters.
1. Introduction Behaviour of trace metals in natural waters is of fundamental and environmental interest. Occurring at trace levels in natural conditions, they can be introduced by industrial wastes. So it is important to know their behaviour to quantify and predict the effects of these contributions. On account of the very low amounts of nickel and cobalt in natural fresh waters, there is a lack of knowledge about their concentrations. Graphite-furnace atomic absorption spectrometry (GFAAS) and classic polarographic methods are not sensitive enough to allow precise measurements and therefore need preconcentration steps which increase the contamination risk of the sample. Zhang et al.
(1989) have proposed a square-wave voltammetric method to perform these analyses. It is a reliable technique, faster than differentialpulse voltammetry, and has better sensitivity. As defined by Pihlar et al. (1981), they used dimethylglyoxime as a complexing agent to enhance the adsorption of Ni and Co onto a mercury drop electrode. An electrolytic buffer containing triethanolamine (TEA), NH4C1 and ammonia is added. Waters more or less far from water-rock equilibrium were sampled in French granitic areas. Surface waters (springs, rivers, lake), shallow mine waters of various salinity, and geothermal waters have been studied.
2. Sampling Surface waters are from the Margeride granitic plateau (south Massif Central, France). The Aydat Lake is in the middle part of the Massif Central, on the Hercynian basement. Waters from two uranium mines were sampied, one in Limousin (northeast of the Massif Central), the other one in Vend6e (south of the Brittany peninsula). The geothermal waters are from the French Eastern Pyr6n6es. Water samples were filtered using 450 nm pore size filters and acidified with Suprapur ® grade nitric acid to p H = 2 . They were stored in previously washed polycarbonate or poly-
418
ethylene bottles. Cleanness tests were carried out upon bottles, after storage of a standard solution over increasing times. No tests were made for the filtration step. Results show that polycarbonate and polyethylene bottles do not modify significantly the Ni or Co content of the water, even after two months. Surface water samples were UV-irradiated to prevent dissolved organic matter complexation or redox reaction which can interfere with the electrochemical analysis.
3. Analytical method Previously developed for seawater analysis, this method has been modified for freshwater analysis without difficulties. The supporting electrolyte is used as an ionic strength buffer. All reagents are of Suprapur ® grade except TEA which is of analytical reagent grade. The sample aliquot is weighed into the cell to avoid contamination. The borosilicate polarographic cell contains 10 g of sample, and 0.4 ml and 50/zl of added electrolyte-buffer solution and DMG solution, respectively. The pH is close to 8.0. The adsorption time is 240 s at an adsorption potential of - 0 . 7 0 0 V vs. AgAgC1-KC1 standard electrode. The electrode is a hanging drop used with a medium size mercury drop. Standard addition method has been used. Before measurements a blank was estimated by replacing the sample by deionized water. Protocol analysis consists of measuring a blank then two solutions and so on. The blank is subtracted from the value found for the two following solutions. Each sample was measured three times, and only exceptionally did results differ more than _+ 10%. The detection limit is ~1-10-~1 and 3- 10-~o M for Co and Ni, respectively.
4. Results and discussion We sampled 27 springs and rivers in Mageride. The Co concentrations range from
N. GASSAMA ET AL.
< 1.10 - ~ to 4.47.10 -9 M. The Ni concentrations vary from 7.10 -l° to 7.62-10 -8 M. Ni and Co distributions show no trend, neither with any other element nor with pH. They are mobile cations in such waters. In Aydat Lake, we sampled water column profiles and pore waters in the surficial sediment (from 0 to 52.5 cm depth). The water column was sampled during the time of maximal thermal stratification of the lake. The bottom waters were anoxic because of the oxygen consumption during the organic matter mineralization. The different redox states control the distribution of transition metals like Fe and Mn. As shown by Sarazin and Devaux ( 1991 ) no soluble species of Fe and Mn are present in the oxic waters. They are present as insoluble Fe (III)- and Mn (IV)-oxyhydroxides compounds. In the reduced waters, Fe and Mn concentrations increase from the thermocline to the bottom due to the reduction and dissolution of oxyhydroxide compounds. Ni and Co distributions are not so easy to explain. As traces, they are influenced by local fluctuations more than minor elements. Ni distribution does not roughly vary along the water column profile, and lies around 3.5" 10 -9 M. The Co distribution is quite different. It is almost absent in the upper waters and appears below the thermocline just after Fe and Mn reduction. Its concentration increases till the bottom of the lake to ~3.2-10 -l° M. These results are in good agreement with those presented by Balistrieri et al. (1992) on Lake Sammamish, Washington, U.S.A., only for the Co distribution. The pore water measurements show a Ni amount below the detection limit. Ni should be present in the particulate phase and Co should be concentrated in the dissolved phase. In the studied lake, Co is in the particulate phase in the oxic waters and is removed in the reduced waters. This behaviour can be connected to an adsorption-oxidation reaction taking place at the MnO2 surface. In the surficial sediment, Co remains in the aqueous
419
BEHAVIOUR OF Ni AND Co IN NATURAL WATERS OF GRANITIC AREAS
phase. Ni does not react as a function of the redox state in the water column. In the surficial sediment, it is present in the particulate phase although calculations show that Ni-sulfide or Ni-hydroxide cannot precipitate. In the Limousin mine, the 14 waters sampled at different depths show unequilibrated oxic waters with mean pH around 8.0 and an up-flow temperature around 20°C. The Ni amounts vary from 3" l0 -I° to 2.16- l0 -s M, and the Co amounts from l ' 1 0 -I~ to 4.05-10 -9 M. Two groups of water can be identified using S O ~ - / C 1 - ratio. SO~--rich waters should result from pyrite alteration. They exhibit a log (Co (II) ) vs. log (SO42- ) linear relationship (Fig. 1a) which can be fit by the equation, where R is the correlation coefficient:
l o g ( N i ( I I ) ) = 1.82 l o g ( U ( I V ) ) + 7 . 2 9 ,
log(Co(II) ) =3.03 log(SO~- ) - 1.17,
These results show a different behaviour between Ni-Co and Cu-Cd. The Eastern Pyrenean hot waters are alkaline, reducing and HS--rich. They are equilibrated with rocks at 110°C which is the calculated temperature based upon chalcedony equilibrium. The Ni and Co amounts are very low, close to the limit of detection. Co and SO42- seems to be lightly correlated (Fig. l d), which may be caused by uncertainties due to low level concentrations. We retain the calculated equation:
R=0.843 Ni amounts do not show the same trend. The Vendfe mine waters are quite different. They are C1--rich with amounts ranging from 2.45-10 - 3 to 2.25-10-~ M. They are neutral oxic waters where C1- is the major anion and which are equilibrated with chalcedony at a temperature around 40 ° C. Ni and Co amounts vary from 5- 10- t° to 8.10- 10-7 M a n d 7- 10 -11 to 2.21- 10-7 M, respectively. They show good correlation with each other and l o g ( S O 4 - ) (Fig. lb and c) and l o g ( U ( I V ) ) . The calculated equations are: log(Co(II) ) =0.91 log(Ni(II) ) - 1.96, R=0.947 log(Co(II) ) =3.22 log(SOl- ) +0.38, R=0.907 log(Ni(II) ) = 2.34 log(SOl- ) - 1.16, R=0.899 log(Co(II) ) = 1.78 l o g ( U ( I V ) ) +9.02, R=0.950
R=0.897 Cu and Cd concentrations can be measured by GFAAS in some samples (amounts > 5- 10 - 9 and > 1- 10 -s M of Cd and Cu, respectively). Their concentrations increase with the CI- concentration. With only five points, we find: log(Cu(II) ) =0.33 log(Cl- ) - 7 . 4 6 , R=0.894 log(Cd(II) ) =0.61 log(Cl- ) - 7 . 2 5 , R=0.935 log(Cd(II) ) = 1.21 log(Cu(II) ) + 1.59, R=0.973
log(Co(II) ) = 1.58 log(SO42- ) - 4 . 5 7 , R=0.678 In such waters Ni and Co have different behaviours, but both seem to be reduced by the presence of sulfur. Ni and Co have different behaviours except in C1--rich waters. Since the first evolved stage of water, Co is linked to SO42-, with a typical relation: log(Co(II) ) = K log(SO~- ) +constant with K ranging between 1.6 and 3.2. This relation can be seen as an enhancement of the Co dissolution by way of sulfate corn-
420
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-7.DO
Limousin
ET AL.
u
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Fig. 1. a. Relationship between Co and SO42- in SO 2--rich waters in the Limousin mine. b. Relationship between Co and SO~- in Vende6 mine waters. c. Relationship between Ni and SO 2- in Vende6 mine waters. d. Relationship between Co and SO~- in geothermal waters.
plexation even if Co 2+ is the major dissolved species o f Co (COSO4° considered as the single sulfate complex). Ni shows no control except in C1--rich waters where it evolves like Co, giving a relation near: l o g ( N i ( I I ) ) = 2 . 3 log(SO 2- ) - 1.2 In these waters, U shows the same behaviour, Cu and Cd are linked to C l - , suggesting
that the formation of chloride complexes enhanced their dissolution. 5. Conclusions These analytical conditions have permitted measurement of solutions containing ~ 1 0 - 9 M Ni and ~ 10-,o M C o in a reliable manner. This first approach shows the importance of complex formation in the solubility o f trace
l
t
BEHAVIOUR OF Ni AND Co IN NATURAL WATERS OF GRANITIC AREAS
metals in natural granitic fresh waters. Nowadays thermodynamic data are lacking so it is difficult to explain more accurately these results. Laboratory experiments must be done to fulfil this study, by separating each influencing parameter. References Balistrieri, L.S., Murray, J.W. and Paul, B., 1992. The biogeochemical cycling of trace metals in the water column of Lake Sammamish, Washington: Response to seasonally anoxic conditions. Limnol. Oceanogr., 37(3): 529-548.
421 Pihlar, B., Valenta, P. and NiJrnberg, H.W., 1981. New high-performance analytical procedure for the voltammetric determination of nickel in routine analysis of waters, biological materials and food. Fresenius Z. Anal. Chem., 307: 337-346. Sarazin, G. and Devaux J., 1991. Diag6n6se prdcoce de la mati~re organique dans la colonne d'eau et le sddimenl d'un lac eutrophe: le lac d'Aydat (Puy-de-D6me). Oc6anis, 17(5): 533-560. Zhang, H., Wollast, R., Vire, J.-C. and Patriarche, G.J., 1989. Simultaneous determination of cobalt and nickel in sea water by adsorptive cathodic stripping squarewave voltammetry. Analyst (London), 114: 15971602.