Because of the high concern of lead(II) in the environment, its speciation had been largely investigated in the past years. Different ligands of lead(II) can be present in natural waters ranging from inorganic anions, often at high concentration (chloride, carbonate) with side reaction coefficient around 30 (1), to very strong complexing sites present in NOM (natural organic matter). Side reaction coefficients of lead(II) slightly higher than those for inorganic ligands have been reported for humic substances (2). These sites are at low concentration but display a high complexation strength. Consequently they will be the first to take up the metal, while the weaker sites contribute to complexation only at higher total metal concentrations. Stronger lead(II) ligands have been detected in natural waters using a method with detection window much higher than the usual ones, based on the partition of the metal ion on complexing resins (3). Side reaction coefficients as high as about 106 were evaluated in natural waters. A similar method (4) was here used to determine the complexing properties for lead(II) of a fulvic acid extracted from a sediment (FA), at low concentration, 10-500 nM. It is based on the sorption of lead(II) on the ionexchange complexing resins Chelex 100 and Amberlite CG 50. In the FA at pH around neutrality strong complexation sites of lead(II) were detected, with concentration 2 10-3 mmol g-1-0.04 mmol g-1 similar to that determined by other methods (2), but conditional complexation constant as high as log K=13-15, much higher than that previously obtained, but similar to those found in natural waters (3). These sites heavily determine the lead(II) complexation since the metal in natural waters is present at nM level. A large influence of the solution pH on the complexing properties of the strong ligands has been found. On the other hand, using an ion exchange resin (Dowex 50W-X8) with lower detection window, lead(II) ligands with lower side reaction coefficient, near to that determined in previous investigations (2), were detected. (1) D. Turner, M. Whitfield, A.G. Dickson, Geochim. Cosmochim. Acta, 45 (1981) 855-874. (2) M. Filella, R.M. Town, Sci. Tot. Environ. 300 (2002) 143–154. (3) G. Alberti, R. Biesuz, M. Pesavento, Anal. Sci. 24 (2008) 1605-1611. (4) M. Pesavento, A. Profumo, R. Biesuz, G. Alberti, Solv. Extr.Ion Exch. 26 (2008) 301-320. (5) R. Biesuz, G. Alberti, M. Pesavento, J. Sol. Chem. 37 (2008) 527–541.
Strong complexation of lead(II) by fulvic substances under environmental relevant conditions
PESAVENTO, MARIA;ALBERTI, GIANCARLA;BIESUZ, RAFFAELA;
2012-01-01
Abstract
Because of the high concern of lead(II) in the environment, its speciation had been largely investigated in the past years. Different ligands of lead(II) can be present in natural waters ranging from inorganic anions, often at high concentration (chloride, carbonate) with side reaction coefficient around 30 (1), to very strong complexing sites present in NOM (natural organic matter). Side reaction coefficients of lead(II) slightly higher than those for inorganic ligands have been reported for humic substances (2). These sites are at low concentration but display a high complexation strength. Consequently they will be the first to take up the metal, while the weaker sites contribute to complexation only at higher total metal concentrations. Stronger lead(II) ligands have been detected in natural waters using a method with detection window much higher than the usual ones, based on the partition of the metal ion on complexing resins (3). Side reaction coefficients as high as about 106 were evaluated in natural waters. A similar method (4) was here used to determine the complexing properties for lead(II) of a fulvic acid extracted from a sediment (FA), at low concentration, 10-500 nM. It is based on the sorption of lead(II) on the ionexchange complexing resins Chelex 100 and Amberlite CG 50. In the FA at pH around neutrality strong complexation sites of lead(II) were detected, with concentration 2 10-3 mmol g-1-0.04 mmol g-1 similar to that determined by other methods (2), but conditional complexation constant as high as log K=13-15, much higher than that previously obtained, but similar to those found in natural waters (3). These sites heavily determine the lead(II) complexation since the metal in natural waters is present at nM level. A large influence of the solution pH on the complexing properties of the strong ligands has been found. On the other hand, using an ion exchange resin (Dowex 50W-X8) with lower detection window, lead(II) ligands with lower side reaction coefficient, near to that determined in previous investigations (2), were detected. (1) D. Turner, M. Whitfield, A.G. Dickson, Geochim. Cosmochim. Acta, 45 (1981) 855-874. (2) M. Filella, R.M. Town, Sci. Tot. Environ. 300 (2002) 143–154. (3) G. Alberti, R. Biesuz, M. Pesavento, Anal. Sci. 24 (2008) 1605-1611. (4) M. Pesavento, A. Profumo, R. Biesuz, G. Alberti, Solv. Extr.Ion Exch. 26 (2008) 301-320. (5) R. Biesuz, G. Alberti, M. Pesavento, J. Sol. Chem. 37 (2008) 527–541.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
