CHAPTER 8 . Speciation of Metals in Natural Waters
217
S.S
Future ofthe Model
The present model provides reliable activity coefficients for a number of cations and
anions from 0 to 50°C. It can also be used to determine the speciation of divalent and
trivalent metals in natural waters. The effect of the addition of organic ligands with a
known or estimated stability constant can also be examined. The model has been
shown to be reliable for the major components of natural waters, but little data is available to examine the speciation of metals in natural waters. Solubility measurements
of trace metal oxides and carbonates in sea water as a function of pH would be useful
in testing the reliability of the model. New measurements of the stability constants
for the complexation of OH-, CO~-, etc. with divalent and trivalent metals in NaCI solutions over a wide range of temperature (0 to 50°C) and ionic strength (0 to 6 m) are
needed to derive more reliable Pitzer coefficients for trace metal ion pairs. Extensions
of the model for the minor anions of natural waters at the present time are difficult
due to the lack of reliable activity coefficient data for Na +, K+, Mg2+ and Ca 2 + salts over
a wide range of temperatures. The carbonic acid pK measurements of He and Morse
(1993) can be used to extend the carbonate model to 100°C. More measurements of
this kind are needed to extend the model to higher temperatures for other acids and
trace metal ion pairs.
Acknowledgements
The authors would like to acknowledge the support of the Oceanographic Section of
the National Science Foundation for supporting our marine physical chemistry work.
References
Anderson MA, Morel FM (1982) The influence of aqueous iron chemistry on the uptake of iron by the
coastal diatom Thalassiosira weissflogii. Limnol Oceanogr 27:789-813
Baes CF, Mesmer RE (1976) The hydrolysis of cations. John Wiley and Sons, New York
Berg CMG van den (1982) Determination of copper complexation with natural organic ligands in seawater
by equilibration with MnOz. II. Experimental procedures and application to surface seawater. Mar
Chern 11:323-342
Berg CMG van den (1984) Determination of the complexing capacity and conditional stability constants
of complexes of copper(Il) with natural organic ligands in seawater by cathodic stripping
voltammetry of copper-catechol complexions. Mar Chern 15:1268-1274
Berg CMG van den (1995) Evidence for organic complexation of iron in seawater. Mar Chern 50:139-157
Breeman N van (1973) Calculation of activity coefficients in natural waters. Geochim Cosmochim Acta
37:101-107
Bruland KW (1989) Complexation of zinc by natural organic ligands in the central North Pacific. Limnol
Oceanogr 34:269-285
Bruland KW (1992) Complexation of cadmium by natural organic ligands in the central North Pacific.
Limnol Oceanogr 37:1008-1017
Byrne RH Jr, Kester DR (1974) Inorganic speciation of boron in seawater. J Mar Res 32:119-127
Byrne RH, Kester DR (1976) Solubility of hydrous ferric oxide and iron speciation in seawater. Mar Chern
4:255-274
Byrne RH, Luo Y-R (2000) Direct observations of nonintegral hydrous ferric oxide solubility products:
K*so= [Fe H ][H+r Z . 86 • Geochim Cosmochim Acta 64:1873-1877
Campbell DM, Millero FJ, Roy R, Roy L, Lawson M, Vogel KM, Moore CP (1993) The standard potential
for the hydrogen - silver, silver chloride electrode in synthetic seawater. Mar Chern 44:221-233
Clegg SL, Whitfield M (1991) Activity coefficients in natural waters. In: Pitzer KS (ed) Activity coefficients in electrolyte solutions. CRS, Boca Raton, FL, pp 279-434
217
S.S
Future ofthe Model
The present model provides reliable activity coefficients for a number of cations and
anions from 0 to 50°C. It can also be used to determine the speciation of divalent and
trivalent metals in natural waters. The effect of the addition of organic ligands with a
known or estimated stability constant can also be examined. The model has been
shown to be reliable for the major components of natural waters, but little data is available to examine the speciation of metals in natural waters. Solubility measurements
of trace metal oxides and carbonates in sea water as a function of pH would be useful
in testing the reliability of the model. New measurements of the stability constants
for the complexation of OH-, CO~-, etc. with divalent and trivalent metals in NaCI solutions over a wide range of temperature (0 to 50°C) and ionic strength (0 to 6 m) are
needed to derive more reliable Pitzer coefficients for trace metal ion pairs. Extensions
of the model for the minor anions of natural waters at the present time are difficult
due to the lack of reliable activity coefficient data for Na +, K+, Mg2+ and Ca 2 + salts over
a wide range of temperatures. The carbonic acid pK measurements of He and Morse
(1993) can be used to extend the carbonate model to 100°C. More measurements of
this kind are needed to extend the model to higher temperatures for other acids and
trace metal ion pairs.
Acknowledgements
The authors would like to acknowledge the support of the Oceanographic Section of
the National Science Foundation for supporting our marine physical chemistry work.
References
Anderson MA, Morel FM (1982) The influence of aqueous iron chemistry on the uptake of iron by the
coastal diatom Thalassiosira weissflogii. Limnol Oceanogr 27:789-813
Baes CF, Mesmer RE (1976) The hydrolysis of cations. John Wiley and Sons, New York
Berg CMG van den (1982) Determination of copper complexation with natural organic ligands in seawater
by equilibration with MnOz. II. Experimental procedures and application to surface seawater. Mar
Chern 11:323-342
Berg CMG van den (1984) Determination of the complexing capacity and conditional stability constants
of complexes of copper(Il) with natural organic ligands in seawater by cathodic stripping
voltammetry of copper-catechol complexions. Mar Chern 15:1268-1274
Berg CMG van den (1995) Evidence for organic complexation of iron in seawater. Mar Chern 50:139-157
Breeman N van (1973) Calculation of activity coefficients in natural waters. Geochim Cosmochim Acta
37:101-107
Bruland KW (1989) Complexation of zinc by natural organic ligands in the central North Pacific. Limnol
Oceanogr 34:269-285
Bruland KW (1992) Complexation of cadmium by natural organic ligands in the central North Pacific.
Limnol Oceanogr 37:1008-1017
Byrne RH Jr, Kester DR (1974) Inorganic speciation of boron in seawater. J Mar Res 32:119-127
Byrne RH, Kester DR (1976) Solubility of hydrous ferric oxide and iron speciation in seawater. Mar Chern
4:255-274
Byrne RH, Luo Y-R (2000) Direct observations of nonintegral hydrous ferric oxide solubility products:
K*so= [Fe H ][H+r Z . 86 • Geochim Cosmochim Acta 64:1873-1877
Campbell DM, Millero FJ, Roy R, Roy L, Lawson M, Vogel KM, Moore CP (1993) The standard potential
for the hydrogen - silver, silver chloride electrode in synthetic seawater. Mar Chern 44:221-233
Clegg SL, Whitfield M (1991) Activity coefficients in natural waters. In: Pitzer KS (ed) Activity coefficients in electrolyte solutions. CRS, Boca Raton, FL, pp 279-434