CHAPTER 8 . Speciation of Metals in Natural Waters
213
where the subscript T is used to denote the total analytical concentrations. The values
of [M'] and [1'] are related to the free metal and ligand by:
[M'] = [Mn+] + IMXj
(8.31)
[1'] = [L n -] + INjL
(8.32 )
where Xj are the inorganic ligands (OH-, CO~-, etc.) that complex the metal and Nj are
the cations that can complex the ligand (Mgz+, Ca z +, and other trace metals). Because
natural organic ligands cannot normally be studied in simple solutions, it is not possible to determine the free ligand concentrations [L n-], and the values of [1'] are normally reported. The concentration of the free metal not complexed to inorganic ligands
can be determined by the methods discussed above:
[Mn+] = [M'] aM
(8·33)
where aM is the fraction of free metal in the solution without the organic ligand determined from:
aM = 1/ (1 + IKMX;[X];)
(8.34)
To examine the competition between organic and inorganic ligands, it is more appropriate to use the stability constant defined in terms of the free metal:
KML = [ML] / [Mn+][1']
(8·35)
The free metal concentration in the solution with the organic ligand can be determined from:
[Mn+] = [Mlr~
(8·36)
where
£4 = 1/ (1 + IKMX;lXl; + KMd1'])
(8·37)
Because the concentrations of the inorganic ligands are normally much higher than
that of the organic ligands, one can use the fraction of free metals determined in sea
water without organics to make a reasonable estimate of the value from:
KML"'KML£4.
(8.38)
The values of £4, the fraction of free metal in sea water, with various concentrations of inorganic and organic ligands can be estimated from Eq. 8.37. For the organic
complexes to dominate the speciation of a metal KMd1'] > IKMX; [XL. This can occur when
KML or [1'] is large. In more simple terms, if the value of [1'] > 1 / KML or KML > 1/ [1'], or-
213
where the subscript T is used to denote the total analytical concentrations. The values
of [M'] and [1'] are related to the free metal and ligand by:
[M'] = [Mn+] + IMXj
(8.31)
[1'] = [L n -] + INjL
(8.32 )
where Xj are the inorganic ligands (OH-, CO~-, etc.) that complex the metal and Nj are
the cations that can complex the ligand (Mgz+, Ca z +, and other trace metals). Because
natural organic ligands cannot normally be studied in simple solutions, it is not possible to determine the free ligand concentrations [L n-], and the values of [1'] are normally reported. The concentration of the free metal not complexed to inorganic ligands
can be determined by the methods discussed above:
[Mn+] = [M'] aM
(8·33)
where aM is the fraction of free metal in the solution without the organic ligand determined from:
aM = 1/ (1 + IKMX;[X];)
(8.34)
To examine the competition between organic and inorganic ligands, it is more appropriate to use the stability constant defined in terms of the free metal:
KML = [ML] / [Mn+][1']
(8·35)
The free metal concentration in the solution with the organic ligand can be determined from:
[Mn+] = [Mlr~
(8·36)
where
£4 = 1/ (1 + IKMX;lXl; + KMd1'])
(8·37)
Because the concentrations of the inorganic ligands are normally much higher than
that of the organic ligands, one can use the fraction of free metals determined in sea
water without organics to make a reasonable estimate of the value from:
KML"'KML£4.
(8.38)
The values of £4, the fraction of free metal in sea water, with various concentrations of inorganic and organic ligands can be estimated from Eq. 8.37. For the organic
complexes to dominate the speciation of a metal KMd1'] > IKMX; [XL. This can occur when
KML or [1'] is large. In more simple terms, if the value of [1'] > 1 / KML or KML > 1/ [1'], or-