CHAPTER 8 . Speciation of Metals in Natural Waters
211
8.7
Formation of Metal Organic Complexes
When one examines the solubility of Fe(lII) in natural waters (Liu and Millero 1999,
2002) one finds that the solubility in S = 35 sea water (200 pM) is much greater than
in 0.7 m NaCI (10 pM) at a pH near 8 (Fig. 8.15). Since measurements made in the major
sea salts and artificial sea water (I = 0.7 m) are similar to the values in NaCI (Fig. 8.16),
one can attribute this to the effect of organic ligands (L) increasing the solubility due
to the formation of Fe3+ complexes (FeL) (Liu and Millero 2002). The dilution of sea
water with NaCI (Fig. 8.17) and the UV irradiation of sea water yield solubilities equal
Fig. 8.15. Comparison of the
2
solubility of Fe(III) in 0.7 M
0
o NaCI
NaCI and sea water (S = 35) at
25°C
' 2.
•
Seawater
4
6
~
~ I
'-CL
0 8
8' 8
T
.... I
e
lOr
'0-"
«(roo
"I
0
2
4
6
8
10
12
14
pH
Fig. 8.16. The solubility of
11.6
Fe(III) in the major sea salts
and artificial sea water at
11.4 1
pH=8.1
1= 0.7 m, 25°C and pH = 8
11.2
~ 11.0
,g.
~ 10.8
~ 10.6
10.4
10.2
10.0
NaCi
Ca
Mg
S04
F
ASW