CHAPTER 9 • Binding Ability of Inorganic Major Components of Sea Water
243
phospholipids, phosphonucleotides) as a consequence of enzymatic hydrolytic processes. Thus, the study of phosphorus compounds in sea water is mainly concerned
with the chemical behaviour of the phosphate group. A comprehensive picture of the
distribution of the different forms of phosphorus in sea water was drawn up by
Armstrong (1965). Although there is no evidence of the presence of dissolved
polyphosphates in sea water slowly leading to the formation of phosphate groups as a
result of hydrolytic processes, it is well-known that phosphoric acid can undergo condensation to form poly-acids such as pyrophosphoric acid or poly-meta-phosphoric
anions, (HP0 3 )n> with n = 3 up to 70 per chain. Polyphosphates can also be present in
coastal sea waters containing sewage and industrial wastes. Therefore, these compounds too must be taken into account in chemical speciation studies of phosphorus
compounds in sea water. Studies of the solution chemistry of the phosphate group in
natural waters are complicated by interactions with macro constituent cations such as
ci+ and Mg2+, which, under certain pH and free concentration conditions, can lead
to the formation of insoluble species.
The speciation of phosphate in sea water has been investigated by few authors
(Kester and Pytkowicz 1967; Atlas et al. 1976; Dickson and Riley 1979; Johansson
and Wedborg 1979). The shift in the apparent protonation constants of phosphoric
acid with changes in the composition of the ionic medium (containing macrocomponents of sea water, Na +, Mg2+ and Ca 2 +) was interpreted by the aut110rs in terms
of the association of orthophosphate with medium cations using ion association
models. Hershey et al. (1989) studied the ion pairing of phosphate with Mg2+ and
evaluated Pitzer interaction parameters for the major components of sea water.
Table A9.6 ~f the appendix (Sect. A9.2) shows apparent protonation constants, 10gfJj w,
for p;ogtlb in SSWE. For purposes of comparison, speciation diagrams for different
forms of phosphate ligand in SSWE (S = 35) and in NaCl (0.75 mol rl) are shown in
Fig. 9.11.
As can be seen, curves for the different protonated species in SSWE have
shifted significantly to lower pH values in comparison with those in the NaCI
medium. The lowering effect on 10gf3t can be simply explained by takin&. into account the formation of simple and mixed protonated B 1.1 17+ - p;ogtl1) species
(Table 9.14).
The speciation diagrams obtained by also including species formation as a result
of the interaction of phosphate ligands with the sea water cation (B) are shown in
Fig. 9.12.
9.3.3
Metals and Organometallic Compounds
9.3.3.1
Divalent Metal Ions
Trace metals interact significantly with both SO~- and cr. Many divalent cations, such
as Mn 2 +, Fe 2 +, C0 2 +, etc., form ion pairs witl1 SO~- (K = 400 m- 1 ) and witl1 cr (K= 1 M- 1 ).
The ion pairs CdCI+ and CdCI~, whose stability is much higher, constitute an exception. Moreover, most divalent and trivalent cations undergo strong hydrolysis and often hydrolytic species are very important at the pH value of sea water. To give an ex-
243
phospholipids, phosphonucleotides) as a consequence of enzymatic hydrolytic processes. Thus, the study of phosphorus compounds in sea water is mainly concerned
with the chemical behaviour of the phosphate group. A comprehensive picture of the
distribution of the different forms of phosphorus in sea water was drawn up by
Armstrong (1965). Although there is no evidence of the presence of dissolved
polyphosphates in sea water slowly leading to the formation of phosphate groups as a
result of hydrolytic processes, it is well-known that phosphoric acid can undergo condensation to form poly-acids such as pyrophosphoric acid or poly-meta-phosphoric
anions, (HP0 3 )n> with n = 3 up to 70 per chain. Polyphosphates can also be present in
coastal sea waters containing sewage and industrial wastes. Therefore, these compounds too must be taken into account in chemical speciation studies of phosphorus
compounds in sea water. Studies of the solution chemistry of the phosphate group in
natural waters are complicated by interactions with macro constituent cations such as
ci+ and Mg2+, which, under certain pH and free concentration conditions, can lead
to the formation of insoluble species.
The speciation of phosphate in sea water has been investigated by few authors
(Kester and Pytkowicz 1967; Atlas et al. 1976; Dickson and Riley 1979; Johansson
and Wedborg 1979). The shift in the apparent protonation constants of phosphoric
acid with changes in the composition of the ionic medium (containing macrocomponents of sea water, Na +, Mg2+ and Ca 2 +) was interpreted by the aut110rs in terms
of the association of orthophosphate with medium cations using ion association
models. Hershey et al. (1989) studied the ion pairing of phosphate with Mg2+ and
evaluated Pitzer interaction parameters for the major components of sea water.
Table A9.6 ~f the appendix (Sect. A9.2) shows apparent protonation constants, 10gfJj w,
for p;ogtlb in SSWE. For purposes of comparison, speciation diagrams for different
forms of phosphate ligand in SSWE (S = 35) and in NaCl (0.75 mol rl) are shown in
Fig. 9.11.
As can be seen, curves for the different protonated species in SSWE have
shifted significantly to lower pH values in comparison with those in the NaCI
medium. The lowering effect on 10gf3t can be simply explained by takin&. into account the formation of simple and mixed protonated B 1.1 17+ - p;ogtl1) species
(Table 9.14).
The speciation diagrams obtained by also including species formation as a result
of the interaction of phosphate ligands with the sea water cation (B) are shown in
Fig. 9.12.
9.3.3
Metals and Organometallic Compounds
9.3.3.1
Divalent Metal Ions
Trace metals interact significantly with both SO~- and cr. Many divalent cations, such
as Mn 2 +, Fe 2 +, C0 2 +, etc., form ion pairs witl1 SO~- (K = 400 m- 1 ) and witl1 cr (K= 1 M- 1 ).
The ion pairs CdCI+ and CdCI~, whose stability is much higher, constitute an exception. Moreover, most divalent and trivalent cations undergo strong hydrolysis and often hydrolytic species are very important at the pH value of sea water. To give an ex-