121
Minor Elements in Seawater
the equilibrium between kaolinite and montmorillonite in a five- component system with
Na + , we have
1.5 Al 2 Si 2 O 5 (OH) 4 (s) + Na + → NaAl 3 Si 3 O 10 (OH) 2 (s) + 1.5 H 2 O + H +
(3.12)
Kaolinite
Montmorillonite
The ratio of H + /Na + is also near the ratio in seawater. Since fresh clays are transformed in a
day or two, forming new phases in a couple of years, most workers have found the silicate
theory to be reasonable. Recent workers have also demonstrated that SiO 2 dissolves more
rapidly in seawater than was once thought. Sillén also considered a more complicated
nine- component system:
1. Seawater
2. SiO 2 (quartz)
3. CaCO 3 (calcite)
4. Kaolinite
5. Illite
6. Chlorite
7. Montmorillonite
8. Phillipsite
9. Atmosphere
log (-K SO MOH)
0
5
10
15
20
25
30
log (EC
50 )
–9
–8
–7
–6
–5
–4
–3
–2
–1
0
Hg
Cu
Pb
Zn
Co
Mn
Cd
Ca
Mg
Figure 3.30
The effective concentration of metal that reduces phytoplankton growth rate by 50% (EC 50 ) plotted versus the
solubility of metal hydroxide. (From Fisher, N.S., Limnol. Oceanogr., 3, 443, 1986. With permission.)