Environmental Engineering Reference
In-Depth Information
FIGURE 11.3
Concentration of Dissolved Metals as a Function
of pH Value
10
2
Pb(OH)
10
1
Zn(OH)
2
Metal hydroxides are generally more soluble
than metal sulphide, and they are amphoteric: a
metal hydroxide has one pH at which its solubil-
ity is at a minimum
10
0
Ag(OH)
10
1
Cu(OH)
2
10
2
Cd(OH)
2
10
3
10
4
Covelite (CuS)
10
5
10
6
Sphalerite (ZnS)
Grenochite (CdS)
10
7
Galena (PbS)
10
8
10
9
10
10
10
11
10
12
Argentite (Ag
2
S)
10
13
2
3
4
5
6
7
8
9
10
11
12
13
14
pH
Metal Hydroxide
Metal Sulphide
Stephens and Ahern 2001). It should also be noted that some combinations of metals act
antagonistically or even synergistically in solution: e.g. nickel and zinc, copper and zinc,
and copper and cadmium in combination are more toxic than their individual toxicities
would suggest (Down and Stocks 1977). The most prominent metals in the context of an
environmental impact study of a metal mine are discussed in the following section.
Some combinations of metals
act antagonistically or even
synergistically in solution.
11.2 SOME NOTES ON SELECTED METALS
By the eighteenth century 12 metals had been discovered, which doubled to 24 in the fol-
lowing century. Today there are 86 known metals, of which the 7 metals of the antiquity
are the metals on which civilization was based (although not classed as elements at that
time): gold (5000BC), copper (4300BC), silver (4000BC), lead (3500BC), tin (1800-1600BC),
iron (1400BC), and mercury (750BC) (Ball 2002). After the Renaissance the seven known
metals at that time became linked with the seven known celestial bodies and the seven
days of the week (
Figure 11.4
)
.
By the eighteenth century 12
metals had been discovered,
which doubled to 24 in the
following century.
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