Chemistry Reference
In-Depth Information
adsorption maximum for the adsorbent, and
K
is the estimated affinity parameter
for the adsorbent that reflects the bond strength involved in adsorption (Newman
1995). Numerous examples show that adsorption differences can be related to coor-
dination chemistry metrics. The
K
values for a series of class (a) metals adsorbing to
Spirogyra
sp. (Crist et al. 1988) were correlated with polarizing power,
Z
2
r
−1
, of the
metals where
Z
is the ion charge and
r
is the ion radius (Figure 1.1 top panel). The
Z
2
r
−1
metric quantifies the energy of the ion during electrostatic interaction with a
ligand. The general conclusion from Crist et al.'s (1988) metal-algal sorption study
was that the affinity parameter (
K
) was dictated by charge density if adsorption
involved strong metal-ligand bonds, but by energy of hydration if weak metal-
ligand bonds were involved. Similarly, maxima for adsorption of a series of class
(a), intermediate, and class (b) metals to
Saccharomyces cerevisiae
(Chen and Wang
2007) increased as the χ
2
r
of the metal ion increased (Figure 1.1 bottom panel). (χ is
electronegativity and
r
is the ion radius.) The χ
2
r
metric reflects the relative degree of
covalent versus electrostatic nature of bonds during metal interaction with a ligand
(Newman et al. 1998). Similar studies include those exploring simple or competitive
metal adsorption to other microalgae (Crist et al. 1992; Xue et al. 1988), brown mac-
roalgae (Raize et al. 2004), and bacteria (Can and Jianlong 2007; Zamil et al. 2009).
6000
C
a
2+
5000
Mg
2+
4000
N
a
+
Ba
2+
3000
K
+
Sr
2+
2000
Li
+
C
s
+
1000
0
0
2
4
6
Z
2
r
-1
0.5
A
g
+
Pb
2+
0.4
C
r
3+
Zn
2+
C
u
2+
Cd
2+
Co
2+
Ni
2+
0.3
0.2
Sr
2+
0.1
Cs
+
0
0
2
4
6
8
2
r
FIGURE 1.1
Trends in adsorption metrics as a function of coordination chemistry for alkali
and alkali earth (class [a]) metals and the alga,
Spirogyra
sp. (top panel), and a series of class
(a), intermediate, and class (b) metals and the bacterium,
Saccharomyces cerevisiae
(bottom
panel). The units of K in the top panel are M
-1
from an algal suspension with 0.5 × 10
−3
to
0.1 × 10
−1
M of dissolved metal.
