Geoscience Reference
In-Depth Information
Table 3.9
Zeta Potential of highly decomposed peat (
after
Asadi, 2010).
Hydrated
Cation
Concentration
Zeta potential
Cation
radius (nm)
valence
mol L
−
1
pH
(mV)
Na
0.36
1
1.00E-02
3.1
−
10.1
1.00E-03
3.08
−
11
1.00E-03
6.9
−
21.2
1.00E-04
3.08
−
12.3
1.00E-04
11.2
−
32.37
Ca
0.41
2
1.00E-02
3.32
−
3
1.00E-02
4.4
−
7.1
1.00E-02
10.89
−
19.1
1.00E-03
3.16
−
4.1
1.00E-04
9.78
−
19.6
Al
0.48
3
1.00E-03
5.04
−
1.5
1.00E-04
7.4
−
9.3
1.00E-04
9.63
−
21.2
The zeta potential of the highly decomposed peat is higher than that of very slightly
decomposed peat, indicating that the higher degree of peat humification results a higher
zeta potential. The same conclusions are found in the presence of K
+
,Mg
2
+
,Ca
2
+
and
Al
3
+
, indicating that the higher concentration of ions results in a zeta potential, and
that higher pH results in a higher zeta potential.
The zeta potential of peat in the presence of Al
3
+
at the same concentration and
pH is lower than the zeta potential of peat in the presence of Na
+
, indicating that the
higher the valence of the cation the lower the zeta potential. However, since variations
in peat arise from the variety of plants whose residues contribute to peat formation
and from the environmental conditions in which humification takes place, the degree
of humification can affect the zeta potential. As a result of those variations, a higher
degree of humification results in a higher zeta potential (Asadi, 2010; Asadi and Huat,
2010).
The simple alkali metal ions, such as Na
+
and K
+
, are known as indifferent ions
(Hunter, 1993). These ions are attracted to a charged surface by simple electrostatic
forces. The Na
+
and K
+
ions can accumulate as counter ions in the electrical double
layer. Consequently, they compress the electrical double layer and change the mag-
nitude of the zeta potential. However, they could also lower the surface potential by
charge neutralization, reducing the zeta potential.
The effect of ion concentration in decreasing the thickness of the diffuse layer
could be higher than the valence effect according to the formula of Usui (1984):
1
κ
=
3
ZC
1
/
2
(3.11)
where
1
κ
=
Thickness of the diffuse layer (Å)
Z
=
Valence of ion
Concentration of ion (mol L
−
1
)
C
=
