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Figure 3.17 Zeta potential - von Post degree of peat humification ( after Asadi et al ., 2009d).
The ζ potential of organic and peaty soils increases with increasing humification
(Figure 3.17). The natural ζ ranges of soils with high fibrous content are usually less
than the natural ζ ranges of soils with low fibrous content. Decomposition involves
the loss of organic matter in either gas or solution form through the disappearance of
the physical structure and changes in chemical state. Normally, the higher temperature
of a tropical area would enhance decomposition activity.
The degree of peat humification can influence ζ , as depicted in Figure 3.17. A
higher degree of humification means lower fibrous content and higher pH. Since the
charge peat is strongly pH-dependent, humified peat has a higher ζ with a negative
mathematical sign and more charge than undecomposed peat (Asadi et al ., 2009a).
However, not only are the composition and structure of soil humus complex and incom-
pletely known, but the clay and organic fractions also strongly affect the electrical
properties of organic soils Asadi et al ., 2009e).
Hunter (1981) provides a detailed description of experiments to show the signif-
icance of pH for the ζ of soils. Vane and Zang (1997) showed that pH and ζ vary
depending upon the types of mineral for mineral soils. In peat, ζ is dependent mainly
on organic content, degree of humification and mineral fraction (Asadi et al ., 2009d).
It is noteworthy that with increasing degree of decomposition, the pH at the iso-
electric point decreases (Figure 3.18). The pH ranges at the iso-electric points of soils
with high fibrous content are higher than those for soils with low fibrous content.
The zeta potentials of organic soils and peat are affected by the type of cation,
valence of cations, concentration of cations and pH (Asadi et al. , 2010; Asadi, 2010).
The zeta potential of the peat decrease as the pH or the concentration of cations
increases (Tables 3.8 and 3.9).
The effects of pH on the zeta potential of the peat are in good agreement with
soils that have variable surface charges (Hunter, 1981; Forsberg and Alden, 1988;
Hamed et al ., 1991; West and Stewart 1995; Vane and Zang, 1997; Yu, 1997; Alkan
et al ., 2005; Fang and Daniels, 2006; Yukselen and Erzin 2008). However, in peat
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