Engineering properties of peat and organic soils - Geotechnics of Organic Soils and Peat - page 62

Figure 3.12 CEC vs. von Post degree of peat humification ( after Asadi et al ., 2009d).
pH 7, causing large overestimates of CEC for acidic organic soils. Fibrous peat is low-
humified and undecomposed peat is more acidic. Therefore fibrous peat can show a
lower CEC at the soil pH (Asadi, 2009b).
The CEC ranges of soils with high fibre content are usually less than the CEC
ranges of soils with low fibrous content. Fibric peat is mostly undecomposed, and
low-humified, and has a distinct plant structure. A greater degree of humification
results in a higher CEC (Asadi, 2010).
3.12.2 Zeta potential of organic soils and peat
The ζ (zeta) potential is the electric potential developed at the solid-liquid interface
in response to the movement of colloidal particles; i.e. ζ is the electrical potential at
junction between the fixed and mobile parts of the electrical double layer. ζ is less than
the surface potential of the particles and shows the value at the slip plane, which is
located at a small unknown distance from the colloidal surface (Hunter, 1981; Hunter,
1993). Figure 3.13 shows the zeta potential.
The magnitude and sign of ζ depends on the interfacial chemistry of both liquid
and solid phase (Eykholt and Daniel, 1994). This potential is also influenced by ion
exchange capacity, size of ion radius, and the thickness of the double layer (Fang and
Daniels, 2006).
The concentration of electrolyte, type of electrolyte, valence of ions and pH are
important factors and can affect ζ values.
Since the electroosmotic flow correlates with ζ and pH (Bowen et al. , 1986; Bed-
diar et al. , 2005), it is crucial to know the microscopic electrical properties of the
soil samples. The zeta potential can be determined by electrophoresis (Hunter, 1981;
Hunter, 1993). Soil samples with different organic content can be prepared by sieving