Engineering properties of peat and organic soils - Geotechnics of Organic Soils and Peat - page 65

Figure 3.15 Zeta potential vs. pH ( after Asadi et al ., 2009d).
Figure 3.16 pH at iso-electric point of peat in comparison with some minerals ( after Asadi et al ., 2009d).
At a certain pH, the soil surface charge could drop to zero, rendering a zero ζ ,or
what is called the iso-electric point (Lorenz, 1969). The peat surface charge drops to
zero ζ at pH 2.5 to 3.5 (Figure 3.15).
Figure 3.16 shows the values of the iso-electric point of some minerals in compari-
son with peats from this study (Mohamed and Anita, 1998). Since all charge in humus
is strongly pH-dependent, the sensitivity of organic soils to pH changes is greater than
that of mineral soils. Despite this high sensitivity, the iso-electric point of organic soils
is less than that of amorphous iron, gibbsite and kaolinite.