3.1 The Variation of Current and Calculated Resistance
The EK process involves the construction of an electrical field within
the salty soil and leads to the generation of electrical potential,
which caused the movement and the migration of ionic species and induces
the changing of electrical current (Kim et al., 2011). Meanwhile, soil
resistivity is a comprehensive characterization of soil physical
properties, which is correlated with soil salinity, moisture, porosity,
saturation, permeability coefficient, etc. (Beck et al., 2011; Chang &
Cheng, 2007). Therefore, the resistance of soil columns (R) were
calculated in this study by Ohm ’s Law (R=U/I) to reflect the changing
of soil salinity.
The calculated resistances across the salty soil column as a function of
the duration of the treatment under different applied voltages as the
water level raised gradually are shown in Fig. 2. The variations of the
electrical current across the column are shown in Fig. S1. Results
indicated that the electrical current in all columns were increased to
the maximum value of 27 mA, 68 mA and 114 mA in the first few days with
the voltage at 4 V, 10 V and 20 V, respectively. Then declined sharply
and kept at the range of 8-26 mA, 20-34 mA, 13-38 mA, respectively. The
final electrical current in the soil with the voltage at 4V, 10V and 20V
were 14 mA, 20 mA and 16 mA, respectively, and showed in the order of 10
V > 20 V >4 V. Similarly, the calculated
resistances of soil were reduced to the minimum value at 137 Ω, 135 Ω
and 164 Ω after few days under the application of voltage at 4 V, 10 V
and 20 V, respectively, then showed a slow increasing trend. The final
calculated resistances of soil with the voltage at 4 V, 10 V and 20 V
were 266 Ω, 487 Ω and 1272 Ω, respectively, and showed in the order of
20V> 10V> 4V.
The similar trends have been observed in previous studies (Klouche et
al., 2020; Bessaim et al., 2019). As capillary water gradually raised,
the electric gradient was established. Simultaneously, desorption and
mobilization of ions from soil generate the liberation of free charged
ionic species, result reduction of the salty soil column resistance and
therefore raising the current intensity (Cameselle and Reddy 2012; Wu et
al. 2015). Moreover, the generations of hydrogen and hydroxide ions
during the pore fluid water by electrolysis may also another reason for
the above phenomenon in the first few days (Bahemmat et al. 2015). The
specific process included the charged ions in the soil media moved
towards the electrode of opposite charge by electromigration and the
pore water moved towards the cathode by electro-osmosis (Bahemmat et
al., 2015; Li et al., 2014). Since water is the necessary medium for the
movement of ions, soil moisture plays a very important role in V-EK
process, a low degree of soil moisture increases the electrical
resistance of the soil. The final soil moisture at different conditions
were shown in Fig. S2. High resistance of soil reduces the efficiency of
the process drastically, thus reduces the EK effects and most of the
charged energy will be lost as heat (Fahadani et al., 2018). The
resistance of soil with voltage at 20 V is about three times than that
of soil with voltage at 10 V. It proves that why maximum electrical
current was observed in soil with voltage at 10 V.