## 3 Results
### Analysis of Current and Potential  
As stated before, the electric field plays a key role in the integration of reduction and remediation. Therefore, the potential and current are analyzed for groups T1, T3, T4, and T6 to understand the changes in the electrical parameters of Cu-contaminated and pollution-free soils and to assess the benefits of their integrated decontamination. Figure 15 presents the change curve of current with time under electro-osmosis and vacuum elect-osmosis tests. All four groups show a trend of rapid decline followed by a slow decline. The current fitting equations are obtained for the four groups of tests based on exponential function-fitting as follows:  
\[\rm T1:\ \ I=0.153\ e^{(-0.017t)}-0.042 \tag{9}\]  
\[\rm  
The fitted R-squares are 0.970, 0.987, 0.983, and 0.993, respectively, indicating that the current shows a significant exponential decay trend. The initial current is larger in the first period, and the initial values for T3 and T6 are 0.34 A and 0.36 A under vacuum electro-osmosis methods. While the initial values for T1 and T4 are 0.12 A and 0.25 A under electro-osmosis method. First, a more significant improvement in the current occurred in the process of vacuum electro-osmosis in comparison to the process of electro-osmosis, which is consistent with the law of drainage. It is demonstrated that for different methods, the improvement of the current brings an intuitive influence on the discharge capacity. Secondly, the initial current in the contaminated soil also increased compared to that in pollution-free, indicating that copper ions enhanced the conductivity of the soil. However, it does not lead to a larger volume of drained water of the contaminated soil, thus the effect of the presence of contaminants on the volume of drained water is underestimated in the magnitude of the current. Combined with the amount of change in current, for pollution-free soil, the current attenuation is 0.09 A for T1 and 0.29 A for T3. The attenuation of current is related to both electro-osmosis and vacuum, and is strongly influenced by the moisture content of the soil. For contaminated soil, the current attenuation is 0.22 A for T4 and 0.23 A for T6, and the current attenuation is less correlated with vacuum than with electro-osmosis. It is mainly attributed to the fact that the conductivity of contaminated soil is primarily influenced by the copper ion content. Copper ions in the electric field are under the functions of both electro-osmosis and electro-migration; thus, the conductivity changes with the change in ion concentration. Moreover, the current attenuation of electro-osmosis for contaminated soil is much larger than that for polluted soil, indicating that the effect of electro-migration is greater than that of electro-osmosis drainage for copper ions. Figure 16 shows the change curve of effective potential with time for groups T1, T3, T4, and T6. The applied voltage of this test is 30 V, and due to the existence of interfacial resistance between the electrode and the soil, the potential reaching the soil body will be discounted. The actual potential on both sides of the soil is the effective potential. As can be seen from the figure, the four groups of effective potentials show increasing and then decreasing trends. It is probably due to the fact that at the early stage of treatment, the soil is compressed and the volume becomes smaller. The drainage board is in close contact with the soil, the contact resistance becomes smaller and, thus, the effective potential  
Figure 15: Change curve of current with time. of the soil increases slowly. Afterward, the moisture content of the soil near the anode decreases significantly. The soil dries, cracks, and detaches from the anode drainage board. The interface resistance becomes larger and the effective potential decreases rapidly. The effective potential of T1 and T4 electro-osmosis tests decreases significantly.