## 2 Experimental Program
### Experimental Design  
As one of the thermal treatment methods, an electrical resistance heating technology developed for this study allowed for thermal desorption, as well as vitrification of multi-contaminated silty sand by heavy oils and heavy metals. As seen in Figure 2, by allowing high electric current to flow through a resistor that was located in the soil, the soil volume was rapidly heated, resulting in an increase in \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type** & **Unit** & **Criteria** & **Results** & **Remarks** \\ \hline Copper (Cu) & mg/kg & 2000 & 27.1 & \\ Lead (Pb) & mg/kg & 700 & 39.8 & \\ Zinc (Zn) & mg/kg & 2000 & 243.8 & \\ Nickel (Ni) & mg/kg & 500 & 15.7 & \\ Hexavalent chrome (C\({}^{\theta+}\)) & mg/kg & 40 & 0.8 & \\ Cyanide (CN) & mg/kg & 120 & 55.6 & \\ Mercury (Hg) & mg/kg & 20 & 21.63 & Exceeded \\ Arsenic (As) & mg/kg & 200 & 5.42 & \\ Benzene & mg/kg & 3 & 0.7 & \\ TPH & mg/kg & 2000 & 21,081 & Exceeded \\ Benzo(a)Pyrene & mg/kg & 7 & 0.901 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Contaminants in multi-contaminated soil sample. Figure 1: Particle size distribution curve of multi-contaminated soil sample (ASTM D-6913 [10]). temperature, which evaporated volatile (organic) contaminants and isolated (inorganic) heavy metal contaminants as crystal structures (solidification) in soil [5]. The remediation experimental device, as shown in Figure 3a, simply consists of a power supply, with a capacity of 10 kW, and a heating resistor using the flow of AC electricity. The commercial voltage was designed to be 220 V/60 Hz. The secondary voltage was designed to ensure safety during the experiment by setting the maximum output voltage to 8 V. The experimental device could control the secondary voltage, from 0 to 8 V, in the primary voltage range of 0-220 V and adjust the input current. In addition, the current could be controlled within a range of up to 1250 A according to the load condition of the secondary current. The soil container was made of stainless steel with dimensions of 30 \(\times\) 80 \(\times\) 100 cm, and a polycarbonate panel was installed on the front side of soil container to observe internal changes. As shown in Figure 3b, there are holes in which resistors as a heat source can be installed at a horizontal distance of 10 cm and a vertical distance of 20 cm. It was designed to analyze heat transfer and thermal influence range according to the location of the heat source. Moreover, there is an outlet on the top of soil container as shown in Figure 3c, which was designed to discharge the gas generated by the volatilization of contaminants during the thermal treatment process. An electrical resistance heating test was conducted for 24 and 48 h with a power consumption of 6 kW/h and target temperature of 700 \({}^{\circ}\)C. The temperature variations at each section in the soil container were measured using GRAPTHTEC's DATA LOGGER (GL840) and K-type thermocouple, as shown in Figure 4.  
Figure 3: Diagram of (**a**) electrical resistance heating device; (**b**) side view of soil container; (**c**) top view of soil container. Figure 2: Schematic diagram of electrical resistance heating device. While the temperature of silty sand was increased through thermal conduction, volatile contaminants contained in contaminated silty sand were purified, as seen in Figure 7. The TPH of multi-contaminated silty sand was entirely eliminated by 99% from 21,081 mg/kg, and the mercury was also eliminated below the concern level. Heavy metals, such as copper, lead, zinc, nickel, cyanide, arsenic and chromium, contained in contaminated silty sand were immobilized in the solid. In other words, all of the heavy metals contained in the contaminated silty sand were vitrified by high temperature from the electrical resistance heating technology, as shown in Figure 8.  
After thermal treatment in 48 h, the leaching of heavy metals, except for lead, was not detected, as presented in Table 3.  
Figure 8: Vitrified heavy metals. Figure 7: Removal efficiency of TPH and mercury.