# Enhanced Electrokinetic Remediation for the Removal of Heavy Metals from Contaminated Soils
## 2 Materials and Methods
### Electrokinetic Setup and Testing  
Figure 1 shows the electrokinetic cell used in this study. The cell was composed of a central tube (20 cm long and 4 cm diameter) that holds the soil specimen. 320 g of contaminated soil was used in each test. The soil specimen was introduced manually in the central tube, and it was compacted with a plastic piston. The central tube was connected to two electrode chambers filled with the processing fluid selected in each test (deionized water, citric acid, EDTA or NaOH), as shown in Table 3. The volume of the electrode chambers was 300 mL, and the total volume of the processing fluid, including the electrode chamber and the expansion vessel, was 500 mL. The soil specimen was separated into the processing fluid by a porous stone and filter paper. The electrodes were installed in the electrode chambers immersed in the processing fluid and connected to a DC power supply. All the tests were conducted at constant DC electric potential (20 V) for 30 days, except test 4 with citric acid 0.5 M in analyte and catholyte that was run for 65 days. The anode was made of titanium, and the cathode was made of stainless steel.  
At the end of the tests, the electrode chambers were emptied, and the processing fluid was collected in plastic bottles and stored in the fridge at 4 \({}^{\circ}\)C until analysis. The soil was extracted from the central tube and divided into 6 equal sections. Solid and liquid samples were digested with nitric acid and hydrochloric acid as per the USEPA method 3010A (acid digestion of aqueous samples and extracts for total metals for analysis by FLA or ICP spectroscopy) [22] or method 3050B (acid digestion of sediments, sludges, and soils) [23]. Metal concentrations were determined by ICP-OES in the supernatant solution of the acid digestions. Soil pH was determined by the ASTM D1293 [16] method using 1 g of soil and  
\begin{table}
\begin{tabular}{l c c} \hline \hline
**Parameter** & **Value** & **Testing Method** \\ \hline pH & 4.4 & ASTM D1293 [16] \\ Electrical conductivity (mS/cm) & 3.15 & ASTM D1293 [16] \\ Specific gravity (dry basis, g/cm\({}^{3}\)) & 2.7 & ASTM D 854 [17] \\ Water holding capacity & 48.5\% & ASTM D 2980 [18] \\ Moisture content (wet basis) & 22.4\% & ASTM D2216 [19] \\ Soil organic content (dry basis) & 4.5\% & ASTM D 2974 [20] \\ \hline Particle size analysis & & ASTM D 422 [21] \\ Clay (<0.002 mm) & 44.3\% & \\ Silt (0.002–0.05 mm) & 43.2\% & \\ Sand (0.05–2 mm) & 12.5\% & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of soil used in the experiments.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Metal Species** & **Metal Salt** &
\begin{tabular}{c} **Spiking Concentration** \\ **(mg/kg)** \\ \end{tabular} \\ \hline Cd\({}^{2+}\) & Cd(NO\({}_{3}\))\({}_{2}\) 4H\({}_{2}\)O & 141 \\ Cr(VI) & K\({}_{2}\)Cr\({}_{2}\)O\({}_{7}\) & 1000 \\ Co\({}^{2+}\) & CoCl\({}_{2}\) 6H\({}_{2}\)O & 185 \\ Cu\({}^{2+}\) & CuSO\({}_{4}\) 5H\({}_{2}\)O & 1023 \\ Pb\({}^{2+}\) & PbCl\({}_{2}\) & 1000 \\ Zn\({}^{2+}\) & ZnSO\({}_{4}\) 7H\({}_{2}\)O & 1001 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Metal concentration in the contaminated soil.  
2.5 mL of 1 M KCl solution. The mixture was shaken for 1 h, and the pH was measured in the supernatant fluid.