## 2 Materials and Experimental Procedures
### Experimental Procedures  
#### 2.2.1 Adsorption Tests  
In this work, the main objective of the adsorption tests was to supply preliminary information about the adsorption capacity of the soil towards the different heavy metals tested, and to preliminary evaluate if the addition of MWCNTs or montmorillonite could improve the adsorption capacity of the soil. As referred, both MWCNTs and montmorillonite were subjected to a previous treatment to guarantee an adequate dispersion of these additives. The pre-dispersing procedure consisted in the application of ultrasonic energy (20 kHz, 500 W, amplitude 75% during 15 min, using a sonicator probe Sonics Vibracell 501) to the aqueous suspension of MWCNTs or montmorillonite enriched with the surfactant SDBS (used in a concentration of 0.03%, _w/w_) which, besides enabling dispersion of the particles, can contribute to the adsorption of the heavy metals due to its charge. It must be noticed that in the present study, it was possible to guarantee a good dispersion of the MWCNTs using a much lower concentration of the anionic surfactant than in the previous work [31] where a different surfactant was used (Pluronic F-127, non-ionic type) with a concentration of 2%. This stategy proved to be efficient for the dispersion of the additives.  
The quality of the MWCNTs dispersion was evaluated by measuring the size distribution of the aqueous MWCNTs suspensions, additivated with SDBS, prepared in the above-mentioned conditions. The Z average diameter (D\({}_{z}\)) of the optimized MWCNTs suspension was 216.9 nm (measured by the Dynamic Light Sattering technique, Malvern Instruments Nanosizer ZN [61]).  
Three different tests were performed:  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Components** & **Na\({}_{2}\)O** & **MgO** & **Al\({}_{2}\)O\({}_{3}\)** & **SiO\({}_{2}\)** & **P\({}_{2}\)O\({}_{5}\)** & **SO\({}_{3}\)** & **K\({}_{2}\)O** & **CaO** & **TiO\({}_{2}\)** & **Mn\({}_{3}\)O\({}_{4}\)** & **Fe\({}_{2}\)O\({}_{3}\)** \\ \hline \% (_w/w_) & 2.03 & 2.26 & 19.16 & 58.6 & 0.05 & 0.9 & 0.55 & 1.26 & 0.17 & 0.02 & 3.69 \\ \hline
**Minerals** & \multicolumn{3}{c}{**Dioctahedral smectite**} & \multicolumn{3}{c}{**Quartz**} & **Illite** & **Opal** & \multicolumn{3}{c}{**Potassium feldspar**} \\ \hline \% & \multicolumn{3}{c}{85–90} & \multicolumn{3}{c}{5} & \multicolumn{3}{c}{2} & \multicolumn{3}{c}{2} & \multicolumn{3}{c}{trace} \\ \hline \hline \end{tabular}
\end{table}
Table 4: Chemical and mineral composition of Montmorillonite according to the supplier.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Components** & **CaO** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **MgO** & **SO\({}_{3}\)** \\ \hline \% (_w/w_) & 63 & 19 & 5 & 3 & 3 & 3 \\ \hline \end{tabular}
\end{table}
Table 3: Chemical composition of the Portland CEM I 42.5R according to the supplier.  
1. Adsorption tests with soil alone contaminated with the heavy metals (reference test) with the objective to evaluate the adsorption capacity of the soil particles by themselves to be used as reference for the remaining studies;
2. Adsorption tests using a suspension of MWCNTs or montmorillonite (applied independently) dispersed in an aqueous solution of heavy metals, and pre-treated with ultrasounds and surfactant, with the objective to evaluate the adsorption capacity of these additives by themselves;
3. Adsorption tests using soil contaminated with heavy metals combined with carbon nanotubes or clay mineral (montmorillonite), and pre-treated with ultrasounds and surfactant, with the objective to evaluate the benefits in the adsorption capacity of using the two dual systems (soil + MWCNTs or soil + montmorillonite).  
Figure 1 supplies a scheme of the adsorption tests conducted.