## 3 Results and Discussions
To understand the behavior of the elements, present in the waste, the masses of all elements after each cycle of treatment were calculated using the following equation:  
\[m_{k}=C_{k}\cdot M_{T} \tag{5}\]  
where \(C_{k}\) and \(m_{k}\) represent the concentration and the mass of element, respectively, and \(M_{T}\) is the total mass of the waste used in each cycle. Figure 4 shows that the masses of elements decrease after each cycle of treatment. This diminution can be attributed to the vaporization of these elements under the high \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Element**} & **Mn** & **Co** & **Ba** & **La** & **Ga** & **Se** & **Sr** & **Zr** & **Ag** & **Cd** & **Sn** & **Ce** & **Pb** & **As** \\ \hline \multirow{3}{*}{C (mg/kg)} & 1 st Cycle & 27.3 & 6.1 & 58.0 & 3.6 & 2.9 & 4.0 & 10.5 & 4.0 & 19.8 & 1.3 & 7.3 & 1.3 & 12.7 & 1.1 \\  & 2 nd Cycle & 21.7 & 6.1 & 59.2 & 4.6 & 3.6 & 4.6 & 11.1 & 1.6 & 13.6 & 1.4 & 8.1 & 2.7 & 12.4 & 1.2 \\  & 3 rd Cycle & 29.0 & 7.6 & 88.3 & 5.2 & 3.9 & 1.8 & 16.6 & 4.2 & 42.4 & 1.3 & 18.5 & 3.1 & 18.46 & 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Concentrations of minor elements present in the waste after treatment obtained by ICP. Figure 3: EDX analysis of fly ash (**a**) before treatment, (**b**) after 1 st cycle of treatment, (**c**) after 2 nd cycle of treatment, (**d**) after 3 rd cycle of treatment. temperature of the plasma. These results were confirmed by the model calculation (Figure 5). This figure shows that the vaporization speed and the vaporized quantity are important for many elements, such as Ba, K, and Ti. Other elements like Mg, Rh, and Ca, are vaporized in the first 10 s, and after this time they are stable. This effect is due the combustion of carbon in the first 10 s. Elements like Fe, Ni, Si, and Al are not volatile and their mole numbers remains constant. These results are logical because the vaporization temperatures of these elements are very high. In contrast, the experimental results show a decrease in the quantities of Fe, Ni, and Al, after each cycle of treatment. This difference between the experimental measurements and the code results is due to the loss of waste in the components of the plasma system (furnace and exchanger) during the treatment, and because the initial used masses of these elements are very low (2.4 g for Ni, 2.01 g for Fe, and 0.135 g for Al). To know the compounds responsible on the volatility of the toxic elements, Figure 6 depicts the variation of titanium components in the liquid and gas phases. Initially, titanium was in the form of TiC (0.013 moles) and this compound disappears in the first second, which confirms that the combustion of carbon is responsible for the vaporization of Ti. Titanium continues to vaporize in the form of TiO\({}_{2}\) after the vanishing of carbon. Figure 4: Mass (mg) of elements after each cycle of treatment. Figure 5: Variation of the mole number of elements present in the waste. Many parameters influenced the vaporization or the incorporation of toxic elements in the confinement matrix during the treatment. Of these parameters, we cited the bath surface temperature, the presence of oxygen in the carrier gas, and the composition of confinement matrix. Pb and As are chosen to study the effect of these parameters using our computer code. To have the same experimental conditions, the plasma current was fixed on the code at 250 A, and the total pressure P at 1.013 \(\times\) 10\({}^{5}\) Pa. The influence of the bath surface temperature on the arsenic volatility was presented in Figure 7. This figure shows that arsenic is not volatile for temperatures less than 2000 K, whereas for temperatures beyond 2100 K, the vaporization speed increases and the arsenic quantity that leaves the furnace becomes important. These results can be explained by the stability of the arsenic components with temperature.