## 3 Results and Discussions  
Figure 2 depicts the chemical composition of the waste before the treatment measured by XRF analysis. This figure shows that Ni, Fe, S, V, Ca, P, Sr and Mo are the waste's major constituents. The concentrations of elements present in the wastes were measured using ICP-AES, and were presented in Table 2. The elements with very low concentration are not listed in Table 2. The elements such as, Ni, V, Fe, Mg, Ca, Na, and Al represent the major constituents of wastes (100-1000 mg/kg), whereas the minor constituents (1-100 mg/kg) include Mo, Ba, Zn, Cr, Ti, Pb, and Mn. Toxic elements such as Cd and Sr, are present in the wastes but with relatively low concentrations. These results confirm the XRF analysis (Figure 2). \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline
**Element** & **Na** & **Mg** & **Rh** & **Al** & **Ti** & **K** & **Ca** & **Ba** & **Ni** & **Si** & **Mn** & **Fe** \\ \hline \hline Mole Numbers & 0.074 & 0.78 & 0.023 & 0.79 & 0.013 & 0.84 & 0.741 & 0.265 & 0.024 & 0.074 & 0.196 & 0.262 \\ \hline \end{tabular}
\end{table} 
Table 1: Mole numbers of elements present in the waste used in the computer calculation. Figure 3a presents the EDX analysis of the waste before the treatment. The obtained results show that the waste consists mainly of carbon, but it also contains a significant amount of sulfur (4%). For this reason, the principal objective of this study is the separation of carbon present in the waste from metals. Several trials were carried out to optimize the best operating conditions for the waste treatment, such as plasma current and the flow rate of the air that was used as a carrier gas in the plasma. To obtain a maximum reduction of carbon, the fly ash collected in the filter bag was re-introduced in the furnace to complete the combustion of carbon. Initially, 1 kg of waste was introduced into the furnace, and the masses of the waste collected in the filter after the first, second and third cycle of treatment are, 696 g, 260 g, and 130 g, respectively. These results show that the waste's mass was reduced after each cycle, reaching a reduction of 85% during the third cycle, and this reduction is due to the combustion of carbon during the treatment. After each cycle, the treated waste was analyzed with XRF, ICP, and EDX. Figure 3 predicts the principal elements remaining in the waste after each cycle of treatment. These Figures show that the waste kept these main constituents (NiO, Fe\({}_{2}\)O\({}_{3}\), SO\({}_{3}\), \(V_{2}\)O\({}_{5}\), CaO, P\({}_{2}\)O\({}_{5}\), SrO and MoO\({}_{3}\)). EDX analysis, presented in Figure 3b-d, shows a reduction in the percentage of carbon in the waste, but the carbon remains the major constituent of the waste. Tables 3 and 4 give the concentrations of major and minor elements present in the waste after each cycle of treatment. The waste kept the same major and minor elements before and after treatment. The concentrations of major and minor elements were increased after each cycle of treatment. These results can be explained by the decreases of the concentration of carbon in the waste due to the combustion of carbon during the treatment. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Element** & **V** & **Ni** & **Fe** & **Mg** & **Na** & **Ca** & **Al** & **Mo** & **Ba** & **Zn** \\ \hline C (mg/kg) & 5663 & 2420.2 & 2027 & 1917.4 & 587.4 & 386.5 & 135.5 & 51.5 & 33.4 & 22.8 \\ \hline Element & Cr & Pb & Mn & Sr & Ti & Cu & Co & K & Ga & As \\ \hline C (mg/kg) & 14.7 & 11.6 & 11.2 & 5.7 & 5.2 & 4.9 & 4.7 & 3.6 & 3.3 & 2.8 \\ \hline \end{tabular}
\end{table} 
Table 2: Concentrations of elements present in the waste before treatment obtained by ICP. Figure 2: XRF analysis for Fly ash before treatment.