## 3 Results and Discussion
### Morphological Analysis  
Some interesting insights regarding the morphology of nonmagnetic and magnetic particles of Uong Bi (UB) and Pha Lai (PL) fly ash sample are revealed by Scanning electron microscopic study (SEM) (Figure 4a,b). According to Figure 4a,b, the non-magnetic and magnetic elements were found to be distinctly different. Although according to the literature, the non-magnetic components are commonly irregular in both size and shape while magnetic components generally tend to be spheroidal. However, observations of fly ash from thermal power plant showed that both magnetic and non-magnetic grains have almost spherical forms of various sizes, From the SEM results if can conclude that particles have either a smooth or corrugated surface.  
Figure 3: results of XRD Analysis of the UB and PL samples. Mu: Mullite; Mt: Magnetite; Q: Quartz.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Element (\%)**} & \multicolumn{2}{c}{**The Concentration of Trace Elements (ppm) of Magnetic Fly Ash**} \\ \cline{2-3}  & \multicolumn{1}{c}{**UB**} & \multicolumn{1}{c}{**PL**} \\ \hline Co & 26.13 & 34.27 \\ Ni & - & - \\ Cu & 42.92 & 39.38 \\ Zn & 15.51 & - \\ Mo & 1.24 & 1.15 \\ Cd & - & 0.23 \\ Pb & 27.22 & 21.73 \\ Mn & 739.38 & 1237.46 \\ Mg & 700.94 & 754.2 \\ Cr & 148.75 & 132.18 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Trace elements concentrations (ppm) in magnetic fractions of UB and PL fly ashes as determined ICP-MS analysis.  
The SEM-EDS results, shown in Figure 5a,b, indicate that the UB and PL samples contain variable amounts of Fe. The EDX analyses of magnetic fly ash indicate that the grains are mostly iron oxides although these oxides of metals were regularly present in incrustations, and some empty form. Moreover, EDX analyses reveal that the main elements are Fe and Si with Mg, Al, and K as minor elements. Although aluminum is primarily associated with silicon. Moreover, based on SEM and EDX analyses, the magnetic grains from the UB and PL samples were derived from different sources regarding the fossil fuel combustions or furnaces conditions. In fact, formation of such particles may be described in a plausible mechanism: (a) prior to fusion and melting, the mineral matters observed in coal (both extrinsic and intrinsic) undergo some transformations, (b) next, the melted matters condense and form smaller spheroidal particles, and (c) iron oxide (Fe\({}^{+2}\), Fe\({}^{+3}\))/elemental Fe (obtained from iron carbonate in fly ash) deposit on the surfaces of these spheroidal particles.  
[PERSON] studied the condensation phenomena of iron oxides/elemental iron on the surface of the alumino-siliceous particles [40]. Other studies have also highlighted such interesting conclusions regarding the crystallite deposition on the surface of the magnetic components (e.g., [PERSON] [36], and [PERSON], et al. [41]). Accordingly, crystal deposition can take place in diverse forms and  
Figure 4: (a) Morphotypes of nonmagnetic (**1**) and magnetic particles (**2–8**) of Uong Bi (UB) fly ash; (b) Morphotypes of nonmagnetic (**1**) and magnetic particles (**2–8**) of Pha Lai (PL) fly ash.  
shapes. Some magnetic particles, particularly those are related to finer fractions, are cauterized by perfect spheroidal shapes with well-classified crystallites on the surfaces. Such particles are morphologically classified in other studies as Ferrospheres (e.g., [PERSON], et al. [42], [PERSON], et al. [43], [PERSON], et al. [44], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [43]). The morphologies of the non-magnetic components and magnetic components of fly ash are completely different. The non-magnetic components usually have a high carbon content.  
Figure 5: _Cont._