# Separation of Conospheres from Lignite Fly Ash Using Acetone-Water Mixture
## 3 Results and Discussion
### Morphological Study  
The morphologies of enospheres are presented in Figures 7-9. The as-received enospheres were glassy, had open pores, and were spherical in shape, as seen in the XRF images in Figure 7. At a higher magnification, the enospheres were found to exhibit a perforated shell and an irregular spherical shape of the particles (see Figure 8). It should be noted that the spherical shape of the particles is an important factor in improving, to some extent, flowability or workability in mixing enospheres as fillers with a matrix such as polymer resin. The spherical shape, possessing a low surface area/volume ratio, requires a lower amount of binder matrix to wet the surface [24]. The cell wall thickness observed for the cenospheres collected from acetone-water mixtures varied from 2 to 30 \(\upmu\)m. The broken enospheres could be observed in a small proportion. The non-uniform wall thickness, with a thin wall and thick wall on the same particle, is seen in Figure 8a. Figure 6: Dependence of (**a**) SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) contents, (**b**) Fe\({}_{2}\)O\({}_{3}\) and Al\({}_{2}\)O\({}_{3}\), and (**c**) the SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) ratio and Al\({}_{2}\)O\({}_{3}\) content. The data were taken from Table 3.  
Using higher acetone ratios of 80% and 100%, the surface of the larger cenospheres was found to be clean, no noticeable amount of small aggregates deposited on the cenosphere surface as seen for the samples collected from using high water content condition (see Figure 8g,h). The magnified surface of cenospheres, shown in Figure 9a, revealed various morphologies of the aggregates forming on the surface of cenospheres. Those precipitates are in various sizes and shapes such as spherical and nonspherical particles, needles, small spheres with whiskers, and corrugated surfaces. Such morphological characteristics of corrugated, rough surfaces, noticeably indicated in fine fractions, are classified as crystallite depositions on the surfaces of magnetic components such as iron oxides, which are mostly found on magnetic spheres [51; 52; 53; 54]. In cenospheres with a high iron content, part of the outer surface contains heterogeneous regions with extended linear inclusions of ferrospinels, while on the inner surface, the pores contain the underlying aluminosilicate phase [31]. The formation of such aggregate particles on the surface may involve a nanoscale dissolution-precipitation mechanism for alkali activation reactions in an aluminosilicate phase. Fly ash and cenosphere reactivity is based on the alkaline dissolution of disordered aluminosilicate networks. Many studies have described the conceptual mechanism of an alkali attack on the ash surface, leading to sodium aluminosilicate hydrate N-A-S-H gel polymerization from inside and outside the particle shell and ultimately to reaction products precipitating on the inner and outer surfaces [55; 56]. The hollow spheres were found to be broken, and hence it became possible to observe the inner wall surface (see Figure 9b). With a prolonged soaking time up to 24 h, it was found that the entire surface of the cenospheres was covered with a remarkable amount of the aggregate crystals, as presented in Figure 9c,d. The elemental composition by EDX was further investigated for this sample, and the results indicated that those aggregates mainly contained \(39.17\pm 1.23\) wt.% Ca, \(12.90\pm 1.27\) wt.% C, and \(47.93\pm 0.04\) wt.% O: data were obtained from five measurements. It should be noted that the theoretical molar mass percentage ratio of calcium carbonate (CaCO\({}_{3}\)) was 40.04 wt.% Ca, 12.00 wt.% C, and 47.96 wt.% O [57; 58]. It could be presumed from this finding that the aggregates were prone to calcium carbonate according to such close relevancy. The large amount of aggregates covering the cenosphere particles was taken into consideration in the determination of the cenosphere recovery yield.