# Separation of Conospheres from Lignite Fly Ash Using Acetone-Water Mixture
## 3 Results and Discussion
### Chemical Composition
This monotonically varying composition of cenospheres affected by the fly ash/medium variables for the reused conditions seemed to be fairly similar, except for the 50% acetone condition prone to the comparatively lower values. This result implies that the quality of cenospheres drastically reduced with more incorporation of water into the medium. A wide range of these compositions has been reported for cenospheres obtained from fly ash from different sources [27; 32; 33]. For both the freshly prepared and the reused mixtures, an overview of the trend of the SiO\({}_{2}\) + Al\({}_{2}\)O\({}_{3}\) + Fe\({}_{2}\)O\({}_{3}\) composition seemed to show no certain correlation between the weight composition of these three components and the ash concentration in the medium. However, in the relation of size and composition, for larger particle size the SiO\({}_{2}\)-Al\({}_{2}\)O\({}_{3}\) content in the cenospheres is higher, as SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) are the main characteristics determining mechanical properties and inertness [32]. Particularly comparing the 80:20 to the 100:0 proportions, the increase in SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) contents with the increased acetone content appeared to be fairly inconspicuous. Thus, one could understand that this result suggests that the reduced density for the large-sized cenospheres was probably because of the hollow structure rather than the inherent chemical composition characteristics. For the 50% and 80% water contents of the reused conditions, the higher contribution of CaO was seen more clearly. As seen from Figure 4b, the SiO\({}_{2}\) + Al\({}_{2}\)O\({}_{3}\) + Fe\({}_{2}\)O\({}_{3}\) composition in the 50:50 and 20:80 ratios apparently dropped due to the enhancement of CaO in the cenospheres: the occupied areas of CaO were obviously intense in the whole fraction of each stacked column. Summarizing this observation, such a rich CaO phase formation existed in tandem with a reduction in the particle size of cenospheres. The CaO and SO\({}_{3}\) contents increased monotonically with an increase in the water content (see Figure 5a,b). The data for the freshly prepared and the reused conditions were demonstrated for comparison. The CaO content varied from 10 wt.% to 30 wt.%, and the SO\({}_{3}\) content varied from 1 wt.%  
Figure 4: Stacked column plots of chemical compositions of cenospheres collected from using different acetone/water ratios, a 4-h soaking period, and fly ash/medium ratios of 1:2.5, 1:5, and 1:10. Data of (**a**) the freshly prepared and (**b**) the reused mixtures are presented for comparison. to 8 wt.%. The substantial rise of the weight percentage of CaO and SO3 was clearly seen at 80% _v/v_ water content in the mixture, in which the fractions of smaller particles were produced. Using 100% water as a medium and a 1:5 fly ash/medium ratio, the CaO composition found in the cenospheres was up to 36.21 wt.%. Figure 6a,b shows the pair dependence of SiO2-Al2O3 and Al2O3-Fe2O3 of the cenospheres, respectively. In Figure 6a, the SiO2 content was dependent upon the Al2O3 content described in the linear equation. The trend revealed the same characteristic, that the dependence of SiO2-Al2O3 was independent of the ash content in the medium. The Al2O3-Fe2O3 pair dependence in Figure 6b is described by a linear regression equation. This trend exhibited an increase in the Fe2O3 content with a decrease in the Al2O3 content. The results obtained from this analysis were in satisfactory agreement with the data ranges reported for the category of magnetic cenospheres [31]. SiO2, Al2O3, and Fe2O3 participate in the composition of the glass phase and can differently affect the morphology and thus the properties of the aluminosilicate matrix of the cenosphere shell. Oxides of Si and Al involve the formation of mullite, and oxides of Fe and Al participate in the formation of ferrospinel [31].