# Separation of Conospheres from Lignite Fly Ash Using Acetone-Water Mixture
## 3 Results and Discussion
### Particle Size and Distribution  
Particle size and distribution were analyzed by laser particle size analyzer. The average size of particles was determined by means of the volume mean diameter, _D [4,3]_. The particle size distribution of the fly ash used in this study widely varied (1-15 \(\upmu\)m (38.40%), 15-30 \(\upmu\)m (16.80%), 30-45 \(\upmu\)m (10.10%), 45-60 \(\upmu\)m (7.20%), 65-75 \(\upmu\)m (5.10%), and \(>\)100 \(\upmu\)m (22.40%)): the percentage value shown in parentheses conformed to the approximate weight fraction in fly ash. The _D [4,3]_ of fly ash was 41.51 \(\upmu\)m. This type of fly ash contained particles mostly in the small size range \(<\)100 \(\upmu\)m, 77%. As the plots shown in Figure 1a, the percentages of cencosphere recovery for the acetone/water ratio of 100:0 were significantly lower than those of the ratios of 20:80 or 0:100. This was also evident in the lesser fractions of particles with a density less than 0.79 g/cc contained in the fly ash sample collected in the specific density range of the 100:0 mixture. As a combination effect, such large fractions of small particles of the feeding fly ash are believed to make a significant contribution to the isolation-floating ability of the larger (to some extent meaning the lighter) particles in escaping from their agglomeration and floating to the upper surface [24]. An analysis of the particle size and weight percentage distribution of cencospheres is available in Table 2 and Figure 2. It is apparent that the dependence of the mean diameter on the medium proportions for the fly ash/medium ratios of 1:2.5 and 1:10 was approximately similar. The higher acetone contents, with a corresponding lower medium density, resulted in a larger size of cencospheres  
Figure 1: Plots of accumulative percentages of cencosphere recovery against (**a**) the ratio of the acetone–water mixture, comparing the results obtained from the freshly prepared and the reused mixtures, and (**b**) the density of the cencosphere fractions obtained from using the freshly prepared mixtures. All data points were obtained from five measurements, and the SD of all points shown in (**b**) is less than 0.005. Due to the small SD values demonstrated in Table 1 and in the results in Figure 1b, the error bars for the data in Figure 1a,b are fairly invisible. Cencospheres were collected from using different ratios of acetone–water mixtures, a 4-h soaking period, and fly ash/medium ratios of 1:2.5, 1:5, and 1:10.  
being obtained. That is, for the acetone/water ratios of 100:0 and 80:20, the average particle size lay in the range of approximately 110 \(\upmu\)m to 150 \(\upmu\)m. For the ratios of 50:50 and 20:80, with a higher medium density, the average particle size lay in the lower range of 30 \(\upmu\)m to 80 \(\upmu\)m.  
Two exceptions to this trend were observed for the fly ash/medium ratios of 1:5 and 1:10: the decrease in size with the increase in water content appeared to be inconspicuous. For the ratio of 1:5, the average particle size of the cenosphere fraction collected from using the acetone/water ratio of 80:20 (_D [4,3]_, 141.21 \(\upmu\)m) was greater than that of the 100:0 ratio (_D [4,3]_, 91.56 \(\upmu\)m), which was a mean size smaller than expected in the \(<\)100 \(\upmu\)m region. Meanwhile, in the ash content ratio of 1:10, the average particle size of the cenosphere fraction collected from using the acetone/water ratio of 20:80 (_D [4,3]_, 82.85 \(\upmu\)m) was larger than that of the 50:50 ratio (_D [4,3]_, 60.67 \(\upmu\)m). This could be attributed to the disproportionate loss of the particles when collecting the cenosphere fractions. For instance, in the case of the ash/medium ratio of 1:10, the loss of fine particles could possibly be due to the pronounced effect of crystal formation on the surface of the fine ash particles and possible agglomeration creating large-sized aggregates; as a result, the particle size distribution is seen shifted to the larger size region.