# Separation of Conospheres from Lignite Fly Ash Using Acetone-Water Mixture
## 3 Results and Discussion
### Carbonate Concentration  
The generation of calcium carbonate crystals on the ash surface due to the hydration of calcium silicate and free lime producing the calcium hydroxide product has been explained well in many reports [59; 60]. The Ca(OH)\({}_{2}\) product can react with CO\({}_{2}\) gas and generate CaCO\({}_{3}\) crystals, as shown in Equation (2). The dissolution of calcium carbonate can also occur in water containing carbon dioxide:  
\[\text{Ca(OH)}_{2}\text{ (aq)}+\text{CO}_{2}\text{ (g)}\rightarrow\text{CaCO}_{3}\text{ (s)}+\text{H}_{2}\text{O (l)}, \tag{2}\]  
\[\text{CO}_{2}\text{ (g)}+\text{H}_{2}\text{O (l)}\leftrightarrow\text{H}_{2} \text{CO}_{3}\text{ (aq)}, \tag{3}\]  
\[\text{CaCO}_{3}\text{ (s)}+\text{H}_{2}\text{CO}_{3}\text{ (aq)}\leftrightarrow\text{Ca(HCO}_{3})_{2}\text{ (aq)}. \tag{4}\]  
In this study, the ash dissolution raised the pH of the liquid medium substantially (to 13), along with silicate ion, Al\({}^{3+}\), and Ca\({}^{2+}\) concentrations. The original alkalis can recycle and play a key role in the subsequent alkaline activation reactions, finally forming secondary reaction products such as a carbonate phase [56]. It was of interest to investigate the influence of chemical component dissolution on the properties of the liquid medium. The CaCO\({}_{3}\) concentration in the liquid medium, after being used for cenosphere separation, was analyzed according to the standard measurement of APHA (2012), 2320 B, for carbonate alkalinity. Figure 10 shows the increase in the CaCO\({}_{3}\) concentration as a function of the acetone/water  
Figure 9: (**a**) The outer surface of cenospheres with different morphologies of aggregates deposited on the surface. (**b**) The broken particle of cenospheres, showing the inner wall surface. (**c**,**d**) Almost the entire surface of a cenosphere particle covered with a large amount of the aggregates: this particle was collected after a soaking period of 24 h using a 1:5 fly ash/medium ratio and 100% water as a medium. ratio. Varying the water contents between 20%, 50%, 80%, and 100%, the attainable values were 5, 15, 38, and 40 mg/L, respectively. For 100% acetone content, less than 1 mg/L of the CaCO\({}_{3}\) concentration was detectable due to the threshold of detectability of the instrument, which is not shown in the graph. Incorporating more water, from 50% to 100%, a significant rise in the carbonate concentration was seen. This tendency was similar to the increase in the CaO composition (shown in the inset) found in the cenosphere fractions collected from these ratios. Further considering the properties of the acetone-water mixture, the acetone content of the surface layer was remarkably higher than that of the bulk phase, and this difference became more pronounced at low acetone mole fraction in the bulk liquid phase [61]. [PERSON] et al. studied an interesting insight into the strong adsorption ability of the acetone molecules with solvents that was remarkably related to the presence of its apolar methyl (-CH\({}_{3}\)) groups, leading to the unlike molecules tending to separate from each other, with the extent of the energy difference between the two molecules being in contact. The self-association ability of acetone and water was estimated to be relatively lower for the higher acetone fraction in the mixture system, and higher for the lower acetone fraction in the like molecule water. Thus, one could assume for this study that the diffusion of water-soluble species would be considerably influenced by this. Such a hindrance effect of the low self-association in the high acetone-low water mixture is believed to have played an important role in limiting the solubility, mobility, and reactivity of those water-soluble species and moving ions, thereby essentially having a strong impact on reaction kinetics and the formation of the reaction products, such as calcium carbonates, consequently affecting the separation efficiency, recovery yield, and quality of the cenospheres.