## 2 Materials and Methods
### Experimental Design  
In the preparation of high-purity anhydrous scandium chloride in the process, the main objective is to prevent hydrolysis of the scandium chloride generated (ScOCI). Owing to the high and low back, the ScOCI content influences the of scandium recovery rate. The preparation process of aluminum magnesium alloy among scandium also has adverse effect. Two kinds of dehydration methods to remove water contained in the crystallization of rare earth chlorides are vacuum dewatering and inert gases flow. The process of preparation and equation of scandium hydrolysis and combination reaction are shown in Equations (1) and (2):  
\[\text{ScCl}_{3(s)}+H_{2}O_{(g)}\to ScOCI_{(s)}+2 HCl_{(g)} \tag{1}\]  
\[\text{ScOCI}_{(s)}+2 NH_{4}Cl_{(s)}\xrightarrow{\Delta}ScCl_{3(g)}+2 NH_{3(g)}+ H_{2}O_{(g)} \tag{2}\]  
Scandium oxide is first dissolved by heating with concentrated hydrochloric acid. Then, the auxiliary salt and ammonium chloride are dissolved by heating with distilled water \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sc\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **MnO** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **CaO** & **MgO** & **K\({}_{2}\)O** & **Na\({}_{2}\)O** \\ \hline
81.16 & 4.56 & 0.56 & 3.01 & 1.76 & 2.23 & 1.79 & 1.46 & 0.89 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition analysis results of scandium oxide (%). After mixing the two solutions, the mixture is filtered, and the fully stirred filtrate is put in an ordinary electric furnace for heating and evaporation. When a large number of crystals in the solution precipitate, the solution is transferred to a constant temperature water pot for heating, so that the water can evaporate as completely as possible. The solution is moved to a vacuum drying oven for vacuum evaporation and most of the crystallized water is removed. After the water evaporation of scandium chloride molten salt is complete, the molten salt block is taken out and ground into powder. Finally, the molten salt is put into a vacuum tube atmosphere furnace to remove ammonium chloride. The remaining crystal and the prepared anhydrous scandium chloride molten salt is stored in a dryer. By analyzing the content of scandium in molten salt and calculating the hydrolysis rate of scandium is determined. The calculation formula is shown in Equation (3). The process of preparing anhydrous scandium chloride is shown in Figure 1.  
\[\text{Hydroolysis rate of scandium}=\left(S^{T}-Sc^{S}\right)/Sc^{T}\times 100\% \tag{3}\]  
where Sc\({}^{S}\) is the soluble scandium content of anhydrous scandium chloride molten salt/% and Sc\({}^{T}\) is the scandium content of anhydrous scandium chloride molten salt/%. The EDTA standard solution was prepared at a concentration of about 0.04 mol/L. Then, the scandium content in scandium chloride salt was determined by EDTA complexometric titration. Scandium chloride oxide (ScOCI) formed by the hydrolysis of scandium chloride containing crystal water is insoluble in water, while scandium chloride is soluble in water. Therefore, the total scandium and soluble scandium contents in molten salt could be determined first. The method for determination of the content of soluble scandium was: 0.5 g anhydrous scandium chloride molten salt samples were put in 100-mL beaker, 40 mL was added of distilled water to dissolve and fully mixed after filtration. Then, 10 mL pH material 4 drips of HAc--NaAc buffer solution was added the filtrate. Then, a small amount of ascorbic acid was added, with x  
Figure 1: Scheme of preparing anhydrous scandium chloride molten salt. indicator. Titration was completed with EDTA standard solution; the titration end solution changed from red to yellow. The content of soluble scandium in molten salt was calculated according to the consumption and concentration of EDTA standard solution and the weight of sample. The total content of scandium was determined as follows: Another sample of 0.5 g molten salt was added to a 100-mL beaker.