## 2 Materials and Methods
The solutions remained after sampling were collected together and evaporated for the crystallization of alum to obtain a total sample (TS-alum), which was used in experiments on the purification of alum by recrystallization (stage B*); for preliminary experiments (stage B), the portion of alum with high impurity content was used to make the difference in the Fe, Na, and K behavior easier to detect. For such experiments, weighed 10 g portions of alum were placed in 100 mL thin-layer glasses with 25 mL of distilled water and heated until complete dissolution of alum. Then, the solutions were cooled and kept for 18 h at room temperature, after which the alum was filtered off, dissolved in water, and the alum solutions and mother liquors were analyzed. In a number of experiments, various chemicals, such as phosphoric acid, sodium thiosulfate, and granules of aluminum, were added to the solutions before precipitation to study their effect on the composition of obtained alum. An example of a material balance for the main components in the alum recrystallization process, which demonstrates that the accuracy of analytical procedures applied is presented in Table 2.  
Experiments were carried out to precipitate and insulate aluminum hydroxide (C1) or its derivatives (C2) from alum solutions using 25% solution of ammonia or ammonium hydro-carbonate (NH4 HCO3). Alum used for these experiments was preliminarily purified by recrystallization of TS-alum with sodium thiosulfate for what: 20 g of TS-alum and 0.2 g of Na2S2O3.2H2O were dissolved in 50 mL of hot water, and alum obtained after cooling and crystallization was filtered and washed with the saturated solution of (NH4)2 SO4. Procedure for obtaining aluminum hydroxide: 7 g of the purified alum were dissolved in 35 mL of water and neutralized with ammonia solution according to the methods described in [21; 22]. For this purpose, solutions of alum and ammonia were alternately added to a flask containing 30 g of 9.66% solution of (NH4)2 SO4 and heated to 90 \({}^{\circ}\)C so that the pH was in the range of 6-8. After the end of the process, the resulting mass was filtered on a vacuum filter, collected back into the flask, and washed at least five times with 30 mL of hot distilled water every time until sulfate was no longer detected in the wash water by test reaction with BaCl2. Then, the resulting precipitate was placed in a flask with 10 g \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Sample** & **Mass, g** & **Al** & & **Fe** & & **K** \\ \hline  & & Mass\% & g & Mass\% & g & Mass\% & g \\ \hline  & & & & Input & & & \\ \hline Na2S2O3 & 0.20 & & & & & & \\ \hline Initial alum & 10 & 5.94 & 0.594 & 0.064 & 0.006 & 0.30 & 0.030 \\ \hline H2O & 25 & & & & & & \\ \hline  & & & & Output & & & \\ \hline Recrystallized alum & 9.07 & 5.93 & 0.538 & 0.005 & 0.000 & 0.18 & 0.016 \\ \hline Residual solution & 25.80 & 0.24 & 0.063 & 0.023 & 0.006 & 0.05 & 0.014 \\ \hline Disbalance, g & \(-\)0.332 & & 0.007 & & 0.000 & & 0.000 \\ \hline Disbalance, \% & \(-\)0.94\% & & 1.19\% & & 1.50\% & & \(-\)1.27\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Material balances for Al, Fe, and K at the stage of alum recrystallization. of ammonia solution and left stirring at room temperature for 15 h. After that, the mass was filtered on a vacuum filter and washed with 30 mL of distilled water. The resulting precipitate was dried at 150 \({}^{\circ}\)C to constant weight and analyzed by the XRF method. Obtaining a precipitate of base aluminum ammonium carbonate: 8.03 g from the recrystallized alum were dissolved in 20 mL of water and poured through a filter into a 28% NH\({}_{4}\)HCO\({}_{3}\) solution, held for 2.5 h at a temperature 70 \({}^{\circ}\)C and filtered. The resulting precipitate was washed by repulpation in deionized water, followed by filtration, and the presence of sulfate ion in the filtrate was controlled by reaction with barium chloride. No sulfate was detected after the third washing.