## 2 Materials and Methods  
The starting materials were: a sample of nepheline concentrate provided by JSC \"Apatit\" (Russia) and solutions of ammonium bisulfate. The concentrate contained 71% nepheline, the main impurity minerals were: feldspar, aegirinaugite, biotite, magnetite, titanite, apatite, and eudialtye. The X-ray diffraction pattern of concentrate is shown in Figure 3; and chemical composition of the nepheline sample is shown in Table 1. Ammonium bisulfate solutions were prepared by dissolving ammonium sulfate and sulfuric acid, both of chemical purity, in distilled water in ratios advising three types of solutions: 30 wt% NH4 HSO4 + 1 wt% H2 SO4, 40% NH4 HSO4 + 1 wt% H2 SO4, and 60% NH4 HSO4 + 1 wt% H2 SO4. Three stages of the process were experimentally studied, and it required different experimental procedures; their relationships are schematically shown in Figure 4.  
For decomposition of concentrate (stage A), a 20 g sample was added to 180 mL of the ammonium bisulfate solution. The leaching stage and maturation of the reaction mixture were carried out in a 500 mL glass conical flask placed in a water bath. The temperature 95 \({}^{\circ}\)C was maintained, and the mixture was stirred using a magnetic unit with automatic temperature control. To minimize water loss due to evaporation, the flask was equipped with a reflux condenser. After aging for 5 h, the mass was filtered while hot on a specially made Buchner funnel with a diameter of 125 mm with an electric heater. The undecomposed residues (tailings) were returned to the reactor flask and mixed with \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Al\({}_{2}\)O\({}_{3}\)**} & \multicolumn{1}{c}{**Na\({}_{2}\)O**} & \multicolumn{1}{c}{**K\({}_{2}\)O**} & \multicolumn{1}{c}{**SiO\({}_{2}\)**} & \multicolumn{1}{c}{**\({}^{\star}\)Fe\({}_{2}\)O\({}_{3}\)**} & \multicolumn{1}{c}{**TiO\({}_{2}\)**} & \multicolumn{1}{c}{**P\({}_{2}\)O\({}_{5}\)**} & \multicolumn{1}{c}{**CaO**} & \multicolumn{1}{c}{**MnO**} & \multicolumn{1}{c}{**MgO**} & \multicolumn{1}{c}{**SO\({}_{3}\)**} \\ \hline
26.61 & 11.2 & 6.87 & 49.63 & 2.95 & 0.32 & 0.26 & 1.34 & 0.05 & 0.38 & 0.31 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Nepheline concentrate sample composition according to XRF data in terms of oxides wt%. Figure 3: X-ray diffraction pattern of the nepheline concentrate sample. Patterns of nepheline, natrolite, microcline, biotite, titanite, and pyroxene are given from Ruff database. 90 mL of hot water. The hot suspension was filtered, and the washings were collected in a separate plastic container. This procedure was repeated twice, and a hot solution of the mother liquor with the first and second washing solutions was obtained. Figure 4: Schematic diagram of experiments: (**A**) nepheline decomposition; (**B**) alum recrystallization (B*–variant, used for obtaining purified alum for the future experiments); (**C**) alumina product precipitation stages: C1– for aluminum hydroxide, C2– for ammonium aluminum carbonate hydroxide. Each of the hot filtrates was poured into a separate polyethylene container for cooling to room temperature and for alum precipitation. The samples of precipitated alums from the primary filtrate, the first and second washing solutions were separated by vacuum filtration after 18-24 h of their storage at room temperature, and each precipitate was dissolved in 1000 mL of distilled water. These solutions of alums and separated filtrates were taken for analyses by the ICP-AES method for metals and titration for ammonium. Based on the data obtained, the dependences of the distribution coefficients of elements between phases on the concentration of sulfates in an equilibrium solution were built.