Low temperature hydrothermal processing to recover aluminum from nepheline syenite roast-leach residue

Nepheline syenite is primarily an alumino-silicate rock which contains a major amount of potassium and aluminum. After potassium recovery through chloridizing roasting followed by water leaching method, the roast leach residue of nepheline syenite was considered for the aluminum extraction process due to its ample aluminum content. Sulfuric acid is chosen over other acids as it prevents the leaching of calcium. A 2^3 full factorial design was employed to study the effects of acid concentration, time, and temperature. Furthermore, to enhance the recovery and to forbid the leaching of silicon, autoclave leaching was preferred.