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

Abstract

ABSTRACT 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. Iron is generally leached with aluminum in the acid leaching process which could be removed effectively by pH adjustment. The leached liquor obtained after purification is evaporated by using a hot water bath. The liquor concentrated on slow evaporation to a point where aluminum sulfate started precipitating. Then, the concentrated liquor was kept overnight at 8°C in a cooling incubator. Aluminum sulfate was produced with 99.80% purity.