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

ABSTRACTNepheline 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.KEYWORDS: Nepheline syenitealuminumhydrothermal process, aluminum sulfate AcknowledgmentsThe authors also appreciatively recognize the technical assistance provided by the institute staff for the characterization studies. One of the authors (JS) expresses her gratitude to CSIR for providing the fellowship under XII plan period projects.Disclosure statementNo potential conflict of interest was reported by the author(s).Statement of noveltyThe residues obtained after potassium recovery by chloridizing roasting followed by water leaching of silicate minerals and rocks such as feldspar, nepheline syenite etc. are rich in silicon, aluminum, calcium, and iron due to which these can be utilized in various ways. Hence, processing of these residues would be a value addition to the potassium recovery process by increasing the number of products.In our present work, we have tried to recover aluminum from the roast leach residue of nepheline syenite containing 21.43% aluminum as its oxide employing the acid leaching method. Among various acids, leaching with sulfuric acid was better for downstream processing for aluminum recovery. Three parameters chosen for a two[Citation3] full factorial design were time, temperature, and acid concentration. The leaching extent obtained at the design conditions was fed to Minitab 17, and regression equations were generated. Furthermore, to enhance the recovery and to forbid the leaching of silicon, model equations were utilized for autoclave leaching. As the liquor constitutes iron along with aluminum, hence it was removed by pH adjustment to get aluminum-rich liquor which was further processed to get aluminum sulfate crystals.