Nepheline Syenite-An Alternative Source for Potassium and Aluminium

Abstract

An integrated approach has been made to extract potassium and aluminium from a silicate mineral, i.e. nepheline syenite with 5.4% K2O, 19.9% Al2O3, 55.5% SiO2. Chloridising-roasting experiments were carried using CaCl2 at 900 degrees C for 1 h and water leaching at ambient temperature for 1 h. The leach liquor contains impurities like Ca and Na; hence, selective extraction of potassium was carried out through precipitation using perchloric acid at freezing temperatures. XRD data of the final KCl product obtained after decomposition of KClO4 indicated cubical crystal system and was found to be 99.5% pure. In the second stage, leaching of the residue was carried out with HCl, H2SO4 and H2SiF6. For selective aluminium recovery, sulphuric acid was found to be the better leachant. A 2(3) full factorial design with time, temperature and acid concentration was used. Finally, aluminium sulphate crystals were produced from the leach liquor after removing iron through pH adjustment.