Studies on extraction of potassium values from nepheline syenite

Abstract

Nepheline syenite is a complex rock consisting of different mineral phases such as nepheline, alkali feldspar, and biotite. It is a promising source for the recovery of potassium and alumina values. India is importing most of its potassium demand from the global market. An attempt is therefore made to extract potassium values from nepheline syenite available in the state of Odisha. It contains 2.8% Fe2O3, 19.9% Al2O3, 55.5% SiO2 and 5.4% K2O as its prime constituents. Magnetic separation and flotation techniques are found unsuitable to recover appreciable amounts of potassium values. Chemical leaching with dilute sulphuric acid could recover only ~40% of the potassium values. The potassium values present in nepheline syenite are unlocked through roasting with calcium chloride followed by water leaching. In this approach, it is possible to recover ~99.6% K2O value at 900°C temperature and 30min of roasting time. The results indicate that the use of planetary mill grinding prior to roasting is favorable for potassium extraction due to mechanical activation of the potassium bearing phases. The different mineral phases present in the feed and the leach residue have been characterized by using optical microscope, XRD and SEM-EDX which shows a phase conversion of locked potassium into sylvite which is soluble in water.