Investigation of microwave roasting for potash extraction from nepheline syenite

• Nepheline syenite contains 5.4% K2O.
• Microwave heating attempted for K extraction.
• Charcoal and CaCl2 used as heat source and reactant.
• Formation of water soluble sylvite within 6 min.
• 88% potash values could be extracted.

Nepheline syenite is an igneous rock, which contains around 5.4% of potassium oxide (K2O), but finely dispersed and, locked in the host matrix. The characterization studies reveal the presence of orthoclase, nepheline and biotite as the major potassium bearing mineral phases. The present study aims at the extraction of potash values through microwave heating for its possible application as fertilizer. The microwave assisted roasting studies of nepheline syenite have been carried out and optimized using a statistical approach based on Taguchi design. It is possible to extract around 88% K2O values at 900 W microwave power and 6 min of roasting time using 20% charcoal and 50% calcium chloride. Charcoal is used as a microwave absorbing material that raises its temperature in a much lesser time, while calcium chloride for the favorable formation of KCl. The transformation of different mineral phases of nepheline syenite is characterized using XRD, and SEM showing the formation of a soluble potassium bearing phase (Sylvite) along with calcium aluminum silicate.