Advanced process to dephosphorize monazite for effective leaching of rare earth metals (REMs)

Abstract

The present paper reports an improved process using cheaper reagent at atmospheric conditions compared to the expensive pressure leaching technique (Temperature = 140 °C) as well as other processes available at higher temperature. An effective baking reagent, potassium hydroxide (KOH) was used to dephosphorize monazite. Roasting studies were carried out to optimize various process parameters such as temperature, time and doses of baking reagents. The dephosphorization of monazite was completed in 30 min at temperature 250 °C and monazite:KOH ratio of 1:1 (wt/wt). The experimental data was validated scientifically using TG-DTA. Further, leaching studies with selected lixiviant was carried out to optimize various process parameters viz. leachant concentration, time, pulp density, temperature and dosage of hydrogen peroxide (H2O2). More than 90% rare earth metals (REMs) were found to be leached from dephosphorized and washed residue using hydrochloric acid (HCl) at optimized condition i.e. 1 M HCl with 10% H2O2 (v/v), temperature 80 °C, time 120 min and pulp density 50 g/L. The novel process flow-sheet after scale-up studies can be used for monazite processing in industries.