Feasibility of extraction of cerium dioxide (CeO2) from monazite at Pulmoddai

Abstract

Monazite concentration in Pulmoddai mineral sand deposit in Sri Lanka is 1.38%. Its Rare Earth Elements (REE) composition is about 61%. Currently, only heavy minerals are separated and cerium rich monazite is discarded. Therefore, the study is focused on finding feasibility of extraction of CeO2 from Pulmoddai monazite. The research was conducted under four stages, removal of phosphate ions, removal of radioactive elements, purified Rare Earth oxide (REO) preparation and selective separation of CeO2. The optimum concentration of NaOH solution is found as 80% (w/v)/ 20M. Alkaline digestion was done for 4hrs at 150oC by adding 25 ml of NaOH to 25 g of monazite, followed by acid leaching with 50 ml of 60%(w/v) HCl at 90°C for 1hr. Concentration of 20 g/L (0.22M) oxalic acid should be added to the RE chloride mixture until the complete precipitation of RE oxalates. Purified REO was obtained by calcination at 900°C for 2hrs using RE oxalate precipitated. Purified REO was used to recover CeO2 by subjecting to selective precipitation. Selective precipitation of CeO2 was carried out using solid form of KMnO4 and (15wt%) Na2CO3 solution with maintaining average pH value 4 by manual addition of Na2CO3 solution ([15 g /100 L]/0.001M).