Optimization of Multistage Precipitation Processes for Rare Earth Element Purification from Indonesian Zircon Tailings

This study investigated the effects of temperature, pH, and stirring speed of multistage precipitation processes. The purification process consists of uranium and thorium precipitation, oxalate precipitation, calcination, HNO3 leaching, and oxidation; finally, multistage precipitation is performed using Na2CO3 and NH4OH. The precipitation efficiencies of light rare earth elements (LREEs) and heavy rare earth elements (HREEs) reached 88% and 74%, respectively, during precipitation with 15% Na2CO3 at a temperature of 50 degrees C, pH of 4.5, and 200 rpm. The precipitation process was continued by adding 10% NH4OH to the first precipitation raffinate. A total of 45% of the LREEs were recovered at a temperature of 30 degrees C, pH of 8, and 300 rpm. Meanwhile, 72% of the HREEs were recovered at a temperature of 30 degrees C, pH of 7, and 200 rpm. It was observed that Na2CO3 was effective in precipitating rare earth elements (REEs) at higher temperatures, whereas NH4OH was better at precipitating the HREEs from an REE-nitrate solution under the same processing conditions.