Selection of a hydrometallurgical process for rare earths extraction from a Brazilian monazite

This work describes the processing of a monazite concentrate containing iron mineral phases in order to recover the rare earth elements (lanthanum was taken as representative for REEs) with minimum iron interference. Three classical routes were tested: acid leaching, alkaline conversion and acid baking. Control of iron bearing mineral phases was performed during REEs leaching. The most important variables of each process were determinated using experimental design planning. The acid leaching presented high lanthanum extraction but this route was not selective as high Fe extraction was found. Leaching temperature was the most important variable. Alkaline conversion presented medium-to-high lanthanum extraction and a relatively selectivity for iron. Temperature was also the most important variable. Temperature was also the most important variable for the acid baking route, but the amount of acid added to the system and the leaching time were also relevant for iron extraction. High yields were achieved for lanthanum, together with moderate yields for iron. The choice of the best route was determined using the Desirability Function as multiresponse methodology. The alkaline conversion route presented the best combined recovery and selectivity results for lanthanum (with a maximum of 77 wt%) and iron extraction (below 5 wt%).

Automated summary

This work focuses on processing a monazite concentrate containing iron mineral phases to recover rare earth elements, with the alkaline conversion route showing the best combined recovery and selectivity results for lanthanum and iron. Various experimental designs were used to determine the key variables for each processing route, with temperature playing a significant role in all three routes.