Often unnoticed, radioactivity handling in the rare earth elements (REE) mining industry is an environmental and economic concern that needs to be properly addressed. Actinides, such as uranium and thorium, are frequently co-dissolved with REEs in currently used hydrometallurgical processes, which results in radioactive contamination of the infrastructure across the extraction cycle. The present study investigates, through an optimization approach based on experimental design, a sequential leaching procedure with Na2CO3/NaHCO3 and HCl for the rapid and selective dissolution of REE and actinides. The experimental design investigated takes into consideration the main operating parameters (i.e. time, temperature and concentration) and the different types of minerals, REE composite and ores. The final sequential procedure was rapid (1 h), effective and led to segregation between Th, U and REE with limited dissolution of the gangue constituents, notably Fe, Si and Ca.