Selective Extraction of Rare Earth Elements from Complex Monazite Ores

Rare Earth Elements (REE) are fundamental for modern life products and green technologies. Supply constraints and the price peak of 2011 boosted intensive research for alternatives for processing and separation. Complex monazite-type, rare earth ores usually contain high acid consumption impurities, such as iron and aluminum, and radioactive thorium in their composition. These impurities are not removed by conventional concentration processes due to fine, micro-level association between the REE carrying minerals and the gangue minerals. This work presents a selective process route for REE extraction from iron-rich, monazite ores. The process involves sulfation by addition of concentrated sulfuric acid and pyrohydrolysis at temperatures of approximately 700–750 °C. Experimental results show REE extraction higher than 70% and low iron (below 5%) and thorium extraction (below 10%). A method based on thermogravimetric analyses was shown to be adequate to predict the behavior of a given ore sample in the sulfation-selective pyrolysis-leaching process.