Direct Production of Rare Earth Oxides from a Fresh REE Ore through Thermal Cracking in a Fluidized Bed Reactor

The rare earth elements (REE) are demanding metals with a vast number of applications in advanced technologies. The rare earth elements such as neodymium, dysprosium, europium, terbium and yttrium are the critical metals in the rapidly growing green energy and high technology sectors whereas China is the main supplier of the rare earth elements in the world (more than 85 %). In the past seven years, rare earths’ market has been volatile due to the strategic dependency of developed countries on China. That reliance caused a market crisis of the rare earths elements that was induced by the new policies on Chinese’s export quotas implemented in 2011. The event pushed the rest of the world (ROW) to invest in their own supplies, as it can be seen by the recently emerging commercial plants or researches.

There is no known technology and adequate infrastructure for recovery of the REE from the ores in ROW due to definite dependency on China. Due to special characteristics of the REE deposits, the REE mineral processing is not as easy as mineral processing of other metals such as gold and copper. Also, although there are quite a lot of the REE-bearing minerals, only a few of them are viable to be processed for the REE recovery.

Carbonatite type bastnäsite (REE.F.CO3) and phosphate type monazite (REE.Th.PO₄) are two REE bearing minerals from which extraction of the rare earth elements is viable. Conventional production of the rare earth elements, in the form of oxides, from an ore of bastnäsite and monazite usually includes physical beneficiation, minerals cracking, hydrometallurgy, and calcination steps.

Physical beneficiation’s objective is to produce a concentrate of the above-mentioned REE bearing minerals, which is usually a complex array of unit operation of magnetic, gravity and electrostatic separation as well as froth flotation.

The acid/alkali baking of the concentrate is another challenge in conventional REE production process because the consumption of acid or alkali imposes economic, e.g. capital cost and operational cost, and safety challenges to the process. The presence of fluorine in bastnäsite is another challenge since toxic fluoride gases can be produced during acid baking of the rare earth concentrate. Therefore, an improper handling of these substances can result in extensive environmental damages. A serious drawback in sulfuric acid baking is the production of SO₂ and SO₃ that would cause serious environmental issues like acid rain advent. In addition to the formation of SOx, applying sulfuric acid baking to such an ore mixture (bastnästie and monazite) is related to the production of hazardous gases such as HF and SiF₄ off the bastnäsite and sulfates of thorium and uranium off the monazite.

To overcome serious issues of physical beneficiation and minerals cracking steps of the conventional REE production processes, authors developed a direct production of the rare earth element oxides from bastnäsite and monazite REE bearing minerals through a process that is much simpler, more environmentally friendly and economical. Therein, the fresh ore directly undergoes thermal cracking with air to produce rare earth oxides in a fluidized bed reactor. Therefore, physical beneficiation, i.e. concentrate production, and minerals cracking, i.e. liberation of elements by acid/alkali baking of the conventional processes are eliminated.

Operating in a bubbling regime, the fluidized bed reactor provided a uniform heat and mass transfer in the bed of ore particles of Geldart's group A so that a maximum temperature of 800 ^oC was required under which particles agglomeration was not observed, and full conversion was achieved.