High Recovery of Rees through Acid Baking of Their Bearing Minerals in a Fluidized Bed Reactor

There is a fast growth in new applications of Rare Earth Elements (REE), especially, in energy, environment and high technology fields where durability, high efficiency and low carbon emissions are required. The REE are called “rare” not because their abundance is low but because these elements are found in the deposits from which extraction is extremely difficult. Also, due to the fact that the REE have similar chemical properties, there was no known technique to produce these elements in individual forms until the twentieth century. Due to serious difficulties in the REE extraction, the total process would include a complex network of unit operations.

A REE production process from the mine to the final oxide form includes geology, mining, ore physical beneficiation, baking, hydrometallurgy and separation of individual elements. A concentrated ore is usually produced through a physical beneficiation process. Afterwards, it undergoes an acid baking process to crack the heavy molecules of the REE minerals as well as the associated gangues in order for easier extraction of the REE from undesired elements in a downstream hydrometallurgical process.

Being the most common process, baking with sulfuric acid at a temperature below its boiling point is carried out in rotary kilns; however, it suffers from serious challenges such as mass transfer limitations (i.e. causing high consumption of acid) and material handling due to stickiness of material inside the reactor.

Authors, have developed and commissioned a new fluidized bed reactor where a bed of concentrated REE ore particles (with average Sauter mean diameter of 100 μm) is fluidized at a temperature higher than sulfuric acid boiling point (~ 350 ^oC) where acid is atomized into the bed and the vapor gets in contact with ore particles. Bastnaesite and monazite are the main REE bearing minerals of the ore. Upon optimization of the superficial gas velocity, acid consumption declines, the bed stays being fluidized (with negligible detrimental effect of particles agglomeration) whereas conversion of REE bearing minerals to leachable REE sulfates is above 95%.