Technospheric Mining of Rare Earth Elements from Bauxite Residue (Red Mud): Process Optimization, Kinetic Investigation, and Microwave Pretreatment

Abstract

Some rare earth elements (REEs) are classified under critical materials, i.e., essential in use and subject to supply risk, due to their increasing demand, monopolistic supply, and environmentally unsustainable and expensive mining practices. To tackle the REE supply challenge, new initiatives have been started focusing on their extraction from alternative secondary resources. This study puts the emphasis on technospheric mining of REEs from bauxite residue (red mud) produced by the aluminum industry. Characterization results showed the bauxite residue sample contains about 0.03 wt% REEs. Systematic leaching experiments showed that concentrated HNO3 is the most effective lixiviant. However, because of the process complexities, H2SO4 was selected as the lixiviant. To further enhance the leaching efficiency, a novel process based on microwave pretreatment was employed. Results indicated that microwave pretreatment creates cracks and pores in the particles, enabling the lixiviant to diffuse further into the particles, bringing more REEs into solution, yielding of 64.2% and 78.7% for Sc and Nd, respectively, which are higher than the maximum obtained when HNO3 was used. This novel process of “H2SO4 leaching-coupled with-microwave pretreatment” proves to be a promising technique that can help realize the technological potential of REE recovery from secondary resources, particularly bauxite residue.

Rare Earth Element Phases in Bauxite Residue

“…In a Canadian bauxite residue sample (Jonquière, Québec), REE-containing particles were noted as bright spots in electron backscatter imaging, sub-µm in size. A STEM-EDS elemental mapping also showed the presence of REE-containing particles, where cerium and titanium presence were correlated [53]. Based on the observations of bauxite residue leaching behaviour, Bayer process secondary minerals like cancrinite and hydrogarnet have also been proposed as the possible hosts of REEs [54].…”

“…The mentioned perovskite was also crystallographically characterised and matched with perovskite structure reference with some deviations from the conventional data, possibly due to the incorporation of sodium on the A site of perovskite [52]. Cerium and titanium correlating presence was found in a Canadian bauxite residue sample [53]. Bayer process derived REE titanate compounds were mentioned in a patent describing the recovery of REEs from bauxite residue [51].…”

Leaching Characteristics of Low Concentration Rare Earth Elements in Korean (Samcheok) CFBC Bottom Ash Samples

“…There are numerous studies on the extraction of REEs from secondary sources [2,20]. REEs mining from red mud with extraction yields of 70-80% were documented [21][22][23]. There also exist studies on extraction and recovery of REEs from permanent magnets [24,25], or from fluorescent lamps [26].…”

Recovery of Gallium from Bauxite Residue Using Combined Oxalic Acid Leaching with Adsorption onto Zeolite HY

“…It is available at a multimillion ton scale worldwide as the global inventory of bauxite residue already reached an estimated 2.7 billion tons by 2011 [8] with an annual production rate of 150 million tons [9]. Numerous studies have focused on the utilization of bauxite residue as a source for the production of major elements (e.g., blast furnace for pig iron production [10][11][12][13][14]) or as a source of rare earth elements (REEs) [15][16][17][18][19] as well as the combination of these [20]. Fewer efforts have been made to use the bauxite residue as a secondary source of other CRMs such as V and Ga [18,21,22].…”

“…The most widely used strategy for extraction of economically interesting elements from bauxite residue is direct hydrometallurgical leaching [16,18,[28][29][30]. Technologies have been investigated for major metal (Al, Fe, and Ti) recovery by pyrometallurgical/mechanical operations (reductive smelting, roasting) and combinations of the latter with hydrometallurgical leaching [11,12,20,31,32].…”