Technospheric Mining of Rare Earth Elements from Bauxite Residue (Red Mud)

Due to their inherent physicochemical properties, rare earth elements (REEs) are used in many critical and emerging technologies. The demand for some REEs is increasing sharply in line with increasing demand for these technologies. Such elements are classified as critical â i.e., those that are essential in use and subject to supply risk. To satisfy the increasing demand for REEs, initiatives have been started to recover them from secondary sources, also known as technospheric mining. This study puts the emphasis on technospheric mining of REEs from bauxite residue produced by the aluminum industry. The thesis is divided into five segments: 1) thorough characterization of the bauxite residue obtained from Rio Tinto; 2) development of the leaching process to extract REEs from the bauxite residue; 3) kinetic investigation of the leaching process; 4) development of microwave pretreatment process; and 5) development of the purification process to separate REEs from the leach solution.M.A.S

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