Processing of Kazakh Red Mud (KRM) for the Selective Recovery of Rare Earth Elements (REEs) through microwave-assisted acid leaching

Abstract

Bauxite residue, also known as Red Mud (RM), is generated through the Bayer Process and is considered one of the most environmentally hazardous by-products of aluminum production. It is also viewed as a secondary source of several other valuable metals, including Rare Earth Elements (REEs). However, the recovery of these REEs is hampered because they are strongly associated with various mineral phases, including iron oxide, aluminosilicate, and Ti-bearing minerals, making it difficult to extract them through conventional leaching. In this thesis, we have investigated how Microwave Assisted Pretreatment can be used to improve the Recovery of selected REEs (Ce, Nd, Sm and Eu) from Kazakhstan Red Mud (KRM) when microwave treatment was utilized in an effort to create changes at a micro level to the structure of KRM particles to disrupt the size of particles, to cause cracking within particles, and modify the mineral phases containing the REE's. Once pre-treatments had been completed, leach solutions were prepared utilizing various types of acidic media under controlled experimental conditions. Both treated and untreated samples were analyzed using X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), and Fourier Transform InfraRed Spectroscopy (FTIR) in order to assess changes in the mineral composition and structural properties of KRM. The obtained results demonstrated that microwave-assisted pre treatment significantly improved leaching yields over those obtained directly via leaching. We also found that the primary mechanisms responsible for this enhancement included increased structural disruption in KRM, resulting in better access for the leaching agent into the solid phase. Of note, significant enhancements in the leaching of Ce and Nd occurred, however, Sm and Eu showed minimal enhancement in leaching due to their association with more stable mineral phases.