Base metals (Fe, Al, Ti) and rare earth elements (Ce, La, Pr) leaching from red mud through an efficient chemical-biological hybrid approach

• Published in: Minerals engineering 2024-03, Vol.208, p.108603, Article 108603
• Main Authors: Ilkhani, Zahra, Vakilchap, Farzane, Sadeghi, Niloofar, Mohammad Mousavi, Seyyed
• Format: Article
• Language: English
• Subjects: Bioleaching; Heterotrophic bacteria; Oxalic acid; Rare earth elements; Red mud
• ISSN: 0892-6875; 1872-9444
• DOI: 10.1016/j.mineng.2024.108603

[Display omitted] •A chemical-biological hybrid approach was proposed for metal leaching from RM.•Fe (98.4%), Al (98.4%), and Ti (80%) from RM were leached by an organic agent.•One-step bioleaching of REEs from pretreated RM was done by Bacillus foraminis.•Bioleaching of REEs from initial RM was negligible compared to pretreated one.•Total leaching of Pr (55%), Ce (15.3%), and La (15%) were obtained. Metal recycling from solid waste is now widely recognized as an effective solution to tackle environmental threats, enhance human safety, and mitigate the depletion of natural metal resources. Red mud (RM), a by-product produced in significant quantities by the alumina industry, is commonly disposed of in landfills without proper utilization. The European Commission has identified this waste as a critical raw material containing valuable metals and rare earth elements (REEs), highlighting the urgent need for proper recycling and reutilization. This study presents a novel chemical-biological hybrid procedure, assisted by a chelating agent and a one-step bioleaching from RM. Initially, a leaching process as a pretreatment was conducted using 0.23 M oxalic acid at 80 °C, with 200 rpm agitation for 4 h, at a pulp density of 10 g/L. This process was effective in leaching of Fe (98.4 %), Al (98.4 %), and Ti (80 %), which act as barriers hindering the bioleaching of REEs. Subsequently, Bacillus foraminis, an alkali-tolerant heterotrophic bacterium, was employed for one-step bioleaching of REEs from pretreated RM. The process resulted in the biological leaching of 35 % Pr, 6.3 % Ce, and 1 % La. To confirm the structural changes of the RM powder caused by the chemical and biological leaching, comprehensive analyses were conducted using X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and Field Emission Scanning Electron Microscope (FE-SEM) both before and after leaching processes.