Bioleaching of rare earth elements from spent automobile catalyst as pretreatment method to improve Pt and Pd recovery: Process optimization and kinetic study

In this study, the extraction of rare metals from the spent automobile catalyst using Aspergillus niger (A. niger) was investigated. The effect of different factors including initial glucose, initial pH, inoculum percentage, and Solid to Liquid (S/L) ratio on the A.niger growth was done. Then in the condition of initial glucose of 100 g/L, initial pH of 5, inoculum percentage of 2.5 %, S/L ratio of 1 %(w/v), the extraction efficiency were 25.9 % of cerium (Ce), 43.0 % of aluminum (Al) for 240 h, and 23.9 % of lanthanum (La) for 48 h. After the bioleaching section, the spent residue was applied for platinum (Pt) and palladium (Pd) recovery using aqua regia, which results in a 100 % recovery of these metals. The shrinking core model results showed that both chemical reaction and diffusion on the surface controlled the overall reaction rate. Additionally, the characterization methods including SEM, FTIR, HPLC, and XRD before and after bioleaching were performed. © 2021