Hydrometallurgical Recycling of Rare Earth Metal–Cerium from Bio-processed Residual Waste of Exhausted Automobile Catalysts

Abstract

The hydrometallurgical recycling of cerium from a secondary residue of exhausted auto-catalyst was investigated. Cerium dissolution was significantly improved up to 96% when HF was additionally introduced into a 2.0 mol/L H2SO4 solution. The activation energy (E-a, 31.8 kJ/mol) indicated the diffusion-controlled mechanism prevailed in cerium leaching. Subsequently, the leach liquor containing 4.2 g/L cerium was equilibrated with Cyanex 923 for solvating the post-extraction species Ce(SO4)(2.)22(P = O)center dot HSO4-](org) into the organic phase. Thermodynamic properties revealed that the affinity of Cyanex 923 toward cerium was spontaneous (Delta G degrees(298K), -6.58 kJ/mol) and exhibited outer-sphere coordination for the exothermic process (Delta H degrees, -21.42 kJ/mol). Furthermore, cerium was quantitatively stripped (> 98%) from the loaded organic using the strippant mixture of 1.0 mol/L H2SO4 + 0.5 mol/L H2O2. Eventually, high-purity Ce-2(C2O4)(3).10H(2)O was precipitated by adding oxalic acid at an optimized dosage of Ce3+:H2C2O4 = 1:5.