Recovery of Rare Earth Element Cerium from Spent Automotive Exhaust Catalysts Using a Novel Method

Abstract

This study developed a new method for the recovery of the rare earth element cerium (Ce) from spent automotive exhaust catalysts. The content of Ce was 5.31% (wt%) in the spent catalyst sample. Sulfuric acid (2 mol/L) and hydrofluoric acid (0.9 mol/L) were used as a mixed acid leaching agent to successfully decompose the ceria-zirconia solid solution of the catalyst, which is resistant to dissolve in acids. The leaching efficiency of Ce reached 99.25% under the optimal conditions of a catalyst particle size range of 76–96 µm, an S/L of 1/10 (w/v), a leaching temperature of 70 °C, a leaching time of 4 h, and 200 rpm. The Al3+ that was leached from the catalyst scrubbed F− in the leachate, allowing the separate extraction of Ce4+ using di-2-ethylhexyl phosphoric acid (D2EHPA) in sulfuric acid media. Potassium permanganate (KMnO4) with a concentration of 20% was added during the extraction to increase the oxidation rate of Ce and to diminish the reduction effect of the organic solution. The results indicated that 87.23% of Ce4+ was extracted into the D2EHPA-kerosene solution with a concentration of 0.8 mol/L D2EHPA, a stoichiometric quantity of KMnO4 of 175%, and contact for 15 min at room temperature. Reduction stripping was performed using hydrochloric acid (2 mol/L) with 3% H2O2 to obtain the CeCl3 solution. The recovered amount of Ce was 85.54% with high purity from the spent automotive exhaust catalyst.