Abstract
Recovery of platinum group metals (PGMs) from waste three-way catalysts (TWCs) was usually achieved by dissolving them in an acid solution. However, their dissolution requires the addition of oxidizing agents such as Cl2 and aqua regia, which could cause high environmental risks. Therefore, the development of new methods without the addition of oxidant agents will contribute to the green recovery of PGMs. In this paper, the process and mechanism of PGMs recovery from waste TWCs by Li2CO3 calcination pretreatment-HCl leaching were studied in detail, and molecular dynamics calculations were performed for the formation processes of Pt, Pd, and Rh complex oxides. The results showed that the leaching rates of Pt, Pd, and Rh could reach about 95%, 98%, and 97%, respectively, under the optimal conditions. Li2CO3 calcination pretreatment cannot only oxidize Pt, Pd, and Rh metals to HCl-soluble Li2PtO3, Li2PdO2, and Li2RhO3, but also remove the carbon accumulation in waste TWCs and open the wrapping of PGMs by the substrate and Al2O3 coating. The embedding of Li and O atoms in metallic Pt, Pd, and Rh is an interacting embedding process. Although the Li atoms are faster than O, O will accumulate on the metal surface first before embedding.
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