Catalytic dissolution of ceria–lanthanide mixed oxides provides environmentally friendly partitioning of lanthanides and platinum

The reductive dissolution of cerium–lanthanide mixed oxides was investigated under mild conditions in weakly acid media. The dissolution is catalyzed by platinum nanoparticles (Pt NPs) deposited onto oxide surfaces. The deposition of Pt NPs was performed by sonochemical reduction of Pt(IV). The dissolution efficiency was studied as a function of different parameters such as stirring, sonication at 20 kHz, dissolution media and oxide composition. The quantitative dissolution of these oxides can be performed in 0.25 M HNO3–1 M HCOOH–0.2 M [N2H5][NO3] and 0.125 M H2SO4–1 M HCOOH under stirring at 40 °C in the presence of argon, or in 0.125 M H2SO4 under sonication in the presence of Ar–CO gas mixture at 40 °C. In nitric acid solutions mechanical stirring is more efficient than sonication due to the secondary denitration triggered by ultrasound. The incorporation of trivalent (Gd, Nd) or tetravalent (Tb) lanthanides into the ceria matrix resulted in faster dissolution. After dissolution, lanthanides and platinum can be separated by simple filtration. The catalytic dissolution of ceria-based mixed oxides offers a simple way of lanthanide and noble metal partitioning which could appear of interest for catalyst recycling.