New insight into the adsorption of ruthenium, rhodium,and palladium from nitric acid solution by a silica-polymer adsorbent

A porous silica-polymer-based adsorbent, isoBu-BTP/SiO₂-P, was prepared by a vacuum impregnation method and used for the recovery of ruthenium, rhodium, and palladium from nitric acid solution. The experimental results revealed that iso Bu-BTP/SiO₂-P exhibited unique adsorption properties such as high saturation adsorption capacity (Ru: 0.35 mmol g^-1, Rh: 0.32 mmol g^-1, Pd: 1.05 mmol g^-1) and excellent selectivity over other metal ions, such as lanthanides (SF_PGM/M > 40) in 1 M HNO₃ solution. The adsorption process conformed to the pseudo-second-order model and Langmuir model. From the UV, FTIR, and XPS analyses, it can be concluded that the strong affinity between functional groups (C-N=C) and metal ions as well as NO₃^- played a role in coordination during the adsorption process. Furthermore, the desorption behavior was studied, and it was found that the adsorbed Pd, Rh, and Ru could be eluted with a 0.01 M nitric acid-0.1 M thiocarbamide solution, 5 M hydrochloric acid, and sodium hypochlorite (CP) solution, respectively. Finally, based on those findings, a simple process for the separation and recovery of Pd, Rh, and Ru from high-level liquid waste using iso Bu-BTP/SiO₂-P was designed and proposed. (authors)