Selective and Preferential Separation of Rhodium (III) from Palladium (II) and Platinum (IV) Using a m-Phenylene Diamine-Containing Precipitant

• Published in: Scientific reports Vol. 9; no. 1; pp. 12414 - 8
• Main Authors: Matsumoto, Kazuya, Yamakawa, Sumito, Haga, Kazutoshi, Ishibashi, Katsuyuki, Jikei, Mitsutoshi, Shibayama, Atsushi
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 27.08.2019; Nature Publishing Group
• Subjects: 140/131; 140/146; 704/172; 704/172/169; Cations; Humanities and Social Sciences; Hydrochloric acid; multidisciplinary; Palladium; Platinum; Rhodium; Science; Science (multidisciplinary)
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-48920-9

Although Rh is an industrially important and the most expensive platinum group metal (PGM), the selective and preferential separation of Rh from PGM mixtures still remains as a big challenge. In this work, the separation of Rh (III) from Pd (II) and Pt (IV) in a hydrochloric acid (HCl) solution was studied using a m -phenylene diamine-containing precipitant ( m - PDA ). At high HCl concentrations (6.0–8.0 M), most of the Rh (III) (>90%) was precipitated, and Pd (II) and Pt (IV) were hardly precipitated (<5%). On the other hand, over 85% of Pd (II) and Pt (IV) precipitated along with small amount of Rh (III) (<25%) at low HCl concentrations (1.0–2.0 M). As a consequence, m - PDA enabled selective and preferential precipitation of Rh (III) at high HCl concentrations. XPS and TG analyses revealed that the Rh-containing precipitate is an ion-pair complex composed of one [RhCl 6 ] 3− anion and three m - PDA cations. The Rh desorption from the precipitate as well as the recovery of m - PDA was successfully achieved using an NH 4 OH solution. This method is a promising practical approach to Rh recovery.