JAEA develops ion-pair extraction technology enabling efficient separation of platinum group elements

A research group comprising Yuji Sasaki and Group Leader Yuta Kumagai from the Research Group for Nuclear Chemistry, Nuclear Science and Engineering Center, Nuclear Science Research Institute, Japan Atomic Energy Agency (JAEA), along with Professor Masahiko Matsumiya from the Graduate School of Environment and Information Sciences at Yokohama National University and Associate Professor Masashi Kaneko from the Graduate School of Science, the University of Osaka, announced the development of a technology enabling the efficient solvent extraction of the platinum group elements palladium (Pd), ruthenium (Ru), and rhodium (Rh) from waste materials. This is an application of originally developed separation techniques for radioactive materials. Notably, it achieves a 10-fold increase in efficiency compared with conventional methods for ruthenium, which has been difficult to selectively extract and separate. This development is expected to improve recycling efficiency from urban mines. The results were published in the Journal of Molecular Liquids on December 6.

Among platinum group elements, Ru is used in computer HDDs, while Pd and Rh are employed in automotive exhaust gas purification catalysts. Since there exists demand to replace these products, they generate substantial industrial waste. With limited resource availability and its production being concentrated in few countries, recycling has become increasingly important. However, conventional solvent extraction technologies required complex processing that combined multiple techniques.

Therefore, the research group explored the application of solvent extraction mechanisms developed through nuclear research. The three platinum group elements are fission products of uranium, which are contained in high-level radioactive waste liquid.

JAEA had previously identified conditions enabling extraction of these platinum group elements. They developed extractants which generate no secondary waste after extraction when incinerated. Solvent extraction involves removing metal ions using two layers: an organic phase containing the extractant and an aqueous phase. Shaking causes the metal ions in the aqueous phase to bind to the extractant and transfer to the organic phase. To maintain the two-layer system, electrical neutrality must be preserved within the organic phase.

In this study, the research group established that by using extractants which become cations under acidic conditions, "ion-pair extraction" occurs. Within this, the extractants pair with anions formed by platinum group elements and hydrochloric acid, enabling their extraction.

Furthermore, the results confirmed that ion-pair extraction is applicable not only to Rh, as previously proposed, but also to Pd and Ru. They also verified that heating with the previously developed extractants - "TDGA," "MIDOA," and "NTAamide" - improves extraction efficiency. Additionally, they devised and experimentally verified a method for separately recovering the three platinum group elements into aqueous solutions.

The group also confirmed that the extractants can be reused by back-extracting the platinum group elements into the aqueous phase using reagents. In particular, the back-extraction conditions developed for Ru achieved world-leading performance.

They further proposed a mutual separation flow enabling continuous extraction by employing specific extractants for each platinum group element.

Sasaki commented: "This proposal involves recovering platinum group elements in aqueous solution, which will facilitate processing according to subsequent uses. We would be pleased if the method we developed is used for recovering precious metals from scrap."

Journal Information
Publication: Journal of Molecular Liquids
Title: Mutual separation of Ru, Rh, and Pd via reflux-assisted extraction and reverse-extraction using ion-pair and solvation with S- and amino-N-donor reagents
DOI: 10.1016/j.molliq.2025.129013