Electrochemical Nuclear Waste Management Using Ionic Liquids: Controlled Electrodeposition of Fission Platinoids

Ionic liquids (ILs) have low flammability, wide liquidus range, metal complexing ability, moderate-to-high conductivity, and wide electrochemical window (1, 2). Utilizing these properties of ILs, processes for nuclear waste management could be developed which are safer, more tunable and more streamlined than existing processes based on extracting agents such as tri-n-butyl phosphate (TPB) and volatile organic compounds such as kerosene or dodecane (3). In such IL-based processes, electrodeposition of metals will follow their extraction from aqueous sludge of nuclear wastes (4). Hence, understanding electrodeposition behavior of metals in ILs is of critical importance to the IL-based nuclear waste management processes.

In this work electrodeposition of fission platinoids (Pd, Rh and Ru) in ILs is investigated using their non-radioactive counterparts. The recovery of fission platinoids is important not only from the nuclear waste management perspective, but also from economic viewpoint as these metals are expensive and highly utilizable (5).

First, electrochemical behaviors of Pd, Rh and Ru were studied in suitable ILs. The objective of the studies was to understand how the electrochemical behavior of Pd in candidate ILs changes in the presence of Rh and Ru. Similar studies were also done with Rh and Ru to find out how their electrochemical behavior changes in the presence of other fission platinoids. Then, electrodeposition behaviors of the metals were examined on Ni substrates. Pd was found to electrodeposit on Ni substrate in 1-butyl-1-methylpyrrolidinium dicyanamide ([Bmpyrr][DCA]) forming an uniform film as shown in Figure 1. Similarly, electrodeposition of Rh and Ru were carried out. The goal was to do selective electrodeposition of these metals guided by the knowledge gained from the electrochemical behavior studies.

References

1.         S. Z. E. Abedin, M. Polleth, S. A. Meiss, J. Janek and F. Endres, Green Chemistry, 9, 549 (2007).

2.         A. P. Abbott, G. Frisch and K. S. Ryder, Annual Review of Materials Research, 43, 335 (2013).

3.         S. Ha, R. Menchavez and Y.-M. Koo, Korean Journal of Chemical Engineering, 27, 1360 (2010).

4.         X. Sun, H. Luo and S. Dai, Chemical Reviews, 112, 2100 (2011).

5.         Z. Kolarik and E. V. Renard, Platinum Metals Review, 49, 79 (2005).

Figure 1. SEM image of Pd deposits on Ni substrate after potential hold of -0.524 V vs Fc/Fc⁺ for 1 h in a solution of 25 mM PdCl₂ in 1-butyl-1-methylpyrrolidinium dicyanamide ([Bmpyrr][DCA]) at room-temperature.