When the 𝐵𝐵𝐵𝐵 𝑃𝑃𝑃𝑃 second solvation shell, it is apparent that the 𝐵𝐵𝐵𝐵 𝑀𝑀𝑀𝑀𝑀𝑀 + values hardly change with the change of RE cation implying a negligible effect of second solvation shell on the separation mechanism. Therefore, it can be concluded that the RTIL-anionic part, which mainly drives the complexation with RE cations, is more selective for heavy RE over light RE, which supports the results observed by Chaumont et al. .