Prevailing mechanisms in pseudo-protic ionic liquid metal extractions

This work presents an evaluation of three different mechanisms that are present in ionic liquid (IL) metal extractions: the interaction that exists between the metal ion and the protic ionic liquid (PIL), the Hofmeister effect and the Van't Hoff–LeChatelier effect. Three different pseudo-protic ILs were used: trioctylammonium cyclohexanoate, trioctylammonium benzoate and trioctylammonium salicylate, without the need to use a chelating agent. The interaction between the metal ion and the PIL is most visible with copper and silver extraction. The position of the nitrate on the Hofmeister series causes high nitrate extraction efficiencies even when cobalt and nickel were extracted at very low efficiencies. The nitrate in these cases was extracted through an anion exchange mechanism. The Van't Hoff–LeChatelier effect causes an increase in extraction efficiencies, when all four metals are present in the aqueous phase, due to the high nitrate presence.