A Novel Mechanism for the Extraction of Metals from Water to Ionic Liquids

Abstract

We present a novel mechanism for the extraction of metals from aqueous phases to room-temperature ionic liquids (ILs) by use of a high-temperature salt as an extraction agent. The mechanism capitalizes on the fact that charged metal complexes are soluble in ILs; this allows for extraction of charged complexes rather than the neutral species, which are formed by conventional approaches. The use of a well-chosen extraction agent also suppresses the competing ion-exchange mechanism, thus preventing degradation of the ionic liquid. The approach permits the use of excess extractant to drive the recovery of metals in high yield. This work presents both a thermodynamic framework for understanding the approach and experimental verification of the process in a range of different ILs. The method has great potential value in the recovery of metals, water purification and nuclear materials processing.

Copper extraction using protic ionic liquids: Evidence of the Hofmeister effect

“…The observed anion:copper ratios do not necessarily indicate that the anions are coordinated with the copper, as previous work indicates that charged metal complexes are soluble in ILs [14,15] and uncoordinated ions can move into the IL phase in tandem with a charged metal complex to maintain electroneutrality [59,60]. As indicated in Table 3, all three mineral anions used in the present study coordinate relatively weakly with copper(II).…”

“…Ion exchange mechanisms involving metals and IL cations have been studied extensively [55][56][57][58][59][60], and it is observed that strongly hydrophobic cations such as 1-decyl-3-methylimidazolium generally do not undergo extensive ion exchange [61]. The trialkylammonium species in the ILs used in the current study are sufficiently hydrophobic that it would be quite surprising if they engaged in ion exchange to a significant degree.…”

Selective Extraction of Metal Ions from Aqueous Phase to Ionic Liquids: A Novel Thermodynamic Approach to Separations

“…Both the cation and anion, however, must be extracted to maintain electroneutrality. We have demonstrated17 that the method not only provides high yields in extracted ions, it also suppresses the ion exchange mechanism noted in the Introduction, preserving the integrity of the IL. Note that this is distinct from conventional salting out approaches used to precipitate biomolecules.…”

“…We have shown previously17 that the extraction of ions from aqueous to IL phase can be promoted by using a salt as a co‐extractant. The process is shown schematically in Figure 2.…”

Using Crystal Structures of Ionic Compounds to Explore Complexation and Extraction of Rare Earth Elements in Ionic Liquids

“…Nevertheless, extraction studies in ILs are often conducted with the goal of promoting a neutral extraction mechanism over ion exchange. This is achieved by controlling the components of the IL, the extractant, and the aqueous phase (often empirically) so that the extracted metal species is neutral [51,52].…”