Cation Effect of Chloride Salting Agents on Transition Metal Ion Hydration and Solvent Extraction by the Basic Extractant Methyltrioctylammonium Chloride
| Autor: | Koen Binnemans, Bieke Onghena, Rayco Lommelen |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
chemistry.chemical_classification
Aqueous solution 010405 organic chemistry Chemistry Metal ions in aqueous solution Inorganic chemistry Extraction (chemistry) Aqueous two-phase system Salt (chemistry) 010402 general chemistry 01 natural sciences Chloride 0104 chemical sciences Inorganic Chemistry Metal Transition metal visual_art medicine visual_art.visual_art_medium Physical and Theoretical Chemistry medicine.drug |
| Zdroj: | Inorganic Chemistry |
| Popis: | The addition of a nonextractable salt has an important influence on the solvent extraction of metal ions, but the underlying principles are not completely understood yet. However, relating solute hydration mechanisms to solvent extraction equilibria is key to understanding the mechanism of solvent extraction of metal ions as a whole. We have studied the speciation of Co(II), Zn(II), and Cu(II) in aqueous solutions containing different chloride salts to understand their extraction to the basic extractant methyltrioctylammonium chloride (TOMAC). This includes the first speciation profile of Zn(II) in chloride media with the three Zn(II) species [Zn(H2O)6]2+, [ZnCl3H2O]-, and [ZnCl4]2-. The observed differences in extraction efficiency for a given transition metal ion can be explained by transition metal ion hydration due to ion-solvent interactions, rather than by ion-solute interactions or by differences in speciation. Chloride salting agents bearing a cation with a larger hydration Gibbs free energy reduce the free water content more, resulting in a lower hydration for the transition metal ion. This destabilizes the transition metal chloro complex in the aqueous phase and increases the extraction efficiency. Salting agents with di- and trivalent cations reduce the transition metal chloro complex hydration less than expected, resulting in a lower extraction efficiency. The cations of these salting agents have a very large hydration Gibbs free energy, but the overall hydration of these salts is reduced due to significant salt ion pair formation. The general order of salting-out strength for the extraction of metal ions from chloride salt solutions is Cs+ < Rb+ < NH4+ ≈ K+ < Al3+ ≈ Mg2+ ≈ Ca2+ ≈ Na+ < Li+. These findings can help in predicting the optimal conditions for metal separation by solvent extraction and also contribute to a broader understanding of the effects of dissolved salts on solutes. ispartof: INORGANIC CHEMISTRY vol:59 issue:18 pages:13442-13452 ispartof: location:United States status: published |
| Databáze: | OpenAIRE |
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