Metal ions, extraction using ligand metals

We see that the distribution coefficient for metal ion extraction depends on pH and ligand concentration. It is often possible to select a pH where D is large for one metal and small for another. For example. Figure 23-4 shows that Cu2+ could be separated from Pb2+ and Zn2+ by extraction with dithizone at pH 5. Demonstration 23-1 illustrates the pH dependence of an extraction with dithizone. Box 23-1 describes crown ethers that are used to extract polar reagents into nonpolar solvents for chemical reactions. 

The catalytic role of the interface was recognized in various liquid/liquid extraction systems. Interfacial adsorption of reactants was the key step in the interfacial catalysis in the extraction of metal ions. The interfacial ligand-substitution mechanism has great importance in the kinetic synergism. Some essential guidelines proposed here are highly useful, not only in solvent extraction but also in interfacial synthesis. 

Habtu MM, Bourne SA, Koch KR, Luckay RC. Competitive bulk liquid membrane transport and solvent extraction of some transition and post-transition metal ions using acylthiourea ligands as ionophores. New J Chem (S Afr) 2006 30 1155-1162. 

Fluoride can be determined by means of an iron(iii) thiocyanato complex extracted into isobutylketone. Iron is extracted back into the aqueous phase with the fluoride sample solution. The atomic absorption signal of iron is directly proportional to the concentration of fluoride (0.5-6 ju,g F ml ). EDTA can be determined by a similar technique. Copper is first extracted as the hydroxyquinolinato complex into isobutylketone, and then extracted back into the aqueous solution with the EDTA sample solution. In these methods the analyte anion must form a more stable complex compound with the metal ion than the ligand used for the first solvent extraction. These kind of... 

We would like to stress the mesmerizing underlying implications of the results discussed in this section. Efficient extraction of pure IL phases opens the route to totally new systems, purely (and simply) discarding the notion of ligand which has been in use for decades in the field of metallic ion extraction. On a more classical approach, selective successive extractions could be envisioned, some elements being extracted by the pure IL phase, and once these have been back extracted, the now clean pure IL phase could act as a solvent for a ligand able to extract the remaining elements of interest from... 

Beta-diketones have been used as efficient extractants for actinides from weakly acidic medium (Manchanda et al., 2009). In view of being acidic extractants, an increase in the feed acidity decreases the metal ion extraction. On the other hand, the presence of neutral donor ligands leads to S5mergism and hence to higher metal ion extraction compared to the beta-diketone alone at a given acidity. 

Liquid-liquid extractions using ammonium pyrrolidine dithiocarbamate (APDC) as a metal chelating agent are commonly encountered in the analysis of metal ions in aqueous samples. The sample and APDC are mixed together, and the resulting metal-ligand complexes are extracted into methyl isobutyl ketone before analysis. 

Cupferron is a ligand whose strong affinity for metal ions makes it useful as a chelating agent in liquid-liquid extractions. The following distribution ratios are known for the extraction of Hg +, Pb +, and Zn + from aqueous solutions to an organic solvent. 

While certain TSILs have been developed to pull metals into the IL phase, others have been developed to keep metals in an IL phase. The use of metal complexes dissolved in IL for catalytic reactions has been one of the most fruitful areas of IL research to date. LLowever, these systems still have a tendency to leach dissolved catalyst into the co-solvents used to extract the product of the reaction from the ionic liquid. Consequently, Wasserscheid et al. have pioneered the use of TSILs based upon the dissolution into a conventional IL of metal complexes that incorporate charged phosphine ligands in their stmctures [16-18]. These metal complex ions become an integral part of the ionic medium, and remain there when the reaction products arising from their use are extracted into a co-solvent. Certain of the charged phosphine ions that form the basis of this chemistry (e.g., P(m-C6H4S03 Na )3) are commercially available, while others may be prepared by established phosphine synthetic procedures. 

Macrocyclic ligands such as crown ethers have been widely used for metal ion extraction, the basis for metal ion selectivity being the structure and cavity size of the crown ether. The hydrophobicity of the ligand can be adjusted by attachment of alkyl or aromatic ligands to the crown. Impressive results have been obtained with dicyclohexano-18-crown-6 as an extractant for Sr in [RMIM][(CF3S02)2N] IL/aque-... 

The nature of the donor atoms in the chelating agent. Ligands which contain donor atoms of the soft-base type form their most stable complexes with the relatively small group of Class B metal ions (i.e. soft acids) and are thus more selective reagents. This is illustrated by the reagent diphenylthiocarbazone (dithizone) used for the solvent extraction of metal ions such as Pd2+, Ag+, Hg2+, Cu2+, Bi3+, Pb2+, and Zn2 +. ... 

Sulfate process streams are commonly used in metal recovery because they are readily derived by leaching with sulfuric acid or by oxidation of sulfidic ores. Metal recovery from such streams rarely involves the formation of metal sulfate complexes because the sulfate ion is a weak ligand for base metal cations and consequently acidic ion exchange extractants are commonly employed (see Section 9.17.5), which generate sulfuric acid which can be returned to the leaching stage,... 

Lee, S. S. Yoon, I. Park, K.-M. Jung, J. H. Lindoy, L. F. Nezhadali, A. Rounaghi, G. Competitive bulk membrane transport and solvent extraction of transition and post transition metal ions using mixed-donor acyclic ligands as ionophores. J. Chem. Soc.-Dalton Trans. 2002, 2180-2184. 

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