Charge extraction selectivity

Controlling Electrode Polarity and Charge Extraction Selectivity... 

A secondary, more subtle, effect that can be utilized in the achievement of selectivity in cation exchange is the selective complexation of certain metal ions with anionic ligands. This reduces the net positive charge of those ions and decreases their extraction by the resin. In certain instances, where stable anionic complexes form, extraction is suppressed completely. This technique has been utilized in the separation of cobalt and nickel from iron, by masking of the iron as a neutral or anionic complex with citrate350 or tartrate.351 Similarly, a high chloride concentration would complex the cobalt and the iron as anionic complexes and allow nickel, which does not form anionic chloro complexes, to be extracted selectively by a cation-exchange resin. 

The beam leaving the expansion chamber via the skimmer aperture is electrically neutral and heavily dominated by neutral Ar atoms, forcing all entities to move with the same velocity [21, 22]. A negatively charged extraction lens selectively attracts the positive ions and repels the negatively charged entities (electrons and ions), which are removed by the vacuum system together with the neutral particles, which... 

Sulfate solutions of leaching are of a big importance in hydrometallurgy of copper. With regard to above mentioned results sulfate media interesting in terms of influence of aqueous phase ion composition on copper extraction selectivity in the presence of iron. As double charged sulfate ion is solvated with water much better, and can t form extracting ion-associates with lipophilic cations it can believed that Fe(III) will be extracted from sulfate solutions with reagent under study only per mechanism (2) that can be implemented in a weak acid media. 

Method of Rh(III) - Ru(III) separation and isolation them from rai e and nonferrous metals based on formation of different charged complexes with varied stability has been proposed. Possibility of sepai ation of Ru(III), Rh(III), Pd(II), Pt(II) by water-soluble extractants from concentrated thiocyanate solutions has been displayed. Accelerated procedures of extraction-photometric determination of Rh(III), Ru(III) in solutions and waste products, which ai e chai acterized by high selectivity, availability, usage of non-toxic extractants have been worked out. 

When ionic liquids are used as replacements for organic solvents in processes with nonvolatile products, downstream processing may become complicated. This may apply to many biotransformations in which the better selectivity of the biocatalyst is used to transform more complex molecules. In such cases, product isolation can be achieved by, for example, extraction with supercritical CO2 [50]. Recently, membrane processes such as pervaporation and nanofiltration have been used. The use of pervaporation for less volatile compounds such as phenylethanol has been reported by Crespo and co-workers [51]. We have developed a separation process based on nanofiltration [52, 53] which is especially well suited for isolation of nonvolatile compounds such as carbohydrates or charged compounds. It may also be used for easy recovery and/or purification of ionic liquids. 

Recent development of the use of reversed micelles (aqueous surfactant aggregates in organic solvents) to solubilize significant quantities of nonpolar materials within their polar cores can be exploited in the development of new concepts for the continuous selective concentration and recovery of heavy metal ions from dilute aqueous streams. The ability of reversed micelle solutions to extract proteins and amino acids selectively from aqueous media has been recently demonstrated the results indicate that strong electrostatic interactions are the primary basis for selectivity. The high charge-to-surface ratio of the valuable heavy metal ions suggests that they too should be extractable from dilute aqueous solutions. 

Only recently, we have shown experimentally for a selection of neutral ionophores and carefully purified, typical PVC plasticizers that in absence of ionic sites Nernstian EMF responses could not be obtained [55]. For plasticizers of low polarity no EMF responses were observed at all. Transient responses due to salt extraction even with the highly hydrophilic counterion chloride were observed in the case of the more polar nitrobenzene. Lasting primary ion-dependent charge separation at the liquid liquid interfaces of ISEs, resulting in a stable EMF response, seemed therefore only possible in the presence of ionic sites confined to the membrane phase. Because membranes free of impurity sites... 

---