Extractants chelating nonionic

Further Preparative Reactions. When pulps are to be used in the production of materials that do not retain the original fiber stmcture, such as rayon or ceUulose acetate film, the lignin, hemiceUulose, and other components must be reduced to the lowest possible concentrations. A surfactant (ionic or nonionic) is often added during a hot, weakly alkaline extraction step after chlorination. Another approach, sometimes used in addition to the surfactant step, is to treat the pulp with 6—10% NaOH after most of the oxidative bleaching is finished. This treatment removes most of the hemiceUulose. In most purification plants the final stage includes use of sulfuric acid chelators are optional. 

Cloud point extraction of metal ions. The use of cloud point extraction as a separation technique was first introduced by Watanabe for the extraction of metal ions forming sparingly water soluble complexes [109], Since then, the technique has been applied successfully to the extraction of metal chelates for spectrophotometric, atomic absorption, or flow injection analysis of trace metals in a variety of samples [105-107,110]. Other metal complexes such as AUCI4 or thiocyanato-metal complexes can be extracted directly using nonionic surfactants such as polyoxyethylene... 

Table 13.2 Summary of Cloud Point Extractions of Metals Chelates Using Nonionic... 

A plot of the temperatures required for clouding versus surfactant concentration typically exhibits a minimum in the case of nonionic surfactants (or a maximum in the case of zwitterionics) in its coexistence curve, with the temperature and surfactant concentration at which the minimum (or maximum) occurs being referred to as the critical temperature and concentration, respectively. This type of behavior is also exhibited by other nonionic surfactants, that is, nonionic polymers, // - a I k y I s u I Any lalcoh o I s, hydroxymethyl or ethyl celluloses, dimethylalkylphosphine oxides, or, most commonly, alkyl (or aryl) polyoxyethylene ethers. Likewise, certain zwitterionic surfactant solutions can also exhibit critical behavior in which an upper rather than a lower consolute boundary is present. Previously, metal ions (in the form of metal chelate complexes) were extracted and enriched from aqueous media using such a cloud point extraction approach with nonionic surfactants. Extraction efficiencies in excess of 98% for such metal ion extraction techniques were achieved with enrichment factors in the range of 45-200. In addition to metal ion enrichments, this type of micellar cloud point extraction approach has been reported to be useful for the separation of hydrophobic from hydrophilic proteins, both originally present in an aqueous solution, and also for the preconcentration of the former type of proteins. 

Based upon the use of nonionic surfactant systems and their cloud point phase separation behavior, several simple, practical, and efficient extraction methods have been proposed for the separation, concentration, and/or purification of a variety of substances including metal ions, proteins, and organic substances (429-441. 443.444). The use of nonionic micelles in this regard was first described and pioneered by Watanabe and co-workers who applied the approach to the separation and enrichment of metal ions (as metal chelates) (429-435). That is, metal ions in solution were converted to sparingly water soluble metal chelates which were then solubilized by addition of nonionic surfactant micelles subsequent to separation by the cloud point technique. Table XVII summarizes data available in the literature demonstrating the potential of the method for the separation of metal ions. As can be seen, factors of up to forty have been reported for the concentration effect of the separated metals. 

TABLE XVII. Summary of the Reported Extraction of Metal Ions as Metal Chelates by the Phase Separation Behavior of Nonionic Surfactants... 

A series of 4-alkylamido-2-hydroxybenzoic acids containing a different number of carbon atoms in the alkyl-amido group has been studied as model ligands for metal ion extraction in aqueous micellar solutions of nonionic surfactants. Their acid-base properties and reactivity towards metal ions in the presence of micelles were investigated. By operating at a proper temperature, the separation of the iron (III) chelate complexes into a micellar rich phase was achieved and the extraction efficiency was correlated with the ligand hydrophobicity. 

The phase separation of nonionic micellar solutions above the cloud point has been succesfully applied to the liquid-liquid extraction of some metal chelate complexes (5, 6J. In these systems the concentration of the analyte takes place in the micellar rich layer, which can be readily analyzed. 

There are also sample concentration/separation techniques used as pretreatment methods for trace analysis. Commonly used methods include chelating ion-exchange and, for trace organic analysis, solvent extraction, carbon adsorption, and resin adsorption using nonionic macroeticular resins. 

These initial treatments are followed by procedures to further isolate and concentrate the lead. Liquid-liquid extractions are most common for analyses of lead concentrations in aqueous matrices. These extractions typically use a water-immiscible solvent, an aqueous solution, and a complexing agent that forms a nonionic or neutral chelate with lead. A second type of... 

Chem. Descrip. Synergistic blend of nonionic and anionic surfactants with extracting and chelating agents... 

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