Extractants chelating acidic

For simple acidic extractants, such as carboxylic or sulfonic acids, the similarity in formation constants does not produce cobalt-nickel separation factors (Sn° 2) sufficiently large for commercial operation (Fig. 11.4). Data for pH versus extraction for some chelating acid extractants does seem to offer the possibility of separation [e.g., for the hydroxyoxime Acorga P50, the pHso for nickel(II) is 3.5 and for cobalt(II) 5.0]. Normally, this pH difference would be suitable for a separation process, but this particular system has hidden complications. The rate of nickel extraction is very slow compared with cobalt and, in addition, although cobalt is initially extracted... 

Extraction with 8-quinolinol derivatives, which can act as either a chelating acid or, after protonation, as an anion extractant. It was observed [35] that palladium extraction was favored at low acidity, but platinum was extracted best at high acidity (Fig. 11.16). At about 2 mol dm acid, the two metals were extracted equally. This suggested the following extraction equations ... 

Sekine, T. Dyrssen, D. Solvent extraction of metal ions with mixed ligands - IV. Extraction of Eu(III) with chelating acids and neutral adduct-forming ligands, J. Inorg. Nucl. Chem. 29 (1967) 1475-1480. 

The increase in extraction efficiency, evaluated by the distribution coefficients DM, is often considered to be the result of an increase in the overall lipophilicity of a system. Synergism has been studied systematically using four types of extractant combinations 1) chelating extractant/neutral extractant 2) acidic extractant/neutral extractant 3) two neutral extractants 4) two chelating extractants, with the observed synergistic effect generally decreasing from class 1 to 4. [49]... 

Chemcatcher (metals version) Chelating and C18 Empore sorbent disks Cellulose acetate membrane Range of heavy metals included in priority pollutant lists, including organotin and mercury compounds Integrative, speciation 2-4 weeks Extraction with acid 55,56... 

Ecoscope Hexane (organics) chelating resin (metals) Polyethylene membrane (organics), porous membrane (metals) Hydrophobic organic compounds, heavy metals Qualitative screening 2-4 weeks Direct injection of solvent or after concentration or extraction with acid 59... 

The hexavalent state of uranium ion is the usually encountered ion in the solution chemistry of uranium and its exceptional stability, relative to its other oxidation states as well as to other hexavalent actinide ions, makes studies with this ion much simple. Though chelating acids, in general, extract U(VI) by the equilibrium,... 

Moderately strong neutral donors were reported76 to replace the additional chelating acid molecule and give synergism in the extraction of U(VI) by HIPT-B mixtures, according to the equilibrium,... 

Table 11. Equilibrium constant data for the extraction of thorium by chelating acid - neutral donor combinations...

The extraction of Am(III) by the chelating acids HCF or HOx in presence of TPPO was studied138 and the results are given in Table 18. While Am(CF)3 was found to form two adducts Am(Ox)3 was found to form only the first adduct. This may be due to the stronger complexing of Am(III) by oxine, which makes the residual coordination unsaturation in the metal chelate, much less. The steric hindrance could also play a role in preventing the second adduct formation. 

The effect of mixing two chelating acids, HTTA and HOx, on the extraction of U(VI) was studied where synergism was observed197. Though the enhanced extraction was attributed to the mixed chelate formation, many species are likely to get extracted in these systems in view of the ability of the undissociated chelating acids to behave as neutral donors. 

In the extraction of a metal ion by chelating acids, as well as organophosphorus acids, addition of increasing amounts of a neutral donor results in an initial increase in extraction (synergism), followed by a fall in the enhancement (destruction of synergism) and... 

Lavandula pedunculate subsp. lusitanica (Chaytor) Franco.Thc essential oil and polar extracts of Lavandula pedunculate subsp. lusitanica (Chaytor) Franco collected in south Portugal contain camphor (40.6 %) and fenchone (38.0 %), with hydroxycinnamic acids (3-O-caffeoylquinic, 4-O-caffeoylquinic, S-O-caffeoylquinic, and rosmarinic acids) and flavones (luteolin and apigenin) in the polar extracts. Rosmarinic acid is the main compound in most of them. The bioactive compounds from L. pedunculate polar extracts acts as free-radical scavengers, Fe2+ chelators, and inhibitors of malondialdehyde production, and the essential oil is an active acetylcholinesterase inhibitor [258]. 

Hydroxylamine derivatives are used in determination of certain metals [112,113]. For example, the substitution of a benzoyl group (CeHsCO) for one of hydrogen atoms in hydroxylamine gives benzohydroxamic acid. Other important reagents in this group are N-benzoyl-N-phenylhydroxylamine (BPHA), also called N-phenylbenzohydroxamic acid [114,115] and N-furoylphenylhydroxylamine. All these reagents form extractable chelates and are used for determination of metals, e.g., V(V), Mn, Ti, Fe(III), and Nb. 

With both simple and chelating acidic extractants the metal extraction reaction generally follows the fomi... 

Most samples for analysis by plasma emission spectrometry are dissolved in acids, because metal elements are more soluble in acids. The acidic nature of the solution prevents elements from adsorbing onto the surface of the glassware. Some bases, such as tetramethyl ammonium hydroxide (TMAH), are used to prepare solutions but care needs to be taken to avoid the formation of insoluble metal hydroxides. Organic solvents may be used to dissolve organometallic compounds directly or to extract chelated metals from aqueous solution into the solvent as part of separation and preconcentration steps in sample preparation. 

A variety of chelates of B-compounds are formed by polyols. For instance, phenyl glycol may be used to extract sodium borate from dilute aqueous solutions. Recently, 2-ethyl-hexanol in kerosene was used to extract boric acid from aqueous solutions (57). 

Solvating extractants and chelating acidic extractants also may be used together to extract metal ions. The acidic chelating extractant provides the charge neutralization, although will not necessarily be sufficient to extract the metal ion to a significant... 

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