Neutral species extractants

Bidentate phosphate compounds. The organophosphorus bidentate extractants are neutral species extractants that undergo no keto-enolization and have no exchangeable hydrogens (as is the case in extraction by the bidentate diketones). They contain either two P=0 groups or one P=0 and one C=0 group. The carbamoylmethyl-phosphonates (CMPs) and carbamoylphosphonates (CPs) are examples of the latter, while the tetraalkyldiphosphonates and tetraalkyl-diphosphinedioxides [or bis-(disubstituted phosphinyl)-alkanes] are examples of the former. 

Neutral-Species Extractants. Ketones, ethers, linear poly-ethers, and more recently, macrocyclic or "crown ethers all have useful properties as extractants if they are sufficiently water insoluble. Sulfoxides, the trialkyl phosphates, the trialkylphosphine oxides, and the carbamoylmethylphosphonates are among the stronger coordinators classified as neutral species extractants. These compounds usually coordinate directly with the metal ion and supply coordination that would be suppli by water in the aqueous phase. 

It is characteristic of all of these neutral species extractants that they vary widely in their selectivity and extractive strength as the concentration of both the aqueous-phase anion and acid vary. The first because the concentration of the neutral... 

Co-extraction of Mo and Cu is potentially a problem with certain feed solutions,14 and again selectivities are very dependent on the nature of modifiers present in formulated reagents.142 The Mo species extracted have not been fully characterized, but may include a neutral dioxo complex, [Mo02L2], which can be assumed to have an N2022 donor set similar to that in the Cu11 complex, and molybdate complexes solvated by neutral phenolic oxime ligands such as [M0O4112 LI l].143 Formation of solvated forms of molybdic acid is supported by evidence that extraction is favorable at very low pH values and that the complexes are readily stripped by aqueous ammonia to produce ammonium molybdate,144... 

Owing to the inadequacy of the mathematical model available for analysis of the amine extraction system (7), accurate values of the stability constants could not be evaluated for the Hs Pbn1-" system in the presence of NaCl. However, using the values of stability constants obtained by Bertazzi for the system (C2H5)3PbCln1 n in LiCl at 8.0 m (10), viz. 0 = 3.5, 02 = 1.0, 0s = 0.1, the neutral species Hs PbCl0 (n = 1) is seen to be dominant. Therefore a simple solvent extraction would be expected to remove a certain amount of triethyl lead from solution. As shown in Table II, this is seen to be so. However,... 

Formation and subsequent extraction of a neutral species such as (C2H5)3PbCl° suggest that a combined chemical complexing-solvent extraction technique might be more effective in terms of a lower Cr/Cl ratio than direct precipitation. This is confirmed by the results of the chemical complexing solvent-extraction studies. 

Figures 4 and 5 for Vaq/Vorg = 5.0 show that removal of organic lead corresponds closely to that which would be obtained for a theoretical 1 1 complex in the absence of sodium chloride. Variations in extraction efficiency are observed for different solvents, but for all of the solvents employed a ratio Cr/Cl = 1.0 is sufficient to reduce an initial triethyl lead chloride level of 10 ppm to <1 ppm. A comparison of solvents used suggests an approximate order of effectiveness (corresponding to solubility of the organo-lead complex Hs PbSCSN Hs and also the neutral species Hs PbCl0 in the solvent) of the form shown in Table IV.

In order to examine the influence of sodium chloride concentration on the distribution of triethyl lead chloride between an organic and aqueous phase, distribution studies were initiated. The solvent chosen for the initial studies was benzene because it had been shown that up to 30% of triethyl lead chloride is transferred to the organic phase as the neutral species Hs PbCl0 when using the chemical complexing-solvent extraction technique. 

Experiments with 35S-labelled sulfate solutions have shown that part of the extracted uranium is transferred across the interface as the neutral species U02S04, especially at low concentrations of aqueous sulfate 203 the principal extraction reactions for the secondary amine used, di- -decylamine, are reported to be... 

On the other hand, acidic compounds (A ) in the sample will already be charged and will thus not be enriched. Moreover, the neutral species (N) could be extracted, but not enriched, and the size and charge of macromolecules (if they are ionizable) will prevent them from entering the membrane. But even if some macromolecules do enter the liquid membrane, their low diffusion coefficients will cause a slow rate of transport. Accordingly, enrichment of small basic compounds and... 

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