Sulfur-donors extractants

Sulfur-donor Extractants The CYANEX 301 Process. Various dialkyl-(mono/di)-thio(phosphoric/phosphinic) acids, such as di(2-ethylhexyl)-di-thiophosphoric acid (HDEHDTP), bis(2,4,4-trimethylpentyl)-thiophosphinic acid (CYANEX 272), bis(2,4,4-trimethylpentyl)-monothiophosphinic acid (CYANEX... 

Sulfur donor extractants are less common, althongh dialkylsulfides have been used in precious metal extraction, and a trialkylphosphine sulfide, R3PS (Cyanex 471X, Cytec Inc., New Jersey), is available commercially. Such sulfur donating extractants will need to be considered when extracting and separating soft metals, such as second- and third-row transition metals (e.g., cadminm, mercury, and palladium). 

Musikas, C. 1984. Actinide-lanthanide group separation using sulfur and nitrogen donor extractant. In Actinide/Lanthanide Separations, eds. G.R. Choppin, J.D. Navratil, W.W. Schulz, pp. 19-30. World Scientific, Singapore. 

The host guest chemistry of crown ethers continues to be exploited for the development of new ionophores for the selective recovery of Hg(II). A novel crown ring system containing a redox switchable trithiadiazapentalene/trithiotriuret unit (17/18) allows control of Hg(II) in solvent extraction experiments between chloroform and water. The thiocar-bonyl sulfur donor sites outside the macrocycUc cavity of (18) are responsible for strong complexation and extractabiUty into chloroform. 

These oxygen-donor type extractants have potential for co-extraction of trivalent lanthanide and actinide ions. For the mutual separation between trivalent actinides and lanthanides, so-called soft-donor (nitrogen-donor type and sulfur-donor type) extractants are promising and widely investigated for the application of nuclear waste treatment as follows. 

Cyanex-301 system. The sulfur type soft-donor extractant, thiophosphoric acid has potential for selective separation of trivalent actinides from lanthanides (Musikas 1985). Zhu et al. (Zhu 1995 Zhu et al. 1996) developed dithiophosphinic acid type extractant, Cyanex-301... 

Although the majority of acidic extractants is based on oxygen donor groups, some commercial compounds include a sulfur donor atom. These, of course, would be favored when the extraction of a soft metal is required. These generally consist of elements in low oxidation states or the heavier elements in any group in the Periodic Table. 

The soft S2 donor sets presented by these bidentate ligands lead to very strong binding of heavy metals (Table 7) which are not stripped by sulfuric acid, ensuring that these deleterious elements do not transfer to the Zn electrolyte.196 However, co-extraction of copper is accompanied by reduction to Cu1 which has proved very difficult to strip to regenerate the reagent and will lead to poisoning of the extractant unless all traces of copper are removed from the feed solution. 

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