Phase behavior of cationic/anionic surfactant mixtures of the same chain length (n=10, 12 or 14) strongly depends on the molar ratio and actual concentration of the surfactants. Precipitation of catanionic surfactant and mixed micelles formation are observed over the concentration range investigated. Coacervate and liquid crystals are found to coexist in the transition region from crystalline catanionic surfactant to mixed micelles. The addition of oppositely charged surfactant diminishes the surface charge density at the mixed micelle/solution interface and enhances the apparent degree of counterion dissociation from mixed micelles. Cationic surfactants have a greater tendency to be incorporated in mixed micelles than anionic ones.

Phase behavior in mixtures of cationic and anionic surfactants in aqueous solutions

The extraction of zinc, cadmium and mercury from chloride and sulphate media by solvating extractants, liquid anion and liquid cation exchangers has been reviewed both from the literature and by experiment. The results have been discussed in terms of both practical process possibilities and the use of slope analysis to identify the extracted species. These show that slope analysis cannot give positive unambiguous identification of extraction stoichiometry in systems in which the extracted metal species contains coordinating ligands from the aqueous phase. However, in the extraction of Zn and Cd from sulphate media by di(2-ethylhexyl)phosphoric acid (DEHPA) the extracted species is shown to be an MR2(HR)2 monomer by slope analysis demonstrating its use in simple systems. In the case of amines and solvating reagents such as TBPc and TOPO zinc appears to be extracted from Cl– media as either ZnCl2 or sometimes HZnCl3 whereas Cd and Hg(II) appear to be always extracted as HCdCl3 and HHgCl3 species. The use of aqueous phase complexing by Cl– to improve the separation of Zn and Cd by extraction is clear. Some results are presented for the recovery of zinc from sulphate media by oximes and mercury from sulphuric acid media by amines and DEHPA.

Recovery of zinc, cadmium and mercury (ii) from chloride and sulphate media by solvent extraction†

Solubility and activity of high-molecular amine hydrochlorides in organic solvents

Amine extractants, regardless of structure, have been of limited utility for the extraction of complex metallic anions from alkaline solution due to an inability to increase the amine's basicity. This situation is contrasted to acid extractants in which case such control of extractant strength is possible. Recent studies with amine extractants have shown that the use of specific modifiers allows for the control of amine basicity over an appreciable pH range for certain anions. Particularly significant is the potential for the extraction of gold from alkaline cyanide solutions.

A.S. Kertes

Papers

Solubility and activity of high-molecular amine hydrochlorides in organic solvents

Solubility parameters of long-chain alkylamines and their activities in organic solvents☆

On the third phase formation in extraction systems involving aminehydrochlorides