Amines as Extractants—Studies of the Organic Phase

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Abstract
The extraction of acids and of metals by solutions of long-chain alkyl amines can be described as a process of neutralization of the amine in the organic phase by acid extracted from the aqueous phase and of exchange of anions between the phases. A complete description of the equilibrium process should include identification of the extracted anions, measurements of the affinities of the various anions for the alkylammonium ions in the organic solutions, and the character of the bonding in which the anions take part. It should also include the roles played by the large excesses of acid which extract from the higher aqueous acid concentrations, the extracted water, and the organic diluent. In this paper affinities of tri-n-octylamine for various mineral acids and the extraction of stoichiometric excesses of these acids by tri-n-octylamine solutions are discussed. Analyses of water content of the amine solutions and proton magnetic resonance measurements are combined with those of excess acid to describe the amine solutions in equilibrium with concentrated acids. Amine concentration dependence of extraction, capacities of amine solutions for metals, and absorption spectra have been used to establish the identity of metal species which extract into alkyl ammonium solutions. The results obtained for extraction of various metals from several acid solutions are discussed, with emphasis on tetra- and hexavalent actinides.

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