THE USE OF DICYCLOHEXANO-18-CROWN-6 AS AN EXTRACTANT-CARRIER FOR THE RECOVERY OF CHROMIC-ACID

The solvent extraction and transfer through a bulk liquid membrane of chromic acid in sulphate media by dicyclohexano 18 crown 6 (DC18C6, L) in dichloromethane takes place due to the formation of the complex io n pair [(H(3)O(+)L] [HCr2O] in the organic phase. In spite of the pres ence of a large a excess of sulphuric acid, the co-extraction and co-t ransport of sulphuric acid is very slight. The extraction and transpor t are also selective with respect to Ni2+, Cr3+ and Fe3+ cations. The selectivity of the transfer process characterizes the semi-permeabilit y of the liquid membrane, which is able to concentrate chromic acid ac cording to the Donnan equilibrium. The transport kinetics are explaine d by the two-film theory, applied to the liquid membrane (diffusion th rough the stagnant films, reaction equilibrium at the interfaces).