A. Zouhri et al., THE USE OF DICYCLOHEXANO-18-CROWN-6 AS AN EXTRACTANT-CARRIER FOR THE RECOVERY OF CHROMIC-ACID, Hydrometallurgy, 38(3), 1995, pp. 299-313
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).