Uranium transport using a PTFE flat-sheet membrane containing alamine 336 in toluene as the carrier

Abstract

Transport of uranyl ion from HCl medium was investigated using 0.2 micron PTFE filters as the membranesupport and 30% alamine 336 in toluene as the carrier while distilled water was used as the strippant. In an experimentcarried out to understand the effect of the organic diluents, the observed trend was toluene > t-Bu-benzene > chloroform > 1,2-dichloroethane > hexane > 1-decanol. In view of the higher transport of uranyl ion with tolueneas the diluent, all subsequent experiments were carried out using toluene. The permeability coefficient values increased with increasing HCl concentration (1 M HCl: 6.53×10−4 cm/s; 6 M HCl: 2.56×10−3 cm/s) suggesting the extraction of anionic species into the membrane phase. The permeation of ion pairs is expected to be higher for more polar diluents such as CHCl3 and 1,2-dichloroethane. However, the lower trend observed with these diluents as compared to aromatic diluents such as toluene or t-butyl benzene was ascribed to H-bonded interaction with thecarrier. In order to optimize the carrier concentration an experiment was carried out at varying concentration ofalamine 336 in toluene. Maximum transport rate was observed with 20% (v/v) alamine 336 in toluene as the carrier (P = 3.33×10−3 cm/s). Though an increase in transport rate (5% to 20% alamine 336) is expected with increasingcarrier concentration, the decrease beyond 20% alamine 336 is attributed to the increased viscosity of the carriersolution which retards metal diffusion. The effect of membrane pore size was studied using four different membranes with varying pore sizes. A sharp decrease in the transport rate with increasing membrane pore size was observed (P = 2.56×10−3 cm/s for 0.2 micron pore size; P = 6.78×10−4 cm/s for 5.0 micron pore size).