Di-(2-ethylhexyl) phosphoric acid (D2EHPA) is a commonly used extraction reagent for the separation of uranium from aqueous solutions. Previous work showed the suitability of a polymer inclusion membrane (PIM) based on D2EHPA and poly(vinyl chloride) (PVC) for the extraction and transport of uranium(VI) from sulfate solutions. This study details the improvement of the membrane transport by optimising the composition of the source and receiving solutions on one hand and membrane composition with the use of a plasticizer on the other. Initial fluxes of uranium as high as 3.0 x 10(-6) mol m(-2) s(-1) corresponding to permeability of 7.2 x 10(-6) m s(-1) were recorded using a membrane composed of 35% (m/m) D2EHPA, 10% (m/m) o-nitrophenyloctyl ether and 55% (m/m) PVC from a solution containing 100 mg L-1 U(VI) in 0.1 mol L-1 H2SO4 into a solution containing 6 mol L-1 H2SO4, although transport across a membrane containing 45% (m/m) D2EHPA and 55% (m/m) PVC was only slightly slower. The effect of the acid anion in the source and receiving solutions on the extraction and back extraction of U(VI) is discussed and the membranes are tested for durability over repeated cycles of extraction and back-extraction. Using a 45% (m/m) D2EHPA and 55% (m/m) PVC PIM (m/m), U(VI) is completely separated thermodynamically from a range of common metal cations and successfully separated from Fe(III) kinetically. (C) 2012 Elsevier B.V. All rights reserved.