Surface effects on metal ion transport across porous alumina membranes. 2.Trivalent cations: Am, Tb, Eu, and Fe

Transport behavior of trivalent solutes across mesoporous Anopore gamma-alu mina membranes was investigated as a function of re diameter, pH, ionic str ength, and nature of the salt in solution. Radiotracers, Fe-55, Eu-152, Tb- 157, and Am-241, were present in the feed solutions at concentrations rangi ng from 10(-8) to 10(-10) M. Total salt concentrations in the feed ranged f rom 1.0 to 10(-4) M. Order of magnitude differences between experimental an d theoretical diffusion rates for the membranes can be explained in terms o f electrostatic interactions between the cations and the positively charged membrane surface. The rates of Am3+ and Tb3+ transport across the alumina membranes were greatly increased by raising the ionic strength from 10(-3) to 0.1 M in both the feed and permeate solutions; however, EU3+ diffusion r ates were only slightly affected in this range of ionic strength. Trivalent cation transport rates at total salt concentrations greater than 0.1 M wer e slower than divalent cations due to enhanced electrostatic interactions b etween the alumina surface and the higher valent 3+ cations. Alkali metals present in both the feed and permeate solutions slightly influenced iron tr ansport.