Cesium adsorption in hydrated iron oxide particles suspensions: An NMR study

Cs-137 is an important component of nuclear waste which may pollute water. Its migration in natural environments is slowed down by adsorption on minerals. Cesium adsorption on akaganeite (beta-FeOOH) particles, dextran-coated ferrihydrite (5 Fe2O3-9H(2)O) particles, and ferritin in aqueous solutions is studied with Cs-133 nuclear magnetic resonance measurements. The longitudinal relaxation time (T-1) of Cs-133 in the presence of such magnetic particles depends on whether the ions bind to the particle or not. T-1 of Cs-133 ions in aqueous solutions containing the same amount of magnetized particles will not depend on cesium concentration if relaxation is governed by diffusion (when cesium is not able to bind), but it will depend on cesium concentration if exchange governs relaxation (when cesium is able to bind). The method is successfully tested using TEMPO, a nitroxide stable free radical whose relaxation is due to diffusion. Cs-133 relaxation in solutions of ferritin, akaganeite, and dextran-coated ferrihydrite particles is found to result from a cationic exchange of cesium ions between particles surface and bulk ions, owing to adsorption. The effect of pH on Cs-133 relaxation in solutions of the particles is consistent with the adsorption properties of cations on hydrated iron oxides. (C) 2002 Elsevier Science (USA).