The sorption behaviour of synthetic sodium nona-titanate and zeolite A for removing radioactive strontium from aqueous wastes

Sodium nona-titanate is a layered material that contains exchangeable sodium ions between layers. Zeolite A is an aluminosilicate structure that also contains exchangeable sodium ions inside the silica and alumina tetrahedral 'cages'. Both of these inorganic materials are known to selectively trap divalent metals. This paper describes the preparation/characterization of these inorganic samples and a comparative study of their sorption properties. Several types of experiments were performed: first, the experimental conditions for the sorption properties were assessed; then, the thermodynamics of sorption were studied; and finally, these two sorbents were compared in actual radioactive solutions (with low salinity and then with high salinity to simulate liquid waste from the Fukushima site). The maximum sorption capacity, the selectivity for Na/Sr and Ca/Sr, and the adsorption exchange free energy were obtained for the sodium nona-titanate and zeolite A samples. Sodium nona-titanate exhibited satisfactory decontamination properties for solutions with low amounts of calcium and was less affected by the presence of sodium when the strontium content was low. Zeolite A samples were also good candidates for strontium decontamination but were less efficient in a strong saline effluent. (authors)