Investigation of chabazitic materials as Cs-137 sorbents from cementitious aqueous solutions

The ability of a chabazite-bearing tuff (AT), a synthetic chabazite (SYN) and pure natural chabazite crystals (CHA) to sorb cesium (C-cs: 10(-9)-10(-2) M) from young concrete pore water (YCW), an aqueous medium that can potentially leach from cement-based barriers of radioactive waste disposal facilities, was investigated using a batch technique and (CsCl)-Cs-137-spiked solutions. The sorbents were mineralogically characterized prior and after the sorption tests, whereas their uptake ability was determined by the ammonium acetate saturation (AMAS) method. Two series of experiments were performed using sorbate solutions in pH similar to 13 and pH similar to 7 YCW (contact time: 14 days and 100 days). The Cs-uptake by the zeolites was determined by counting the 661.6 keV Cs-137 gamma-rays in the liquid phase. SYN presented the highest Cs-uptake ability followed by CHA and AT. The Cs-uptake, which remained constant between 14 and 100 days, depended on the zeolite content of the sorbents and the Cs-concentration of the solutions. The zeolites remained stable in the YCW environment for the total duration of the experiment. Kinetic experiments, performed for AT at 23, 35 and 50 degrees C using a 10(-3) M Cs-solution in pH similar to 13 YCW spiked with Cs-137, showed that the equilibrium was established, for all temperatures, in less than 30 min. Cs-leaching tests (duration: 14 days and 100 days) performed using pH similar to 13 YCW as eluent, indicated that AT was the most sensitive to leaching losing ca. 60% of the sorbed Cs in less than 10 min, whereas SYN and CHA ca. 30%. No further leaching was observed at prolonged contact of the Cs-loaded zeolites with YCW.