Effect of Humic Acid on the Sorption and Kinetic Desorption of Radiocaesium Ions on/from Na-Rectorite Studied by the Batch Technique and a Chelating Resin

Abstract

The sorption of radiocaesium ions onto Na-rectorite was studied at a pH value of 5.0 ± 0.2 using the batch technique under ambient conditions. The effect of humic acid on the Cs + ion sorption was also investigated. The results indicated that the presence of humic acid significantly enhanced the sorption of Cs + ions onto rectorite. The kinetic desorption of Cs + ions from bare and HA-bound rectorite, respectively, was studied by the addition of a chelating resin. The results obtained indicated that Cs + ion sorption onto rectorite generated reversible and irreversible sorption sites, with the irreversible sorption sites consisting of at least two kinds, i.e. “weak” and “strong”. With increasing ageing time, surface-sorbed Cs + ions on solid colloids can move from “weak” sites to “strong” sites, whereas that corresponding to irreversible sorption are incapable of movement irrespective of the length of the aging time. The results obtained are important for the evaluation of the behaviour of radionuclides in the natural environment.